Abstract 1453: The cannabinoid Win55, 212-2 enhances the response of breast cancer cells to radiation

Abstract

Abstract Win55, 212-2 (Win2) is a full efficacy agonist for the endocannabinoid system, which is the target of Δ9-tetrahydrocannabinol (THC), the psychoactive compound in marijuana. Cannabinoids have demonstrated antiproliferative actions in many preclinical cancer models both in vitro and in vivo. The current studies were performed in the MCF-7, MDA-MB-231, or 4T1 breast cancer cell lines. Trypan blue exclusion was utilized as a measure of cell viability. Flow cytometry with propidium iodide was used for cell cycle analysis, while apoptosis and necrosis were assessed by Annexin V/PI staining. Win2, at concentrations of 4, 8 and 12μM, enhanced the antiproliferative effects of ionizing radiation (2, 4 and 8 Gy doses) in MCF-7 cells. The combination of Win2 and IR was also shown to be effective in MDA-MB-231 and 4T1 cells. This interaction was confirmed in vivo in 4T1 cells using 5mg/kg Win2 administered twice weekly in combination with one 10Gy dose of radiation. Win2 (8μM) for 24 hrs and 1 x 2Gy radiation was used for all subsequent experiments (Win/IR). Interestingly, neither THC nor the non-psychoactive cannabinoid, Cannabidiol, enhanced the response to radiation in MCF-7 cells, suggesting a possible drug-class specific effect. A time course study using Win/IR in MCF-7 cells suggested that Win2 and IR each alone induced growth arrest while the combination caused cell death. Cell cycle analysis indicated that at 24 hrs radiation alone (2 Gy) had no significant effect on cell cycle distribution; however, Win2 either alone or in combination with radiation produced a robust G1 accumulation. At 48 hrs, Win2 alone or in combination with radiation caused a significant increase in the subG1 population, implicating necrosis or apoptosis; however Annexin V/ PI staining was not consistent with either mode of cell death. The absence of apoptosis or necrosis lead us to believe that autophagy may be involved; however, the late autophagic inhibitor, Chloroquine (CQ), was unable to alter the effects of Win/IR, suggesting that autophagy is also not playing a primary role. Taken together, the absence of strong evidence for apoptosis, necrosis or autophagy suggests that the subG1 population could reflect necroptosis, and studies are underway to assess this possibility. Although the mechanisms of drug-radiation interaction remain to be defined, it is clear that Win2 does enhance the effects of radiation in breast cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1453. doi:1538-7445.AM2012-1453