AXL-Driven Stemness and Hedgehog Signaling in HER2-Positive Breast Cancer with Acquired Trastuzumab Resistance: Synergistic Potential of AXL and HER2 Co-Targeting

Stemness is a critical factor in tumor initiation, progression, metastasis, and resistance to treatment. The AXL receptor and hedgehog (Hh) signaling pathways play significant roles in regulating stemness, making them potential therapeutic targets. This study explores the involvement of AXL and hedgehog signaling in maintaining stemness and contributing to trastuzumab resistance in HER2-positive breast cancer. The expression of AXL and Hh markers was assessed in trastuzumab-resistant SKBR3 and HCC1954 cell lines and their parental counterparts. Trastuzumab resistance was associated with upregulation of AXL expression, with the GAS6/AXL axis identified as a regulator of stemness. Although inhibition of hedgehog signaling using GANT61 did not affect AXL expression, overexpression of AXL led to increased levels of hedgehog markers (e.g., <i>Gli1</i>, <i>Ptch1</i>) and stemness markers (e.g., <i>Sox2</i>, <i>Oct4</i>, <i>Nanog</i>), while silencing AXL resulted in their downregulation. Furthermore, AXL overexpression enhanced stemness in resistant cells, suggesting its role in resistance mechanisms. The combination of AXL inhibition and trastuzumab treatment significantly reduced stemness and hedgehog marker expression, indicating a synergistic effect. These results emphasize the pivotal role of AXL in regulating both stemness and hedgehog signaling in HER2-positive breast cancer. The study suggests that targeting both AXL and HER2 could be a promising strategy to overcome trastuzumab resistance and improve treatment outcomes.