Résumé
Abstract only 5069 Background: Expressed on most OC subtypes while displaying a restricted expression profile in adult normal tissues, MISRII represents a potentialtarget for OC immunotherapy. We present here the preclinical assessment of a humanized anti-MISRII EMABling mAb, 3C23K. Methods: Either quantitative RT-PCR or immunohistochemistry (IHC) studies were performed to confirm MISRII expression profile in Granulosa Cell Tumor (GCT) or Epithelial OC (EOC) patient samples and to evaluate tissue cross-reactivity. For in vitro and in vivo experiments, we have generated 4 patient-derived MISRII expressing EOC cell lines. Xenograft studies were conducted in swiss nude mice on established tumors (100 mm 3 ). Mice received 2 to 3 weekly i.p. injections (10 mg/kg/inj) for 4 to 6 wks and tumor volumes were compared with control groups. Comparison of i.p. vs i.v. injections were assessed as well as combination with carboplatin (once a week for 4 weeks, 60 mg/kg/inj). In addition, 3C23K plasma level was monitored to determine half-life. Results: 1) Target validation: we confirmed by IHC the expression of MISRII in most OC tissue sections (4/4 GCT and 13/14 EOC), meanwhile, MISRII mRNA was only detected in 7/48 normal tissues. 2) In vitro assessment: tested in vitro 3C23K displayed both cytotoxic (ADCC) and anti-proliferative activities. 3) In vivo assessment: in the mouse xenograft models 3C23K exhibited a strong anti-tumoral activity as measured by tumor volume, with T/C ratios reaching values below 0.42 shortly after the initiation of treatment. No differences in efficacy were noticed between i.p. and i.v. injections or between thrice vs twice a week administrations. In addition, similar half lives were observed for 3C23K injected either i.v. (96.9 h) or i.p (113.5 h). Finally, the combination of 3C23K with carboplatin (CP), a standard of care in OC, exhibited an even stronger anti-tumor activity with T/C values at D22 of 0.06 (3C23K+CP), 0.18 (3C23K) and 0.69 (CP) vs vehicle. Conclusions: 3C23K represents a promising candidate for OC targeted therapy and a dose-escalation phase I study is planned in patients with OC.