Immunology, Endocrine & Metabolic Agents in Medicinal Chemistry (Discontinued) - Volume 9, Issue 4, 2009

Pancreatic cancers are classified as either exocrine or endocrine tumors depending on which type of tissue they arise from within the gland. Endocrine tumors of the pancreas are very rare, accounting for only 5% of all pancreatic cancers. The majority of endocrine pancreatic tumors are functional adenocarcinomas that overproduce a specific hormone. Pancreatic cancer is a devastating disease and has an extremely poor prognosis. Most patients die within a year of diagnosis and the overall 5-year survival rate is <1% despite the use of extensive treatment approaches, including surgery, chemotherapy, and radiation. Therefore, innovative anti-tumor therapies for this group of patients is of a great significance. Recent preclinical and clinical studies demonstrated that immunotherapy, in particular vaccination with dendritic cells (DCs) loaded with tumor antigens, is a potential approach with promising anti-tumor effects. Therefore, augmenting the efficacy of immunotherapy with DCs would significantly improve the health of this group of patients. One strategy to augment DC-based vaccination is the use of potent adjuvants that can induce the full activation and maturation of the injected antigen-loaded DCs and their migration to the tumor draining lymph nodes, the site of antigen recognition by T cells. One of the most potent adjuvants is the microbial products that are recognized by more than 13 toll-like receptors expressed on DCs. This review article will highlight the use of DC-based vaccination toward pancreatic cancer and how it can be augmented by toll-like receptor agonists.

Phorbol 12-myristate 13-acetate (PMA) affects a variety of cell processes, including proliferation and differentiation. In most normal cell types, PMA enhances proliferation by a protein kinase C (PKC)- dependent mechanism, while the proliferation of cancer cell lines is inhibited by PMA. PMA has been shown to induce cyclooxygenase-2 (COX-2) production in many cell lines. We examined the effect of PMA on functions of induced COX-2 on proliferation of head-and-neck UMSCC-22B cancer cells. PMA was found to inhibit head-and-neck cancer cell proliferation in a cell viability assay and to induce apoptosis. Abundance of p21 protein and p53 in these cells was increased by PMA treatment. The phorbol ester increased p21 expression in 22B cells through the classical PKC pathway and independently of activation of p53. In addition, PMA increased expression of COX-2 in a time-dependent, PKC-requiring manner. COX-2 siRNA increased abundance of both p53 and p21 in 22B cells and importantly potentiated the anti-proliferative effect of PMA. Confocal microscopy revealed that PMA increased nuclear accumulation of COX-2, but not COX-1, and that COX-2 formed complexes with p53, p21 and the coactivator, p300. Chromatin immunoprecipitation showed that nuclear fraction COX-2 and p53 bound to the promoter region of p21. PMA did not significantly increase PGE2 levels in cultured medium of 22B cells, but did increase by 13-fold the levels of PGE2 in the medium of immortalized normal (293T) cells. In conclusion, our results show that PMA inhibits cell proliferation in head-and-neck cancer cells by a mechanism that is potentiated by COX-2 siRNA. The latter results in an increase of p53 and p21 in PMA-treated cancer cells. In the absence of its siRNA, COX-2 is increased in PMAexposed cancer cells and becomes a nucleoprotein, where it complexes with p53 and p21. Thus, the antiproliferative activity of PMA in 22B cells is moderated by concurrent induction by PMA of COX-2 accumulation; this moderation may be due to reduction by COX-2 of availability of p21 and p53 in the nucleus.

We report a preliminary investigation of the use of pegylated quantum dots (PEG-QDs) conjugated to tetraiodothyroacetic acid (tetrac), a thyroid hormone antagonist and anti-proliferative agent, as a luminescent probe for live cell imaging and treatment of human pancreatic cancer. PEG-QDs were conjugated to epoxyactivated tetrac through primary amino groups present on the PEG-QDs. Cellular entry of tetrac-conjugated PEG-QDs (tetrac-PEG-QDs) in vitro was examined by confocal microscopy and effects of PEG-QDs on cell proliferation were examined by CyQUANT® Cell Proliferation Assay. Tetrac-PEG-QDs exhibited a higher level of entry into pancreatic cancer (PANC-1) cells than unconjugated PEG-QDs. In addition, pre-incubation of cells with the thyroid hormone analogue L-thyroxine (T4) increased fluorescent intensity, indicating enhanced uptake of tetrac-PEG-QDs. Proliferation of PANC-1 cells was significantly inhibited by treatment with tetrac-PEG-QDs.

Adaptation to the environment is essential for pathogenic bacteria during the infection of host tissues. Remodeling of the lipid A portion of lipopolysaccharides in the outer membrane is involved in the adaptation of Gram-negative bacteria. Modifying lipopolysaccharides which are also known as endotoxins help pathogenic bacteria to increase their resistance to host-derived antimicrobial peptides as well as to evade host immune surveillance by Toll-like receptor 4-MD2 complex. In Salmonella typhimurium, the expression of lipid A modification enzymes is regulated by a two-component regulatory system, PhoP-PhoQ, formed from sensor kinase PhoQ and cognate response regulator PhoP. In addition to the transcriptional regulation, recent studies have accumulated evidence that outer membrane conditions greatly affect the activity of outer membrane lipid A modification enzymes, including PagL, PagP, and LpxR. The PhoP-activated gene product PagL encodes lipid A 3-O-deacylase. Lipid A deacylation decreases endotoxin activity, suggesting that the deacylation helps bacteria to evade host immune surveillance. However, lipid A deacylation is usually not observed, because PagL is latent in the outer membrane. Membrane aminoarabinose-modification, which changes cell surface charge, is essential for latency. Alanine-scanning mutagenesis of extracellular loops of PagL revealed that cationic amino acid residues, including Arg-43 and Arg-135, are involved in recognition of the aminoarabinose-modification. These findings suggest that PagL is a sensor as well as an enzyme. These observations constitute an emerging paradigm of outer membrane enzyme regulation. This paper focuses on the regulation and functions of outer membrane lipid A modification enzymes in S. typhimurium.

Severe asthma afflicts only a small portion of the population of asthmatics; however, due to the severity of the disease, treatment of these patients generates disproportionately high costs, which account for as much as spent for treatment of all other asthmatics. This issue gains even more importance since currently available medications are often not sufficient to treat or even dampen the inflammatory response in the airways of severe asthmatics. Whereas mild-to-moderate asthma is characterized by reversibility of airway obstruction, severe asthma frequently includes a degree of fixed airflow limitation and corticosteroid refractoriness. In contrast to mild-to-moderate asthma, the inflammatory response in the airways appears to be much more complex including neutrophils as the dominating leukocyte subpopulation. A plethora of neutrophilderived mediators and enzymes appears to perpetuate or aggravate the inflammatory response and its pathophysiologic consequences by forming several positive feedback loops. Although neutrophil infiltration into the airways is a common feature of acute asthma exacerbations, these cells are observed in the airways of severe asthmatics in the absence of bacterial infections. Since the identification of T helper 17 (TH17) cells in airway infiltrates of severe asthmatics, TH17 cells are also implicated in the immunopathology of the disease. By secreting interleukin 17A TH17 cells are able to induce the airway epithelial cell production of IL-8, the most potent chemoattractant for neutrophils. However, understanding the role of these cells within the context of the immunopathology of severe asthma is just in the fledging stages. This review aims at summarizing the actual knowledge on the immunopathologic mechanisms underlying this disease.