ACY-241, a Novel, HDAC6 Selective Inhibitor: Synergy with Immunomodulatory (IMiD®) Drugs in Multiple Myeloma (MM) Cells and Early Clinical Results (ACE-MM-200 Study)
Authors: Niesvizky Ruben , Richardson Paul G. , Gabrail Nashat Y. , Madan Sumit , Yee Andrew J. , Quayle Steven N , Almeciga-Pinto Ingrid , Jones Simon S , Houston Lee , Hayes Denise , Van Duzer John , Wheeler Catherine , Trede Nikolaus S. , Raje Noopur S. 
Published: October 2019

Abstract
Histone deacetylase (HDAC) enzymes are attractive therapeutic targets in oncology, but non-selective HDAC inhibitors have led to dose-limiting toxicities in patients, particularly in combination with other therapeutic agents. Ricolinostat (ACY-1215), a first-in-class orally available HDAC inhibitor that is 11-fold selective for HDAC6, synergizes in vitro and in vivo in models of MM and lymphoma with bortezomib (Santo, Blood, 2012; Amengual, Clin Cancer Res, 2015) or carfilzomib (Mishima, Br J Haematol, 2015; Dasmahapatra, Mol Cancer Ther, 2014). Furthermore, ricolinostat has demonstrated an excellent safety and tolerability profile in phase I trials as an oral liquid formulation (Raje, Haematologica, 2014, Suppl 1). We have now identified ACY-241 as a structurally related and orally available selective inhibitor of HDAC6 that is undergoing clinical evaluation in tablet form.
In combination with ricolinostat, the immunomodulatory (IMiD®) class of drugs, including lenalidomide (Len) and pomalidomide (Pom), exhibit striking anti-myeloma properties in a variety of MM models (Quayle, AACR, 2014) and have demonstrated clinical activity in MM patients (Yee, ASH, 2014). In support of our ongoing development of ACY-241, we show here that combination with either Len or Pom leads to synergistic decrease in MM cell viability in vitro. Time course studies demonstrated cell cycle arrest followed by progressive induction of apoptosis after prolonged exposure to Len or Pom. Notably, the addition of ACY-241 to either Len or Pom resulted in synergistic increases in apoptosis of MM cells. At the molecular level, treatment with IMiDs reduced expression of the critical transcription factors MYC and IRF4, which was further reduced by combination treatment with ACY-241. Current studies are exploring the molecular mechanism underlying this effect, which may be a consequence of low level inhibition of HDAC1, 2, and 3 by ACY-241. Prolonged treatment with ACY-241 plus Pom was well tolerated in vivo with no evidence of toxicity, and the combination resulted in a significant extension of survival in a xenograft model of MM. Given the comparable tolerability profiles of ricolinostat and ACY-241 and the similar preclinical activity in combination with IMiDs, a clinical trial (NCT02400242) is currently evaluating ACY-241 in combination with Pom and low-dose dexamethasone in MM patients.
Predicated upon the clinical experience with ricolinostat and the non-clinical pharmacokinetics of ACY-241, we designed an expedited first-in-human phase 1a/1b clinical trial of a single cycle of ACY-241 monotherapy followed by ACY-241 in combination with Pom and dexamethasone in MM patients. A merged monotherapy/combination trial design was chosen to grant patients access to combination therapy with an established regimen while enabling insight into the safety, pharmacokinetics, and pharmacodynamics of ACY-241 monotherapy. Patients with relapsed or relapsed-and-refractory MM previously treated with at least two cycles of Len and a proteasome inhibitor were eligible for this trial. The first patient was enrolled in June 2015. This patient tolerated monotherapy well and pharmacokinetics showed maximal plasma levels of ACY-241 in the micromolar range, consistent with predictions. An update on enrollment, pharmacokinetic and pharmacodynamic profiles as well as safety of monotherapy and combination therapy will be provided.

Disclosures
Niesvizky: Celgene: Consultancy, Speakers Bureau. Richardson:Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; Millennium Takeda: Membership on an entity's Board of Directors or advisory committees; Gentium S.p.A.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees. Gabrail:Onyx: Honoraria, Speakers Bureau; BI: Honoraria, Speakers Bureau; Janssen: Speakers Bureau; Sanofi: Honoraria, Speakers Bureau. Madan:Onyx: Speakers Bureau; Celgene: Speakers Bureau. Quayle:Acetylon Pharmaceuticals, Inc.: Employment, Equity Ownership. Almeciga-Pinto:Acetylon Pharmaceuticals, Inc: Employment. Jones:Acetylon Pharmaceuticals, Inc.: Employment, Equity Ownership. Houston:Acetylon Pharmaceuticals, Inc: Employment. Hayes:Acetylon Pharmaceuticals, Inc: Employment. Van Duzer:Acetylon Pharmaceuticals, Inc: Employment. Wheeler:Acetylon Pharmaceuticals, INC: Employment. Trede:Acetylon Pharmaceuticals, Inc: Employment. Raje:Acetylon: Research Funding; Celgene Corporation: Consultancy; BMS: Consultancy; Amgen: Consultancy; Millenium: Consultancy; AstraZeneca: Research Funding; Novartis: Consultancy; Onyx: Consultancy; Eli Lilly: Research Funding; Takeda: Consultancy.