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Controlled release from biodegradable polymers is a novel approach to replace daily painful injections of protein drugs. A major obstacle to development of these polymers is the need to retain the structure and biological activity of encapsulated proteins during months of incubation under physiological conditions. We encapsulated bovine serum albumin (BSA) in injectable poly(DL-lactide- co-glycolide) (PLGA) 50/50 cylindrical implants and determined the mechanism of BSA instability. Simulations of the polymer microclimate revealed that moisture and acidic pH (<3) triggered unfolding of encapsulated BSA, resulting in peptide bond hydrolysis and noncovalent aggregation. To neutralize the acids liberated by the biodegradable lactic/glycolic acid-based polyester, we coincorporated into the polymer an antacid, Mg(OH)2, which increased microclimate pH and prevented BSA structural losses and aggregation for over one month. We successfully applied this stabilization approach in both cylinder- and microsphere-injectable configurations and for delivery of angiogenic basic fibroblast growth factor and bone-regenerating bone morphogenetic protein-2.

No abstract

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No abstract

Injectable controlled-release systems based on biodegradable copolymers of lactic and glycolic acids (PLGAs) have become widely used for delivery of protein therapeutics and vaccine antigens. Over the last five years, great strides have been made toward overcoming the difficulty of stabilizing PLGA-encapsulated proteins. In addition to stabilizing proteins during encapsulation with anhydrous methods, two approaches have proven highly effective to stabilize proteins during 1-month release incubation under physiological conditions: protein complexation with zinc and control of PLGA microclimate pH with antacid excipients. Described here are recent advances in the stabilization of proteins encapsulated in PLGA delivery systems.

Acidification of the internal poly(lactide-co-glycolide) (PLGA) microenvironment is considered one of the major protein stresses during controlled release from such delivery systems. A model protein, bovine serum albumin (BSA), was incubated at 37 degrees C for 28 days to simulate the environment within the aqueous pores of PLGA during the release phase and to determine how acidic microclimate conditions affect BSA stability. Size-exclusion high performance liquid chromatography (SE-HPLC), SDS-PAGE, and infrared spectroscopy were used to monitor BSA degradation. BSA was most stable at pH 7, but rapidly degraded via aggregation and hydrolysis at pH 2. These simulated degradation products were nearly identical to that of unreleased BSA found entrapped within PLGA 50/50 millicylinders. At pH 2, changes in BSA conformation detected by various spectroscopic techniques were consistent with acid denaturation of the protein. By contrast, at pH 5 and above, damage to BSA was insufficient to explain the instability of the protein in the polymer. Thus, these data confirm the hypothesis that acid-induced unfolding is the basis of BSA aggregation in PLGA and the acidic microclimate within PLGA is indeed a dominant stress for encapsulated BSA. To increase the stability of proteins within PLGA systems, formulations must protect against potentially extreme acidification such that native structure is maintained.

To increase access to long-acting contraception, we developed a reversible contraceptive microneedle patch that is simple-to-administer, slowly releases contraceptive hormone (levonorgestrel) for >1 month, and generates no biohazardous sharps waste. After manually pressing the patch to skin for 1 min, microneedles rapidly separate from the patch within the skin due to effervescence triggered by contact with skin’s interstitial fluid, as demonstrated in rats and human participants. Long-acting contraception is achieved by formulating microneedles with a biodegradable polymer [poly(lactic-co-glycolic) acid] that slowly releases levonorgestrel for ~1 month in vitro. In rats, the patch maintained levonorgestrel concentration above the human contraceptive threshold level for >1 month, and a placebo microneedle patch was well-tolerated in human participants. Women of reproductive age in three continents demonstrated interest in and preference for long-acting contraception by microneedle patch. These studies indicate that an effervescent microneedle patch could facilitate greater access to long-acting contraception.