Tryptoline urea derivatives for sensitizing resistant breast cancer cells to doxorubicin

Drug resistance is a major challenge in cancer therapy. One promising approach to address this problem is the development of compounds that, when used together with anticancer drugs, can synergistically improve their therapeutic effectiveness. Aiming at sensitizing resistant human breast adenocarcinoma cells (MCF-7/DXR), a set of new urea derivatives (2-9) was prepared by reaction of the natural β-carboline indole alkaloid tryptoline (1) with different aromatic and aliphatic isocyanates. The P-glycoprotein (P-gp) inhibitory potential of compounds 1-9 was assessed by a functional assay. The most significant results were obtained for N-[N2'-(4″-acetylphenyl)carbamoyl]tryptoline (9), in agreement with molecular docking studies that revealed significant binding affinity to P-gp. Western blot and immunocytochemistry analyses showed that compound 9 led to downregulation of ABCB1 expression, associated with concurrent downregulation of AKT1 signaling. Co-administration of compound 9 with doxorubicin (DOX) significantly reduced fold resistance in MCF-7/DXR cells, almost restoring their sensitivity to levels similar to the parental cell line (from 16.34- to 0.98-fold resistance). Moreover, compound 9 acted synergistically with DOX, markedly increasing its cytotoxicity, associated with a strong increase in apoptosis, reaching approximately 85% apoptotic cells. Molecular analysis showed activation of the intrinsic apoptotic pathway, with increased levels of pro-apoptotic proteins (p53, Bax, caspase-3, and caspase-9) and reduced levels of the anti-apoptotic protein Bcl-2. By increasing ROS production and subsequently inducing oxidative DNA damage, compound 9 markedly amplified DOX-induced cytotoxicity, reinforcing its potential as an effective chemosensitizing agent and warranting further preclinical investigation for potential therapeutic applications.