Abstract PO2-24-10: Anti-Tumorigenic Immuno-Microenvironment by AB-329, a Potent and Selective AXL inhibitor, combined with paclitaxel in Triple-Negative Breast Cancer Preclinical Model

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Abstract BACKGROUND The Gas6/AXL signaling pathway plays a substantial role in cancer cell survival, proliferation, immunosuppression, and metastasis. Elevated AXL expression is associated with advanced cancer stages and decreased overall survival rates, underscoring its potential as a therapeutic target for metastatic cancers. We investigated this possibility by utilizing AB-329, a selective small molecule AXL kinase inhibitor, to treat triple-negative breast cancer (TNBC). TNBC, typified by the lack of ER, PR, and HER2 expression, frequently displays mesenchymal characteristics and carries a significant risk of metastasis and an immunosuppressive tumor microenvironment. METHODS We assessed AXL protein expression in 28 human and 11 mouse breast cancer cell lines using Western blotting. The Microarray database was utilized to examine AXL gene expression in 40 human breast cancer cells. The Sulforhodamine B proliferation and soft agar assays measured the antiproliferative effect of AB-329 in TNBC cell lines. The in vitro anti-metastatic impact of AB-329 was evaluated through migration and invasion assays. We appraised the anti-tumor effects of AB-329 in combination with paclitaxel using 4T1 and E0771-LMB mouse TNBC xenograft models. We used FACS and CIBERSORTx to perform immune cell type profiling in E0771-LMB xenograft tumor tissues. To understand AB-329’s immunomodulatory effects in tumors, single-cell RNA sequencing was conducted in a humanized mouse model with SUM149 human TNBC xenografts. RESULTS Microarray data revealed higher AXL expression in TNBC cells compared to non-TNBC cells. Western blotting supported this, showing higher AXL protein expression, particularly in basal and mesenchymal subtypes of TNBC cells, compared to luminal breast cancer cells. AB-329 presented moderate antiproliferative effects as a monotherapy in the TNBC cell lines tested, with half-maximal inhibitory concentrations exceeding 5 µM. Nevertheless, combining AB-329 with paclitaxel resulted in significant growth inhibition in all tested TNBC cell lines (p < 0.05). Importantly, AB-329 alone could inhibit TNBC migration and invasion at a concentration of 1 µM (p < 0.01) and showed enhanced inhibition rates when paired with paclitaxel (p < 0.05). The combination of AB-329 and paclitaxel considerably reduced tumor growth in the 4T1 and E0771-LMB xenograft models compared to paclitaxel or AB-329. Total RNA sequencing and CIBERSORTx analysis indicated that the AB-329 and paclitaxel combination increased Natural Killer (NK) cells’ infiltration into E0771-LMB mouse TNBC xenograft tumors compared to single agent-treated tumors. A nearly 2.5-fold increase in NKT cell infiltration was also detected with AB-329 treatment compared to Control in SUM149 human TNBC xenografts. CONCLUSIONS Our preclinical data suggest that AB-329, an AXL inhibitor, could synergize effectively with paclitaxel in TNBC treatment, notably inhibiting tumor cell proliferation and migration while enhancing NK cell infiltration. Intriguingly, we observed an increased infiltration of NKT cells into tumors following AB-329 treatment, which may promote an anti-tumorigenic immuno-microenvironment. These results underscore the necessity for further investigation into the role of AB-329 in modulating the tumor immuno-microenvironment through AXL pathway inhibition and accentuate the potential for combining AB-329 with immunotherapy. Citation Format: Dileep Reddy Rampa, Jon Fuson, Huey Liu, Max Pan, Naoto Ueno, Jangsoon Lee. Anti-Tumorigenic Immuno-Microenvironment by AB-329, a Potent and Selective AXL inhibitor, combined with paclitaxel in Triple-Negative Breast Cancer Preclinical Model [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-24-10.