Psidium guajava']java L. anti-neoplastic effects: induction of apoptosis and cell differentiation

Objectives: Curative properties of medicinal plants such as Psidium guajava L. (Myrtaceae) have often been indicated by epidemiological studies on populations in which these fruits are consumed daily. However, complete characterization of the active principles responsible for this ability has never been performed. Here, we have characterized P. guajavas anti-cancer potential and identified the parts of the fruit involved in its anti-neoplastic action. Materials and methods: We studied morphology of our cells, cell cycle characteristics and apoptosis and performed immunostaining, differentiation and western blot analyses. Results: We report that the P. guajava extract exerted anti-cancer control on both haematological and solid neoplasias. P. guajava extract's antitumour properties were found to be tightly bound to induction of apoptosis and differentiation. Use of ex vivo myeloid leukaemia blasts corroborated that P. guajava was able to induce cell death but did not exhibit anti-cancer effects on all malignant cells investigated, indicating selective activity against certain types of tumour. Analyses of P. guajava pulp, peel and seeds identified the pulp as being the most relevant component for causing cell cycle arrest and apoptosis, whereas peel was responsible for causing cell differentiation. P. guajava itself and its pulp-derived extract were found to induce apoptosis accompanied by caspase activation and p16, p21, Fas ligand (FASL TNF super-family, member 6), Bcl-2-associated agonist of cell death (BAD) and tumour necrosis factor receptor super-family, member 10b (DR5), overexpression. Conclusions: Our findings showed that P. guajava L. extract was able to exert anti-cancer activity on cultures in vitro and ex vivo, supporting the hypothesis of its anti malignant pro-apoptotic modulation.