Bortezomib, a proteasome inhibitor with efficacy in multiple myeloma, is associated with thrombocytopenia, the cause and kinetics of which are different from those of standard cytotoxic agents. We assessed the frequency, kinetics, and mechanism of thrombocytopenia following treatment with bortezomib 1.3 mg/m 2 in 228 patients with relapsed and/or refractory myeloma in 2 phase 2 trials. The mean platelet count decreased by approximately 60% during treatment but recovered rapidly between treatments in a cyclic fashion. Among responders, the pretreatment platelet count increased significantly during subsequent cycles of therapy. The mean percent reduction in platelets was independent of baseline platelet count, M-protein concentration, and marrow plasmacytosis. Plasma thrombopoietin levels inversely correlated with platelet count. Murine studies demonstrated a reduction in peripheral platelet count following a single bortezomib dose without negative effects on megakaryocytic cellularity, ploidy, or morphology. These data suggest that bortezomib-induced thrombocytopenia is due to a reversible effect on megakaryocytic function rather than a direct cytotoxic effect on megakaryocytes or their progenitors. The exact mechanism underlying bortezomib-induced thrombocytopenia remains unknown but it is unlikely to be related to marrow injury or decreased thrombopoietin production. (Blood. 2005; 106:3777-3784)

• Lenalidomide-bortezomibdexamethasone resulted in partial response or better in nearly two-thirds of relapsed/ refractory myeloma patients.• The regimen had substantial activity despite high rates of prior bortezomib/thalidomide and regardless of poor prognostic characteristics.In this prospective, multicenter, phase 2 study, 64 patients with relapsed or relapsed and refractory multiple myeloma (MM) received up to 8 21-day cycles of bortezomib 1.0 mg/m 2 (days 1, 4, 8, and 11), lenalidomide 15 mg/day (days 1-14), and dexamethasone 40/20 mg/day (cycles 1-4) and 20/10 mg/day (cycles 5-8) (days of/after bortezomib dosing). Responding patients could receive maintenance therapy. Median age was 65 years; 66% were male, 58% had relapsed and 42% had relapsed and refractory MM, and 53%, 75%, and 6% had received prior bortezomib, thalidomide, and lenalidomide, respectively. Forty-eight of 64 patients (75%; 90% confidence interval, 65-84) were alive without progressive disease at 6 months (primary end point). The rate of partial response or better was 64%; median duration of response was 8.7 months. Median progression-free and overall survivals were 9.5 and 30 months, respectively (median follow-up: 44 months). Common treatment-related toxicities included sensory neuropathy (53%), fatigue (50%), and neutropenia (42%); common grade 3/4 treatment-related toxicities included neutropenia (30%), thrombocytopenia (22%), and lymphopenia (11%). Grade 3 motor neuropathy was reported in 2 patients. Lenalidomidebortezomib-dexamethasone appears effective and tolerable in patients with relapsed or relapsed and refractory MM, demonstrating substantial activity among patients with diverse prior therapies and adverse prognostic characteristics. This trial is registered with

Background: Preclinical work from our group and others has demonstrated that the combination of a farnesyl transferase inhibitor (FTI) and the proteasome inhibitor bortezomib results in enhanced plasma cell apoptosis and is associated with AKT activation (David, Blood 2005). More recently, further preclinical data suggests that the mechanism responsible for this profound synergy is due to inhibition of HDAC6 with a resultant inhibition of both the proteasome and aggresome pathway (David ASH 2007). Based upon these observations, with the MMRC we initiated a phase I trial combining the FTI tipifarnib with bortezomib to clinically evaluate the efficacy of this combination. Methods: Patients with relapsed or refractory myeloma were treated with bortezomib at 1.0 mg/m2 given on days 1,4,8, and 11 in conjunction with escalating doses of tipifarnib (100–400mg/BID) given on days 2–15 every 21 days. Dose escalation was accomplished using an adaptive phase I design (Escalation With Overdose Control (EWOC)). Eligibility criteria included a serum creatinine of <2.5, normal liver function, ANC>500, and platelets >25. If dose escalation is able to proceed to 400mg of tipifarnib with 1.0 mg/m2, the tipifarnib dose escalation will restart with bortezomib given at 1.3 mg/m2. Results: Sixteen patients have been enrolled to date into respective tipifarnib dose levels 100 mg(n=6),200mg (n=5) and 300mg (n=5). Median age for the enrolled patients is 59 (range 43–76) and median time from myeloma diagnosis was 4.7 years. 15/16 patients had received prior high dose therapy. The average number of prior therapies was 4.5, and of the16 patients, 8 were refractory to prior bortezomib (relapsed on therapy or within 6 months) 4 were bortezomib naïve, and 4 were previously exposed to bortezomib but not known to be refractory. Among these patients with advanced myeloma and refractory disease, stabilization of disease or better was seen among 7/16 patients with 2 of the 7 achieving an MR. Of note, among the patients achieving clinical benefit, 1 patient had a stable M-protein, but experienced an 80% reduction in circulating plasma cells while on therapy, and another has had a 75% reduction in the free light chain assay. The most common drug related side effects were was Gr2 diarrhea (23.5%). Hematologic toxicities were difficult to ascertain as patients had advanced myeloma and many were entered onto study with platelet counts between 25 and 50. Additional grade 3 toxicities included renal insufficiency (related to progression), pneumonia and altered mental status which were all considered unrelated to study drug, but were associated with progression of disease. There were no Grade 3 –5 drug related toxicities. There were no cardiac events or DVT, and 1 patient experienced grade 2 peripheral neuropathy who did not have pre existing PN at baseline. Conclusions: The combination of bortezomib and tipifarnib is supported by preclinical rationale and has produced stable disease or better among a group of patients with refractory and advanced myeloma. To date the optimal dose of both tipifarnib and bortezomib have yet to be defined, and additional patients will be enrolled to define the MTD for tipifarnib with 1.0mg/m2 of bortezomib, followed by escalation of tipifarnib with 1.3mg/m2 of bortezomib. Correlative studies evaluating the effect of the combination on HDAC6 and plasma cell apoptosis will be presented.

3034 Background: The combination of lenalidomide (R), bortezomib (V), and dexamethasone (D) (RVD) in newly diagnosed MM patients is well tolerated and associated with a very high overall response rate. The goal of the current trial is to improve on the CR rate compared with RVD by adding a novel targeted agent. Preclinical studies have demonstrated that vorinostat (Vor), an HDAC inhibitor, is synergistic with bortezomib, immunomodulatory (IMiD®) compounds and dexamethasone. Clinical studies in the relapsed setting using either bortezomib or lenalidomide with vorinostat have yielded promising results with manageable toxicity. The aim of this study is to determine the tolerability and preliminary efficacy of the combination of RVD with vorinostat in newly diagnosed patients with symptomatic MM. Methods: Patients (Pts) received the current standard RVD regimen (lenalidomide 25 mg days 1–14, bortezomib 1.3 mg/m2 days 1, 4, 8, 11 and dexamethasone 20/10 mg PO [cycles 1–4/5-8] days 1, 2, 4, 5, 8, 9, 11, 12 for up to 8 21 day cycles) combined with oral vorinostat (Vor), provided by Merck and Co. Inc., at 100, 200, 300 or 400 mg daily days 1 – 14 of each cycle. Pts were assigned to one of the four dosing cohorts according to the Bayesian Escalation with Overdose Control (EWOC) algorithm. DLT (≥ G3 non hematologic toxicity, G4 hematologic toxicities defined as G4 thrombocytopenia of any duration; failure of recovery of ANC to ≥1,000/μL or platelets to ≥50,000/μL within 14 days of the last treatment; or inability to receive Day 1 dose for Cycle 2 due to continued drug-related toxicity from cycle 1) was determined in the first cycle of therapy. Toxicities were assessed and graded for all cycles using the NCI CTCAE v 3.0. Responses were assessed by modified EBMT and Uniform criteria. Pts with PR or better could proceed to autologous transplant after ≥ 4 cycles. Results: Eleven pts (median age 54, 82% men, 54.5% ISS Stage II/III) have been enrolled to date with n=4 pts each in cohorts 1 (Vor 100mg) and 2 (Vor 200mg), and 3 pts in cohort 3 (Vor 300 mg). One patient has completed 8 cycles, 1 pt completed 4 cycles and proceeded to transplant, 6 pts remain on study treatment and 3 pts have discontinued therapy (1 for significant peripheral neuropathy {grade 3}, 1 for patient choice unrelated to toxicity and 1 for non adherence). Two DLTs have occurred: syncope (cohort 1) and asymptomatic grade 3 elevation of ALT (cohort 2) with none in cohort 3.The episode of syncope was not related to cardiac arrhythmia. One study related SAE has occurred (syncope). One other episode of grade 3 elevation of ALT occurred in a pt in cycle 3 in cohort 1. Both episodes of increased ALT resolved and patients remained on study with dose modification. One patient developed grade 3 diarrhea in cohort 1. No patients have developed a grade 4 toxicity. Treatment emergent peripheral neuropathy occurred in 6 patients (4 grade 1, 1 grade 2 and 1 grade 3). No episodes of study related grade 3 fatigue, nausea, or vomiting have occurred. The MTD has not been reached. Eight patients are evaluable for response. All have responded to study therapy with 3 CRs, 1 VGPR and 4 PRs. Three patients went on to stem cell collection after 4 cycles and all collected an adequate dose for transplant of >5 ×106 CD34+ cells/kg. Conclusion: The combination of RVD with vorinostat has been generally well tolerated to date. No unexpected toxicity has been noted with side effects commensurate with prior experience with each of the drugs and no additive toxicity seen to date. While asymptomatic elevation of ALT has been seen and will require ongoing monitoring, grade 3 ALT elevation was a DLT in the original RVD study and related to dexamethasone, so may not be related to the addition of vorinostat. Early efficacy data is promising with 50% of patients achieving a VGPR or higher. Accrual is ongoing to determine the MTD. Disclosures: Kaufman: Celgene, Millenium: Consultancy; Celgene, Merck: Research Funding. Off Label Use: Use of lenalidomide as upfront therapy. Use of vorinostat as upfront therapy. Shah:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium Pharmaceuticals, Inc.: Research Funding; Novartis: Research Funding. Heffner:Millenium: Consultancy, Honoraria, Research Funding. Richardson:Celgene: Membership on an entity's Board of Directors or advisory committees; Millennium: Membership on an entity's Board of Directors or advisory committees; Johnson & Johnson: Membership on an entity's Board of Directors or advisory committees. Orlowski:Celgene: Consultancy, Research Funding; Millenium: Consultancy, Research Funding. Lonial:Millennium: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; BMS: Consultancy, Speakers Bureau.

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