Search

Waldenström’s macroglobulinemia (WM) is an incurable low-grade lymphoproliferative disorder characterized by bone marrow (BM) infiltration of a clonal population of small B-lymphocytes, plasmacytoid lymphocytes and plasma cells that secrete monoclonal IgM antibody. Because it is difficult to obtain tumor metaphases for karyotype studies, few recurrent chromosomal abnormalities have been reported and the genetic basis of the disease remains poorly defined. Therefore, we performed a comprehensive high-resolution study to identify genomic abnormalities involved in WM pathogenesis. Fifty-seven WM patients were analyzed using a combination of array-based comparative genomic hybridization (aCGH)(N=42); gene expression profiling (GEP)(N=22), DNA sequencing (N=24) and cIgM-FISH (N=57). Agilent 244A and Affymetrix U133 platforms were used in the aCGH and GEP experiments, respectively. An NF-κB index was calculated from GEP data, as a surrogate marker of NF-κB transcription activity. NFKB2 sub cellular localization was determined by immunofluorescence staining. Overall, 83% of samples have aCGH defined chromosomal abnormalities, with a median of 3 abnormalities per patient (range 0 to 27). We identified 16 recurrent regions of copy number change found in >5% (3 or more patients); 10 deleted and 6 amplified regions. The most common abnormality was the entire or partial deletion of 6q, identified in 40% of cases. Four nonoverlapped minimal deleted regions were identified on 6q (MDR1 to MDR4), each of them being present in at least 14 of 17 patients with the abnormality. Gain of 6p was the second most common abnormality (17%) and its presence was always concomitant with 6q loss. Other recurrent deletions were 13q14 (10%) and 7q22, 8p, 11q22-q23, 11q23-q24 and 17p11-p13 (7% each). Copy gains were identified as partial or entire gains of chromosomes 18 (17%), 4 (12%) and 3 (10%), 8q (10%) and Xq27.1-q28 (10%). Three patients had either homozygous deletions or LOH with mutations affecting both alleles of TRAF3 on 14q32. TRAF3 inactivation was correlated with an increased NF-kB transcriptional signature and it was associated with activation of the non-canonical NFkB pathway. Additionally, we identified the inactivation of TNFAIP3, another negative regulator of the NF-kB pathways, in one of 24 patients. Finally, interstitial deletions identified in 4 patients at 13q14 identified a 1.1 Mb MDR, including MIRN15A and MIRN16-1. These findings confirm that focal 13q14 deletion is not restrict to B-CLL and that the MIRN15A/MIRN16-1 abnormalities might be common to several indolent B-cell diseases. Overall, we identified TRAF3 and TNFAIP3 inactivation in 5.3% and 2.4%, respectively. To our knowledge, this is the first study showing the inactivation of bona fide tumor suppressor genes in WM patients. Furthermore, these genes are negative regulators of NF-kB signaling pathway, highlighting its biologic importance in sustaining and limiting growth in WM. Mutational activation of this pathway, which is normally activated by ligand-receptor interactions within the BM microenvironment, suggest a therapeutic role for inhibitors of NF-KB pathway activation in the treatment of WM.

We have successfully generated the first immuno-competent transgenic mouse model of multiple myeloma (MM), Vk*MYC, in which sporadic MYC activation in the germinal center is AID dependent and mediated by the somatic hypermutation process. All of Vk*MYC mice develop monoclonal PC expansion by 50 weeks of age, that is manifested by high levels of serum IgGs and major M-spikes by SPEP. The PCs in Vk*MYC mice are fully differentiated, somatically mutated, have a very low proliferation index and are found exclusively in the BM. Associated with the long lifespan (medium survival = 661d), Vk*MYC mice develop anemia and diffuse bone disease (osteoporosis with low bone mineral density), with sporadic occurrence of lytic bone lesions and hind limb paralysis. The phenotypic fidelity of the Vk*MYC mice translates in a therapeutic fidelity, as Vk*MYC mice show response to known clinically active anti-myeloma drugs (bortezomib, melphalane, dexamethasone), but not to drugs that have shown no clinical activity as single agents (vincristine, hydroxyurea, fludarabine). Furthermore, acquired bortezomib resistance could efficiently be induced in Vk*MYC mice after only four cycles of suboptimal treatment, and studies are in progress to identify genetic events associated with bortezomib resistance. Preliminary aCGH experiments on a high resolution Agilent 244K array, using genomic DNA from six Vk*MYC CD138+ selected PCs, showed that the genomic complexity of Vk*MYC tumors is quite low, with only few unbalanced rearrangements, such as trisomy of chromosome 15 detected in two samples or trisomy 9 present in another tumor. The most common abnormalities found are small focal monoallelic deletions, six of which are present in more than one tumor. A focal homozygous deletion of several exons of a gene was identified in two tumors samples. Remarkably, a comparative analysis of the syntenic chromosomal region in human MM cell lines and primary patient samples identified similar recurrent homozygous deletion in this putative novel tumor suppressor gene. Overall, these data suggest that the genomic complexity in this inbred strain of transgenic mice is significantly less then in patients with MM, simplifying the search for critical loci involved in MM tumorigenesis and drug resistance and further validate the Vk*MYC mice as a particularly faithful model of human MM.

Previous work in our laboratory has identified the importance of the NFB signaling pathway for plasma cell (PC) survival and accumulation in Multiple Myeloma (MM). Although up to 43% of patient PCs appear to have activated NFkB by gene expression profiling (GEP), the remainder must rely on an alternate signaling pathway for their survival. We examined our MM GEP datasets and supervised the clustering of patients according to an index of NFkB activity. The majority of patients not activating NFkB were associated with a high IL-6/Stat3 signature, which included the protein phosphatase of regenerating liver-3 (PRL-3). Interestingly, analysis of the PRL-3 promoter revealed competing binding sites for both NFkB and STAT3 within the first intron, suggesting that these play a role in the transcriptional regulation of this gene. PRL-3 has been previously demonstrated to be absent in most normal tissues while its expression in MM cells is quite elevated. As normal PCs have low levels of PRL-3 expression, we determined the upper limit of normal to be 3SD above the mean of these cells. Using this cutoff we report that elevated PRL-3 expression is observed in plasma cells from 1/15 normal individuals, 4/22 MGUS patients and 47/126 patients with either smoldering or overt MM (6.7%, 18.2% and 45.6% respectively). Less than 10% of patients were seen to have both an elevated NFkB index and high PRL-3 expression. Patients with higher expression of PRL-3 were found to have statistically significant higher mean values of creatinine, C-reactive protein, lower albumin levels and a lower overall survival in our Mayo Clinic MM dataset. To examine the role PRL-3 in MM biology we first stimulated MM cell lines with IL-6 and observed PRL-3 up-regulation in two cell lines (INA6, OPM1) but not in JK6L (an NFkB activated cell line). Using a luciferase reporter we have determined that STAT3 induction of PRL3 expression requires the first intron of the PRL3 gene which contains the putative STAT3 binding site. Finally we show that PRL-3 inhibition by shRNA leads to decreased cell growth and loss of IL-6 responsiveness in vitro in at least one cell line. Based on these results, we propose that the majority of MM patients depend on either the NFkB or STAT3 signaling pathways for their survival and that these are to a large degree mutually exclusive. Our experimental results suggest that PRL-3 plays a role in IL-6/STAT3 signaling and that it is a promising target for drug development.

Constitutive activation of NF-κB signaling pathways has been identified in a variety of malignancies, however the molecular basis has remained largely unknown. Recently, we have shown mutations in 10 genes encoding positive and negative regulators of NF-κB signaling pathways in 20% of multiple myeloma (MM) patients, with TRAF3 being the most commonly affected gene. TRAF3 is a negative regulator of NF-κB signal and its inactivation results in the constitutive activation of the alternative or noncanonical NF-κB signaling pathway. With the exception of two recent studies in MM, there is no available data regarding the mechanisms that dysregulate NF-κB in other B-cell malignancies. The aim of this study was to analyze the TRAF3 status in a cohort of Waldenström's macroglobulinemia (WM) patients. Forty-nine WM were analyzed by using a combination of array-based comparative genomic hybridization (aCGH) and cIgM-FISH. Genome sequencing from 28 of these patients was performed on all coding exons of TRAF3 and the adjacent intron-exon junctions. A NF-κB index, as a measure of NF-κB transcription activity, was calculated from 21 patients with gene expression data. The index is the mean expression level of four probe sets differentially expressed between human myeloma cell lines with identified mutations compared to those without identified NF-κB pathway mutations (CD74, IL2RG and 2x TNFAIP3). By performing aCGH we identified a small monoallelic deletion (∼460 Kb), including the TRAF3 locus in one of 22 patients. Genome sequencing identified a missense mutation (D483N) in the remaining allele. This substitution affects a highly conserved amino acid throughout vertebrate evolution, suggesting its functional relevance. We used cIgM-FISH to screen 27 patients with no available aCGH data and we found one biallelic TRAF3 deletion and one chromosome 14 monosomy. In the later case, no DNA was available to sequence the remaining allele. Both samples with biallelic inactivation of TRAF3 possess the two highest NFKB index values of our WM cohort, suggesting NF-κB transcription activity. Moreover, the case with biallelic deletion showed the lowest level of TRAF3 gene expression. Additionally, the entire TRAF3 coding region was sequenced in 28 of these 49 patients and one homozygous nonsense mutation (K286X) was identified. No GEP was available in this sample to calculate the NF-κB index. TRAF3 was only recently implicated in a malignant process, when inactivating mutations and biallelic deletions were reported in approximately 13% of MM patients, making it the most frequently inactivated tumor suppressor in MM. Our study has identified biallelic TRAF3 inactivation in at least 3 of 49 WM patients, suggesting that the constitutive activation of NF-κB signaling pathways may be involved in the pathogenesis of WM. Recent findings showing an association between TRAF3 loss of function and good response to bortezomib in MM patients suggest that proteasome inhibitor-based therapy may be an attractive option in the treatment of the WM patients with constitutive activation of NF-κB signaling pathways. Additional mutational screening of TRAF3 and other regulators of these pathways are ongoing to determine the extent of constitutive activation present in WM and other B-cell malignancies.

Events mediating transformation from the pre-malignant MGUS to MM is largely unknown. Previous studies have highlighted RAS mutation as a progression event. However, this abnormality is present in only a small subset of patients. Global gene expression differences between MGUS and MM have been reported but provided little coherent biological insights. To define progression events, we examined the differences in gene expression profiles (GEP, Affymetrix U133A genechip) between 101 MM and 22 MGUS using a powerful functional genomic tool, Gene Set Enrichment Analysis (Subramanium et al PNAS 2005), that allow extraction of biological information based on enrichment of genes associated with a phenotype within gene-sets derived experimentally or extracted from database. We found that a predominant theme relating to MM progression is the over-expression of proliferation related genes in MM highlighted by the enrichment of cell cycle related gene-sets. Another common theme is the enrichment of gene-sets relating to MYC activation. Seven of eight gene-sets related to MYC activation in the database are significantly enriched (p-value <0.05 and false detection rate <0.05). Leading edge (enriched genes) analysis of enriched MYC-related and proliferation-related gene-sets revealed a core, overlapping signature of 8 genes specific to MYC and not proliferation. These genes are further verified as MYC transcriptional targets using Metacore, a network analysis tool. In addition, 7 of the 8 genes had been validated as MYC target genes by chromatin immunoprecipitation previously (www.myccancergene.org). We validated this signature in independent publicly available cell lines and mouse gene expression experiments where this signature is present in mammary epithelial cell lines engineered to over-express MYC but not E2F3, SRC and BCAT, and mouse embryonic fibroblast over-expressing MYC but not HER2 or with RB knocked-out. In addition, analysis of proliferation index in these datasets showed that there is dissociation of proliferation from this signature. This showed conclusively that our signature is MYC specific and not related to proliferation. Of interest, the signature is also present in cell lines with activating RAS mutation, which also have high expression of MYC, suggesting that MYC activation is a downstream effect of activated RAS signaling. Indeed, in our patient cohort, most patients with RAS mutation express this signature. When applied to 2 large GEP MM patient cohorts, this signature was not present in normal plasma cells, rarely present in MGUS, and present in a significant proportion of MM and almost all the human myeloma cell lines. When analyzed in the context of other B-cell malignancies, the signature is very strong in Burkitt’s lymphoma, present in most myeloma but absent in chronic lymphocytic leukemia, Waldenstrom Macroglobulinemia, and normal B-cells. Our analysis therefore suggests that MYC activation may be a unifying pathological event in MGUS to MM progression. As MYC translocations occur in only about 13% of newly diagnosed MM patients, activating RAS mutations and other trans-mechanisms may mediate MYC activation. Our recent demonstration that sporadic MYC activation in a mouse strain prone to monoclonal gammopathy led to MM development provides important functional proof.

The availability of human myeloma cell lines (HMCLs) has drastically benefited out understanding of multiple myeloma (MM). They represent essential resources to the myeloma research community at large who use them to identify and more importantly validate oncogenic events in MM. Furthermore, they represent the front line tools in efforts to identify novel therapeutic agents for MM patients. However, the myeloma research community is not immune to problems of cell line contamination (mixed populations) or systemic errors where HMCLs are labeled incorrectly. As the community evolves towards the development of tailor medicine it is essential that our basic tools are both pure and correct. Otherwise, a potentially beneficial therapeutic agent designed for a specific patient subset maybe lost simply because of a simple laboratory mix-up at some point over the years. To that end we have developed a simple PCR based method that can be used to validate the purity and authenticity of HMCLs. First two reference collections of over 50 HMCL maintained at the NCI and Mayo Clinic Arizona were compared using microsatellite fingerprinting. This process identified several previously unnoticed discrepancies. First, in both labs several cell lines that reportedly originated from different patients had the same fingerprints. These include the following unexpected pairs; ANBL-6 and DP–6, CAG and ARP–1, KMS–11 and KMS–20, KMS–11 and KMS–21PE/BM, JIM3 and KPMM2. Second, both KP–6 and KAS6/1 showed a level of cross-contamination with ANBL–6. All of the discrepant cell lines were requested from the original contributor and those that were available were retested. After this step we had identified unique fingerprints for ANBL–6, DP–6, KMS–11, and KMS–20. Furthermore, pure populations of KP–6 and KAS6/1 were confirmed. However, CAG and ARP–1 still had an identical fingerprint. Since the use of microsatellite fingerprinting is an expensive task and the identification of cross-contamination is not very robust we set out to develop better method. We decided to use a simple qualitative PCR method, as the binomial presence or absence of a band makes the interpretation of the fingerprint extremely easy. Furthermore, the high sensitivity of a qualitative PCR can pick up a small amount of contamination in the culture that can be lost in microsatellite analysis. This method involves a multiplex PCR screen that simultaneously interrogates 10 regions of the human genome. The screen is divided into two reactions, one with a panel of highly polymorphic copy number variations (CNV) that are often completely absent in some individuals, and a second one based on known biologic events present in the cell lines. The integration of the results from the CNV and Biological Fingerprints will identify each HMCL as a unique entity. We validated the methodology by confirming that this qualitative screen could pick up the cross–contamination identified in the original KP–6 and KAS6/1 samples. As our understanding of myeloma increases and we strive to develop new therapies for specific biological entities it will be essential that groups confirm both the authenticity and purity of their test cultures. We hope that widespread use of this simple screening methodology will significantly improve the quality and reproducibility of assays carried out in labs around the world.

Activation of NFkB has been noted in late B-cell malignancies, but no genetic basis for this activation has been shown except for rare mutations of the NFkB pathway in lymphoma and none have been described in MM. Bortezomib, highly tumoricidal in a subset of MM patients, inhibits NFkB suggesting it’s role as a therapeutic target. Here we show for the first time the critical importance of mutations that dysregulate this potential survival pathway in human myeloma cell lines (HMCL) and new diagnosis MM patients. We performed high-density oligonucleotide array CGH (Agilent 44k) on CD138+ selected MM cells from 68 patients and 42 unique HMCL. Initially we focused on small loci, bi-allelically deleted, as markers for inactivation of potential tumor suppressor genes. We next developed FISH probes for the identified loci to confirm the bi-allelic deletions seen by aCGH. We next sequenced all samples with monoallelic deletions, and additional unselected patients, and identified additional inactivating mutations. Multiple novel tumor suppressor genes (TSG) were identified and validated, whose loss of function (both in patients and HMCL) leads to activation of the non-canonical NFkB pathway including: TRAF2 (9q34), TRAF3 (14q32), BIRC2/BIRC3 (11q22) and CYLD (16q12). Functional studies showed that HMCL with deletion or mutations in these genes have markedly increased NFkB2 p52/p100 ratios relative to other HMCL (and for BIRC2/BIRC3 relative to an isogenic line that retains one copy of BIRC2/BIRC3), indicating genetic activation of the non-canonical NFkB pathway. Reintroduction of deleted TSG into HMCL inhibited cell growth and resulted in cell death (see data on abstract by J. Keats et al). We next focused our analysis (of combined aCGH and GEP data) on positive regulators of this pathway. Rare IgH translocations of NIK have recently been identified in MM. By aCGH we identified amplification and rearrangements of NIK. We identified dysregulated expression of TNF family receptors that activate the non-canonical pathway: CD40 (translocation), TACI (amplification) and LTBR. All of the HMCL with these mutations also showed increased NFkB2 p52/p100 ratios, consistent with activation of the non-canonical NFkB. These mutations correlate with a gene expression profile of NFkB activation that is detected in one half of patients. In summary, we have determined for the first time the genetic basis for constitutive NFkB activation - present in 19/42 HMCL, and we estimate in at least one quarter of newly diagnosed patients (approximately one half of those with evidence of NFkB activation by GEP). We propose a mechanism in which positive (TACI, CD40, LTBR) and negative regulators (TRAF2, TRAF3, BIRC2/BIRC3, CYLD) of the pathway converge on NIK to mediate the processing of NFKB2 p100 to p52. The preponderance of genetic evidence suggests that drugs that target the non-canonical NFkB pathway, will be most effective in treating the 50% of MM patients with NFkB activation.

In an attempt to identify novel genetic abnormalities in multiple myeloma (MM) we analyzed 68 MM patient samples and 42 human myeloma cell lines (HMCL) with high-resolution (60kb) array-based comparative genomic hybridization (aCGH). We concentrated on bi-allelic genomic deletions with the expectation that these regions might contain novel tumor suppressor genes and identified a common abnormality at 14q32. Fine mapping of the 14q32 microdeletion by PCR demonstrated a 45 kb minimal deletion encompassing two genes; TRAF3, a negative regulator of the non-canonical NF-kB pathway, and AMN. To determine the frequency of copy number abnormalities of this region a cohort of 161 patients were screened with a FISH probe mapping to the minimally deleted region. This identified 7 (4.4%) patients with bi-allelic deletion and 19 (11.8%) patients with a single copy of the target region. Sequencing of all TRAF3 coding exons in 62 patients and 42 HMCL identified inactivating mutations in 9 patient samples and 4 HMCL. Overall, the incidence of TRAF3 inactivation, bi-allelic deletion or mutation, is 7/42 (16.7%) in HMCL and 12/62 (19.4%) in patients, making it one of the most common genetic abnormalities identified in MM. Importantly, dysregulation of NF-kB pathways is a common event in MM, but the mechanism for this dysregulation is largely unknown. Although TRAF3 is a negative regulator of the non-canonical NF-kB pathway it has not previously been implicated in cancer. Therefore, we tested the tumor suppressor function of TRAF3 by reintroducing TRAF3 into HMCL harboring TRAF3 abnormalities using an adenovirus gene transfer system. Expression of TRAF3 in HMCL with TRAF3 abnormalities rapidly reversed cellular processing of NFKB2 from p100 (an inactive isoform) to p52 (active) and additionally led to a 60% reduction in cellular proliferation (range, 10–89%) associated with Go/G1 cell cycle arrest and induction of cell death by apoptosis. At 48 hrs post infection the proportion of cells entering S-phase or G2/M declined by 31% (range, 8.1–56.1) and the proportion undergoing apoptosis increased by 28% (range 11.7–47.4%). In contrast, over-expression of TRAF3 in control HMCL without TRAF3 abnormalities had no effect. Overall, TRAF3 is identified as a novel tumor suppressor that regulates the non-canonical NF-kB pathway and is inactivated in ~ 20% of MM patients. Given the involvement of the NF-kB pathway in multiple human malignancies and the near constitutive expression of TRAF3 we propose that inactivation of TRAF3, a novel tumor suppressor identified for the first time in this study, may occur in other cancers. In this regard, we have recently identified a Burkitt lymphoma cell line that does not express TRAF3 and thus has constitutive processing of p100 to p52. The clinical and therapeutic consequences of this finding and its frequency in other tumor types are currently the focus of further investigation. In conclusion, the abnormalities identified in this study represent the first mutations identified that cause constitutive NF-kB activation in MM.

The search for novel and clinically effective anti-myeloma therapies has been hampered by a paucity of good pre-clinical animal models. Most established animal models of multiple myeloma (MM) fail in one or more crucial features to resemble human MM, frequently exhibiting extramedullary tumors or lacking a competent immune system. In addition, competing models are either too expensive or time consuming to generate and maintain. Finally, no model has been shown to reliably predict both drug response and drug inactivity. We have previously described a C57Bl6/J transgenic mouse model in which the expression of the human c-myc oncogene is activated in post-germinal B cells by somatic hypermutation. These mice (Vk*myc) spontaneously develop monoclonal gammopathies and plasma cell expansion beginning at 20 weeks of age. However, in contrast to other models, their plasma cells cannot be found in secondary lymphoid tissues. Now, we report that this model closely reproduces the clinical behavior of human MM. Serum protein electrophoresis (SPEP) as well as ELISA for serum IgG demonstrate that the incidence and quantity of monoclonal paraproteinemia are greatly elevated in the Vk*myc mice as compared to age matched wild type C57Bl6/J controls (50 weeks mean IgG 1.92g/dL Vk*myc vs 0.2g/dL controls; peak IgG levels up to 7.5g/dL). As these mice age, their paraproteins continue rising and remain far higher than that of controls at every time point. Mice with significant paraproteinemia demonstrate marrow with up to 50% plasma cells with evidence of a low proliferative index, similar to what is observed in human MM and unlike what is seen in other models of MM. Anemia is observed, with a mean hemoglobin of 8.9g/dL in the Vk*myc mice vs 13.4g/dL in the wild type. Vk*myc mice analyzed show marked bone thinning with a 20% reduction in total bone volume and in the number of trabeculae per unit area as shown by microCT. In addition a 15% reduction in bone mineral density was demonstrated in affected mice. We next demonstrated the efficacy of 3 drugs, used commonly in clinical practice to treat myeloma (melphalan, dexamethasone and bortezomib). These were given as single courses of daily IP injections for 5 days, for the first two drugs, and bi-weekly IP for 4 weeks for the third. As early as two weeks post treatment, a statistically significant reduction in serum paraprotein levels was observed in the treated mice versus vehicle treated controls. The reductions were maximal at 21d post treatment in the melphalan (-77.2%±39 p<0.02) and dexamethasone (-67.4%±29 p<0.02) groups and at 28d in the bortezomib group (-68.9%±9 p<.001). No reduction was seen in the vehicle treated controls at any time point. As with human myeloma, the effect of one course of treatment was transient in nature. In contrast, treatment of VK*myc mice with 3 drugs that have not shown clinical activity against myeloma as single agents (hydroxyurea, vincristine and fludarabine) did not reduce serum monoclonal proteins. We conclude that our Vk*myc model closely reproduces the clinical characteristics of human MM. We have also shown that this model responds to drugs known to be clinically active, while showing no response to drugs that have little or no effect against human MM. To our knowledge, this is the first time that this level of fidelity to human MM has been demonstrated in a pre-clinical animal model. Our model therefore represents a unique and powerful tool for pre-clinical anti-myeloma drug development.

H-MM affects about 40–50% of patients, and a similar proportion of MGUS/SMM. The genetic evolution of the disease and the clinical implications of the co-existence of 13q- or t(14q32) are unknown. We conducted a global survey of genetic abnormalities in H-MM in order to describe genetic evolution pathways. H-MM cases from the Mitelman cancer genetic database were combined with cases from the Mayo Clinic MM genetic database. All abnormalities (regional/whole chromosome gains/losses, breakpoints and translocations) were plotted against a 344-chromosome band profile created in a matrix format, and the number of genetic abnormalities per tumor (NAPT) logged. The abnormalities present in more than 5% of tumors were considered recurrent and each karyotype was scored for the presence or absence of each of the recurrent abnormalities. To investigate the temporal pattern of acquisition of genetic abnormalities, all tumors with a given abnormality were selected and the distributions of NAPT plotted. The modes of these distributions were used as a value of ‘lateness’, referred to as time of occurrence (TO). The impact of co-existence of 13q- and t(14q32) on progression free survival (PFS) and overall survival (OS) in H-MM was determined for MM patients entered into an Eastern Cooperative Oncology Group chemotherapy trial. Four hundred and sixty-nine H-MM patients were included in the karyotypic analysis. The median chromosome number was 53 (range 48–74) and the median NAPT was 10 (range 1–25). The distribution of NAPT revealed a normal distribution, suggesting an obligatory acquisition of a given number of genetic abnormalities. The most common abnormalities were trisomies of chromosomes 3,5,7,9,11,15,19 and 21 affecting a third or more of the patients. Deletions and abnormalities of even-numbered chromosomes occur in 20% or less of patients. None of the more than 300 specific translocations detected were recurrent. However, 5 translocation breakpoints were recurrent including 14q32, 8q24 and 11q13. TO analysis suggest that for H-MM, the trisomies are early genetic events, translocations occur midway and deletions tend to be later events. Amongst the trisomies, correlation analysis does not suggest a particular order of acquisition. Clustering analysis using principal component analysis suggests that in H-MM, IgH translocations are secondary events associated with disease evolution rather than defining unique biological entities. Consistent with this, survival of H-MM patients is not affected by 13q- status but is negatively impacted by the presence of t(14q32) especially those with unknown partners (p<0.05). The data presented suggest that H-MM fit a proposed aneuploid model of cancer due to auto-catalytic chromosome reassortment (Duesberg et al Cell Cycle2003:2:202–210). The presence of tumor specific trisomies and the apparent similar phenotype induced by various combinations of trisomies are consistent with this model.

Hyperdiploid MM (H-MM), characterized by recurrent trisomies constitute about 50% of MM, yet very little is known about its pathogenesis and oncogenic mechanisms. Studies in leukemia and solid tumors have shown gene dosage effect of aneuploidy on gene expression. To determine the possible gene dosage effect and deregulated cellular program in H-MM we undertook a gene expression study of CD138-enriched plasma-cell RNA from 53 hyperdiploid and 37 non-hyperdiploid MM (NH-MM) patients using the Affymetrix U133A chip (Affymetrix, Santa Clara, CA). Gene expression data was analyzed using GeneSpring 7 (Agilent Technologies, Palo Alto, CA). Genes differentially expressed between H-MM and NH-MM were obtained by t-test (p<0.01). The majority of the differentially expressed genes (57%) were under-expressed in H-MM. Genes located on the commonly trisomic chromosomes were mostly (but not always) over-expressed in H-MM and constitute 76% of over-expressed genes. Chromosome 1 contained the most differentially expressed genes (17%) followed by chromosome 12 (9%), and 19 (8%). To examine the relationship of gene copy number to gene expression, we examined the expression of genes on chromosomes 9 and 15 in subjects with 2 copies (15 normal control and 20 NH-MM) and 3 copies (12 H-MM) of each chromosome as detected by interphase FISH. We then derived a ratio of the mean expression of each gene on these chromosomes between patients with 3 copies and 2 copies of the chromosome. If a simple relationship exists between gene expression and gene copy number, one would expect the ratio of expression of most genes on these two chromosomes to be about 1.5 in H-MM compared to NH-MM. However, many genes have ratios either higher than 2 or lower than 0.5. Furthermore, when the heterogeneity of cells with underlying trisomies is taken into consideration by correcting the ratio for the number of cells with trisomies, the actual ratio is always lower than the expected ratio. When the expression of genes on a chromosome was compressed to a median value, this value was always higher in the trisomic chromosomes for H-MM compared to NH-MM. The data suggests that although gene dosage influence gene expression, the relationship is complex and some genes are more gene dosage dependent than others. Amongst the differentially expressed genes with known function, 33% are involved in mRNA translation/protein synthesis. Of note, 37 of the top 100 differentially expressed genes are involved in these processes. In particular, 60 ribosomal protein (RP) genes are significantly (p<0.05) upregulated in H-MM. This signature in H-MM is not associated with increase proliferation as measured by PCLI. This predominant signature suggests that deregulated protein synthesis may be important for the biology of H-MM. Many of these RPs are involved in the synthesis of product of oncogenic pathways (e.g. MYC, NF-KB pathways) and may mediate the growth and survival of tumor cells. It is therefore possible that these tumor cells may be sensitive to the disruption of mRNA translation/protein synthesis. Targeting the mTOR pathway with rapamycin may therefore be useful for treatment of H-MM.

Cancer/testis antigens (CTAs), comprising the MAGE, CTAG, SSX and GAGE families, are expressed in different tumor types and restricted in normal tissues to germ cells of the testis. Many CTAs contain epitopes recognized by cytotoxic T cells and are potential targets for active immunotherapy. In MM, different CTAs have been shown to be expressed in cell lines and patient cells, and are associated with more proliferative and advance stage tumors. However, correlation with survival has never been reported. We undertook a global survey of CTA expression using gene expression profiling of CD138-enriched plasma-cell (PC) RNA in 15 normal, 101 MM, 22 MGUS and 24 SMM samples using the Affymetrix U133A chip (Affymetrix, Santa Clara, CA). 22 CTA genes were differentially expressed across the samples and unsupervised clustering using these genes clearly identifies a group of patients with high CTA expression. Most CTAs have significantly higher expression in MM as compared to SMM and especially MGUS, which has similar expression as normal PCs. As these antigens are not expressed in normal PCs, an upper limit of normal expression (ULN) was derived based on mean+3SD of expression in normal PCs for each CTA. A strict cut-off of normalized expression value greater than 2xULN was used to assign positive expression for each CTA genes. Using this method, the most commonly expressed CTAs are MAGE-A3 (73% of MM), MAGE-C1 (45%), MAGE-A6 (35%), SSX-1 (21%), GAGE-5 (18%) and NY-ESO-1 (14%). We then assigned patients with expression of more than 2 of these genes as having a CTA signature and correlated with clinical parameters. 45 patents (41 MM and 4 SMM) have the CTA signature. These patients have a significantly higher PCLI (median 0.2 v 0.7, p=0.0003). In fact, there is a significant correlation between the number of positive CTAs and PCLI (r=0.59, p<0.0001). Interestingly, there is no association between patients with a CTA signature and any of the recurrent genetic abnormalities (IgH translocations, chromosome 13 deletion and TC classes), yet MM patients with this signature have a significantly shorter survival (median 459 days vs not reached, log-rank p=0.017). A prognostic hierarchy exists amongst these CTAs. Only MAGE-A6, MAGE-A12, SSX-1 and SSX-5 expression has significant prognostic implications with the SSX family conferring the worse prognosis. Using a restricted panel of 3 CTAs (SSX-1, -5 and MAGE-A12), about 28% of MM patients expressing one or more of these genes can be identified with poor survival (median less than 1 year) that is independent of genetic subtypes. The genes differentially expressed between patients with and without the CTA signature are mainly involved in cell cycle regulation. Since the expression of this large set of CTAs appears to be under epigenetic control, we speculate that the same epigenetic processes that lead to dysregulation of the cell cycle also cause ectopic expression of CTA genes. As CTA expression is rare in MGUS, epigenetic processes may therefore also mediate transformation from MGUS to MM. These poor prognosis patients represent good candidates for novel therapies targeting the epigenetic machinery.

Introduction: The analysis of what goes awry in a malignant cell has focused primarily on mutations of protein-encoding genes and their regulatory sequences. However, recent work on microRNA (miRNA) has shed light on the possible involvement of miRNA genes in human disease. miRNA are small “noncoding” or “non-messenger” RNAs of about 21–25 nucleotides in length that function as regulators of gene expression essentially by pairing to the mRNA of protein-coding genes to initiate mRNA degradation or repression of translation. We are interested in characterizing miRNA expression profiles in human myeloma cell lines (HMCLs) and myeloma patient samples. Multiple myeloma (MM) is a plasma cell tumor characterized by frequent chromosomal translocations. Materials and methods: The expression of miRNA in HMCLs, primary MM cells (hyperdiploid samples) and normal plasma cells was determined using human microRNA chips. The GenoExporerTM Human microRNA chips were developed by GenoSensor (Tempe, AZ) and the microarray contains 226 human microRNA sequences in addition to control sequences. The DNA oligo probes are synthesized and immobilized on the chips (1”x 3” standard glass microslide). The probes are designed based on the active mature miRNA sequences and some of their flanking sequences. Our analysis included seven myeloma patients (hyperdiploid MM), eight different HMCLs (MM1, 8226 with t(14;16); SKMM2, U266, INA-6 with t(11;14) and H929, KMS11, UTMC-2 with t(4;14)), and eight normal human plasma cells. The normal human plasma cells were collected at Mayo Clinic Rochester from bone samples of patients undergoing orthopedic surgery. For the assay 5–10 μg of total RNA per sample were used at a concentration of 1 μg/μL. The RNA is directly labeled with biotin and used as a target for the on-chip hybridization assays. A streptavidin-Alexa dye is used to stain the hybridized targets and the fluorescent signals are captured and analyzed. The gene signal intensities were normalized to tRNA signal intensity. Results: The primary MM cells and HMCLs displayed a distinctive miRNA expression profile compared with normal plasma cells. Using the GeneSpring 7 (Agilent Technologies, Palo Alto, CA) for gene expression analysis we have identified miRNA genes with significant variation in expression levels between tumor and normal samples including miR-125b, miR-133a, miR1, and miR-124a (p<0.01). Recently defined algorithms were used to identify putative targets for the miRNA genes of interest such as leukemia inhibitory factor (LIF) as targets of miR-125b and Stat3 and angiopoietin-1 precursor as targets of miR-124a (Lewis et al. 2003). Of note, miR-15 and miR-16, previously identified to be downregulated in CLL, were expressed at low levels in some MM patients and HMCLs, but not in the normal plasma cells. Further analysis will be carried out to validate the data from miRNA profiling using northern blot analysis or real-time RT-PCR to measure expression levels of miRNA genes and that of their target genes. Conclusion: Analysis of miRNA expression pattern (along with aCGH and gene expression profiling studies) will undoubtedly refine our understanding of the various genotypic subtypes of multiple myeloma.

Hyperdiploid myeloma (H-MM) affects about 50% of MM. These patients exhibit significant karyotypic and clinical heterogeneity. In this study, we addressed possible biological heterogeneity within H-MM by gene expression profiling of CD138-enriched plasma-cell RNA from 53 H-MM patients using the Affymetrix U133A chip (Affymetrix, Santa Clara, CA). Analysis was performed using GeneSpring 7 (Agilent Technologies, Palo Alto, CA). Unsupervised hierarchical clustering performed using the top 100 most variable genes (generated by ANOVA) identifies 4 putative patient clusters. These clusters were reproduced using principal component analysis. Cluster 1 was characterized by high expression of a large group of cancer testis antigens and mitosis/proliferation related genes (TOP2A, NEK, ASPM, CENPA). Cluster 2 was characterized by high expression of genes involved in IL-6 and HGF signaling (MET, IL6R, SOCS3, SPINT1). Cluster 3 was characterized by high expression of genes involved in TNF/NF-KB signaling and anti-apoptosis (NFKB2, CFLAR, BIRC3, TNFAIP3, RRAS2). Cluster 4 was characterized by high expression of genes involve in angiogenesis (protocadherin, EDNRB). Unsupervised hierarchical clustering using the same set of genes in an independent cohort of H-MM patients (n=60) yielded the same 4 patient clusters over-expressing similar genes. The gene expression profile of these clusters were not driven by differences in trisomies (only about 25% of genes that define the clusters were located on the commonly trisomic chromosomes). Association between the 4 clusters and clinical parameters such as survival, chromosome 13 deletion (Δ13), presence of IgH translocations, PCLI, RAS mutation and p16 methylation was analyzed. Cluster 1 tumors were more proliferative (median PCLI 3.8, p<0.05). Cluster 2 was associated with presence of Δ13 (56%, p<0.05) although none of the genes that defined this cluster falls on chromosome 13. p16 methylation was also less common in cluster 2 (13%, p=0.06). Cluster 3 was associated with low PCLI (median 0.2, P<0.05). Most of the patients with p16 methylation also belonged to this cluster (67%, p=0.06). There was a complete absence of Δ13 in Cluster 4. Patients in the 4 clusters also had significantly different survival (log-rank p=0.002.). The difference in survival was independent of Δ13 since Δ13 has no impact on survival in this patient cohort. The molecular profiles of these subclasses may explain some of these associations. CTA expression is associated with proliferative tumors with poor prognosis. IL-6 is an important survival factor and HGF signaling has been associated with poor survival in MM which may explain the relative poor prognosis of this group. Cluster 3 may have better survival as it is associated with an anti-apoptotic signature rather than proliferative signature. In summary, gene expression profiling identified 4 sub-classes within H-MM (validated on an independent dataset and using different clustering techniques) with distinct clinical and biological associations. The gene signature associated with each sub-classes provide a molecular basis for the different clinical behaviour and further insights into deregulated pathways in H-MM.

Hyperdiploid (>48 chromosomes) multiple myeloma (H-MM) and high hyperdiploid (>50 chromosomes) acute lymphoblastic leukemia (H-ALL) are characterized by aneuploidy and multiple recurrent trisomies (chromosome 3,5,7,9,11,15,19 for H-MM and chromosomes X,4,6,10,14,17,18,21 for H-ALL). Little is known about the oncogenic events, consequences of the trisomies and reasons for the different recurrent trisomies. In an attempt to answer these questions, we undertook a combined gene expression and network/pathway analysis approach. Gene expression data was generated using the Affymetrix U133A chip (Affymetrix, Santa Clara, Ca) for 53 H-MM and 37 non-hyperdiploid MM (NH-MM) cases using CD138-enriched plasma-cell RNA. Gene expression data using the same chip for ALL was obtained from previous published data (Ross ME et al Blood2004; 104: 3679–3687). Analysis was performed using Genespring 7 (Agilent Technologies, Palo Alto, CA). By comparing the median expression of all genes on each chromosome between H-MM/H-ALL and their non-hyperdiploid counterparts (NH-MM and NH-ALL) for the 23 chromosomes (excluding Y), one can clearly identify the commonly trisomic chromosomes in H-ALL and H-MM. However, the relationship of gene expression was highly variable for H-MM and NH-MM as compared to H-ALL and NH-ALL which tended to have expression ratios close to 1 for the non-trisomic chromosomes. Sixty-nine percent of the differentially expressed genes generated by ANOVA analysis (p<0.001) in H-ALL were on the commonly trisomic chromosomes and were upregulated whereas the corresponding figure in H-MM is 40%. These similarities and differences probably reflect both an overall gene dosage effect and the different complexities of the karyotypes of H-MM and H-ALL compared to NH-MM and NH-ALL respectively (MM karyotypes are more complex, hence difference between H and NH-MM is greater and less confined to the trisomic chromosomes). We next performed network analysis using a curated web-based software (MetaCore, GeneGo Inc, St Joseph, MI) using the 2 sets of differentially expressed genes. Majority of genes differentially expressed in H-MM are involved in mRNA translation/protein synthesis whereas the genes differentially expressed in H-ALL were mainly involved in signal transduction. Therefore the transcriptional program that characterize the difference between H and NH-MM/ALL seem to recapitulate normal cellular function: protein synthesis in the mature secretory plasma cells and signal transduction in response to cytokines in a differentiating early-B cell. However, due to the concurrent deregulation of many genes on these trisomic chromosomes, these and other cellular programs are deregulated resulting in malignant transformation. We also intersected the 2 lists of differentially expressed genes to find genes that are up- or downregulated in both H-MM and H-ALL relative to the NH tumors. Thirteen genes including interferon response genes (TNFSF10, MX1, ZNF185) and transcription factors like RUNX1 were upregulated, whereas 13 genes including a cancer testis antigen gene (MAGED4) were downregulated in both H-MM and H-ALL. These genes may point to common oncogenic mechanisms.

Over 40% of cases of multiple myeloma (MM) are associated with translocations of the immunoglobulin heavy (IgH) chain gene gene. The t(4;14) translocation, present in ca. 20% of myeloma cases, results in the overexpression of two potential oncogenes, MMSET and FGFR3, via juxtaposition of their endogenous promoters to regulatory elements of the IgH locus. The presence of t(4;14), and MMSET overexpression, is an adverse prognostic factor in MM irrespective of FGFR3 expression. MMSET contains several conserved motifs found in proteins involved in chromatin function (PWWP, HMG, PHD domains) and in the epigenetic control of transcription (SET domain). Accordingly, we found that the two main isoforms of the MMSET protein exhibit exclusive nuclear localization in both transfected fibroblasts and myeloma cells carrying t(4;14). Towards our goal of defining the ability of MMSET to affect gene regulation and contribute to the disease pathogenesis, we found that the SET domain of MMSET possesses in vitro methyltransferase activity specific for core histones H3 and H4. Using a computational approach and theoretical extrapolation from the solved NMR structure of vSET, we identified residues in the active site of MMSET essential for catalysis, whose mutation drastically reduces enzymatic activity. Reporter assays using Gal4 fusion constructs showed that both the amino terminus of MMSET, containing the PWWP and HMG domains, as well as the SET-containing carboxy terminus act as transcriptional repressors. MMSET interacts physically and functionally with a number of known co-repressor molecules, such as HDAC1, HDAC2, Sin3a, and SIRT1, but not HDAC4 or HDAC6. As such, MMSET co-expression enhances HDAC1 and HDAC2-mediated repression in transcriptional reporter assays, and MMSET repression is partially relieved by the addition of an HDAC inhibitor. A yeast two hybrid screen identified a number of other functional partners of MMSET, including ZNF331/RITA (Rearranged in Thyroid Adenoma), a KRAB domain/zinc finger protein previously implicated in malignancy. MMSET and ZNF331 co-localize in the nuclei of transfected fibroblasts, co-immunoprecipitate, and display cooperative repression in reporter assays. Collectively, these data support the idea that MMSET is a biologically active, bifunctional transcriptional mediator acting as a HMT enzyme in chromatin remodeling and as a complex adaptor in the recruitment of repressor species. Presently we are modeling the biological effects of MMSET through a conditional overexpression system in a B cell line. While low levels of MMSET are ubiquitiously expressed, induction of high levels of MMSET expression in the B cell line is associated with growth suppression and G1 arrest. While paradoxical for a presumed oncoprotein, such actions have been observed for other disease-associated proteins such as Runx1/MTG8. In contrast, a myeloma cell line harboring t(4;14) proliferates in the presence of high level MMSET expression. RNAi-mediated knockdown of MMSET in these cells induces apoptotic cell death. This suggests that MMSET may be critical for growth and survival of myeloma cells. Profiling of gene expression changes in these systems should link the transcriptional and biological activities of MMSET.

The time in cellular differentiation at which the expression of an oncogene is dysregulated is thought to determine the phenotype of the resulting neoplasia. We tested this assumption in C57BL6/J transgenic mice expressing an HA-tagged c-myc oncogene in B cells under the control of kappa light chain regulatory elements. Two transgenes were engineered that differed by only one nucleotide. The first set of mice carries a wild type HA-MYC transgene, develops pro-B cell tumors, and succumbs rapidly to pronounced lymphosplenomegaly. In the second set of mice, a point mutation in the HA-tag portion of the transgene creates a stop codon that abrogates HA-MYC translation. This stop codon was engineered to be a hotspot for somatic hypermutation. Thus sporadically, in a germinal center B cell, somatic hypermutation may revert the stop codon, allowing translation of HA-MYC. In two independently derived lines, mice spontaneously develop monoclonal gammopathies (50% incidence at 30 weeks (n=35), 80% at 40 weeks (n=35)). Serum protein electrophoresis detects M-spikes that increase in intensity over time, and 6 out of 7 cases tested so far were of IgG1 isotype. Unlike other mouse models of plasma cell neoplasia, no lymphosplenomegaly nor ascites were detected. In analogy to human multiple myeloma, that is a disease of isotype-switched and hypermutated cells homing to the bone, large populations of plasma cells were found in the bone marrow. Bone marrow (but not spleen) lysates reacted for HA and human MYC proteins by western blot and immunohistochemistry, thus indicating that reversion of the stop codon occurred. Remarkably, in two young mice, monoclonal spikes appeared 2 weeks after vaccination with NP-CGG. These spikes were sustained and the monoclonal protein was reactive to the NP antigen. Together, comparison of the two sets of mice demonstrates that activation of the same transgene at distinct B cell developmental stages results in dramatically different tumor phenotypes. In addition, and opposite to most engineered mice, we have created a system where the oncogene is turned on sporadically, as occurs in the human disease. Furthermore, we have developed a model that faithfully reproduces important clinical aspects of monoclonal gammopathy of undetermined significance (MGUS) and its progression to multiple myeloma. This model will be useful to develop immunologic and chemoterapeutic approaches.

Dysregulation of D type cyclins is an almost universal event in multiple myeloma. Overexpression of cyclin D1 may occur by chromosomal translocation of t(11:14)(q13:32), and also in association with hyperdiploidy. To investigate the role of cyclin D1 in the growth of human myeloma cell lines, we used both shRNA plasmid constructs, and an siRNA Smartpool against cyclin D1 and compared to control cells transfected with anti-GFP or GAPDH constructs. siRNA was electroporated into multiple myeloma cell lines overexpressing cyclin D1 (KMS12PE, U266, H929) which gave a 50–60% transfection efficiency, assessed using a GFP plasmid. Successful reduction in levels of cyclin D1 was confirmed by western blotting and normalization to a beta actin standard. Cyclin D1 protein in sh- or siRNA transfected cells was reduced on average to 32% of that in cells transfected with an anti-GAPDH or anti-GFP siRNA. In individual experiments reduction of cyclin D1 protein to as little as 10% of control was observed. However, we found no sign of increased apoptosis by Annexin V/Propidium iodide staining. Furthermore, cell cycle analysis by ethidium bromide staining and flow cytometry revealed no significant change in the cell cycle of sh- or siRNA transfected cells when compared to control cells. qPCR analysis revealed no acute compensatory increase in the RNA levels of other D-type cyclins (D2, D3) following reduction of cyclin D1 levels. These results may be explained by the residual presence of sufficient cyclin D1 protein for cell cycle progression. An alternative explanation is that changes that frequently occur in myeloma to other cell cycle regulators, for example p16(INK4a) and Rb are able to circumvent cell cycle effects of reducing cyclin D1protein. These results suggest that the human myeloma cell lines tested are not acutely sensitive to cyclin D1 level.

Approximately 15% of multiple myeloma (MM) is characterized by a t(4;14) translocation that causes the simultaneous dysregulation of MMSET on der(4) and fibroblast growth factor receptor 3 gene (FGFR3) on der(14). We reported several lines of evidence indicating a role for FGFR3 in myeloma tumorigenesis. First, activated FGFR3 is an oncogene capable of transforming fibroblasts. Second, FGFR3 activating mutations are acquired by MM cells during tumor progression. Third, targeted inhibition of FGFR3 leads to terminal differentiation and apoptosis in two t(4;14) MM cell lines. However, expression of FGFR3, but never of MMSET, is lost in about 25% of t(4;14) MM. Therefore, the overexpression of MMSET in all MM tumors with a t(4;14) translocation, and its homology to MLL, the oncogene on 11q23 translocated in acute leukemia suggest a critical role for MMSET in MM. To determine whether MMSET is an oncogene in vivo, we have generated transgenic mice in which MMSET expression in driven in lymphocytes by the lck proximal promoter juxtaposed to the Emu enhancer. Using the same expression vector we and others have obtained specific, high levels of transgene expression in B and T cells from spleen, bone marrow and thymus. Four transgenic lines were generated and although we detected MMSET expression in T cells in each of them, unexpectedly no expression in B cells was seen. This is consistent with our inability to ectopically express MMSET in B cell lines. Nevertheless B lymphoid tumors expressing MMSET developed at 23 month of age in each line (18/51 mice). Only 1/19 wild type matching control mice developed a splenomegaly. By Southern blot, monoclonal rearrangements of IgH, IgL and TCR β were detected within the same tumor population. In conclusion, this is the first report that MMSET is an oncogene capable of transforming lymphoid cells in an animal model. We are currently crossing these mice with FGFR3 transgenic mice to assess cooperation between these two oncogenes in tumorigenesis. Obviously a more restricted expression of MMSET in germinal center cells is required to investigate the role of MMSET in MM. Therefore, as we have done for c-myc, we are generating new transgenic mice in which MMSET expression will be activated sporadically in germinal center B cells by somatic hypermutation.

FGFR3 is disregulated in approximately 15% of cases of multiple myeloma (MM) occurring by chromosomal translocation in the Igh switch region which results in the juxtaposition of FGFR3 next to the regulatory elements of the IgH locus, causing its ectopic expression in plasma cells. The acquisition of FGFR3 activating mutations in some tumors indicate a role for FGFR3 in tumor progression. In order to study its role in MM progression we developed a strain of transgenic mice in which the expression of the activated form of FGFR3 is mediated by isotype switch recombination by replacing the IgH gamma1 costant region with an FGFR3-IRES-EGFP cassette in a BAC that covers the entire murine IgH locus. We predict that in the transgenic mice B cells that undergo switch recombination to g1 on the productive allele will also undergo switch recombination to g1 at the transgenic locus and express FGFR3 and EGFP. To evaluate FGFR3 expression in vitro, we collected splenocytes from our transgenic mice and induced their proliferation and differentiation to plasma cells (mainly IgG1) using LPS and IL4. After four days of stimulation, the average number of EGFP positive cells went from 0.2% to 80%. We then analyzed FGFR3 expression by RT PCR, Northern and Western blot and detected LPS/IL4 inducible FGFR3 expression in plasma cells mediated mainly by the Igamma1 promoter and in a subset of them by the Vh promoter. We then tested if forced FGFR3 expression in B cells would affect their proliferation rate and ability to differentiate in vitro by MTT assay, cell cycle analysis and PI staining on LPS/IL4 stimulated splenocytes at different time points. With this system, we did not observe any FGFR3 mediated alteration of splenocytes growth parameters when compared to wild type controls. Similarly, in vivo no monoclonal gammopathy has been observed by serum protein electrophoresis and all the transgenic mice remaine tumor free at 1.5 years. Although we have not been able to demonstrate a tumorigenic role for FGFR3 in switched plasmacells we were able to obtaine regulated FGFR3 expression in them. It is possible that FGFR3 expression alone is not sufficient to induce plasma cells transformation and that FGFR3 has a dispensable role in tumor initiation, but that it could still play a role in tumor progression. Consistently, FGFR3 expression is lost in about 25% of multiple myeloma wih a t(4;14). To address this hypotesis we are currently crossing these mice with MMSET (the other gene disregulated in the t(4;14)) transgenic mice to investigate a possible collaborative role between these two genes in the development of MM.

Background: Dysregulation of the cell cycle and apoptosis are two critical events in the pathophysiology of MM. This notion is supported by: 1)A high tumor burden is often present despite a low rate of tumor cell proliferation. 2)G1 arrest is common in MM cells while normal plasma cells are permanently withdrawn from cell cycle. 3) Cyclin D1 is often overexpressed without a defined genetic substrate. Herein, we show that cell cycle evaluation in vivo is feasible and that the histone-deacetylase inhibitor depsipeptide might be effective in selected patients with MM. Patients and Methods: In vitro studies were performed in 12 human MM cell lines with defined cytogenetic abnormalities. The IC50 for depsipeptide was determined by evaluation of apoptosis by standard methods. In vivo studies where done as correlates in a phase II protocol. These include: Immunohistochemistry (IHC) for co-expression of CD138/Ki-67 as a proliferation index (PCPI), cyclin D1, D3, caspase 3 cleavege, CD31 and bcl-2 before treatment and at 24 hrs and 30 days after treatment. Gene array studies are being performed on selected patients at those timepoints. To date, four stage III patients (PTS) with relapsed MM with four or fewer prior lines of therapy have been treated with one to three cycles of depsipeptide at a dose of 13mg/m2,as a 4-hour infusion on days 1, 8, and 15, repeated every 28 days. Mean age was 63 years (range, 56 to 72). KPS of >80%. Mean albumin was 3.5, (range, 3.2 to 4), mean LDH was 243 (range, 179 to 315). Results: 1)Depsipeptide induces apoptosis in several MM cell lines. All lines were susceptible to depsipeptide, however, differential sensitivities were noted. Three cell lines (ie U266) that contained 11q13 translocation (cyclin D1 overexpression) were the most sensitive with IC50s at least 2 fold lower than other lines. 2) Cell cycle changes are induced by depsipeptide: In 2/4 PTS, a significant increase of the PCPI was seen, whereas a marked reduction in the PCPI in a patient with cyclin D3 overexpression (27% to 16%) was also noted. One patient had an increase of cyclin D1 post treatment. No changes where seen in bcl-2, CD-31, or cleaved caspase-3 expression. 3) Depsipeptide is safe in a limited cohort of MM PTS: Grade 2 fatigue and anorexia were the most common toxicities. Mild thrombocytopenia (mean of 67) did not require transfusions. One patient had stable disease after 3 cycles of treatment, one patient had progression of disease after 3 cycles, one patient progressed after the 1st cycle, and one patient is too early for evaluation. Conclusions: 1)Patients with 11q13 translocation should be a target for treatment with depsipeptide. 2)Depsipeptide given on this schedule is safe and can stabilize tumor-mass in PTS with otherwise progressive relapsed and refractory disease.3) Evidence of cell cycle modulation can be seen during treatment with depsipeptide. No profound changes in apoptosis is evident.4)Further studies may help to understand the mechanism of transcriptional regulation by depsipeptide and will help design rational therapy and combinations. This study continues to accrue patients as part of New York Phase II Consortium. Supported by NCI grant (SAIC1N01-CO-12400-02) and a SCOR for Myeloma grant from the Leukemia and Lymphoma Society of America.

The B-Cell Lymphoma 6 (BCL6) gene encodes for a zinc finger motifs containing transcriptional repressor that is frequently dysregulated by chromosomal translocations in germinal center lymphomas. A putative protooncogene, its transforming ability in vivo was reported in I-mu-HA-BCL6 knock-in mice by Cattoretti et al last year. We also tested this assumption in transgenic mice expressing BCL6 in B cells under the control of kappa light chain regulatory elements. We replaced the murine C-kappa locus with the 16kb human BCL6 genomic locus in a construct containing the murine kappa light chain regulatory elements (Vk, EiK, 3′RR). While control transgenics were readily obtained (5/32 founders), only 3/68 founders were positive for the BCL6 transgene, of which only one (bearing a single copy of the transgene) was able to transmit the transgene to its progeny, thus suggesting embryonal toxicity of exogenous BCL6. In the bone marrow, flow cytometry revealed a nearly complete block of B cell development at the pro-B to pre-B transition. This was also the stage at which we first detected expression of EGFP in control reporter mice that were generated in parallel. Spleens of transgenic mice weighed about 50% of control spleens and less than 5% of splenocytes were CD19+ B cells. These were IgM high, IgD intermediate, corresponding to an immature B cell phenotype. Lymph nodes were smaller and B cells barely detected. Peyers’ patches were not visible. Combined, our analysis of 6–8 weeks old VkHABCL6 transgenic mice reveals that enforced expression of BCL6 early in development results in a profound block of B lymphocyte differentiation. How transgenic BCL6 modulates this effect at the transcriptional level remains to be investigated. To test the oncogenic potential of BCL6 in B cells, it will be interesting to precisely turn on this gene in the germinal center.