Investigation of ITGB3 Heterogeneity to Overcome Trastuzumab Resistance in HER2-Positive Breast Cancer

HER2-positive breast cancer has an aggressive tumour progression among breast cancers characterized by the overexpression of HER2. Trastuzumab is an FDA-approved drug and has significantly improved outcomes for patients; however, drug resistance remains a major challenge. Tumour heterogeneity, describing genetic, epigenetic, and phenotypic differences within and between tumours, complicates tumour treatment and contributes to drug resistance. Understanding the mechanisms underlying Trastuzumab resistance, such as tumour heterogeneity, is crucial for developing new and effective therapeutic strategies. This study investigates the role of <i>ITGB3</i> heterogeneity in Trastuzumab resistance, focusing on its impact on TGF-β signalling and migration marker response. It also evaluates the potential of combining Trastuzumab with the integrin β3 inhibitor cilengitide to overcome resistance associated with <i>ITGB3</i> levels. Trastuzumab-resistant HER2-positive HCC1954 and SKBR3 breast cancer cell lines were generated and analysed for <i>ITGB3</i> expression heterogeneity. The impact of <i>ITGB3</i> on TGF-β-responsive genes <i>(WWP1</i>, <i>CARM1</i>, <i>RASGRP1</i>, <i>THBS1</i>, <i>KCTD5</i>, <i>SGCA</i>, <i>EIF3S6</i>, <i>MCAM</i>, <i>FXR2</i>, <i>MTMR3</i>, <i>SOCS3</i>, <i>SLC2A4RG</i>, <i>MMP2</i>, <i>MMP9</i>, and <i>HSP47)</i> and cell migration (<i>Col4a1</i>, <i>fibronectin</i>, <i>ICAM1</i>, <i>Timp2</i>, and <i>vimentin</i>) was analysed using luciferase reporter assays and real-time PCR. The effects of combined treatment with Trastuzumab and cilengitide were also evaluated via wound closure assay. <i>ITGB3</i> expression varied significantly among resistant clones, correlating with increased expression of TGF-β-responsive genes and enhanced migration markers. Combined treatment with Trastuzumab and cilengitide significantly reduced TGF-β signalling and migration-related gene expression, particularly in high <i>ITGB3</i>-expressing cells. <i>ITGB3</i> plays a critical role in Trastuzumab resistance through the modulation of TGF-β signalling, migration, and contributing to tumour heterogeneity. Targeting ITGβ3, alone or in combination with cilengitide, offers a promising strategy to resensitize resistant HER2-positive breast cancer cells to Trastuzumab. These findings provide valuable insights into the mechanisms of Trastuzumab resistance and suggest potential therapeutic avenues for improving patient outcomes.