Supplementary Fig. S1. Identification of pitavastatin in IRIF persistence screen of NIH Clinical Collection in MCF7GFP-IBD and PANC02GFP-IBD cell lines; Supplementary Fig. S2. Mevalonic acid abrogates radiosensitization effects of pitavastatin in irradiated MCF7 GFP-IBD cells. Supplementary Fig. S3. Reduction in targeted protein expression by shRNA; Supplementary Fig. S4. Targeting mevalonate pathway affects protein prenylation; Supplementary Fig. S5. Farnesyl pyrophosphate abrogates radiosensitization effects of statins in irradiated MCF7 GFP-IBD cells; Supplementary Fig. S6. Silencing GGPS impacts DNA damage response; Supplementary Fig. S7. Clonogenic survival of B16.SIY cells treated with 5 μmol/L or 10 μmol/L veliparib 1 hour prior to the indicated irradiation dose; Supplementary Fig. S8. Flow cytometry co-staining assay for apoptosis and necrosis in tumor cells treated with pitavastatin and/or radiation.
ARTICLE ABSTRACT
Despite significant advances in combinations of radiotherapy and chemotherapy, altered fractionation schedules and image-guided radiotherapy, many cancer patients fail to benefit from radiation. A prevailing hypothesis is that targeting repair of DNA double strand breaks (DSB) can enhance radiation effects in the tumor and overcome therapeutic resistance without incurring off-target toxicities. Unrepaired DSBs can block cancer cell proliferation, promote cancer cell death, and induce cellular senescence. Given the slow progress to date translating novel DSB repair inhibitors as radiosensitizers, we have explored drug repurposing, a proven route to improving speed, costs, and success rates of drug development. In a prior screen where we tracked resolution of ionizing radiation-induced foci (IRIF) as a proxy for DSB repair, we had identified pitavastatin (Livalo), an HMG-CoA reductase inhibitor commonly used for lipid lowering, as a candidate radiosensitizer. Here, we report that pitavastatin and other lipophilic statins are potent inhibitors of DSB repair in breast and melanoma models both in vitro and in vivo. When combined with ionizing radiation, pitavastatin increased persistent DSBs, induced senescence, and enhanced acute effects of radiation on radioresistant melanoma tumors. shRNA knockdown implicated HMG-CoA reductase, farnesyl diphosphate synthase, and protein farnesyl transferase in IRIF resolution, DSB repair, and senescence. These data confirm on-target activity of statins, although via inhibition of protein prenylation rather than cholesterol biosynthesis. In light of prior studies demonstrating enhanced efficacy of radiotherapy in patients taking statins, this work argues for clinical evaluation of lipophilic statins as nontoxic radiosensitizers to enhance the benefits of image-guided radiotherapy. Mol Cancer Ther; 17(2); 407–18. ©2017 AACR.See all articles in this MCT Focus section, “Developmental Therapeutics in Radiation Oncology.”
