SummaryThere is a significant unmet need in effective therapy for relapsed myeloma patients once they become refractory to bortezomib and lenalidomide. While data from the front line setting suggest bendamustine is superior to melphalan, there is no information defining optimal bendamustine dose in multiply-treated patients. We report a multi-centre randomized two-stage phase 2 trial simultaneously assessing deliverability and activity of two doses of bendamustine (60 mg/m 2 vs. 100 mg/m 2 ) days 1 and 8, thalidomide (100 mg) days 1-21 and low dose dexamethasone (20 mg) days 1, 8, 15 and 22 of a 28-d cycle. Ninety-four relapsing patients were treated on trial, with a median three prior treatment lines. A pre-planned interim deliverability and activity assessment led to closure of the 100 mg/m 2 arm due to excess cytopenias, and led to amendment of entry criteria for cytopenias. Non-haematological toxicities including thromboembolism and neurotoxicity were infrequent. In the 60 mg/m 2 arm, treatment was deliverable in 61Á1% subjects and the partial response rate was 46Á3% in the study eligible population, with 7Á5 months progression-free survival. This study demonstrates bendamustine at 60 mg/m 2 twice per month with thalidomide and dexamethasone is deliverable for repeated cycles in heavily pretreated myeloma patients and has substantial clinical activity.

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Introduction: Histone deacetylase inhibitors (HDACis) have demonstrated clinical efficacy in multiple myeloma, particularly in combination with proteasome inhibitors. CHR-3996 is a class 1 selective HDACi with potent anti-myeloma activity in vitro. Aminopeptidase inhibitors act downstream of the proteasome and prevent breakdown of proteasome generated peptides into amino acids. Synergistic cytotoxicity was observed in vitro when CHR-3996 was combined with the aminopeptidase inhibitor, tosedostat through rapid activation of NFkB followed by increased expression of the repressors IκBα, A20, CYLD, BIRC3. The MUK-three study was designed to translate these pre-clinical findings into a phase 1 clinical trial. This dose escalation study aimed to determine the maximum tolerated dose, safety and preliminary activity of CHR-3996 administered in combination with Tosedostat for patients with relapsed, refractory MM. Here we present the final study results. Methods: MUK-three was an open label multi-centre UK Phase I/IIa trial for patients with relapsed and relapsed/ refractory myeloma who had failed conventional treatments. Patients were permitted to meet the haematological entry criteria using growth factor and/or blood product support. During dose escalation subjects received CHR-3996 (20-40mg days1-28) and Tosedostat (0-60mg days 1-28) (Table 1) every 28 day cycle until disease progression or withdrawal. Dose limiting toxicities (DLTs) were evaluated during cycle 1 and dose escalation followed the 3+3 design. Responses were assessed using modified IMWG uniform response criteria, with the primary endpoint for the expansion phase of stable disease (SD) rate after 4 cycles of therapy. Toxicity was graded by CTCAE V4.0. Results: The trial was open to recruitment from July 2012 to December 2015. 20 patients were treated during dose escalation, including 8 at the recommended dose (RD) and 12 at dose levels (DL) 1-3. Only 1 DLT was observed at DL3 (grade 4 thrombocytopenia); however, this DL was deemed not tolerable due to the high incidence of low grade gastrointestinal toxicities. Hence the RD was determined as DL3b, CHR-3996 20mg and Tosedostat 60mg. A further 2 patients were treated at RD during dose expansion to make the required 10 patients for the protocol defined initial analysis at which point the trial closed. At the RD (n=10) median age was 63 years (range 47-73). 80% of patients had received at least 4 prior lines of therapy (median 4, range 2-9); 50% were ISS II, 30% ISS III; 4/6 patients with evaluable FISH data had 1q gain. The median time from diagnosis to treatment for the overall population was 85.3 months (27.5-198.8). The median number of cycles received was 2.5 (range 2-8) and 2 patients remain on treatment with 8 stopped due to disease progression. The 2 patients ongoing (received 5 & 9 prior lines) had their schedule adjusted to a 5 day a week dosing to further improve tolerability. Both had a clinical response (1MR, 1PR) and remained progression free at 6 months. 3/10 patients had SD after 4 cycles, the overall response rate (≥PR) was 1/10(10%) and the clinical benefit rate (≥MR) 2/10 (20%). Overall outcomes were: PR 10%, MR 10%, and SD 30%. Median time to maximum response was 1.84 months (95% CI [1.09, 8.65]). Toxicities at the RD were manageable, 30% of patients required a dose reduction. 22 serious adverse events were reported in 16 patients across all doses, mainly infections (10/22, 45.5%). The commonest grade 3-4 toxicities reported for all 22 patients were: platelet count decrease (12, 54.5%), white blood cell decreased (6, 27.2%), diarrhoea (5, 22.7%). The most frequent grade 1-2 toxicities were fatigue (15, 68.2%), nausea (14, 63.3 %), anorexia (14, 63.6%), anaemia (13, 59.1%). 1 patient withdrew due to toxicity, and there were no treatment related deaths. Conclusions: This study demonstrated that the novel combination of CHR-3996 and tosedostat was safe and tolerable in multiply relapsed, refractory myeloma patients many of which had poor bone marrow function. The recommended dose of the combination was 20mg and 60mg, respectively. Following further adjustment to an intermittent 5 day/ week dosing schedule, treatment was well tolerated and clinical benefit observed. This suggests that further evaluation of this novel combination is warranted. Acknowledgments: This trial was part of the Myeloma UK Clinical Trial Network, ISRCTN: 24989786. Disclosures Williams: Novartis: Honoraria; Janssen: Honoraria, Other: Travel support, Speakers Bureau; Celgene: Honoraria, Other: Travel support, Speakers Bureau; Takeda: Honoraria, Other: Travel support, Speakers Bureau; Amgen: Honoraria, Speakers Bureau. Yong:Autolus Ltd: Equity Ownership, Patents & Royalties: APRIL based chimeric antigen receptor; Janssen: Research Funding. Cook:Takeda Oncology: Consultancy, Research Funding, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Sanofi: Consultancy, Speakers Bureau; Glycomimetics: Consultancy; Celgene: Consultancy, Research Funding, Speakers Bureau; Janssen: Consultancy, Research Funding, Speakers Bureau. Jenner:Amgen: Consultancy, Honoraria, Other: Travel support; Takeda: Consultancy, Honoraria, Other: Travel support; Janssen: Consultancy, Honoraria, Other: Travel support, Research Funding; Novartis: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding. Morgan:Univ of AR for Medical Sciences: Employment; Bristol Meyers: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Janssen: Research Funding; Celgene: Consultancy, Honoraria, Research Funding. Davies:Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Takeda: Consultancy, Honoraria.

Introduction: Bortezomib (Velcade) and dexamethasone is a standard combination for relapsed myeloma. Both in vitro data and initial clinical trials signalled the efficacy of the combination of intravenous bortezomib and the oral histone deacetylase inhibitor vorinostat. Although the randomised phase 3 VANTAGE 088 trial identified an improvement in progression free survival with the combination of bortezomib and vorinostat compared to bortezomib monotherapy in relapsed myeloma, 50% of patients in the vorinostat group had at least one dose reduction compared with 25% in the placebo group, with potential impact on clinical outcomes. Subcutaneous bortezomib has now become the standard route of administration because of lower rates of peripheral neuropathy. MUK four is a single arm phase 2 multi-centre UK trial to evaluate the toxicity profile and efficacy of an alternative dosing schedule of vorinostat in combination with subcutaneous bortezomib and oral dexamethasone. We report the final analysis of toxicity and response data. Methods: Patients with relapsed myeloma treated with 1-3 prior lines of therapy received up to 8 cycles of V2 D (bortezomib 1.3 mg/m2 subcutaneously days 1, 4, 8 and 11, vorinostat 400 mg orally days 1-4, 8-11 and 15-18 and dexamethasone 20 mg orally days 1, 2, 4, 5, 8, 9, 11 and 12 of a 21 day cycle). Following completion of a minimum of 3 cycles of V2 D, participants received maintenance vorinostat (400 mg days 1-4 and 15-18 of a 28 day cycle) until disease progression, intolerance or participant withdrawal. Responses were assessed using the modified IMWG response criteria and toxicities graded using CTCAE v4.0. Results: Between August 2013 and November 2014, 16 participants were recruited to MUK four. Median age was 69.5 years (range 50.0-78.0) and median lines of prior treatment was 1 (1-3). Prior treatment included thalidomide-based combinations in 13/16 (81.3%), bortezomib-based in 7/16 (43.8%) and lenalidomide-based in 2/16 (12.5%). 9/16 (56.3%) participants had received prior high dose melphalan ASCT. Median time from diagnosis was 38.6 months (9.3-120.4). At analysis in June 2015 8/16 (50%) participants continued on maintenance vorinostat. All 16 patients were evaluable for response within the first 8 cycles of V2 D. Overall response rate was 81.3% (13/16, 95% CI [55.4-96.0]) consisting of CR in 4/16 (25.0%), VGPR 2/16 (12.5%) and PR in 7/16 (43.8%). The remaining 3/16 (18.8%) achieved MR giving a clinical benefit response rate of 16/16 (100%). Participants received a median of 6 cycles of initial treatment with 6/16 (37.5%) receiving all 8 cycles. Treatment was discontinued in 4/8 (50%) because of disease progression, in 2/8 (25%) because of toxicity and in 2/8 (25%) for clinician discretion. Overall 12/16 (75%) participants experienced a dose reduction of either vorinostat or bortezomib or terminated treatment early as a result of toxicity. 11/16 (68.8%) reduced vorinostat and 10/16 (62.5%) reduced bortezomib. The most frequent grade 2 toxicities during the first 8 cycles were fatigue in 8/16 (50%), anaemia in 7/16 (43.8%), diarrhoea in 5/16 (31.3%), nausea in 4/16 (25.0%) and peripheral neuropathy in 4/16 (25.0%). The most frequent grade 3-4 toxicities encountered during the first 8 cycles were thrombocytopenia in 8/16 (50%), anaemia in 1/16 (6.3%), diarrhoea in 1/16 (6.3%) and fatigue in 1/16 (6.3%). During maintenance vorinostat only 1 participant experienced an adverse reaction above grade 2 (grade 3 neutropenia). Conclusion: Bortezomib, vorinostat and dexamethasone is a highly effective combination in relapsed myeloma with good response rates. Maintenance vorinostat is well tolerated. Although toxicity and dose reductions are observed with combination therapy, this study demonstrates that the combination of proteasome inhibitor, HDAC inhibitor and dexamethasone offers promise. Further data on PFS will be presented. Disclosures Jenner: Amgen: Honoraria; Takeda: Honoraria. Off Label Use: Vorinostat for treatment of myeloma. Pawlyn:Celgene: Honoraria, Other: Travel support; The Institute of Cancer Research: Employment. Williams:Celgene: Consultancy, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Takeda: Consultancy, Speakers Bureau. Davies:Array-Biopharma: Membership on an entity's Board of Directors or advisory committees; Takeda-Millennium: Membership on an entity's Board of Directors or advisory committees; University of Arkansas for Medical Sciences: Employment; Onyx-Amgen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees.