Abstract 49: Brain penetrant HDAC inhibitor RG2833 induces DIPG cell death and synergizes with lomustine

Abstract

Abstract Diffuse intrinsic pontine glioma (DIPG) is a universally fatal pediatric brain tumor. The pan-histone deacetylase (HDAC) inhibitor panobinostat showed great activity against DIPG in pre-clinical models, but has poor blood brain barrier penetration and demonstrated significant toxicity in clinical trials. RG2833 (RGFP109) is a selective HDAC1/3 inhibitor with established brain penetration. In clinical trials, the Cmax(plasma) of RG2833 was 32uM. RG2833 demonstrated cytotoxicity against temozolomide-resistant glioblastoma and downregulated the NFĸB pathway. Because this pathway is overexpressed in DIPG and may play a role in DIPG cell growth and survival, we hypothesized that RG2833 would kill DIPG cells. Treatment of DIPG cell lines with RG2833 as a single agent inhibits cell growth in the 5 to 10μM range (MTS assay for HSJD007 p=0.0004 10μM vs DMSO, JHH-DIPG1 p=0.001 10μM vs DMSO, SF-7761 p=0.04 10μM vs DMSO, SU-DIPG13 p=0.01 10μM vs DMSO by t-test). RG2833 induces apoptosis by 48 hours as measured by Western blot for cPARP and cleaved caspase 3 immunofluorescence (HSJD007 p<0.003 8μM vs DMSO, JHH-DIPG1 p=0.0026 10μM vs DMSO by t-test). RG2833 also slows cell proliferation as measured by Western blot for phospho-Rb and immunofluorescence for BrdU (HSJD007 p=0.008 8μM vs DMSO, JHH-DIPG1 p=0.0002 10μM vs DMSO by t-test). Western blot confirmed a dose-dependent increase in histone 3 acetylation with RG2833 treatment. We detected increased acetylated p65 and decreased expression of the NFĸB regulated pro-survival genes BCL2, BCL-xL, and XIAP with RG2833 treatment in vitro. Treatment of DIPG flank tumor mouse models with RG2833 alone for 5 days suppressed tumor growth (p< 0.005 by t-test). Combination treatment with RG2833 and lomustine was synergistic against DIPG cell lines in vitro (ZIP synergy scores by SynergyFinder for JHH-DIPG1 17.8 and HSJD007 17.7). We will next assess combination treatment in vitro and in vivo for apoptotic effects. This data indicates that selective HDAC inhibitor RG2833 may be a promising therapeutic candidate for DIPG. Citation Format: Katherine K. Barnett, Orlandi Novak, Charles Eberhart, Eric Raabe. Brain penetrant HDAC inhibitor RG2833 induces DIPG cell death and synergizes with lomustine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 49.