Efficacy and Safety of Histone Deacetylase Inhibitors in Multiple Myeloma - a Systematic Review of Early Phase Clinical Trials
Authors: Samuel Sharoon , Tariq Muhammad Junaid , Usman Muhammad , Khalid Amna , Fraz Muhammad Asad , Ijaz Awais , Jamil Faiza , Yasir Muhammad , Ahmad Malik Qistas , Khalil Muhammad Jahanzeb , Aslam Shehroz , Shafqat Madeeha , Durer Ceren , Shah Zunairah , Anwer Faiz 
Published: October 2019

Abstract
Introduction
Recent studies in novel therapies have created opportunities for new treatment regimens to be used in the management of multiple myeloma. Histone deacetylase (HDAC) inhibitors lead to epigenetic manipulation of multiple myeloma (MM) cells by reducing resistance to pro-apoptotic signals. Panobinostat is an FDA approved HDAC inhibitor for multiple myeloma. The aim of this article is to study the safety, efficacy and dose limiting toxicities of HDAC inhibitors in the early phase clinical trials in multiple myeloma.
Methods
We performed a comprehensive literature search for phase I & I/II trials of HDAC inhibitors during last ten years using following databases: PubMed, Embase, AdisInsight, and Clinicaltrials.gov. Studies involving HDAC inhibitors in multiple myeloma other than panobinostat irrespective of the age, sex or specific eligibility criteria were included.
Results
Out of 2537 studies, we included 25 trials (23 phase I, 2 phase I/II) of HDAC inhibitors in this systematic review having a total of 518 patients. Of these, 471(90.9%) patients were evaluable for response.
Vorinostat (Vor) is the most studied drug used in 13 trials (n=281). Two trials had Vor-only regimen and the remaining 11 had combination regimens mostly with lenalidomide and bortezomib. Vor, in combination with lenalidomide (R), bortezomib (V) and dexamethasone (d) has showed 100% overall response rate (ORR) in 30 newly diagnosed multiple myeloma (NDMM) patients, (Kaufmann et al., 2016), fifty two percent patients achieved very good partial response (VGPR) and 28% patients showed complete response (CR). Another study using Vor + R regimen after autologous stem cell transplant in 16 NDMM patients showed VGPR in 7, stringent complete response (sCR) in 4, partial response (PR) in 2 and CR in 3 patients (Sborov et al.). Grade 3 neutropenia was seen in 1 patient in this study.
Richter et al, 2011 showed an ORR of 24% in 29 relapsed refractory multiple myeloma (RRMM) patients with Vor only regimen. Another study (Kaufmann et al., 2012) with Vor only regimen used in 10 RRMM patients showed stable disease (SD) in 9 and minimal response (MR) in 1 patient. ORR of 65% was achieved in 31 RRMM patients receiving Vor in combination with doxorubicin & bortezomib (Vorhees et al, 2017). Thrombocytopenia & neutropenia were reported in 94% and 59% patients respectively.
Ricolinostat in combination with Rd and Vd achieved an ORR of 55% and 29% respectively in two studies with 38 and 57 evaluable patients (NCT01583283, NCT01323751). Another ricolinostat regimen with pomalidomide & dexamethasone achieved ≥PR in 6/11 RRMM patients (Madan et al., 2016). Table 1 illustrates the efficacy, number of patients and regimens used in all the studies in this systematic review.
Quisinostat in a 2017 study by Moreau P et al. (NCT01464112) showed an ORR of 88% in a combination regimen with Vd in RRMM patients (N=18). Drug related adverse events were seen in 13 patients, thrombocytopenia being most common in 11 patients, 2 patients had grade 3 cardiac disorders and 1 patient had a cardiac arrest.
Romidepsin in a phase I/II study (Harrison et al., 2011) combined with Vd was used in 25 RRMM patients. ORR was 60% with VGPR n=7, CR n=2, PR n=6, SD n=5 and PD n=1. Grade ≥3 thrombocytopenia in 16, neutropenia in 9 and peripheral neuropathy in 2 patients was seen.
Popat et al used combination of two HDAC inhibitors CHR 3996 and tosedostat in 20 RRMM patients. ORR was 10% and SD was seen in 30% patients. Grade 3/4 toxicities seen were thrombocytopenia (n=12), leukopenia (n=6) and diarrhea (n=5).
A phase I study on AR-42 drug in 17 RRMM patients (Sborov et al., 2017) showed SD in 10, PD in 4, MR in 3 patients with progression free survival (PFS) of 8.2 months. Thrombocytopenia, neutropenia and lymphopenia were seen in 11, 10 and 6 patients respectively. A detail of all grade 3 and higher adverse events along with dose limiting toxicity is given in table 2. Three trials (NCT02576496, NCT01947140, NCT03051841) of Edo-S101, romidepsin and CKD-581 are currently recruiting with 84, 93 and 18 planned number of patients.
Conclusion
Regimens containing vorinostat have shown an ORR up to 100% in NDMM patients. HDAC inhibitors have also shown promising efficacy up to 88% ORR in RRMM population. Majority of the patients developed cytopenias as hematological adverse events.

Disclosures
No relevant conflicts of interest to declare.