This study aimed to evaluate the preclinical activity and explore potential predictive biomarkers associated with polo-like kinase 1 (PLK1) inhibitors in experimental models of small cell lung cancer (SCLC). Cytotoxic responses to three PLK1-selective inhibitors—rigosertib, volasertib, and onvansertib—were examined across a panel of SCLC cell lines. Their therapeutic potential was further verified in subcutaneous xenografts from selected lines and in four patient-derived xenograft (PDX) systems established from both platinum-sensitive and platinum-resistant SCLC cases. Comprehensive genomic and transcriptomic analyses were conducted to determine possible markers linked to responsiveness or resistance in laboratory-developed resistant lines. All three agents—volasertib, rigosertib, and onvansertib—demonstrated potent nanomolar-level cytotoxicity against human SCLC cells in vitro. In vivo, their therapeutic effects paralleled those of standard-of-care treatments (cisplatin and irinotecan), with volasertib showing enhanced tumor growth suppression relative to cisplatin in both platinum-sensitive and resistant PDX models. Elevated YAP1 levels and loss-of-function TP53 mutations correlated with greater PLK1 inhibitor efficacy. Comparative transcriptomic profiling of onvansertib-resistant H526 derivatives revealed upregulation of NAP1L3, CYP7B1, AKAP7, and FOXG1, alongside reduced expression of RPS4Y1, KDM5D, USP9Y, and EIF1AY, indicating likely molecular resistance mechanisms. PLK1 inhibition demonstrated consistent efficacy across preclinical SCLC systems, including PDX models representing relapse under platinum sensitivity and resistance. These findings prompted the initiation of a phase II clinical investigation evaluating onvansertib in SCLC patients (ClinicalTrials.gov identifier: NCT05450965).
