Synthesis of platelet-activating factor (PAF) in transformed cell lines of a different origin

The Potential Role of Dietary Platelet-Activating Factor Inhibitors in Cancer Prevention and Treatment

Cancer is the second leading cause of mortality worldwide. The role of unresolved inflammation in cancer progression and metastasis is well established. Platelet-activating factor (PAF) is a key proinflammatory mediator in the initiation and progression of cancer. Evidence suggests that PAF is integral to suppression of the immune system and promotion of metastasis and tumor growth by altering local angiogenic and cytokine networks. Interactions between PAF and its receptor may have a role in various digestive, skin, and hormone-dependent cancers. Diet plays a critical role in the prevention of cancer and its treatment. Research indicates that the Mediterranean diet may reduce the incidence of several cancers in which dietary PAF inhibitors have a role. Dietary PAF inhibitors such as polar lipids have demonstrated inhibitory effects against the physiological actions of PAF in cancer and other chronic inflammatory conditions in vitro and in vivo. In addition, experimental models of radiotherapy and chemotherapy demonstrate that inhibition of PAF as adjuvant therapy may lead to more favorable outcomes. Although promising, there is limited evidence on the potential benefits of dietary PAF inhibitors on cancer prevention or treatment. Therefore, further extensive research is required to assess the effects of various dietary factors and PAF inhibitors and to elucidate the mechanisms in prevention of cancer progression and metastasis at a molecular level.

Modulation of Tumor-Associated Macrophages (TAM) Phenotype by Platelet-Activating Factor (PAF) Receptor

Platelet-activating factor (PAF) plays an important role in the pathogenesis of several types of tumors. The biological effects of PAF are mediated by the PAF receptor (PAFR), which can be expressed by tumor cells and host cells that infiltrate the tumor microenvironment. In the present study, we investigated the role of PAFR expressed by leukocytes that infiltrate two types of tumors, one that expresses PAFR (TC-1 carcinoma) and another that does not express the receptor (B16F10 melanoma) implanted in mice that express the receptor or not (PAFR KO). It was found that both tumors grew significantly less in PAFR KO than in wild-type (WT) mice. Analysis of the leukocyte infiltration shown in PAFR KO increased the frequency of neutrophils (Gr1⁺) and of CD8⁺ lymphocytes in B16F10 tumors and of CD4⁺ lymphocytes in TC-1 tumors. PAFR KO also had a higher frequency of M1-like (CD11c⁺) and lower M2-like (CD206⁺) macrophages infiltrated in both tumors. This was confirmed in macrophages isolated from the tumors that showed higher iNOS, lower arginase activity, and lower IL10 expression in PAFR KO tumors than WT mice. These data suggest that in the tumor microenvironment, endogenous PAF-like activity molecules bind PAFR in macrophages which acquire an M2-like profile and this promotes tumor growth.

Palliation of bone cancer pain by antagonists of platelet-activating factor receptors

Bone cancer pain is the most severe among cancer pain and is often resistant to current analgesics. Thus, the development of novel analgesics effective at treating bone cancer pain are desired. Platelet-activating factor (PAF) receptor antagonists were recently demonstrated to have effective pain relieving effects on neuropathic pain in several animal models. The present study examined the pain relieving effect of PAF receptor antagonists on bone cancer pain using the femur bone cancer (FBC) model in mice. Animals were injected with osteolytic NCTC2472 cells into the tibia, and subsequently the effects of PAF receptor antagonists on pain behaviors were evaluated. Chemical structurally different type of antagonists, TCV-309, BN 50739 and WEB 2086 ameliorated the allodynia and improved pain behaviors such as guarding behavior and limb-use abnormalities in FBC model mice. The pain relieving effects of these antagonists were achieved with low doses and were long lasting. Blockade of spinal PAF receptors by intrathecal injection of TCV-309 and WEB 2086 or knockdown of the expression of spinal PAF receptor protein by intrathecal transfer of PAF receptor siRNA also produced a pain relieving effect. The amount of an inducible PAF synthesis enzyme, lysophosphatidylcholine acyltransferase 2 (LPCAT2) protein significantly increased in the spinal cord after transplantation of NCTC 2472 tumor cells into mouse tibia. The combination of morphine with PAF receptor antagonists develops marked enhancement of the analgesic effect against bone cancer pain without affecting morphine-induced constipation. Repeated administration of TCV-309 suppressed the appearance of pain behaviors and prolonged survival of FBC mice. The present results suggest that PAF receptor antagonists in combination with, or without, opioids may represent a new strategy for the treatment of persistent bone cancer pain and improve the quality of life of patients.

Critical role for matrix metalloproteinase-9 in platelet-activating factor-induced experimental tumor metastasis

In this study, the roles of matrix metalloproteinase (MMP)-2 and MMP-9 in platelet-activating factor (PAF)-induced experimental pulmonary metastasis of the murine melanoma cell, B16F10, were investigated. An injection of PAF resulted in increases in mRNA expression, protein levels and the activities of both MMP-2 and MMP-9 in the lungs. The overall expression of MMP-9 was stronger than that of MMP-2. The increased MMP-9 expression was inhibited by both NF-kappaB and AP-1 inhibitors, whereas the increased MMP-2 expression was inhibited by only AP-1 inhibitors. Immunohistochemical analysis revealed that MMP-9 was expressed in bronchial epithelial cells as well as in the walls of blood vessels, whereas MMP-2 expression was observed only in bronchial epithelial cells. PAF significantly enhanced the pulmonary metastasis of B16F10, which was inhibited by both NF-kappaB and c-jun inhibitors. MMP-9 inhibitor, but not that of MMP-2, completely inhibited PAF-induced B16F10 metastasis. These data indicate that MMP-9, the expression of which was regulated by NF-kappaB and AP-1, plays a critical role in PAF-induced enhancement of pulmonary melanoma metastasis.

Platelet-activating factor (PAF) is the effector of IFNγ-stimulated invasiveness and motility in a B16 melanoma line

In this study, we investigated whether PAF synthesized by F10-M3 cells (a clone of B16-F10 melanoma line) mediates the increased capacity of these cells to penetrate into Matrigel upon stimulation with IFN gamma. The determination of PAF synthesized by IFN gamma-stimulated tumor cells revealed that 70% of newly synthesized PAF was released into growth media, while the remaining 30% was associated with the cell bodies. An experimental protocol based on the use of WEB 2086, a PAF receptorial antagonist, was designed to explore which of the two fractions of PAF synthesized by IFN gamma-stimulated F10-M3 cells (released into the growth medium or associated with the cell bodies) is essential to their capacity to migrate through Matrigel. We found that the PAF secreted into growth medium is the fraction responsible for the enhanced invasiveness of melanoma cells stimulated with IFN gamma. We also investigated whether motility of melanoma cells is stimulated by IFN gamma, and, if so, whether PAF is involved in this effect. We found that WEB 2086 prevented the remodeling of stress fibers, examined as an index of cell motility, that we observed in F10-M3 cells stimulated with IFN gamma. Furthermore, the observation that PAF receptor is expressed in IFN gamma-stimulated melanoma cells suggests that the invasive phenotype (e.g. migration through a reconstituted basement membrane and motility) promoted by PAF is based on an autocrine mechanism. On the whole, these results might indicate that PAF contributes to the expression of properties typical of an invasive phenotype in tumor cells stimulated with cytokines.

Tissue concentrations of platelet-activating factor in colorectal carcinoma: inverse relationships with Dukes' stage of patients

The lipid mediator platelet-activating factor (PAF) plays a role in cancer. We investigated its presence in human colon carcinoma by assessing the levels of tissue phospholipase A(2) (PLA(2), the key enzyme in the generation of the lyso-PAF precursor), lyso-PAF, PAF and acetylhydrolase activity (AHA, the key enzyme in PAF degradation) in colorectal cancer patients and by correlating them with Dukes' classification. The results highlighted that the tumour tissues of Dukes' A and B patients had significantly higher PLA(2), lyso-PAF, PAF and AHA levels as compared with nontumour tissues. Dukes' C patients had higher PLA(2), lyso-PAF and AHA levels but unchanged PAF. Dukes' D patients had higher AHA levels but unchanged PLA(2), lyso-PAF and PAF. A pathophysiological role for PAF is suggested in human colon carcinoma.