Exceptional responders to abexinostat (ABX) plus pazopanib (PAZ) in pretreated renal cell carcinoma (RCC) and other solid tumors: Long-term follow-up of a phase 1b study.

person Rahul Raj Aggarwal UCSF Helen Diller Family Comprehensive Cancer Center, San Francisco, CA info_outline Rahul Raj Aggarwal, Scott Thomas, Nela Pawlowska, Jennifer A. Grabowsky, Susan Calabrese, Phu Lam, Kathleen Comerford, Daphne Bautista, Pamela N. Munster

Authors person Rahul Raj Aggarwal UCSF Helen Diller Family Comprehensive Cancer Center, San Francisco, CA info_outline Rahul Raj Aggarwal, Scott Thomas, Nela Pawlowska, Jennifer A. Grabowsky, Susan Calabrese, Phu Lam, Kathleen Comerford, Daphne Bautista, Pamela N. Munster Organizations UCSF Helen Diller Family Comprehensive Cancer Center, San Francisco, CA, University of California San Francisco, San Francisco, CA, UC San Francisco Helen Diller Family Comprehensive Cancer Center, San Francisco, CA, UC San Francisco, San Francisco, CA Abstract Disclosures Research Funding Pharmaceutical/Biotech Company Background: We previously reported the initial phase 1b study results of PAZ + ABX, a potent pan-HDAC inhibitor, demonstrating acceptable toxicity profile and encouraging anti-tumor activity (Aggarwal et al. JCO 2017). We report the long-term follow up of exceptional responders and additional correlative analyses associated with clinical outcomes. Methods: Key efficacy endpoints included objective response rate and duration of response. Peripheral blood histone acetylation, HDAC expression, and plasma VEGF levels were analyzed and associated with clinical outcomes. Results: 51 pts (RCC subset; N = 22) were enrolled between June 2012 and October 2015. 10 pts (20%) had experienced disease progression on prior PAZ; 59% had received any prior VEGF-targeting therapy. 9 evaluable pts (18%) (N = 6 RCC; 2 thyroid; 1 mesothelioma) achieved partial tumor response (PR), of which 6 had prior progression on VEGF-targeting therapy. 7/10 (70%) of pts with prior disease progression on PAZ monotherapy had reduction in tumor burden on study. The median duration of response was 9.1 months (range 1.2 to 70+), and clinical benefit rate (PR or stable disease > 6 months) was 33%. Five treatment-refractory pts achieved durable PRs lasting for > 2 years duration, and one previously PAZ-refractory patient with RCC remains on treatment with ongoing PR for > 6 years. Higher HDAC2 expression was associated with prolonged progression-free survival (median PFS 5.9 vs. 3.5 months, log-rank p = 0.02). Induction of histone acetylation on ABX lead-in treatment was associated with subsequent time to progression (p = 0.002). On-treatment plasma VEGF levels were inversely correlated with PBMC histone acetylation (p = 0.02). Conclusions: Markedly durable responses with PAZ + ABX are achievable, including in pts with PAZ- and VEGF-refractory RCC and other solid tumor malignancies. Host factors including HDAC expression and acetylation status may identify those most likely to benefit. A randomized phase 3 study is underway of PAZ + ABX as a first- or second-line therapy in pts with locally advanced or metastatic RCC (RENAVIV; NCT03592472). Clinical trial information: NCT01543763