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Purpose: Fibroblast activation protein (FAP)-expressing cancer-associated fibroblasts confer treatment resistance, promote metastasis and immunosuppression. Because FAP is overexpressed in many cancers, radiolabeled molecules targeting FAP are studied for their use as pan-cancer theranostic agents. This study aims to establish the spectrum of FAP expression across various cancers by immunohistochemistry and to explore whether gallium-68 FAPi-46 (68Ga-FAPi-46) PET biodistribution faithfully reflects FAP expression from resected cancer and non-cancer specimens. Methods: We conducted a FAP expression screening by using immunohistochemistry on a pan-cancer human tissue microarray (TMA) (141 patients, 14 different types of cancer) and an interim analysis of a prospective exploratory imaging trial in cancer patients. Volunteer patients underwent one whole body 68Ga-FAPi-46 PET/CT scan and subsequently, surgical resection of their primary tumor and/or metastasis. 68Ga-FAPi-46 PET maximum standardized uptake value (SUVmax and SUVmean) was correlated with FAP immunohistochemistry score in cancer and non-cancer tissues for each patient. Results: FAP was expressed across all 14 cancers types on TMA with variable intensity and frequency, ranging from 25 to 100% (mean 76.6±25.3%). Strong FAP expression was observed in 50-100% of cancers of the bile duct, bladder, colon, esophagus, stomach, lung, oropharynx, ovary and pancreas. Fifteen patients with various cancer types (colorectal (n = 4), head and neck (n = 3), pancreas (n = 2), breast (n = 2), stomach (n = 1), esophagus (n = 2) and uterus (n = 1)) underwent surgery following their 68Ga-FAPi-46 PET/CT scan within a mean time interval of 16.1±14.4 days. 68Ga-FAPi-46 SUVs and immunohistochemistry scores were higher in cancer than in normal tissue: mean SUVmax 7.7 vs 1.6 (p

Prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy (RNT) may increase tumor immunogenicity. We aimed at exploiting this effect by combining RNT with immunotherapy in a mouse model of prostate cancer (PC). Methods: C57BL/6-mice bearing syngeneic RM1-PGLS tumors were treated with 225Ac-PSMA617, an anti-PD-1 antibody, or both. Therapeutic efficacy was assessed by tumor volume measurements (CT), time to progression (TTP), and survival. Results: PSMA RNT or anti-PD-1 alone tended to prolong TTP (isotype control, 25 d; anti-PD-1, 33.5 d [P = 0.0153]; RNT, 30 d [P = 0.1038]) and survival (control, 28 d; anti-PD-1, 37 d [P = 0.0098]; RNT, 32 d [P = 0.1018]). Combining PSMA RNT and anti-PD-1 significantly improved disease control compared with either monotherapy. TTP was extended to 47.5 d (P ≤ 0.0199 vs. monotherapies), and survival to 51.5 d (P ≤ 0.0251 vs. monotherapies). Conclusion: PSMA RNT and PD-1 blockade synergistically improve therapeutic outcomes in our PC model, supporting the evaluation of RNT and immunotherapy combinations for PC patients.

FlhDC is a heterohexameric complex that acts as a master regulator of flagellar biosynthesis genes in numerous bacteria. Previous studies have identified a single flhDC operon encoding this complex. However, we found that two flhDC loci are present throughout Paraburkholderia, and two additional flhC copies are also present in Paraburkholderia unamae. Systematic deletion analysis in P. unamae of the different flhDC copies showed that one of the operons, flhDC1, plays the predominant role, with deletion of its genes resulting in a severe inhibition of motility and biofilm formation. Expression analysis using promoter-lacZ fusions and real-time quantitative PCR support the primary role of flhDC1 in flagellar gene regulation, with flhDC2 a secondary contributor. Phylogenetic analysis shows the presence of the flhDC1 and flhDC2 operons throughout Paraburkholderia. In contrast, Burkholderia and other bacteria only carry the copy syntenous with flhDC2. The variations in impact each copy of flhDC has on downstream processes indicate that regulation of FlhDC in P. unamae, and likely other Paraburkholderia species, is regulated at least in part by the presence of multiple copies of these genes. IMPORTANCE Motility is important in the colonization of plant roots by beneficial and pathogenic bacteria, with flagella playing essential roles in host cell adhesion, entrance, and biofilm formation. Flagellar biosynthesis is energetically expensive. Its complex regulation by the FlhDC master regulator is well studied in peritrichous flagella expressing enterics. We report the unique presence throughout Paraburkholderia of multiple copies of flhDC. In P. unamae, the flhDC1 copy showed higher expression and a greater effect on swim motility, flagellar development, and regulation of downstream genes, than the flhDC2 copy that is syntenous to flhDC in Escherichia coli and pathogenic Burkholderia spp. The flhDC genes have evolved differently in these plant-growth-promoting bacteria, giving an additional layer of complexity in gene regulation by FlhDC.

Fibroblast activation protein (FAP)-expressing cancer-associated fibroblasts confer treatment resistance and promote metastasis and immunosuppression. Because FAP is overexpressed in many cancers, radiolabeled molecules targeting FAP are studied for their use as pancancer theranostic agents. This study aimed to establish the spectrum of FAP expression across various cancers by immunohistochemistry and to explore whether

Prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy (RNT) may increase tumor immunogenicity. We aimed at exploiting this effect by combining RNT with immunotherapy in a mouse model of prostate cancer (PC).

3066 Background: Fibroblast activation protein (FAP)-expressing cancer-associated fibroblasts (CAF), a major component of tumor stroma, confer treatment resistance, promote local progression, metastasis and immunosuppression. Because FAP is selectively expressed in the tumor stroma of many cancers, radiolabeled small molecule ligands targeting FAP are being explored for their use as pan-cancer theranostic agents. The objective was to establish the spectrum of FAP expression across various cancers by immunohistochemistry (IHC) and to explore whether 68Ga-FAPi-46 PET image biodistribution faithfully reflects tumor FAP expression from resected tumor and non-tumor specimens. Methods: This study was a prospective, exploratory, imaging trial in cancer patients. Referred volunteer patients scheduled to undergo surgical resection of the primary tumor and/or metastases were eligible. Patients underwent one whole body 68Ga-FAPi-46 PET/CT scan. Subsequently, patients underwent surgical resection of the primary tumor and/or metastasis. The outcome measure was the correlation of 68Ga-FAPi-46 PET maximum standardized uptake value (SUVmax) with FAP IHC score in patient-matched cancer and non-cancer tissue. Results: The frequency of FAP expression across 14 cancers on tissue microarrays ranged from 25 to 100% (mean 76.6±25.3%). For imaging and IHC correlation, fifteen patients with the following cancer types were prospectively included: colorectal (n = 4), head and neck (n = 3), pancreas (n = 2), breast (n = 2),stomach (n = 1), esophagus (n = 2) and uterus (n = 1). All 15 patients underwent surgery following their 68Ga-FAPi-46 PET scan within a mean time interval of 16.1±14.4 days (range 1 – 50 days). For two patients the tumor was deemed unresectable. 68Ga-FAPi-46 SUVmax and IHC scores were higher in cancer tissue than in normal tissue: mean 68Ga-FAPi-46 SUVmax 7.4±4.6 (range 1.5-15.9) vs 1.6±1.2 (range 0.4-5.1), (p < 0.001) and mean FAP IHC score 2.38±0.65 vs 0.54±0.66 (p < 0.001), respectively. The FAP IHC scores strongly correlated with 68Ga-FAPi-46 SUVmax (p = 0.001, repeated measures correlation r = 0.85 (95% CI 0.53-0.95), p < 0.001). Conclusions: 68Ga-FAPi-46 PET biodistribution across multiple cancers strongly correlates with FAP tissue expression as measured by IHC. This translational validation paves the way for large scale prospective trials on the use of 68Ga-FAPi-46 PET/CT as a biomarker and stratification tool for FAP-targeted therapies. Clinical trial information: NCT04147494.