Epigenetics and Lymphoma: Can We Use Epigenetics to Prime or Reset Chemoresistant Lymphoma Programs?

Non-Hodgkin lymphoma is a diverse group of lymphocyte-derived neoplasms. Although a heterogeneous group of malignancies, it has become apparent that epigenetic alterations, such as disturbances of DNA methylation and histone modification, are a common occurrence in both B cell and T cell lymphomas, contributing to lymphomagenesis. As a result, the use of epigenetic targeted therapy has been incorporated into various pre-clinical and clinical studies, demonstrating significant efficacy in lymphoma, with vorinostat becoming the first epigenetic therapy to receive FDA approval in any malignancy. The role of epigenetic drugs is evolving, with its potential use in combination therapy as well as a means of overcoming chemotherapy resistance. In this review, we discuss the epigenetic alterations in non-Hodgkin lymphomas as well as provide an overview of current epigenetic drugs and their role in clinical practice, and on-going clinical trials.

Will new drugs change the standard of care for patients with mantle cell lymphoma?

Mantle Cell lymphoma is a heterogeneous malignancy that has different subtypes with variable levels of aggressiveness. Research on the pathobiology of this disease is helping us understand the etiology for this heterogeneity and has the potential to guide future therapeutic options. The availability of the Ki67 proliferation index and the use of the MIPI score can help determine which of the numerous therapeutic options might be utilized. Minimal Residual Disease testing can act as a guide as to the potential benefit of maintenance therapy. This article discusses the current standard of care for Mantle Cell lymphoma and our current understanding of the pathobiology of the disease leading to strategies to improve patient outcomes with some of the newer targeted agents.

Emerging therapies in relapsed and refractory peripheral T-cell lymphoma

The peripheral T-cell lymphomas (PTCLs) account for 5% to 10% of all non-Hodgkin lymphomas. In the up-front setting, approximately one-quarter of patients experience a long-term remission. In the setting of relapsed and refractory disease, the median progression-free survival and overall survival are reported to be only 3.7 and 6.5 months, respectively. Unfortunately, the molecular and genetic characterization of PTCL has lagged well behind that of the B-cell lymphomas, although several recent experiences are shedding light on the remarkable molecular heterogeneity that has come to define these diverse diseases. The need to identify new active drugs for patients with PTCL has been addressed in part over the last several years, as 4 drugs have now been approved by the US Food and Drug Administration for patients with relapsed or refractory disease, and a plethora of new studies exploring novel combinations have begun to emerge. More advanced techniques in molecular biology, such as next-generation sequencing, gene expression profiling, and comparative genomic hybridization, have helped identify subtleties among subtypes and potentially identify new targets. Many of these recent clinical advances have been based on the recognition that PTCL is a disease that may be broadly characterized by gross epigenetic dysregulation with sensitivity to histone deacetylase inhibitors. In this report, we discuss emerging new therapies in relapsed and refractory PTCL and try to place these new findings in the evolving biological understanding of the disease.

Phase I Study of the Novel Investigational NEDD8-Activating Enzyme Inhibitor Pevonedistat (MLN4924) in Patients with Relapsed/Refractory Multiple Myeloma or Lymphoma

PURPOSE

Evaluate the safety, pharmacokinetic profile, pharmacodynamic effects, and antitumor activity of the first-in-class investigational NEDD8-activating enzyme (NAE) inhibitor pevonedistat (TAK-924/MLN4924) in patients with relapsed/refractory lymphoma or multiple myeloma.

EXPERIMENTAL DESIGN

Patients with relapsed/refractory myeloma (n = 17) or lymphoma (n = 27) received intravenous pevonedistat 25 to 147 mg/m(2) on days 1, 2, 8, 9 (schedule A; n = 27) or 100 to 261 mg/m(2) on days 1, 4, 8, 11 (schedule B; n = 17) of 21-day cycles.

RESULTS

Maximum tolerated doses were 110 mg/m(2) (schedule A) and 196 mg/m(2) (schedule B). Dose-limiting toxicities included febrile neutropenia, transaminase elevations, muscle cramps (schedule A), and thrombocytopenia (schedule B). Common adverse events included fatigue and nausea. Common grade ≥3 events were anemia (19%; schedule A), and neutropenia and pneumonia (12%; schedule B). Clinically significant myelosuppression was uncommon. There were no treatment-related deaths. Pevonedistat pharmacokinetics exhibited a biphasic disposition phase and approximate dose-proportional increases in systemic exposure. Consistent with the short mean elimination half-life of approximately 8.5 hours, little-to-no drug accumulation in plasma was seen after multiple dosing. Pharmacodynamic evidence of NAE inhibition included increased skin levels of CDT-1 and NRF-2 (substrates of NAE-dependent ubiquitin ligases), and increased NRF-2-regulated gene transcript levels in whole blood. Pevonedistat-NEDD8 adduct was detected in bone marrow aspirates, indicating pevonedistat target engagement in the bone marrow compartment. Three lymphoma patients had partial responses; 30 patients achieved stable disease.

CONCLUSIONS

Pevonedistat demonstrated anticipated pharmacodynamic effects in the clinical setting, a tolerable safety profile, and some preliminary evidence that may be suggestive of the potential for activity in relapsed/refractory lymphoma.

Aurora A Kinase Inhibition Selectively Synergizes with Histone Deacetylase Inhibitor through Cytokinesis Failure in T-cell Lymphoma

PURPOSE

Aurora A kinase (AAK) is expressed exclusively during mitosis, and plays a critical role in centrosome duplication and spindle formation. Alisertib is a highly selective AAK inhibitor that has demonstrated marked clinical activity of alisertib across a spectrum of lymphomas, though particularly in patients with T-cell lymphoma (TCL). We sought to compare and contrast the activity of alisertib in preclinical models of B-cell lymphoma (BCL) and TCL, and identify combinations worthy of clinical study. High-throughput screening of pralatrexate, the proteasome inhibitor (ixazomib), and the histone deacetylase (HDAC) inhibitor (romidepsin) revealed that only romidepsin synergized with alisertib, and only in models of TCL. We discovered that the mechanism of synergy between AAK inhibitors and HDAC inhibitors appears to be mediated through cytokinesis failure.

EXPERIMENTAL DESIGN

A high-throughput screening approach was used to identify drugs that were potentially synergistic in combination with alisertib. Live-cell imaging was used to explore the mechanistic basis for the drug: drug interaction between alisertib and romidepsin. An in vivo xenograft TCL model was used to confirm in vitro results.

RESULTS

In vitro, alisertib exhibited concentration-dependent cytotoxicity in BCL and TCL cell lines. Alisertib was synergistic with romidepsin in a T-cell-specific fashion that was confirmed in vivo. Live-cell imaging demonstrated that the combination treatment resulted in profound cytokinesis failure.

CONCLUSIONS

These data strongly suggest that the combination of alisertib and romidepsin is highly synergistic in TCL through modulation of cytokinesis and merits clinical development.

Belinostat in patients with refractory or relapsed peripheral T-cell lymphoma: a perspective review

Peripheral T-cell lymphoma (PTCL) is a disease with poor prognosis and limited treatment options. Recent advances in cancer biology suggest that PTCL may be characterized by gross epigenetic dysregulation, which may help explain its sensitivity to histone deacetylase (HDAC) inhibitors. HDAC inhibitors have demonstrated significant activity in T-cell neoplasms and recently, the BELIEF trial evaluated belinostat leading to its approval in the US. This review discusses the development of belinostat, its mechanism of action, pivotal clinical trials, drug toxicity and its recent approval for patients with relapsed or refractory PTCL. Key clinical trials covered include phase I/II evaluation of belinostat in hematologic malignancies, cutaneous T-cell lymphoma (CTCL) and PTCL. In addition, the BELIEF trial in PTCL leading to FDA approval of belinostat is reviewed in detail.

The combination of hypomethylating agents and histone deacetylase inhibitors produce marked synergy in preclinical models of T-cell lymphoma

T-cell lymphomas (TCL) are aggressive lymphomas usually treated with CHOP (cyclophsophamide, doxorubicin, vincristine, prednisolone)-like regimens upfront. Recent data suggest that TCL are driven by epigenetic defects, potentially rendering them sensitive to epigenetic therapies. We explored the therapeutic merits of a combined epigenetic platform using histone deacetylase inhibitors (HDACIs) and DNA methyltransferase inhibitors (DNMT) in in vitro and in vivo models of TCL. The 50% inhibitory concentration (IC50 ) values revealed romidepsin was the most potent HDACI, with an IC50 in the low nanomolar range. The combination with a hypomethylating agent produced synergy across all cell lines, which was confirmed in cytotoxicity and apoptosis assays. An in vivo xenograft study demonstrated inhibition of tumour growth in the combination cohort compared to the single agent. Gene expression array and global methylation profiling revealed differentially expressed genes and modulated pathways for each of the single treatment conditions and the combination. Most of the effects induced by the single agent treatment were maintained in the combination group. In total, 944 unique genes were modulated by the combination treatment, supporting the hypothesis of molecular synergism. These data suggest combinations of hypomethylating agents and HDACIs are synergistic in models of TCL, which is supported at the molecular level.

Putting the clinical and biological heterogeneity of non-hodgkin lymphoma into context

The lymphomas represent one of the most heterogeneous groups of malignancies in all of cancer medicine. Whether one attempts to understand these diseases in the context of their complicated ontogeny, unique biologic features, or clinical presentation, this heterogeneity has been a mixed blessing. On the one hand, it has created an ever-changing way to classify these diseases, as classification schemes have been compelled to reflect the rapidly emerging information that seems to split the disease into smaller and smaller subtypes. On the other hand, the biologic and clinical dissection of these diseases has allowed for the identification of unique biologic features-features that have led to novel targets and generated a plethora of new drugs. Virtually every subtype of non-Hodgkin lymphoma has benefited from these efforts to understand the biology of the different subtypes. This paradigm has led to new clinical trials that tailor novel drug regimens to specific biologic disease subtypes. As a prelude to this CCR Focus section, we attempt to put this evolving heterogeneity into context, bridging historical and modern-day views of classification of these diseases. Then, some of the world's leading lymphoma researchers share their perspectives on how to formulate new concepts of care in this era of biologic discovery. Over a relatively short time, the advances in lymphoma research have been nothing short of stunning. There now seems to be little doubt that these recent breakthroughs will redound favorably on the majority of patients diagnosed with a lymphoproliferative malignancy. See all articles in this CCR Focus section, "Paradigm Shifts in Lymphoma."

Changing the paradigms of treatment in peripheral T-cell lymphoma: from biology to clinical practice

Despite enormous advances in our understanding of aggressive lymphomas, it is clear that progress in the peripheral T-cell lymphomas (PTCL) has lagged well behind other B-cell malignancies. Although there are many reasons for this, the one commonly cited notes that the paradigms for diffuse large B-cell lymphoma (DLBCL) were merely applied to all patients with PTCL, the classic "one-size-fits-all" approach. Despite these challenges, progress is being made. Recently, the FDA has approved four drugs for patients with relapsed/refractory PTCL over the past 5 years, and if one counts the recent Japanese approval of the anti-CCR4 monoclonal antibody for patients with adult T-cell leukemia/lymphoma, five drugs have been approved worldwide. These efforts have led to the initiation of no fewer than four randomized clinical studies exploring the integration of these new agents into standard CHOP (cyclophosphamide-Adriamycin-vincristine-prednisone)-based chemotherapy regimens for patients with newly diagnosed PTCL. In addition, a new wave of studies are exploring the merits of novel drug combinations in the disease, an effort to build on the obvious single-agent successes. What has emerged most recently is the recognition that the PTCL may be a disease-characterized by epigenetic dysregulation, which may help explain its sensitivity to histone deacetylase (HDAC) inhibitors, and open the door for even more creative combination approaches. Nonetheless, advances made over a relatively short period of time are changing how we now view these diseases and, hopefully, have poised us to finally improve its prognosis. See all articles in this CCR Focus section, "Paradigm Shifts in Lymphoma."

Dual Targeting of Protein Degradation Pathways with the Selective HDAC6 Inhibitor ACY-1215 and Bortezomib Is Synergistic in Lymphoma

PURPOSE

Pan-class histone deacetylase (HDAC) inhibitors are effective treatments for select lymphomas. Isoform-selective HDAC inhibitors are emerging as potentially more targeted agents. HDAC6 is a class IIb deacetylase that facilitates misfolded protein transport to the aggresome for degradation. We investigated the mechanism and therapeutic impact of the selective HDAC6 inhibitor ACY-1215 alone and in combination with bortezomib in preclinical models of lymphoma.

EXPERIMENTAL DESIGN

Concentration-effect relationships were defined for ACY-1215 across 16 lymphoma cell lines and for synergy with bortezomib. Mechanism was interrogated by immunoblot and flow cytometry. An in vivo xenograft model of DLBCL was used to confirm in vitro findings. A collection of primary lymphoma samples were surveyed for markers of the unfolded protein response (UPR).

RESULTS

Concentration-effect relationships defined maximal cytotoxicity at 48 hours with IC50 values ranging from 0.9 to 4.7 μmol/L. Strong synergy was observed in combination with bortezomib. Treatment with ACY-1215 led to inhibition of the aggresome evidenced by acetylated α-tubulin and accumulated polyubiquitinated proteins and upregulation of the UPR. All pharmacodynamic effects were enhanced with the addition of bortezomib. Findings were validated in vivo where mice treated with the combination demonstrated significant tumor growth delay and prolonged overall survival. Evaluation of a collection of primary lymphoma samples for markers of the UPR revealed increased HDAC6, GRP78, and XBP-1 expression as compared with reactive lymphoid tissue.

CONCLUSIONS

These data are the first results to demonstrate that dual targeting of protein degradation pathways represents an innovative and rational approach for the treatment of lymphoma.

Belinostat in Patients With Relapsed or Refractory Peripheral T-Cell Lymphoma: Results of the Pivotal Phase II BELIEF (CLN-19) Study

PURPOSE

Peripheral T-cell lymphomas (PTCLs) represent a diverse group of non-Hodgkin lymphomas with a poor prognosis and no accepted standard of care for patients with relapsed or refractory disease. This study evaluated the efficacy and tolerability of belinostat, a novel histone deacetylase inhibitor, as a single agent in relapsed or refractory PTCL.

PATIENTS AND METHODS

Patients with confirmed PTCL who experienced progression after ≥ one prior therapy received belinostat 1,000 mg/m(2) as daily 30-minute infusions on days 1 to 5 every 21 days. Central assessment of response used International Working Group criteria. Primary end point was overall response rate. Secondary end points included duration of response (DoR) and progression-free and overall survival.

RESULTS

A total of 129 patients were enrolled, with a median of two prior systemic therapies. Overall response rate in the 120 evaluable patients was 25.8% (31 of 120), including 13 complete (10.8%) and 18 partial responses (15%). Median DoR by International Working Group criteria was 13.6 months, with the longest ongoing patient at ≥ 36 months. Median progression-free and overall survival were 1.6 and 7.9 months, respectively. Twelve of the enrolled patients underwent stem-cell transplantation after belinostat monotherapy. The most common grade 3 to 4 adverse events were anemia (10.8%), thrombocytopenia (7%), dyspnea (6.2%), and neutropenia (6.2%).

CONCLUSION

Monotherapy with belinostat produced complete and durable responses with manageable toxicity in patients with relapsed or refractory PTCL across the major subtypes, irrespective of number or type of prior therapies. These results have led to US Food and Drug Administration approval of belinostat for this indication.

The novel kinesin spindle protein (KSP) inhibitor SB-743921 exhibits marked activity in in vivo and in vitro models of aggressive large B-cell lymphoma

The kinesin spindle protein (KSP) is a mitotic protein essential for cell cycle control and motility. SB-743921 (hereafter SB-921) is an inhibitor that selectively targets the ATP-binding domain of the KSP. The preclinical activity of SB-921 was evaluated in models of diffuse large B-cell lymphoma (DLBCL). The cytotoxicity of SB-921 was evaluated in a series of germinal center (GC-DLBCL) and post-germinal center (ABC-DLBCL) DLBCL cell lines and a murine lymphoma xenograft model. GC-DLBCL lines generally demonstrated greater sensitivity to SB-921. IC50 values ranged between 1 nM and 900 nM for GC-DLBCL compared to 1 nM to 10 μM for ABC lines. SB-921 demonstrated marked activity in a xenograft model of Ly-1 (GC-DLBCL). While SB-921 was relatively more active in GC derived cell lines, ABC-derived lines still underwent apoptosis at higher concentrations. These results demonstrate that SB-921 inhibits proliferation and induces apoptosis in both GC-DLBCL and ABC-DLBCL.

The novel IKK2 inhibitor LY2409881 potently synergizes with histone deacetylase inhibitors in preclinical models of lymphoma through the downregulation of NF-κB

PURPOSE

To evaluate the pharmacologic activity of a novel inhibitor of IκB kinase β (IKK2), LY2409881, in preclinical models of B- and T-cell lymphoma, as a single agent and in combination with histone deacetylase (HDAC) inhibitors.

EXPERIMENTAL DESIGN

The in vitro activity of LY2409881 was determined using an ATP-based growth inhibition assay and flow cytometric assay of apoptosis in lymphoma cell lines. The in vivo activity of LY2409881 was determined using SCID-beige xenograft mouse model. The mechanism of action was determined using immunoblotting, immuofluorescence, and electrophoretic mobility shift assay. Synergy of LY2409881 with other drugs active in lymphoma was determined by calculating relative risk ratio (RRR) and combination index (CI).

RESULTS

LY2409881 inhibited constitutively activated NF-κB, and caused concentration- and time-dependent growth inhibition and apoptosis in lymphoma cells. In models of diffuse large B-cell lymphoma (DLBCL), the cytotoxicity of LY2409881 correlated with the overall activation status of NF-κB, but not simply in a pattern predicted by the cell-of-origin classification of these cell lines. LY2409881 was safe to mice at three dose levels, 50, 100, and 200 mg/kg, all of which caused significant inhibition of tumor growth. LY2409881 suppressed the activity of the NF-κB subunit p65 in lymphoma cells treated by the HDAC inhibitor romidepsin, underlying a potential mechanism of the marked synergy observed of these two drugs.

CONCLUSION

Collectively, these data strongly suggest that targeting the NF-κB pathway in combination with romidepsin could represent a novel and potent regimen for the treatment of B- and T-cell lymphoma.

Development and characterization of a Mantle Cell Lymphoma Cell Bank in the American Type Culture Collection

Mantle cell lymphoma (MCL) is a rare B-cell malignancy that carries a relatively poor prognosis compared to other forms of non-Hodgkin lymphoma. Standardized preclinical tools are desperately required to hasten the discovery and translation of promising new treatments for MCL. Via an initiative organized through the Mantle Cell Lymphoma Consortium and the Lymphoma Research Foundation, we gathered MCL cell lines from laboratories around the world to create a characterized MCL Cell Bank at the American Type Culture Collection (ATCC). Initiated in 2006, this collection now contains eight cell lines, all of which have been rigorously characterized and are now stored and available for distribution to the general scientific community. We believe the awareness and use of these standardized cell lines will decrease variability between investigators, harmonize international research efforts, improve our understanding of the pathogenesis of the disease and hasten the development of novel treatment strategies.

Abstract 4296: Correlation of the apparent diffusion coefficient of water assessed by diffusion-weighted imaging with treatment outcome in refractory lymphoma patients

The contrast of MR images can be made sensitive to the average motion of water molecules (diffusivity) giving rise to diffusion-weighted imaging (DWI). Intensity maps of the apparent diffusion constant (ADC) of water can be generated from the DWI information and average ADC values of anatomical regions can be assessed. Malignant tissues generally exhibit hypercellularity, increased nucleus-to-cytoplasm ratios, and an increased amount of macromolecules resulting in decreased water diffusivity (lower ADC). Additionally, a response-related ADC increase has been demonstrated in malignancies under therapy. We previously reported that the ADC mean value (in 10-3 mm2 s-1 [SD, n]) of masses of refractory lymphoma patients prior to a new treatment was lower than the ADC mean value of lymph nodes of healthy volunteers (0.91 [0.23, 15] vs. 1.13 [0.14, 10], respectively). This difference was significant (p < 0.01) despite of a large dispersion on the ADC data from the patients. Given this dispersion, we wanted to prove if refractory lymphoma patients with lower ADC values responded differently than those with higher ADC values. Experimental Design: Under ethical review board approval, refractory lymphoma patients underwent a pretreatment MR exam. DWI was acquired using echo-planar imaging with fat suppression and b-values of 0 and 1000 s/mm2 and the ADC of water in the tumor obtained. Time to treatment failure (TTF) was defined as the time between the end of one treatment and the start of a new one. Results: ADC and TTF were obtained in 12 refractory lymphoma patients and divided into those with TTF ≤ 75 days and those with TTF > 75 days. The ADC mean value [SD, n] in patients with TTF ≤ 75 days was 0.73 [0.20, 5] while in those with TTF > 75 days was 1.04 [0.20, 7]. These mean values were significantly different (p < 0.02). Furthermore, the comparison of the ADC mean value of lymph nodes of healthy volunteers with the ADC mean value of refractory patients with TTF ≤ 75 days was highly significant (p < 0.0005) while the comparison between healthy volunteers and patients with TTF > 75 days was not. Discussion: Our results demonstrate that refractory lymphoma patients with tumor masses displaying abnormally low ADC values prior to the start of treatment have poorer treatment outcome than those patients with ADC tumor values that are comparable to those in normal lymph nodes. If low ADC is due to increased tumor cellularity in patients with poorer outcome, this could produce reduced drug availability, thus explaining the substandard outcome. Our results demonstrate an important predictive value of the ADC determination by DWI in refractory lymphoma patients. This together with the fact that DWI is a noninvasive technique and its acquisition is fairly quick makes the ADC a parameter that could become critical for the clinical examination of the patient with refractory lymphoma.

Citation Format: Fernando Arias-Mendoza, Hamed Mojahed, Ahmed Sawas, Owen A. O'Connor. Correlation of the apparent diffusion coefficient of water assessed by diffusion-weighted imaging with treatment outcome in refractory lymphoma patients. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4296. doi:10.1158/1538-7445.AM2014-4296

Manipulating the epigenome in germinal center lymphomas: is it getting easier and ezier?

Mutations affecting key epigenetic modifiers tend to cluster in malignancies in which cells of origin lie in the germinal center (GC). EZH2, as transcriptional repressor, is mutated in high frequency in Chinese and Western patients with follicular lymphoma and may represent a rational target for GC-derived lymphomas. .

Everolimus for patients with mantle cell lymphoma refractory to or intolerant of bortezomib: multicentre, single-arm, phase 2 study

The multicentre, open-label, two-stage, single-arm, phase 2, PILLAR (PIvotaL Lymphoma triAls of RAD001)-1 study (NCT00702052) assessed the efficacy and safety of everolimus 10 mg/d in adults with confirmed mantle cell lymphoma (MCL) refractory to or intolerant of bortezomib who received ≥1 other antineoplastic agent, either separately or in combination with bortezomib. Primary endpoint was overall response rate (ORR) per investigator review according to the response criteria for malignant lymphoma. Secondary endpoints included progression-free survival (PFS), overall survival (OS) and safety. Fifty-eight patients were enrolled from August 2008-January 2011. Five partial responses were observed (ORR 8·6%; 90% confidence interval [CI] 3·5-17·3%); the study did not meet the prespecified objective of ≥8 objective responses among 57 patients. Median PFS and OS were 4·4 months (95% CI 3·5-6·1) and 16·9 months (95% CI 14·4-29·9), respectively. Grade 3/4 non-haematological toxicities occurred in 70·7% of patients. Based on laboratory values, grade 3/4 thrombocytopenia, neutropenia and anaemia occurred in 13·8%, 13·8% and 8·6% of patients, respectively. Everolimus demonstrated modest activity and acceptable tolerability in heavily pretreated patients with MCL refractory to or intolerant of bortezomib. Future studies evaluating everolimus in a less refractory population or in combination with other targeted therapies in refractory MCL are warranted.

Noninvasive phosphorus magnetic resonance spectroscopic imaging predicts outcome to first-line chemotherapy in newly diagnosed patients with diffuse large B-cell lymphoma

RATIONALE AND OBJECTIVES

Based on their association with malignant proliferation, using noninvasive phosphorus MR spectroscopic imaging ((31)P MRSI), we measured the tumor content of the phospholipid-related phosphomonoesters (PME), phosphoethanolamine and phospholcholine, and its correlation with treatment outcome in newly diagnosed patients with diffuse large B-cell lymphoma (DLBCL) receiving standard first-line chemotherapy.

EXPERIMENTAL DESIGN

The PME value normalized to nucleoside triphosphates (PME/NTP) was measured using (31)P MRSI in tumor masses of 20 patients with DLBCL before receiving standard first-line chemotherapy. Response at 6 months was complete in 13 patients and partial in seven. Time to treatment failure (TTF) was ≤11 months in eight patients, from 18 to 30 months in three, and ≥60 months in nine.

RESULTS

On a t test, the pretreatment tumor PME/NTP mean value (SD, n) of patients with a complete response at 6 months was 1.42 (0.41, 13), which was significantly different from the value of 2.46 (0.40, 7) in patients with partial response (P < .00001). A Fisher test significantly correlated the PME/NTP values with response at 6 months (sensitivity and specificity at 0.85, P < .004) while a Cox proportional hazards regression significantly correlated the PME/NTP values with TTF (hazard ratio = 5.21, P < .02). A Kaplan-Meier test set apart a group entirely composed of patients with TTF ≤ 11 months (hazard ratio = 8.66, P < .00001).

CONCLUSIONS

The pretreatment tumor PME/NTP values correlated with response to treatment at 6 months and time to treatment failure in newly diagnosed patients with DLBCL treated with first-line chemotherapy, and therefore they could be used to predict treatment outcome in these patients.

PCDH10 promoter hypermethylation is frequent in most histologic subtypes of mature lymphoid malignancies and occurs early in lymphomagenesis

PCDH10 is epigenetically inactivated in multiple tumor types; however, studies in mature lymphoid malignancies are limited. Here, we have investigated the presence of promoter hypermethylation of the PCDH10 gene in a large cohort of well-characterized subsets of lymphomas. PCDH10 promoter hypermethylation was identified by methylation-specific PCR in 57 to 100% of both primary B- and T-cell lymphoma specimens and cell lines. These findings were further validated by Sequenom Mass-array analysis. Promoter hypermethylation was also identified in 28.6% cases of reactive follicular hyperplasia, more commonly occurring in states of immune deregulation and associated with rare presence of clonal karyotypic aberrations, suggesting that PCDH10 methylation occurs early in lymphomagenesis. PCDH10 expression was down regulated via promoter hypermethylation in T- and B-cell lymphoma cell lines. The transcriptional down-regulation resulting from PCDH10 methylation could be restored by pharmacologic inhibition of DNA methyltransferases in cell lines. Both T- and B-cell lymphoma cell lines harboring methylation-mediated inactivation of PCDH10 were resistant to doxorubicin treatment, suggesting that hypermethylation of this gene might contribute to chemotherapy response.

CYP3A-mediated drug-drug interaction potential and excretion of brentuximab vedotin, an antibody-drug conjugate, in patients with CD30-positive hematologic malignancies

Brentuximab vedotin is an antibody-drug conjugate (ADC) that selectively delivers monomethyl auristatin E (MMAE) into CD30-expressing cells. This study evaluated the CYP3A-mediated drug-drug interaction potential of brentuximab vedotin and the excretion of MMAE. Two 21-day cycles of brentuximab vedotin (1.2 or 1.8 mg/kg intravenously) were administered to 56 patients with CD30-positive hematologic malignancies. Each patient also received either a sensitive CYP3A substrate (midazolam), an effective inducer (rifampin), or a strong inhibitor (ketoconazole). Brentuximab vedotin did not affect midazolam exposures. ADC exposures were unaffected by concomitant rifampin or ketoconazole; however, MMAE exposures were lower with rifampin and higher with ketoconazole. The short-term safety profile of brentuximab vedotin in this study was generally consistent with historic clinical observations. The most common adverse events were nausea, fatigue, diarrhea, headache, pyrexia, and neutropenia. Over a 1-week period, ∼23.5% of intact MMAE was recovered after administration of brentuximab vedotin; all other species were below the limit of quantitation. The primary excretion route is via feces (median 72% of the recovered MMAE). These results suggest that brentuximab vedotin (1.8 mg/kg) and MMAE are neither inhibitors nor inducers of CYP3A; however, MMAE is a substrate of CYP3A.

Phase III trial of brentuximab vedotin and CHP versus CHOP in the frontline treatment of patients (pts) with CD30+ mature T-cell lymphomas (MTCL)

TPS8611

Background: MTCL including systemic anaplastic large cell lymphoma (sALCL) are aggressive neoplasms. Anthracycline-based multiagent chemotherapy regimens have demonstrated response rates ranging from 76 to 88%. Five-year overall survival rates range from 12 to 49% depending on the histologic subtype. Brentuximab vedotin is an antibody drug conjugate that has shown efficacy in a pivotal phase 2 study as a single agent in relapsed sALCL (Pro et al., J Clin Oncol, 2012) and evidence of clinical activity in combination with CHP in the frontline treatment of MTCL including sALCL in a phase 1 study (Fanale et al., ASH 2012). Methods: This randomized, double-blind, placebo-controlled, multicenter, phase 3 study (NCT01777152) is evaluating the safety and efficacy of 1.8 mg/kg brentuximab vedotin with CHP (A+CHP) vs CHOP for frontline treatment of CD30+ MTCL. Pts must have FDG-avid disease by PET and measureable disease of at least 1.5 cm by CT. Approximately 300 pts will be randomized 1:1 to receive A+CHP or CHOP for 6–8 cycles (q3wk). Randomization will be stratified by ALK+ sALCL vs other histologic subtypes and IPI score (0–1, 2–3, or 4–5). The target proportion of pts with a diagnosis of sALCL will be 75%. The primary objective is to compare progression-free survival (PFS) between the 2 treatment arms as determined by an independent review facility (IRF). Secondary objectives include comparisons of PFS per IRF in sALCL patients, safety, overall survival, and complete remission rate between the 2 arms. After completion of treatment, pts will be followed for disease progression, medical resource utilization, quality of life, and survival. Post-treatment stem cell transplant is permitted. Efficacy assessments will use the Revised Response Criteria for Malignant Lymphoma (Cheson 2007). CT and PET scans will be performed at baseline, after Cycle 4, and after the completion of treatment. CT scans will also be performed at regular intervals during follow-up until disease progression, death, or analysis of the primary endpoint. Safety assessments will occur throughout the study until 30 days after last dose of study treatment. Enrollment for this global trial began in early 2013. Clinical trial information: NCT01777152.

A phase I dose-escalation trial of ublituximab (TG-1101), a novel anti-CD20 monoclonal antibody (mAb), for rituximab relapsed/refractory B-cell lymphoma patients

8575

Background: Anti-CD20 therapy (rituximab or RTX) in treating patients (pts) with B-cell lymphomas has resulted in significant improvement in treatment response and clinical outcomes. Despite advances, pts continue to relapse from, or are refractory to, RTX-based regimens. Ublituximab (UTX) is a novel, chimeric mAb targeting a unique epitope on the CD20 antigen. UTX has been glycoengineered to enhance affinity for all variants of FcγRIIIa receptors, and therefore demonstrates greater ADCC activity than RTX (Le Garff-Tavernier, 2011). UTX displayed greater antitumor activity compared to RTX in NHL in vivo models and in low CD20 expressing tumors (ASH 2011). A phase I trial with UTX used as a single agent in pts with relapsed/refractory CLL reported a response rate of 45%. Herein we report on the phase I dose-escalation of UTX in pts with RTX relapsed/refractory B-cell lymphoma. Methods: Eligible pts have B-cell lymphoma relapsed or refractory to a RTX containing regimen. Pts are required to have measurable/evaluable disease, ECOG PS < 2 and no active hepatitis B/C. The phase I dose-escalation uses a sequential 3+3 design in dose cohorts of 450mg, 600mg and 900mg respectively. UTX is administered once weekly for 4 infusions followed by monthly maintenance therapy. PK and correlative PD data are being collected. Primary endpoint: Maximum Tolerated Dose (MTD) and Dose Limiting Toxicities (DLT). Efficacy is a secondary endpoint. Results: Nine pts (5 FL, 3 MZL, 1 MCL) have been enrolled (3 each cohort). Median age 63; 3/6 (M/F). Median prior Rx = 4 (2-6). RTX refractory (44%). 8/9 pts are evaluable for safety; no DLT’s observed and no Grade 3/4 AE’s to date. 7/9 pts have had at least one response assessment (8 wk scan), which includes: 1 CR (rituximab refractory MZL); 2 PR’s (1 MZL, 1 FL); 2 SD (FL) and 2 PD (1 transformed FL, 1 MCL). PK analysis is ongoing. Conclusions: UTX has been well tolerated to date with no G 3/4 AE’s with demonstrated early clinical activity at all doses. 7/9 patients continue to receive UTX treatment (range 1–25 wks). Enrollment in the 900mg expansion cohort is now open with an emphasis on RTX relapsed/refractory indolent or low CD20-expressing lymphomas. Clinical trial information: NCT01647971.

Belinostat, a novel pan-histone deacetylase inhibitor (HDACi), in relapsed or refractory peripheral T-cell lymphoma (R/R PTCL): Results from the BELIEF trial

8507

Background: Therapies approved in US for R/R PTCL have overall response rates (ORR) of 25%-27%. The need for new therapies persists. BELIEF is a pivotal, single-arm study of belinostat in patients with R/R PTCL after failure of ≥1 prior systemic therapies. Methods: Entry criteria were measurable PTCL, platelets ≥ 50,000/µL, no prior HDACi therapy, and adequate organ function. PTCL was confirmed by central pathology review (CPRG). Belinostat 30 min IV infusion at 1000 mg/m2was administered on days 1–5 of a 3 week cycle until progression or unacceptable toxicity. Tumor response was assessed by Cheson 2007 criteria. The primary endpoint was ORR. Results: Patients with R/R PTCL (N=129, 53% male, median age 63 y) received belinostat a median of 2 cycles (range 1–33). The median number of prior therapies was 2 (1-8) including CHOP/CHOP-like (96%) and stem cell transplant (23%). The median administered dose intensity was 98%. One and two dose reductions of 25% occurred in 12% and 1% of patients, respectively, due to adverse events (AEs). For patients with CPRG confirmed PTCL (N=120), the ORR was 26% (n=31; 10% CR; 16% PR). The median time to response was 5.6 weeks (range 4.3-50.4). The median duration of response (DoR) was 8.3 months; longest DoR was 29.4 months. Seven patients remain on study in response. For the subgroup of patients with CPRG confirmed PTCL and baseline platelets ≥100,000/μL (N=100) ORR was 28% (CR 11%; PR 17%). The most frequent (≥ 5%) grade 3-4 treatment emergent AEs were thrombocytopenia (13%), neutropenia (13%), anemia (10%), dyspnea (6%), pneumonia (6%), and fatigue (5%). Patients with platelets <100K tolerated belinostat, with 98% dose intensity. Belinostat was well tolerated with a low incidence of myelosuppression. Discontinuations were due to PD (64%), death (11%), AEs (7%), patient request (8%), and other (4%). Conclusions: Belinostat demonstrated a 26%-28% ORR in BELIEF and was well tolerated with a favorable safety profile in patients with R/R PTCL including those with low platelets. The low incidence of myelosuppression observed warrants further investigation of belinostat combination therapy to develop new treatment paradigms for R/R PTCL. Clinical trial information: NCT00865969.

Safety and efficacy of pralatrexate in the treatment of patients with relapsed or refractory peripheral T-cell lymphoma

T-cell lymphomas (TCL) are a diverse and heterogeneous group of malignancies that represent less than 15% of all non-Hodgkin lymphomas. Initial refinements of the clinical classification of these complex diseases have been made, but a better understanding of their molecular pathogenesis is still needed. Even if the paucity of insights into the underlying pathogenesis of TCLs has hindered our ability to develop rational targeted therapies, significant advances have been made. Pralatrexate (10-propargyl 10-deazaaminopterin) is a unique antifolate that has been rationally designed to have high affinity for the reduced folate receptor (RFC) and the folylpolyglutamate synthetase (FPGS) and was the first drug ever approved for the treatment of relapsed and refractory peripheral T-cell lymphomas (PTCL). This review describes the preclinical development of pralatrexate that led to early-phase clinical trials in lung cancer and lymphoma and its subsequent approval in PTCL. The review also describes how pralatrexate has been combined with other agents in both the preclinical and clinical settings. FDA approval for the use of pralatrexate in PTCL has been granted based on the results of the pivotal Phase II trial of this agent in relapsed and refractory PTCL patients. clinical development, pralatrexate, preclinical data, T-cell lymphoma.

Phase I clinical, pharmacokinetic, and pharmacodynamic study of KOS-862 (Epothilone D) in patients with advanced solid tumors and lymphoma

PURPOSE

To determine the maximum tolerated dose and safety of the epothilone, KOS-862, in patients with advanced solid tumors or lymphoma.

PATIENTS AND METHODS

Patients were treated weekly for 3 out of 4 weeks (Schedule A) or 2 out of 3 weeks (Schedule B) with KOS-862 (16-120 mg/m(2)). Pharmacokinetic (PK) sampling was performed during cycles 1 and 2; pharmacodynamic (PD) assessment for microtubule bundle formation (MTBF) was performed after the 1st dose, only at or above 100 mg/m(2).

RESULTS

Thirty-two patients were enrolled, and twenty-nine completed ≥1 cycle of therapy. Dose limiting toxicity [DLT] was observed at 120 mg/m(2). PK data were linear from 16 to 100 mg/m(2), with proportional increases in mean C(max) and AUC(tot) as a function of dose. Full PK analysis (mean ± SD) at 100 mg/m(2) revealed the following: half-life (t (½)) = 9.1 ± 2.2 h; volume of distribution (V(z)) = 119 ± 41 L/m(2); clearance (CL) = 9.3 ± 3.2 L/h/m(2). MTBF (n = 9) was seen in 40% of PBMCs within 1 h and in 15% of PBMC at 24-hours post infusion at 100 mg/m(2). Tumor shrinkage (n = 2, lymphoma), stable disease >3 months (n = 5, renal, prostate, oropharynx, cholangiocarcinoma, and Hodgkin lymphoma), and tumor marker reductions (n = 1, colorectal cancer/CEA) were observed.

CONCLUSION

KOS-862 was well tolerated with manageable toxicity, favorable PK profile, and the suggestion of clinical activity. The maximum tolerated dose was determined to be 100 mg/m(2) weekly 3-on/1-off. MTBF can be demonstrated in PBMCs of patients exposed to KOS-862.

Brentuximab vedotin

Brentuximab vedotin (SGN-35), an intravenously administered CD30-specific antibody-drug conjugate, has recently been approved by the U.S. Food and Drug Administration for two indications, including (i) patients with Hodgkin lymphoma relapsing after autologous stem-cell transplantation (ASCT), or after two multidrug regimens in patients with Hodgkin lymphoma who are not candidates for ASCT; and (ii) patients with systemic anaplastic large cell lymphoma (ALCL) who failed at least one prior multidrug chemotherapy regimen. Patients with Hodgkin lymphoma and ALCL treated with brentuximab vedotin showed markedly high response rates for a single agent, exceeding 70% and 80% for Hodgkin lymphoma and ALCL, respectively. The complete response rate was equally as impressive, at 34% and 57% for Hodgkin lymphoma and ALCL, respectively. Results like these and from many other upcoming clinical trials, in which brentuximab vedotin is being investigated in the frontline setting, promise to profoundly change how we manage the CD30-positive lymphoproliferative malignancies. The mechanism of action, preclinical antitumor activity, and clinical activity of brentuximab vedotin against Hodgkin lymphoma, ALCL, and other CD30-expressing lymphomas are reviewed.

A phase I single-agent study of twice-weekly consecutive-day dosing of the proteasome inhibitor carfilzomib in patients with relapsed or refractory multiple myeloma or lymphoma

PURPOSE

Carfilzomib is a next-generation, selective, proteasome inhibitor with clinical activity in relapsed and/or refractory multiple myeloma. The objectives of this phase I study were to establish the safety, tolerability, pharmacokinetic, and pharmacodynamic profiles of escalating doses of carfilzomib in patients with relapsed or refractory hematologic malignancies.

EXPERIMENTAL DESIGN

Carfilzomib (doses ranging from 1.2-27 mg/m(2)) was administered i.v. on 2 consecutive days for 3 weeks of a 4-week cycle. Single-agent dose escalation (n = 37) was followed by a dose-expansion phase (n = 11) that comprised 2 cohorts (carfilzomib or carfilzomib + dexamethasone). During dose expansion, carfilzomib was administered starting with 20 mg/m(2) during the first week (days 1, 2) and then escalated to 27 mg/m(2) thereafter.

RESULTS

A maximum tolerated dose (MTD) was not reached during dose escalation. Dosing in the expansion cohort was well tolerated. Adverse events were manageable and primarily of grade I or II. The main hematologic adverse events of ≥ grade III were anemia and thrombocytopenia. Notably, there were no observations of grade III or more peripheral neuropathy. Carfilzomib was cleared rapidly with an elimination half-life of less than 30 minutes but still induced dose-dependent inhibition of the 20S chymotrypsin-like proteasome activity. At doses of 15 to 27 mg/m(2), there was evidence of activity among patients with multiple myeloma and with non-Hodgkin lymphoma.

CONCLUSIONS

Escalated dosing of carfilzomib on a schedule of 2 consecutive days for 3 weeks of a 4-week cycle was tolerable and showed promising activity. This dose regimen has been selected for ongoing and future clinical studies, including PX-171-003A1 and the pivotal trial ASPIRE.

Murine models in mantle cell lymphoma

Mantle cell lymphoma (MCL), an aggressive, heterogeneous B-cell lymphoma associated with a relatively short survival has been challenging to study in the laboratory due to the lack of in vitro and in vivo models that accurately recapitulate the disease. Advancement has been made in the characterization of MCL cell lines through the generation of the ATCC MCL bank, enabling their use in xenograft murine models. These models provide valuable but limited information for the preclinical evaluation and development of targeted therapies for MCL despite their deficiencies of a functioning immune system and correct micro-environment. Currently, there is only one double transgenic murine model known to develop spontaneous MCL. There is an urgency to develop innovative transgenic murine models that could be used to better predict therapeutic responses and precisely decipher mechanisms of action, to foster refinement of novel therapeutics for mantle cell lymphoma.

Abstract 4705: Dual targeting of epigenetic pathways and NF-kappaB in diffuse large B-cell lymphoma

INTRODUCTION: Current immunochemotherapy can cure approximately two-thirds of patients with diffuse large B cell lymphoma (DLBCL), the most common type of non-Hodgkin's lymphoma. Drugs that selectively target specific mechanisms of pathogenesis to which the disease is known to be addicted, offer a unique opportunity to intervene in the natural history of the disease, and may hold the key to future breakthroughs in treating DLBCL. While several unique pathogenetic events have been recently identified in driving lymphomagenesis, two potentially interrelated events contributing to the underlying molecular pathogenesis of DLBCL have come to light. The first involves constitutive activation of NF-kappaB, as noted by Rosenwald and colleagues in their identification of the activated B-cell (ABC) subtype of DLBCL, while the second involves dysregulation of the protein acetylation-deacetylation balance due to either inactivating mutations of histone acetyltransferases (HATs) like p300 and CBP, or overexpression of histone deacetylases (HDACs). HATs and HDACs operate epigenetic pathways to modulate gene expression and to control the activity of important oncoproteins such as Bcl6 through posttranslational modification. While Bcl6 and NF-kappaB are known to be closely associated with the pathogenesis of GCB (germinal center B-cell) and ABC subtypes of DLBCL respectively, it has become clear that many ABC lymphomas can have dysregulation of Bcl6, and many cases of GCB DLBCL can have dysregulation of NF-kappaB. Therefore, strategies oriented toward modulation of these biological traits could offer a unique opportunity to treat DLBCL at its molecular roots, potentially sensitizing them to traditional chemotherapy approaches. RESULTS: We have conducted pharmacological and molecular studies of a novel IKKbeta inhibitor, LY2409881, in DLBCL cell lines. We found that LY2409881 specifically inhibited the activation of NF-kappaB and increased apoptosis, and inhibited both ABC and GCB cells that are addicted to NF-kappaB, with moderate potentcy. Furthermore, LY2409881 demonstrated marked anti-lymphoma synergism with HDAC inhibitors; the synergism varied significantly in a cell line and HDAC inhibitor-dependent manner. The discrete patterns of synergism among different HDAC inhibitors with LY2409881 were not solely attributable to acetylation of p65/RelA mediated by HDAC inhibitors, as these inhibitors all stimulated binding of p65/RelA to its target DNA. We will determine the mechanism of the drug: drug synergism by investigating whether knocking down HDAC molecules in lymphoma cells make them hypersensitive to IKK inhibitors. We are using xenograft lymphoma models in mice to confirm the in vivo activity of LY2409881, as a single agent and in combination with HDAC inhibitors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4705. doi:1538-7445.AM2012-4705

Abstract A12: Validation of a novel bioluminescent mouse model of Sezary syndrome for preclinical drug screening

Background: Sezary syndrome (SS) is an aggressive leukemic form of cutaneous T cell lymphoma (CTCL). Until now no true animal model for SS exists which could be used for the screening of novel compounds against the disease. We successfully developed a bioluminescent xenograft mouse model for SS to noninvasively monitor tumor cell engraftment and progression and to measure the effects of treatments on tumor burden.

Methods: A fusion protein was constructed consisting of the monomeric mutant red fluorescent mCherry, and the synthetic-firefly Luciferase by cloning the mCherry gene into the plasmid vector pGL4.13 [luc2/SV40] (Promega) carrying the luciferase gene, thus obtaining the pGLCherryLuciferase plasmid, where the Cherry and the luciferase genes formed one open reading frame. H9 cell line derived from a SS patient was transfected with this plasmid using the transfection reagent, Effectene. Transfected H9 cells were injected subcutaneously into the 5–7 week old female SCID-Beige and NOG (NOD/Shi-scid/IL-2R null) mice. After confirmation of a bioluminescent signal, NOG mice were assigned to the vehicle control group or treatment groups, which received romidepsin (1.2 or 2.3mg/kg on day1, 4, 8 and 11, ip) or pralatrexate (30mg/kg on day1, 4, 8 and 11, ip). In vivo bioluminescence imaging over 3 weeks was performed using an IVIS imaging system (Caliper Life Sciences).

Results: SCID-Beige mice did not permit any engraftment of the H9 injected cells whereas all the NOG mice exhibited tumor growth and progression. This suggests that the NOG mice are superior animal recipients for xenotransplantation of Sezary cells, potentially making them a preclinical tool to understand tumorigenesis and drugs effects in this malignancy. Sequential quantitative signals from bioluminescent imaging over the 3-week period were significantly lower in the mice treated with pralatexate compared with the control group. The mice treated with 1.2mg/kg of romidepsin had no effect on tumor suppression whereas the mice that received the higher dose of romidepsin demonstrated decrease of tumor growth suggesting dose-dependent tumor inhibition. Mice treated with pralatrexate demonstrated diminished bioluminescent signal as early as after the first dose compared to the mice treated with higher dose of romidepsin which produced a slower time to onset of activity. No mice treated with pralatrexate or with the higher dose of romidepsin exhibited toxicity.

Conclusion: This novel bioluminescent xenograft mouse model of SS enables non-invasive, sensitive, quantitative evaluation of disease progression in living animals and evaluation of pharmacologic factors in real time. We are able to detect and monitor lymphoma cell growth before the presentation of clinical manifestations. Further this model recapitulates our understanding of behavior of drugs used in the treatment of lymphomas such as pralatrexate which has a rapid onset of action compared to romidepsin that has a delayed time to onset of activity. This represents the first bioluminescent animal model of human CTCL that is intended to be used to investigate novel treatment platforms in preclinical studies. This preclinical model also compliments the ongoing phase 2 trial of pralatrexate in relapsed or refractory CTCL. Further in vivo studies to evaluate synergy of promising new agents in this novel mouse model of SS have begun and will be reported.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A12.

Histone deacetylase inhibitors demonstrate significant preclinical activity as single agents, and in combination with bortezomib in Waldenström's macroglobulinemia

We studied the role of histone deacetylase inhibitors in Waldenstrom's macroglobulinemia (WM). Gene expression profiling of bone marrow CD19+ cells from 30 patients and 10 healthy donors showed overexpression of HDAC4, HDAC9, and Sirt5, with validation of HDAC9 overexpression by q-PCR in primary and BCWM.1 cells. Suberoylanilide hydroxamic acid, trichostatin A, panobinostat, and sirtinol demonstrated dose-dependent killing of BCWM.1 cells. TSA showed the greatest potency with IC50 of 70 nM. Importantly, HDAC9 activity was decreased following TSA treatment suggesting an essential role for this HDAC in WM therapy. The combination of bortezomib plus HDAC inhibitors resulted in at least additive tumor cell killing in BCWM.1 cells. TSA and bortezomib-induced apoptosis depended on a similar set of caspase activation, whereas their effect on cell cycle regulators was distinctly different. These results provided a framework for examining HDAC inhibitors as monotherapy, as well as combination therapy with bortezomib in WM.