T-cell redirected killing and cure of pancreatic and gastric cancer xenografts by targeting Trop-2.

Abstract

262 Background: Trop-2 [also called tumor-associated calcium signal transducer 2 (TACSTD2), EGP-1 (epithelial glycoprotein-1), GA733-1, or M1S1]is a 35 kDa transmembrane glycoprotein that is overexpressed relative to normal tissues in a variety of human cancers, including pancreatic and gastric carcinomas, where increased expression correlates with poor prognosis. Trop-2 appears to be more tumor-specific than the related molecule, EpCAM (Trop-1). MT110, the EpCAM antibody x CD3 bispecific T-cell engager (BiTE), is currently undergoing a Phase I study in various solid tumors, including lung, gastric, colorectal, breast, prostate, and ovarian cancers. We produced a similar T-cell redirecting bispecific tandem scFv, E1-3, using the variable domains of hRS7 (humanized anti-Trop-2 mAb) and Okt-3 (anti-CD3 mAb). Methods: T-cell activation, cytokine induction and cytotoxicity were evaluated ex vivo using PBMCs or purified T cells with human pancreatic (Capan-1 and BxPC3) and gastric (NCI-N87) cancer cell lines as target cells. In vivo activity was assayed with NCI-N87 xenografts that were inoculated s.c. in a mixture with twice the number of human PBMCs and matrigel. Results: In the presence of target cells and PBMCs, E1-3 potently induced T-cell activation, proliferation, and dose-dependent cytokine production of IL-2 (>2 ng/mL), IL-6 (>1 ng/mL), IL-10 (>7 ng/mL), TNF-α (>1 ng/mL) and IFN-γ (>50 ng/mL). In vitro, E1-3 mediated a highly potent T-cell lysis of BxPC3 [IC50=0.09(±0.04) pM], Capan-1 [IC50=1.2(±1.1) pM] and NCI-N87 [IC50=1.2(±1.2) pM] target cells. In vivo, two 50-µg doses of E1-3 given three days apart cured all of the mice (N=8) bearing NCI-N87 xenografts (P=0.0005; Log-Rank). Tumors in the control group (PBMCs only) reached the endpoint (TV>1 cm3) with a median of 39.5 days. All mice remained tumor-free in the E1-3 group at 78 days. Conclusions: Trop-2 is an attractive target for T-cell-mediated killing of pancreatic, gastric and other epithelial cancers.