Abstract 5558: Lurbinectedin (PM01183) specifically targets RNA Pol II for degradation via the proteasome pathway in a TC-NER-dependent fashion.

Lurbinectedin (PM01183), a new synthetic tetrahydroisoquinoline alkaloid, is a minor groove specific DNA binder that interacts directly with specific factors involved in DNA repair and transcription pathways. In living cells, PM01183-DNA adducts stall replication and transcription giving rise to double strand breaks, inducing accumulation of cells in the S-phase of the cell cycle and triggering apoptosis. In both the ongoing phase II trials (pancreas and platinum-resistant ovarian cancer) the first stage was concluded with positive results in clinical activity, ensuring the continuity of the studies. Also, phase I trials in combination with doxorubicin and gemcitabine as well as in advanced acute leukemia are ongoing. Here, we examined the effects of PM01183 on the activity and stability of the RNAPol II as well as on other factors of the transcriptional machinery, including TBP (TFIID), p62 (TFIIH), XPG and XPF. Our results showed that PM01183 induced a rapid, time- and concentration-dependent degradation of RNA Pol II in a panel of different human tumor cell lines, including HCT-116 (colon), A549 (NSCLC), HeLa (cervix) and A763 (sarcoma). This degradative process was efficiently abrogated in the presence of transcriptional (DRB or Actinomycin D) or proteasome inhibitors (MG132), demonstrating that PM01183 specifically targets the transcriptionally active RNA Pol II for degradation via the proteasome pathway. In addition, it was also shown that the effect of PM01183 on the RNA Pol II was dependent on the presence of a functional TC NER repair machinery. PM01183 induced degradation of 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 RNA Pol II, since other factors of the transcriptional machinery, such as TBP (TFIID), p62 (TFIIH), XPG or XPF or the RPA194 subunit of the RNA Pol I were not affected. Together, these results show up the complex mechanism of action of the drug on tumor cells. Citation Format: Gema Santamaria, Juan F. Martinez-Leal, Carmen Cuevas, Luis F. Garcia-Fernandez, Carlos M. Galmarini. Lurbinectedin (PM01183) specifically targets RNA Pol II for degradation via the proteasome pathway in a TC-NER-dependent fashion. [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 5558. doi:10.1158/1538-7445.AM2013-5558