Prognostic role of RLF/MYCL1 and circPVT1 in SCLC

Background Small Cell Lung Cancer (SCLC) is a highly metastatic form of lung cancer and the therapies remain unchanged since 40 years. Therefore, the discovery of novel transcriptomic alterations contributes to develop more effective targeted therapies. Among them, RLF/MYCL1 was described as a recurrent chimera implicated in tumor growth. The non-protein-coding RNA PVT1, linked to MYC expression, and its circular variant circPVT1 are also dysregulated in several malignancies and associated to tumor progression. Nevertheless, their functional and clinical role was only partially explored. We investigated these transcriptomic alterations in SCLC patients and cell lines, aiming at exploring a possible prognostic significance. Methods 12 SCLC cell lines harboring MYC, MYCN or MYCL1 amplifications were tested by RNA-sequencing and RT-PCR for the recurrence of RLF/MYCL1. Moreover, the relative expression of PVT1/circPVT1 was evaluated by RT-qPCR. To investigate whether these transcriptomic alterations could serve as prognostic markers, overall survival (OS) and progression free survival (PFS) curves were plotted by Kaplan-Meier method according to the recurrence of RLF1/MYCL1 and the PVT1/circPVT1 expression levels in a cohort of 29 SCLC patients. Results RNA-seq analysis by ChimeraScan and FusionMap tools identified the occurrence of RLF/MYCL1 in four cell lines, showing the occurrence of two splicing variants originated by the fusion of RLF exon 1 to alternatively MYCL1 exon 2 (longer) or 3 (shorter). The longer variant was also found as recurrent in 16/28 (57.1%) SCLC patients, correlating with a shorter OS (median survival of 11 vs 17 months). Conversely, circPVT1 expression levels, according to the median expression of all SCLC samples, were associated with a better OS (median survival of 14 vs 8 months). No differences were found regarding the DFS and the recurrence of RLF1/MYCL1 or the PVT1/circPVT1 expression levels. Conclusions Our results confirmed the recurrence of the RLF/MYCL1 chimera in a high percentage of SCLC samples. Interestingly, our clinical investigations clearly disclosed that both the chimera and circPVT1 could be used as prognostic markers in SCLC, respectively negative and positive, although our results need to be confirmed in a wider cohort of patients. Legal entity responsible for the study The authors. Funding University of Bari, Italy. Disclosure All authors have declared no conflicts of interest.