(P 32) EFFECTIVENESS OF LURBINECTEDIN PLUS IRINOTECAN IN PRECLINICAL MODEL OF DESMOPLASTIC SMALL ROUND CELL TUMOR

Objective: Conventional multimodal treatments failed to improve outcome in desmoplastic small round cell tumor (DSRCT). We demonstrated the effectiveness of the combination trabectedin plus irinotecan in a PDX model of DSRCT. Here, we aimed at i) testing lurbinectedin instead of trabectedin; ii) analyzing effect of the combination in a different DSRCT preclinical model; and iii) investigating the effect of lurbinectedin plus irinotecan on the EWS::WT1 translocation.

Methods: JN-DSRCT cells were exposed to increasing concentrations of lurbinectedin and SN38 (irinotecan’s active metabolite), alone or in combination, for 24 hours to assess antiproliferative activity. Drug interactions were analyzed using a dose-response matrix, and synergy was evaluated with the Loewe additivity model via SynergyFinder software. Apoptosis was measured by TUNEL assay. Expression of the EWS–WT1 fusion protein was assessed by western blot. In vivo efficacy of the treatment combination (lurbinectedin 0.13 mg/kg, irinotecan 2.5 mg/kg) was tested in a DSRCT PDX model by monitoring tumor volume over time after treatment with single agents or their combination.

Results: JN-DSRCT cells showed high sensitivity to both agents, with IC₅₀ values of 1 ± 0.06 nM for lurbinectedin and 5 ± 0.3 nM for SN38. Combination treatment produced a dose-dependent inhibition of cell proliferation, and the synergy analysis indicated a mildly synergistic activity of lurbinectedin and SN38. TUNEL assay revealed significantly increased apoptosis in the combination group compared to single-agent treatments. Western blot analysis demonstrated a reduction in EWS–WT1 expression after 24 hours of treatment with either each drug alone or in combination, relative to untreated JN-DSRCT cells. In vivo, treatment combination resulted in complete response lasting 38 days after treatment in all tumors, outperforming each drug alone.

Conclusion: Lurbinectedin and irinotecan exhibit potent antiproliferative activity in DSRCT models. These results lead to the design of a phase II study of lurbinectedin and irinotecan in adult and young adult patients with advanced DSRCT (EU 2024-519261-21-00). Further molecular studies on the effect of drugs on EWS::WT1 modulation both in vitro and in vivo are ongoing.