Ricolinostat (ACY-1215), the First Selective HDAC6 Inhibitor, Combines Safely with Pomalidomide and Dexamethasone and Shows Promosing Early Results in Relapsed-and-Refractory Myeloma (ACE-MM-102 Study)

Background:

Ricolinostat, an oral selective HDAC6 inhibitor, is well tolerated as monotherapy (Raje Blood 2012;120:4061) and demonstrates potent synergistic activity with lenalidomide (Len) and pomalidomide (Pom) in preclinical models (Quayle Blood 2013;122:1952).  In an ongoing trial of ricolinostat in combination with Len and dexamethasone (Dex) in patients with relapsed or refractory multiple myeloma (MM), no dose limiting toxicities (DLTs) were observed at up to doses of 160 mg BID, with excellent activity and tolerability (Yee Blood 2014;124:4772).  Pan-HDAC inhibitors vorinostat and panobinostat are active in MM in combination with bortezomib (Btz) and Len, but toxicities (thrombocytopenia, fatigue, and GI events) limit dosing exposure.  This trial explores activity of ricolinostat in combination with Pom and Dex in a patient population comparable to that in MM-003 (San Miguel Lancet Oncol 2013;14:1055-66).  At the time of achieving the primary endpoint of PFS in MM-003, the ORR was 16.6% at 18.1 weeks median follow-up (EMA Pom Celgene Assessment Report EMA/CHMP/427059/2013), and was 31% at 10 months in the same clinical trial (San Miguel Lancet Oncol 2013;14:1055-66).

Methods:

Phase 1b was a 3+3 design which explored ricolinostat 160 mg QD or BID combined with Pom (4 mg) for 21 days of a 28 day cycle with Dex (40 mg) on days 1, 8, 15 and 22.  Patients had measurable disease, adequate BM reserve and hepatic function with CrCl ≥45 mL/min.  Refractory was defined as PD on or within 60 days of last therapy.  Patients with non-secretory MM, prior Pom or HDAC inhibitor therapy were excluded.  Peripheral blood samples were obtained for PK/PD assessment of acetylated tubulin and histones.  Patients with serum FLC only disease were excluded from Phase 2.  The dose level of 160 mg dose was chosen based on prior experience in which PK plateau was reached at 160 mg of ricolinostat.  A sample size of 66 was determined to be adequate to detect an ORR of 44% against a historical rate of 29%.  

Results:

7 patients were treated in phase 1b: 3 at 160 mg QD and 4 at 160 mg BID.  No DLTs were observed; however, all 4 patients had grade 2 diarrhea in the 160 mg BID cohort and grade 3 fatigue and grade 3 or 4 neutropenia attributed to Pom were reported in patients in phase 1b.  1 patient remained on study for 12 cycles before PD; the other 6 Phase 1b patients were withdrawn for PD at 2-4 cycles.  Following safety review committee (SRC) review, phase 2 opened at a dose of 160 mg BID, with a predetermined SRC review to occur after 6 patients had completed 1 cycle of therapy.  3 of the 6 patients had clinically relevant diarrhea requiring ricolinostat dose reduction to 160 mg QD in cycle 2 leading to SRC recommendation of QD dosing of ricolinostat.  As of April 28, 2015 39 phase 2 patients were evaluable for safety and 28 evaluable for response.  Median age was 68 and median number of prior regimens was 4 (2-9) in 3 (2-6) line of therapy.  37 patients were refractory to Len as defined in the entry criteria.  Common toxicities were predominantly low grade and included fatigue (40%), diarrhea (38%), neutropenia (36%), anemia (31%), thrombocytopenia (26%), and constipation (21%).  Important grade 3/4 related toxicities included neutropenia (5 patients, 13%) and diarrhea (3 patients, 8%).  PK of ricolinostat was similar to that observed in combination with Btz and Len.  There was no evidence of ricolinostat accumulation or drug-drug interaction with Pom.  Median follow-up of 12 (4-32) weeks; ORR (≥PR) was 29% with 3 VGPR and clinical benefit rate (≥MR) was 50% with 68% SD or better for the 28 response evaluable patients.  Updated safety and efficacy data will be presented as enrollment continues and data matures including for the 49 patients enrolled in phase 2 to date.

Conclusion:

These early data with a median follow-up of 12 weeks (compared to historical control of 16.6% ORR at 18.1 weeks for Pom/Dex alone in MM-003) in a rigorously defined patient population suggest that selective HDAC6 inhibition is associated with encouraging tolerability and promising clinical activity.  Accrual is continuing in US, Canada, and Europe.  Overall, ricolinostat is an active and safe oral agent which combines favorably with Pom and Dex in relapsed-and-refractory MM.