Abstract 6003: Developing Mediator kinase deficient mouse models of CDK8/19 inhibitor therapy
Authors: Mogila Vladic , Bruter Alexandra A. , Varlamova Ekaterina A. , Korshunova Diana S. , Tatarskiy Victor V. , Shtil Aleksander A. , Roninson Igor B. 
Published: June 2022

Abstract
CDK8 and CDK19 are two paralogous kinases of transcription-regulating Mediator complex, which mediate transcriptional reprogramming by potentiating the induction of previously silent genes that are activated by different signal-responsive transcription factors. CDK8 is ubiquitously expressed while CDK19 is highly expressed in only some tissues or tumors. Small molecule CDK8/19 kinase inhibitors are being developed for breast and prostate cancers and leukemias and potentially for other cancers; their tumor-suppressive effects are mediated via effects on transcriptional reprogramming in both tumor and stromal cells. Mediator kinase deficient mice would provide valuable models for CDK8/19 inhibitor therapy. Cdk8 knockout in mouse embryonic stem cells leads to early embryonic lethality (Westerling et al., Mol Cell Biol 2007;27:6177) but conditional Cdk8 knockout in adult mice was reported to yield no phenotype (McCleland et al., J Pathol 2015;237:508). The latter animals, however, still expressed Cdk19, which could have compensated for the loss of Cdk8. To evaluate the effects of the deficiency in both Mediator kinase paralogs, we have now developed and characterized mice with stable CRISPR/CAS9 Cdk19 knockout. In contrast to Cdk8 knockout mice, Cdk19-/- animals are viable, with no apparent diminution of the lifespan. Following multiple generations of back crosses to eliminate potential off-target mutations, Cdk19 homozygous knockout mice display no consistent phenotypic aberrations, except for the early onset of infertility in homozygous Cdk19-/- females (but not males), starting from 3-4 months of age. To achieve conditional knockout of Cdk8 in Cdk19-deficient background, Cdk19-/- mice were crossed with previously developed mice with floxed Cdk8 (McCleland et al., ibid) and with ROSA tamoxifen-inducible Cre recombinase. Following tamoxifen administration at 700 mg/kg/day for 5 days, we observed massive Cdk8 knockout in all the tested organs (liver, lungs, spleen, bone marrow). Despite the lack of both Cdk8 and Cdk19, these mice remain viable and show no apparent abnormalities for at least 3 weeks of observation. The newly developed mice with constitutive Cdk19 and inducible Cdk8 knockout will be used to study the different physiological roles of Mediator kinase, to evaluate the stromal effects of Mediator kinase inhibition on tumor growth and to predict potential side effects of long-term CDK8/19 inhibitor therapy. (Supported by Megagrant 14.W03.31.0020 from the Ministry of Science and Education of the Russian Federation).
Citation Format: Vladic Mogila, Alexandra A. Bruter, Ekaterina A. Varlamova, Diana S. Korshunova, Victor V. Tatarskiy, Aleksander A. Shtil, Igor B. Roninson. Developing Mediator kinase deficient mouse models of CDK8/19 inhibitor therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6003.