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Targeted inhibition of proteins modulating epigenetic changes is an increasingly important priority in cancer therapeutics, and many small molecule inhibitors are currently being developed. In the case of neuroblastoma (NB), a paediatric solid tumour with a paucity of intragenic mutations, epigenetic deregulation may be especially important. In this study we validate the histone methyltransferase G9a/EHMT2 as being associated with indicators of poor prognosis in NB. Immunological analysis of G9a protein shows it to be more highly expressed in NB cell-lines with MYCN amplification, which is a primary determinant of dismal outcome in NB patients. Furthermore, G9a protein in primary tumours is expressed at higher levels in poorly differentiated/undifferentiated NB, and correlates with high EZH2 expression, a known co-operative oncoprotein in NB. Our functional analyses demonstrate that siRNA-mediated G9a depletion inhibits cell growth in all NB cell lines, but, strikingly, only triggers apoptosis in NB cells with MYCN amplification, suggesting a synthetic lethal relationship between G9a and MYCN. This pattern of sensitivity is also evident when using small molecule inhibitors of G9a, UNC0638 and UNC0642. The increased efficacy of G9a inhibition in the presence of MYCN-overexpression is also demonstrated in the SHEP-21N isogenic model with tet-regulatable MYCN. Finally, using RNA sequencing, we identify several potential tumour suppressor genes that are reactivated by G9a inhibition in NB, including the CLU, FLCN, AMHR2 and AKR1C1-3. Together, our study underlines the under-appreciated role of G9a in NB, especially in MYCN-amplified tumours.

Mutations in the tumor suppressor gene TP53 contribute to the development of approximately half of all human cancers. One mechanism by which mutant p53 (mtp53) acts is through interaction with other transcription factors, which can either enhance or repress the transcription of their target genes. Mtp53 preferentially interacts with the erythroblastosis virus E26 oncogene homologue 2 (ETS2), an ETS transcription factor, and increases its protein stability. To study the mechanism underlying ETS2 degradation, we knocked down ubiquitin ligases known to interact with ETS2. We observed that knockdown of the constitutive photomorphogenesis protein 1 (COP1) and its binding partner De-etiolated 1 (DET1) significantly increased ETS2 stability, and conversely, their ectopic expression led to increased ETS2 ubiquitination and degradation. Surprisingly, we observed that DET1 binds to ETS2 independently of COP1, and we demonstrated that mutation of multiple sites required for ETS2 degradation abrogated the interaction between DET1 and ETS2. Furthermore, we demonstrate that mtp53 prevents the COP1/DET1 complex from ubiquitinating ETS2 and thereby marking it for destruction. Mechanistically, we show that mtp53 destabilizes DET1 and also disrupts the DET1/ETS2 complex thereby preventing ETS2 degradation. Our study reveals a hitherto unknown function in which DET1 mediates the interaction with the substrates of its cognate ubiquitin ligase complex and provides an explanation for the ability of mtp53 to protect ETS2.

Mutant p53 (mtp53) is an oncogene that drives cancer cell proliferation. We found that mtp53 associates with the promoters of numerous nucleotide metabolism genes (NMG). Mtp53 knockdown reduced NMG expression and substantially depleted nucleotide pools. Decreased GTP levels correlated with reduced activation of GTP dependent proteins (GTPases) and reduced invasiveness. Addition of exogenous GTP restored the invasiveness of mtp53 knockdown cells, suggesting that mtp53 promotes invasion by increasing GTP. Additionally, mtp53 creates a dependency on the nucleotide salvage pathway enzyme deoxycytidine kinase (dCK) for the maintenance of a proper balance in dNTP pools required for proliferation. These data indicate that mtp53 harboring cells have acquired a synthetic sick or lethal phenotype relationship with the nucleotide salvage pathway. Finally, elevated expression of NMG correlates with mutant p53 status and poor prognosis in breast cancer patients. Thus, mtp53's control of nucleotide biosynthesis has both a driving and sustaining role in cancer development. Citation Format: Luis A. Martinez, Madhusudhan Kollareddy. Regulation of nucleotide metabolism by mutant p53 contributes to its gain-of-function activities. [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 2108. doi:10.1158/1538-7445.AM2015-2108

Carboplatin, cisplatin and oxaliplatin are structurally similar anticancer drugs and their mechanism of action is permanent coordination to DNA and interfering with DNA repair. However, these drugs have different anticancer activities in human tumors, adverse effects and dose limiting toxicities. Therefore, we performed complex proteomic profiling in order to characterize cellular effects of all three platinum based anticancer drugs. To identify the molecular basis of different pharmacological properties, expressional characteristics of cells exposed to vincristine and daunorubicin were used in parallel as prototypes of drugs with different mechanism of action. T-lymphoblastic leukemia CCRF-CEM cells were treated with 5x IC50 concentrations of individual drugs for time equivalent to half-time to induction apoptosis. Untreated (control) cells were cultured with heavy amino acid labeled media in order to enable relative quantification of peptide expression using SILAC technology, LC-MS/MS and LC-MALDI-TOF/TOF. Results were processed by Proteinscape software equipped by Mascot and Phenyx analytical algorithms. We identified 646 ± 133 proteins by ESI and 312 ± 85 proteins by MALDI in average of all fifteen replicates. Identified results were further processed by in-house written script to remove outlier peptides and to normalize individual runs. All replicates were summed, and statistic analysis was done. To see up- and down- regulated proteins, the hierarchical clustering and PCA analysis was performed. Hierarchical clustering revealed that cisplatin and carboplatin shares the same cluster what is conclusive with literature. Surprisingly, the cluster of daunorubicin and vincristine was close to cisplatin and carboplatin and the oxaliplatin was in the separated cluster from rest of four drugs. PCA analysis revealed 30 proteins with contribution higher than 1 %. The highest contribution (7.5 %) to drug clustering have proteins involved in DNA remodeling. These proteins could be used as specific biomarkers of therapy by platinum based compounds. Citation Format: Petr Dzubak, Tomas Ozdian, Dusan Holub, Gabriela Rylova, Jiri Rehulka, Madhusudhan kollareddy, Daniela Mlcuchova, Marian Hajduch. Proteomic profiling of platinum based anticancer drugs. [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 4652. doi:10.1158/1538-7445.AM2013-4652

Aurora kinase inhibitors are being developed as anti-cancer drugs and more than 10 small molecules are currently undergoing clinical trials. CYC116, an Aurora kinase inhibitor, discovered and developed by Cyclacel Ltd. is currently in phase I clinical trial in patients with advanced solid tumors. CYC116 showed significant anti-proliferative activity in preclinical studies. However tumor cell resistance mechanisms towards this Aurora kinase inhibitor have not been yet established. We developed several HCT116 p53 wild-type and HCT116 p53 null resistant clones towards CYC116 by exposing the cells to high drug concentrations. In order to compare resistance mechanisms, another Aurora kinase inhibitor, ZM447439, was used as a reference compound. Here we present the preliminary data characterizing CYC116-resistant clones. In MTT cytotoxicity assays all the clones showed CYC116 resistance and cross resistance to other Aurora kinase inhibitors, and to some anticancer drugs, which suggest a multidrug resistance phenotype. However the degree of resistance is variable between the clones. All CYC116-resistant clones irrespective of their p53 background became tetraploid. This was not observed for the ZM447439-resistant clones. PH3 (ser10), an Aurora kinase B phosphorylation site, was not inhibited in all resistant clones, suggesting that this kinase is still active. DNA and RNA synthesis were also not inhibited in these clones. Flow cytometry based studies revealed no up regulation of PgP drug transporter in all CYC116-resistant clones, whereas two HCT116 p53 null ZM447439-resistant clones displayed an increase in PgP levels. Up regulation of MRP was only detected in one HCT116 p53 null CYC116-resistant clone, which expressed high levels of this drug transporter. From the initial data it is obvious that there were no common resistance mechanisms towards the studied Aurora kinase inhibitors. We are continuing the characterization of these resistant clones, which include microarray gene expression studies, 2-D electrophoresis and mass spectrometry studies, Aurora A and B sequencing (target mutations), and other drug transporter (e.g. BCRP & LRP) expression studies. These will further help the understanding of the molecular basis of acquired tumor resistance to CYC116 and will aid us in predicting the clinical response as well as in designing combination treatment regimens for overcoming resistance hence furthering clinical development. This work was kindly supported by the Czech ministry of education. Grant number: MSM6198959216 and LC07017. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 633.

Summary The Aurora kinases (serine/threonine kinases) were discovered in 1995 during studies of mutant alleles associated with abnormal spindle pole formation in Drosophila melanogaster. They soon became the focus of much attention because of their importance in human biology and association with cancer. Aurora kinases are essential for cell division and are primarily active during mitosis. Following their identification as potential targets for cancer chemotherapy, many Aurora kinase inhibitors have been discovered, and are currently under development. The binding modes of Aurora kinase inhibitors to Aurora kinases share specific hydrogen bonds between the inhibitor core and the back bone of the kinase hinge region, while others parts of the molecules may point to different parts of the active site via noncovalent interactions. Currently there are about 30 Aurora kinase inhibitors in different stages of pre-clinical and clinical development. This review summarizes the characteristics and status of Aurora kinase inhibitors in preclinical, Phase I, and Phase II clinical studies, with particular emphasis on the mechanisms of action and resistance to these promising anticancer agents. We also discuss the validity of Aurora kinases as oncology targets, on/off-target toxicities, and other important aspects of overall clinical performance and future of Aurora kinase inhibitors.