PLGA Implants for Controlled Release of Immune Checkpoint Inhibitors, Cpg, and Docetaxel for the Treatment of Glioblastoma

Abstract

Poly(lactic-co-glycolic acid) (PLGA) is the most commonly investigated biodegradable polymer for long-acting release (LAR) applications and has been used in 19 FDA-approved products. Despite this success, there has been a slow increase in PLGA-based commercial products since the first approval in the 1980s. There are no existing options for controlled release of large molecules which are far more complicated than small molecules and can undergo stability issues during or after encapsulation in PLGA. Glioblastoma is a devastating disease with a median survival of 12-14 months and a high rate of recurrence, complicated by an immunosuppressive tumor environment with few treatment options due to the blood brain/blood tumor barriers without systemic toxicity, and thus a local sustained release option could be beneficial. To approach the immunosuppressive, heterogenic, and abnormal solid stress tumor environment of GBM we have formulated immune checkpoint inhibitors, anti-PD-1 and anti-CTLA-4, immune-stimulatory agent, CpG, and penetration-enhancer, docetaxel, into PLGA LAR implants. Coated PLGA implants achieved high loading (6-8% w/w) of anti-PD-1 and anti-CTLA-4 and released in vitro over 60 days with minimal monomer content, secondary structure and immunoreactivity losses. CpG implants (loading ~6% w/w) released continuously in vitro over 40 days with >95% cumulative release and showed retained TLR-9 binding activity. Docetaxel implants (loading ~50% w/w) released over 110 days with >80% total cumulative release. Anti-PD-1 and anti-CTLA-4 implants combined with radiation resulted in enhanced median survivals of 71 days and 74 days, respectively, relative to controls. Two long-term survivors from each mAb group were resistant to tumor cell re-challenge, indicating the generation of an immunological memory response. To bridge the gap between slow development of FDA-approved controlled release products using PLGA, including those for delivery of large molecules, we investigated 17 different PLGAs from five different manufacturers and compared their in vitro degradation and erosion behaviors as drug-free films, microspheres, and implants as a function of L/G ratio, MW, end-capping, manufacturer, and formulation geometry. We found that comparable PLGAs from different manufacturers could vary in their in vitro performance due to differences in their microstructural properties and possibly their manufacturing conditions. Higher glycolic sequence blockiness or block lengths, led to increased initial degradation due to the increased hydrolysis rate of glycolic-glycolic linkages. We found that the increased auto-catalysis preferentially increased the loss of glycolic units over lactic units in 75/25 PLGA implants compared to microspheres, with implants becoming ~97% lactic acid within two weeks, while microspheres only gradually lost glycolic units faster than lactic units, indicating differences in their hydrolytic mechanisms. Better knowledge and control of relevant macro/micro-properties of the polymer may help bridge the gap between the effects of raw materials and the product performance, allowing for better polymer selection and potentially increase the number of approved PLGA-based LAR products. This thesis develops PLGA LAR implants for monoclonal antibodies, which are injectable through a small gauge needle. The implants are applied to five different drugs, and exhibit high drug loading, ideal slow and continuous release over months, maintained stability, efficacy in a glioblastoma model and investigates formulations for intraocular delivery. To address the disproportion of LAR products available on the market, and especially lack thereof for large molecules, this work investigates the effects of PLGA raw material on performance behavior and establishes key differences between manufacturers and effects of macro/micro-properties of PLGA on degradation and erosion.