Roles of Macrophages in Cisplatin-induced Hearing Loss - PROJECT SUMMARY (See instructions): Cisplatin, a widely used chemotherapeutic drug, is toxic to mechanosensory hair cells in the inner ear, resulting in permanent hearing loss in up to 60% of cancer patients. However, limited treatment strategies are available that are effective in treating cisplatin-induced hearing loss without reducing the antitumor efficacy of cisplatin, highlighting the need for continued development of therapies. Macrophages, the major resident immune cells in the cochlea, are important drivers of inflammatory and tissue repair responses. Specifically, perivascular macrophages are closely associated with the blood-labyrinth barrier (BLB) in the inner ear and regulate BLB permeability. Macrophage ablation using Pexidartinib (PLX3397) has been shown to provide complete protection against cisplatin-induced hearing loss and reduce cisplatin entry into the inner ear. Given that cisplatin is known to enter the inner ear through the BLB, this suggests that macrophages may play a role in BLB breakdown in response to cisplatin. The goal of this proposal is to identify the mechanism(s) by which macrophages regulate BLB permeability in response to cisplatin-induced ototoxicity in both non-tumor-bearing and tumor-bearing mice, while also determining whether Pexidartinib (PLX3397) compromises the antitumor efficacy of cisplatin. Aim 1A will investigate the contribution of VEGF-A-Flt1 signaling to macrophage-mediated regulation of BLB permeability following cisplatin treatment, using conditional knockout mice that disrupt this pathway. BLB permeability will be assessed through tracer assays, junctional protein expression will be evaluated, and cisplatin levels will be quantified in inner ear tissues to determine the extent of drug accumulation. Aim 1B will identify additional soluble factors that contribute to regulation of BLB permeability within specific cell types of the stria vascularis. Single-nucleus RNA sequencing will be employed to characterize transcriptional changes induced by cisplatin exposure. Aim 2 will address whether macrophage ablation using Pexidartinib (PLX3397) regulates BLB permeability while preserving the antitumor efficacy of cisplatin, using a newly developed tumor-bearing mouse model that exhibits cisplatin-induced hearing loss. Findings from this study will inform the rational design of treatment strategies to prevent cisplatin-induced ototoxicity by regulating BLB permeability and controlling drug delivery into the inner ear. Additionally, the results will provide clinical insights into the potential repurposing of PLX3397 as an otoprotective agent for patients undergoing cisplatin-based chemotherapy.
