Safety and preliminary efficacy of ivaltinostat, an HDAC inhibitor, plus capecitabine in patients with pretreated metastatic pancreatic adenocarcinoma (mPDAC): Results of a phase Ib study.

742 Background: Front-line chemotherapy for patients (pts) with mPDAC typically consists of mFOLFIRINOX or gemcitabine/nab-paclitaxel given until disease progression or intolerable toxicity. For pts with durable disease control on front-line treatment, maintenance therapy that can effectively delay disease progression while preserving quality of life with minimal cumulative toxicity is highly desirable. Ivaltinostat (ival) is a pan-histone deacetylase inhibitor that increases histone acetylation, suppresses cell proliferation, and promotes apoptosis. Preclinical data demonstrated synergy with 5-FU/capecitabine (cape) in mouse models. We report here results of the Phase Ib portion of a Ib/2 trial evaluating the safety and recommended phase 2 dose (RP2D) of this combination to use in a randomized study of ival + cape vs cape as maintenance therapy. Methods: Key eligibility criteria for phase 1b included unresectable or metastatic PDAC; ≥18 years old; ≥1 prior therapy; ECOG PS 0-1; and no known germline BRCA1/2 mutation. Three cohorts were enrolled, receiving ivaltinostat at 60, 125, or 250mg/m 2 iv (weekly on days 1 and 8) in combination with cape (1000mg/m 2 po BID on days 1-14) of a 21-day cycle. 1o objectives: safety, tolerability and RP2D; 2o objectives: pharmacokinetics (PK) of ival + cape. Results: A total of 28 patients were enrolled at the 60 (n=6), 125 (n=10) and 250 (n=12) mg/m 2 ival dose levels. Median prior lines of therapy: 2 (range 1-7). Median age: 67 years (range 50-83). Only one DLT (G4 thrombocytopenia) was observed at 250mg/m 2 dose level. Treatment-emergent AE profile was similar across dose levels, with common TEAEs including fatigue (n=15, 53.6%), nausea (n=14, 50.0%), palmar-plantar erythrodysesthesia syndrome (n=12, 42.9%), diarrhea (n=10, 35.7%), and constipation (n=9, 32.1%). G3 AEs included neutropenia (n=6, 21.4%), anemia (n=4, 14.3%), abdominal pain (n=3, 10.7%) and diarrhea (n=3, 10.7%). G4 AEs included 1 (3.6%) event of neutropenia and 1 (3.6%) of thrombocytopenia. No SAEs related to study drugs occurred in any of the 3 dose cohorts. PK analyses indicated dose proportional increases in exposure with increasing doses of ival. Histone H3K27 acetylation for ival showed the similar trend in optical density evaluation. Across all dose levels and prior treatments, median OS and PFS were 9.6 and 3.3 months, respectively. Conclusions: The combination of ival and cape was generally well tolerated in this heavily pretreated patient population. Ival 250 mg/m 2 is the dose selected for the ongoing randomized study of ival + cape vs cape in the maintenance setting for mPDAC pts post-FOLFIRINOX, which is expected to finish accrual in 2025. Clinical trial information: NCT05249101 .