Abstract 5418: The immunomodulatory drug lenalidomide restores a Vitamin D sensitive phenotype to the Vitamin D resistant breast cancer cell line MDA-MB-231: Potential for breast cancer therapeutics

Abstract

Abstract 1α,25-Dihydroxyvitamin D3, (1,25 D3) the biologically active form of vitamin D, is well established as an inhibitor of cancer cell growth in addition to its primary role in maintaining bone mineralization. In breast cancer cell lines, inhibitory effects on cell cycle arrest, angiogenesis, invasion and metastasis have been observed in addition to pro-apoptotic effects. 1,25 D3 also inhibits and prevents breast cancer growth in several mouse models, and a correlation between vitamin D receptor expression on breast cancer cells and disease free survival of breast cancer patients has also been observed. However, resistance to vitamin D and hypercalcaemia at higher doses are key limiting factors in clinical use. The drug Revlimid ® (lenalidomide) which has shown great promise in multiple myeloma, can also modulate signalling in apoptotic and cell growth pathways leading to inhibition of cell growth, inhibition of metastasis and invasion. Our study aimed to determine whether lenalidomide treatment of breast cancer cells resistant to vitamin D would result in an acquisition of sensitivity to vitamin D and a resultant inhibition of cell growth. The cell lines MCF-12A, MCF-7 and MDA-MB-231,representing non-tumorigenic, tumorigenic and metastatic breast lines respectively were used. The latter line was also vitamin D resistant. Cells were treated with lenalidomide and/or 1,25 D3 using a dose of 100 nM 1,25 D3 (a clinically tolerable dose giving IC50 inhibition of MCF-7 and MCF-12A cells). Results showed that whereas lenalidomide had no effect on the growth of the vitamin D sensitive lines, and gave only 20% inhibition of growth of MDA-MB-231 at 10 µM, a 50% inhibition of cell growth by 1,25 D3 (equivalent to that seen with the sensitive lines) was achieved in the presence of lenalidomide at a concentration of 1 µM. Further investigation revealed that the mechanism of this effect was an increase in apoptosis of the cell line, shown by an increase in parp cleavage and annexin V expression. An array measuring proteins associated with several signalling cascades showed that the combination of 1,25 D3 and lenalidomide resulted in an increase in proapoptotic proteins (phosphorylated P53, P21 and claspin, in addition to a decrease in BCL-2. Although both drugs had individual effects on pro-apototic proteins, and anti-apoptotic proteins, the combination resulted in an overall increase of pro-apoptotic protein expression leading to the observed inhibition of cell viability and growth. These results demonstrate the potential for the use of lenalidomide and 1,25 D3 in combination for tumours that are refractory to vitamin D. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5418.