Novel Dual Inhibitor of LSD1-HDAC6/8 for Treatment of Cancer

Introduction: Lysine specific demethylase 1 (LSD1) and histone deacetylases (HDACs) are known to modulate the expression of several disease specific genes as part of repressor complexes, including CoREST. In addition, they also have complex mutually exclusive roles in cancer cells. Accordingly, several studies have shown that combined inhibition of these proteins to have a profound effect in inhibiting tumor growth. In this regard, although class I HDAC inhibition has been well studied, dose limiting toxicities associated with these inhibitors is still a challenge in the clinic, it has been hypothesized that isoform selective HDAC6 inhibition could provide desired efficacy with minimal safety concerns. To study the effect of dual inhibition of LSD1 and HDAC6, we used JBI-802, a novel, dual LSD1 and HDAC6 isoform selective inhibitor by rational design. JBI-802 shows superior efficacy in select AML models as compared to LSD1 or HDAC6 selective inhibitors and also has a better tolerability profile. We also performed several mechanistic studies with JBI-802 to understand the interaction of LSD1 and HDAC6 and to dissect out the molecular mechanism of LSD1/HDAC6 inhibition. Methods: To assess in vitro LSD1 and HDAC6 potency, TR-FRET and fluorescence based activity assays were performed. Western blotting, co-immunoprecipitation and qRT-PCR studies were used to assess biomarkers of LSD1 and HDAC inhibition. Transcriptome studies and AI based analysis was performed to delineate the mechanism of single agents (LSD1 or HDAC6) vs. LSD1/HDAC6 dual inhibition. Xenograft and syngeneic disease models were used to assess the in vivo efficacy.

Results: JBI-802 shows an IC₅₀ of ~0.05 µM for LSD1 and ~ 0.01 µM for HDAC6 and a strong dose-dependent modulation of biomarkers specific for both these targets. JBI-802 showed anti-proliferative activity against a panel of haematological cancers with EC₅₀ ranging from 0.01 to 0.3 µM. Co-immunoprecipitation studies clearly showed that in addition to HDAC1, HDAC6 also co-immuno-precipitated with LSD1 suggesting that HDAC6 is a part of the CoREST complex. These findings also correlated well with stronger biomarker modulation of some key proteins by JBI-802, in comparison with the single agent LSD1 or HDAC6 selective inhibitors. Additional genomic and transcriptome based studies analyses led to the identification of a biomarker that is specific for dual inhibition. Interestingly, neither LSD1 nor HDAC6 inhibition alone lead to the modulation of this specific biomarker, which was observed only in cell lines that were sensitive to the dual inhibitor. These studies not only pave way for patient stratification in the clinic, but also could be a robust biomarker for treatment response. Data generated so far highlight the promise of this dual inhibitor in several heamatological cancers and more specifically in neoplasms with certain gain-of-function mutations. JBI-802 has optimal oral exposure and has been tested in multiple animal models by oral administration. Consistently, it showed superior efficacy in these models as compared to single agent inhibitors. Exploratory toxicity studies have clearly demonstrated that JBI-802 has an excellent safety profile.

Conclusion: JBI-802 is currently being evaluated in IND-enabling studies to be progressed into clinical trials and such inhibitors could serve as powerful therapeutic agents for the treatment of specific cancers.