Oleanolic acid-selenocyanate hybrids trigger replication-associated DNA damage responses and suppress tumour growth in vitro and in vivo.

Oleanolic acid (OA) is a privileged pentacyclic triterpenoid scaffold displaying moderate antiproliferative properties, whereas selenocyanates are recognized organoselenium pharmacophores with promising anticancer potential. To explore possible synergistic effects, we designed and synthesized an unprecedented library of OA-selenocyanate hybrids through derivatization at both the C-3 and C-28 positions using linkers of different length and conformational flexibility. Biological evaluation against a panel of six human solid tumour cell lines identified several potent derivatives with GI50 values below 2.5 μM, representing up to a 19-fold improvement over native OA and markedly higher activity than the reference drug abiraterone and the widely-used CDDP (cisplatin) in multidrug resistant tumour cell lines. Structure-activity relationship studies revealed that substitution at C-28, short-to-medium linker lengths, and preservation of the free C-3 hydroxyl group are critical determinants for activity. Continuous live-cell holotomographic imaging demonstrated rapid tumour cell death through a necrotic mechanism. Importantly, mechanistic studies identified replication-associated DNA damage as a key molecular event underlying the antiproliferative activity of lead compound 18. Treatment induced γH2AX and 53BP1 accumulation preferentially in HeLa cells, triggered DNA damage responses during S-phase, impaired DNA replication, and reduced mitotic progression. In vivo evaluation using Caenorhabditis elegans revealed excellent selectivity toward tumour tissues, with minimal toxicity in normal germlines and significant suppression of tumour germline growth. Collectively, these findings identify OA-selenocyanate hybrids as a promising class of tumour-selective antiproliferative agents acting through induction of DNA damage responses and disruption of cell-cycle progression.