Intratumoral delivery of β-lapachone via polymer implants for prostate cancer therapy

Purpose: β-Lapachone (ARQ 501, a formulation of β-lapachone complexed with hydroxy- propyl- β-cyclodextrin) is a novel anticancer agent with selectivity against prostate cancer cells overexpressing the NAD (P) H :quinone oxidoreductase-1 enzyme. Lack of solubility and an efficient drug delivery strategy limits this compound in clinical applications. In this study, we aimed to develop β-lapachone- containing polymer implants (millirods) for direct implantation into prostate tumors to test the hypothesis that the combination of a tumor-specific anticancer agent with site-specific release of the agent will lead to significant antitumor efficacy. Experimental Design: Survival assays in vitro were used to test the killing effect of β-lapachone in different prostate cancer cells. β-Lapachone release kinetics from millirods was determined in vitro and in vivo. PC-3 prostate tumor xenografts in athymic nude mice were used for antitumor efficacy studies in vivo. Results: β-Lapachone killed three different prostate cancer cell lines in an NAD(P)H:quinone oxidoreductase-1 - dependent manner. Upon incorporation of solid-state inclusion complexes of β-lapachone with hydroxypropyl-β-cyclodextrin into poly(o,L-lactide-co-glycolide) millirods, β-lapachone release kinetics in vivo showed a burst release of ∼0.5 mg within 12 hours and a subsequently sustained release of the drug (sim; 0.4 mg/kg/d) comparable with that observed in vitro. Antitumor efficacy studies showed significant tumor growth inhibition by β-lapachone millirods compared with controls (P « 0.0001; n = 10 per group). Kaplan-Meier survival curves showed that tumor-bearing mice treated with β-lapachone millirods survived nearly 2-fold longer than controls, without observable systemic toxicity. Conclusions: Intratumoral delivery of β-lapachone using polymer millirods showed the promising therapeutic potential for human prostate tumors.