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Interleukin-1 receptor-associated kinases (IRAK1, IRAK2, IRAK3 [IRAK-M], and IRAK4) are serine-threonine kinases involved in toll-like receptor and interleukin-1 signaling pathways, through which they regulate innate immunity and inflammation. Evidence exists that IRAKs play key roles in the pathophysiologies of cancers, and metabolic and inflammatory diseases, and that IRAK inhibition has potential therapeutic benefits. Molecules capable of selectively interfering with IRAK function and expression have been reported, paving the way for the clinical evaluation of IRAK inhibition. Herein, we focus on IRAK1, review its structure and physiological roles, and summarize emerging data for IRAK1 inhibitors in preclinical and clinical studies., Competing Interests: CONFLICTS OF INTEREST AF – Speakers bureau (Incyte), travel/accomodations (Incyte, Gilead) AA – Research funding (CTI) SAF – Employment, equity ownership, travel/accomodations (CTI) JM – Consulting/advisory role (CTI), research funding (CTI, Incyte, Janssen, Novartis, Merck, Promedior) QY – Nothing to disclose JS – Employment, leadership role, equity ownership (CTI).

Importance: Myelofibrosis is a hematologic malignancy characterized by splenomegaly and debilitating symptoms. Thrombocytopenia is a poor prognostic feature and limits use of Janus kinase 1 (JAK1)/Janus kinase 2 (JAK2) inhibitor ruxolitinib., Objective: To compare the efficacy and safety of JAK2 inhibitor pacritinib with that of best available therapy (BAT), including ruxolitinib, in patients with myelofibrosis and thrombocytopenia., Design, Setting, and Participants: For this phase 3 randomized international multicenter study-the PERSIST-2 study-of pacritinib vs BAT, 311 patients with myelofibrosis and platelet count 100 × 109/L or less were recruited for analysis. Crossover from BAT was allowed after week 24 or for progression of splenomegaly., Interventions: Patients were randomized 1:1:1 to pacritinib 400 mg once daily, pacritinib 200 mg twice daily, or BAT., Main Outcomes and Measures: Coprimary end points were rates of patients achieving 35% or more spleen volume reduction (SVR) and 50% or more reduction in total symptom score (TSS) at week 24. Efficacy analyses were performed on the intention-to-treat efficacy population, comprising all patients with a randomization date allowing for week 24 data., Results: Overall, 311 patients (mean [SD] age, 63.70 [9.08] years; 171 men [55%] and 140 women [45%]) were included in the study; 149 patients (48%) had prior ruxolitinib. The most common BAT was ruxolitinib (44 patients [45%]); 19 patients (19%) received watchful-waiting only. The intention-to-treat efficacy population included 75 patients randomized to pacritinib once daily; 74, pacritinib twice daily, and 72, BAT. Pacritinib (arms combined) was more effective than BAT for 35% or more SVR (27 patients [18%] vs 2 patients [3%]; P = .001) and had a nonsignificantly greater rate of 50% or more reduction in TSS (37 patients [25%] vs 10 patients [14%]; P = .08). Pacritinib twice daily led to significant improvements in both end points over BAT (≥35% SVR: 16 patients [22%] vs 2 patients [3%]; P = .001; ≥50% reduction in TSS: 24 patients [32%] vs 10 patients [14%]; P = .01). Clinical improvement in hemoglobin and reduction in transfusion burden were greatest with pacritinib twice daily. For pacritinib once daily, pacritinib twice daily, and BAT, the most common (>10%) grade 3 or 4 adverse events were thrombocytopenia (32 patients [31%], 34 patients [32%], 18 patients [18%]), and anemia (28 patients [27%], 23 patients [22%], 14 patients [14%]). In the pacritinib once daily, twice daily, and BAT arms, discontinuation owing to adverse events occurred in 15 patients (14%), 10 patients (9%), and 4 patients (4%)., Conclusions and Relevance: In patients with myelofibrosis and thrombocytopenia, including those with prior anti-JAK therapy, pacritinib twice daily was more effective than BAT, including ruxolitinib, for reducing splenomegaly and symptoms., Trial Registration: clinicaltrials.gov Identifier: NCT02055781.

Background: Available therapies for myelofibrosis can exacerbate cytopenias and are not indicated for patients with severe thrombocytopenia. Pacritinib, which inhibits both JAK2 and FLT3, induced spleen responses with limited myelosuppression in phase 1/2 trials. We aimed to assess the efficacy and safety of pacritinib versus best available therapy in patients with myelofibrosis irrespective of baseline cytopenias., Methods: This international, multicentre, randomised, phase 3 trial (PERSIST-1) was done at 67 sites in 12 countries. Patients with higher-risk myelofibrosis (with no exclusions for baseline anaemia or thrombocytopenia) were randomly assigned (2:1) to receive oral pacritinib 400 mg once daily or best available therapy (BAT) excluding JAK2 inhibitors until disease progression or unacceptable toxicity. Randomisation was stratified by risk category, platelet count, and region. Treatment assignments were known to investigators, site personnel, patients, clinical monitors, and pharmacovigilance personnel. The primary endpoint was spleen volume reduction (SVR) of 35% or more from baseline to week 24 in the intention-to-treat population as assessed by blinded, centrally reviewed MRI or CT. We did safety analyses in all randomised patients who received either treatment. Here we present the final data. This trial is registered with ClinicalTrials.gov, number NCT01773187., Findings: Between Jan 8, 2013, and Aug 1, 2014, 327 patients were randomly assigned to pacritinib (n=220) or BAT (n=107). Median follow-up was 23·2 months (IQR 14·8-28·7). At week 24, the primary endpoint of SVR of 35% or more was achieved by 42 (19%) patients in the pacritinib group versus five (5%) patients in the BAT group (p=0·0003). 90 patients in the BAT group crossed over to receive pacritinib at a median of 6·3 months (IQR 5·8-6·7). The most common grade 3-4 adverse events through week 24 were anaemia (n=37 [17%]), thrombocytopenia (n=26 [12%]), and diarrhoea (n=11 [5%]) in the pacritinib group, and anaemia (n=16 [15%]), thrombocytopenia (n=12 [11%]), dyspnoea (n=3 [3%]), and hypotension (n=3 [3%]) in the BAT group. The most common serious adverse events that occurred through week 24 were anaemia (10 [5%]), cardiac failure (5 [2%]), pyrexia (4 [2%]), and pneumonia (4 [2%]) with pacritinib, and anaemia (5 [5%]), sepsis (2 [2%]), and dyspnoea (2 [2%]) with BAT. Deaths due to adverse events were observed in 27 (12%) patients in the pacritinib group and 14 (13%) patients in the BAT group throughout the duration of the study., Interpretation: Pacritinib therapy was well tolerated and induced significant and sustained SVR and symptom reduction, even in patients with severe baseline cytopenias. Pacritinib could be a treatment option for patients with myelofibrosis, including those with baseline cytopenias for whom options are particularly limited., Funding: CTI BioPharma Corp., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Purpose: Monocytes and their progeny are abundant constituents of the tumor microenvironment in lymphoproliferative disorders, including chronic lymphocytic leukemia (CLL). Monocyte-derived cells, including nurse-like cells (NLC) in CLL, promote lymphocyte proliferation and survival, confer resistance to chemotherapy, and are associated with more rapid disease progression. Colony-stimulating factor-1 receptor (CSF-1R) regulates the homeostatic survival of tissue-resident macrophages. Therefore, we sought to determine whether CSF-1R is similarly required for NLC survival., Experimental Design: CSF-1R expression by NLC was examined by flow cytometry and IHC. CSF-1R blocking studies were performed using an antagonistic mAb to examine its role in NLC generation and in CLL survival. A rational search strategy was performed to identify a novel tyrosine kinase inhibitor (TKI) targeting CSF-1R. The influence of TKI-mediated CSF-1R inhibition on NLC and CLL viability was examined., Results: We demonstrated that the generation and survival of NLC in CLL is dependent upon CSF-1R signaling. CSF-1R blockade is associated with significant depletion of NLC and consequently inhibits CLL B-cell survival. We found that the JAK2/FLT3 inhibitor pacritinib suppresses CSF-1R signaling, thereby preventing the generation and survival of NLC and impairs CLL B-cell viability., Conclusions: CSF-1R is a novel therapeutic target that may be exploited in lymphoproliferative disorders, like CLL, that are dependent upon lymphoma-associated macrophages. Clin Cancer Res; 22(24); 6118-28. ©2016 AACR., Competing Interests: Conflict-of-interest disclosure: Jack W. Singer is employed by CTI Biopharma. The remaining authors declare no competing financial interests., (©2016 American Association for Cancer Research.)

Background: Pacritinib (SB1518) is a highly selective kinase inhibitor with specificity for JAK2, FLT3, IRAK1, and CFS1R. This multicenter phase 1/2 study evaluated the maximum tolerated dose (MTD), safety, and clinical activity of pacritinib in patients with myelofibrosis (MF) and other advanced myeloid malignancies., Methods: In the phase 1 dose-escalation part of the study, 43 adults with advanced myeloid malignancies received pacritinib 100 to 600 mg once daily (QD). In the phase 2 part of the study, 31 adults with refractory or intermediate- or high-risk newly diagnosed MF and any degree of cytopenia received pacritinib 400 mg QD. The primary endpoint is a ≥35% reduction in spleen volume at week 24 as determined by magnetic resonance imaging., Results: Five patients (11.6%) experienced a dose-limiting toxicity during cycle 1 of phase 1. The clinical benefit rate was 86.0% (13 patients achieving clinical improvement and 24 patients having stable disease). The MTD was established at 500 mg QD, and the recommended phase 2 dose was 400 mg QD. In phase 2, the primary endpoint was achieved by 23.5% of evaluable patients (4/17), with 47.4% (9/19) achieving a ≥50% spleen length reduction at week 24 as measured by physical examination. At week 24, 38.9% of evaluable patients (7/18) achieved a ≥50% decrease in MF Quality of Life and Symptom Assessment total score. Gastrointestinal toxicities were the most common adverse events and were predominantly grade 1/2 in severity. Grade 3/4 anemia was reported in 5/31 patients and grade 3/4 thrombocytopenia was reported in 3/31 patients. The most frequent AEs considered to be treatment related were diarrhea (28/31), nausea (15/31), vomiting (9/31), and fatigue (4/31). Grade 3 treatment-related AEs were reported in seven patients (22.6%), four of whom had diarrhea. No grade 4/5 treatment-related AEs were reported. No leukopenia, neutropenia, or lymphopenia were reported., Conclusions: Pacritinib was well tolerated and demonstrated clinical activity in MF. The study suggests that pacritinib has unique characteristics, namely a lack of substantial myelosuppression and manageable side effects, making it an attractive target for further evaluation in MF., Trial Registration: Retrospectively registered at www.clinicaltrials.gov (# NCT00719836 ) on July 20, 2008.

Pacritinib, potent inhibitor of Janus kinase 2 (JAK2), JAK2V617F, and fms-like receptor tyrosine kinase 3, is in Phase III development in myelofibrosis. Among type 1 inhibitors, pacritinib shows a lack of myelosuppression at doses that both inhibit JAK2/signal transducer and activator of transcription 3 pathway and demonstrate clinical efficacy. To elucidate these mechanisms and identify other disease targets, a kinome analysis screened 439 recombinant kinases at 100 nM pacritinib concentration. For kinases with >50% inhibition, pacritinib was titrated from 1 to 100 nM. JAK2, JAK2V617F, FLT3, colony-stimulating factor 1 receptor, and interleukin-1 receptor-associated kinase 1 achieved half-maximal inhibitory concentrations <50 nM. Pacritinib did not inhibit JAK1 (82% control at 100 nM). Lack of myelosuppression may stem from inhibiting JAK2 without affecting JAK1 and reducing hematopoietic inhibitory cytokines by suppressing interleukin-1 receptor-associated kinase 1 or colony-stimulating factor 1 receptor. The pacritinib kinome suggests therapeutic utility in acute myeloid leukemia, myelodysplastic syndrome, chronic myelomonocytic leukemia, solid tumors, and inflammatory conditions.

Purpose: Aggressive non-Hodgkin's lymphoma (aNHL) is associated with poor long-term survival after relapse, and treatment is limited by a lack of consensus regarding standard of care. Pixantrone was studied in a randomized trial in patients with relapsed or refractory aNHL who had failed ≥ 2 lines of therapy, demonstrating a significant improvement in complete or unconfirmed complete response and progression-free survival (PFS) compared with investigators' choice of single-agent therapy. The objective of this study was to assess the health economic implications of pixantrone versus current clinical practice (CCP) in the United Kingdom for patients with multiply relapsed or refractory aNHL receiving their third or fourth line of treatment., Methods: A semi-Markov partition model based on overall survival and PFS was developed to evaluate the lifetime clinical and economic impact of treatment of multiply relapsed or refractory aNHL with pixantrone versus CCP. The empirical overall survival and PFS data from the PIX301 trial were extrapolated to a lifetime horizon. Resource use was elicited from clinical experts, and unit costs and utilities were obtained from published sources. The analysis was conducted from the perspective of the United Kingdom's National Health Service and personal social services. Outcomes evaluated were total costs, life-years, quality-adjusted life-years (QALYs), and cost per QALY gained. Deterministic and probabilistic sensitivity analyses were conducted to assess uncertainty around the results., Findings: Pixantrone was estimated to increase life expectancy by a mean of 10.8 months per patient compared with CCP and a mean gain of 0.56 discounted QALYs. The increased health gains were associated with an increase in discounted costs of approximately £18,494 per patient. The incremental cost-effectiveness ratio of pixantrone versus CCP was £33,272 per QALY gained. Sensitivity and scenario analyses suggest that the incremental cost-effectiveness ratio was sensitive to uncertainty in the PFS and overall survival estimates and the utility values associated with each health state., Implications: Pixantrone may be considered both clinically effective and cost-effective for patients with multiply relapsed or refractory aNHL who currently have a high level of unmet need., (Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.)

Cardiotoxicity from the antitumor anthracycline doxorubicin correlates with doxorubicin cardiac levels, redox activation to superoxide anion (O(2)(.-)) and hydrogen peroxide (H(2)O(2)), and formation of the long-lived secondary alcohol metabolite doxorubicinol. Cardiotoxicity may first manifest during salvage therapy with other drugs, such as the anthracenedione mitoxantrone. Minimal evidence for cardiotoxicity in anthracycline-pretreated patients with refractory-relapsed non-Hodgkin lymphoma was observed with the novel anthracenedione pixantrone. We characterized whether pixantrone and mitoxantrone caused different effects on doxorubicin levels, redox activation, and doxorubicinol formation. Pixantrone and mitoxantrone were probed in a validated ex vivo human myocardial strip model that was either doxorubicin-naïve or preliminarily subjected to doxorubicin loading and washouts to mimic doxorubicin treatment and elimination in the clinical setting. In doxorubicin-naïve strips, pixantrone showed higher uptake than mitoxantrone; however, neither drug formed O(2)(.-) or H(2)O(2). In doxorubicin-pretreated strips, neither pixantrone nor mitoxantrone altered the distribution and clearance of residual doxorubicin. Mitoxantrone showed an unchanged uptake and lacked effects on doxorubicin levels, but synergized with doxorubicin to form more O(2)(.-) and H(2)O(2), as evidenced by O(2)(.-)-dependent inactivation of mitochondrial aconitase or mitoxantrone oxidation by H(2)O(2)-activated peroxidases. In contrast, pixantrone uptake was reduced by prior doxorubicin exposure; moreover, pixantrone lacked redox synergism with doxorubicin, and formed an N-dealkylated product that inhibited metabolism of residual doxorubicin to doxorubicinol. Redox inactivity and inhibition of doxorubicinol formation correlate with the cardiac safety of pixantrone in doxorubicin-pretreated patients. Redox inactivity in the face of high cardiac uptake suggests that pixantrone might also be safe in doxorubicin-naïve patients.

Background: In Phase I evaluation of CT-2103 (paclitaxel poliglumex), prolongation of prothrombin time (PT) and activated thromboplastin time (aPTT) was observed, without clinical consequence, with doses 1.3-1.5 times higher than the current clinical dose of 175 mg/m(2). This Phase I, open-label, nonrandomized pilot study was performed to study the effect of the standard dose regimen on blood coagulation., Methods: Seven previously treated solid tumor patients received CT-2103 175 mg/m(2) intravenously on day 1 of 21-day cycles for a mean of 5.4 cycles (median 4, range 2-14). Plasma samples were collected for cycle 1 predose and at hours 1, 24, 48, and 72 after the end of administration for drug levels, and for PT and aPTT assays., Results: No coagulopathy-related adverse events were documented. Bleeding time remained normal in the six patients tested, with transient increases in PT and aPTT noted but resolving within 72 hours. Titration studies at 100 μg/mL of CT-2103 (corresponding to the standard clinical dose) prolonged PT and aPTT clotting times, produced a modest dose-dependent reduction of thrombin and factor Xa, and no significant changes in factors IXa, XIa, or XIIa. Two patients achieved stable disease for ≥10 cycles., Conclusion: CT-2103 is associated with transient prolongation of PT and aPTT without clinical sequelae.

Purpose: Data from two randomized phase III trials were analyzed to evaluate prognostic factors and treatment selection in the first-line management of advanced non-small cell lung cancer patients with performance status (PS) 2., Patients and Methods: Patients randomized to combination chemotherapy (carboplatin and paclitaxel) in one trial and single-agent therapy (gemcitabine or vinorelbine) in the second were included in these analyses. Both studies had identical eligibility criteria and were conducted simultaneously. Comparison of efficacy and safety was performed between the two cohorts. A regression analysis identified prognostic factors and subgroups of patients that may benefit from combination or single-agent therapy., Results: Two hundred one patients were treated with combination and 190 with single-agent therapy. Objective responses were 37 and 15%, respectively. Median time to progression was 4.6 months in the combination arm and 3.5 months in the single-agent arm (p < 0.001). Median survival times were 8.0 and 6.6 months, and 1-year survival rates were 31 and 26%, respectively. Albumin <3.5 g, extrathoracic metastases, lactate dehydrogenase >or=200 IU, and 2 comorbid conditions predicted outcome. Patients with 0-2 risk factors had similar outcomes independent of treatment, whereas patients with 3-4 factors had a nonsignificant improvement in median survival with combination chemotherapy., Conclusion: Our results show that PS2 non-small cell lung cancer patients are a heterogeneous group who have significantly different outcomes. Patients treated with first-line combination chemotherapy had a higher response and longer time to progression, whereas overall survival did not appear significantly different. A prognostic model may be helpful in selecting PS 2 patients for either treatment strategy.

Background: Patients with advanced non-small cell lung cancer (NSCLC) and impaired performance status (PS >or= 2) have limited life expectancies and decreased tolerance for drug-induced toxicities. Current treatment guidelines indicate that PS 2 patients benefit from systemic therapy. Further refinement of treatment in these patients requires reduction of treatment-associated toxicities while maintaining or improving efficacy. Paclitaxel poliglumex (PPX), a macromolecular polymer-drug conjugate of paclitaxel and poly-l-glutamic acid, may enhance the therapeutic index of paclitaxel., Methods: Chemotherapy-naive PS 2 patients with advanced NSCLC randomly received single-agent PPX (175 mg/m) or a comparator (single-agent vinorelbine or gemcitabine). The primary end point of this study was overall survival., Results: Overall survival was similar between treatment arms (hazard ratio [HR] = 0.95; log-rank p = 0.686). Median and 1-year survival were 7.3 months and 26%, respectively, for PPX versus 6.6 months and 26% for the control arm. There was a nonsignificant trend toward improved survival in women in the PPX arm compared with standard single agents (HR = 0.65; p = 0.069). The most frequent grade 3/4 adverse events in the treatment versus control arm were dyspnea (13% versus 17%, respectively) and fatigue (10% versus 9%). Grade 3/4 neutropenia and anemia were reduced in the PPX arm (2% versus 8% and 3% versus 9%, respectively). Neuropathy, a taxane-specific toxicity, was more common in the PPX arm; grade 3 neuropathy was limited to 3%., Conclusions: Single-agent PPX, dosed at 175 mg/m, is active and well tolerated in PS 2 patients with advanced NSCLC. Patients on PPX required fewer red blood cell transfusions, hematopoietic growth factors, opioid analgesics, and clinic visits than patients receiving gemcitabine or vinorelbine.

Introduction: Performance status (PS) 2 patients with non-small cell lung cancer (NSCLC) experience more toxicity, lower response rates, and shorter survival times than healthier patients treated with standard chemotherapy. Paclitaxel poliglumex (PPX), a macromolecule drug conjugate of paclitaxel and polyglutamic acid, reduces systemic exposure to peak concentrations of free paclitaxel and may lead to increased concentrations in tumors due to enhanced vascular permeability., Methods: Chemotherapy-naive PS 2 patients with advanced NSCLC were randomized to receive carboplatin (area under the curve = 6) and either PPX (210 mg/m/10 min without routine steroid premedication) or paclitaxel (225 mg/m/3 h with standard premedication) every 3 weeks. The primary end point was overall survival., Results: A total of 400 patients were enrolled. Alopecia, arthralgias/myalgias, and cardiac events were significantly less frequent with PPX/carboplatin, whereas grade > or =3 neutropenia and grade 3 neuropathy showed a trend of worsening. There was no significant difference in the incidence of hypersensitivity reactions despite the absence of routine premedication in the PPX arm. Overall survival was similar between treatment arms (hazard ratio, 0.97; log rank p = 0.769). Median and 1-year survival rates were 7.9 months and 31%, for PPX versus 8 months and 31% for paclitaxel. Disease control rates were 64% and 69% for PPX and paclitaxel, respectively. Time to progression was similar: 3.9 months for PPX/carboplatin versus 4.6 months for paclitaxel/carboplatin (p = 0.210)., Conclusion: PPX/carboplatin failed to provide superior survival compared with paclitaxel/carboplatin in the first-line treatment of PS 2 patients with NSCLC, but the results with respect to progression-free survival and overall survival were comparable and the PPX regimen was more convenient.

Purpose: Lysophosphatidic acid acyltransferase (LPAAT)-beta catalyzes the conversion of lysophosphatidic acid to phosphatidic acid, an essential component of several signaling pathways, including the Ras/mitogen-activated protein kinase pathway. Inhibition of LPAAT-beta induces growth arrest and apoptosis in cancer cell lines, implicating LPAAT-beta as a potential drug target in neoplasia., Experimental Design: In this study, we investigated the effects of CT32228, a specific LPAAT-beta inhibitor, on BCR-ABL-transformed cell lines and primary cells from patients with chronic myelogenous leukemia., Results: CT32228 had antiproliferative activity against BCR-ABL-positive cell lines in the nanomolar dose range, evidenced by cell cycle arrest in G2-M and induction of apoptosis. Treatment of K562 cells with CT32228 led to inhibition of extracellular signal-regulated kinase 1/2 phosphorylation, consistent with inhibition of mitogen-activated protein kinase signaling. Importantly, CT32228 was highly active in cell lines resistant to the Bcr-Abl kinase inhibitor imatinib. Combination of CT32228 with imatinib produced additive inhibition of proliferation in cell lines with residual sensitivity toward imatinib. In short-term cultures in the absence of growth factors, CT32228 preferentially inhibited the growth of granulocyte-macrophage colony-forming units from chronic myelogenous leukemia patients compared with healthy controls., Conclusion: These data establish LPAAT-beta as a potential drug target for the treatment of BCR-ABL-positive leukemias.

Membranes of mammalian cells contain lysophosphatidic acid acyltransferase (LPAAT) activities that catalyze the acylation of sn-1-acyl lysophosphatidic acid (lysoPA) to form phosphatidic acid. As the biological roles and biochemical properties of the six known LPAAT isoforms have yet to be fully elucidated, we have characterized human LPAAT-beta activity using two different assays. In a membrane-based assay, LPAAT-beta used lysoPA and lysophosphatidylmethanol (lysoPM) but not other lysophosphoglycerides as an acyl acceptor, and it preferentially transferred 18:1, 18:0, and 16:0 acyl groups over 12:0, 14:0, 20:0, and 20:4 acyl groups. The fact that lysoPM could traverse cell membranes permitted additional characterization of LPAAT-beta activity in cells: PC-3 and DU145 cells converted exogenously added lysoPM and (14)C-labeled 18:1 into (14)C-labeled phosphatidylmethanol (PM). The rate of PM formation was higher in cells that overexpressed LPAAT-beta and was inhibited by the LPAAT-beta inhibitor CT-32501. In contrast, if lysoPM and (14)C-labeled 20:4 were added to PC-3 or DU145 cells, (14)C-labeled PM was also formed, but the rate was neither higher in cells that overexpressed LPAAT-beta nor inhibited by CT-32501. We propose that LPAAT-beta catalyzes the intracellular transfer of 18:1, 18:0, and 16:0 acyl groups but not 20:4 groups to lysoPA.

Paclitaxel poliglumex (PPX) is an innovative macromolecular taxane designed to increase the therapeutic index of paclitaxel. This large macromolecular conjugate of paclitaxel and poly-L-glutamic acid accumulates in tumor tissues by taking advantage of the enhanced permeability of tumor vasculature and lack of lymphatic drainage. Preclinical studies in animal tumor models demonstrate that PPX is more effective than standard paclitaxel and is associated with prolonged tumor exposure to active drug while minimizing systemic exposure. Phase 1 and 2 clinical studies with PPX showed encouraging outcomes compared to standard taxanes with reduced neutropenia and alopecia and allowed a more convenient administration schedule without the need for routine premedications. Human pharmacokinetic data are consistent with prolonged tumor exposure to active drug and a limited systemic exposure. Three phase 3 trials in nonsmall cell lung cancer (STELLAR 2, 3, and 4) have completed enrollment and results are expected in 2005.

Purpose: Lysophosphatidic acid acyltransferase-beta (LPAAT-beta) is a transmembrane enzyme critical for the biosynthesis of phosphoglycerides whose product, phosphatidic acid, plays a key role in raf and AKT/mTor-mediated signal transduction., Experimental Design: LPAAT-beta may be a novel target for anticancer therapy, and, thus, we examined the effects of a series of inhibitors of LPAAT-beta on multiple human non-Hodgkin's lymphoma cell lines in vitro and in vivo., Results: We showed that five LPAAT-beta inhibitors at doses of 500 nmol/L routinely inhibited growth in a panel of human lymphoma cell lines in vitro by >90%, as measured by [3H]thymidine incorporation. Apoptotic effects of the LPAAT-beta inhibitors were evaluated either alone or in combination with the anti-CD20 antibody, Rituximab. The LPAAT-beta inhibitors induced caspase-mediated apoptosis at 50 to 100 nmol/L in up to 90% of non-Hodgkin's lymphoma cells. The combination of Rituximab and an LPAAT-beta inhibitor resulted in a 2-fold increase in apoptosis compared with either agent alone. To assess the combination of Rituximab and a LPAAT-beta inhibitor in vivo, groups of athymic mice bearing s.c. human Ramos lymphoma xenografts were treated with the LPAAT-beta inhibitor CT-32228 i.p. (75 mg/kg) daily for 5 d/wk x 4 weeks (total 20 doses), Rituximab i.p. (10 mg/kg) weekly x 4 weeks (4 doses total), or CT-32228 plus Rituximab combined. Treatment with either CT-32228 or Rituximab alone showed an approximate 50% xenograft growth delay; however, complete responses were only observed when the two agents were delivered together., Conclusions: These data suggest that Rituximab, combined with a LPAAT-beta inhibitor, may provide enhanced therapeutic effects through apoptotic mechanisms.

In this study, we examined the effects of isoform-specific functional inhibitors of lysophosphatidic acid acyltransferase (LPAAT), which converts lysophosphatidic acid to phosphatidic acid, on multiple myeloma (MM) cell growth and survival. The LPAAT-beta inhibitors CT-32176, CT-32458, and CT-32615 induced >95% growth inhibition (P < 0.01) in MM.1S, U266, and RPMI8226 MM cell lines, as well as MM cells from patients (IC(50), 50-200 nM). We further characterized this LPAAT-beta inhibitory effect using CT-32615, the most potent inhibitor of MM cell growth. CT-32615 triggered apoptosis in MM cells via caspase-8, caspase-3, caspase-7, and poly (ADP-ribose) polymerase cleavage. Neither interleukin 6 nor insulin-like growth factor I inhibited CT-32615-induced apoptosis. Dexamethasone and immunomodulatory derivatives of thalidomide (IMiDs), but not proteasome inhibitor PS-341, augmented MM cell apoptosis triggered by LPAAT-beta inhibitors. CT-32615-induced apoptosis was associated with phosphorylation of p53 and c-Jun NH(2)-terminal kinase (JNK); conversely, JNK inhibitor SP600125 and dominant-negative JNK inhibited CT-32615-induced apoptosis. Importantly, CT-32615 inhibited tumor necrosis factor-alpha-triggered nuclear factor-kappaB activation but did not affect either tumor necrosis factor-alpha-induced p38 mitogen-activated protein kinase phosphorylation or interleukin 6-triggered signal transducers and activators of transcription 3 phosphorylation. Finally, although binding of MM cells to bone marrow stromal cells augments MM cell growth and protects against dexamethasone-induced apoptosis, CT-32615 induced apoptosis even of adherent MM cells. Our data therefore demonstrate for the first time that inhibiting LPAAT-beta induces cytotoxicity in MM cells in the bone marrow milieu, providing the framework for clinical trials of these novel agents in MM.

Lysophosphatidic acid acyltransferase beta (LPAAT-beta) is an intrinsic membrane protein that catalyzes the synthesis of phosphatidic acid (PA) from lysoPA. Given that PA is a cofactor in a number of signaling cascades that are constitutively active in tumors, we evaluated the role of PA produced by LPAAT-beta in Xenopus oocyte meiotic maturation assays and an isoform-specific inhibitor of LPAAT-beta in mammalian cell assays. We found that ectopic overexpression of LPAAT-beta cooperates in activation of the Ras/Raf/Erk pathway in Xenopus oocytes and that inhibition of LPAAT-beta inhibits signaling in both the Ras/Raf/Erk and PI3K/Akt pathways. When LPAAT-beta activity is suppressed by CT32228 (N-(4-bromo-phenyl)-6-(5-chloro-2-methyl-phenyl)-[1,3,5]triazine-2,4-diamine), an isoform-specific noncompetitive inhibitor, tumor cells undergo mitotic catastrophe while most normal cells simply arrest or become quiescent. The data presented here suggest that PA produced by LPAAT-beta plays an important role in signaling pathways critical to tumor cell survival.

Phosphatidic acid (PA) is a component of cellular membranes that is also a mediator of certain cell signalling functions associated with oncogenesis. These include ras/raf/Erk and Akt/mTor [1-3]. The authors have investigated whether it would be possible to interrupt these known oncogenic pathways through the inhibition of lysophosphatidic acid acyltransferase (LPAAT), an enzyme that catalyses the biosynthesis of PA. The expression and activity of the LPAAT-beta isoform are elevated in human tumours, and the respective gene displays transforming capacity when overexpressed in vitro. Inhibition by either genetic means or by isoform-specific small molecules results in a block to cell signalling pathways and apoptosis. Furthermore, the small-molecule inhibitors of LPAAT-beta are not cytotoxic to a number of normal cell types, including primary bone marrow progenitors, indicating a differential dependence of tumour cells on LPAAT-beta function. These discoveries indicate that LPAAT-beta represents a potential novel cancer therapy target.

Poly-alpha-(l-glutamic acid) (PG) conjugates of 20(S)-camptothecin (1, CPT) displayed improved aqueous solubility compared to CPT, were stable in aqueous solution at neutral pH, and were potent antitumor agents in vivo. Evaluation of PG molecular weight, CPT loading, aqueous solubility, and CPT equivalent dosing with respect to in vivo antitumor potencies of various linked conjugates led to identification of a preferred conjugate composition.