Abstract 2584: Specific antitumor activity of the splicing modulator sudemycin and cooperation with ibrutinib in chronic lymphocytic leukemia
Authors: Xargay-Torrent Sílvia , López-Guerra Mónica , Rosich Laia , Montraveta Arnau , Roldán Jocabed , Rodríguez Vanina , Villamor Neus , Aymerich Marta , Lagisetti Chandraiah , Webb Thomas R. , Campo Elias , Colomer Dolors 
Published: August 2015

Abstract
Chronic lymphocytic leukemia (CLL) is the most frequent adult leukemia in western countries. A core component of the spliceosome, SF3B1, is among the most frequently mutated genes in CLL affecting up to 5-18% of patients. Clinically, SF3B1 mutations correlate with a more aggressive behavior of the disease, poorer clinical outcome and shorter time to treatment, as well as treatment refractoriness. Consistent with the crucial role of the spliceosome in CLL, mutations in other genes of the mRNA splicing, processing and transport machinery are also found to be frequently mutated in this tumor. Thus, our aim was to evaluate the antitumor effect of the spliceosome modulator sudemycin in SF3B1-mutated and -unmutated CLL cells in the in vitro and in vivo settings.
For this purpose, cytotoxicity was measured by flow cytometry, in vivo activity of the compound was evaluated in an adoptive transfer mouse model of CLL, splicing products were analyzed by RT-PCR with specific primers and NF-κB activity was determined with the TransAM NF-κB p65 kit.
Our results demonstrate that the spliceosome modulator sudemycin showed selective cytotoxicity in primary CLL cells when compared with healthy lymphocytes and tumor cells from other malignancies, with a slight bias for CLL cases with mutations for spliceosome-RNA maturation genes. Consistently, sudemycin exhibited considerable antitumor activity in a xenograft CLL model. At the molecular level, the antileukemic effect of sudemycin involved the splicing modulation of several target genes important for tumor survival, both in SF3B1-mutated and -unmutated cases. Thus, the apoptosis induced by this compound was related to the alternative splicing switch of MCL1 toward its proapoptotic isoform. Sudemycin also functionally disturbed NF-κB pathway through the induction of a spliced RELA variant lacking its DNA binding domain. Importantly, we show that the modulation of the alternative splicing of the inhibitor of Btk(IBTK) by sudemycin leaded to an enhanced antitumor effect in combination with ibrutinib.
In conclusion, we provide first evidence that the spliceosome is a relevant therapeutic target in CLL, supporting the use of splicing modulators in combination with ibrutinib as a promising approach for the treatment of CLL patients.
Citation Format: Sílvia Xargay-Torrent, Mónica López-Guerra, Laia Rosich, Arnau Montraveta, Jocabed Roldán, Vanina Rodríguez, Neus Villamor, Marta Aymerich, Chandraiah Lagisetti, Thomas R. Webb, Elias Campo, Dolors Colomer. Specific antitumor activity of the splicing modulator sudemycin and cooperation with ibrutinib in chronic lymphocytic leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2584. doi:10.1158/1538-7445.AM2015-2584