Background: Overexpression of P-cadherin, a calcium-dependent cell-to-cell adhesion glycoprotein, correlates with increased tumor cell invasiveness in breast, colon, lung and pancreatic tumors. FF-21101 is a human-mouse chimeric monoclonal antibody directed against P-cadherin, conjugated with 111In for dosimetry and biodistribution and 90Y for therapy. We report the biodistribution and preliminary anti-cancer activity of FF-21101(90Y) in a first-in-human study.

Methods: Patients (pts) received 5 mCi/5mg FF-21101(111In) 1 week before the FF-21101(90Y) therapeutic dose to assess biodistribution and ensure 90Y radiation dose estimates did not exceed the maximum tolerated dose (MTD) for each organ. Single therapeutic dose cohorts were planned for FF-21101(90Y) (8 mCi/mg) at 5, 10, 15, 20 or 25 mCi/m2 (3+3 dose escalation schema), with repeat doses allowed every 4 months in pts demonstrating clinical benefit. Disease assessments were based on RECIST V1.1. Pre-treatment tumor samples were assessed for P-cadherin expression by immunohistochemistry (IHC). Pharmacokinetics (PK) of FF-21101 were also assessed.

Results: Fourteen pts (6M, 8F) with advanced primary solid tumors and loco-regional metastases were treated in the 5 dose cohorts. Median (range) values: age 58 years (31 – 69), number of prior systemic treatments 3 (0 – 9), tumor types: soft-tissue sarcoma (3), ovarian carcinoma (CA) (2), and vaginal CA, pancreatic neuroendocrine tumor (PNET), desmoplastic small round cell tumor, colorectal CA, appendiceal CA, cholangiocarcinoma, squamous cell CA (SCC) of the anus, papillary thyroid CA and carcinoid (1 each). Primary and/or metastatic tumors from 12 of 14 pts (85.7%) demonstrated uptake of FF-21101(111In) with highest uptake seen in epithelial tumors, consistent with P-cadherin targeting. Median (range) time on study following the therapeutic dose was 21 (2 - 62) weeks, with 3 pts on study > 1 year (2 ovarian CA, 1 carcinoid). Four pts have received multiple treatments. One ovarian CA pt achieved a partial response (65% reduction); this pt also had the highest H score by IHC staining. High H scores (≥ 100) were demonstrated in 5 of 13 pts: 2 ovarian, 1 PNET, 1 SCC of the anus, 1 cholangiocarcinoma; 4 remained on study for 49 - 62 weeks, thus demonstrating the potential predictive utility of pre-treatment tumor P-cadherin expression.

FF-21101(90Y) has been well-tolerated; the MTD has not been reached. The most frequently reported drug-related AEs include lymphopenia (n = 8), thrombocytopenia (n = 4) and leukopenia (n = 3); Gr 3 lymphopenia was observed in 3 pts, all reversible. There have been no drug-related serious AEs. Mean FF-21101 Cmax and AUC0-t increased with dose, suggesting linear PK.

Conclusions: Tumor P-cadherin overexpression provides an attractive target for RIT. Radiolabeled FF-21101 exhibits favorable dosimetry and biodistribution, good tolerability and preliminary evidence of anti-cancer activity. Pre-treatment tumor P-cadherin expression may be an important biomarker for patient selection.

Citation Format: Vivek Subbiah, William Erwin, Osama Mawlawi, Carlos Gonzalez-Lepera, Masahiko Tokura, Michael Kurman, Holly Liu, David S. Hong, Funda Meric-Bernstam, Shubham Pant, Mary Johansen, Timothy Madden, Elmer Santos, Gregory Ravizzini. Phase 1 study of FF-21101(90Y), a radioimmunotherapeutic (RIT) targeting P-cadherin, in advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT128.