Selective HDAC3 Inhibitors with Potent In Vivo Antitumor Efficacy against Triple-Negative Breast Cancer

Abstract

HDAC3 modulation shows promise for breast cancer, including triple-negative cases. Novel <i>pyrazino</i>-hydrazide-based HDAC3 inhibitors were designed and synthesized. Lead compound <b>4i</b> exhibited potent HDAC3 inhibition (IC₅₀ = 14 nM) with at least 121-fold selectivity. It demonstrated strong cytotoxicity against triple-negative breast cancer cells (IC₅₀: 0.55 μM for 4T1, 0.74 μM for MDA-MB-231) with least normal cell toxicity. Metabolically stable <b>4i</b> displayed a superior pharmacokinetic profile. A dose-dependent therapeutic efficacy of <b>4i</b> was observed in a tumor-bearing mouse model. The biomarker analysis with tumor tissues displayed enhanced acetylation on <i>Ac</i>-H3K9, <i>Ac</i>-H3K27, and <i>Ac</i>-H4K12 compared to <i>Ac</i>-tubulin and <i>Ac</i>-SMC3 indicating HDAC3 selectivity of <b>4i</b> in vivo. The immunoblotting study with tumor tissue showed upregulation of apoptotic proteins caspase-3, caspase-7, and cytochrome <i>c</i> and the downregulation of proliferation markers Bcl-2, CD44, EGFR, and Ki-67. Compound <b>4i</b> represents a promising candidate for targeted breast cancer therapy, particularly for cases with triple-negative breast cancer.