217 In Vitro Study of Yondelis in Combination with a Panel of PARP Inhibitors

Background: Splicing is a process of removing non-coding introns from pre-mRNA before mature mRNA is formed and subsequently translated into protein. Cancer cells have increased splicing rates and are more prone to splicing inhibitors. Targeting the spliceosome may cause tumor inhibition at drug levels that do not affect normal cells. Spliceostatin A and related derivatives have been reported to inhibit spliceosome assembly by interacting with SF3b, an essential component of spliceosome, and block angiogenesis by inhibiting global gene expression including VEGF. However, development of this chemical series was delayed due to the severe toxicity and the lack of treatment window. It is therefore desirable to identify/generate novel analogs that can be well tolerated, yet still exhibit differential killing of tumor cells. Material and Methods: Bacterium Pseudomonas sp. (FERM BP-3421) was fermented in various media, under varied conditions, or co-cultured with a panel of bacteria and fungi. Metabolites with MS and UV spectrum similar with spliceostatins have been isolated and their structures were elucidated by NMR spectroscopy. Purified compounds were tested in NCI60 tumor cell lines screening. Results: Several new analogs of spliceostatin A without the epoxide functionality have been generated by changing fermentation time, media composition and co-culturing the producing bacterium strain with other bacteria. Most of these novel metabolites showed potent and differential anti-proliferation activities in the NCI60 screen, with GI50s between <0.1 nM − 25 nM. Conclusions: This approach has produced several new spliceostatin analogs with potent antitumor activities, and opened a new opportunity to understand the SAR and the biosynthesis of spliceostatin related compounds.