Pyrimethamine Conjugated Histone Deacetylase inhibitors: Design, Synthesis and Evidence for Triple Negative Breast Cancer Selective Cytotoxicity

Abstract Signal transducer and activator of transcription 3 (STAT3) is an oncogenic transcription factor which has been recognized as a promising cancer therapeutic target. Small molecule pyrimethamine (PYM) is a known direct inhibitor of activated STAT3 and it is currently under clinical trial. Also, histone deacetylase (HDAC) inhibition has been shown to indirectly attenuate STAT3 signaling through inhibition of STAT3 activation. Herein we described the design and biological profiling of two classes of PYM-conjugated HDAC inhibitors (HDACi). We observed that the class I PYM-HDACi compounds 12a-c potently inhibited HDACs 1 and 6 in cell free assays while a lead class II PYM-HDACi compound 23 showed a strong HDAC 6 selective inhibition. In a cell-based assay, 12a-c are preferentially cytotoxic to MDA-MB-231, a TNBC cell line that is highly STAT3-dependent, while 23 showed no such selective toxicity. Subsequent target validation studies revealed that a representative class I PYM-HDACi compound 12c elicited a signature of HDAC and STAT3 pathway inhibition intracellularly. Collectively, these data suggest that PYM-HDACi compounds are promising leads to develop targeted therapy for TNBC.