104 Background: The Warburg effect describes the ability of cancer cells to consume larger amounts of glucose in comparison to normal tissue, due to the overexpression of insulin-independent glucose transporters (e.g. GLUT1). This effect can be used to enhance the selectivity and reduce side effects of cytotoxic anticancer molecules by its conjugation to sugar residues, thus, generating cytotoxic agents showing higher selectivity to cancer cells. In continuation of our research on anticancer natural 1,4-naphthoquinones we have investigated a large series of novel semi-synthetic molecules containing 1,4-naphthoquinones element conjugated with glucose molecule via -S-CH2- bond. Methods: We performed screening examinations for 35 novel synthetic molecules in human prostate cancer in vitro. The selected most active compounds were tested in several human prostate cancer cell lines harboring different levels of drug resistance, as well as in non-malignant cells to specify their selectivity. Compounds with the highest cytotoxicity and selectivity were further investigated. The mode of action was assessed including effects on apoptosis induction, oxidative stress, mitochondria, AR-signaling as well as glucose uptake and ER stress were assessed. In vivo dose finding and efficacy analyses were performed. Results: We identified two promising derivatives, showing IC50s at low micro- and nanomolar concentrations. Glucose depletion from the culture media led to increased cytotoxicity and cotreatment with a GLUT1-inhibitor showed an antagonistic effect, suggesting a concurrent uptake and therefore a Warburg effect targeting. The selected compounds exhibited most pronounced cytotoxic activity in DU145 cells as well as 22Rv1 cells. Non-malignant cells were generally less affected. The mode of action involves a loss of mitochondrial membrane potential, a release of cytochrome c and AIF into the cytosol and an upregulation of caspase-9, caspase-3 and cleaved PARP, as well as downregulation of Bcl-2 and Survivin, indicating that mitochondria are a major target, leading to the activation of the intrinsic apoptotic pathway. Early events in treated cells are ROS production and calcium release into the cytosol, a marker of ER-stress. Furthermore, downregulation of the AR and its signaling was observed on mRNA- and protein-level. In vivo experiments revealed antitumor activity in a 22Rv1-xenograft mouse model without severe side effects. Conclusions: In conclusion, we were able to identify two glucose-conjugated 1,4-naphthoquinones exhibiting potent in vitro and in vivoactivity and selectivity in human prostate cancer cells due to the Warburg effect targeting. Cytotoxic activity was exerted via initial ROS production and ER stress leading to mitochondrial damage and the induction of the intrinsic apoptotic pathway.
Demethylzeylasteral (T-96) initiates extrinsic apoptosis against prostate cancer cells by inducing ROS-mediated ER stress and suppressing autophagic flux
