Fibroblast activation protein (FAP) expression in CK5/6 expressed (Basal subtype) & CK20 expressed (Luminal subtype) urothelial bladder carcinoma: an immunohistochemical study

Phases of tight junction barrier disruption during transurothelial migration of invasive urothelial cancer cells

Bladder cancer is characterised by its multifocal nature and a high recurrence, yet the underlying mechanisms of these phenomena remain only partially understood. In the present study, we aimed to investigate transurothelial invasion of urothelial cancer cells as a potential mechanism for dissemination of bladder cancer and to identify the key molecules involved in urothelial barrier disruption. Using confocal and electron microscopy, we were able to show that within a 24-hour timeframe muscle-invasive urothelial cancer cells T24 adhere to the partially differentiated normal urothelial in vitro model and initially cause localised disruption of the tight junctions between urothelial cells. Subsequently, urothelial cells separate and individual T24 cells migrate paracellularly through the urothelium. qPCR analysis identified fibroblast activation protein (FAP)/seprase as the candidate most likely to be involved in urothelial barrier disruption. In addition, treatment of T24 cells with Pefabloc resulted in the inhibition of T24 cell invasion. Our results contribute to the understanding of the mechanisms underlying transurothelial invasion of urothelial cancer cells. Among the molecules tested, FAP/sepraseis likely involved in cancer cell-induced disruption of the urothelial barrier, suggesting its potential as a therapeutic target to prevent progression and recurrence of bladder cancer.

Initial Experience with 68Ga-FAP-2286 PET Imaging in Patients with Urothelial Cancer

Improved imaging modalities are needed to accurately stage patients with muscle-invasive bladder cancer (MIBC) and metastatic urothelial carcinoma. Imaging with small-molecule ligands or inhibitors of fibroblast activation protein (FAP) is a promising modality that has demonstrated initial efficacy across a broad range of tumors. We present our experience with the novel FAP-peptide binder 68Ga-FAP-2286 in patients with MIBC. Methods: Patients with histopathologically confirmed bladder cancer who had either localized disease at diagnosis (localized cohort, n = 13) or known metastatic disease (metastatic cohort, n = 8) were imaged with 68Ga-FAP-2286 PET as part of a clinical trial (NCT04621435). The SUVmax of 68Ga-FAP-2286 PET-positive lesions and lesion size were documented. In patients who had available 18F-FDG PET performed within 45 d of 68Ga-FAP-2286 PET (n = 5), uptake on the 2 scans was compared. When there was a discrepancy between imaging modalities on retrospective review, biopsy of suggestive lesions was performed as the standard of care. Results: In the metastatic and localized cohorts, 36 and 18 68Ga-FAP-2286-avid lesions, respectively, were identified across multiple anatomic locations, including lymph nodes, visceral metastases, and bones. Fourteen of 36 lesions in the metastatic cohort and 14 of 18 lesions in the localized cohort were lymph nodes measuring less than 1 cm. Among lesions measuring less than 0.5 cm, 0.5-1 cm, and more than 1 cm, average SUVmax was 5.2 ± 2.6, 9.6 ± 3.7, and 13.0 ± 4.3, respectively, in the metastatic cohort and 10.5 ± 5.1, 10.8 ± 5.7, and 9.9 ± 5.4, respectively, in the localized cohort. Five patients had 18F-FDG PET available for comparison. The average SUVmax for lesions avid on 68Ga-FAP-2286 PET and 18F-FDG PET was 9.9 ± 3.4 versus 4.2 ± 1.9, respectively (n = 16 lesions). For 3 patients in the localized cohort, 68Ga-FAP-2286 PET informed clinical management, including identification of both false-positive findings on 18F-FDG PET and false-negative findings on conventional CT. Conclusion: 68Ga-FAP-2286 imaging is highly sensitive in patients with urothelial cancer and is effective in identifying metastatic lesions across a variety of anatomic sites, including subcentimeter lymph nodes that would not have raised suspicion on conventional scans. This novel imaging modality may inform clinical decision-making in patients with MIBC both by refining local nodal staging and by defining metastatic disease that would otherwise be undetectable on conventional imaging.