Modular Approach for the Synthesis and Bioactivity Profiling of 8,8'-Biflavones

In this work, we report the scalable and modular synthesis of a library of 55 monomeric and dimeric flavonoids including 14 8,8'-biflavones. The sterically demanding tetra-ortho-substituted axis of an acetophenone dimer key intermediate was constructed in a regioselective manner using Fe-mediated oxidative coupling. This step was systematically optimized and performed on up to multigram scale. The biological activities of this compound library were evaluated, including cytotoxicity against healthy and malignant human cell lines, antimicrobial activity against the apicomplexan parasite Toxoplasma gondii, and antioxidant capacity. A marked increase in activity for the 8,8'-dimeric structures compared to that of their monomeric counterparts was observed. Several biflavones were identified with high selectivity indices (low cytotoxicity and high antiprotozoal activity), showing that this class of natural products may serve as lead structures for further investigations.

The Golgi stacking protein GRASP55 is targeted by the natural compound prodigiosin

BACKGROUND

The bacterial secondary metabolite prodigiosin has been shown to exert anticancer, antimalarial, antibacterial and immunomodulatory properties. With regard to cancer, it has been reported to affect cancer cells but not non-malignant cells, rendering prodigiosin a promising lead compound for anticancer drug discovery. However, a direct protein target has not yet been experimentally identified.

METHODS

We used mass spectrometry-based thermal proteome profiling in order to identify target proteins of prodigiosin. For target validation, we employed a genetic knockout approach and electron microscopy.

RESULTS

We identified the Golgi stacking protein GRASP55 as target protein of prodigiosin. We show that prodigiosin treatment severely affects Golgi morphology and functionality, and that prodigiosin-dependent cytotoxicity is partially reduced in GRASP55 knockout cells. We also found that prodigiosin treatment results in decreased cathepsin activity and overall blocks autophagic flux, whereas co-localization of the autophagosomal marker LC3 and the lysosomal marker LAMP1 is clearly promoted. Finally, we observed that autophagosomes accumulate at GRASP55-positive structures, pointing towards an involvement of an altered Golgi function in the autophagy-inhibitory effect of this natural compound.

CONCLUSION

Taken together, we propose that prodigiosin affects autophagy and Golgi apparatus integrity in an interlinked mode of action involving the regulation of organelle alkalization and the Golgi stacking protein GRASP55. Video Abstract.

Prodigiosin Sensitizes Sensitive and Resistant Urothelial Carcinoma Cells to Cisplatin Treatment

Cisplatin-based treatment is the standard of care therapy for urothelial carcinomas. However, complex cisplatin resistance mechanisms limit the success of this approach. Both apoptosis and autophagy have been shown to contribute to this resistance. Prodigiosin, a secondary metabolite from various bacteria, exerts different biological activities including the modulation of these two cellular stress response pathways. We analyzed the effect of prodigiosin on protein levels of different autophagy- and apoptosis-related proteins in cisplatin-sensitive and -resistant urothelial carcinoma cells (UCCs). Furthermore, we investigated the effect on cell viability of prodigiosin alone or in combination with cisplatin. We made use of four different pairs of cisplatin-sensitive and -resistant UCCs. We found that prodigiosin blocked autophagy in UCCs and re-sensitized cisplatin-resistant cells to apoptotic cell death. Furthermore, we found that prodigiosin is a potent anticancer agent with nanomolar IC50 values in all tested UCCs. In combination studies, we observed that prodigiosin sensitized both cisplatin-sensitive and -resistant urothelial carcinoma cell lines to cisplatin treatment with synergistic effects in most tested cell lines. These effects of prodigiosin are at least partially mediated by altering lysosomal function, since we detected reduced activities of cathepsin B and L. We propose that prodigiosin is a promising candidate for the therapy of cisplatin-resistant urothelial carcinomas, either as a single agent or in combinatory therapeutic approaches.

In vitro selective cytotoxicity of the dietary chalcone cardamonin (CD) on melanoma compared to healthy cells is mediated by apoptosis

Malignant melanoma is an aggressive type of cancer and the deadliest form of skin cancer. Even though enormous efforts have been undertaken, in particular the treatment options against the metastasizing form are challenging and the prognosis is generally poor. A novel therapeutical approach is the application of secondary plant constituents occurring in food and food products. Herein, the effect of the dietary chalcone cardamonin, inter alia found in Alpinia species, was tested using human malignant melanoma cells. These data were compared to cardamonin treated normal melanocytes and dermal fibroblasts representing healthy cells. To investigate the impact of cardamonin on tumor and normal cells, it was added to monolayer cell cultures and cytotoxicity, proliferation, tumor invasion, and apoptosis were studied with appropriate cell biological and biochemical methods. Cardamonin treatment resulted in an apoptosis-mediated increase in cytotoxicity towards tumor cells, a decrease in their proliferation rate, and a lowered invasive capacity, whereas the viability of melanocytes and fibroblasts was hardly affected at such concentrations. A selective cytotoxic effect of cardamonin on melanoma cells compared to normal (healthy) cells was shown in vitro. This study along with others highlights that dietary chalcones may be a valuable tool in anticancer therapies which has to be proven in the future in vivo.