Β-Carboline Alkaloid Harmine Induces DNA Damage and Triggers Apoptosis by a Mitochondrial Pathway: Study in Silico, in Vitro and in Vivo

Harmine, a tricyclic β-carboline alkaloid is an important metabolite present in Passiflora incarnata L. and Passiflora edulis f. flavicarpa Degener. Fruits of these plants are highly consumed in tropical countries and are popularly known as passion fruit, a natural product with potential antitumour activity. The cytotoxicity and selectivity effects were evaluated in vitro using tumour cell lines (MCF-7, HeLa) and normal mouse fibroblasts (McCoy cells). Molecular assays were performed using CT-DNA analysed by UV-Visible spectroscopy, fluorescence spectroscopy and circular dichroism, followed by in silico simulation (AutoDock Vina and GROMACS) and Comet assay. In vitro antitumour activity was assessed in Balb/c mice bearing Ehrlich ascitic tumour. Harmine presented cytotoxicity and selectivity to tumour cells. Spectrometry, molecular simulations and Comet assay suggested that harmine binds onto DNA nucleo base pairs by intercalation, consequently inducing DNA fragmentation. Furthermore, harmine decreased the PARP1-dependent DNA repair mechanism, causing cell cycle arrest in the G2/M phase through inhibition of pRb phosphorylation and reduced expression of CDK2, cyclin A and cyclin B1. Moreover, harmine decreased mitochondrial membrane potential and caused mitochondrial-related cellular Bax-dependent and p53-independent apoptosis in MCF-7 cells. This β-carboline alkaloid also decreased tumour growth, body weight, volume of ascitic fluid and volume of packed tumour cells, while increased the non-viable/viable tumour cells ratio, which consequently increased the lifespan of animals bearing tumours. Mechanistically, our findings indicate a putative antitumor effect of harmine, which associates DNA damage, DNA repair repression, cell cycle arrest and triggering apoptosis through mitochondrial pathway. The results suggest that harmine, present in the pulp and seed of the passion fruit, could be used in future as a promising coadjutant anticancer agent and we suggest to address this fruit as a functional food.