D,L-Sulforaphane (SFN) is a synthetic racemic analogue of broccoli constituent L-sulforaphane with in vivo evidence of cancer chemopreventive effect in rodent models. For example, we showed previously that oral administration of 6 μmol (about 1 mg/mouse) SFN (3x/week) modestly inhibited incidence and/or burden of prostatic intraepithelial neoplasia and well-differentiated cancer, but not poorly-differentiated (advanced) prostate cancer, in Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) mice in association with apoptosis induction. Previous studies from our laboratory have also revealed that SFN treatment causes autophagy in cultured human prostate cancer cells, which serves to inhibit apoptotic cell death by delaying release of cytochrome c due to sequestration of mitochondria in autophagosomes. However, the in vivo significance of these cellular observations was unclear. The present study demonstrates, for the first time, in vivo augmentation of SFN-mediated prostate cancer chemoprevention by pharmacologic suppression of autophagy using chloroquine (CQ). A total of 128 four-week old TRAMP mice were randomized into one of the following four groups: (1) control (n=32), (2) SFN (n=32), (3) CQ (n=35), and (4) SFN + CQ (n=29). Termination of the experiment was planned after 18 weeks of treatment, but early sacrifice was necessary for some mice in each group (mostly from groups 1-3) due to a variety of reasons but not unique to any treatment group, including weight loss, premature death, morbidity, or early tumor onset. Nevertheless, % mice with prostate weight of >1g, an indicator of advanced (poorly-differentiated) prostate cancer, was significantly lower in the SFN + CQ group compared with control (P=0.006 by Fisher's exact test), SFN alone (P=0.017), and CQ alone group (P=0.072). Likewise, the incidence and burden of microscopic poorly-differentiated prostate cancer was significantly lower in the mice of the SFN + CQ group compared with control. Transmission electron microscopy confirmed in vivo autophagy induction by SFN administration in the dorsolateral prostate. Augmentation of SFN-mediated prostate cancer chemoprevention by CQ was associated with reduced cell proliferation. Plasma proteomics indicated protein level changes unique to the SFN + CQ combination compared with other groups (control or SFN), including hemopexin, serpina1c protein, and fructose-bisphosphate aldolase A isoform precursor. Cluster analysis of proteomics data revealed significant enrichment for gene ontology (GO) terms proteasome and threonine protease (2.8), protease inhibitor (2.7), and protein-lipid complex (2.6). These results merit determination of the efficacy of SFN + CQ combination for prevention of prostate cancer in a clinical setting. This investigation was supported by the NCI grant CA115498-07.
Citation Format: Avani R. Vyas, Eun-Ryeong Hahm, Julie A. Arlotti, Dhimant Desai, Shantu Amin, Shivendra V. Singh. Augmentation of D,L-sulforaphane-mediated prostate cancer chemoprevention by pharmacologic inhibition of autophagy using chloroquine in a transgenic mouse model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3695. doi:10.1158/1538-7445.AM2013-3695