N-Alkylated Monoterpene Indole Alkaloid Derivatives as Chemotherapy Adjuvants That Overcome P-glycoprotein-Mediated Multidrug Resistance in Cancer Cells, Spheroids and Patient-Derived Colorectal Cancer Organoids.

PURPOSE: Chemotherapy efficacy is often limited by multidrug resistance (MDR), largely driven by P-glycoprotein (P-gp). This study aimed to evaluate previously prepared N-alkylated dregamine and tabernaemontanine derivatives as potential adjuvants to overcome P-gp-mediated chemoresistance. PATIENTS AND METHODS: Twenty-one N-alkylated derivatives (1-21) were tested for cytotoxicity and chemosensitizing activity in sensitive and doxorubicin (DOX)-resistant ovarian (A2780, A2780DOX) and breast cancer cell lines (MCF-7, MCF-7R), as well as in nonmalignant kidney epithelial cells (hRPTEC). P-gp modulation was assessed using rhodamine 123 accumulation and Pgp-Glo Assay Systems kit. The activity of the most promising compound was further evaluated in 3D monocellular and multicellular spheroids, patient-derived colorectal cancer organoids (PDOs), and peripheral blood mononuclear cells (PBMCs). Computational docking was performed to support mechanistic insights. RESULTS: The derivatives exhibited moderate cytotoxicity toward cancer cells and low toxicity toward hRPTEC. All compounds sensitized resistant cell lines, with the most active ones reducing DOX IC50 by >20-fold at 10 μM and >8-fold at 1 μM. For most derivatives, increased accumulation of rhodamine 123 confirmed modulation of P-gp efflux activity. N-(4-methoxybenzyl) dregamine (compound 11) showed the strongest potential, enhancing DOX sensitivity >7-fold in monocellular and >4-fold in multicellular spheroids. In combination with DOX, compound 11 also increased the sensitivity of colorectal cancer PDOs, thereby reducing their viability from 70% to 30%. No increased toxicity of DOX was observed in PBMCs. CONCLUSION: N-alkylated monoterpene-indole alkaloids, particularly compound 11, effectively overcome P-gp-mediated chemoresistance without inducing cytotoxicity in healthy cells and represent promising candidates for further in vivo evaluation.