First-in-Class Selective HDAC6 Inhibitor (ACY-1215) Has a Highly Favorable Safety Profile in Patients with Relapsed and Refractory Lymphoma.

LESSONS LEARNED Oral selective HDAC6 inhibitors could allow for decreased toxicity compared to pan-class inhibitors, and increased ease of use. ACY-1215 is well tolerated and led to disease stabilization in 50% of patients treated on a twice-daily dosing schedule. Rational drug combinations with ACY-1215 improve efficacy in patients with lymphoma. Biomarkers such as XBP-1 level or HDAC6-score may improve patient selection. BACKGROUND ACY-1215, ricolinostat, is an oral, first-in-class isoform-selective HDAC6 inhibitor. HDAC6 is a class IIb deacetylase and plays a critical role in protein homeostasis via the unfolded protein response (UPR). Lymphocytes generate a large repertoire of antibodies and depend on an activated UPR to maintain proteostasis. Lymphomas utilize this biology to evade programmed cell death. In preclinical models of lymphoma, ACY-1215 disrupted proteostasis, triggering apoptosis. METHODS We translated these findings into a multi-institution, open-label, dose-escalation phase Ib/II study aimed to determine the safety and efficacy in patients with relapsed and refractory lymphoma. RESULTS Twenty-one patients with heavily pretreated lymphoma were accrued. Patients in the phase Ib portion were enrolled on one of two dose cohorts [Arm A: 160 mg daily (n = 3) or Arm B: 160 mg twice daily (n = 10)]. ACY-1215 was well tolerated. There were no dose limiting toxicities. Most adverse events were grade 1-2, including diarrhea (57%), nausea (57%), and fatigue (43%). Grade 3-4 toxicities were rare and included anemia (9.5%) and hypercalcemia (9.5%). An additional 8 patients were enrolled on the phase II portion, at 160 mg twice daily. Sixteen patients were evaluable for response. ACY-1215 did not result in any complete or partial responses in patients treated. Eight patients had stable disease (50%) lasting a median duration of 4.5 months, all of whom were treated twice daily. Disease progressed in eight patients (50%) at cycle 2. Five patients were not evaluable due to disease progression prior to cycle 2. The median PFS was 56 days. CONCLUSION ACY-1215 is an oral selective HDAC6 inhibitor that was safe in patients with relapsed and refractory lymphoid malignancies and led to disease stabilization in half of the evaluable patients.