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Abstract 3427 Recently, early results of the ENESTnd phase III trial showing superiority of nilotinib over imatinib, led to accelerated approval of Nilotinib as initial treatment of ECP CML at a dose of 300mg BID. Independently, since December 2008, ICORG, the All-Ireland Cooperative Oncology Research Group has been conducting an open-label, single stage, multicenter, phase II study (ClinicalTrials.gov NCT00809211) to investigate the safety and efficacy of nilotinib 300 mg BID in untreated, ECP, Ph-pos CML patients. The primary endpoint is the CCyR rate at 6 months; secondary endpoints include the kinetics of molecular response, determined by RQ-PCR at baseline and 3 monthly from start of treatment as well as an evaluation of a new rapid turnaround PCR system “GeneXpert” with IS BCR-ABL RQ-PCR. To date a total of 37 patients have been enrolled on the trial. The median age of these 37 patients is 51 (range 20 –77); 50% have low risk Sokal score, 22% intermediate and 28% high risk. Median follow up is currently 8 months (range 1–17) with 25 patients evaluable for response following at least 3 months on study. Results: By intent to treat analysis the CCyR rate is 64% (16/25) at 3 months and 95% (19/20) at 6 months, with all patients actually tested Ph negative by 6 months. By 6 months 12/20 patients have achieved MMR (60%). This analysis includes 1 patient with variant transcripts and 2 patients bordering on MMR at 3 months who had insufficient RNA for analysis at 6 months. While none of the patients have progressed on study, three patients are now off the study: persistent grade 3 thrombocytopenia in one, persistent LFTS abnormalities in a second case and one death due to progressive multiple system atrophy, which was unrelated. 3 of 25 patients (12%) have undergone dose escalation to 400mg BID for suboptimal response. The median daily dose was 600mg; 16/34 (47%) have interrupted nilotinib at least once with a median duration of interruption of 0.5 days. The dose of nilotinib at the last visit was > 300mg BID in 82% (28/34). Haematologic toxicity was minimal with grade III thrombocytopenia seen in 2 patients (5%). Grade III non-haematologic toxicity included an elevated lipase in 6/36 (17%). The only other grade III toxicities noted were musculo-skeletal pain and an elevated ALT in 1 patient each. Analysis of 71 follow-up paired samples from 21pts at 3 monthly intervals by “GeneXpert” and RQ-PCR showed an encouraging correlation between the methodologies. At 3 months the median BCR-ABL/ABL % was 0.45 as calculated by “GeneXpert” and 0.67 by IS RQ-PCR and at 6 months 0.06 and 0.01 respectively. However in individual patients, there was a trend for “GeneXpert” to underestimate Bcr-Abl/Abl % and therefore overestimate attainment of MMR. Conclusion: In this preliminary analysis, nilotinib 300mg BID induces high rates of CCyR and MMR equivalent to those reported previously in the phase II and III studies of nilotinib in ECP CML. This trial provides independent confirmation that nilotinib 300mg BID is safe and effective treatment for ECP CML. “GeneXpert” provides rapid results both at diagnosis and follow–up and would be further enhanced by calculation of a conversion factor to the IS scale. Disclosures: Conneally: Novartis: Honoraria. Giles:Novartis: Consultancy, Honoraria. Egan:Novartis: Employment. O'Dwyer:Novartis: Honoraria.

Abstract 18 In a significant proportion of older patients with AML intensive chemotherapy is not considered a viable option[1]. Such patients may receive low-dose Ara-C (LDAC), best supportive care (BSC) with hydroxyurea or an experimental agent but outcomes are poor. We have shown that LDAC is superior to BSC [2], but only in patients who enter CR (fewer than 20%).[2]. There is therefore scope to improve outcomes in these patients, and a number of possible treatments have been evaluated in the randomised UK NCRI AML16 trial, one of which is gemtuzumab ozogamicin (GO), which we have shown to benefit the majority of younger patients when given in conjunction with standard chemotherapy[3]. In AML16 novel agents or combinations are tested in untreated older patients with AML or high risk MDS (marrow blasts >10%) using a “pick a winner” design. The design allows unpromising treatments to be identified early (typically after 50 or 100 patients per arm): only those arms which show promise will continue to a trial with OS and DFS as endpoints. The aim is to at least double the remission rate from 15% to 30%, and thus improve overall survival. We now report the results of LD Ara-C (20mg bd days 1–10 for 4 courses) versus LDAC combined with GO (at a fixed dose of 5mg on day 1 of each course for 4 courses at 6–8 week intervals). Patient Details: The comparison opened as part of the UK LRF AML14 trial and was carried forward to AML16 unchanged. Between June 2004 and June 2010, 495 patients were randomised, 249 to LDAC plus ATO, 246 to LDAC. The median age was 75 years (range 54–90); 83% of patients were aged over 70 years, and 61% were male. To be eligible patients’ LFTs had to be less than twice ULN. Treatment arms were balanced for age, gender, performance status, de novo/secondary AML/high risk MDS, presenting WBC and cytogenetic risk group. Follow-up is complete to 1st January 2010, with median follow up of 21 months. Survival and remission data is available on 412, 404 patients respectively. Treatment Results: The trial passed through both stopping hurdles based on CR/CRi rates and therefore continued to full accrual, with overall survival as primary outcome measure. The table shows the distribution of outcomes: there was no heterogeneity by recruitment period (AML14 vs AML16). The causes of death (316) were:- There were no significant interactions between treatment and any of the baseline variables on either remission or survival outcomes. Likewise there were no major toxicity implications, although resource usage tended to be higher in patients given GO. Discussion: While the addition of GO significantly improves CR rate, achieving the 30% response originally sought, this does not translate into survival. This is predominantly due to an increase in relapse, indicating that if GO is to have a role in this setting, it will require effective treatment to maintain remission. [1] Juliusson G et al. Blood 2009; 113: 4179 – 4187 [2] Burnett et al. Cancer 2007 109: 1114–1124 [3] Burnett et al. JCO 2010 to appear. Disclosures: Off Label Use: Mylotarg (gemtuzumab ozogamicin).

Abstract 3083 Introduction: Suppressor of cytokine signaling protein 3 (SOCS3) is an important regulator of the erythropoietin receptor and the receptor-associated JAK2 kinase. We hypothesize that the mechanism of JAK2 mutant-mediated transformation in myeloproliferative neoplasms (MPN) involves overcoming SOCS3 inhibition. In co-expression studies SOCS3 protein is stabilized and tyrosine phosphorylated in the presence of JAK2 V617F (Hookham et al., Blood 2007) and exon 12 mutations (Elliott et al., Haematologica 2009) but not wild-type JAK2, rendering SOCS3 unable to downregulate phosphorylation of these JAK2 mutants. The purpose of this study was to determine if these observations can be reproduced in vivo, by comparing SOCS3 expression and phosphorylation in MPN patients and healthy volunteers. Methods: Patients with polycythaemia vera (PV) and essential thrombocythaemia (ET) were recruited from Belfast City Hospital. The mutational status of the JAK2 gene had been previously assessed. Granulocytes were isolated from peripheral blood of patients and healthy volunteers by Ficoll density gradient centrifugation, dextran sedimentation and hypotonic red cell lysis. Estimation of the JAK2 V617F/wild type allelic ratio was performed by pyrosequencing. SOCS3 expression levels were measured by quantitative real-time reverse transcriptase-PCR. Granulocyte whole cell lysate was immunoprecipitated with anti-SOCS3 and Western blots were probed with anti-phosphotyrosine. SOCS3 phosphorylation was estimated by densitometry. Results: To date, 63 MPN patients and 27 healthy volunteers have been recruited. This total is comprised of 47 patients with PV (JAK2 V617F n=38, JAK2 exon 12 n=4, unknown n=5) and 16 patients with ET (JAK2 V617F n=15). Median V617F allele burden was 45% in PV (range 0–99%) and 20% in ET (range 7–84%). In 67% of patients with PV, SOCS3 expression was greater than healthy volunteers. Compared to healthy volunteers, SOCS3 phosphorylation in PV patients was higher in 67%, equivalent in 17% and lower in 17% of cases. Similarly in ET, SOCS3 phosphorylation was higher in 73%, equivalent in 18% and lower in 9% of patients compared with healthy volunteers. SOCS3 tyrosine phosphorylation was observed in association with both JAK2 V617F and exon 12 mutants. Conclusion: The presence of aberrant tyrosine phosphorylation of SOCS3 protein observed in some PV and ET patients supports the hypothesis that this is a potential mechanism by which mutant JAK2 escapes inhibition and leads to constitutive downstream signaling in MPN. Disclosures: No relevant conflicts of interest to declare.

Graft-vs-host-disease (GVHD) can complicate allogeneic bone marrow transplantation (BMT) and usually targets host skin, liver and gut. Reports of central nervous system (CNS) GVHD are very rare and diagnosis is challenging due to the range of potential neurological complications following BMT. We report a 20-year-old male, on cyclosporin following allogeneic BMT 18 months previously for acute myeloid leukaemia (AML), who presented with a right hemiparesis. He previously had cutaneous and hepatic GVHD which stabilised with immunotherapy manipulation. MRI brain demonstrated acute infarction in the left basal ganglia and left periventricular white matter. Magnetic resonance angiography (MRA) demonstrated irregularity of middle and anterior cerebral arteries. Cerebrospinal fluid (CSF) analysis did not reveal evidence of opportunistic infection. CSF cytology and vasculitic serology were negative. Repeat bone marrow aspiration revealed that his haematological malignancy had changed morphology. Despite maximising his immunotherapy, sequential brain imaging and blood films showed disease progression. His cutaneous and hepatic GVHD recurred and biopsies confirmed inflammatory vascular changes. The progressive course, sequential imaging findings and lack of evidence for alternative diagnoses is compatible with CNS-GVHD. It is important to consider CNS-GVHD in BMT patients presenting with neurological symptoms as it has significant treatment and prognostic implications.

An erythrocytosis arises when the red cell mass is increased. This can be due to a primary intrinsic defect in the erythroid progenitor cells or secondary to erythropoietin production from some source. Primary and secondary causes can be congenital or acquired. Rare, primary congenital defects are due to mutations leading to truncation of the erythropoietin receptor. The main acquired, primary erythrocytosis is polycythaemia vera. Among the congenital secondary causes, a number of defects in the genes in the oxygen-sensing pathway have recently been described, which lead to a secondary erythrocytosis. An extensive list of acquired secondary causes needs to be considered. A number of patients do not have an identifiable cause of erythrocytosis and are therefore described as having idiopathic erythrocytosis. Investigation should commence with careful clinical evaluation. Determination of the erythropoietin level is then a first step to guide the further direction of investigation. In those with congenital defects, a number of serious thromboembolic events have been described, but there is little information available about outcomes in these individuals and, therefore, no evidence to guide management. In this group, consideration should be given to the use of venesection to attain an achievable haematocrit level, and also low-dose aspirin therapy.

Abstract 433 A common constitutional JAK2 haplotype termed 46/1 (also known as GGCC) predisposes to V617F JAK2-positive myeloproliferative neoplasms (MPN) but the underlying mechanism is obscure. Two hypotheses have been postulated: (i) ‘hypermutability' of JAK2 on 46/1 compared to other haplotypes and (ii) a functional difference of JAK2 on 46/1 that positively interacts with V617F and thus provides ‘fertile ground' for development of an MPN. To investigate these possibilities we analyzed patients with essential thrombocythemia entered into the PT-1 studies. As expected, 46/1 was highly overrepresented in V617F positive cases (n=404) compared to population controls (n=1492; P=3.9×10-11) and in informative individuals V617F preferentially arose on the 46/1 chromosome (P Disclosures: Schnittger: MLL Munich Leukemia Laboratory: Equity Ownership. Green:Bristol Myers Squibb: Consultancy; Shire: Consultancy; Incyte: Consultancy; Astex Therapeutics: Consultancy, Research Funding.

486 A significant proportion of older patients with AML are not treated with conventional intensive chemotherapy [1] because they are unfit or not considered likely to benefit from an intensive treatment approach. Their outcomes are poor. Such patients have typically been treated with low-dose Ara-C (LDAC) or best supportive care (BSC) with hydroxyurea, and unrandomised studies of new agents have been used in this population. A recent randomised trial has shown that LDAC is superior to BSC in these patients [2]. Randomised trials are underway to assess the value of other novel treatments compared to LDAC. In an unrandomised phase 2 trial in 64 patients, Roboz et al found encouraging results using the combination of Arsenic Trioxide and LDAC. [3]. The UK NCRI AML16 trial is a programme of development which aims to test novel agents or combinations in untreated older patients with AML or high risk MDS (marrow blasts >10%) following a “pick a winner” design. The intention is to identify a “winner” which will produce a remission rate in excess of 30%, compared with 15-20% with LDAC. Using LDAC as the standard arm,the design allows unpromising treatments to be identified early (typically after 50 patients per arm), so that only those arms which show promise will continue to a trial with OS and DFS as endpoints. We report our experience of LD Ara-C (20mg bd days 1-10 for 4 courses) versus LDAC combined with Arsenic Trioxide (ATO, 0.25 mg/kg d1-5, d9, d11 for 4 courses at 6-8 week intervals). Patient Details: Between December 2006 and until its conclusion in May 2009, 166 patients were randomised, 84 to LDAC plus ATO, 82 to LDAC. The median age was 74 years; 80% of patients were aged over 70 years, 62% were male. There were no differences between the treatment arms with respect to age distribution, gender, performance status, de novo/secondary AML, high risk MDS, presenting WBC or cytogenetic risk group. Follow-up is complete to 1st January 2009, with median follow up for survivors of 8 months (range 0.1-17), at which point 122 patients had been recruited, and there were a total of 60 deaths (LDAC n=25; LDAC+ ATO, n=35). CR status is known on 113 patients. Overall, 24 patients have entered CR/CRi (LDAC n=13, LDAC+ATO n=11) with 8 relapses (2 vs 6; 1 vs 3 patients have died following relapse). | | CR | CRi | 30-day mortality | 8 week mortality | 6 month survival from CR | 12 month OS | |:--------------------- | -------------------- | ------------------------ | ---------------- | ---------------- | ------------------------ | ---------------- | | All patients | 15/113 (13%) | 9 (8%) | 13% | 22% | 91% | 33% | | LD Ara-C (n=60) | 7/54 (13%) | 6 (11%) | 12% | 22% | 83% | 41% | | LD Ara-C + ATO (n=62) | 8/59 (14%) | 3 (5%) | 13% | 22% | 100% | 27% | | OR/HR & 95% CI | CR: 0.95 (0.32-2.81) | CR/CRi: 1.28 (0.56-3.39) | | | 2.31 (0.31-17.0) | 1.46 (0.88-2.44) | | P-value | 0.9 | 0.6 | | | 0.4 | 0.03 | Treatment Results: The causes of death (60) were:- | | Infection | Haemorrhage/CVA | Resistant disease | Cardiac | Relapse | Other | |:--------------------- | --------- | --------------- | ----------------- | ------- | ------- | ----- | | LD Ara-C (n=25) | 11 | | 12 | | | 2 | | LD Ara-C + ATO (n=35) | 13 | 1 | 15 | 1 | 2 | 3 | The DMEC recommended closure of the LDAC + ATO arm of the trial because follow-up data on the first 50 patients per arm showed that ATO had failed to provide the 2.5% improvement in CR/CRi required for continued recruitment and that the required improvement in remission was unlikely with LDAC + ATO. Conclusions: While ATO has a definite role in treating patients with APL, and may be of benefit in combination with other drugs in AML, the combination of LDAC + ATO in this patient population was not beneficial. [1] Juliusson G et al. Blood 2009; 113: 4179—4187 [2] Burnett et al. Cancer 2007 109: 1114—1124 [3] Roboz Gail J et al. Cancer 2008;113(9):2504—11. Disclosures: Off Label Use: Arsenic Trioxide is not licensed in this indication.

Abstract 3904 Poster Board III-840 While about 95% of patients with polycythemia vera carry the unique V617F mutation in JAK2 exon 14, several mutations in exon 12 have been described in the minority of JAK2 (V617F)-negative subjects. The initial study [N Engl J Med 2007 Feb 1;356(5):459-68] led to the conclusion that JAK2 exon 12 mutations define a distinctive myeloproliferative syndrome that affects patients who currently receive a diagnosis of polycythemia vera or idiopathic erythrocytosis. Very recent studies suggest that the 'GGCC' haplotype of JAK2 confers susceptibility to the somatic acquisition of both JAK2 (V617F) and exon 12 mutations [Nat Genet 2009 Apr;41(4):450-4, Leukemia 2009 May 14, Epub ahead of print]. Indeed, we reported pedigrees with familial polycythemia vera in which there were both JAK2 (V617F)-positive and JAK2 exon 12 mutation-positive siblings [Blood 2008 Feb 1;111(3):1686-9]. The myeloproliferative neoplasm associated with JAK2 exon 12 mutations is a rare disorder, and only small groups of patients have been reported so far by various investigators. We therefore started a collaborative study in Europe with the aim of collecting about 100 patients with this condition in order to define the molecular and clinical features of this myeloproliferative neoplasm. An ad hoc database was developed for data collection and management. As of August 1, 2009, 77 patients with the required clinical and hematologic data at diagnosis have been recruited (median follow-up 3.2 years, range 0-27 years), while complete follow-up information was available for 57 of these patients. Various approaches were employed for the detection of JAK2 exon 12 mutations, including genomic DNA sequencing, allele-specific PCR assays, and high resolution melting. Overall, 16 different exon 12 mutations were identified. The most frequent mutation were N542-E543del (26 patients), K539L (12 patients), R541-E543delinsK (6 patients), and F537-K539delinsL (6 patients); the remaining mutations occurred less frequently. With respect to the clinical phenotype at presentation, the Kruskal-Wallis test did not reveal any significant difference between the above most frequent mutations. Median age at diagnosis was 53 years (range 15-92), and the male/female ratio was 43/34. Mean hemoglobin level was 19.3 ± 2.2 g/dL, mean WBC count 8.5 ± 3.2 × 109/L, and mean PLT count 334 ± 197 × 109/L. Overall, 48 out of 77 (62%) patients presented with isolated erythrocytosis, 12 (16%) with erythrocytosis and leukocytosis (WBC count > 10 × 109/L), 8 (10%) with erythrocytosis and thrombocytosis (PLT count > 400 × 109/L), and 8 (10%) displayed a full myeloproliferative pattern (erythrocytosis, leukocytosis and thrombocytosis). Serum erythropoietin level was below the lower normal limit in 46 out of 58 (79%) patients. Twenty-one of 25 (84%) patients had endogenous erythroid colonies. During follow-up, two patients had deep venous thrombosis, two progressed to post-polycythemia vera myelofibrosis (diagnosed according to the IWG-MRT criteria) and two developed a myelodysplastic syndrome. In conclusion, the available data indicate that the myeloproliferative neoplasm associated with JAK2 exon 12 mutations is mainly associated with isolated erythrocytosis at clinical onset, but also suggest that the subsequent clinical course may be similar to that of JAK2 (V617F)-positive polycythemia vera, at least in a portion of patients. Disclosures: No relevant conflicts of interest to declare.

Abstract 3294 Poster Board III-1 Imatinib (IM) 400 mg daily is currently the standard treatment for early chronic phase (ECP) CML. Nilotinib, a more potent, second generation Abl inhibitor, is highly effective in IM resistant patients and two recent phase II trials have demonstrated impressive activity of nilotinib 400mg BID in ECP. Given the relatively favourable prognosis of this population with IM 400mg alone, any significant increase in toxicity compared to IM could be problematic. Thus, while initial results with nilotinib 400mg BID have been very encouraging, we wished to explore a lower dose schedule, 300mg BID, believing this could be equally effective but with the potential for fewer adverse events, such as lipase and bilirubin elevations and QT prolongation. To investigate the safety and efficacy of nilotinib 300 mg BID in untreated, ECP, Ph-pos CML patients, ICORG, the All-Ireland Cooperative Oncology Research Group is conducting an open-label, single stage, multicenter, phase II study (ClinicalTrials.gov NCT00809211). The primary endpoint is the CCyR rate at 6 months; secondary endpoints include the kinetics of molecular response, determined by Q-PCR at baseline and 3 monthly from start of treatment. To date, 15 patients have been enrolled on the trial. The median age is 56 (range 26 –77); 47% have low risk Sokal score, 20% intermediate and 33% high risk. Median follow up is currently 70 days (range 10–250). RESULTS: At 3 months 5 patients are evaluable for response: the CHR rate is 100%, the CCyR is 80% and MMR rate is 60%. No patient in the cohort (n=15) has progressed on study and there have been no dose escalations. The median daily dose was 415mg (range 261–600mg n=15); 5/15 interrupted nilotinib at least once with a median duration of interruption of 6 days. The dose of nilotinib at the last visit was 300mg BID in 11/15 patients (73%) and 200mg BID in 4/15 patients (27%). There was no grade III/IV haematologic toxicity. Grade III non-haematologic toxicity included an elevated lipase in 3/15 (20%). The only other grade III toxicity noted was musculo-sleketal pain in 1 patient. There were no grade IV toxicities. CONCLUSION: In this preliminary analysis, nilotinib 300mg BID induces high rates of CCyR. The current results are similar to those previously reported with nilotinb 400mg BID with less haematolgic toxicity noted but with haematologic, cytogenetic and molecular responses occuring within 3 months. Disclosures: Off Label Use: Nilotinib 300mg bid for newly diagnosed CML . Giles:Merck: Research Funding; BMS: Research Funding; Novartis: Research Funding; Millenium: Research Funding. le Coutre:BMS: Honoraria; Novartis: Honoraria. McMullin:BMS: Honoraria; Novartis: Honoraria. Egan:Novartis: Employment. Conneally:BMS: Honoraria; Novartis: Honoraria.

Chronic myeloid leukemia (CML) is a malignant disorder of the hematopoietic stem cell, characterised by the constitutively active tyrosine kinase BCR-ABL. The current first-line therapy for CML is the tyrosine kinase inhibitor imatinib. Although imatinib induces durable responses, a number of patients develop resistance to this treatment, highlighting the need to identify new molecular targets in this disease. Proteasome inhibition has recently emerged as a novel anti-cancer therapy. There is evidence to suggest that the proteasome is a valid target in CML. We have previously reported that proteasome activity is higher in bone marrow from patients with CML than normal controls. Furthermore, we demonstrated using a cell line model that Bcr-Abl positive cells were more sensitive to induction of apoptosis by proteasome inhibition than Bcr-Abl negative cells. The present study investigates the relationship between Bcr-Abl expression and proteasome activity and the effect of proteasome inhibition on primary human CML cells. Conventional fluorogenic substrate assays for all three catalytic activities of the proteasome [chymotrypsin-like (CT-L), trypsin-like (T-L), post glutamyl peptide hydrolysing (PGPH)] and proteasome activesite label DansylAhx3L3VS were used to profile proteasome activity levels in ts-Bcr-Abl FDCP-Mix cells and mock transfected FDCP-Mix cells. Both methods confirmed that Bcr-Abl positive cells have higher levels of proteasome activity than Bcr-Abl negative cells (p ≤ 0.04; Figure 1a). Conversely, downregulation of BCR-ABL using si-RNA was associated with a significant decrease in proteasome activity (p < 0.05; Figure 1b). The ability of the proteasome inhibitor BzLLLCOCHO to induce apoptosis in primary human CML cells was evaluated using Mitosensor™ and Hoescht/Propidium Iodide staining. Treatment with BzLLLCOCHO (1μM), selectively induced apoptosis in primary CML cells compared to normal mononuclear cells (39 ± 9.6 % vs 18.1 ± 4.02 %, 72 hrs, p = 0.01). Drug combination experiments were performed with BzLLLCOCHO (1 μM) and imatinib (1 μM) in ts-Bcr-Abl FDCP-mix cells and primary CML cells. Using Calcusyn software to generate the median effect of Chou-Talalay, the sequential addition of imatinib followed by BzLLLCOCHO was found to synergistically enhance the induction of apoptosis in ts-Bcr-Abl FDCP-Mix cells and resulted in additive effects in primary CML cells (n=4). The effect of the compounds on Bcr-Abl kinase activity was assessed by immunoblotting for phosphorylated Crkl. No effect on Bcr-Abl activity was seen following treatment of ts-Bcr-Abl FDCP-Mix cells and primary CML cells with BzLLLCOCHO alone, however, the combination of BzLLLCOCHO and imatinib resulted in a greater reduction of Bcr- Abl activity (59.8 ± 9.9 %) than imatinib alone (34.1 ± 9.6 %). Finally, we investigated the effect of BzLLLCOCHO on two human CML cell lines which are resistant to imatinib (KCL22-r, LAMA84-r). Imatinib resistant cells were found to be equally as sensitive to induction of apoptosis by BzLLLCOCHO as their imatinib sensitive counterparts (KCL22-s 30.7 ± 5.7 % vs KCL22-r 32 ± 1.7 %; LAMA84-s 56.3 ± 3.2 % vs Lama84-r 57.2 ± 7.9 %; 72 hrs). The present findings suggest that higher proteasome activity in Bcr- Abl positive cells may render these cells more susceptible to induction of apoptosis by proteasome inhibition and provide a rational basis to examine the potential of proteasome inhibitors as a therapeutic target in CML, particularly in imatinib resistant disease. Figure 1a. Bcr-Abl+ cells contain significantly greater levels of proteasome activity than Bcr-Abl cells siRNA directed against BCR-ABL decreases proteasome activity. Figure 1a. Bcr-Abl+ cells contain significantly greater levels of proteasome activity than Bcr-Abl cells . / siRNA directed against BCR-ABL decreases proteasome activity.

Transcriptionally erythropoietin (Epo) synthesis is tightly regulated by the hypoxia inducible factor (HIF), which is composed of one alpha and one beta subunit that are constitutively expressed. The beta subunit is non-variable, but three different alpha subunits give rise to three isoforms of HIF. The alpha subunit is proteasomally regulated in the presence of oxygen by hydroxylation of the proline in the LXXLAP motif of the oxygen dependent degradation (ODD) domain of HIFalpha, catalysed by members of the prolyl hydroxylase domain (PHD) family of enzymes. This allows the von Hippel Lindau (VHL) protein to associate with the alpha subunit, which is subsequently tagged with ubiquitin and degraded by the proteasome. Any defect in the oxygen sensing pathway that allows the alpha subunit to escape proteasomal regulation leads to elevated expression of HIF target genes. Recently mutations in both VHL and PHD2 have been identified in a cohort of patients with erythrocytosis, but no mutations were found in the ODD domain of HIF1alpha. Instead, investigation of the homologous region in HIF-2alpha revealed four different mutations, Pro534Leu, Met535Val, Gly537Arg and Gly537Trp in seven individuals/families. Affected individuals presented at a young age with elevated serum Epo. Several individuals have a clinical history of thrombosis, but no evidence of a von Hippel Lindau-like syndrome. To define how the four mutations relate to the erythrocytosis phenotype functional assays were performed in vitro. Binding of PHD2 to the four HIF-2alpha mutants was impaired to varying degrees, with both the Gly537 mutants showing the greatest reduction. The association of VHL with the hydroxylated Met535Val mutant peptide was similar to wild type HIF- 2alpha, but was decreased in the other three HIF-2alpha mutants. Expression of three HIF- 2alpha target genes, adrenomedullin, NDRG1 and VEGF, was significantly up-regulated in cells stably transfected with the mutants under normoxia compared to wild type HIF-2alpha. Mutations in the ODD domain of HIF-2alpha disrupt proteasomal regulation by reducing the association with PHD2 and hence hydroxylation. Furthermore the binding of VHL is also impaired, even when HIF-2alpha is hydroxylated. Examination of the three-dimensional structure of hydroxylated HIF-1alpha bound to VHL confirms that amino acids close to site of hydroxylation (Pro-531 in isoform 2) are important for this association. These observations, together with recent studies utilising murine models of erythrocytosis, support the PHD2-HIF-2alpha-VHL axis as the major regulator of erythropoietin.

In their response, Ostrovsky et al.1 suggest the lack of concordance between their findings and our findings may reflect differences between the populations studied. As stated by Ostrovsky et al.,1 their patient and control populations were heterogeneous, including individuals from several Jewish and non-Jewish ethnic groups. In contrast, all of the patient and control individuals included in our study2 were of Northern Irish origin. Due to its geographical isolation and historically low levels of inward migration, the population of Northern Ireland may be considered to be genetically more homogeneous relative to other populations, such as the Israeli population, studied by Ostrovosky et al. As such, we suggest that the influence of genetic factors predisposing to complex conditions, such as ALL, may be more apparent in our population.

Acute myeloid leukemia (AML) is a heterogeneous group of hematological malignancies with individual cases showing wide variations in response to treatment. Pre-treatment karyotype analysis may be used to stratify cases into one of three prognostic classes: favorable, intermediate or adverse. Favorable karyotypes, t(15;17), t(8;21) and inv(16), are associated with the presence PML-RARα, AML1-ETO and CBFβ-MYH11 gene rearrangements respectively. The adverse cytogenetic abnormalities are monosomy 5, monosomy 7, deletion of chromosome 5q, abnormalities of chromosome 3q and a complex karyotype. All remaining abnormalities are associated with an intermediate prognosis. Approximately 5–10% of cases cannot be stratified due to failure of cytogenetic analysis. Cryptic gene rearrangements, which cannot be detected by karyotyping, may lead to assignment of cases to incorrect prognostic classes. These problems may result in sub-optimal or over-treatment of patients. Using an artificial neural network-based analysis of HOX gene expression profiles generated by real-time quantitative PCR (RT-QPCR) we have previously shown that the favorable and intermediate cytogenetic classes are characterised by low HOXA5 (Ct value > 29.5) and high HOXB3 (Ct value < 25) expression respectively (Blood2006; 108: Abstract 2318). We have now measured HOXA5 and HOXB3 expression levels by RT-QPCR in a fresh set of 78 newly diagnosed cases of AML (31 favorable, 38 intermediate and 9 adverse karyotypes as determined by conventional cytogenetic analysis). All 31 cases with favorable cytogenetics had HOXA5 Ct values > 29.5 with twenty-nine (93.5%) having Ct values > 33. Therefore, using a HOXA5 Ct ≥; 33 to define membership of the favorable prognostic class and HOXA5 Ct < 33 to define membership of a non-favorable class, 72 cases (92.3%) were correctly assigned (29 favorable and 43 non-favorable). Of the 4 cases with non-favorable cytogenetics, originally misclassified by HOXA5 expression profiling, two were subsequently found to have cryptic rearrangements of PML-RARα and therefore should have been included within the favorable group. This increased the percentage of cases correctly assigned by HOXA5 expression profiling alone to 94.9%. We also found that within the favorable group, AML with t(15;17) or t(8;21) was characterized by low expression of HOXB3 (Ct range 30.9 to 37.4, median Ct 34.1) whereas AML with inv(16) had a distinct signature characterized by higher HOXB3 expression (Ct range 26.4 to 30.1, median Ct 28.0). In addition, we have identified a subset of patients with intermediate cytogenetics who have high white cell counts, low HOXB3 expression and an inferior response to treatment. Therefore, in AML, the measurement of expression levels of only two HOX genes, HOXA5 and HOXB3 , complements cytogenetic analysis and may improve the yield of favorable gene rearrangements detected and provide additional prognostic information for cases with intermediate or failed cytogenetics.

Human diseases have provided important insights into the function of fundamental physiological processes, and studying erythrocytosis has increased our understanding of the oxygen sensing pathway. In some cases this rare disorder arises specifically from dysregulation of the erythropoietin (Epo) axis. Epo gene transcription is under the control of a negative feedback mechanism involving the kidneys, which sense tissue hypoxia at the molecular level via the hypoxia inducible factor (HIF) transcription complex. Both subunits of the HIF complex, alpha and beta, are constitutively expressed but only the beta subunit is detectable in the presence of oxygen. Key prolines in the oxygen degradation domain of HIFalpha are hydroxylated by a family of prolyl hydroxylase enzymes, PHD1-3. Of these PHD2 has the most widespread tissue distribution. Upon hydroxylation of HIF, the von Hippel Lindau (VHL) protein, a component of an E3 ligase complex, promotes the ubiquitination of the alpha subunit. HIFalpha is then targeted to the proteasome and the transcription of HIF target genes is prevented. In hypoxia the activity of the PHD enzymes is low and the HIF complex assembles causing upregulation of genes such as Epo. Over the last ten years we have maintained a registry of individuals with erythrocytosis. To date 181 patients have been included with clinical details and consented DNA samples have been collected. There is a preponderance of males with ratio of 1.7 males to each female. The mean age of erythrocytosis individuals on the registry is 37 years. The majority of erythrocytosis patients have inappropriately normal (46%) or raised (26%) serum Epo levels as compared to PV, where the Epo level is often undetectable. Thus it can be inferred that dysregulation of the Epo axis via the oxygen sensing pathway would be a significant cause of erythrocytosis. Consequently, PHD2 and VHL have been investigated. We have now identified 2 different mutations, Pro317Arg and Arg371His, in PHD2. In the tertiary structure of PHD2, Pro317and Arg371 are close to essential iron binding residues and furthermore suggest the location of a HIF binding groove. The Arg200Trp VHL mutation, commonly described as the Chuvash mutation, has been detected in 8 Asian families and their large kindred. Two Western European individuals were found to be compound heterozygous for the Arg200Trp and either the novel Pro192Thr or Gly144Arg variants. Intriguingly 2 further individuals possess one wild type and one mutated allele, Arg200Trp or Leu188Val. Screening other genes of the oxygen sensing pathway has failed to reveal further defects in these individuals. In summary, defects in the oxygen sensing pathway are associated with the development of erythrocytosis. Mutations in VHL are more common than PHD2 and highlight the importance of these proteins in the maintenance of red cell homeostasis.

Idiopathic Erythrocytosis (IE) is a diagnosis given to patients who have an absolute erythrocytosis (red cell mass more than 25% above their mean normal predicted value) but who do not have a known form of primary or secondary erythrocytosis (BCSH guideline, 2005). We report here the results of a follow-up study of 80 patients (44 male and 36 female) diagnosed with IE from the United Kingdom and the Republic of Ireland over a 10 year period. Baseline information was initially collected when investigating for molecular causes of erythrocytosis in this group. The diagnosis of IE was made on the basis of a raised red cell mass >25% above mean normal predicted value, absence of Polycythaemia Vera (PV) based on the criteria of Pearson and Messinezy (1996), and the exclusion of secondary erythrocytosis (oxygen saturation >92% on pulse oximetry, no history of sleep apnoea, no renal or hepatic pathology, and a normal oxygen dissociation curve (if indicated). The average age at diagnosis of erythrocytosis was 34.5 (2–74 years). Erythropoietin levels were available for 77/80 of the patients and were low in 18 (23%) and normal or high in 59 (74%). Ultrasound imaging was carried out in 67 patients (84%) at time of diagnosis and no significant abnormalities found. Fourteen patients had a family history of erythrocytosis. These patients have now been followed up for an average of 9.4 years (range 1–39). Out of 80 patients 56 patients can still be classified as having IE, of whom 52 are living (cause of death in the other 4 - lung cancer, RTA, sepsis, unknown). Thirty-five of these patients are regularly venesected, 3 take hydroxyurea (one also venesected), 11 receive no treatment while treatment is unknown in 2. Twenty take aspirin, 1 warfarin and 31 no thromboprophylaxis. Four of these patients had suffered thromboembolic complications (3 with CVA/TIAs and 1 with recurrent DVT) at or before their original diagnosis. Since diagnosis 8 patients have had 9 thrombotic events of which 7 were arterial (1 CVA, 3 TIAs, 1 MI, 2 PVD) and 2 venous (DVT/PE). Twenty take aspirin, 1 dipyridamole, 1 warfarin and 30 take no thromboprophylaxis. Out of the 24 patients who now have a diagnosis other than IE, 8 have been diagnosed with myelo-proliferative disease. Thirteen patients have a molecular abnormality which is likely to account for their erythrocytosis (11 VHL, 1 PHD-2, 1 EPO-receptor mutations). Three patients have secondary erythrocytosis. Older case studies identified a heterogenous group of patients, some of whom probably had apparent erythrocytosis and some who had either primary polycythaemia or secondary causes later identified (Modan and Modan, Najean et al). More recent reviews have identified a more homogenous group with low rates of transformation to myelofibrosis/acute leukaemia and low rates of thrombosis of around 1% patient-year. Follow up of our initial patient group does indeed reveal a heterogeneous group of patients with 10% now diagnosed with an MPD, although when analysis is confined to those patients who continue to fulfil the criteria for IE, the clinical course has been more stable. There has been no progression to MDS or leukaemia in this group (one patient with PV progressed to AML). The rate of thrombosis is 1.6% patient-years which is lower than the rate seen in PV and is consistent with the rate identified in other series. Molecular defects continue to be identified in this group and future investigation is likely to reveal further abnormalities.

The acute myeloid leukemias (AMLs) are a heterogeneous group of hematological malignancies with diverse clinical outcomes. Pre-treatment karyotype analysis identifies biologically distinct subgroups and is currently used as a predictor of response to induction chemotherapy and risk of relapse. Cases may be stratified into one of three prognostic groups as follows: relatively favorable prognosis [t(8;21), t(15;17) and inv(16)]; adverse prognosis [−5/del(5q), −7, abnormalities of chromosome 3q and complex karyotype]; and intermediate prognosis [remainder including normal karyotype]. HOX genes encode master transcription factors which regulate key developmental processes including differentiation, proliferation and apoptosis. Humans have 39 HOX genes and multiple lines of evidence implicate their deregulated expression in the pathogenesis of AML. Drabkin et al. (Leukemia2002; 16: 186–95) have reported that AMLs with a relatively favorable prognostic karyotype are associated with low levels of HOX gene expression whereas AMLs with an adverse prognostic karyotype have higher levels of expression. To further characterize HOX gene expression in cytogenetic prognostic groups we determined the expression profiles of 26 HOX genes by real-time quantitative PCR (Q-PCR) in diagnostic samples, representative of the three prognostic groups, from 26 patients with de novo AML. Profiles were then analyzed using Artificial Neural Network based computational approaches to identify a subset of HOX genes which could discriminate between prognostic groups in a predictive fashion. Predictive models were developed for each prognostic group. Predictive classification performance for prognostic groups based on blind data of 88%, 92%, and 97% (with equal sensitivity and specificity) were achieved for the three prognostic groups. The models were interrogated to determine the nature of the relationship between the key HOX genes identified and prognostic group. The relatively favorable prognosis group was primarily defined by downregulation of HOXA5 and upregulation of HOXC4. The intermediate prognosis group was characterized by upregulation of HOXB3 and downregulation of HOXD10 and the adverse prognosis group by downregulation of both HOXC5 and HOXD3. Although the sample size is small, the results show that Artificial Neural Network based computational approaches are capable of further characterizing HOX gene expression within AML prognostic groups as determined by presenting karyotype and that measuring the expression levels of a small number of HOX genes at diagnosis can provide useful clinical information in cases where karyotype analysis has been unsuccessful.

Molecular classification of acute myeloid leukemia (AML) has identified several candidate genes that could potentially define prognosis and response to therapy. One such candidate, identified from microarray studies, is the Class I homeobox gene HOXA9. The HOX gene network encodes master regulators of developmental processes including hemopoiesis. To quantify the contribution of this network of genes in AML, we carried out specific RQ-PCR analysis on twenty-four de novo patient samples using a subset of genes (12 HOX and MEIS1 ) selected on the basis of their recently reported expression in AML. HOXA6 was ranked, as the most highly expressed gene (range 1 x 103 – 2 x 107 copies per 50 ng RNA), substantially higher than HOXA9 (see Table). Further analysis identified high expression of HOXA6 in both human myeloid cell lines and CD34+ enriched primary progenitors. Parallel studies with murine progenitors (c-Kit+, Lin−) and cell lines also showed a preponderance of Hoxa6 expression over other family members including Hoxa9 and Hoxb4 . Several hemopoietic cell lines, namely Ba/F3, EML, FDCP-Mix A4 and 32Dcl3 were subsequently used to investigate Hoxa6 regulation following differentiation or growth factor stimuli. Hoxa6 expression decreased with cell differentiation and growth factor depletion/replenishment studies indicated a cell-cycle component for Hoxa6 regulation. Direct evaluation of cell-cycle status, using Hoechst 33342 staining and cell sorting, identified peak expression of Hoxa6 during S-phase. Gene deletion studies involving Hox tend to result in either a moderate or no phenotype, presumably due to intrinsic compensatory mechanisms. We therefore overexpressed HOXA6 in the Ba/F3 cell line to gain functional insights. Ba/F3- A6 cells were compared to mock-transfected and vector controls on the basis of proliferation, maturation, cell-cycle status, growth factor-dependence and apoptosis. The Ba/F3- A6 cells displayed a growth advantage over normal cells in the presence of IL-3 and maturation was not impaired. Cell-cycle analysis showed a reduction in the number of cells in both G2M and S-phase, associated with accumulation in the pre G1-phase, indicative of increased apoptosis. IL-3 depletion studies of Ba/F3- A6 cells indicated substantial factor-independent growth compared to controls, implying oncogenic potential for HOXA6 . In support of this, a recent report (Mamo et al, Blood. 2006 Jul 15;108(2):622–9) indicated Hoxa6 as a potential collaborator in a Meis1 -induced model of AML. Taken together these findings identify Hoxa6 as a novel candidate gene in AML with the capacity to alter growth and survival of hemopoietic cells. | GENE | EXPRESSION RANGE | MEAN RANK | S.D. | OVERALL RANK | |:--------------------------------------------------------------------------------------------------------------------------------:| --------------------- | --------- | ---- | ------------ | | Expression values (copies per 50 ng RNA) compiled from primary AML patient samples (n=24) or * (n=12). S.D = standard deviation. | | HOXA6 | 1.2 x 103 – 1.7 x 107 | 2.2 | 1.6 | 1 | | HOXB3 | 9.3 x 101 – 8.4 x 106 | 3.2 | 2.5 | 2 | | HOXB2 * | 7.9 x 102 – 5.4 x 106 | 3.4 | 2.0 | 3 | | HOXA9 | 4.0 x 101 – 5.3 x 106 | 5.3 | 2.4 | 4 | | MEIS1 | 0.6 x 101 – 8.4 x 106 | 5.4 | 2.7 | 5 | | HOXA10 * | 2.4 x 102 – 1.7 x 105 | 5.5 | 3.2 | 6 | | HOXB4 | 1.5 x 102 – 7.8 x 105 | 5.5 | 3.2 | 7 | | HOXA7 * | 5.3 x 103 – 1.8 x 106 | 5.7 | 1.7 | 8 | | HOXB6 | 2.3 x 101 – 8.8 x 105 | 6.6 | 2.8 | 9 | | HOXA4 | 4.1 x 101 – 1.1 x 105 | 7.9 | 3.4 | 10 | | HOXA5 * | 3.4 x 101 – 4.3 x 104 | 9.3 | 2.8 | 11 | | HOXC6 | 1.0 x 101 – 3.2 x 103 | 9.7 | 2.3 | 12 | | HOXA11 * | 4.0 x 101 – 6.1 x 103 | 10.6 | 2.2 | 13 | Gene Expression Ranking of HOX and MEIS1 in AML.

X-linked sideroblastic anaemia (XLSA; OMIM 301 300) is characterised by accumulation of inorganic iron in erythroblast mitochondria, visualised on staining as distinctive perinuclear rings. It arises from a deficiency of the erythroid specific isoenzyme of δ-aminolaevulinate synthase (ALAS2; E.C. 2.3.1.3.7), caused mainly by mutations affecting the catalytic or substrate-binding domains.1,2 ALAS2 uses pyridoxal-5-phosphate as a cofactor to catalyse the first, rate-limiting step of erythroid haem synthesis and pyridoxine treatment can alleviate anaemia in many cases, although the response is variable and affected by factors such as mutation, age and iron load.3,4 …

Normal erythropoiesis is precisely regulated by a negative feedback mechanism based on the oxygen status of the body. Whenever a deficit in oxygen supply is detected erythropoietin (Epo) is rapidly synthesised to increase circulating red cells. This process is under the control of the HIF transcription complex, which is composed of one alpha and one beta subunit. Although the alpha subunit is constitutively synthesized, it is maintained at a low level by continual targeting to the proteasome. Prolines 402 and 564 in the oxygen dependent degradation (ODD) domain of HIF-1α are hydroxylated in the presence of oxygen by members of the PHD family of prolyl hydroxylases. Once hydroxylated HIF-1α is captured by the von Hippel Lindau tumour suppressor gene product (VHL), ubiquitylation follows and HIF-1α is then targeted for proteasomal degradation. Defects in the hypoxia response pathway appear to be the most common cause of erythrocytosis associated with inappropriately normal or elevated serum Epo. Several different mutations in the VHL gene have been detected in erythrocytosis individuals. Although these mutations explain a significant number of cases there remains a large cohort where the molecular defect is undefined. Thus we screened a group of such individuals for base changes in PHD 1–3. Two affected siblings and their deceased father were found to possess a heterozygous C to G change at base 950 in the coding sequence of PHD2, causing loss of proline at codon 317 and replacement with arginine. This base change was not present in their normal mother nor in 200 normal controls. Residue 317 is located in the enzyme’s active site and at a position two residues C-terminal to Asp315, which chelates the active site iron moiety. Functional analysis indicated that the Pro317Arg PHD2 variant bound to HIF-1α and HIF-2α more weakly and displayed substantially less HIF hydroxylase activity than the wild type protein. These results indicate that the Pro317Arg PHD2 mutant protein’s function will be impaired, less hydroxylation of HIF will occur, allowing more HIF to escape proteasomal degradation and to increase transcription of HIF target genes. Consequently, Epo gene expression will be elevated thereby allowing increased erythrocyte production and the development of erythrocytosis.

The NCRI AML14 Trial was devised for patients aged over 60 years with de novo or secondary AML or high risk MDS (defined as >10% blasts). There was a non-intensive option which compared Low Dose Ara-C vs Hydroxyurea each with or without All-Trans Retinoic Acid which has been reported previously (Burnett et al Blood2004: 249a), and an intensive approach which we now report. This compared two dose levels of Daunorubicin (50mg/m2 vs 35mg/m2) and Ara-C (200mg/m2 vs 400mg/m2) within a Daunorubicin/Ara-C (3+10) followed by (3+8) schedule. After a 3rd course (MidAC: Mitoxantrone/Ara-C), patients were randomised to receive or not a 4th course (ICE: Idarubicin/Ara-C/Etoposide). In addition some patients (n=200) were randomised to receive PSC-833 in addition to Dauno 35. The results of this randomisation have been reported previously (Burnett et al Blood 2003614a). A total of 1273 patients entered the trial between December 1998 and closure in May 2005, from 136 centres. Follow-up is complete to 1st April 2005, with median follow-up of 33 months. The median age was 67 (range 44-88). Cytogenetics were known for 67% of patients: of these, 3% had favourable, 74% intermediate and 23% adverse cytogenetics. 72% had de novo AML, 17% had secondary disease and 11% had high risk MDS. The overall CR rate was 62% and the Relapse Risk (RR), Disease Free Survival (DFS), and Overall Survival (OS) were 84%, 13%, and 13% at 5 years. 896 patients were randomised to D50 vs D35. No significant differences were found in CR (63% vs 64% OR 1.04 (95% CI 0.78–1.37)), RR (84% vs 85% OR 0.85 (95%CI 0.65–1.06)), DFS 14% vs 13% OR 0.86 (95% CI 0.70–1.06)), or OS (15% vs 13% OR 0.92, 95% CI (0.72–1.08)). Likewise, there were no significant differences in outcome for the 1264 patients randomised to Ara-C 200 vs 400: CR (62% vs 62% OR 1.00 (95% CI 0.80–1.27)), RR (84% vs 85% OR 1.14 (95% CI 0.95–1.37)), DFS (13% vs13% OR 1.14 (95% CI 0.96–1.14)) or OS (13% vs 12% OR 1.00 (95%CI 0.87–1.14)). In the 255 patients randomised to a total of 4 vs 3 courses the RR (83% vs 76% OR 0.90 95%CI 0.66–1.24), DFS (16% vs 18% OR 0.94 95% CI 0.69–1.28) and OS (23% vs 22% OR 1.05, 95% CI 0.75–1.47) were not significantly different. From this preliminary analysis we conclude that there is no difference between a reduced dose of Daunorubicin (35mg/m2) compared with standard dose, or between enhanced Ara-C dose (400mg/m2) or standard dose and the confidence intervals are consistent with at most a moderate difference in treatment effect. We found no benefit for giving more than 3 courses of total treatment to patients in this age group, although the confidence intervals here do not rule out moderate, but potentially meaningful differences.

Deficiency of NADH-cytochrome b 5 reductase (c b 5r) causes two clinically distinct phenotypes of recessive congenital methemoglobinemia (RCM). Type I patients often manifest cyanosis from birth, and in type II patients the cyanosis is accompanied by severe neurological impairment. The mechanisms responsible for the phenotypic differences between the two subgroups remain to be defined. The majority of patients harbor two different mutant alleles. To date 39 mutant variants of c b 5r have been identified, 2 of which are common to both types of RCM. In order to characterize the individual c b 5r variant proteins we have developed a novel heterologous expression system based on the structures of the rat and human proteins derived by X-ray crystallography. The system permits the investigation of the catalytic efficiencies, protein thermostability, FAD cofactor properties and substrate (NADH/NAD+) affinities of the variants. We have investigated four patients with type I RCM, one of whom was homozygous for the D239G mutation. The other three were compound heterozygous: R159-/D239G; G75S/V252M; and P275L/G291D, and one mutation, P275L, was novel. All patients showed reduced enzyme activity, in the range 0.5 to 5.8 IU/g Hb compared to normal values of 7.2 to 26.9 IU/g Hb. Individual variant proteins were prepared and the analytical data are summarised in the Table below. | Variant | Catalytic Efficiency (% of normal) | Thermal Stability (T50°C) | NADH affinity (Km) | NAD+ affinity (Ks) | |:-------------------:| ---------------------------------- | ------------------------- | ------------------ | ------------------ | | ND - not determined | | G75S | 11 | 48 | Normal | 9-fold ↑ | | R159- | | ND | ND | ND | | D239G | 2 | 56 | 40-fold ↓ | ND | | V252M | 9 | 53 | 9-fold ↓ | 18-fold ↑ | | E255- | 0.4 | 51 | 100-fold ↓ | ND | | P275L | 0.2 | 53 | 437-fold ↓ | ND | | G291D | 43 | 49 | 1.3-fold ↓ | 1.1-fold ↑ | | Wild type | 100 | 57 | normal | normal | As expected all of the variants generated had decreased enzyme activity compared to wild type heterologous protein, supporting the validity of this approach. Thermal stability was decreased in the G75S, V252M and G291D variants. G75 is present in a highly conserved region in the FAD-binding lobe. Although it does not interact directly with the FAD prosthetic group it is important for association with cytochrome b 5. Substitution of glycine at residue 75 by serine resulted in decreased enzyme activity and stability, with a marginal decrease in NADH affinity. The R159- variant protein was unstable and could not be isolated. Both the D239G and P275L mutations significantly reduced the affinity of c b 5r for NADH, by 40-fold and 437-fold respectively. The rat c b 5r model suggests that residue D239 is key for selecting between the NADPH and NADH pyridine nucleotides. This was confirmed by the 40-fold decrease in affinity for NADH and a 125-fold increase in affinity for NADPH. Residue P275 is located in a highly conserved region, which is important for the correct positioning and binding of NADH. Consequently, substitution of proline at 275 would affect the affinity of c b 5r towards NADH, which was confirmed by the affinity constant measurements. These studies provide important information about the structure-function relationships of the variant c b 5r proteins which may impart useful insights into the pathophysiological differences between type I and type II RCM.

The molecular basis of inherited erythrocytosis in most patients remains to be defined. Although all such patients have an absolute increase in red cell mass, their erythropoietin (EPO) levels differ widely, so they constitute a heterogeneous group of disorders known collectively as idiopathic erythrocytosis (IE). A proportion of individuals with IE progress to polycythemia vera (PV), a clonal disorder arising from a multipotent progenitor. Recently a gain-of-function mutation in Janus kinase 2 (JAK2), V617F, has been described in myeloproliferative disorders (MPD) and a stream of publications has confirmed its presence in the majority of patients with PV. Screening IE patients for this mutation will provide a useful additional means for delineating inherited and clonal disorders of erythrocytosis. Over the last decade we have maintained a registry of British and Irish erythrocytosis patients, consisting of clinical information and DNA samples obtained following full ethical approval. Screening the EPO receptor (EPO-R) in 120 patients identified one patient with a G6002A mutation, which leads to truncation of the receptor by 70 amino acids, increased sensitivity to EPO, and erythrocytosis. Screening the same patients for mutations in the von Hippel Lindau (VHL) gene has revealed individuals from 8 families of Asian origin who are homozygous for the Chuvash (R200W) mutation causing erythrocytosis. In addition, one Caucasian individual of English descent is compound heterozygous for R200W and the recently described G144R VHL mutation. A further individual, D1 (Percy et al, 2003Blood102:1097), of the same ethnicity is heterozygous for the Chuvash mutation and has been found to express the wild type allele. Both his mother and son, who are heterozygous for the Chuvash mutation, do not have IE, suggesting that the patient harbors a second unidentified genetic defect. Several such individuals have already been described (reviewed by Randi et al, 2005 Haematologica 90:689). In order to estimate the proportion of IE patients likely to progress to PV, 65 individuals from the registry with EPO levels in the low to normal range were screened by amplification refractory mutation system (ARMS) PCR for the MPD-associated V617F JAK2 mutation. Two individuals were positive, one of whom subsequently proceeded rapidly to PV, while the other has remained stable without any disease progression. In addition 9 families with VHL mutations were also screened and all were found to be negative for the JAK2 mutation, suggesting that the occurrence of these mutations tends to be mutually exclusive. Also the V617F JAK2 mutation does not constitute the second genetic defect in patient D1 who is heterozygous for the Chuvash VHL mutation. Although VHL mutations are the most frequent cause of inherited erythrocytosis in our registry they are present in only ~10% of patients, while the gain-of-function of JAK2 mutation is rare, leaving ~90% of the IE cases unexplained. Further study of this group may reveal additional regulatory mechanisms involved in red cell homeostasis.

There is no adequate treatment for older patients with AML who are not considered fit for intensive chemotherapy who comprise a significant proportion of the AML population. As part of the ongoing NCRI (formerly MRC) AML14 Trial in patients over 60 years patients were randomised to Low Dose Ara-C (20mg bd for 10 days every 4–6 weeks) versus Hydroxycarbamide (Hydroxyurea). Because of preclinical studies showing sensitization to Ara-C, patients were in addition randomised to receive All-transretinoic acid or not (45mgs/m2 for 60 days). Two hundred and four patients entered; 129 had a WHO score of 65 yrs; 108 had do novo, 53 secondary disease and 28 had high risk MDS (blasts >10%). One hundred and ninety-nine patients entered the HU vs LD-Ara-C randomisation and 204 entered the ATRA randomisation. The arms were balanced with respect to age; sex; disease type; WBC and performance score. Complete remission was seen in 1 of 92 (1%) patients in the HU arm and 15 of 94 (17%) in the LD Ara-C arm (P=0003). Overall survival was considerably improved (hazard ratio 0.61, 95% Cl 0.45 to 0.82, p=0.001). This improvement in outcome was not obtained at the expense of less well tolerated treatment: toxicity and supportive care requirements were similar between the two groups. However, there were no significant differences in outcome between patients given ATRA or not overall or within the treatment arms, although numbers were too small to rule out moderate benefits or disbenefits of treatment (hazard ratio for OS 0.97, 95% Cl 0.73 to 1.28, p=0.8). We conclude that LD-Ara-C in the schedule chosen could be adopted as a standard of care for older patients not fit for intensive chemotherapy but the outcome remains poor. Future strategies could combine Low Dose Ara-C with novel agents. This trial received a research grant from the UK Leukaemia Research Fund.

Background The hypoxia-inducible factor (HIF) transcription complex, which is activated by low oxygen tension, controls a diverse range of cellular processes including angiogenesis and erythropoiesis. Under normoxic conditions, the α subunit of HIF is rapidly degraded in a manner dependent on hydroxylation of two conserved proline residues at positions 402 and 564 in HIF-1α in the oxygen-dependent degradation (ODD) domain. This allows subsequent recognition by the von Hippel-Lindau (VHL) tumor suppressor protein, which targets HIF for degradation by the ubiquitin-proteasome pathway. Under hypoxic conditions, prolyl hydroxylation of HIF is inhibited, allowing it to escape VHL-mediated degradation. The transcriptional regulation of the erythropoietin gene by HIF raises the possibility that HIF may play a role in disorders of erythropoiesis, such as idiopathic erythrocytosis (IE).

Serum erythropoietic activity and reticulocyte response to anemia were investigated using a rabbit model. In hemolytic anemia, induced by injections of phenylhydrazine on Day 0 the hemoglobin reached a nadir (mean, 6.23 g/dl) on Day 4 when SEA was maximal (mean, 765 mU/ml). In animals venesected on Day 0 and Day 1 to produce anemia of equal severity, the SEA was maximal (mean 235 mU/ml) on Day 2. In both groups the reticulocyte response peaked on Day 7--at 34% for the hemolytic group and 21% for the venesected group. The 2,3-diphosphoglycerate, measured on Day 4, was significantly reduced in the PHZ-treated group. In the venesected group the 2,3-DPG increased between Day 0 and Day 4. There were no concurrent changes in acid-base balance. These results imply that the degree of anemia is only one of the factors which influence the level of circulating SEA.

The mouse spleen cell assay (MSCA) has been compared with a radioimmunoassay for the measurement of serum erythropoietin (Ep). In 20 normal subjects the serum values ranged from 15 to 73 mU/ml for the MSCA compared with 5-30 mU/ml for the RIA. For normal sera there was no correlation between the results of the two assays. In 37 patients with anaemias of differing aetiologies and at various stages of treatment values ranged from 10 to 3645 mU/ml for the MSCA and 13-10,000 mU/ml for the RIA. Although patient values from the two assays were highly correlated (r = 0.98, P less than 0.001), the MSCA results were generally lower. These discrepancies can be largely accounted for by two factors. Firstly the MSCA is sensitive to non-specific matrix effects. Secondly, heat inactivation of serum, a prerequisite for the MSCA, but not for the RIA, destroys a variable and unpredictable proportion of the Ep in the test sera leading to an underestimation of Ep in the MSCA. We conclude that the RIA is more reliable than the MSCA which, in its present form, cannot be recommended for the accurate measurement of serum erythropoietin.

7058 Background: PAC is a novel JAK2/IRAK1 inhibitor that has shown significant activity in pts with MF, including those with platelet (plt) counts 9/L. Recently, JAK inhibitors have come under increased scrutiny due to specific, emerging toxicities with drugs in this class. This safety analysis focuses on these toxicities of interest for pts treated with PAC 200 mg BID and best available therapy (BAT), including ruxolitinib (RUX), on the Phase 3 PERSIST-2 and Phase 2 PAC203 studies. Data are presented as risk-adjusted incidences to account for differential time at risk for adverse events (AEs) between arms due to cross-over. Methods: Pts treated with PAC 200 mg BID on PERSIST-2 and PAC203, and those treated with BAT on PERSIST-2, were included. Risk-adjusted AEs, representing event rate per 100 patient-years (pt-yrs), were calculated for overall and fatal AEs, bleeding AEs (determined by Standardized Medical Dictionary for Regulatory Activities Query [SMQ]), cardiac AEs (by SMQ), major cardiac events (per major adverse cardiovascular events [MACE] classification), infections, thromboses, and secondary malignancies. Results: A total of 160 pts were analyzed as the pooled PAC group (n=106 in PERSIST-2; n=54 in PAC203) and 98 pts in the BAT group (44 on RUX). At baseline, median plt count was 57×109/L; 61% had prior JAK2 inhibitor therapy. The rate of AEs was higher on PAC versus BAT, while the rate of fatal AEs was lower (Table). Both bleeding and cardiac events occurred at slightly lower rates on PAC compared to BAT. There were no MACE events on PAC, whereas there were on BAT. Malignant neoplasms occurred at similar rates on PAC and BAT, though rate of non-melanoma skin cancers was lower in pooled PAC (3/100 pt-yrs) versus BAT (7/100 pt-yrs), including RUX (11/100 pt-yrs). Infection occurred more frequently on PAC, though fungal and viral infections occurred less frequently, as did herpes zoster reactivation (pooled PAC: 0/100 pt-yrs vs BAT: 2.4/100 pt-yrs, including RUX: 5.5/100 pt-yrs). Thrombosis occurred at similar rates on PAC and BAT. Conclusions: Risk-adjusted analysis demonstrates that the safety profile of PAC 200 mg BID is comparable or superior to BAT, including RUX. PAC 200 mg BID may represent a full-dose therapeutic option for pts with MF, including those with thrombocytopenia. Clinical trial information: NCT02055781; NCT04884191. [Table: see text]

BACKGROUND: Anemia is considered a negative prognostic risk factor for survival in patients with myelofibrosis. Most patients with myelofibrosis are anemic, and 35-54 % present with anemia at diagnosis. Ruxolitinib, a potent inhibitor of Janus kinase (JAK) 1 and JAK2, was associated with an overall survival benefit and improvements in splenomegaly and patient-reported outcomes in patients with myelofibrosis in the two phase 3 COMFORT studies. Consistent with the ruxolitinib mechanism of action, anemia was a frequently reported adverse event. In clinical practice, anemia is sometimes managed with erythropoiesis-stimulating agents (ESAs). This post hoc analysis evaluated the safety and efficacy of concomitant ruxolitinib and ESA administration in patients enrolled in COMFORT-II, an open-label, phase 3 study comparing the efficacy and safety of ruxolitinib with best available therapy for treatment of myelofibrosis. Patients were randomized (2:1) to receive ruxolitinib 15 or 20 mg twice daily or best available therapy. Spleen volume was assessed by magnetic resonance imaging or computed tomography scan.RESULTS: Thirteen of 146 ruxolitinib-treated patients had concomitant ESA administration (+ESA). The median exposure to ruxolitinib was 114 weeks in the +ESA group and 111 weeks in the overall ruxolitinib arm; the median ruxolitinib dose intensity was 33 mg/day for each group. Six weeks before the first ESA administration, 10 of the 13 patients had grade 3/4 hemoglobin abnormalities. These had improved to grade 2 in 7 of the 13 patients by 6 weeks after the first ESA administration. The rate of packed red blood cell transfusions per month within 12 weeks before and after first ESA administration remained the same in 1 patient, decreased in 2 patients, and increased in 3 patients; 7 patients remained transfusion independent. Reductions in splenomegaly were observed in 69 % of evaluable patients (9/13) following first ESA administration.CONCLUSIONS: Concomitant use of an ESA with ruxolitinib was well tolerated and did not affect the efficacy of ruxolitinib. Further investigations evaluating the effects of ESAs to alleviate anemia in ruxolitinib-treated patients are warranted (ClinicalTrials.gov identifier, NCT00934544; July 6, 2009).

The role of antiplatelet therapy as primary prophylaxis of thrombosis in low-risk essential thrombocythemia has not been studied in randomized clinical trials. We assessed the benefit/risk of low-dose aspirin in 433 patients with low-risk essential thrombocythemia (271 with a CALR mutation, 162 with a JAK2(V617F) mutation) who were on antiplatelet therapy or observation only. After a follow up of 2215 person-years free from cytoreduction, 25 thrombotic and 17 bleeding episodes were recorded. In CALR-mutated patients, antiplatelet therapy did not affect the risk of thrombosis but was associated with a higher incidence of bleeding (12.9 versus 1.8 episodes per 1000 patient-years, P=0.03). In JAK2(V617F)-mutated patients, low-dose aspirin was associated with a reduced incidence of venous thrombosis with no effect on the risk of bleeding. Coexistence of JAK2(V617F)-mutation and cardiovascular risk factors increased the risk of thrombosis, even after adjusting for treatment with low-dose aspirin (incidence rate ratio: 9.8; 95% confidence interval: 2.3-42.3; P=0.02). Time free from cytoreduction was significantly shorter in CALR-mutated patients with essential thrombocythemia than in JAK2(V617F)-mutated ones (median time 5 years and 9.8 years, respectively; P=0.0002) and cytoreduction was usually necessary to control extreme thrombocytosis. In conclusion, in patients with low-risk, CALR-mutated essential thrombocythemia, low-dose aspirin does not reduce the risk of thrombosis and may increase the risk of bleeding. This work was supported by the grants from the Instituto de Salud Carlos III, Spanish Health Ministry, PI13/00557, PI1300393, and RD012/0036/0004. Florence team was supported by AIRC project number 1005 "Special program Molecular Clinical Oncology 5x1000 to Associazione Italiana per la Ricerca sul Cancro Gruppo Italiano Malattie Mieloproliferative (AGIMM). PG was supported by AIRC IG-2014-15967."