ESTRO 2025 - Abstract Book

S3872

Radiobiology - Immuno-radiobiology

ESTRO 2025

268

Proffered Paper Enhanced radiation therapy outcomes via TGFβ inhibition in the tumor microenvironment using bifunctional antibody TLX250-TRAP Ria Kumari 1 , Wonjong Jin 1 , Paul A Clark 1 , Michael P Wheatcroft 2 , Kwame Twumasi-Boateng 2 , Zachary S Morris 1 1 Human Oncology, University of Wisconsin-Madison, Madison, USA. 2 Research & Innovation, Telix Pharmaceuticals, Melbourne, Australia Purpose/Objective: Tumor-associated antigen (TAA)-targeted antibody therapy shows a synergistic antitumor response when combined with tumor radiation in preclinical tumor models. A bifunctional protein simultaneously targeting TAA and pro tumorigenic factors is a promising strategy to enhance this antitumor response. We investigate TLX250-TRAP, a newly generated fusion protein consisting of an anti-carbonic anhydrase IX (CAIX) antibody and the ectodomain of transforming growth factor protein β (TGFβ) receptor II (TGFβRII), to test treatment efficacy when combined with radiation therapy. Material/Methods: TLX250-TRAP was obtained from Telix (patent# AU2023900642). We tested tumor binding capacity and functional effects of TLX250-TRAP on tumor cell proliferation and TGFβ-mediated intracellular signaling activity using hCAIX expressing murine breast cancer cell lines 4T1 (4T1-hCAIX) and EMT6 (EMT6-hCAIX). Mammary fat pad tumor bearing syngeneic mice received 177Lu-labeled TLX250-TRAP intravenously to trace the agent delivery and accumulation. TGFβ neutralizing kinetics were tested using serum collected after a single dose of TLX250-TRAP administration. EBRT (8 Gy), TLX250-TRAP (200 or 400 µg), and anti-PD-L1 antibody (200 µg) were administered to determine therapeutic efficacy in tumor-bearing mice. Results: TLX250-TRAP showed dose-dependent binding to hCAIX-expressing tumor cells compared to IgG control. TLX250 TRAP efficiently captured recombinant mouse TGFβ1 (rmTGFβ1) but did not directly alter tumor cell proliferation. Combined TLX250-TRAP and tumor radiation showed no change in colony formation ability in a standard clonogenic assay. TLX250-TRAP significantly inhibited TGFβ1-stimulated SMAD2 phosphorylation compared to IgG or TLX250 (mAb without TRAP). Administration of 177Lu-TLX250-TRAP showed high uptake to tumor, liver, and spleen compared to other tissues in mice bearing orthotopic EMT6-hCAIX or 4T1-hCAIX tumors. Compared to IgG or TLX250, TLX250-TRAP neutralized TGFβ1 in serum. In EMT6-hCAIX tumor-bearing mice, combined TLX250-TRAP, anti-PD-L1 antibody, and EBRT (8 Gy) inhibited tumor growth compared to either EBRT alone or TLX-250-TRAP and anti-PD-L1 dual therapy. EMT6-hCAIX tumor growth was also inhibited by 177Lu-TLX250-TRAP when compared to IgG. Conclusion: These findings establish that TLX250-TRAP targets TAA and inhibits TGFβ downstream signaling. They also provide evidence of enhanced therapeutic outcomes when combined with EBRT and anti-PDL1 immune checkpoint inhibition. Therapeutic isotope labeling of TLX250-TRAP shows promising anti-cancer potential through antigen specific delivery of radiation to tumors combined with TGFβ neutralization.

Keywords: TGFB Neutralization, Radiopharmaceutical Therapy