Imaging at the nexus: how state of the art imaging techniques can enhance our understanding of cancer and fibrosis

The Development of Al18F-NOTA-FAP-2286 as an FAP-Targeted PET Tracer and the Translational Application in the Diagnosis of Acquired Drug Resistance in Progressive Prostate Cancer

Objectives: Tumor heterogeneity and acquired resistance to prostate-specific membrane antigen (PSMA) radioligand therapy (PRLT) pose significant challenges to PSMA PET-based diagnosis. This study aimed to develop an Al18F-labeled FAP-targeted tracer and explore the diagnostic value in acquired drug-resistant tumor models. Methods: To identify potential targets for imaging drug-resistant prostate cancer, bioinformatic analysis was employed to correlate FAP expression levels with genes associated with tumor progression and radiotherapy resistance. Molecular docking technology simulations were utilized to screen FAP ligands for optimal binding affinity and target specificity. The most promising ligand, FAP-2286, was radiolabeled with 18F to develop a novel PET imaging agent, Al18F-NOTA-FAP-2286 PET. To evaluate the diagnostic potential of this agent, various tumor models were established. U87 cells were used to optimize the imaging protocol and assess targeting efficiency and 22RV-1-resistant cells co-xenografted with NIH-3T3 cells were used to model acquired drug-resistant prostate cancer. The diagnostic efficacy of Al18F-NOTA-FAP-2286 PET in this acquired drug-resistant model was assessed and validated through immunohistochemical staining of tumor tissue. Results: Bioinformatic analysis confirmed the association between FAP expression and key genes involved in radiotherapy resistance, such as HIF1α, BCL2, ATM, and EGFR. Molecular docking studies demonstrated the strong binding affinity of FAP-2286 to FAPα (-10 kcal/mol). Al18F-NOTA-FAP-2286 PET/CT imaging in U87 tumor-bearing mice revealed accurate targeting of high FAP-expressing xenografts. The imaging characteristics of Al18F-NOTA-FAP-2286 were comparable to 18F-FDG and 68Ga-FAP-2286 but with a prolonged imaging window compared to 68Ga-FAP-2286. In acquired drug-resistant prostate cancer xenograft nude mice, Al18F-NOTA-FAP-2286 could effectively detect tumor lesions, as confirmed by immunohistochemical analysis. Conclusions: Al18F-NOTA-FAP-2286, as a PSMA-independent imaging agent, holds promise as a valuable complementary molecular imaging tool for assessing acquired resistance to PRLT.

Myofibroblasts persist through immune privilege mechanisms to mediate oral submucous fibrosis: Uncovering the pathogenesis

Immune privilege is the ability to tolerate foreign antigens without eliciting an inflammatory immune response. Several mechanisms explain a structure's immune privilege status, which is regulated by innate and adaptive immune responses. The role of myofibroblasts in perpetuating fibrosis by acquiring an immune privileged phenotype against the backdrop of oral submucous fibrosis (OSF) is evolving. Myofibroblasts persist through the Fas/FasL autocrine pathway and induce apoptosis in epithelial cells, explaining the juxtaposition of apoptotic cells in areas of fibrosis. However, increased matrix stiffness, in addition to activating TGF-β, reduces Fas surface expression in myofibroblasts, increasing their resistance to apoptosis. The reciprocal amplification loop between the immune checkpoint proteins programmed death-ligand 1 (PD-L1) and TGF-β involves the YAP-TAZ and SMAD2,3 pathways and dramatically enhances profibrotic signalling. Increased matrix stiffness also enhances cMYC expression, which subsequently amplifies PD-L1 levels on myofibroblasts. The increase in PD-L1 on the myofibroblast microengineers the phenotype of CD4+ T cells homing to fibrotic areas by acting on the programmed cell death protein 1 (PD-1) receptor on the T-cell surface, converting these cells from antifibrotic cells to profibrotic cells that produce IL-17A and TGF-β. This manuscript provides mechanistic insight into how myofibroblasts avoid apoptosis in OSFs by evading the immune system. Targeting an immune-privileged phenotype in myofibroblasts with FAS-FASL pathway-dependent characteristics is an ideal strategy for reversing OSF.