Purpose: TROP2 is overexpressed in many tumor types and is being actively pursued as a target. Sacituzumab govitecan (SG), a humanized anti-TROP2 antibody conjugated with SN-38, was approved for treatment of metastatic triple negative breast cancer, with the greatest efficacy in patients with medium or high TROP2 levels. We sought to enhance efficacy of TROP2-targeted therapies by pharmacological regulation of TROP2 expression.
Methods: TROP2 levels were assessed by immunohistochemistry (IHC) in two sets of breast tumors: a set of surgical samples and a tissue microarray. TROP2 mRNA expression was assessed in surgical samples and breast cancer patient-derived xenografts (PDXs) with RNAseq and assessed in the TCGA. In cell lines, expression of TROP2, E-cadherin (E-cad), and Schlafen family member 11 (SLFN11) were assessed by immunoblotting and qPCR following drug treatment or cell line manipulation. Epithelial-mesenchymal transition was evaluated by cell migration, cell invasion, and anchorage-independent growth assays. Antitumor efficacy of drug combination was assessed by cell survival, cell colony formation, and apoptosis assays.
Results: By IHC, TROP2 was expressed in only 40% of metaplastic breast cancers (MpBC), but nearly all non-MpBC tumors. TCGA database evaluation further showed higher TROP2 levels in non-MpBC tumors than metaplastic tumors. In breast cancer surgical specimens, breast cancer PDXs, and the TCGA, there was a strong correlation between TROP2 and E-cad expression. In vitro, we demonstrated that downregulating transcriptional factor zinc finger E-box binding homeobox 1 (ZEB1) led to mesenchymal-epithelial transition with upregulation of both E-cad and TROP2 expression in breast cancer cells, leading to increased sensitivity to SG treatment. Screening of epigenetic modulators identified DNA methyltransferase inhibitor decitabine as an enhancer of TROP2 and E-cad expression in PDX cell lines of metaplastic cancer origin and mesenchymal subtype breast cancer cell lines. Decitabine increased TROP2 expression by decreasing TROP2 promoter methylation. Decitabine was significantly synergistic with SG, and enhanced apoptosis. Similarly, overexpression of TROP2 (by plasmid) in cell lines enhanced activity of SG. Furthermore, decitabine increased expression of SLFN11, a putative biomarker of SN38 sensitivity, and was synergistic with SG in TROP2 expressing, SLFN11 low breast cancer cell lines.
Conclusion: TROP2 is expressed in most breast cancers, but is expressed less frequently in MpBC, an aggressive subtype unresponsive to traditional therapies. Epigenetic modulator decitabine upregulates TROP2 and SLFN11 expression and enhances antitumor efficacy of SG. Combinatorial treatment of TROP2 ADCs with epigenetic modulators of TROP2 represent a novel therapeutic strategy for tumors with low TROP2 or SLFN11 expression.
Citation Format: Ming Zhao, Timothy P. DiPeri, Gabriela Raso, Yasmeen Q. Rizvi, Xiaofeng Zheng, Kurt Evans, Argun Akcakanat, Fei Yang, Debu Tripathy, Ecaterina Ileana Dumbrava, Senthil Damodaran, Funda Meric-Bernstam. Epigenetically upregulating TROP2 enhances therapeutic efficacy of TROP2 ADC sacitizumab govitecan [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1791.