Metformin and Anti-Cancer Therapeutics: Hopes for a More Enhanced Armamentarium Against Human Neoplasias?

Metformin, a natural product from Galega officinalis, is an oral drug, now in the forefront of the therapeutic management of type-2 diabetes mellitus. A series of clinical observations of the last decades, support that metformin may contribute to lowering the risk of cancer development in diabetic patients, and also to improvement of response-to-therapy and survival in individuals with certain types of malignancies. Moreover, several preclinical in vitro and in vivo data indicate that metformin indeed exerts anti-proliferative capacities upon tumor cells mediated through a variety of mechanisms. Interestingly, metformin has been shown to act in synergy with certain anti-cancer agents and also to overcome chemo- and/or radio-resistance of various types of tumors, providing a hopeful rationale for novel therapeutic strategies against cancer development and progression. However, this remains an issue of controversy, since significant contradictions exist among the available data. Limitations of preclinical studies and caveats of epidemiological works, together with significant variances among the several types of cancer and the fact that the mode of metformin's action is largely unknown, make longitudinal surveys urgently needed. Now, a plethora of large clinical trials are active worldwide, aiming at determining the effect of metformin in the prevention or prognosis of a variety of human cancers. If encouraging results arise, metformin will be an attractive candidate adjuvant in the management of human neoplasias, due to its safety, tolerability and low-cost, expected to mitigate adverse effects and no-response parameters of current anti-cancer therapeutics, thus improving the quality of life and survival of cancer patients.