DP021 | WGS-BASED TELOMERE CONTENT IN MYELOID NEOPLASIA

Background: Telomerase inhibitor imetelstat has been successfully tested and FDA-approved in MDS but to date data on biomarkers of response and, overall, the impact of telomere content (TC) in myeloid neoplasia (MN) has been poorly investigated. Methods: We adopted WGS-based pipelines to measure TC in a genotypically characterized and well-annotated cohort of MN (1804) and 158 non-malignant controls including PNH/AA [n=102], polyclonal B lymphocytosis (n=50) and healthy subjects [n=6]). RNA sequencing was performed to investigate the expression of telomerese machinery genes. c-circle assays were performed in exemplary cases to establish the mechanisms of telomeres elongation (Fig.1A). Results: Results: We observed a general decrease in TC in MDS/AML irrespective of age. Correlating TC with cytogenetics, we detected higher TC in del(5q) (p<.0001) and lower TC in patients with balanced translocations (p<.0001) when compared to normal karyotype. TC analysis according to genetic landscape revealed higher TC in ETV6 (p=0.0172), SF3B1 (p=0.0015), SRSF2 (p=0.0005) and TP53 (p=0.0025) mutant cases and lower TC in those carrying FLT3 (p<.0001), JAK2 (p=.0191), KRAS (p=.0001), NPM1 (p<.0001) and NRAS (p=.0234) mutations compared to disease controls (Fig.1B). In a multivariate model nor diagnosis, age or karyotype correlated to TC, whereas we detected an independent indirect correlation with blast percentage (p<.0001). In contrast there was a direct impact (p=.001) of TP53 mutations on TC (Fig.1C). We then studied the association of TP53 hits with alternative telomere elongation (ALT) via C-Circle assays, which were performed in samples with high and low TC, both in TP53-mutant and wt samples as well as in healthy controls. None of the subgroups exhibited significant signs of ALT (Fig.1D). Once lack of contribution of ALT to telomere extension was established, we sought to determine whether increased TC may be due to higher telomerase activity imprinted by TP53 mutations. Thus, we analyzed the differential expression of telomere machinery genes in MNs. In cases with increased TC MNs (above 90th percentile), increased expression of RAP1A, TERC, TINF2, TPP1, CTC1 and a downregulation of TERF1 was detected. In TP53-mutated MN, DKC1, TERT and TERC were significantly overexpressed as compared to wt cases, while TEP1 was downregulated. Conclusion: TC varies significantly across MN phenotype and thus could identify patient subgroups eligible for imetelstat treatment.