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RNA Pol II in global NER (XPC) deficient cells, but failed to do it in TC NER (CSB, XPD and XPG) deficient cells. Importantly, these effects were confirmed to be specific for the Rpb1 subunit of RNA Pol II, since other subunits were not affected (Rpb2 and Rpb4) as well as other factors of the transcriptional machinery, such as TBP (TFIID), p62 (TFIIH), XPD or the RPA194 subunit of the RNA Pol I. Finally, it was also demonstrated that, contrary to what occurs after DNA damage with UV light, the transcription of p53 target genes important for DNA repair, including p21 or mdm2, was irreversibly inhibited after PM01183 treatment. Together, these results show the mechanism by which PM01183 inhibits trans-activated transcription process on tumor cells.

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