Contemporary cancer immunotherapy has exhibited clinical success; however, it is limited by patient response variability and the occurrence of severe side effects. Consequently, there is a demand for a safer and more efficacious approach. Src homology 2 domain containing phosphatase 1 (SHP1) is a protein that negatively reguates lymphoid and myeloid cell activation, thereby presenting a promising target for immunotherapy. Nevertheless, the utilization of SHP1 for therapeutic purposes remains unexplored due to the absence of small molecule inhibitors.

Through the implementation of high-throughput screening on a meticulously chosen library of cysteine-focused fragments, coupled with extensive SAR investigations, we have successfully identified M029 as the inaugural and potent covalent inhibitor of SHP1. Remarkably, M029 exhibits >25-fold selectivity for SHP1 over other proteins. Evidenced by its ability to elevate the levels of pLCK and pERK upon stimulation with OKT3 in Jurkat T cells, M029 effectively enhances T cell activation. Proteomics studies further affirm M029's exceptional selectivity within cellular contexts, as SHP1 emerges as the most labeled protein. Furthermore, M029 displays no discernible cytotoxicity towards cancerous or non-cancerous cell lines, underscoring its lack of on-target toxicity upon SHP1 inhibition.

Animal studies have demonstrated the oral bioavailability of M029, with no observed acute toxicity up to a dosage of 100 mg/kg. Notably, treatment with M029 significantly retards the progression of MC38 tumors at a concentration of 10 mg/mL. This outcome is achieved by eliciting the infiltration of CD8+ T cells and NK cells into the tumors. Additionally, M029 administration promotes the activation and cytotoxicity of CD8+ T cells, effectively delaying their exhaustion. These data, combined with the absence of in vitro toxicity towards MC38 cells, substantiate the hypothesis that the anti-cancer effects of M029 are primarily attributed to augmented immune responses against tumor cells.

To conclude, this study has successfully generated a first-in-class, bioavailable covalent inhibitor of SHP1 that exerts anti-cancer effects primarily through immune activation. By validating the therapeutic potential of targeting the overlooked SHP1 as an alternative strategy for cancer immunotherapy, this investigation also provides valuable insights into the development of small molecule inhibitors against "undruggable" protein tyrosine phosphatases.

Dr. Zhong-Yin Zhang

Professor, Purdue University

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