Utilizing in vitro drug release assays to predict in vivo drug retention in micelles.

In the present work, we aim at developing an in vitro release assay to predict circulation times of hydrophobic drugs loaded into polymeric micelles (PM), upon intravenous (i.v.) administration. PM based on poly (ethylene glycol)-b-poly (N-2-benzoyloxypropyl methacrylamide) (mPEG-b-p(HPMA-Bz)) block copolymer were loaded with a panel of hydrophobic anti-cancer drugs and characterized for size, loading efficiency and release profile in different release media. Circulation times in mice of two selected drugs loaded in PM were evaluated and compared to the in vitro release profile. Release of drugs from PM was evaluated over 7 days in PBS containing Triton X-100 and in PBS containing albumin at physiological concentration (40 g/L). The results were utilized to identify crucial molecular features of the studied hydrophobic drugs leading to better micellar retention. For the best and the worst retained drugs in the in vitro assays (ABT-737 and BCI, respectively), the circulation of free and entrapped drugs into PM was examined after i.v. administration in mice. We found in vivo drug retention at 24 h post-injection similar to the retention found in the in vitro assays. This demonstrates that in vitro release assay in buffers supplemented with albumin, and to a lesser degree Triton X-100, can be employed to predict the in vivo circulation kinetics of drugs loaded in PM. Utilizing media containing acceptor molecules for hydrophobic compounds, provide a first screen to understand the stability of drug-loaded PM in the circulation and, therefore, can contribute to the reduction of animals used for circulation kinetics studies.

Polymeric micelles loaded with carfilzomib increase tolerability in a humanized bone marrow-like scaffold mouse model.

Carfilzomib-loaded polymeric micelles (CFZ-PM) based on poly(ethylene glycol)-b-poly(N-2-benzoyloxypropyl methacrylamide) (mPEG-b-p(HPMA-Bz)) were prepared with the aim to improve the maximum tolerated dose of carfilzomib in a "humanized" bone marrow-like scaffold model. For this, CFZ-PM were prepared and characterized for their size, carfilzomib loading and cytotoxicity towards multiple myeloma cells. Further, circulation and tumor & tissue distribution of fluorescently labeled micelles were determined. Tolerability of CFZ-PM versus the clinical approved formulation - Kyprolis® - was assessed. CFZ-PM presented small diameter below 55 nm and low PDI < 0.1. Cy7-labeled micelles circulated for extended periods of time with over 80% of injected dose in circulation at 24 h after intravenous injection and 1.3% of the injected dose of Cy7-labeled micelles accumulated in myeloma tumor-bearing scaffolds. Importantly, CFZ-PM were well tolerated whereas Kyprolis® showed adverse effects. Kyprolis® dosed at the maximum tolerated dose, as well as CFZ-PM, did not show therapeutic benefit, while multiple myeloma cells showed sensitivity in vitro, underlining the importance of the bone marrow crosstalk in testing novel formulations. Overall, this work indicates that PM are potential drug carriers of carfilzomib.