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Updated: Jan 8, 2026
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Automated Preparation of [68Ga]Ga-3BP-3940 on a Synthesis Module for PET Imaging of the Tumor Microenvironment
Published on: April 25, 2025
Novel immunotheranostic FAP-inhibitor target modules for imaging and elimination of FAP-positive cells by UniCAR
Hugo Boutier1, Jürgen Kogler1,2, Liliana R Loureiro1
1Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany.
Abstract:
The fibroblast activation protein alpha (FAPα) is overexpressed in the tumor microenvironment of most solid cancers and, in some cases, in cancer cells, making it an interesting target for theranostic applications. T-cells modified to express a chimeric antigen receptor (CAR) against FAP have recently been described. We previously established the UniCAR system, in which UniCAR T-cells can be repeatedly switched on and off via dosing with a bifunctional adaptor molecule, known as target module (TM). Here, we describe the first FAPI-based immunotheranostic UniCAR TMs (FAPI TMs), enabling both non-invasive molecular imaging and UniCAR T-cell immunotherapy. The FAPI TMs consist of the UAMC-1110 FAPI moiety, the NODA-GA chelator for copper-64 labeling, and the UniCAR epitope (E5B9). Following computational analyses, three FAPI TMs with polyethylene glycol (PEG) spacers of either four, twelve, or 24 units were synthesized. Although the three novel TMs specifically accumulate in FAP-positive tumors in xenograft mice, only the FAPI TMs with an extended spacer (PEG12 and PEG24) redirect UniCAR T-cells to FAP-positive target cells both in vitro and in an immunodeficient mouse model. In line with the computational studies, the E5B9 epitope is not accessible for binding when the PEG4-based FAPI TM is bound to FAP. Our work demonstrates that the length of the spacer in FAPI TMs is critical for the effective redirection of UniCAR T-cells to FAP-positive cells. Overall, our novel FAPI TMs may represent highly promising immunotheranostic tools for personalized non-invasive diagnostic imaging and immunotherapy of cancer patients.
Insights
Novel fibroblast activation protein alpha (FAPα) targeted theranostic tools enable non-invasive imaging and immunotherapy. Spacer length in FAPI target modules (TMs) is critical for effective UniCAR T-cell redirection to FAP-positive cancer cells.
Area of Science:
- Oncology
- Immunotherapy
- Molecular Imaging
Background:
- Fibroblast activation protein alpha (FAPα) is overexpressed in most solid tumors, making it a promising target for cancer theranostics.
- Chimeric antigen receptor (CAR) T-cells targeting FAP are under investigation.
- The UniCAR system allows for inducible control of T-cell activity using target modules (TMs).
Purpose of the Study:
- To develop and characterize novel FAPI-based immunotheranostic UniCAR TMs (FAPI TMs) for simultaneous molecular imaging and immunotherapy.
- To evaluate the impact of spacer length on FAPI TM efficacy in targeting FAP-positive cells and redirecting UniCAR T-cells.
Main Methods:
- Computational analysis was used to design FAPI TMs with varying polyethylene glycol (PEG) spacer lengths (4, 12, and 24 units).
- Three FAPI TMs incorporating the UAMC-1110 FAPI moiety, NODA-GA chelator, and E5B9 UniCAR epitope were synthesized.
- In vitro and in vivo studies in xenograft mouse models were conducted to assess tumor accumulation, T-cell redirection, and imaging capabilities.
Main Results:
- All synthesized FAPI TMs specifically accumulated in FAP-positive tumors.
- FAPI TMs with longer spacers (PEG12 and PEG24) effectively redirected UniCAR T-cells to FAP-positive cells in vitro and in vivo.
- The shortest spacer (PEG4) resulted in inaccessible binding of the E5B9 epitope, hindering T-cell redirection.
Conclusions:
- The length of the spacer in FAPI TMs is a critical determinant for effective UniCAR T-cell-mediated immunotherapy.
- Novel FAPI TMs with optimized spacer lengths show significant potential as theranostic tools for personalized cancer imaging and treatment.
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