Abstract 5914: Non-muscle myosin IIA as a promising therapeutic target in breast cancer

Abstract

Abstract We aimed to determine the role of non-muscle myosin IIA (NMIIA) in breast cancer using various cancer cell lines including estrogen receptor (ER)+, HER2+ and triple negative breast cancers (TNBC). Myosin heavy chain 9 (MYH9) gene encodes for the heavy chain of the hexameric protein NMIIA. We have recently identified that NMIIA serves as a binding partner for HER3 following the inhibition of the HER family member compared to the vehicle control treatment, as observed in HER3 immunoprecipitates. We checked the basal protein and mRNA levels of NMIIA in different breast cancer cell lines and found higher levels of NMIIA in both HER2+ and TNBC cell lines compared to ER+ cell lines. These data correlate with clinical data of primary breast cancer patients with high MYH9 being less likely in ER+ breast cancer patients and more likely in the PAM50 subtypes basal and HER2 enriched breast cancer patients. By employing a pool of four siRNA targeting MYH9, our data indicated a reduction in proliferation of HER2+ and TNBC cell lines when compared to the control siRNA. We have previously found that loss of MYH9 sensitizes to the HER family inhibitor neratinib treatment as assessed by cell proliferation, colony formation on matrigel, cell migration and invasion. We aimed to determine if pharmacological inhibition of the NMIIA pathway would sensitize to neratinib. RhoA-associated kinase (ROCK) serves as a master regulator of NMIIA activity as it directly phosphorylates the regulatory light chain (RLC) of NMIIA. Pharmacological inhibition of ROCK-NMIIA pathway using the ROCK inhibitor GSK269962A alone or in combination with neratinib reduced the cell proliferation in HER2+ cell lines BT474 and MDA-MB-453 as indicated by MTT and cell proliferation assay. It is well known that HER2-targeted therapies cause the upregulation of HER3. Given our identification of NMIIA as one of the interacting partners of HER3, our focus will be on investigating the NMIIA-HER3 signaling axis to elucidate its contribution to an adaptive response to HER2 inhibition and potential treatment resistance. Furthermore, we will explore strategies to target NMIIA in breast cancer. Citation Format: Wasim Feroz, Rosalin Mishra, Mary Kate Kilroy, Joan T. Garrett. Non-muscle myosin IIA as a promising therapeutic target in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5914.