Although tremendous effort has been made over the past century to treat cancer effectively, the pace of drug development is far behind the increasing rate of cancer incidence and mortality. There are two major hurdles in anticancer drug development: dose-limiting toxic side effects that reduce either drug effectiveness or the quality of life of patients and complicated drug development processes that are costly and time consuming. Drug repositioning has recently gained increasing attention among cancer researchers as this approach utilizes existing drugs and is significantly cost- and time-effective. Existing drugs, particularly non-cancer drugs, have favorable safety profiles in humans and serve as an ever-increasing source for new anticancer drug discovery. Here we review the recent examples of drug repositioning of existing non-cancer drugs for preclinical and clinical introductions of cancer therapy.

Abstract Purpose: Itraconazole is a triazole antifungal drug that has recently been found to inhibit angiogenesis. Itraconazole is a relatively well-tolerated drug but shows hepatotoxicity in a small subset of patients. Itraconazole contains three chiral centers and the commercial itraconazole is composed of four cis-stereoisomers (named IT-A, IT-B, IT-C, and IT-D). We sought to determine whether the stereoisomers of itraconazole might differ in their antiangiogenic activity and hepatotoxicity. Experimental Design: We assessed in vitro antiangiogenic activity of itraconazole and each stereoisomer using human umbilical vein endothelial cell (HUVEC) proliferation and tube formation assays. We also determined their hepatotoxicity using primary human hepatocytes in vitro and a mouse model in vivo. Mouse Matrigel plug and tumor xenograft models were used to evaluate in vivo antiangiogenic and antitumor activities of the stereoisomers. Results: Of the four stereoisomers contained in commercial itraconazole, we found that IT-A (2S,4R,2′R) and IT-C (2S,4R,2′S) were more potent for inhibition of angiogenesis than IT-B (2R,4S,2′R) and IT-D (2R,4S,2′S). Interestingly, IT-A and IT-B were more hepatotoxic than IT-C and IT-D. In mouse models, IT-C showed more potent antiangiogenic/antitumor activity with lower hepatotoxicity compared with itraconazole and IT-A. Conclusions: These results demonstrate the segregation of influence of stereochemistry at different positions of itraconazole on its antiangiogenic activity and hepatotoxicity, with the 2 and 4 positions affecting the former and the 2′ position affecting the latter. They also suggest that IT-C may be superior to the racemic mixture of itraconazole as an anticancer drug candidate due to its lower hepatotoxicity and improved antiangiogenic activity. Clin Cancer Res; 22(11); 2709–20. ©2016 AACR.

Despite standard cancer therapies such as chemotherapy and targeted therapy have shown some efficacies, the cancer in many cases eventually relapses and metastasizes upon stopping the treatment. There is a small subpopulation of cancer cells within tumor, with specific characters similar to those found in stem cells. This group of cancer cells is known as tumor-initiating or cancer stem cells (CSCs), which have an ability to self-renew and give rise to cancer cell progeny. CSCs are related with drug resistance, metastasis and relapse of cancer, hence emerging as a crucial drug target for eliminating cancer. Rapid advancement of CSC biology has enabled researchers to isolate and culture CSCs in vitro, making the cells amenable to high-throughput drug screening. Recently, drug repositioning, which utilizes existing drugs to develop potential new indications, has been gaining popularity as an alternative approach for the drug discovery. As existing drugs have favorable bioavailability and safety profiles, drug repositioning is now actively exploited for prompt development of therapeutics for many serious diseases, such as cancer. In this review, we will introduce latest examples of attempted drug repositioning targeting CSCs and discuss potential use of the repositioned drugs for cancer therapy.

Selective estrogen receptor modulators (SERM) including tamoxifen are known to inhibit angiogenesis. However, the underlying mechanism, which is independent of their action on the estrogen receptor (ER), has remained largely unknown. In the present study, we found that tamoxifen and other SERM inhibited cholesterol trafficking in endothelial cells, causing a hyper-accumulation of cholesterol in late endosomes/lysosomes. Inhibition of cholesterol trafficking by tamoxifen was accompanied by abnormal subcellular distribution of vascular endothelial growth factor receptor-2 (VEGFR2) and inhibition of the terminal glycosylation of the receptor. Tamoxifen also caused perinuclear positioning of lysosomes, which in turn trapped the mammalian target of rapamycin (mTOR) in the perinuclear region of endothelial cells. Abnormal distribution of VEGFR2 and mTOR and inhibition of VEGFR2 and mTOR activities by tamoxifen were significantly reversed by addition of cholesterol-cyclodextrin complex to the culture media of endothelial cells. Moreover, high concentrations of tamoxifen inhibited endothelial and breast cancer cell proliferation in a cholesterol-dependent, but ER-independent, manner. Together, these results unraveled a previously unrecognized mechanism of angiogenesis inhibition by tamoxifen and other SERM, implicating cholesterol trafficking as an attractive therapeutic target for cancer treatment.