From Lead to Drug Candidate: Optimization of 3‑(Phenylethynyl)‑1H‑pyrazolo[3,4‑d]pyrimidin-4-amine Derivatives as Agents for the Treatment of Triple Negative Breast Cancer

Herein we report the sophisticated process of structural optimization toward a previously disclosed Src inhibitor, compound 1, which showed high potency in the treatment of triple negative breast cancer (TNBC) both in vitro and in vivo but had considerable toxicity. A series of 3-(phenylethynyl)-1H-pyrazolo­[3,4-d]­pyrimidin-4-amine derivatives were synthesized. In vitro cell-based phenotypic screening together with in vivo assays and structure–activity relationship (SAR) studies finally led to the discovery of N-(3-((4-amino-1-(trans-4-hydroxycyclohexyl)-1H-pyrazolo­[3,4-d]­pyrimidin-3-yl)­ethynyl)-4-methylphenyl)-4-methyl-3-(trifluoromethyl)­benzamide (13an). 13an is a multikinase inhibitor, which potently inhibited Src (IC50 = 0.003 μM), KDR (IC50 = 0.032 μM), and several kinases involved in the MAPK signal transduction. This compound showed potent anti-TNBC activities both in vitro and in vivo, and good pharmacokinetic properties and low toxicity. Mechanisms of action of anti-TNBC were also investigated. Collectively, the data obtained in this study indicate that 13an could be a promising drug candidate for the treatment of TNBC and hence merits further studies.