Abstract
Purpose :
Intra-ocular retinoblastoma (Rb) treatment modalities include chemotherapy, brachytherapy or enucleation of affected eyes in advanced disease. Enhancing chemotherapeutic effect of currently available drugs at low doses and reducing systemic toxicity remains an unmet clinical need. Thus we tested anti-cancer activities of a series of cationic anti-microbial peptides(CAPs) for potential therapeutic application in Rb tumors.
Methods :
Synergistic and antagonistic effects of CAP with Topotecan was tested in Weri-Rb1 cells using checkerboard assay. Effects of peptides on regulating DNA damage and repair, mitochondrial membrane disruption, apoptosis and 3D tumor spheroid formation was assayed in Weri-Rb1 cells. Orthotopic xenograft tumor model was developed by intravitreal injection of 1.5 × 106 Weri-Rb1 cells over 6 weeks in immunosuppressed rabbits (n=8) followed by intravitreal therapy using Topotecan for additional 4 weeks. Tumor development was monitored by OCT and fundus imaging.
Results :
Two CAPs HC3 and HC5 significantly reduced cancer cell viability (p ≤ 0.01) as well as shrinkage of tumor spheroids (p ≤ 0.01) measured by HCA. Checkerboard assay demonstrated combination of peptides and topotecan caused synergistic effects (FICi ≤ 0.5, p≤ 0.001). IC50 dosages of peptides show activation of caspase 3, caspase 9, PARP as well as p53 and γH2A.X phosphorylation measured by western blot and immunofluorescence. OCT analysis of the rabbit xenograft eyes demonstrated intra and supra-retinal tumors, tumor seeds and increased retinal volume and surface area which reduced upon treatment.
Conclusions :
CAP show significant reduction of Rb null tumor size and integrity specific to cancer cells. The Rb animal model developed demonstrates its utility for efficient testing of anti-cancer drugs or their combinations locally through intra-vitreal delivery.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.