A novel rapid-onset high-penetrance plasmacytoma mouse model driven by deregulation of cMYC cooperating with KRAS12V in BALB/c mice

Our goal is to develop a rapid and scalable system for functionally evaluating deregulated genes in multiple myeloma (MM). Here, we forcibly expressed human cMYC and KRAS12V in mouse T2 B cells (IgM(+)B220(+)CD38(+)IgD(+)) using retroviral transduction and transplanted these cells into lethally irradiated recipient mice. Recipients developed plasmacytomas with short onset (70 days) and high penetrance, whereas neither cMYC nor KRAS12V alone induced disease in recipient mice. Tumor cell morphology and cell surface biomarkers (CD138(+)B220(-)IgM(-)GFP(+)) indicate a plasma cell neoplasm. Gene set enrichment analysis further confirms that the tumor cells have a plasma cell gene expression signature. Plasmacytoma cells infiltrated multiple loci in the bone marrow, spleen and liver; secreted immunoglobulins; and caused glomerular damage. Our findings therefore demonstrate that deregulated expression of cMYC with KRAS12V in T2 B cells rapidly generates a plasma cell disease in mice, suggesting utility of this model both to elucidate molecular pathogenesis and to validate novel targeted therapies.

Effect of a novel agent, SL-401, targeting interleukin-3 (IL-3)-receptor on plasmacytoid dendritic cell (pDC)-induced myeloma cell growth and drug resistance

8582

Background: Multiple myeloma (MM) remains incurable despite novel therapies, highlighting the need for further identification of factors mediating disease progression and drug resistance. The bone marrow (BM) microenvironment confers growth, survival, and drug resistance in MM cells. Our recent study utilized in vitro and in vivo MM xenograft models to show that plasmacytoid dendritic cells (pDCs) were significantly increased in MM BM and promote MM growth (Chauhan et al., Cancer Cell 2009, 16:309). Importantly, we found increased IL-3 levels upon pDC-MM interaction, which in turn, trigger MM cell growth and pDCs survival. IL-3R is highly expressed on pDCs. We utilized SL-401, a novel biologic conjugate that targets IL-3R, to examine whether abrogation of IL-3–IL-3R signaling axis affects pDC-MM interaction and its tumor promoting sequelae. Methods: MM cell lines, patient MM cells, and pDCs from healthy donors or MM patients were utilized to study the anti-MM activity of SL-401. MM cells and pDCs were cultured alone or together in the presence or absence of SL-401, followed by analysis of cell growth or viability. Results: SL-401 significantly decreased the viability of pDCs at low concentrations (IC50: 0.83 ng/ml; P < 0.005, n = 3). SL-401 also decreased the viability of MM cells at clinically achievable doses. Co-culture of pDCs with MM cells induced growth of MM cell lines; and importantly, low doses (0.8 ng/ml) of SL-401 blocked MM cell growth-promoting activity of pDCs. MM patient-derived pDCs induced growth of MM cell lines and primary MM cells as well; conversely, SL-401 inhibited pDC-triggered MM cell growth (P < 0.005, n= 5). Tumor cells from 3 of the 5 patients were from patients whose disease was progressing while on bortezomib, dexamethasone, and lenalidomide therapies. In agreement with these results, SL-401 blocked pDC-induced growth of dexamethasone-resistant MM cell lines. Conclusions: Our study therefore provides the basis for directly targeting pDCs or blocking the pDC-MM interaction, as well as targeting MM, in novel therapeutic strategies with SL-401 to enhance MM cytotoxicity, overcome drug-resistance, and improve patient outcome.

Medical oncologists’ clinical experiences and comfort levels with 20 recently approved agents

e17570

Background: The rapid pace of current oncology drug development has provided medical oncologists (MO) and patients with many additional treatment options, but minimal publicly accessible information exists on how new agents are incorporated into practice. Methods: From 12/15/2012 to 1/21/2013,100 US-based MO were recruited to complete a survey assessing the diseases they treat and their prescribing experiences with 20 oncologic drugs approved between 9/2009 and 11/2012. MO who manage related cancers were asked to self-report on a 3-point scale their comfort level using these agents. A modest honorarium was provided. Results: See Table. MO generally had limited clinical experience, even with drugs used in common cancers. Multiple clinical and logistical factors were cited for not using agents. For only 4 of the drugs did more than half of MO self-rate their prescribing confidence as 3 (very confident). Conclusions: Variation in MO use of recently approved drugs is multifactorial, and the suboptimal comfort levels reported here may reflect the natural evolution of clinical experience over time. Further research is needed to determine if an improved information infrastructure would better and more rapidly prepare MO to incorporate these and other soon-to-be-approved agents into practice. [Table: see text]

Phase I study of TH-302, an investigational hypoxia-targeted drug, and dexamethasone in patients with relapsed/refractory multiple myeloma

8602

Background: TH-302 is an investigational 2-nitroimidazole prodrug of the DNA alkylator Br-IPM designed to be selectively activated in hypoxia. In multiple myeloma (MM) mouse models, diseased animals demonstrate a marked expansion of areas of hypoxia in the bone marrow. TH-302 exhibited anti-tumor activity against MM in vitro and in vivo and synergism was seen when combined with bortezomib (Hu et al, Blood 2010; Chesi et al, Blood 2012). Based on these findings, a phase I/II study of TH-302 plus dexamethasone (dex) was initiated for patients (pts) with relapsed/refractory MM. Methods: Eligible pts in the study (NCT01522872) had ECOG PS ≤ 2, receipt of at least two prior therapies, and acceptable hepatorenal function and hematologic status. A standard 3+3 dose escalation design was used with a fixed oral 40 mg dose of dex and 40% dose increments of TH-302. TH-302 was administered IV with dex on days 1, 4, 8, and 11 of a 21-day cycle. The objectives were to determine DLTs and the MTD; assess the safety, tolerability and preliminary clinical activity of TH-302 plus dex; and study the relationship between hypoxia within the bone marrow and response to TH-302. Results: Eleven pts have been treated: 7M/4F with a median age 61 years (range: 53 – 86) and 6 prior therapies (range: 3 – 10). All received both bortezomib and lenalidomide/thalidomide containing regimens. TH-302 was dosed at 240 (n=5), 340 (n=4), and 480 (n=2) mg/m² for a median of 5 cycles. No DLTs were reported at 240 or 340 mg/m². Two pts treated at 480 mg/m² had DLTs of grade 3 mucositis, exceeding the definition of MTD. A dose expansion is thus ongoing at 340 mg/m2. Two patients had SAEs related to TH-302 (pneumonia). Five pts continue on study after a median of 7 cycles (range: 2–11). Nine pts have had efficacy evaluations: 2 pts with partial responses, 2 pts with minimal responses, and 5 pts with stable disease, for an overall response rate (of MR or better) of 44%. Conclusions: TH-302 can be administered at 340 mg/m2 biweekly + dex, with dose limiting mucositis seen at higher doses. Initial clinical activity has been noted with an ORR of 44% in heavily pretreated MM pts who are relapsed/refractory to both bortezomib and lenalidomide. Clinical trial information: NCT01522872.

Novel heteroclitic XBP1 peptides evoking antigen-specific cytotoxic T lymphocytes targeting various solid tumors

3067

Background: Activation of the unfolded protein response (UPR) allows for tumor cells to survive prolonged endoplasmic reticulum stress and hypoxic conditions. XBP1 is an upstream element and a critical transcriptional activator of the UPR, and its up-regulation in a variety of human solid tumor cancers makes it as a promising immunotherapeutic target. The purpose of these studies was to evaluate immunogenic HLA-A2 XBP1-specific peptides for their ability to elicit cytotoxic T lymphocytes (CTL) against a variety of solid tumor cell lines. Methods: Upon the validation of XBP1 peptides for their strong HLA-A2 bindings and stabilities, peptide-specific CTL were generated ex vivo by repeated stimulation of CD3+ T lymphocytes obtained from HLA-A2+normal donors with XBP1 peptides-pulsed antigen-presenting cells, either dendritic cells or T2 cells. Results: A cocktail of heteroclitic XBP1 US184-192 (YISPWILAV) and heteroclitic XBP1 SP367-375 (YLFPQLISV) peptides with significantly improved HLA-A2 affinity and stability from their native counterparts were used to evoke XBP1 antigen-specific CTL. The CTL were predominantly CD3+CD8+ T cells (>80%) containing a high percentage of Effector Memory (EM; CCR7-CD45RO+) cells, which were distinctively evoked by repeated stimulation with the XBP1 peptides. In addition, the XBP1-CTL displayed a high level of cellular activation (CD69+/CD3+CD8+). The XBP1-CTL demonstrated effective anti-tumor responses including cell proliferation and IFN-g production, as well as degranulation (cytotoxic activity) against HLA-A2+breast cancer (MB231, MCF7), colon cancer (LS180, SW480) and pancreatic cancer (8902, Panc1, PL45) cell lines, which over-express both unspliced and spliced XBP1 antigens. Importantly, the specific anti-tumor activities were detected primarily in the EM CTL subset. Conclusions: These results suggest the immunotherapeutic potential of a cocktail of heteroclitic XBP1 US184-192 and XBP1 SP367-375 peptides to elicit effective anti-tumor responses against various solid tumors, and provide the framework for clinical development of vaccine trials to improve patient outcome.

Pomalidomide (POM) with or without low-dose dexamethasone (LoDEX) in patients (Pts) with relapsed and refractory multiple myeloma (RRMM): MM-002 phase II age subgroup analysis

8532

Background: POM demonstrated clinical efficacy and favorable tolerability in RRMM pts previously treated with lenalidomide (LEN) and bortezomib (BORT), in the randomized, multicenter, open label MM-002 phase II trial. This analysis evaluated whether the efficacy and tolerability of POM+LoDEX treatment is consistent across age subgroups. Methods: Pts with RRMM who had received ≥ 2 prior therapies, including LEN and BORT, and were refractory to their last regimen were randomized to either POM+LoDEX (POM 4 mg/day, days 1–21 of a 28-day cycle; LoDEX 40 mg/week) or POM alone. End points included progression-free survival (PFS), response rate (based on EBMT criteria), response duration, and safety. A post-hoc analysis based on age (≤ 65 vs. > 65 yrs) was conducted. Results: A total of 221 pts with a mean age of 64 yrs (range 34–88) were randomized to POM+LoDEX (n = 113) or POM (n = 108). The efficacy outcomes and the most common treatment emergent grade 3/4 adverse events (AEs) for the age subgroups according to treatment arm are presented in the Table. Conclusions: Regardless of age (≤ 65 vs. > 65 yrs), POM with or without LoDEX was effective and generally well tolerated in heavily pretreated RRMM pts who had already received LEN and BORT. POM with or without LoDEX represents a new clinical option for pts previously treated with numerous lines of therapy. Updated data will be presented at the meeting. Clinical trial information: NCT00833833. [Table: see text]

Long-term safety and efficacy of pomalidomide (POM) with or without low-dose dexamethasone (LoDEX) in relapsed and refractory multiple myeloma (RRMM) patients enrolled in the MM-002 phase II trial

8588

Background: MM-002 is a randomized, open-label, multicenter phase II trial evaluating the safety and efficacy of POM with or without LoDEX in advanced RRMM pts. Methods: Pts who had received ≥ 2 prior therapies, including lenalidomide (LEN) and bortezomib (BORT), and were refractory to their last treatment were randomized to POM+LoDEX (POM 4 mg/day, days 1–21 of a 28-day cycle; LoDEX 40 mg/week) or POM alone. End points included progression-free survival (PFS), response rate (according to EBMT criteria and investigator assessment), response duration, overall survival (OS), and safety. The efficacy outcomes are based on the intent-to-treat population (POM+LoDEX, n = 113; POM, n = 108). Results: The median number of prior therapies in each group was 5 (range 1–13). In the POM+LoDEX arm, 30 (27%) pts had high-risk cytogenetics, including del(17p13) and/or t(4p16/14q32). The overall response rate (≥ partial response) was 34% and 15% with POM+LoDEX and POM, respectively, with a median duration of 8.3 (95% CI: 5.8–10.1) and 8.8 (95% CI: 5.5–11.4) mos, respectively. At least minimal response was observed in 45% and 31% of pts, respectively. Median PFS was 4.6 (95% CI: 3.6–5.5) and 2.6 (95% CI: 1.9–2.8) mos with POM+LoDEX and POM, respectively, with a median follow-up of 16.0 and 12.2 mos. Median OS was 16.5 (95% CI: 12.4–18.5) and 13.6 (95% CI: 9.6–18.1) mos, respectively. The most common treatment emergent Gr 3/4 adverse events (AEs) reported in the safety population (n = 219) were neutropenia (44%), anemia (23%), thrombocytopenia (21%), and pneumonia (18%); there were no reports of Gr 3/4 peripheral neuropathy. The incidence of deep-vein thrombosis was low (2%). AEs were managed through dose reductions or interruptions, and supportive care with G-CSF (52%), RBC transfusions (47%), and platelet transfusions (17%). Discontinuations due to AEs were 10%. Conclusions: POM with or without LoDEX is clinically effective and generally well tolerated in RRMM pts who have received multiple prior treatments, including LEN and BORT. AEs were predictable and manageable. Updated data will be presented at the meeting. Clinical trial information: NCT00833833.

MM-005: A phase I trial of pomalidomide, bortezomib, and low-dose dexamethasone (PVD) in relapsed and/or refractory multiple myeloma (RRMM)

8584

Background: Combinations of lenalidomide (LEN), bortezomib (BORT), and dexamethasone (DEX) have demonstrated preclinical and clinical activity in patients (pts) with multiple myeloma. Pomalidomide with low-dose DEX (LoDEX) has demonstrated efficacy in RRMM pts treated with prior LEN and BORT. MM-005 was designed to identify the optimal PVD dose for a phase 3 trial comparing PVD vs BORT + LoDEX (VD) in RRMM (MM-007). Methods: Eligible pts had RRMM with 1-4 prior therapies including ≥ 2 consecutive cycles of LEN and a proteasome inhibitor. Pts must have been refractory to LEN (progressive disease [PD] during or within 60 days of LEN treatment), but not refractory to BORT (at 1.3 mg/m2 twice-weekly). The maximum tolerated dose (MTD) was determined using a 3 + 3 design in 5 cohorts. Each cohort received 21-day cycles of POM 1-4mg/day on D1-14; BORT 1-1.3mg/m2on D1, 4, 8, 11; and LoDEX 20mg/day on D1-2, 4-5, 8-9, 11-12. An expansion cohort was enrolled at the MTD. Treatment was continued until PD or unacceptable toxicity. Dose-limiting toxicities (DLTs) were assessed during cycle 1. The primary endpoint was MTD; secondary endpoints were safety, overall response rate (ORR; ≥ partial response), duration of response, and time to response (TTR). Results: As of Dec 31, 2012, 21 pts were enrolled (3 pts per escalating dose cohort; 6 in the expansion cohort). Median age was 57 years (36-75). All were LEN-refractory and had prior BORT. No DLTs were observed at any dose level. The most common grade 3/4 adverse events (AEs) were neutropenia (32%) and thrombocytopenia (21%). With thromboprophylaxis, no deep vein thrombosis was observed. 17 pts remain on study and no pts have discontinued treatment due to AE. Thus far, the ORR was 72% (n = 18 evaluable) and responses were rapid (median TTR, 2 cycles). Conclusions: PVD was well-tolerated in RRMM with no DLTs and no discontinuations due to AE to date. PVD has promising activity with a current ORR of 72%. The maximum planned dose of POM 4mg/day on D1-14; BORT 1.3mg/m2 on D1, 4, 8, and 11; and DEX 20mg on D1-2, 4-5, 8-9, 11-12 of a 21-day cycle has now been incorporated into the MM-007 phase III trial comparing PVD with VD in RRMM pts (N = 782 planned). Clinical trial information: NCT01497093.

Strategies to overcome barriers to accrual (BtA) to NCI-sponsored clinical trials: A project of the NCI-Myeloma Steering Committee Accrual Working Group (NCI-MYSC AWG)

8592

Background: Accrual to NCI clinical trials(CT)is often slower than planned at times mandating premature closure resulting in loss of valuable resources and delay of scientific progress. Methods: The NCI-MYSC AWG identified 10 potential BtA. SWOG, ECOG and Alliance investigators were queried and agreed that these barriers impede accrual (results stratified for academic and community sites). The MYSC AWG developed in collaboration with NCI and FDA strategies to overcome these barriers. Results: Strategies listed for the 3 most often cited BtA: 1. Reimbursement for CT related expenses:increase awareness of improved reimbursement for phase II CT; tailor reimbursement according to CT complexity; request funds from industry and other sources ( http://biqsfp.cancer.gov ) for qualifying ancillary CT components. 2. Spectrum of available treatment options influences CT participation: educate patients and providers about the significance of a new CT using social media, presentations at national meetings and by adding educational material to CT protocol; encourage opinion leaders and advocacy groups not to promote a new therapy as “standard” in the absence of phase III data. 3. Requirement of CT specific therapy at NCI designated sites only: “MYSC AWG Drug Administration Table” describes NCI/FDA approved rules for CT specific drug administration; CT protocol will outline which standard treatment components of a CT can be administered at any site as long as protocol specific guidelines are followed and conduct is supervised by enrolling investigator. Examples of additional strategies to overcome identified BtA: determine feasibility, indication and insurance coverage of CT specific tests during protocol development; discourage narrow eligibility criteria; avoid competing CT; allow up to 1 cycle of commercially available therapy prior to enrollment; CIRB support for phase II CT. Conclusions: The MYSC Accrual Working Group developed in collaboration with NCI and FDA strategies to overcome barriers to myeloma clinical trial accrual. These strategies may be applicable to NCI-sponsored clinical trials evaluating interventions in other diseases.

miR-29b sensitizes multiple myeloma cells to bortezomib-induced apoptosis through the activation of a feedback loop with the transcription factor Sp1

MicroRNAs (miRNAs) with tumor-suppressor potential might have therapeutic applications in multiple myeloma (MM) through the modulation of still undiscovered molecular pathways. Here, we investigated the effects of enforced expression of miR-29b on the apoptotic occurrence in MM and highlighted its role in the context of a new transcriptional loop that is finely tuned by the proteasome inhibitor bortezomib. In details, in vitro growth inhibition and apoptosis of MM cells was induced by either transient expression of synthetic miR-29b or its stable lentivirus-enforced expression. We identified Sp1, a transcription factor endowed with oncogenic activity, as a negative regulator of miR-29b expression in MM cells. Since Sp1 expression and functions are regulated via the 26S proteasome, we investigated the effects of bortezomib on miR-29b-Sp1 loop, showing that miR-29b levels were indeed upregulated by the drug. At the same time, the bortezomib/miR-29b combination produced significant pro-apoptotic effects. We also demonstrated that the PI3K/AKT pathway plays a major role in the regulation of miR-29b-Sp1 loop and induction of apoptosis in MM cells. Finally, MM xenografts constitutively expressing miR-29b showed significant reduction of their tumorigenic potential. Our findings indicate that miR-29b is involved in a regulatory loop amenable of pharmacologic intervention and modulates the anti-MM activity of bortezomib in MM cells.

Plasma cell leukemia: consensus statement on diagnostic requirements, response criteria and treatment recommendations by the International Myeloma Working Group

Plasma cell leukemia (PCL) is a rare and aggressive variant of myeloma characterized by the presence of circulating plasma cells. It is classified as either primary PCL occurring at diagnosis or as secondary PCL in patients with relapsed/refractory myeloma. Primary PCL is a distinct clinic-pathological entity with different cytogenetic and molecular findings. The clinical course is aggressive with short remissions and survival duration. The diagnosis is based upon the percentage (≥ 20%) and absolute number (≥ 2 × 10(9)/l) of plasma cells in the peripheral blood. It is proposed that the thresholds for diagnosis be re-examined and consensus recommendations are made for diagnosis, as well as, response and progression criteria. Induction therapy needs to begin promptly and have high clinical activity leading to rapid disease control in an effort to minimize the risk of early death. Intensive chemotherapy regimens and bortezomib-based regimens are recommended followed by high-dose therapy with autologous stem cell transplantation if feasible. Allogeneic transplantation can be considered in younger patients. Prospective multicenter studies are required to provide revised definitions and better understanding of the pathogenesis of PCL.

Emerging therapies targeting tumor vasculature in multiple myeloma and other hematologic and solid malignancies

Research on the formation of new blood vessels (angiogenesis) in general and vascular endothelial growth factor (VEGF) in particular is a major focus in biomedicine and has led to the clinical approval of the monoclonal anti- VEGF antibody bevazicumab; and the second-generation multitargeted receptor kinase inhibitors (RTKIs) sorafenib, sunitinib, and pazopanib. Although these agents show significant preclinical and clinical anti-cancer activity, they prolong overall survival of cancer patients for only months, followed by a restoration of tumor growth and progression. Therefore, there is a clear need to increase our understanding of tumor angiogenesis and the development of resistance. In this review we discuss up-to-date knowledge on mechanisms of tumor angiogenesis, and summarize preclinical and clinical data on existing and potential future anti-angiogenic agents and treatment strategies for Multiple Myeloma (MM) and other hematologic and solid malignancies.

ELOQUENT-2: A phase III, randomized, open-label trial of lenalidomide/dexamethasone (Len/Dex) with or without elotuzumab (Elo) in relapsed or refractory multiple myeloma (RR MM) (CA204-004)

TPS8112

Background: MM remains incurable and patients (pts) typically relapse or become refractory to current treatments. Novel regimens are needed to improve pt outcomes. Elo is a humanized monoclonal IgG1 antibody targeting the cell surface glycoprotein CS1, which is highly expressed on >95% of MM cells. Len/Dex is approved for treatment of relapsed MM and an objective response rate (ORR) of ~60% was reported in phase III trials of this combination in RR MM. In a phase II study (N=73) of Elo (10 or 20 mg/kg) in combination with Len/Dex in pts with RR MM, the 10 mg/kg group (n=36) demonstrated an ORR of 92% and median progression-free survival (PFS) that was not reached after a median follow-up of 14.1 months. Encouraging activity was seen in patients with high-risk cytogenetics and/or stage 2-3 disease. Based on these data, a randomized, open-label phase III trial has been initiated to determine if the addition of Elo to Len/Dex will improve PFS in patients with RR MM compared with Len/Dex alone. Methods: Pts (N=640) with RR MM and 1-3 prior therapies are eligible, including pts with mild or moderate renal impairment. Pts are randomized in a 1:1 ratio to receive 28-day cycles of Len 25 mg PO (days 1-21) and Dex 40 mg PO (days 1, 8, 15 and 22) with or without Elo. Elo dose and schedule is 10 mg/kg IV on days 1, 8, 15, 22 in the first 2 cycles and on days 1 and 15 in subsequent cycles. Dex 8 mg IV + 28 mg PO is used during the weeks with Elo. Treatment will continue until disease progression, death, or withdrawal of consent. Patients will be followed for tumor response every 4 weeks until progressive disease and then survival every 12 weeks. The primary endpoint is PFS (90% power for a hazard ratio [experimental to control arm] of 0.74) and the secondary endpoints are ORR and overall survival. Exploratory endpoints are safety, time to response, duration of response, time to subsequent therapy, health-related quality of life, and pharmacokinetics and immunogenicity of Elo. Potential biomarkers will also be assessed. As of January 10th, 2012, 107 pts were enrolled and 68 pts were treated. NCT01239797.

Pomalidomide (POM) with or without low-dose dexamethasone (LoDEX) in patients (pts) with relapsed/refractory multiple myeloma (RRMM): Outcomes in pts refractory to lenalidomide (LEN) and/or bortezomib (BORT)

8016

Background: Response and survival outcomesare poor in pts with RRMM who are refractory to BORT and immunomodulatory drugs. POM+LoDEX has demonstrated activity in pts with advanced multiple myeloma who have received multiple lines of therapy. This analysis evaluates outcomes in pts with disease refractory to LEN, BORT, or both, as well in pts with disease refractory to both LEN and BORT who had received prior transplant. Methods: In the MM-002 phase II trial, pts received POM (4 mg/day on days 1–21 of each 28-day cycle) alone (n=108) or in combination with LoDEX (40 mg/week) (n=113). Refractory disease was defined as documented progression during treatment or within 60 days of the last dose of treatment. Response rates were assessed using European Group for Bone Marrow Transplantation (EBMT) criteria by independent adjudication committee. Results: Patients who received POM+LoDEX were refractory to LEN (77%), BORT (73%), or both (61%). Forty-two percent were refractory to both LEN and BORT and had received prior transplant. Overall, 20% of pts achieved ≥ PR, median PFS was 3.5 months, and 1-year survival rate was 59%. Response rates and duration were comparable in pts with disease refractory to LEN, BORT, or both, and in pts who had received prior transplant (response rate 25-34%, median duration of response 5.7-7 months). Survival outcomes were similar across the groups (median PFS 3.8-4.6 months; 1-year survival rate 60-67%). Conclusions: POM, given at 4 mg/day on days 1–21 of each 28-day cycle in combination with LoDEX, 40 mg/week, is effective in pts with RRMM refractory to LEN, BORT, or both, and including those with prior transplant. These results suggest a lack of cross-resistance between POM and LEN, and confirm activity not only in BORT-refractory pts but also those for whom transplant has failed. [Table: see text]

Long-term results of the phase II trial of the oral mTOR inhibitor everolimus (RAD001) in relapsed or refractory Waldenstrom macroglobulinemia

8043

Background: The mammalian target of rapamycin (mTOR) signal pathway controls cell proliferation and survival. The trial's goal was to determine the anti-tumor activity and safety of single-agent everolimus (TORC1 inhibitor) in patients with relapsed/refractory Waldenstrom macroglobulinemia (WM). Methods: Eligible patients had measurable disease (IgM monoclonal protein >1000 mg/dL with >10% marrow involvement or nodal masses >2 cm), a platelet count ≥75,000 x 106/L, a neutrophil count ≥1,000 x 106/L. Patients received everolimus 10 mg PO daily. Tumor response was assessed after cycles 2 and 6 and then every 3 cycles until progression. Results: 60 pts were treated. The median age was 64 years (range, 43-85). The median number of prior therapies was 3 (range, 1-11). All but two patients (97%) had received prior rituximab based therapy and 64% of patients had received prior alkylator based therapies. The overall response rate (complete response CR+ partial response PR+ minimal response MR) was 73% (95% CI: 60-84%), with a PR of 50% and 23% MR. The median time to progression (TTP), progression-free survival (PFS), and overall survival (OS) for the entire study population is 28 months (mos), (95% CI: 18-not reached (NR)), 22 mos (95% CI: 12 0-NR), and 55 mos (95% CI: 55-NR), respectively. The estimated PFS at 12 and 24 months is 62% (95%CI: 51-75%), and 48% (95%CI: 37-63%), respectively. The 30 patients who achieved a PR responded after a median of 2 months (range, 1-26) of treatment. The median duration of response (DR) for these patients has not yet been reached and 19 of these patients remain in response after a median follow up of 31 months (range, 3-54). All but two patients had a decrease in their serum IgM. Grade 3 or higher related toxicities were observed in 67% of patients. The most common were hematological toxicities with cytopenias. Pulmonary toxicity occurred in 5% of patients. Dose reductions due to toxicity occurred in 63% of patients. Conclusions: Everolimus has high single-agent activity with an overall response rate of 73% and manageable toxicity in patients with relapsed WM, and offers a potential new therapeutic strategy for this patient population.

ELOQUENT-1: A phase III, randomized, open-label trial of lenalidomide/dexamethasone with or without elotuzumab in subjects with previously untreated multiple myeloma (CA204-006)

TPS8113

Background: Elotuzumab (Elo) is a humanized monoclonal IgG1 antibody targeting the cell surface glycoprotein CS1, which is highly expressed on >95% of MM cells. In a MM xenograft mouse model, the combination of Elo + lenalidomide (Len) significantly reduced tumor volume in a synergistic manner compared with either agent alone. In a phase 2 study (N=73) of Elo (10 or 20 mg/kg) in combination with Len and low-dose-dexamethasone (Dex) in pts with RR MM, the 10 mg/kg dose group (n=36) demonstrated objective response rates (ORR) of 92% in all pts, and 100% in pts who had received only 1 prior therapy (n=16). The higher response rate in pts with fewer prior lines of therapy provides a rationale for investigating this combination earlier in the disease course. This randomized, open-label, phase 3 trial will determine if the addition of Elo to Len/Dex improves progression-free survival (PFS) in pts with newly diagnosed, untreated MM. Methods: Pts (N=750) with newly diagnosed symptomatic MM ineligible for stem cell transplant will be randomized in a 1:1 ratio to receive 28-day cycles of Len 25 mg PO (days1-21) and Dex 40 mg PO (days 1, 8, 15 and 22) with or without Elo. Elo dose and schedule is 10 mg/kg IV on days 1, 8, 15, 22 in the first 2 cycles and on days 1 and 15 of cycles 3-18 followed by 20 mg/kg on day 1 of cycle 19 onward. Dex 8 mg IV + 28 mg PO is used during the weeks with Elo. Treatment will continue until disease progression, death, or withdrawal of consent. Pts will be followed up for response every 4 weeks until progressive disease and for survival every 16 weeks. The primary endpoint is PFS (90% power for a hazard ratio [experimental to control arm] of 0.74) and the secondary endpoints are ORR and overall survival. Exploratory endpoints are safety, time to response, duration of response, time to subsequent therapy, health-related quality of life, and pharmacokinetics and immunogenicity of Elo. Potential biomarkers will also be assessed. As of January 1, 2012, 13 pts were enrolled and 9 pts were treated. NCT01335399.

Participation of BTK in MYD88 signaling in malignant cells expressing the L265P mutation in Waldenstrom’s macroglobulinemia, and effect on tumor cells with BTK-inhibitor PCI-32765 in combination with MYD88 pathway inhibitors

8106

Background: Bruton’s tyrosine kinase (BTK) promotes B-cell receptor signaling along with B-cell expansion and survival through NF-κB and MAPK. MYD88 L265P is a widely expressed somatic mutation in tumor cells from WM patients. MYD88 L265P promotes enhanced tumor cell survival through IRAK 1/4 mediated NF-κB and MAPK signaling. We therefore sought to clarify the role of BTK signaling in MYD88 L265P expressing WM cells, and the impact of BTK and MYD88/IRAK inhibition on WM cell signaling and survival. Methods: Western blot analysis was performed using total and phospho-specific BTK antibodies in MYD88 L265P expressing primary WM patient cells, BCWM.1 and MCWL-1 WM cell lines following MYD88 knockdown by lentiviral transduction, and/or use of MYD88 or IRAK signal inhibitors. Cells were also treated with the BTK inhibitor PCI-32765, in the presence or absence of MYD88 homodimerization or IRAK1/4 inhibitors. Annexin V / PI staining was used to assess cell survival, and synergism assessed with CalcuSyn software. Results: BTK was phosphorylated in MYD88 L265P expressing WM cells. Knockdown of MYD88 by lentiviral transduction, and/or use of MYD88 or IRAK 1/4 kinase inhibitors led to decreased BTK phosphorylation. Phosphorylation of BTK, TIRAP, a major TLR adapter protein for MYD88 signaling, IRAK1, IKBα, ERK1/2 and STAT3 were significantly reduced following treatment with PCI-32765. Treatment with PCI-32765 also induced apoptosis of MYD88 L265P expressing WM cells, and showed synergistic tumor cell killing in the presence of either MYD88 homodimerization or IRAK 1/4 kinase inhibitors. Conclusions: BTK activation is facilitated by MYD88 pathway signaling in L265P expressing WM cells, and participates in MYD88 downstream signaling. Inhibition of BTK by PCI-327625 led to robust tumor cell killing of MYD88 L265P expressing WM,cells, which was potentiated by MYD88 pathway inhibitors. These studies provide the framework for the investigation of BTK inhibitors in WM, as single agents and in combination with MYD88 pathway inhibitors.

Management of treatment-emergent peripheral neuropathy in multiple myeloma

Peripheral neuropathy (PN) is one of the most important complications of multiple myeloma (MM) treatment. PN can be caused by MM itself, either by the effects of the monoclonal protein or in the form of radiculopathy from direct compression, and particularly by certain therapies, including bortezomib, thalidomide, vinca alkaloids and cisplatin. Clinical evaluation has shown that up to 20% of MM patients have PN at diagnosis and as many as 75% may experience treatment-emergent PN during therapy. The incidence, symptoms, reversibility, predisposing factors and etiology of treatment-emergent PN vary among MM therapies, with PN incidence also affected by the dose, schedule and combinations of potentially neurotoxic agents. Effective management of treatment-emergent PN is critical to minimize the incidence and severity of this complication, while maintaining therapeutic efficacy. Herein, the state of knowledge regarding treatment-emergent PN in MM patients and current management practices are outlined, and recommendations regarding optimal strategies for PN management during MM treatment are provided. These strategies include early and regular monitoring with neurological evaluation, with dose modification and treatment discontinuation as indicated. Areas requiring further research include the development of MM-specific, patient-focused assessment tools, pharmacogenomic analysis of patient DNA, and trials to assess the efficacy of pharmacological interventions.

Somatic SF3B1 mutation in myelodysplasia with ring sideroblasts

BACKGROUND

Myelodysplastic syndromes are a diverse and common group of chronic hematologic cancers. The identification of new genetic lesions could facilitate new diagnostic and therapeutic strategies.

METHODS

We used massively parallel sequencing technology to identify somatically acquired point mutations across all protein-coding exons in the genome in 9 patients with low-grade myelodysplasia. Targeted resequencing of the gene encoding RNA splicing factor 3B, subunit 1 (SF3B1), was also performed in a cohort of 2087 patients with myeloid or other cancers.

RESULTS

We identified 64 point mutations in the 9 patients. Recurrent somatically acquired mutations were identified in SF3B1. Follow-up revealed SF3B1 mutations in 72 of 354 patients (20%) with myelodysplastic syndromes, with particularly high frequency among patients whose disease was characterized by ring sideroblasts (53 of 82 [65%]). The gene was also mutated in 1 to 5% of patients with a variety of other tumor types. The observed mutations were less deleterious than was expected on the basis of chance, suggesting that the mutated protein retains structural integrity with altered function. SF3B1 mutations were associated with down-regulation of key gene networks, including core mitochondrial pathways. Clinically, patients with SF3B1 mutations had fewer cytopenias and longer event-free survival than patients without SF3B1 mutations.

CONCLUSIONS

Mutations in SF3B1 implicate abnormalities of messenger RNA splicing in the pathogenesis of myelodysplastic syndromes. (Funded by the Wellcome Trust and others.).

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.

Predictors of high yield and purify of CD34(+) cell-selected PBPC, collected from patients with multiple myeloma

BACKGROUND

Wide ranges i n cell recovery and purity may be observed following CD34(+) cell selection of mobilized HPC componetns. Characteristics of the mobilized HPC, associated with isolation of a high CD34(+) cell yield and purity following cell selection, have yet to be defined.

METHODS

Cell number and purities were determined before and after 56 CD34(+) cell-selection procedures, performed using the CellPro Ceprate SC system from April 1997 to February 1998. HPC were collected from 28 patients with multiple myeloma, following cyclophosphamide (60mg/kg) and G-CSF (10microg/kg) mobilization.

RESULTS

A medium of 47.9% (range 1.5-109.6%) CD34(+) cells were recovered in the enriched (ENR) fraction. A linear correlation existed between total CD34(+) cells in the ENR fraction and total CD34(+) cells in the START fraction (R2=0.93); there was a logarithmic correlation between CD34 ENR fraction purity and START fraction purity (R2=0.73). A START CD34(+) cell purity > 0.42% improved purity in the ENR fraction. A median of one (range one to nine) procedure was required to isolate 2 x 10 6 CD34(+) cells/kg. Three patients pretreated with alkylating agents failed to mobilized adequate numbers of HPC.

DISCUSSION

Isolation of highly purified CD34(+) cell-selected components using the Ceprate SC system in dependent on the CD34(+) purity of the lekapheresis component collected. Mobilization regimens should be used to maximize CD34(+) cell purity in stem cell authografts if CD34(+) cell selection is to be performed. Similar strategies should be used to evaluate other cell-selection devices as they become available.

AT7519, A novel small molecule multi-cyclin-dependent kinase inhibitor, induces apoptosis in multiple myeloma via GSK-3beta activation and RNA polymerase II inhibition

Dysregulated cell cycling is a universal hallmark of cancer and is often mediated by abnormal activation of cyclin-dependent kinases (CDKs) and their cyclin partners. Overexpression of individual complexes are reported in multiple myeloma (MM), making them attractive therapeutic targets. In this study, we investigate the preclinical activity of a novel small-molecule multi-CDK inhibitor, AT7519, in MM. We show the anti-MM activity of AT7519 displaying potent cytotoxicity and apoptosis; associated with in vivo tumor growth inhibition and prolonged survival. At the molecular level, AT7519 inhibited RNA polymerase II (RNA pol II) phosphorylation, a CDK9, 7 substrate, associated with decreased RNA synthesis confirmed by [(3)H] Uridine incorporation. In addition, AT7519 inhibited glycogen synthase kinase 3beta (GSK-3beta) phosphorylation; conversely pretreatment with a selective GSK-3 inhibitor and shRNA GSK-3beta knockdown restored MM survival, suggesting the involvement of GSK-3beta in AT7519-induced apoptosis. GSK-3beta activation was independent of RNA pol II dephosphorylation confirmed by alpha-amanitin, a specific RNA pol II inihibitor, showing potent inhibition of RNA pol II phosphorylation without corresponding effects on GSK-3beta phosphorylation. These results offer new insights into the crucial, yet controversial role of GSK-3beta in MM and show significant anti-MM activity of AT7519, providing the rationale for its clinical evaluation in MM.

The use of novel agents in the treatment of relapsed and refractory multiple myeloma

Although outcomes for patients with multiple myeloma (MM) have improved over the past decade, the disease remains incurable and even patients who respond well to induction therapy ultimately relapse and require additional treatment. Conventional chemotherapy and high-dose therapy with stem cell transplantation (SCT) have historically been utilized in the management of relapsed MM, but in recent years the immunomodulatory drugs (IMiDs) thalidomide and lenalidomide, as well as the proteasome inhibitor bortezomib, have assumed a primary role in this setting. This review focuses on the role of thalidomide, lenalidomide and bortezomib in relapsed and refractory MM, with additional discussion dedicated to emerging drugs in relapsed MM that may prove beneficial to patients with this disease.

International myeloma working group (IMWG) consensus statement and guidelines regarding the current status of stem cell collection and high-dose therapy for multiple myeloma and the role of plerixafor (AMD 3100)

Multiple myeloma is the most common indication for high-dose chemotherapy with autologous stem cell support (ASCT) in North America today. Stem cell procurement for ASCT has most commonly been performed with stem cell mobilization using colony-stimulating factors with or without prior chemotherapy. The target CD34+ cell dose to be collected as well as the number of apheresis performed varies throughout the country, but a minimum of 2 million CD34+ cells/kg has been traditionally used for the support of one cycle of high-dose therapy. With the advent of plerixafor (AMD3100) (a novel stem cell mobilization agent), it is pertinent to review the current status of stem cell mobilization for myeloma as well as the role of autologous stem cell transplantation in this disease. On June 1, 2008, a panel of experts was convened by the International Myeloma Foundation to address issues regarding stem cell mobilization and autologous transplantation in myeloma in the context of new therapies. The panel was asked to discuss a variety of issues regarding stem cell collection and transplantation in myeloma especially with the arrival of plerixafor. Herein, is a summary of their deliberations and conclusions.

Autologous bone marrow transplantation therapy for multiple myeloma

We have begun an autologous bone marrow transplantation (ABMT) treatment protocol for patients with myeloma who achieve a minimal disease (less than 10% marrow plasma cells) status. Sites of bony disease are irradiated before BMT. Melphalan 70 mg/m2 on days 1 and 2 is followed by 1200 rads total-body irradiation administered in fractionated doses over 3 d. Autologous marrow which has been previously treated with anti-CALLA, B1, and PCA-1 monoclonal antibodies is then thawed and reinfused. 4 males and 2 females with median age of 46 yr (41-56) have been treated. Granulocytes greater than 500/mm3 and platelets greater than 20,000/mm3 were noted at 21 (12-46) and 23 (12-53) d post-transplant (PT), respectively. Acute mucositis and dermatomal Herpes zoster developed in 3 patients each; all patients are clinically well at 233 (30-807) d PT. All patients achieved pathologically normal marrows, but monoclonal plasma cells and marrow myelofibrosis were each noted in a single patient at 486 and 272 d PT, respectively. A single patient has responded to alpha 2 interferon therapy PT; all others have received no therapy. AMBT offers an exciting new treatment for myeloma; however, relapses post-ABMT suggest that improved ablative regimens and/or marrow purging methods may be required.

Phenotypic and functional characterization of normal and malignant terminal B (plasma) cells

A number of antigens (Ags) are expressed on normal and malignant terminal B (plasma) cells, including plasma-cell, earlier B-cell, and non-B cell-Ags. These Ags, coupled with indirect and dual fluorochrome labelling techniques, permit characterization of normal and malignant in vitro and in vivo terminal B-cell differentiation. The majority (90%) of B cells within spleen bear Bl and lack PCA-1 Ags. As B cells differentiate to pokeweed mitogen in vitro, immunoglobulin (Ig) secretion precedes the appearance of cell surface PCA-1 and plasmacytoid morphology. Dual fluorescence cell sorting permits characterization of in vivo B-cell differentiation: Bl + PCA-1 + cells are more "differentiated" since they are more prevalent in lymph node than spleen, exhibit plasmacytoid morphology and maximal Ig secretion, and no longer respond to triggers of B-cell proliferation; in contrast, Bl + PCA-1-cells are lymphoid in morphology and may respond to triggers of B-cell proliferation as "resting" B cells. Similar studies of myeloma cells demonstrated that they may also include cells expressing plasma-cell, earlier B, and non-B cell Ags. Although they neither proliferated nor secreted Ig in vitro to G/M-CSF, G-CSF, M-CSF, IL-1, IL-1B, IL-2, or IL-4, proliferation without Ig secretion (Stimulation Index greater than or equal to 3.0) was induced to IL-6 in 6 of 10 patients (pts); to IL-3 (2 pts) and to IL-5 (2 pts).(ABSTRACT TRUNCATED AT 250 WORDS)

Ascorbic acid inhibits antitumor activity of bortezomib in vivo

Earlier studies have shown that ascorbic acid (vitamin C) inhibits bortezomib-induced cytotoxicity against cancer cells in vitro. However, the clinical significance of vitamin C on bortezomib treatment is unclear. In this study, we examined whether daily oral intake of vitamin C inhibits antimultiple myeloma (MM) activities of bortezomib. Vitamin C, at orally achievable concentrations, inhibited in vitro MM cell cytotoxicity of bortezomib and blocked its inhibitory effect on 20S proteasome activity. Specifically, plasma collected from healthy volunteers taking 1 g/day vitamin C reduced bortezomib-induced MM cell death in vitro. This antagonistic effect of vitamin C against proteasome inhibitors is limited to the boronate class of inhibitors (bortezomib and MG262). In vivo activity of this combination treatment was then evaluated using our xenograft model of human MM in SCID (severe combined immune-deficient) mice. Bortezomib (0.1 mg/kg twice a week for 4 weeks) significantly inhibits in vivo MM cell growth, which was blocked by oral vitamin C (40 mg/kg/day). Therefore, our results for the first time show that vitamin C can significantly reduce the activity of bortezomib treatment in vivo; and importantly, suggest that patients receiving treatment with bortezomib should avoid taking vitamin C dietary supplements.

Bone marrow microenvironment and the identification of new targets for myeloma therapy

The development of multiple myeloma (MM) is a complex multi-step process involving both early and late genetic changes in the tumor cell as well as selective supportive conditions by the bone marrow (BM) microenvironment. Indeed, it is now well established that MM cell-induced disruption of the BM homeostasis between the highly organized cellular and extracellular compartments supports MM cell proliferation, survival, migration and drug resistance through activation of various signaling (for example, PI3K/Akt, JAK/Stat-, Raf/MEK/MAPK-, NFkappaB- and Wnt-) pathways. Based on our enhanced understanding of the functional importance of the MM BM microenvironment and its inter-relation with the MM cell resulting in homing, seeding, proliferation and survival, new molecular targets have been identified and derived treatment regimens in MM have already changed fundamentally during recent years. These agents include thalidomide, its immunomodulatory derivative lenalidomide and the proteasome inhibitor bortezomib, which mediate tumor cytotoxicity in the BM milieu. Ongoing studies are further delineating MM pathogenesis in the BM to enhance cytotoxicity, avoid drug resistance and improve patient outcome.

The evolving background for high-dose treatment for myeloma

In the constantly evolving field of myeloma, this special issue is slanted towards how the newer targeted treatments fit in with various transplantation strategies. High-dose treatment for myeloma with autologous stem cell transplantation started 25 years ago, with the consequence of producing complete remissions and a doubling of survival. Since then, its role has been refined and it has been accepted as standard treatment. The current challenge is to optimize its use into a background of the development, availability and regulatory approval of newer targeted therapies such as Thalidomide, Revlimid (Lenalidomide) and Velcade (Bortezomib). This special issue addresses these problems, and gives particular emphasis on the attainment of very long-term survival, with normal quality of life for patients with myeloma who do not necessarily need to be cured of their molecular disease, that is, they are 'operationally cured.' It is hoped that the reader will find the information in this issue useful in the day-to-day management of patients and we hope that this will also inspire new research directions designed to improve the outcome of patients with myeloma.

Biological pathways and in vivo antitumor activity induced by Atiprimod in myeloma

Atiprimod (Atip) is a novel oral agent with anti-inflammatory properties. Although its in vitro activity and effects on signaling in multiple myeloma (MM) have been previously reported, here we investigated its molecular and in vivo effects in MM. Gene expression analysis of MM cells identified downregulation of genes involved in adhesion, cell-signaling, cell cycle and bone morphogenetic protein (BMP) pathways and upregulation of genes implicated in apoptosis and bone development, following Atip treatment. The pathway analysis identified integrin, TGF-beta and FGF signaling as well as Wnt/beta-catenin, IGF1 and cell-cycle regulation networks as being most modulated by Atip treatment. We further evaluated its in vivo activity in three mouse models. The subcutaneous model confirmed its in vivo activity and established its dose; the SCID-hu model using INA-6 cells, confirmed its ability to overcome the protective effects of BM milieu; and the SCID-hu model using primary MM cells reconfirmed its activity in a model closest to human disease. Finally, we observed reduced number of osteoclasts and modulation of genes related to BMP pathways. Taken together, these data demonstrate the in vitro and in vivo antitumor activity of Atip, delineate potential molecular targets triggered by this agent, and provide a preclinical rational for its clinical evaluation in MM.

Targeted treatments to improve stem cell outcome: old and new drugs

Thalidomide, lenalidomide and bortezomib have been approved for the treatment of relapsed or refractory multiple myeloma in the recent years. These agents are now being increasingly integrated into therapeutic regimens for newly diagnosed patients. First data are available on the promising activity of these novel agents in induction therapy, as well as maintenance treatment to improve outcome after stem cell transplantation. Whether these early results will lead to prolonged overall survival and thereby ultimately redefine the role of stem cell transplantation in first-line treatment of multiple myeloma will be one of the most important questions to be answered in the coming years. Bone Marrow Transplantation (2007) 40, 1129-1137; doi:10.1038/sj.bmt.1705829; published online 3 September 2007.

A pivotal role for Mcl-1 in Bortezomib-induced apoptosis

Bortezomib is a proteasome inhibitor for the treatment of relapsed/refractory multiple myeloma (MM). Mechanisms of resistance to Bortezomib are undefined. Myeloid cell leukemia-1 (Mcl-1) is an antiapoptotic protein, which protects tumor cells against spontaneous and chemotherapy-induced apoptosis. In MM, specific downregulation of Mcl-1 induces apoptosis. Here, we examined the role of Mcl-1 in Bortezomib- and doxorubicin-induced apoptosis. We demonstrate that Bortezomib, but not doxorubicin, triggers caspase-dependent generation of a 28 kDa Mcl-1-fragment, in several MM cell lines, including MM.1S cells. Conversely, transient transfection of MM.1S cells with a previously reported 28 kDa Mcl-1(128-350) fragment, but not with the Mcl-1(1-127) fragment, induces apoptosis. Therefore, both downregulation of full-length antiapoptotic Mcl-1, as well as Bortezomib-induced generation of Mcl-1(128-350) cleaved protein, contribute to MM cell apoptosis. To verify further these findings, we next compared effects triggered by Bortezomib, doxorubicin and melphalan in Mcl-1(wt/wt) and Mcl-1(Delta/null) murine embryonic fibroblasts (MEFs). Our results show that Bortezomib, but not doxorubicin or melphalan, triggers Mcl-1 cleavage in Mcl-1(wt/wt), but not Mcl-1(Delta/null) MEFs and induces sub-G(1) phase cells; caspase-3 and -9, and PARP cleavage as well as morphological signs of apoptosis. Taken together, these results support an important role of Mcl-1 and a Mcl-1 fragment in Bortezomib-induced cell death in general, and in MM in particular. To prevent relapse of MM in patients treated with Bortezomib, we therefore recommend the combination of Bortezomib with agents that induce MM cell death independent of Mcl-1.

Novel etodolac analog SDX-308 (CEP-18082) induces cytotoxicity in multiple myeloma cells associated with inhibition of beta-catenin/TCF pathway

We have reported previously that R-enantiomer of etodolac (R-etodolac), which is under investigation in phase 2 clinical trials in chronic lymphocytic leukemia, induces potent cytotoxicity at clinically relevant concentrations in multiple myeloma (MM) cells. In this study, we demonstrated that SDX-308 (CEP-18082), a novel analog of etodolac, has more potent cytotoxicity than R-etodolac against both MM cell lines and patient MM cells, including tumor cells resistant to conventional (dexamethasone, doxorubicine, melphalan) and novel (bortezomib) therapies. SDX-308-induced cytotoxicity is triggered by caspase-8/9/3 activation and poly (ADP-ribose) polymerase cleavage, followed by apoptosis. SDX-308 significantly inhibits beta-catenin/T-cell factor pathway by inhibiting nuclear translocation of beta-catenin, thereby downregulating transcription and expression of downstream target proteins including myc and survivin. Neither interleukin-6 nor insulin-like growth factor-1 protect against growth inhibition triggered by SDX-308. Importantly, growth of MM cells adherent to bone marrow (BM) stromal cells is also significantly inhibited by SDX-308. Our data therefore indicate that the novel etodolac analog SDX-308 can target MM cells in the BM milieu.

Bortezomib as an antitumor agent

The ubiquitin-proteasome pathway (UPP) is the major non-lysosomal proteolytic system in the cytosol and nucleus of all eukaryotic cells. Bortezomib (also known as PS-341 and Velcade) is a proteasome inhibitor, a novel class of cancer therapies. Bortezomib blocks multi-ubiquitinated protein degradation by inhibiting 26S proteasome activity, including regulating cell cycle, anti-apoptosis, and inflammation, as well as immune surveillance. In multiple myeloma (MM) cells, bortezomib directly induces cell stress response followed by activation of c-Jun NH(2) terminal kinase (JNK)/stress-activated protein kinase (SAPK), and triggers caspase-dependent apoptosis of tumor cells. Recent clinical studies demonstrated that bortezomib had remarkable anti-tumor activity in refractory and relapsed MM, providing the basis to approval by FDA. Its anti-tumor activities earlier in the course, in combination therapies, and in other malignancies is ongoing.

A novel proteasome inhibitor NPI-0052 as an anticancer therapy

Proteasome inhibitor Bortezomib/Velcade has emerged as an effective anticancer therapy for the treatment of relapsed and/or refractory multiple myeloma (MM), but prolonged treatment can be associated with toxicity and development of drug resistance. In this review, we discuss the recent discovery of a novel proteasome inhibitor, NPI-0052, that is distinct from Bortezomib in its chemical structure, mechanisms of action, and effects on proteasomal activities; most importantly, it overcomes resistance to conventional and Bortezomib therapies. In vivo studies using human MM xenografts shows that NPI-0052 is well tolerated, prolongs survival, and reduces tumour recurrence. These preclinical studies provided the basis for Phase-I clinical trial of NPI-0052 in relapsed/refractory MM patients.

Bortezomib appears to overcome the poor prognosis conferred by chromosome 13 deletion in phase 2 and 3 trials

In multiple myeloma, deletion of chromosome 13 (del(13)) is associated with poor prognosis regardless of treatment. This study analyzed the impact of del(13) status on response and survival following treatment with either bortezomib or high-dose dexamethasone in patients in the SUMMIT and APEX trials. Additionally, matched-pairs subset analyses were conducted of patients with and without del(13), balanced for age and International Staging System parameters. In both SUMMIT and APEX, prognosis appeared to be poorer in bortezomib-treated patients with del(13) compared with patients with no del(13) by metaphase cytogenetics. In the SUMMIT and APEX matched-pairs analysis, response and survival appeared comparable in bortezomib-treated patients with or without del(13) by metaphase cytogenetics. However, patients with del(13) receiving dexamethasone in APEX appeared to have markedly decreased survival compared with those without del(13) by metaphase cytogenetics. These matched-pairs analyses suggest that bortezomib may overcome some of the poor impact of del(13) as an independent prognostic factor. However, sample sizes were very small; these findings require confirmation from further studies.

Inhibition of p38alpha MAPK enhances proteasome inhibitor-induced apoptosis of myeloma cells by modulating Hsp27, Bcl-X(L), Mcl-1 and p53 levels in vitro and inhibits tumor growth in vivo

Inhibition of p38 kinase blocks the production of tumor-promoting factors in the multiple myeloma (MM) bone marrow microenvironment. Proteasome inhibitors MG132 and bortezomib have been shown to have direct cytotoxic effects on MM cells. We show that a selective inhibitor of p38alpha, SCIO-469, enhances the ability of MG132 and bortezomib to induce the apoptosis of MM cells. Previously, we showed that p38 inhibition with SCIO-469 enhances MM cytotoxicity of bortezomib by inhibiting the transient expression and phosphorylation of Hsp27, a downstream target of p38. Here we show that continued treatment of MM cells with bortezomib leads to a SCIO-469-enhanced downregulation of Hsp27 and to increased MM apoptosis. Furthermore, we show that p38 inhibition enhances the bortezomib-induced MM apoptosis by upregulation of p53 and downregulation of Bcl-X(L) and Mcl-1. In a mouse xenograft plasmacytoma model of MM, we found that inhibiting p38 augments the effects of bortezomib in decreasing MM tumor growth in vivo. Thus, in addition to its role in suppressing an activated MM microenvironment, co-treatment with a p38 inhibitor, such as SCIO-469, may enhance the cytotoxicity of bortezomib by modulating pro-apoptotic and anti-apoptotic factors in MM cells, suggesting great potential for co-therapy.

A novel Bcl-2/Bcl-X(L)/Bcl-w inhibitor ABT-737 as therapy in multiple myeloma

Bcl-2 or Bcl-X(L) confers resistance to chemotherapy in multiple myeloma (MM). Here we characterized the effects of ABT-737, a potent small-molecule inhibitor of antiapoptotic proteins Bcl-2, Bcl-X(L) and Bcl-w with markedly higher affinity than previously reported compounds, on human MM cells. ABT-737 induces apoptosis in MM cells, including those resistant to conventional therapy. Examination of purified patient MM cells demonstrated similar results, without significant toxicity against normal peripheral blood mononuclear cells and MM bone marrow stromal cells. Importantly, ABT-737 decreases the viability of bortezomib-, dexamethasone-(Dex) and thalidomide-refractory patient MM cells. Additionally, ABT-737 abrogates MM cell growth triggered by interleukin-6 or insulin-like growth factor-1. Mechanistic studies show that ABT-737-induced apoptosis is associated with activation of caspase-8, caspase-9 and caspase-3, followed by poly(ADP-ribose) polymerase cleavage. Combining ABT-737 with proteasome inhibitor bortezomib, melphalan or dexamethasone induces additive anti-MM activity. Taken together, our study provides the rationale for clinical protocols evaluating ABT-737, alone and together with botezomib, mephalan or dexamethasone, to enhance MM cell killing, overcome drug resistance conferred by Bcl-2 and improve patient outcome in MM.