Harmine Derivatives as Anticancer Agents Endowed With Potent and Selective Antileukemia Activity: Synthesis, Biological Evaluation, Proapoptotic and Genotoxic Activity

ABSTRACT β‐Carboline alkaloids, such as harmine ( 1 ), have demonstrated notable anticancer properties, making them attractive candidates for anticancer drug development. This study evaluated the antiproliferative activity of compound 1 and thirty‐three N 9 ‐substituted derivatives across a panel of cancer cell lines representing various histotypes. Among these, derivative 6 , a harmine analog bearing a 3,5‐dimethylbenzyl substituent, was the most potent, showing enhanced cytotoxicity and selectivity toward cancer cells. Compound 6 exhibited IC 50 values below 10 µM in all tested cancer cell lines, while its IC 50 in non‐cancerous cells exceeded 100 µM. Viability assays and xCELLigence real‐time monitoring confirmed a concentration‐dependent inhibition of cancer cell growth with minimal effects on non‐malignant cells. Flow cytometry demonstrated G1 phase arrest in MOLT‐4 cells, supported by Western blot data showing reduced phosphorylated Rb and increased p27 protein levels. Apoptosis induction was confirmed through Annexin V/PI staining, TUNEL assays, and caspase activation studies. These revealed the involvement of both intrinsic (caspase‐9) and extrinsic (caspase‐8) apoptotic pathways, along with activation of caspases 3/7. Western blot analysis also showed a concentration‐dependent increase in the Bax/Bcl‐2 ratio. Immunofluorescence microscopy visualization indicated DNA damage through elevated levels of PAR and γH2AX, consistent with single‐ and double‐strand DNA breaks. Importantly, compound 6 exhibited low inhibitory activity against monoamine oxidase A (MAO‐A) and did not promote reactive oxygen species (ROS) generation, minimizing potential off‐target effects. Together, these findings support the potential of compound 6 as a selective and effective candidate for antileukemia therapy.