Multimerization approach to improve a cell surface plectin binding cancer stem cell targeted peptoid drug‑lead

Cancer stem cells (CSCs) or tumor-initiating cells represent a drug-resistant subpopulation with self-renewal and metastatic capacity. There are no CSC-specific drugs that have been developed so far. Plectin is a cytoskeletal protein that uniquely translocates to the outer cell membrane (surface translocated plectin - STP) in CSCs and contributes to proliferation, migration, invasion, and metastasis. We previously identified an STP targeted peptoid-PCS2, and the dimeric version PCS2D1.2, which selectively binds to non-small cell lung cancer (NSCLC) derived CSCs, displayed both in vitro and in vivo anti-cancer activity. The current study reports the identification of the minimum pharmacophore and the optimization of PCS2D1.2 to obtain an improved version of trimeric peptoid PCS2T3.9. Various multimerization strategies with linker optimization and truncation of non-important residues resulted in PCS2T3.9, which demonstrated 21-fold improvement of the cytotoxic activity against high STP expressing H358 non-small cell lung cancer (NSCLC) cells, while showing minimum effects on low STP expressing H460 cells. PCS2T3.9 had no cytotoxic activity on normal bronchial epithelial HBEC-3KT cells. Furthermore, PCS2T3.9 effectively suppressed colony formation and cell migration-hallmarks of CSC phenotype-specifically in H358 cells but not in H460 cells. These findings strongly correlate high STP expression with cancer stemness characteristics and confirm the selective targeting of PCS2T3.9 on CSCs, producing anti-cancer activity. The highly specific and selective cytotoxic effects of PCS2T3.9 on STP-enriched CSCs offer a significant therapeutic advantage by potentially minimizing off-target effects on normal tissues, establishing this peptoid as a promising candidate for CSC-specific NSCLC therapy development.