Radioimmunotherapy of Fibroblast Activation Protein Positive Tumors by Rapidly Internalizing Antibodies

Abstract

Purpose: Fibroblast activation protein (FAP) is a serine protease that has emerged as a promising target for cancer therapy, either by direct abrogation of its proinvasive activity or by specific targeting of FAP-expressing cells with cytotoxic immunoconjugates. We aimed to select novel human-mouse crossreactive antibodies and to test suitability for tumor therapy as radioimmunoconjugates in a preclinical model.Experimental Design: Human Fab fragments that bind to human and murine FAP were selected from an antibody phage library. Two candidates (ESC11 and ESC14) were engineered into fully human IgG1 antibodies and further characterized. We investigated the intracellular trafficking of ESC11 and ESC14 in live cells by confocal microscopy and analyzed the biodistribution and therapeutic effects of anti-FAP antibodies labeled with the b-emitting radionuclide 177 Lu in a melanoma xenograft nude mouse model. Results were compared with vF19, a humanized variant of an anti-FAP antibody that has been previously used in clinical trials.Results: The two antibodies bound selectively to both human and mouse FAP, with affinities in the low nanomolar range. Binding to FAP-expressing melanoma cells resulted in rapid internalization of FAPantibody complexes.

Identification of Cancer-Associated Fibroblasts in Circulating Blood from Patients with Metastatic Breast Cancer

“…A FAPtargeting DNA vaccine has recently been shown to specifically eliminate CAF populations and to mitigate tumor metastasis in a mouse model of breast cancer (6). Sibrotuzumab, an anti-human FAP antibody, has shown remarkable properties targeting the tumor microenvironment in humans (5). Though phase I/II clinical trials results of sibrotuzumab failed to show therapeutic activity, FAP radioimmunoconjugates and antibody drug …”

“…Currently, the most definitive method that is agreed upon for the identification of CAFs is double positivity for both FAP and a-SMA (4). FAP is a type II transmembrane serine protease (5); although the specific function of FAP is unknown, its enzymatic activity has been implicated in tumor progression, ECM remodeling, and metastasis (5).…”

Carcinoma-associated fibroblasts: orchestrating the composition of malignancy

“…Ongoing clinical trials are assessing the therapeutic value of human CD8 + T cells engineered to target FAP-expressing cells (Schuberth et al 2013) and two FAP-antibody/cytokine fusion proteins, RO6874281 and RO6874813 (Table 2). The diagnostic and therapeutic value of radio-immunoconjugates that bind to FAP with high affinity and are internalized rapidly in cancer cells expressing high levels of FAP (such as CAFs) has been validated in vitro and in a murine preclinical model in vivo (Fischer et al 2012).…”

Immuno-PET and Immuno-SPECT of Rheumatoid Arthritis with Radiolabeled Anti–Fibroblast Activation Protein Antibody Correlates with Severity of Arthritis

“…Among these are 131 I-labeled murine F19 (9) and 131 I-labeled sibrotuzumab, a humanized version of the F19 antibody (10). More recently, 2 new anti-FAP antibodies, ESC11 and ESC14, were labeled with 177 Lu, which showed excellent targeting in melanoma xenografts (11).…”