PF663 TRANSCRIPTION ALTERATION OF DNA REPAIR GENES IN PHILADELPHIA CHROMOSOME NEGATIVE MYELOPROLIFERATIVE NEOPLASMS
Authors: M. Kirschner, A. Bornemann, C. Schubert, D. Gezer, K. Kricheldorf, S. Isfort, T.H. Brümmendorf, M. Schemionek, N. Chatain, T. Skorski, S. Koschmieder
Journal: HemaSphere (2019)

Background: In Philadelphia chromosome negative myeloproliferative neoplasms (Ph-neg MPN), curative therapeutic options are still limited. The concept of synthetic lethality provides an alternative strategy to overcome inherent treatment resistance by exploiting tumor-specific vulnerabilities. Altered DNA repair pathways have been implicated in the pathogenesis of myeloproliferative neoplasms (MPN). Aims: Based on these results, the aim of our study was to investigate whether transcriptional alterations of genes involved in DNA repair pathways are present in cells from patients with Ph-neg MPN. Methods: 57 patients from the Aachen MPN-registry of patients with classical, Ph-neg MPN (essential thrombocythemia (ET), polycythemia vera (PV) and myelofibrosis (MF)) and 13 controls were included in our study after written informed consent. Differential expression of 11 genes of DNA repair pathways (Homologous recombination repair pathway (HRR); non homologous end joining pathway (NHEJ) and single strand break repair pathway (SSB)) were analyzed by qRT-PCR. Gene expression data (each gene in % of GAPDH as housekeeping gene) of each entity was compared to expression levels of normal controls using Mann-Whitney U test (IBM SPSS statistics 23; Prism 7 for Windows, Version 7.04, © GraphPad Software inc.). Results: The final analysis included 58 patient samples (17 PV, 15 ET, 14 MF [9 primary MF, 5 secondary MF] and 12 controls). JAK2 mutational status was analyzed in all samples and JAK2 V617F mutations were detected in 94% of PV, 67% of ET and 86% of MF cases. Gene expression data (Figure 1 A+B) of ET samples revealed statistically significant differences in expression compared to controls in the following genes: in the genes affecting the base excision repair, LIG3 showed lower expression (p < 0.05) compared to controls. In the genes of the NHEJ pathway, a statistically significant higher expression was observed for PRKDC (p < 0.05) and XRCC5 (p < 0.01) and for genes of the HRR upregulation was detected for BRCA1 (p < 0.05) and for BRCA2 (p < 0.001). In PV, LIG3 and PRKDC (SBB) expression was lower compared to controls (Figure 1 C+D). Expression of RAD52 was decreased, whereas no differences were detected for BRCA1, BRCA2, RPA1 and RPA2 (HRR), which was different from ET and MF. No alterations in gene expression involved in NHEJ were observed. MF samples showed a markedly different expression pattern compared to the other two entities (Figure 1 E+F). In fact, 9 out of the 11 analyzed genes revealed a significant downregulation, only BRCA1 and BRCA2 expression was not altered. So none of the genes of the NHEJ and the SSB showed expression levels comparable to healthy controls. Furthermore, in ET and MF samples we analyzed differences in gene expression in JAK2 positive and negative samples but detected no significant differences.Summary/Conclusion: In conclusion, our study demonstrates significant alterations in expression of genes involved in DNA-repair in Ph-neg MPN compared to controls as well as marked differences among the three entities. In MF, genes of all analyzed DNA repair mechanisms were significantly downregulated. Although further studies are needed, our data support the relevance of targeting DNA repair pathways and suggest that synthetic lethality may offer a potential new approach in the therapy of Ph-neg MPN.