Synthetic Linear Lipopeptides and Lipopeptoids Induce Apoptosis and Oxidative Stress: In Vitro Cytotoxicity and SAR Evaluation Against Cancer Cell Lines

<b>Background</b>: Cancer remains a major global health challenge, with current therapies often limited by high toxicity and poor selectivity. Lipopeptides, due to their amphiphilic architecture and synthetic accessibility, have emerged as promising anticancer agents. In this study, the in vitro cytotoxic potential and structure-activity relationships (SARs) of a library of 60 synthetic linear lipopeptides (LLPs), including lipopeptide-peptoid chimeras generated via the Ugi four-component reaction, were evaluated against four cancer cell lines (B16F10, HeLa, HT-29, and PC3). <b>Methods</b>: Cytotoxicity was assessed using MTT and crystal violet (CV) assays, and the natural cyclic lipopeptide surfactin was included as a reference. SAR analysis explored the effects of C-terminal functional groups, lipophilic tail length, peptide core size, and side chain modifications. Mechanistic studies involved cell cycle analysis, apoptosis markers (Annexin V/PI staining, caspase-3 activation), and oxidative stress assessment (ROS/RNS and NO production). <b>Results:</b> Several synthetic LLPs showed potent and selective anticancer activity, with IC₅₀ values approximately 3-15 times lower than that of surfactin and with minimal toxicity toward non-cancerous NIH3T3 fibroblasts. Key structural determinants for activity included the presence of a C-terminal ester group, a lipophilic tail of 14-19 carbon atoms, and a tetrapeptide core. LLPs containing phenyl or azide side chains further enhanced cytotoxicity in a cell line-dependent manner. Mechanistic investigations confirmed that active LLPs induce caspase-dependent apoptosis, cell cycle arrest, and oxidative stress. These findings highlight that the synthetic LLPs demonstrate high in vitro anticancer efficacy with favorable selectivity. <b>Conclusions:</b> Synthetic LLPs exhibit potent and selective anticancer activity in vitro. SAR insights and mechanistic findings support their development as next-generation lipopeptide-based therapeutics.