Chloroquine and Chemotherapeutic Compounds in Experimental Cancer Treatment

Chloroquine (CQ) and its derivate hydroxychloroquine (HCQ), the compounds with recognized ability to suppress autophagy, have been tested in experimental works and in clinical trials as adjuvant therapy for the treatment of cancers of different origin to increase the efficacy of cytotoxic agents. Such strategy can be effective to overcome the resistance to standard chemotherapy or anti-angiogenic therapy. This review presents the results of combined application of CQ/HCQ with conventional chemotherapy drugs (doxorubicin, paclitaxel, platinum-based compounds, gemcitabine, tyrosine kinases and PI3K/Akt/mTOR inhibitors, and other agents) for the treatment of different malignancies obtained in experiments on cultured cancer cells and on animal xenograft models, with a few examples of clinical trials. The effects of such approach on viability of cancer cells and tumor growth, as well as autophagy-dependent and independent molecular mechanisms underlying cellular responses of cancer cells to CQ/HCQ are summarized. Although the majority of experimental studies in vitro and in vivo have shown that CQ/HCQ can effectively sensitize the cancer cells to cytotoxic agents and increase the potential of chemotherapy, the results of clinical trials are often inconsistent. Although pharmacological suppression of autophagy remains a promising tool for increasing the efficacy of standard chemotherapy, the development of more specific compounds is required.