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Type I interferons (IFNs) are critical effectors of emerging cancer immunotherapies designed to activate pattern recognition receptors (PRRs). A challenge in the clinical translation of these agents is the lack of noninvasive pharmacodynamic biomarkers that indicate increased intratumoral IFN signaling following PRR activation. Positron emission tomography (PET) imaging enables the visualization of tissue metabolic activity, but whether IFN signaling-induced alterations in tumor cell metabolism can be detected using PET has not been investigated. We found that IFN signaling augments pancreatic ductal adenocarcinoma (PDAC) cell nucleotide metabolism via transcriptional induction of metabolism-associated genes including thymidine phosphorylase (TYMP). TYMP catalyzes the first step in the catabolism of thymidine, which competitively inhibits intratumoral accumulation of the nucleoside analog PET probe 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT). Accordingly, IFN treatment up-regulates cancer cell [18F]FLT uptake in the presence of thymidine, and this effect is dependent upon TYMP expression. In vivo, genetic activation of stimulator of interferon genes (STING), a PRR highly expressed in PDAC, enhances the [18F]FLT avidity of xenograft tumors. Additionally, small molecule STING agonists trigger IFN signaling-dependent TYMP expression in PDAC cells and increase tumor [18F]FLT uptake in vivo following systemic treatment. These findings indicate that [18F]FLT accumulation in tumors is sensitive to IFN signaling and that [18F]FLT PET may serve as a pharmacodynamic biomarker for STING agonist-based therapies in PDAC and possibly other malignancies characterized by elevated STING expression. [ABSTRACT FROM AUTHOR]

Emerging evidence suggests that intratumoral interferon (IFN) signaling can trigger targetable vulnerabilities. A hallmark of pancreatic ductal adenocarcinoma (PDAC) is its extensively reprogrammed metabolic network, in which nicotinamide adenine dinucleotide (NAD) and its reduced form, NADH, are critical cofactors. Here, we show that IFN signaling, present in a subset of PDAC tumors, substantially lowers NAD(H) levels through up-regulating the expression of NAD-consuming enzymes PARP9, PARP10, and PARP14. Their individual contributions to this mechanism in PDAC have not been previously delineated. Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme in the NAD salvage pathway, a dominant source of NAD in cancer cells. We found that IFN-induced NAD consumption increased dependence upon NAMPT for its role in recycling NAM to salvage NAD pools, thus sensitizing PDAC cells to pharmacologic NAMPT inhibition. Their combination decreased PDAC cell proliferation and invasion in vitro and suppressed orthotopic tumor growth and liver metastases in vivo. [ABSTRACT FROM AUTHOR]

The EGFR/PI3K/Akt/mTOR signaling pathway is activated in many cancers including glioblastoma, yet mTOR inhibitors have largely failed to show efficacy in the clinic. Rapamycin promotes feedback activation of Akt in some patients, potentially underlying clinical resistance and raising the need for alternative approaches to block mTOR signaling. AMPK is a metabolic checkpoint that integrates growth factor signaling with cellular metabolism, in part by negatively regulating mTOR. We used pharmacological and genetic approaches to determine whether AMPK activation could block glioblastoma growth and cellular metabolism, and we examined the contribution of EGFR signaling in determining response in vitro and in vivo. The AMPK-agonist AICAR, and activated AMPK adenovirus, inhibited mTOR signaling and blocked the growth of glioblastoma cells expressing the activated EGFR mutant, EGFRvIII. Across a spectrum of EGFR-activated cancer cell lines, AICAR was more effective than rapamycin at blocking tumor cell proliferation, despite less efficient inhibition of mTORC1 signaling. Unexpectedly, addition of the metabolic products of cholesterol and fatty acid synthesis rescued the growth inhibitory effect of AICAR, whereas inhibition of these lipogenic enzymes mimicked AMPK activation, thus demonstrating that AMPK blocked tumor cell proliferation primarily through inhibition of cholesterol and fatty acid synthesis. Most importantly, AICAR treatment in mice significantly inhibited the growth and glycolysis (as measured by 18fluoro-2-deoxyglucose microPET) of glioblastoma xenografts engineered to express EGFRvIII, but not their parental counterparts. These results suggest a mechanism by which AICAR inhibits the proliferation of EGFRvIII expressing glioblastomas and point to- ward a potential therapeutic strategy for targeting EGFR-activated cancers. [ABSTRACT FROM AUTHOR]

Current methodologies that monitor immune responses rely on invasive techniques that sample tissues at a given point in time. New technologies are needed to elucidate the temporal patterns of immune responses and the spatial distribution of immune cells on a whole-body scale. We describe a noninvasive, quantitative, and tomographic approach to visualize a primary anti-tumor immune response by using positron emission tomography (PET). Bone marrow chimeric mice were generated by engraftment of hematopoietic stem and progenitor cells transduced with a trifusion reporter gene encoding synthetic Renilla luciferase (hRluc), EGFP, and Herpes virus thymidine kinase (sr39TK). Mice were challenged with the Moloney murine sarcoma and leukemia virus complex (M-MSV/M-MuLV), and the induced immune response was monitored by using PET. Hematopoietic cells were visualized by using 9-[4-[18F]fluoro-3-(hydroxymethyl)butyl]guanine ([18F]FHBG), a radioactive substrate specific for the sr39TK PET reporter protein. Immune cell localization and expansion were seen at the tumor and draining lymph nodes (DLNs). 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG), which is sequestered in metabolically active cells, was used to follow tumor growth and regression. Elevated glucose metabolism was also seen in activated lymphocytes in the DLNs by using the [18F]FDG probe. When M-MSV/M-MuLV-challenged mice were treated with the immunosuppressive drug dexamethasone, activation and expansion of immune cell populations in the DLNs could no longer be detected with PET imaging. The method we describe can be used to kinetically measure the induction and therapeutic modulations of cell-mediated immune responses. [ABSTRACT FROM AUTHOR]

Emerging evidence suggests that intratumoral interferon (IFN) signaling can trigger targetable vulnerabilities. A hallmark of pancreatic ductal adenocarcinoma (PDAC) is its extensively reprogrammed metabolic network, in which nicotinamide adenine dinucleotide (NAD) and its reduced form, NADH, are critical cofactors. Here, we show that IFN signaling, present in a subset of PDAC tumors, substantially lowers NAD(H) levels through up-regulating the expression of NAD-consuming enzymes PARP9, PARP10, and PARP14. Their individual contributions to this mechanism in PDAC have not been previously delineated. Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme in the NAD salvage pathway, a dominant source of NAD in cancer cells. We found that IFN-induced NAD consumption increased dependence upon NAMPT for its role in recycling NAM to salvage NAD pools, thus sensitizing PDAC cells to pharmacologic NAMPT inhibition. Their combination decreased PDAC cell proliferation and invasion in vitro and suppressed orthotopic tumor growth and liver metastases in vivo., Competing Interests: Competing interest statement: C.G.R. is a cofounder of Sofie Biosciences and Trethera Corporation. He and the University of California (UC) hold equity in Sofie Biosciences and Trethera Corporation. The intellectual property developed by C.G.R. and licensed by UC to Sofie Biosciences and Trethera Corporation was not used in this study.

Deoxycytidine kinase (dCK), a rate-limiting enzyme in the cytosolic deoxyribonucleoside (dN) salvage pathway, is an important therapeutic and positron emission tomography (PET) imaging target in cancer. PET probes for dCK have been developed and are effective in mice but have suboptimal specificity and sensitivity in humans. To identify a more suitable probe for clinical dCK PET imaging, we compared the selectivity of two candidate compounds-[(18)F]Clofarabine; 2-chloro-2'-deoxy-2'-[(18)F]fluoro-9-β-d-arabinofuranosyl-adenine ([(18)F]CFA) and 2'-deoxy-2'-[(18)F]fluoro-9-β-d-arabinofuranosyl-guanine ([(18)F]F-AraG)-for dCK and deoxyguanosine kinase (dGK), a dCK-related mitochondrial enzyme. We demonstrate that, in the tracer concentration range used for PET imaging, [(18)F]CFA is primarily a substrate for dCK, with minimal cross-reactivity. In contrast, [(18)F]F-AraG is a better substrate for dGK than for dCK. [(18)F]CFA accumulation in leukemia cells correlated with dCK expression and was abrogated by treatment with a dCK inhibitor. Although [(18)F]CFA uptake was reduced by deoxycytidine (dC) competition, this inhibition required high dC concentrations present in murine, but not human, plasma. Expression of cytidine deaminase, a dC-catabolizing enzyme, in leukemia cells both in cell culture and in mice reduced the competition between dC and [(18)F]CFA, leading to increased dCK-dependent probe accumulation. First-in-human, to our knowledge, [(18)F]CFA PET/CT studies showed probe accumulation in tissues with high dCK expression: e.g., hematopoietic bone marrow and secondary lymphoid organs. The selectivity of [(18)F]CFA for dCK and its favorable biodistribution in humans justify further studies to validate [(18)F]CFA PET as a new cancer biomarker for treatment stratification and monitoring.