Abstract CT136: Phase I study with rapamycin combined with irinotecan, the SFCE RAPIRI I trial, a new way to target tumor hypoxia in pediatric refractory cancers

Background: Hypoxic environment is a pejorative prognostic factor in pediatric solid tumors (ST). It is favoring neoangiogenesis, tumor progression and resistance to treatments through the activation of mTor and HIF-1α pathways. Those hypoxic markers can be targeted by rapamycin and irinotecan, respectively. Therefore, we designed a dose-escalation phase I trial combining both drugs to inhibit tumor hypoxic mechanisms present in several pediatric refractory/relapsing ST. Procedure: Patients were enrolled in this 3+3 escalation trial with ten dose levels. The primary endpoint was to determine the maximum tolerated dose (MTD) of rapamycin when combined with irinotecan. Rapamycin was administered orally once daily in a 28-day cycle (1 to 2.5 mg/m2/day) and associated biweekly with intravenous irinotecan (125 to 240 mg/m2/dose). Toxicities, pharmacokinetics (PK), efficacy analyses and pharmacodynamics (UGT1A1 status, cytokines/chemokines assessment, MRI markers and proteins9 expression) were evaluated. Results: 42 patients were treated and had mild to moderate reversible toxicities. No MTD was present up to the tenth level. The PK were highly variable. Nevertheless, the usually targeted concentrations of rapamycin over time were reached at 1.5 mg/m2/day dose. When looking to the 2 partial responses (PR) and 19 stable diseases (SD) in 31 assessable patients, the mean irinotecan AUC was 363 min.mg/L and the mean D8 rapamycin AUC was 9.3 min.mg/L. No significant relationship was observed between dose escalation and response, but progressive tumors9 subgroup (PD) had slightly lower mean irinotecan AUC (321 min.mg/L) and D8 rapamycin AUC (6.5 min.mg/L). The two main tumor groups were brain tumors (BTs) and sarcomas. A high proportion of those patients experienced tumor responses (3/4 ependymomas, 2/3 medulloblastomas, 1 rhabdoid tumor, 2/3 high-grade gliomas and 5/6 osteosarcomas). In all 17 assessable patients for immunohistochemistry, the two targeted proteins, mTor and HIF-1α, were expressed, but the resistance to this double strategy was significantly linked to the HIF-2α protein hyperexpression. In the BTs, lower ADC values in MRI were also a prerequisite for tumor responsiveness. Cytokine analyses, distinguished specific proinflammatory and angiogenic signatures during first course of treatment: PR patients had an increase of TNF, associated to a stable PIGF and a decrease of VEGF-C; the SD subgroup had a significant increase of VEGF-D and a stable or increase of sFLT1 and PD group had a constant increase of IL8 and VEGF-D. Conclusion: Despite no MTD, we can propose a next phase II trial with rapamycin dose of 1.5 mg/m2/day associated with 125 mg/m2 irinotecan in STs not expressing HIF-2α protein. A precise PK follow-up will be used to reach an irinotecan AUC up to 360 min.mg/L and a D8 rapamycin blood concentration of 10 µg/L. The cytokine evaluation will help us to predict during first cycle the potential tumor response. Citation Format: Sarah Jannier, Veronique Kemmel, Consuelo Sebastia, Agathe Chammas, Amelia-Naomi Sabo, Erwan Pencreach, Francoise Farace, Benoit Lhermitte, Birgit Geoerger, Isabelle Aerts, Didier Frappaz, Pierre Leblond, Nicolas Andre, Yves Perel, Nadege Corradini, Anne Isabelle Bertozzi, Florence Vincent, Natacha Entz-Werle. Phase I study with rapamycin combined with irinotecan, the SFCE RAPIRI I trial, a new way to target tumor hypoxia in pediatric refractory cancers [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT136.