Jnj-47117096, A Selective Small Molecule Inhibitor Of The Melk Oncogene Decreases Dna Damage Tolerance In Highly Proliferating Cancer Cells

Maternal embryonic leucine zipper kinase (MELK, hMP38, pEG3), a Ser/Thr protein kinase, is highly overexpressed in stem cells and cancer cells. The oncogenic role of MELK is attributed to disabling critical cell cycle check points as well as enhancing replication. Most functional studies have relied on the use of siRNA/shRNA mediated gene silencing, but this often can be associated with off-target effects. Here we want to present a novel, potent and selective small molecule inhibitor JNJ-47117096 that has enabled us to validate the biological function of MELK kinase. Outcome: MELK inhibition in cancer cells with an intact p53 signaling pathway is linked to a replicative senescence phenotype. This phenotype correlates with a rapid ATM activation and phosphorylation of CHK2 without any effects on the alternative ATR/ CHK1 DNA damage pathways. Furthermore, JNJ-47117096 induces strong phosphorylation of p53 and prolonged up-regulation of p21 without the induction of apoptosis. Strikingly, MELK inhibition in several p53 disabled cancer cells showed induction of a mitotic catastrophe phenotype followed by prominent cell killing. Finally, JNJ-47117096 triggers a rapid degradation of cellular MELK protein, independent of the cell cycle phase and its regulation by the E2F pathway. This observation can clearly be linked to a direct binding effect of JNJ-47117096 to cellular MELK protein confirmed by chemical proteomics. Conclusion: Our data generated with JNJ-47117096, confirmed by selective siRNAs, indicate MELK as a key stimulator of proliferation and replication by its ability to increase the threshold for DNA damage tolerance. Targeting MELK function by selective small molecule inhibitors might sensitise tumors to DNA-damaging agents or radiation therapy. Citation Format: Lijs Beke, Joannes T.m. Linders, Cenk Kig, An Boeckx, Erika van Heerde, Dirk Wuyts, Marc Parade, Lieven Meerpoel, Chris Johnson, Monique Beullens, Mathieu Bollen, Dirk Brehmer. JNJ-47117096, a selective small molecule inhibitor of the MELK oncogene decreases DNA damage tolerance in highly proliferating cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2936. doi:10.1158/1538-7445.AM2014-2936