Poloxamer-linked prodrug of a topoisomerase I inhibitor SN22 shows efficacy in models of high-risk neuroblastoma with primary and acquired chemoresistance

High-risk solid tumors continue to pose a tremendous therapeutic challenge due to multidrug resistance. Biological mechanisms driving chemoresistance in high-risk primary and recurrent disease are distinct: in newly diagnosed patients, non-response to therapy is often associated with a higher level of tumor "stemness" paralleled by overexpression of the ABCG2 drug efflux pump, whereas in tumors relapsing after non-curative therapy, poor drug sensitivity is most commonly linked to the dysfunction of the tumor suppressor protein, p53. In this study, we used preclinical models of aggressive neuroblastoma featuring these characteristic mechanisms of primary and acquired drug resistance to experimentally evaluate a macromolecular prodrug of a structurally enhanced camptothecin analog, SN22, resisting ABCG2-mediated export, and glucuronidation. Together with extended tumor exposure to therapeutically effective drug levels via reversible conjugation to Pluronic F-108 (PF108), these features translated into rapid tumor regression and long-term survival in models of both ABCG2-overexpressing and p53-mutant high-risk neuroblastomas, in contrast to a marginal effect of the clinically used camptothecin derivative, irinotecan. Our results demonstrate that pharmacophore enhancement, increased tumor uptake, and optimally stable carrier-drug association integrated into the design of the hydrolytically activatable PF108-[SN22](2) have the potential to effectively combat multiple mechanisms governing chemoresistance in newly diagnosed (chemo-naive) and recurrent forms of aggressive malignancies. As a macromolecular carrier-based delivery system exhibiting remarkable efficacy against two particularly challenging forms of high-risk neuroblastoma, PF108-[SN22](2) can pave the way to a robust and clinically viable therapeutic strategy urgently needed for patients with multidrug-resistant disease presently lacking effective treatment options.