Background and Aim: Pancreatic cancer is one of the most fatal cancers. Cytotoxic chemotherapy remains the mainstream treatment for unresectable pancreatic cancer. This systematic review evaluated and compared the overall survival (OS) and progression-free survival (PFS) outcomes obtained from recent phase 2 and 3 clinical trials of pancreatic cancer chemotherapy. Materials and methods: Thirty-two studies were included and compared based on chemotherapy agents or combinations used. Additionally, outcomes of first-line versus second-line chemotherapy in pancreatic cancer were compared. Results: In studies that investigated the treatments in adjuvant settings, the highest OS reported was for S-1 in patients, who received prior surgical resection (46.5 months). In neoadjuvant settings, the combination of gemcitabine, docetaxel, and capecitabine prior to the surgical resection had promising outcomes (OS of 32.5 months). In non-adjuvant settings, the highest OS reported was for the combination of temsirolimus plus bevacizumab (34.0 months). Amongst studies that investigated second-line treatment, the highest OS reported was for the combination of gemcitabine plus cisplatin (35.5 months), then temsirolimus plus bevacizumab (34.0 months). Conclusions: There is a need to develop further strategies besides chemotherapy to improve the outcomes in pancreatic cancer treatment. Future studies should consider surgical interventions, combination chemotherapy, and individualized second-line treatment based on the prior chemotherapy.

The 'cross-talk' between different types of neurotransmitters through second messenger pathways represents a major regulatory mechanism in neuronal function. We investigated the effects of activation of protein kinase C (PKC) on cAMPdependent signaling by structurally related human D1-like dopaminergic receptors. Human embryonic kidney 293 (HEK293) cells expressing D1 or D5 receptors were pretreated with phorbol-12-myristate-13-acetate (PMA), a potent activator of PKC, followed by analysis of dopamine-mediated receptor activation using whole cell cAMP assays. Unpredictably, PKC activation had completely opposite effects on D1 and D5 receptor signaling. PMA dramatically augmented agonist-evoked D1 receptor signaling, whereas constitutive and dopamine-mediated D5 receptor activation were rapidly blunted. RT-PCR and immunoblotting analyses showed that phorbol ester-regulated PKC isozymes (conventional: a, bI, bII, c; novel: d, e, g, h) and protein kinase D (PKCl) are expressed in HEK293 cells. PMA appears to mediate these contrasting effects through the activation of Ca 2+ -independent novel PKC isoforms as revealed by specific inhibitors, bisindolylmaleimide I, Gö 6976, and Gö 6983. The finding that cross-talk between PKC and cAMP pathways can produce such opposite outcomes following the activation of structurally similar D1-like receptor subtypes is novel and further strengthens the view that D1 and D5 receptors serve distinct functions in the mammalian nervous and endocrine systems.

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In this study, a cleavable signal peptide fused to the enhanced green fluorescent protein (EGFP) was tagged to the extracellular N-terminus of the human dopamine D2 receptor short and long isoforms (D2S and D2L). Ligand-binding properties of EGFP-tagged receptors were essentially unchanged in comparison to their respective wild-type receptors. The dopamine-mediated activation of both EGFP-D2 isoforms generated a robust inhibition of adenylyl cyclase type 5 in intact cells. In addition, the receptor density of EGFP-D2S and EGFP-D2L in transfected human embryonic kidney 293 (HEK293) cells was not altered when compared to cells transfected with the untagged D2S and D2L. However, the receptor densities of untagged and EGFP-tagged D2L were significantly lower in comparison to those measured with D2S constructs. Moreover, the receptor density of EGFP-D2S and EGFP-D2L was differentially upregulated in cells treated with antipsychotic drugs. As assessed by confocal microscopy, both EGFP-D2 isoforms were present on the cell surface. Notably, in contrast to the predominant plasma membrane localization of EGFP- D2S, EGFP-D2L was visualized both on the plasma membrane and intracellularly before dopamine exposure. Importantly, EGFP-D2S and EGFP-D2L are robustly internalized after dopamine treatment. Overall, our data suggest a differential intracellular sorting of D2S and D2L.

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The D1 dopaminergic receptor (D1R) is a seven‐transmembrane protein linked to stimulatory heterotrimeric GTP‐binding proteins. Here, we investigate the role of the cytoplasmic tail (CT) of D1R in regulating intracellular sorting properties of the receptor. We show that wild‐type (WT) D1R and its truncated and phosphorylation‐deficient form (Δ351) were sorted at the plasma membrane of transfected embryonic kidney 293 (HEK293) cells. Antibody feeding and co‐localization studies indicate that similar to WT, Δ351 internalizes through a clathrin‐, CT‐ and receptor phosphorylation‐independent pathway following dopamine (DA) exposure. However, in the absence of DA, Δ351 displays a strong intracellular staining unlike WT as assessed using immunofluorescence studies. Our confocal microscopy analysis shows that Δ351 co‐localizes with the endoplasmic reticulum (ER) markers, calnexin and calreticulin. Intriguingly, we observe an increase in the mature form of Δ351 and a complete rescue of ER‐retained Δ351 following an overnight treatment of transfected HEK293 cells with the inverse agonist flupentixol (Flu), an antipsychotic drug. These data strongly suggest that Flu displays a chaperone‐like effect on ER‐retained Δ351. Overall, our studies underpin a pivotal role of the CT of D1R in regulating the ontogeny and sorting to cell surface of this dopaminergic receptor subtype.Supported by CIHR (MOP‐81341; MT).

The dopamine D3 receptor (D3R) is a seven‐transmembrane‐spanning protein mediating its intracellular effects through the activation of heterotrimeric Gi/o proteins. The D3R‐mediated Gi/o protein activation culminates in an isoform‐specific inhibition of adenylyl cyclase type 5 (AC5) as previously demonstrated using a co‐transfection approach. In the present study, we explore the role of phosphorylation and hetero‐oligomerization in regulating the functional interplay between D3R and AC5 in co‐transfected human embryonic kidney 293 (HEK293) cells using immunoprecipitation, whole cell phosphorylation and cAMP assays. Whole cell phosphorylation experiments show that D3R exhibits basal and dopamine‐induced phosphorylation in cells not expressing AC5. Interestingly, our preliminary studies demonstrate that D3R is dephosphorylated in AC5‐expressing HEK293 cells following dopamine exposure. Moreover, our co‐immunoprecipitation studies imply that D3R and AC5 form hetero‐oligomers under basal conditions. However, dopamine stimulation curtails the D3R‐AC5 hetero‐oligomerization. Overall, our work suggests a novel paradigm in 7TMR‐mediated signaling whereby the phosphorylation of a 7TMR under steady‐state conditions and following agonist stimulation differentially regulate the hetero‐oligomerization process between the receptor and its effector. Supported by CIHR (MOP‐84442; MT).