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The microenvironment of pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense fibrotic stroma (desmoplasia) generated by pancreatic cancer-associated fibroblasts (CAFs) derived from pancreatic stellate cells (PSCs) and pancreatic fibroblasts (PFs). Using an unbiased GPCRomic array approach, we identified 82 G-protein-coupled receptors (GPCRs) commonly expressed by CAFs derived from 5 primary PDAC tumors. Compared with PSCs and PFs, CAFs have increased expression of GPR68 (a proton-sensing GPCR), with the results confirmed by immunoblotting, The Cancer Genome Atlas data, and immunohistochemistry of PDAC tumors. Co-culture of PSCs with PDAC cells, or incubation with TNF-α, induced GPR68 expression. GPR68 activation (by decreasing the extracellular pH) enhanced IL-6 expression via a cAMP/PKA/cAMP response element binding protein signaling pathway. Knockdown of GPR68 by short interfering RNA diminished low pH-induced production of IL-6 and enhancement of PDAC cell proliferation by CAF conditioned media. CAFs from other gastrointestinal cancers also express GPR68. PDAC cells thus induce expression by CAFs of GPR68, which senses the acidic microenvironment, thereby increasing production of fibrotic markers and IL-6 and promoting PDAC cell proliferation. CAF-expressed GPR68 is a mediator of low-pH-promoted regulation of the tumor microenvironments, in particular to PDAC cell-CAF interaction and may be a novel therapeutic target for pancreatic and perhaps other types of cancers.-Wiley, S. Z., Sriram, K., Liang, W., Chang, S. E., French, R., McCann, T., Sicklick, J., Nishihara, H., Lowy, A. M., Insel, P. A. GPR68, a proton-sensing GPCR, mediates interaction of cancer-associated fibroblasts and cancer cells.

G protein-coupled receptors (GPCRs), the largest family of signaling receptors in the human genome, are also the largest class of targets of approved drugs. Are the optimal GPCRs (in terms of efficacy and safety) currently targeted therapeutically? Especially given the large number (∼ 120) of orphan GPCRs (which lack known physiologic agonists), it is likely that previously unrecognized GPCRs, especially orphan receptors, regulate cell function and can be therapeutic targets. Knowledge is limited regarding the diversity and identity of GPCRs that are activated by endogenous ligands and that native cells express. Here, we review approaches to define GPCR expression in tissues and cells and results from studies using these approaches. We identify problems with the available data and suggest future ways to identify and validate the physiologic and therapeutic roles of previously unrecognized GPCRs. We propose that a particularly useful approach to identify functionally important GPCRs with therapeutic potential will be to focus on receptors that show selective increases in expression in diseased cells from patients and experimental animals.

G protein-coupled receptors (GPCRs) are the largest class of signaling receptors in humans and other species and in addition, the most widely targeted class for FDA-approved therapeutics. However, GPCRs are not commonly targeted in cancers other than endocrine tumors. We hypothesize that GPCRs may have been “missed” as targets in cancer, perhaps in part because they have not been frequently identified as driver mutations; however, GPCRs may have unappreciated utility as therapeutic targets in a variety of tumors. To test this hypothesis, we have used unbiased approaches (Taqman GPCR arrays and RNA-seq), mining of publicly available datasets (e.g., The Cancer Genome Atlas, TCGA), and validation studies (e.g., protein and functional analyses) to assess GPCRs in a variety of human tumors, cancer cells and stromal cells (cancer-associated fibroblasts, CAFs). A major focus of our efforts has been on pancreatic ductal adenocarcinoma (PDAC) cells/tumors and pancreatic CAFs (PCAFs). We find that PDAC cells and PCAFs express >70 different GPCRs, including many orphan GPCRs (receptors without known physiologic agonists) and that numerous GPCRs are expressed at much higher levels than in normal precursor cells (pancreatic ductal epithelial cells for PDAC cells and pancreatic stellate cells and pancreatic fibroblasts for PCAFs). We find that a cluster of GPCRs is overexpressed in PDAC tumors. Two such receptors are orphan GPCRs, Orphan 1 and Orphan A, neither of which is mutated but each has high expression, respectively, in PCAFs and PDAC cells. Orphan 1 and Orphan A have at least 2-fold higher expression in >90% of PDAC tumors in TCGA compared to that in normal pancreatic tissue (compiled from the GTEX database). Higher expression of orphan A is associated with decreased survival and remission, while Orphan 1 expression correlates with that of numerous fibrotic genes. Importantly, both Orphan 1 and Orphan A are functional and appear to contribute to the malignant phenotype. For example, siRNA knockdown of Orphan 1 in PCAFs blunts production of profibrotic markers and decreases ability of conditioned media from PCAFs to enhance proliferation of PDAC cells while transfection of Orphan A increases DNA synthesis of normal pancreatic ductal epithelial cells. Taken together, these and other results suggest that in addition to their role in endocrine tumors, GPCRs represent previously unrecognized contributors to cancer through actions on tumor cells and stromal cells. These data suggest the possibility that highly expressed GPCRs (such as Orphan A) may function as oncogenes. Thus, GPCRs may be druggable, novel targets for the treatment of cancer, including pancreatic cancer, a tumor for which new therapeutics are an important, unmet need. Note: This abstract was not presented at the meeting. Citation Format: Paul A. Insel, Krishna Sriram, Shu Z. Wiley, Thalia McCann, Randall P. French, Andrew M. Lowy. G protein-coupled receptors (GPCRs): unrecognized potential therapeutic targets in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1139. doi:10.1158/1538-7445.AM2017-1139

GPCRs as potential therapeutic targets in pancreatic cancer-associated fibroblasts Shu Zhou1, Thalia McCann1, Randall French2, Andrew M. Lowy2,3, Paul A. Insel1,4 1Department of Pharmacology, 2Moor...

The second messenger cAMP, acting through PKA, induces apoptosis in certain lymphoma and leukemia cells. This apoptotic response facilitated the isolation of a cAMP-resistant, clonal variant of wil...

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense fibrotic stromal matrix, composed of activated fibroblasts (PFs)/stellate cells (PSCs), immune/inflammatory cells and other cell types. This unique tumor microenvironment is increasingly recognized as a key mediator of PDAC progression and drug resistance. Targeting the tumor stroma may thus be a therapeutic approach for PDAC. Pancreatic cancer-associated fibroblasts (CAFs), myofibroblast-like cells that produce extracellular matrix proteins, are responsible for the desmoplasia in PDAC. PSCs and PFs are the key progenitors of CAFs. Blocking the activity of CAFs may be a means to improve the therapy and prognosis of PDAC. We hypothesized that G protein-coupled receptors (GPCRs) expressed by pancreatic CAFs are potential therapeutic targets for PDAC. To begin to test this hypothesis, we used an unbiased GPCRomic array approach to identify and quantify the GPCRs expressed by pancreatic CAFs. We discovered that 104 GPCRs have shared expression in CAFs from the primary tumors of five patients; 35 of those GPCRs had at least a 2-fold increased expression in CAFs compared to both PSCs and PFs. An orphan GPCR that we term Orphan 1 is one of the most highly up-regulated GPCRs in CAFs. We found that: 1) co-culture of PSCs with a PDAC cell line (ASPC-1) increases expression of fibrotic markers and Orphan 1 GPCR; 2) Transfection of Orphan 1 GPCR in PSCs increases the expression of fibrotic markers; 3) siRNA knockdown of Orphan 1 in CAFs decreases fibrotic marker expression and cytokine secretion. We conclude that GPCRomics can identify GPCRs that regulate pancreatic CAFs. One such GPCR, Orphan 1, contributes to pro-fibrotic activities in CAFs and is a potential therapeutic target to blunt the fibrosis associated with pancreatic cancer. Citation Format: Shu Zhou, Sarah Chang, Thalia McCann, Randall French, Andrew M. Lowy, Paul A. Insel. GPCRs as potential therapeutic targets in pancreatic cancer-associated fibroblasts. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C156.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense fibrotic stromal matrix, composed of activated fibroblasts/stellate cells, inflammatory cells and other cell types. This unique tumor microenvironment has been increasingly recognized as a key mediator of PDAC progression and drug resistance. Thus, targeting the tumor stroma may be a novel therapeutic approach for PDAC. We hypothesized that G protein-coupled receptors (GPCRs) expressed by pancreatic cancer-associated fibroblasts (CAFs) may be potential therapeutic targets for PDAC. To begin to test this hypothesis, we used an unbiased GPCRomic array approach to identify and quantify the GPCRs expressed by pancreatic CAFs. We found 104 GPCRs, whose expression was shared in CAFs obtained from the primary tumors of five patients. Among those GPCRs, 35 had at least two-fold higher expression in the CAFs compared to normal pancreatic fibroblasts and included GPCRs that link to each of the major classes of G proteins. RT-PCR analysis of the 10 most up-regulated GPCRs correlated well (r2=0.82) with the data from the GPCR array. We conclude that: 1) GPCRomic array analysis can identify and quantify the profile of GPCRs expressed by pancreatic CAFs; 2) the CAF-expressed profile differs from that of normal pancreatic fibroblasts and 3) GPCRs expressed by CAFs may have functional roles and be novel therapeutic targets for PDAC. Citation Format: Shu Zhou, Thalia McCann, Randall French, Andrew Lowy, Paul Insel. GPCRs as potential therapeutic targets in pancreatic cancer-associated fibroblasts. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A57.