Uplift (ENGOT-ov67): A pivotal cohort to evaluate XMT-1536 (upifitamab rilsodotin), a NaPi2b-directed antibody drug conjugate for platinum-resistant ovarian cancer.

TPS5607 Background: XMT-1536 (upifitamab rilsodotin), is a first-in-class Dolaflexin ADC targeting NaPi2b, a sodium-dependent phosphate transport protein, broadly expressed in solid tumors such as serous epithelial ovarian cancer (OC) and non-small cell lung adenocarcinoma. XMT-1536 uses the Dolaflexin platform to deliver approximately 10 DolaLock auristatin payload molecules per antibody and is being evaluated in a Phase I study (NCT03319628). Observation of preliminary antitumor activity was reported in the ovarian cancer expansion cohort, including in patients previously treated with bevacizumab and PARPi (Tolcher et al, ASCO 2019; Richardson et al, ASCO 2019; Hamilton et al, ESMO 2020). Updated data on the OC cohort included 31 patients with higher NaPi2b expression as of December 2020 (Mersana Therapeutics, 2021). In these patients, the ORR was 32% and the DCR was 74%. Complete responses were observed in 2 patients with platinum-resistant ovarian cancer, both of whom had received prior treatment with bevacizumab and PARP inhibitors. Platinum resistant ovarian cancer remains a serious unmet medical need as treatment options are limited and response rates to these treatments are low. Based on the favorable safety and efficacy profile of XMT-1536, UPLIFT was designed as a Phase 2 single-arm registrational cohort of patients with platinum resistant ovarian cancer as part of the ongoing Phase I FIH dose escalation and expansion study to accelerate development and provide a streamlined pathway to regulatory review. Methods: The UPLIFT cohort is enrolling patients with platinum resistant high grade serous ovarian, fallopian tube and primary peritoneal cancer with up to 4 prior lines of therapy. The RP2D of XMT-1536 was determined to be 43 mg/m2 administered intravenously every 4 weeks (q4w) and will be the dose evaluated in the UPLIFT cohort. UPLIFT will enroll approximately 180 patients with platinum-resistant advanced ovarian cancer to obtain approximately 100 patients with higher NaPi2b expression. Prior bevacizumab is required for those patients with 1 or 2 prior lines of therapy. Tumor samples (fresh or archived) will be collected prior to enrollment for retrospective tumor tissue evaluation of NaPi2b expression. The primary objective is assessment of confirmed objective response rate to XMT-1536 as assessed by Investigator in patients with higher NaPi2b expression. Secondary endpoints include confirmed objective response rate regardless of NaPi2b expression, duration of response, and adverse events. Correlative aims include assessing blood and tissue biomarkers for association with clinical benefit. This study is being conducted in collaboration with ENGOT and GOG. Patients will be enrolled globally. Clinical trial information: NCT03319628.