Development of a fibrin-targeted theranostic for gastric cancer

Patients with advanced gastric cancer (GCa) have limited treatment options, and alternative treatment approaches are necessary to improve their clinical outcomes. Because fibrin is abundant in gastric tumors but not in healthy tissues, we hypothesized that fibrin could be used as a high-concentration depot for a high-energy beta-emitting cytotoxic radiopharmaceutical delivered to tumor cells. We showed that fibrin is present in 64 to 75% of primary gastric tumors and 50 to 100% of metastatic gastric adenocarcinoma cores. First-in-human ⁶⁴Cu-FBP8 fibrin-targeted positron emission tomography (PET) imaging in seven patients with gastric or gastroesophageal junction cancer showed high probe uptake in all target lesions with tumor-to-background (muscle) uptake ratios of 9.9 ± 6.6 in primary (<i>n</i> = 7) and 11.2 ± 6.6 in metastatic (<i>n</i> = 45) tumors. Using two mouse models of human GCa, one fibrin-high (SNU-16) and one fibrin-low (NCI-N87), we showed that PET imaging with a related fibrin-specific peptide, CM500, labeled with copper-64 (⁶⁴Cu-CM500) specifically bound to and precisely quantified tumor fibrin in both models. We then labeled the fibrin-specific peptide CM600 with yttrium-90 and showed that ⁹⁰Y-CM600 effectively decreased tumor growth in these mouse models. Mice carrying fibrin-high SNU-16 tumors experienced tumor growth inhibition and prolonged survival in response to either a single high dosage or fractionated lower dosage of ⁹⁰Y-CM600, whereas mice carrying fibrin-low NCI-N87 tumors experienced prolonged survival in response to a fractionated lower dosage of ⁹⁰Y-CM600. These results lay the foundation for a fibrin-targeted theranostic that may expand options for patients with advanced GCa.