Abstract
Hydroxychloroquine (HCQ) is being tested in a number of human clinical trials to determine the role of autophagy in response to standard anticancer therapies. However, HCQ pharmacodynamic (PD) responses are difficult to assess in patients, and preclinical studies in mouse models are equivocal with regard to HCQ exposure and inhibition of autophagy. Here, pharmacokinetic (PK) assessment of HCQ in non-tumor-bearing mice after intraperitoneal dosing established 60 mg/kg as the human equivalent dose of HCQ in mice. Autophagy inhibition, cell proliferation, and cell death were assessed in two-dimensional (2D) cell culture and three-dimensional tumor organoids in breast cancer. Mice challenged with breast cancer xenografts were then treated with 60 mg/kg HCQ via intraperitoneal dosing, and subsequent PK and PD responses were assessed. Although autophagic flux was significantly inhibited in cells irrespective of autophagy-dependence status, autophagy-dependent tumors had decreased cell proliferation and increased cell death at earlier time points compared with autophagy-independent tumors. Overall, this study shows that 2D cell culture, three-dimensional tumor organoids, and in vivo studies produce similar results, and in vitro studies can be used as surrogates to recapitulate in vivo antitumor responses of HCQ. SIGNIFICANCE STATEMENT: Autophagy-dependent tumors but not autophagy-independent tumors have decreased cell proliferation and increased cell death after single-agent hydroxychloroquine treatment. However, hydroxychloroquine causes decreased autophagic flux regardless of autophagy status, suggesting its clinical efficacy in the context of autophagy inhibition.