The combination of the proteasome inhibitor bortezomib and the bcl-2 antisense molecule oblimersen sensitizes human B-cell lymphomas to cyclophosphamide

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.

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.

A computationally designed inhibitor of an Epstein-Barr viral Bcl-2 protein induces apoptosis in infected cells

Because apoptosis of infected cells can limit virus production and spread, some viruses have co-opted prosurvival genes from the host. This includes the Epstein-Barr virus (EBV) gene BHRF1, a homolog of human Bcl-2 proteins that block apoptosis and are associated with cancer. Computational design and experimental optimization were used to generate a novel protein called BINDI that binds BHRF1 with picomolar affinity. BINDI recognizes the hydrophobic cleft of BHRF1 in a manner similar to other Bcl-2 protein interactions but makes many additional contacts to achieve exceptional affinity and specificity. BINDI induces apoptosis in EBV-infected cancer lines, and when delivered with an antibody-targeted intracellular delivery carrier, BINDI suppressed tumor growth and extended survival in a xenograft disease model of EBV-positive human lymphoma. High-specificity-designed proteins that selectively kill target cells may provide an advantage over the toxic compounds used in current generation antibody-drug conjugates.

The investigational agent MLN2238 induces apoptosis and is cytotoxic to CLL cells in vitro, as a single agent and in combination with other drugs

Chronic lymphocytic leukaemia (CLL) is the most common haematological malignancy in the U.S. The course of the disease has been shown to be negatively impacted by increased levels of BCL2. Strategies to downregulate BCL2 and shift the balance towards cellular demise are actively being explored. Therefore, we examined whether the investigational agent MLN2238 could inhibit the proteasomal machinery and induce CLL cell death while also downregulating BCL2. MLN2238-induced cell death was studied in peripheral blood mononuclear cells from 28 CLL patients. MLN2238 produced a dose-dependent reduction in BCL2 and CLL cell viability with maximum cell death observed at a 50 nmol/l concentration by 48 h. Annexin-V staining, PARP1 and caspase-3 cleavage along with an increase in mitochondrial membrane permeability were noted after cells were treated with MLN2238; however, apoptosis was only partially blocked by the pan-caspase inhibitor z-VAD.fmk. Furthermore, we observed enhanced anti-CLL effects in tumour cells treated with either a combination of MLN2238 and the BH3 mimetic AT-101 or MLN2238 and fludarabine. Together, our data suggest the potential for proteasome inhibitor based therapy in CLL and the rationale design of drug combination strategies based on CLL biology.

Successful use of sorafenib after bortezomib failure in metastatic follicular thyroid cancer - a case report

BACKGROUND

Thyroid cancer (TC) is the most commonly diagnosed endocrine malignancy in developed countries. Differentiated thyroid carcinoma (DTC), which includes papillary thyroid carcinoma and follicular thyroid carcinoma (FTC), composes more than 90% of all TC cases. When DTC recurs or metastasizes to distant sites despite the use of local and radiotherapeutic treatment modalities, the currently effective treatment options are limited.

CASE REPORT

A then 40-year-old female Caucasian patient was diagnosed with FTC and underwent surgery and postoperative radioactive iodine therapy. The patient developed metastatic disease, and palliative first-line treatment with the proteasome inhibitor bortezomib was initiated. After 3 months, the patient suffered progressive pulmonary metastatic disease. Treatment with the multikinase inhibitor sorafenib was started, and after 3 months of therapy, tumor restaging demonstrated partial remission. The treatment is ongoing, and the current progression-free survival is 16 months. With the exception of mild diarrhea and hand-foot syndrome, the therapy was well tolerated, and no grade 3/4 adverse toxicities occurred.

CONCLUSION

In our single case of metastatic FTC, sorafenib showed clinically meaningful antitumor activity accompanied by good tolerability. This case report supports the use of this drug as a potential treatment option for advanced/metastatic FTC.

Proteasome inhibition and combination therapy for non-Hodgkin's lymphoma: from bench to bedside

Although patients with B-cell non-Hodgkin's lymphoma (NHL) usually respond to initial conventional chemotherapy, they often relapse and mortality has continued to increase over the last three decades in spite of salvage therapy or high dose therapy and stem cell transplantation. Outcomes vary by subtype, but there continues to be a need for novel options that can help overcome chemotherapy resistance, offer new options as consolidation or maintenance therapy postinduction, and offer potentially less toxic combinations, especially in the elderly population. The bulk of these emerging novel agents for cancer treatment target important biological cellular processes. Bortezomib is the first in the class of proteasome inhibitors (PIs), which target the critical process of intracellular protein degradation or recycling and editing through the proteasome. Bortezomib is approved for the treatment of relapsed or refractory mantle cell lymphoma. The mechanisms of proteasome inhibition are very complex by nature (because they affect many pathways) and not fully understood. However, mechanisms of action shared by bortezomib and investigational PIs such as carfilzomib, marizomib, ONX-0912, and MLN9708 are distinct from those of other NHL treatments, making them attractive options for combination therapy. Preclinical evidence suggests that the PIs have additive and/or synergistic activity with a large number of agents both in vitro and in vivo, from cytotoxics to new biologicals, supporting a growing number of combination studies currently underway in NHL patients, as reviewed in this article. The results of these studies will help our understanding about how to best integrate proteasome inhibition in the management of NHL and continue to improve patient outcomes.

Marizomib, a proteasome inhibitor for all seasons: preclinical profile and a framework for clinical trials

The proteasome has emerged as an important clinically relevant target for the treatment of hematologic malignancies. Since the Food and Drug Administration approved the first-in-class proteasome inhibitor bortezomib (Velcade) for the treatment of relapsed/refractory multiple myeloma (MM) and mantle cell lymphoma, it has become clear that new inhibitors are needed that have a better therapeutic ratio, can overcome inherent and acquired bortezomib resistance and exhibit broader anti-cancer activities. Marizomib (NPI-0052; salinosporamide A) is a structurally and pharmacologically unique β-lactone-γ-lactam proteasome inhibitor that may fulfill these unmet needs. The potent and sustained inhibition of all three proteolytic activities of the proteasome by marizomib has inspired extensive preclinical evaluation in a variety of hematologic and solid tumor models, where it is efficacious as a single agent and in combination with biologics, chemotherapeutics and targeted therapeutic agents. Specifically, marizomib has been evaluated in models for multiple myeloma, mantle cell lymphoma, Waldenstrom's macroglobulinemia, chronic and acute lymphocytic leukemia, as well as glioma, colorectal and pancreatic cancer models, and has exhibited synergistic activities in tumor models in combination with bortezomib, the immunomodulatory agent lenalidomide (Revlimid), and various histone deacetylase inhibitors. These and other studies provided the framework for ongoing clinical trials in patients with MM, lymphomas, leukemias and solid tumors, including those who have failed bortezomib treatment, as well as in patients with diagnoses where other proteasome inhibitors have not demonstrated significant efficacy. This review captures the remarkable translational studies and contributions from many collaborators that have advanced marizomib from seabed to bench to bedside.

The novel antisense Bcl-2 inhibitor SPC2996 causes rapid leukemic cell clearance and immune activation in chronic lymphocytic leukemia

SPC2996 is a novel locked nucleic acid phosphorothioate antisense molecule targeting the mRNA of the Bcl-2 oncoprotein. We investigated the mechanism of action of SPC2996 and the basis for its clinically observed immunostimulatory effects in chronic lymphocytic leukemia (CLL). Patients with relapsed CLL were treated with a maximum of six doses of SPC2996 (0.2-6 mg/kg) in a multicenter phase I trial. Microarray-based transcriptional profiling of circulating CLL cells was carried out before and after the first infusion of SPC2996 in 18 patients. Statistically significant transcriptomic changes were observed at doses 4 mg/kg and occurred as early as 24 h after the first infusion of the oligonucleotide. SPC2996 induced the upregulation of 466 genes including a large number of immune response and apoptotic regulator molecules, which were enriched for Toll-like receptor response genes. Serum measurements confirmed the release of pro-inflammatory cytokines including chemokine (C-C motif) ligand 3 (macrophage inflammatory protein 1α) and tumor necrosis factor-α, thereby validating the in vivo transcriptomic data at the protein level. SPC2996 caused a 50% reduction of circulating lymphocytes in five of 18 (28%) patients, which was found to be independent of its immunostimulatory and anti-Bcl-2 effects.

Novel disease targets and management approaches for diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) responds well to treatment with CHOP and the R-CHOP regimen, but a subset of patients still fail to achieve complete or durable responses. Recent advances in gene expression profiling have led to the identification of three different subtypes of DLBCL, and confirmed that patients with the activated B-cell (ABC) disease subtype are less likely to respond well to CHOP-based regimens than those with germinal centre B-cell-type (GCB) disease. This discovery could herald the use of gene expression profiling to aid treatment decisions in DLBCL, and help identify the most effective management strategies for patients. Treatment options for patients with relapsed or refractory DLBCL are limited and several novel agents are being developed to address this unmet clinical need. Novel agents developed to treat plasma cell disorders such as multiple myeloma have shown promising activity in patients with NHL. Indeed, the immunomodulatory agent lenalidomide and the proteasome inhibitors bortezomib and carfilzomib, as single agents or in combination with chemotherapy, have already demonstrated promising activity in patients with the ABC subtype of DLBCL. One should not be complacent however when applying these agents to new disease types, because dose and drug scheduling can have marked effects on the responses achieved with investigational agents. As more targeted agents are developed, the timing of administration with other agents in clinical trials will become increasingly important to ensure maximal efficacy while minimizing side effects.

Therapeutic potential of antisense oligodeoxynucleotides in downregulating p53 oncogenic mutations in cancers

PURPOSE OF WORK

mutation of the p53 gene is the most common genetic alteration in human cancers. Our study proposes to rationally design a p53 antisense oligonucleotide (ASO) repository, which contains a series of ASOs containing single nucleotide differences to discriminate between each mutant and wild type (WT) p53. The Sfold software was used to predict target-accessibility and we designed an initial series of antisense oligonucleotides (ASO) that target the p53 mutants A161T, R175H and R249S. Western-blot analysis indicated that ASOs strongly inhibited the expression of p53 mutants in a panel of human tumor cell lines (SNU-449, SK-BR-3 and PLC/PRF/5) while having little effect on the expression of WT p53 (HepG2 cells). In three cancer lines harboring each of the p53 mutations, mutant-specific ASO treatment led to a dose-dependent inhibition of cell growth, cell viability, colony formation and invasion, and expression of mutant p53-dependent survival proteins. Our preliminary results indicate that a single nucleotide difference in ASOs can discriminate between mutant and WT p53. These observations support the hypothesis that a p53 ASO repository can be a potentially valuable tool to knock down oncogenic mutant p53 and warrant the testing of a p53 ASO repository in in vivo settings.

Clinical activity of bortezomib in relapsed/refractory MALT lymphomas: results of a phase II study of the International Extranodal Lymphoma Study Group (IELSG)

BACKGROUND

The nuclear factor-kappa B activation in mucosa-associated lymphoid tissue (MALT) lymphoma pathogenesis provided the rationale for the evaluation of bortezomib in this malignancy.

PATIENTS AND METHODS

Thirty-two patients with relapsed/refractory MALT lymphoma were enrolled. Thirty-one patients received bortezomib 1.3 mg/m(2) i.v., on days 1, 4, 8, and 11, for up to six 21-day cycles.

RESULTS

Median age was 63 years (range, 37-82 years). Median number of prior therapies was 2 (range, 1-4). Nine patients had Ann Arbor stage I, 7 patients had stage II, and 16 patients had stage IV. Primary lymphoma localization was the stomach in 14 patients; multiple extranodal sites were present in 10 patients. Among the 29 patients assessable for response, the overall response rate was 48% [95% confidence interval (CI) 29% to 67%], with 9 complete and 5 partial responses. Nine patients experienced stable disease and six had disease progression during therapy. The most relevant adverse events were fatigue, thrombocytopenia, neutropenia, and peripheral neuropathy. After a median follow-up of 24 months, the median duration of response was not reached yet. Five deaths were reported, in two patients due to disease progression.

CONCLUSION

Bortezomib is active in relapsed MALT lymphomas. Further investigations to identify optimal bortezomib dose, schedule, and combination regimens are needed since the frequent detection of dose-limiting peripheral neuropathy.

Pralatrexate is synergistic with the proteasome inhibitor bortezomib in in vitro and in vivo models of T-cell lymphoid malignancies

PURPOSE

Pralatrexate (10-propargyl-10-deazaaminopterin) is an antifolate with improved cellular uptake and retention due to greater affinity for the reduced folate carrier (RFC-1) and folyl-polyglutamyl synthase. Based on the PROPEL data, pralatrexate was the first drug approved for patients with relapsed and refractory peripheral T-cell lymphoma. Bortezomib is a proteasome inhibitor that has shown some activity in patients with T-cell lymphoma.

EXPERIMENTAL DESIGN

Assays for cytotoxicity including mathematical analysis for synergism, flow cytometry, immunoblotting, and a xenograft severe combined immunodeficient-beige mouse model were used to explore the in vitro and in vivo activities of pralatrexate alone and in combination with bortezomib in T-cell lymphoid malignancies.

RESULTS

In vitro, pralatrexate and bortezomib exhibited concentration- and time-dependent cytotoxicity against a broad panel of T-lymphoma cell lines. Pralatrexate showed synergism when combined with bortezomib in all cell lines studied. Pralatrexate also induced potent apoptosis and caspase activation when combined with bortezomib across the panel. Cytotoxicity studies on normal peripheral blood mononuclear cells showed that the combination was not more toxic than the single agents. Western blot assays for proteins involved in broad growth and survival pathways showed that p27, NOXA, HH3, and RFC-1 were all significantly modulated by the combination. In a severe combined immunodeficient-beige mouse model of transformed cutaneous T-cell lymphoma, the addition of pralatrexate to bortezomib enhanced efficacy compared with either drug alone.

CONCLUSION

Collectively, these data suggest that pralatrexate in combination with bortezomib represents a novel and potentially important platform for the treatment of T-cell malignancies.

Romidepsin and belinostat synergize the antineoplastic effect of bortezomib in mantle cell lymphoma

PURPOSE

Romidepsin and belinostat are inhibitors of histone deacetylases (HDACI). HDACIs are known to induce cell death in malignant cells through multiple mechanisms, including upregulation of death receptors and induction of cell cycle arrest. They are also known to be prodifferentiating. Mantle cell lymphoma (MCL) is an aggressive subtype of non-Hodgkin lymphoma characterized by the t(11;14)(q13;q32) translocation leading to the overexpression of cyclin D1.

EXPERIMENTAL DESIGN

Assays for cytotoxicty including mathematical analysis for synergism, flow-cytometry, immunoblottings, and a xenograft severe combined immunodeficient beige mouse model were used to explore the in vitro and in vivo activity of romidepsin and/or belinostat alone or in combination with the proteasome inhibitor bortezomib in MCL.

RESULTS

In vitro, romidepsin and belinostat exhibited concentration-dependent cytotoxicity against a panel of MCL cell lines. Both HDACI showed strong synergism when combined with the proteasome inhibitor bortezomib in MCL. An HDACI plus bortezomib also induced potent mitochondrial membrane depolarization and apoptosis, whereas no significant apoptosis was observed in peripheral blood mononuclear cells from healthy donors with the combination. These events were associated with a decrease in cyclin D1 and Bcl-X(L), and an increase in accumulation of acetylated histone H3, acetylated alpha-tubulin, and Noxa in cell lines. In a severe combined immunodeficient beige mouse model of MCL, the addition of belinostat to bortezomib enhanced efficacy compared with either drug alone.

CONCLUSIONS

Collectively, these data strongly suggest that HDACI such as romidepsin or belinostat in combination with a proteasome inhibitor could represent a novel and rationale platform for the treatment of MCL.

Time to treatment response in patients with follicular lymphoma treated with bortezomib is longer compared with other histologic subtypes

PURPOSE

To determine the antitumor activity of the novel proteasome inhibitor bortezomib in patients with indolent non-Hodgkin's lymphoma.

EXPERIMENTAL DESIGN

Patients with follicular lymphoma (FL), marginal zone lymphoma, mantle cell lymphoma, small lymphocytic lymphoma/chronic lymphocytic leukemia, and Waldenstrom's macroglobulinemia were eligible for study. Bortezomib was given at a dose of 1.5 mg/m(2) as an i.v. push on days 1, 4, 8, and 11 of a 21-day cycle. Eligibility included the following: (a) no more than three prior therapies, (b) at least 1 month since prior chemotherapy, (c) measurable disease, and (d) an absolute neutrophil count of >1,000/microL and a platelet count >50,000/microL for the first dose of any cycle.

RESULTS

Seventy-seven patients were registered, of which 69 were assessable for response based on the completion of two cycles of therapy. Subtypes included FL (59.5%), mantle cell lymphoma (52%), small lymphocytic lymphoma/chronic lymphocytic leukemia (16.2%), marginal zone lymphoma (21.6%), and one Waldenstrom's macroglobulinemia. The median number of prior therapies was three. The most common grade 3 toxicity was lymphopenia (35%) and thrombocytopenia (31%). Twenty-five patients experienced grade <or=2 sensory neuropathy (32), and 8% experienced grade 3 neurosensory toxicity. The overall response rate was 45% (40% on an intention to treat) including 10 complete remissions. Of 18 patients with FL, 9 responded with 4 complete response. The median time to treatment response for FL was 12 weeks, whereas the median time to treatment response for other subtypes of non-Hodgkin's lymphoma was only 4 weeks.

CONCLUSIONS

These data suggest that bortezomib has significant single agent activity in patients with FL, and that longer durations of treatment may improve overall response.

Phase I trial of fludarabine, bortezomib and rituximab for relapsed and refractory indolent and mantle cell non-Hodgkin lymphoma

Based on the hypothesis that bortezomib may potentiate fludarabine activity by inhibiting DNA repair, we designed a phase I trial using this combination with rituximab in patients with relapsed and refractory indolent and mantle cell non-Hodgkin lymphoma. Twenty-four patients were enrolled. Non-Hodgkin lymphoma subtypes included 12 patients with follicular lymphoma, four with marginal zone lymphoma, three with lymphoplasmacytic lymphoma, three with mantle cell lymphoma and two with small lymphocytic/chronic lymphocytic leukaemia. Fludarabine and bortezomib were escalated in cohorts of three patients. Rituximab was added to the maximum tolerated dose of fludarabine and bortezomib and added significant dose-limiting myelosuppression. The maximum tolerated dose was fludarabine 25 mg/m(2) on days 1-3, bortezomib 1.3 mg/m(2) on days 1, 4, 8, 11, with rituximab 375 mg/m(2) on day 1 administered every 21 d. Clinical responses were observed in 11 patients, five of whom were refractory to their most recent treatment regimen. Six additional patients had stable disease for a median of 10 months (range 4-30+). Cumulative myelosuppression and neuropathy was observed. The combination of fludarabine, bortezomib, and rituximab appears to be an active regimen with manageable toxicity for relapsed NHL.

Phase III randomised study of dexamethasone with or without oblimersen sodium for patients with advanced multiple myeloma

Upregulation of the Bcl-2 antiapoptotic protein is reported to be associated with aggressive clinical course in multiple myeloma. Oblimersen sodium is a bcl-2 antisense oligonucleotide complementary to the first six codons of the open-reading frame of bcl-2 mRNA that can decrease transcription of Bcl-2 protein and increase myeloma cell susceptibility to cytotoxic agents. In this phase III randomised trial, we investigated in patients with relapsed/refractory myeloma whether addition of oblimersen to dexamethasone improved clinical outcomes vs. dexamethasone alone. Two hundred and twenty-four patients were randomised to receive either oblimersen/dexamethasone (N = 110) or dexamethasone alone (N = 114). The primary endpoint was time to tumor progression (TTP). Final results of this study demonstrated no significant differences between the two groups in TTP or objective response rate. The oblimersen/dexamethasone regimen was generally well tolerated with fatigue, fever and nausea, the most common adverse events reported.

The anti-histaminic cyproheptadine synergizes the antineoplastic activity of bortezomib in mantle cell lymphoma through its effects as a histone deacetylase inhibitor

Cyproheptadine, an inhibitor of the H1 histamine receptors, has recently shown activity in models of leukaemia and myeloma, presumably through inhibition of cyclin-D expression. Mantle cell lymphoma (MCL) is an aggressive subtype of non-Hodgkin lymphoma characterized by overexpression of cyclin-D1. We investigated the effect of cyproheptadine alone and in combination with the proteasome inhibitor bortezomib in models of MCL. The combination of these drugs was mathematically synergistic, producing significant reductions in the mitochondrial membrane potential leading to apoptosis. In a severe combined immunodeficient beige mouse model, cyproheptadine plus bortezomib demonstrated a statistically significant advantage compared to either agent alone.

The BH3-only mimetic ABT-737 synergizes the antineoplastic activity of proteasome inhibitors in lymphoid malignancies

Overexpression of antiapoptotic members of the Bcl-2 family is observed in approximately 80% of B-cell lymphomas, contributing to intrinsic and acquired drug resistance. Nullifying the antiapoptotic influence of these proteins can potentially overcome this resistance, and may complement conventional chemotherapy. ABT-737 is a BH3-only mimetic and potent inhibitor of the antiapoptotic Bcl-2 family members Bcl-2, Bcl-X(L), and Bcl-w. In vitro, ABT-737 exhibited concentration-dependent cytotoxicity against a broad panel of lymphoma cell lines including mantle cell lymphoma (MCL) and diffuse large B-cell lymphoma (DLBCL). ABT-737 showed synergism when combined with the proteasome inhibitors bortezomib or carfilzomib in select lymphoma cell lines and induced potent mitochondrial membrane depolarization and apoptosis when combined with either. ABT-737 plus bortezomib also induced significant apoptosis in primary samples of MCL, DLBCL, and chronic lymphocytic leukemia (CLL) but no significant cytotoxic effect was observed in peripheral blood mononuclear cells from healthy donors. In severe combined immunodeficient beige mouse models of MCL, the addition of ABT-737 to bortezomib enhanced efficacy compared with either drug alone and with the control. Collectively, these data suggest that ABT-737 alone or in combination with a proteasome inhibitor represents a novel and potentially important platform for the treatment of B-cell malignancies.

Targeting Bcl-2 family members with the BH3 mimetic AT-101 markedly enhances the therapeutic effects of chemotherapeutic agents in in vitro and in vivo models of B-cell lymphoma

Overexpression of antiapoptotic members of the Bcl-2 family are observed in approximately 80% of B-cell lymphomas, contributing to intrinsic and acquired drug resistance. Nullifying antiapoptotic function can potentially overcome this in-trinsic and acquired drug resistance. AT-101 is a BH3 mimetic known to be a potent inhibitor of antiapoptotic Bcl-2 family members including Bcl-2, Bcl-X(L), and Mcl-1. In vitro, AT-101 exhibits concentration- and time-dependent cytotoxicity against lymphoma and multiple myeloma cell lines, enhancing the activity of cytotoxic agents. The IC(50) for AT-101 is between 1 and 10 microM for a diverse panel of B-cell lymphomas. AT-101 was synergistic with carfilzomib (C), etoposide (E), doxorubicin (D), and 4-hydroxycyclophosphamide (4-HC) in mantle cell lymphoma (MCL) lines. In a transformed large B-cell lymphoma line (RL), AT-101 was synergistic when sequentially combined with 4-HC, but not when both drugs were added simultaneously. AT-101 also induced potent mitochondrial membrane depolarization (Delta Psi m) and apoptosis when combined with carfilzomib, but not with bortezomib in MCL. In severe combined immunodeficient (SCID) beige mouse models of drug-resistant B-cell lymphoma, 35 mg/kg per day of AT-101 was safe and efficacious. The addition of AT-101 to cyclophosphamide (Cy) and rituximab (R) in a schedule-dependent manner enhanced the efficacy of the conventional therapy.

Inhibition of CD44 expression in hepatocellular carcinoma cells enhances apoptosis, chemosensitivity, and reduces tumorigenesis and invasion

PURPOSE

CD44 is overexpressed in various tumors including hepatocellular carcinoma (HCC). The purpose of this study was to examine the effects of CD44 antisense oligonucleotide (ASO) alone or combination with doxorubicin on HCC cells in vitro.

METHODS

Cytotoxicity was measured by use of a cell viability assay in HCC cell line SNU-449. Tumorigenesis and invasion were accessed by colony formation, growth in soft agar and ECMatrix invasion assay. Apoptosis and necrosis were evaluated by using double staining with Hoechst 33342 and propidium iodide. Protein expression and mRNA level were detected by Western blot and RT-PCR.

RESULTS

We have designed novel CD44 ASO, which can effectively down-regulate CD44 expression in SNU-449. Colony formation, growth in soft agar and invasion were significantly impaired after CD44 ASO treatment in SNU-499. In company with CD44 down-regulated by CD44 ASO, MDR-1 and Bcl-2 expression were also greatly reduced. CD44 ASO also increased chemosensitivity to doxorubicin significantly, lowered IC(50 )by one order of magnitude. Apoptosis and necrosis were also induced by CD44 ASO alone or in combination treatment with doxorubicin.

CONCLUSIONS

Inhibition of CD44 expression by CD44 ASO significantly induced apoptosis, decreased tumorigenesis and invasion, and increased chemosensitivity. Thus, CD44 ASO is potentially a therapy that is worth investigating in the clinical setting.

Expanding therapeutic options in mantle cell lymphoma

Mantle cell lymphoma (MCL) still carries a poor prognosis. Chemoimmunotherapy (combination with rituximab) is the routine first-line therapy, although data strongly suggest a benefit from intensification through high-dose therapy with stem cell transplantation consolidation or dose-intense chemotherapy with HyperCVAD (fractionated cyclophosphamide/vincristine/doxorubicin/dexamethasone)/rituximab. Unfortunately, most patients still experience relapse, and a multitude of novel agents are currently being tested in this setting, including proteasome inhibitors with bortezomib (the first of its class and first Food and Drug Administration-approved drug in MCL), mammalian target of rapamycin inhibitors, Bcl-2 inhibitors, and antiangiogenesis agents, among others. Because of the relative rarity of the disease-MCL represents 6% of non-Hodgkin lymphoma-an obvious effort is needed to enroll patients on clinical trials. Not surprisingly, as in other non-Hodgkin lymphomas, MCL appears more and more as a heterogeneous disease, which might impact future clinical trial design through pharmacogenomics and hopefully help us develop smaller "molecular" relevant trials.

Therapeutic integration of c-myc and bcl-2 antisense molecules with docetaxel in a preclinical model of hormone-refractory prostate cancer

BACKGROUND

The response of hormone-refractory prostate cancer (HRPC) to chemotherapy remains modest, necessitating the search for new forms of treatment to improve the prognosis. Since an increased expression of oncogenes, including c-myc and bcl-2, accompanies the transition to HRPC, we evaluated whether the concomitant downregulation of these oncogenes by antisense strategy sensitized HRPC to chemotherapy.

METHODS

PC-3 prostate cancer cells were exposed in vitro to c-myc (INX-6295) and bcl-2 (G3139) antisense oligodeoxynucleotides (ODNs) and docetaxel given alone or in combination. Therapeutic efficacy of the different treatments was also evaluated in xenografts.

RESULTS

We show that the triple combination of drugs given in the sequence G3139/docetaxel/INX-6295 was the most active in reducing the survival of PC-3. Likewise, the combination triggered apoptosis in more than 80% of cells. A marked tumor weight inhibition was observed in PC-3 xenografts after G3139/docetaxel/INX-6295 treatment, with a complete tumor regression being noted in half the mice. A 111% overall increase in life survival and a complete cure in two out of eight mice was also reported. This treatment remained effective even when started at a very late stage of tumor growth producing about 80% tumor weight inhibition (TWI), with tumor regression being maintained for 1 month. Finally, the antitumor effect resulted in a significant increase (70%) in mice survival.

CONCLUSIONS

These data indicate that the combined targeting of genes involved in uncontrolled proliferation and evasion of apoptosis renders HRPC responsive to chemotherapy making this treatment a promising antineoplastic strategy.

Molecular-targeted therapies: lessons from years of clinical development

Over the past decade, molecular-targeted therapies have been added to cytotoxic and anti-endocrine drugs in the treatment of cancer, with the aim to target the molecular pathways that underlie the carcinogenic process and maintain the cancer phenotype. Success with some of these agents has suggested that identification and validation of the drug target is the starting point for the route of development of active, safe and effective drugs. Main molecular targets used to the development of anticancer drugs are cell surface receptors, signal transduction pathways, gene transcription targets, ubiquitin-proteasome/heat shock proteins and tumour microenvironment components (especially antiangiogenic agents). Here, we review the development of the main molecular targeted non-cytotoxic agents studied in cancer, highlighting lessons derived from the development of these novel drugs and proposing new horizons for the clinical development of molecular-targeted therapies.

The BH3-mimetic GX15-070 synergizes with bortezomib in mantle cell lymphoma by enhancing Noxa-mediated activation of Bak

Mantle cell lymphoma (MCL) is an aggressive B-cell lymphoma resistant to conventional chemotherapy. The Bcl-2 pathway is deregulated in these tumors and may represent an interesting target for new therapeutic strategies. The new small-molecule pan-Bcl-2 inhibitor GX15-070 mimics BH3-only proteins by binding to multiple antiapoptotic Bcl-2 members. Here we show that GX15-070 induced apoptosis in vitro in MCL cell lines and primary cells from patients with MCL by releasing Bak from Mcl-1 and Bcl-X(L) at short incubation times and low micromolar doses. GX15-070 was effective in cells bearing defective DNA damage-sensor genes or cell-cycle regulators, inducing Bax and Bak conformational changes, mitochondrial depolarization, phosphatidylserine exposure, and caspase-3 activation. Furthermore, GX15-070 synergized with bortezomib, sensitizing MCL cells to low doses of this proteasome inhibitor, by neutralizing bortezomib-induced Mcl-1 accumulation and cooperating with Noxa to induce Bak displacement from this protein. These events led to an increased activation of the mitochondrial apoptotic pathway. Importantly, GX15-070 alone or in combination with bortezomib showed no significant cytotoxic effect in peripheral blood mononuclear cells from healthy donors. All these findings suggest that GX15-070 alone or in combination with bortezomib represents a new attractive therapeutic approach for MCL treatment.

New Directions in the Treatment of Mantle Cell Lymphoma: An Overview

Mantle cell lymphoma (MCL) is one of the most challenging lymphomas to treat. In the first-line setting, high-dose therapy (HDT) and autologous stem cell transplantation or hyperCVAD/rituximab suggest benefit, especially in patients aged < 60 years. Nucleoside analogue-based regimens represent an alternate option in patients ineligible for HDT. Fludarabine in combination with cyclophosphamide or mitoxantrone has shown activity, and the results were superior with the addition of rituximab. Other cytotoxic agents, such as cladribine, clofarabine, or bendamustin, showed promising activity as well. A variety of new monoclonal antibody (MoAb) agents, such as humanized anti-CD20, alemtuzumab, anti-HLA-DR, anti-CD22 (as an immunotoxin carrier), anti-CD40, as well as MoAb-targeting TRAIL-R1 and TRAIL-R2 are being tested. Radioimmunotherapy with Yttrium 90-ibritumomab tiuxetan and Iodine 131 tositumomab have been tested alone or in combination with chemotherapy, including as part of HDT and autologous stem cell transplantation, in which they showed the best results. New vaccine modalities are exploring the use of tumor cell-based vaccines or of agents that block or activate costimulatory pathways/molecules, such as CTLA-4-Ig. Allogenic transplantation represents a potential curative option for MCL, especially nonmyeloablative transplantation, more feasible in that population. A plethora of novel biologic agents have surfaced, such as bortezomib, temsirolimus, thalidomide, lenalidomide, MoAb anti-vascular endothelial growth factor or vascular endothelial growth factor-Trap, and flavopiridol. Other targets include gene transcription through histone regulation; nuclear factor-ķB pathway; protein kinase C inhibitors; small-molecules targeting apoptosis, such as antisense Bcl-2, pan-Bcl-2 family member inhibitors; MoAb agonists of cell death receptors; caspases regulators (inhibitors of apoptosis proteins, survivin); and MDM2 antagonist regulators of p53. A molecular approach to define biomarkers might help identify subgroups of patients and help develop rational therapies.

New Drugs for the Treatment of Advanced-Stage Diffuse Large Cell Lymphomas

The rapid pace of discovering new signaling pathways that influence the growth and survival of different types of cancer cells has produced a daunting array of potentially new, "drugable" targets for the treatment of cancer. This has been particularly true for the lymphomas. The empiric observation that many kinds of "novel targeted" drugs appear to exhibit relatively selective patterns of activity is testament to the concept that the lymphomas represent an incredibly diverse group of human cancers. Targeting one pathway in a subtype of lymphoma may not be universally effective against all subtypes of lymphoma, even closely related ones. These observations suggest that pharmacologically driven "target identification" plays an important role in the continued development of new therapeutic agents, and underscores the need for more research into the biologic basis for different subtypes of lymphoma. Over the past 10 years, there has been an explosion of new drugs making their way through preclinical laboratories and early clinical studies. These experiences have taught us some frustrating lessons. Sometimes, the strongest biologic rationale is associated with the poorest clinical results. Sometimes, where no rationale exists, golden therapeutic opportunities emerge. In either case, both experiences typically end up teaching us something about the disease we didn't historically appreciate. In this review, we will take a close look at some of the more intriguing targets in aggressive large B-cell lymphomas, all of which now have small molecules that can profoundly affect their activity, activity we hope will lead to new treatment opportunities. We will focus on the biologic rationale for targeting novel pathways regulated by Bcl-6, Bcl-2, BLysS, and APRIL for example. In addition, we will review how new concepts in structural biology and chemical design can help produce new generation compounds with novel activity, as is the case for pralatrexate and targeting the reduced folate carrier-type-1. Clearly, given the breadth and depth of information emerging on these and other relevant biologic pathways, we are limited to discussing only a few illustrative examples, which should in no way detract from the importance of other critical signaling and survival pathways now being exploited in the treatment of lymphoma.