CLM296: a highly selective inhibitor targeting ALDH1A3-driven tumor growth and metastasis in breast cancer

Aldehyde dehydrogenase 1A3 (ALDH1A3) increases tumor growth, metastasis, and chemoresistance in many solid tumors, including triple-negative breast cancer (TNBC), glioblastoma, melanoma, lung, and colon cancers, yet no clinically approved inhibitors exist. Here, we present CLM296, a novel and highly selective ALDH1A3 inhibitor designed to address this unmet need. CLM296 exhibits potent inhibition of ALDH1A3 activity in TNBC cells (half-maximal inhibitory concentration = 2 nM) with no off-target effects on the highly homologous ALDH1A1 isoform. RNA sequencing confirmed its specificity, demonstrating selective suppression of ALDH1A3-regulated gene expression only, and a lack of effect in control cells that have minimal ALDH1A3 expression. Transwell assays showed that CLM296 reduced the increased invasion of cells induced by ALDH1A3. Once daily dosing of 4mg/kg CLM296 in mice specifically reduced ALDH1A3-mediated gene expression in tumors and impeded ALDH1A3-driven tumor growth and lung metastasis in TNBC xenografts. There was no observed toxicity in the mice as evidenced by stable mouse body weights and no significant changes in blood creatinine and ALT levels. Pharmacokinetic studies of CLM296 revealed broad tissue distribution, including tumor, lung, liver, and brain. With oral administration the terminal elimination half-life of CLM296 exceeded 12 hours, resulting in sustained ALDH1A3-inhibiting concentrations beyond 24 hours. Together, these findings establish CLM296 as a potential first-in-class ALDH1A3 inhibitor with high selectivity for ALDH1A3, favorable pharmacokinetics, and a positive preclinical safety profile. CLM296 represents a promising therapeutic candidate to complement standard-of-care treatments in ALDH1A3+ cancers.