Polymer micelle formulations of proteasome inhibitor carfilzomib for improved metabolic stability and anticancer efficacy in human multiple myeloma and lung cancer cell lines

Abstract

Carfilzomib (CFZ) is a second-generation proteasome inhibitor drug approved for the treatment of multiple myeloma. Contrary to its excellent antimyeloma activity, CFZ has shown only limited efficacy in patients with solid malignancies. This lack of efficacy has been attributed in part to rapid degradation of CFZ in the body, possibly hindering the ability of CFZ to access the proteasome target in solid tumors. We hypothesized that polymer micelles, a currently Food and Drug Administration-approved nanoparticle drug delivery formulation, may protect CFZ from metabolic degradation and thus expand the clinical utility of the drug as an anticancer agent. To test our hypothesis, we prepared CFZ-entrapped polymer micelle particles with various compositions and drug release profiles and examined the extent of the CFZ metabolism in vitro using mouse liver homogenates. We also assessed the cytotoxic activities of the CFZ-entrapped micelle formulations in human cancer cell lines derived from B lymphocytes (RPMI-8226) and the lung (H460). Our data indicated that polymer micelle-based formulations can improve metabolic stability and cytotoxic effects of CFZ compared with free CFZ in human cancer cell lines tested. Taken together, these results suggest that polymer micelles may have potential as a delivery system for CFZ with an extended therapeutic utility for nonhematologic malignancies in the future.

Graphical abstract

Fig. 1.

In vitro metabolic stability of polymer micelle formulations containing CFZ in the presence of mouse liver homogenates. CFZ remaining was measured at 0, 5 (blank bars), 10 (striped bars), and 20 minutes (checkered bars) following incubation with liver homogenates. Percentage of CFZ remaining values is normalized to 0-minute controls, and results are represented as means ± S.E.M. All polymer micelle groups significantly differ from CFZ control determined by one-way analysis of variance (P < 0.05).

Fig. 2.

In vitro drug release profiles of polymer micelle formulations. CFZ release was measured over 72 hours and represented as percent drug remaining of control. Results are represented as means ± S.E.M., and each data set is fitted to a two-phase decay model (dotted curve).

Fig. 3.

Cytotoxic activities of polymer micelles containing CFZ in H460 (A) and select micelle formulations in RPMI-8226 (B) cell lines. Results are represented as percentage of cell viability of vehicle-only control. Micelle formulations containing CFZ were compared at 50 and 5 nM of equivalent CFZ concentration in H460 and RPMI-8226 cells, respectively. Data are represented as means ± S.E.M.

Fig. 4.

Cytotoxic effects of PM1 and PM2 empty particle controls and coincubation of CFZ with empty particles tested in H460 (A) and RPMI-8226 (B) cells. Results are represented as percentage of cell viability of vehicle-only control. Empty particle controls and coincubation controls were compared at 50 nM equivalent CFZ concentration in both cell lines. Data are represented as means ± S.E.M.