Eight-month sustained delivery of regorafenib from subconjunctival crystal depots for inhibition of corneal neovascularization.

Corneal neovascularization (CoNV) treatment via ocular drug delivery remains challenging because rapid ocular clearance and limited tissue penetration result in low bioavailability, reduced therapeutic efficacy, and the need for frequent administration. Although polymer-based delivery systems can provide sustained release, their clinical translation may be limited by low drug loading, suboptimal release kinetics, and potential toxicity associated with polymer degradation products. Here, we developed a carrier-free subconjunctival depot platform composed of pure regorafenib crystals, including microcrystals (∼5 µm) and nanocrystals (∼260 nm), to achieve sustained release through a dissolution/diffusion-controlled mechanism without the need for a polymer matrix. Both formulations maintained crystallinity and their initial particle size during 12 months of storage at 4 °C. Nanocrystals exhibited faster in vitro dissolution and more rapid in vivo depot depletion than microcrystals, whereas microcrystals provided prolonged local retention, maintaining detectable regorafenib levels through eight months after a single administration. In vivo imaging and histological analyses demonstrated the formation of dense monolithic depots within the subconjunctival space, supporting sustained release and local retention. In prophylactic CoNV models, nanocrystals showed greater apparent ex vivo transport and higher early ocular tissue concentrations and produced greater early inhibition of angiogenic sprouting than microcrystals (p < 0.05). In therapeutic models of established neovascularization, a single 2 mg subconjunctival injection of either formulation induced comparable and sustained regression of neovessels for up to eight months. Nanocrystal group achieved efficacy significantly greater than that of 0.5 mg bevacizumab administered at 2-month intervals (p < 0.01). In addition, treatment with the 1 mg microcrystal formulation reduced TNF-α, IL-1β, and VEGF levels relative to saline-treated controls and was associated with improved corneal epithelial healing compared with bevacizumab. Collectively, these findings demonstrate that carrier-free pure drug crystal depots can provide sustained ocular delivery for at least eight months following a single administration, while crystal size governs the balance between initial tissue exposure and long-term retention.