Ricolinostat (ACY-1215), the First Selective HDAC6 Inhibitor, in Combination with Bortezomib and Dexamethasone in Patients with Relapsed or Relapsed-and-Refractory Multiple Myeloma: Phase 1b Results (ACY-100 Study)

Background:

Ricolinostat, an oral selective HDAC6 inhibitor, is well tolerated as monotherapy (Raje Blood 2012;120:4061). HDAC6 inhibition impairs the aggresome/autophagy pathway, an alternate pathway to proteasome clearance of misfolded proteins (Santo Blood 2012;119:2578-89) providing the rationale for combining ricolinostat with bortezomib (Btz). Pan-HDAC inhibitors vorinostat and panobinostat are active in multiple myeloma (MM) in combo with Btz, but toxicities (thrombocytopenia, fatigue, and GI events) limit dosing exposure. This trial explores activity of ricolinostat in combo with Btz and dexamethasone (Dex) in patients with relapsed or relapsed-and-refractory MM.

Methods:

Phase 1b was a 3+3 design that explored ricolinostat combined with Btz (1.0-1.3 mg/m² IV or SQ on days 1, 4, 8, 11) and Dex (20 mg PO on days 1, 2, 4, 5, 8, 9, 11, 12). Patients previously received at least 2 lines of therapy including a proteasome inhibitor and an immunomodulatory agent, had either progressed after or were ineligible for autologous stem cell transplant, and had adequate BM reserve, hepatic function and CrCl ≥30 mL/min. Patients with prior HDAC inhibitor therapy were excluded. Peripheral blood samples were obtained for PK/PD assessment of acetylated tubulin and histones.

Results:

50 patients were enrolled to 8 combination dose cohorts to date. Median age was 65, median number of prior regimens was 5 (2-12) and 33 patients were refractory to Btz. The first combination cohort was expanded due to a DLT of asymptomatic increase in amylase. No other DLTs have been observed in the cohort escalations. Common toxicities were predominately low grade (grade 1/2) and included diarrhea (46%), anemia (38%), thrombocytopenia (22%), increased creatinine (18%), fatigue (16%), and nausea (16%). Important grade 3/4 related toxicity included thrombocytopenia (9 patients, 18%) and anemia (6 patients, 12%).

Cohorts were expanded sequentially at two dose levels: 160 mg BID and 160 mg QD. Of the 22 patients receiving ricolinostat 160 mg BID common toxicities were diarrhea (68%, grade 1/2), thrombocytopenia (50%, grade 3/4), anemia (45%, grade 2/3), fatigue (36%, grade 1/2), and nausea (36%, grade 1/2). There was a marked increase in the incidence of SAEs related to diarrhea leading to dehydration and hospitalization (27%). Therefore a second cohort expansion at 160 mg QD was initiated. Of the 15 patients receiving ricolinostat at 160 or 240 mg QD common toxicities were diarrhea (33%, grade 1/2), thrombocytopenia (20%, grade 4), anemia (20%, grade 3), increased creatinine (20%, grade 3), hyponatremia (20%, grade 1), and increased ALT (20% grade 3), and peripheral neuropathy (20%, grade 1/2).

PK for ricolinostat is similar to that observed in Phase 1a monotherapy, indicating that co-administration of Btz does not significantly impact ricolinostat exposure. Maximal blood levels of ricolinostat were ≥0.5 µM at ≥80 mg correlating with a >2x increase in the HDAC6 PD marker acetylated tubulin.

48 patients were evaluable for response with median follow-up of 3 (1-18) months; ORR (≥PR) was 39% and clinical benefit rate (≥MR) was 44% with 81% SD or better. Of the 22 patients receiving ricolinostat 160 mg BID with median follow-up of 3 (1-18) months, ORR (≥PR) was 32% and clinical benefit rate (≥MR) was 41% with 62% SD or better. Of the 12 patients receiving ricolinostat at 160 or 240 mg QD with median follow-up of 4 (1-8) months, ORR (≥PR) was 33% and clinical benefit rate (≥MR) was 33% with 67% SD or better. Of the 33 Btz refractory patients, 42% had SD or better, and 12% responded including 1 VGPR.

Conclusion:

Overall, ricolinostat in combination with Btz and Dex was well tolerated. Diarrhea and hematologic toxicity, mostly low grade, was less prevalent with QD than BID dosing and led to fewer hospitalizations and early treatment discontinuation. Response rates were similar between both QD and BID dosing. 160 mg QD is the recommended dose in combination with Btz and Dex.