Exosomes are a subgroup of membrane-bound extracellular vesicles secreted by all cell types and present virtually in all biological fluids. The composition of exosomes in the same cell type varies in healthy and disease conditions. Hence, exosomes research is a prime focus area for clinical research in cancer and numerous age-related metabolic syndromes. Functions of exosomes include crucial cell-to-cell communication that mediates complex cellular processes, such as antigen presentation, stem cell differentiation, and angiogenesis. However, very few studies reported the presence and role of exosomes in normal physiological and pathological conditions of specialized ocular tissues of the eye and ocular cancers. The eye being a protected sense organ with unique connectivity with the rest of the body through the blood and natural passages, we believe that the role of exosomes in ocular tissues will significantly improve our understanding of ocular diseases and their interactions with the rest of the body. We present a review that highlights the existence and function of exosomes in various ocular tissues, their role in the progression of some of the neoplastic and non-neoplastic conditions of the eyes.

Drug resistance (DR) is one of the challenges in treating retinoblastoma (Rb) that warrants novel approaches. With the emerging evidence on the role of small extracellular vesicles (sEVs) as a drug-delivery carrier system, in this study, we derived the drug-resistant (DR) clones of Y79 cells and evaluated the efficacy of sEVs-loaded with carboplatin (sEVs-CPT) to reverse the chemoresistance. Drug-resistant clones of Y79 cells (DR-Y79) were systematically developed through sequential exposure to carboplatin (CPT), showcasing a sixfold increase in inhibitory concentration when compared to parental Y79 cells (IC₅₀: 41.4 µg/mL and 6.2 µg/mL) (P<0.0001). These DR-Y79 cells show higher expression of ABCG2 and higher expression of DR genes than parental Y79 cells (P<0.0001). The sEVs were isolated from the conditioned media of Y79 cells using ultracentrifugation (UC) and characterized. Further, the sEVs were loaded with CPT and achieved higher encapsulation efficiency at one hour, and drug release of sEVs-CPT was highest at ∼80% at pH 5.0. The cytotoxicity of sEVs-CPT on Y79 cells and DR-Y79 was higher when compared to the CPT (IC50: 3.5 µg/mL vs 6.2 µg/mL; 23.1 µg/mL vs 41.2 µg/mL) (p<0.0001). This study demonstrates that sequential exposure to CPT generates DR clones of Y79 cells, which could serve as an appropriate model to evaluate the efficacy of drugs. The sEVs-CPT were highly effective in enhancing cytotoxicity in DR-Y79 cells, and appear to hold promise as a novel complimentary drug delivery system.

Retinoblastoma (Rb) is an intraocular tumor caused by genetic alterations in the RB1 and MYCN genes within developing retinal cells. Chemoresistance and metastasis are major challenges for treatment, with the bone marrow (BM) representing the most common metastatic site. We investigated the effect of tumor-derived sEVs (TDsEVs) on the crosstalk between metastatic site cells (BM-derived mesenchymal stem cells (BM-MSC)) and tumor cells, and characterized them according to MISEV guidelines. The uptake of sEVs and the associated phenotypic changes in the BM-MSCs were analyzed with confocal microcopy. The functional effects were assessed through MTT assays for viability, scratch and Transwell assays for migration, and colony- and sphere-formation assays to evaluate clonogenicity and self-renewal, while stemness marker expression was examined by immunoblotting. Secretome changes following sEV exposure were analyzed using dot blot assays. sEVs were taken up by both cells. TD-sEVs significantly enhanced BM-MSC migration and induced differentiation into a myofibroblast-like phenotype without affecting cell viability. Conversely, BM-MSC-derived sEVs promoted tumor cell viability, migration, and stemness marker expression. Both the BM-MSCs and tumor cells exhibited altered secretory profiles after sEV treatment. The in vitro findings provide cumulative evidence that sEV-mediated interactions contribute to a tumor-supportive milieu or premetastatic niche at the BM in Rb.