Design and development of a B7H3-targeting fluorescent probe for fluorescence-guided surgery of sarcoma

The National Cancer Institute awarded $577,854 to the Board of Regents of the University of Nebraska, through its University of Nebraska Medical Center division, on August 1, 2026, under the Cancer Detection and Diagnosis Research program (CFDA 93.394) to design and develop B7-H3-targeting fluorescent probes for fluorescence-guided surgery of soft tissue sarcoma.

The award funds development of antibody-fluorophore conjugates that target B7-H3, a transmembrane immune checkpoint protein expressed at high levels in soft tissue sarcomas. The research addresses a clinical challenge in wide local excision surgery: surgeons fail to achieve complete tumor removal with adequate negative margins in up to 34 percent of soft tissue sarcoma patients, leading to recurrence in nearly half of these cases. Fluorescence-guided surgery paired with cancer-targeted optical probes enables real-time intraoperative identification of tumor margins and residual disease. The recipient team has developed a conjugate pairing an anti-B7-H3 antibody (enoblituzumab, MGA271) with the fluorophore IRDYE800, which showed promising contrast and tumor specificity in established rodent models of human soft tissue sarcoma xenografts. The project expands this development work based on consistent B7-H3 expression across soft tissue sarcoma subtypes.

Performance takes place in Omaha, Nebraska. The period of performance runs through July 31, 2031.

Abstract

Soft tissue sarcomas (STS) are mesenchymal cancers with >50 subtypes. Wide local excision (WLE)-removal of the primary tumor with a layer of non-cancerous tissue surrounding IT-is required for curative local control. However, surgeons fail to achieve WLE in up to 34% of patients, with recurrence occurring in nearly half of these patients and negative survival effects. Thus, intraoperative recognition of positive margins and immediate removal of residual STS would significantly improve outcomes for patients with STS. Fluorescence-guided surgery-paired with cancer-targeted optical probes-have enabled real-time intraoperative cancer identification, tumor margin assessment, and removal of residual disease. FGS efficacy is optimized when contrast agents have high tumor-to-background contrast. On-going clinical trials with existing agents targeting the epidermal growth factor (EGFR) have demonstrated feasibility for FGS in STS, but results were underwhelming due to inconsistent EGFR expression between patients and intratumoral EGFR heterogeneity. More recent human data demonstrates high expression of the transmembrane protein B7-H3, an immune checkpoint protein, in STS. Antibodies targeting B7-H3, such as enoblituzumab (MGA271), are being investigated as therapeutics towards B7-H3-expressing solid tumors. In a collaborative effort, we conjugated MGA271 to IRDYE800 and deployed the resulting compound in our established rodent models of human STS xenografts; contrast and tumor specificity results are promising. Our team has extensive experience in developing targeted fluorescence imaging agents for FGS, including stss. Herein, we will expand the development of B7-H3-targeting antibody-fluorophore conjugates. We believe these conjugates will be strong candidates for preclinical development due to consistent B7-H3 expression in STS and the availability of mabs targeting B7-H3 in clinical trials. We hypothesize that NIR fluorophore-ANTIB7-H3 MAB conjugates will bind to B7- H3-overexpressing stss and provide strong contrast enhancement to guide surgical resection. Therefore, the goal of this proposal is to perform a thorough preclinical evaluation of NIR fluorescent conjugates of B7- H3-targeting antibodies for FGS of STS. This goal will be addressed by three specific aims: (1) to develop fluorescence-guided surgery probes that target B7-H3 using antibody-derived targeting ligands; (2) to establish the safety and in vivo dynamics of fluorescently labelled B7-H3-targeting agents; and (3) to evaluate the preclinical surgical efficacy of fluorescently-labelled B7-H3 targeting agents in orthotopic models of sarcoma. Animal models are required due to the complexity of factors affecting tumor and tissue/organ accumulation of contrast agents and to evaluate the complex factors of FGS for surgical oncology. Completion of this research project will produce FGS contrast agents that detect and guide removal of STS and accomplish a pivotal step towards future clinical development of a targeted probe for FGS of STS.