Missfeldt, Mckenna

Abstract By regulating gene expression networks that mediate neoplastic behavior, epigenetic protein complexes are the ultimate effectors of oncogenic pathways. This hierarchical position of epigenetic pathways within the mechanisms that regulate cancer makes them ideal candidates for therapeutic targets. The current work was designed to characterize the role of the K9H3 Histone Methyltransferase (HMT) pathway in mediating oncogenic signals downstream of Aurora Kinase A (AurkA), with the goal of designing efficient combinatorial therapies against PDAC. Affinity protein purification, combined with mass spectrometry, demonstrates that HP1γ isolated from mitotic cells interacts with AurkA and the HMTs, G9a and GLP. We also find that this complex is critical for mitotic progression and cell proliferation. Congruently, treatment of PDAC cells with individual drugs against AurkA or HP1-HMT inhibits cell growth by inducing senescence, a cytostatic response. However, the combination of these agents has a synergistic effect of reducing cell growth in both, monolayer and spheroid cultures to result in a cytotoxic effect. Confocal and electron microscopy, along with cell cycle analysis, demonstrate that the cytotoxic effect of this combination is due to induction of mitotic catastrophe, a distinct form of cell death that occurs during mitosis. Molecularly, the combination of AurkA and HP1-HMT inhibition bypasses G2/M arrest with downregulation of the Chk1-Cdc25c pathway. In vivo treatment of PDAC orthotopic xenografts with the HP1-HMT inhibitor alone demonstrated reduced PDAC growth, and increased efficacy in PDAC growth reduction was observed in combination with the AurkA inhibitor over either individual treatment. Thus, our data demonstrate a novel AurkA-HP1-HMT mitotic pathway that holds promise for potential pharmacological targeting in combinatorial therapy for this malignancy. Citation Format: Angela Mathison, Ann Salmonson, Mckenna Missfeldt, Thiago de Assuncao, Jennifer Bintz, Trace Christensen, Sarah Kossak, Asha Nair, Juan Iovanna, Robert Huebert, Gwen Lomberk. Pharmacological targeting of the Aurora A and Histone 3 lysine 9 methyltransferase pathways in pancreatic cancer induces mitotic catastrophe [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4060. doi:10.1158/1538-7445.AM2017-4060

Abstract Pancreatic ductular adenocarcinoma (PDAC) ranks fourth as a cause of cancer death in the USA and is almost universally fatal, with the annual number of deaths equivalent to the number of newly diagnosed cases. Valuable research in the field has revealed genetic aberrations that contribute to PDAC development and progression, with KRAS being one of the most frequent mutations in more than 90% of patient samples. However, to date, any efforts to directly target KRAS have failed in the clinic. Thus, there is indisputably an urgent need to further improve our understanding of molecular mechanisms underlying PDAC development as to identify novel therapeutic targets, including druggable important downstream targets and nodes orchestrated by oncogenic KRAS. In particular, we are interested in epigenetic pathways involved in PDAC development and progression due to the potential reversibility of any alteration, unlike genetic mutation. In the current study, using a cell model that allows inducible expression of mutant KRASG12D, we find that protein levels of the dimethyl-K9H3 histone methyl transferase (HMT), G9a, and its complex partners are increased in response to activation of the oncogenic Kras pathway. Furthermore, the activation of this oncogenic pathway results in the formation of the G9a-GLP-Wiz trimer complex, as determined by affinity protein purification, combined with mass spectrometry. In vivo experiments involving the cross of the Pdx1-CRE/LSL-KRASG12D mice with G9afl/fl animals demonstrate that a loss of the H3K9Me2 mark in the nucleus of exocrine cells is accompanied by a significantly reduced number of PanIN lesions. RNA-Seq experiments from these animals reveal that these mice have reduced levels of typical molecular markers of PanINs. In addition, these experiments show changes in the levels in several genes, which have been previously been shown to synergize with Kras to mediate pancreatic cancer initiation. Congruently, pharmacological inhibition of G9a using BRD4770 displays an inhibitory effect on KRASG12D-induced cell proliferation. Combined, these data provide evidence for a key role of the meK9H3-G9a pathway as a mediator of the oncogenic Kras response and defines a novel point of potential therapeutic intervention for PDAC. Citation Format: Angela Mathison, Ann Salmonson, Brooke Paradise, Mckenna Missfeldt, Juan Iovanna, Daniel Billadeau, Raul Urrutia, Gwen Lomberk. The epigenetic regulator, G9a, is a KRAS-inducible protein and its inactivation inhibits PanIN formation by this oncogene [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1391. doi:10.1158/1538-7445.AM2017-1391

Abstract The current integrative pathobiologic hypothesis states that pancreatic cancer (PDAC) develops and progresses in response to an interaction between known oncogenes and downstream epigenomic regulators. Congruently, this study tests a new combinatorial therapy based on the inhibition of the Aurora kinase A (AURKA) oncogene and one of its targets, the H3K9 methylation–based epigenetic pathway. This therapeutic combination is effective at inhibiting the in vitro growth of PDAC cells both, in monolayer culture systems, and in three-dimensional spheroids and organoids. The combination also reduces the growth of PDAC xenografts in vivo. Mechanistically, it was found that inhibiting methyltransferases of the H3K9 pathway in cells, which are arrested in G2–M after targeting AURKA, decreases H3K9 methylation at centromeres, induces mitotic aberrations, triggers an aberrant mitotic check point response, and ultimately leads to mitotic catastrophe. Combined, these data describe for the first time a hypothesis-driven design of an efficient combinatorial treatment that targets a dual oncogenic–epigenomic pathway to inhibit PDAC cell growth via a cytotoxic mechanism that involves perturbation of normal mitotic progression to end in mitotic catastrophe. Therefore, this new knowledge has significant mechanistic value as it relates to the development of new therapies as well as biomedical relevance. Implications: These results outline a model for the combined inhibition of a genetic-to-epigenetic pathway to inhibit cell growth and suggest an important and provocative consideration for harnessing the capacity of cell-cycle inhibitors to enhance the future use of epigenetic inhibitors. Mol Cancer Res; 15(8); 984–97. ©2017 AACR.