Abstract P5-19-05: Combination vorinostat and lapatinib reverses epithelial-mesenchymal transition, inhibits the cancer stem cell population of HER2+ breast cancer cells and is effective in heavily pretreated advanced tumors

Abstract

Abstract Although strides have been made in the treatment of breast cancer, patients often relapse due to recurrence or metastasis. The targeting of these cellular processes has become essential in the quest for a cancer cure. Previously, we have demonstrated the efficacy of histone deacetylase inhibitors (HDACi) in inducing differentiation and inhibiting metastasis in triple negative breast cancer cells. In addition, we have shown that HER2 regulates the cancer stem cell (CSC) population in AI resistant cells. Based on these previous results, we hypothesize that the combination of both HDACi and HER2 inhibition may be synergistic and further reduce CSC. In this study, we treated a panel of HER2+ breast cancer cell lines with the combination of 1µM vorinostat (HDACi) and 1µM lapatinib (a dual EGFR/HER2 inhibitor) for 72 hours and examined its effects on cell number, mesenchymal and epithelial markers, migratory potential, and cancer stem cell characteristics. The combination reduced cell number when compared to either agent alone (p<0.01 compared to vehicle). Cells treated with the combination exhibited a more epithelial morphology when compared to vehicle treated cells. Furthermore, when compared to vehicle treatment, the combination downregulated the expression of mesenchymal proteins: Twist (p<0.001), Snail (n.s.), and Vimentin (p<0.001) and concurrently upregulated epithelial proteins: cytokeratin 18 (p<0.001) and E-cadherin (n.s.), suggesting that the combination may reverse EMT (epithelial-mesenchymal transition). The combination was also able to inhibit the migratory potential of cells as measured using xCELLigence. In addition to its effects on EMT and migration, the combination also significantly reduced markers of the CSC population. Cellular markers of CSC, including mammary stem cell markers CD49f (p<0.01), CD24lo/CD44hi (p<0.01), and aldehyde dehydrogenase activity (p<0.001) were decreased following treatment with the combination. The self-renewal capability of cells was also affected by the combination, as evidenced by decreased expression of pluripotency proteins BMI-1 (p<0.05) and β-catenin (n.s.), as well as reduction of both primary (p<0.05) and secondary (p<0.05) mammosphere formation. We further conducted a phase I/II clinical trial of vorinostat in combination with lapatinib. There were 12 patients enrolled (9 in phase I and 3 in phase II). The treatment was fairly well tolerated with no DLT observed in phase I. PK analysis showed no evidence of drug-drug interaction. Among 8 patients with HER2-positive (HER2+) breast cancer, the clinical benefit rate (CR, PR, and SD) was 37.5% (1 PR, 2 SD). Intriguingly, we observed that none of the HER2+ breast cancer patients developed metastasis at a new site during the treatment. Their disease progression was due to the enlargement of previously existing lesions. Taken together, these results suggest that the combination of vorinostat and lapatinib may target both metastasis and CSC and that the combination is well tolerated and effective in patients with advanced HER2+ disease. Citation Format: Amanda J Schech, Saranya Chumsri, Preeti Shah, Stephen L Yu, Nancy S Tait, Kenneth S Bauer, Jane C Lewis, Ting Bao, Martin J Edelman, Katherine H Tkaczuk, Angela H Brodie. Combination vorinostat and lapatinib reverses epithelial-mesenchymal transition, inhibits the cancer stem cell population of HER2+ breast cancer cells and is effective in heavily pretreated advanced tumors [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-19-05.