Telomerase Is a Prognostic Marker of Poor Outcome and a Therapeutic Target in Neuroblastoma.

Abstract

Telomere maintenance is a hallmark of high-risk neuroblastoma; however, the contribution of telomerase and alternative lengthening of telomeres (ALT) to clinical phenotypes has remained unclear. We aimed to determine the clinical relevance of telomerase activation versus ALT as biomarkers in pretreatment neuroblastoma and to assess the potential value of telomerase as a therapeutic target. The genomic status of <i>TERT</i> and <i>MYCN</i> was assessed in 457 pretreatment neuroblastomas by fluorescence in situ hybridization. ALT was examined in 273 of 457 tumors by detection of ALT-associated promyelocytic leukemia nuclear bodies, and <i>TERT</i> expression was determined by microarrays in 223 of these. Cytotoxic effects of telomerase-interacting compounds were analyzed in neuroblastoma cell lines in vitro and in vivo. We detected <i>TERT</i> rearrangements in 46 of 457 cases (10.1%), <i>MYCN</i> amplification in 93 of 457 cases (20.4%), and elevated <i>TERT</i> expression in tumors lacking <i>TERT</i> or <i>MYCN</i> alterations in 10 of 223 cases (4.5%). ALT activation was found in 49 of 273 cases (17.9%). All these alterations occurred almost mutually exclusively and were associated with unfavorable prognostic variables and adverse outcome. The presence of activated telomerase (ie, <i>TERT</i> rearrangements, <i>MYCN</i> amplification, or high <i>TERT</i> expression without these alterations) was associated with poorest overall survival and was an independent prognostic marker in multivariable analyses. We also found that the telomerase-interacting compound 6-thio-2'-deoxyguanosine effectively inhibited viability and proliferation of neuroblastoma cells bearing activated telomerase. Similarly, tumor growth was strongly impaired upon 6-thio-2'-deoxyguanosine treatment in telomerase-positive neuroblastoma xenografts in mice. Our data suggest telomerase activation and ALT define distinct neuroblastoma subgroups with adverse outcome and that telomerase may represent a promising therapeutic target in many high-risk neuroblastomas.