Free fatty acid release from human breast cancer tissue inhibits cytotoxic T-lymphocyte-mediated killing

Abstract

Immune-mediated antitumor activities confront a variety of tumor-mediated defense mechanisms. Here, we describe a new mechanism involving FFA that may allow breast cancer to evade immune clearance. We determined the IC 50 at which unbound free fatty acids (FFA u ) inhibit murine cytotoxic T-lymphocyte (CTL)-mediated killing to assess the physiologic relevance of this phenomenon. We found that the IC 50 for unbound oleate is 125 ؎ 30 nM, ‫ف‬ 200-fold greater than normal plasma levels. FFA inhibition, however, may play an important role in breast cancer because we found that large quantities of FFAs are released constitutively into the media surrounding samples of human breast cancer but not normal or benign tissue. Antitumor cytotoxic T-lymphocytes (CTLs) are central to immunotherapeutic anticancer strategies (1-5). Tumorspecific CTLs can be induced by various immunotherapeutic strategies (reviewed in 3), and tumor-infiltrating lymphocytes are found "naturally" in tumors (6). Nevertheless, immunotherapeutic methods are rarely effective in mediating the regression or clearance of established tumors. This lack of effectiveness suggests that factors other than CTL activation may prevent CTL-mediated clearance of tumor in vivo. A number of factors have been identified that reduce CTL effectiveness, including loss of tumor antigen, major histocompatibility complex class I downregulation, and a physical barrier separating CTL and tumor (3). In the present study, we provide evidence for a new mechanism: inhibition of CTL killing of tumor cells by FFAs produced by human breast cancer tumors.Inhibition of CTL activity by increased levels of total FFAs has been demonstrated in several in vitro studies (7-16). Increased levels of cis unsaturated FFAs inhibit CTL signaling pathways and, in particular, inhibit CTLmediated killing of cognate target cells. These inhibitory effects of cis FFAs are attributable to an immediate physical perturbation of the CTL; the effects occur within seconds and are reversed upon extracting FFAs with extracellular albumin. In contrast, saturated FFAs have no effect on signaling or killing. The differential effects of cis and saturated FFAs does not involve FFA metabolism because CTL inhibition can be detected before metabolite levels are significant and because the predominant metabolites of oleic acid (the most potent FFA inhibitor) cannot be extracted with extracellular albumin (9). The differential effects of cis and saturated FFAs, however, are well correlated with differential effects of cis and saturated FFAs on membrane lipid order (10,14), consistent with a physical mechanism of FFA-mediated CTL inhibition.In biological fluids, most FFA is bound to albumin and/ or cells (17,18). Although only a small fraction of total FFA is unbound free fatty acids (FFA u ) (19), it is the FFA u that determine the degree of FFA inhibition of cellular function (14). FFA u levels that inhibit CTL-mediated killing have not been determined. Estimates have been obtained for FFA u levels (IC 50 ) tha...

Tumor Macroenvironment and Metabolism

“…Linoleic acid does not only induce PAI-1 (a prognostic marker for breast cancer) secretion through SMAD4 (similar to mothers against decapentaplegic-4) but also enhances the migratory potential of the highly invasive MDA-MA-468 breast cancer cell line 46 . FFA secreted by primary breast cancer into the interstitial fluid were found to inhibit the cytolytic activity of the infiltrating cytotoxic T lymphocytes (CTLs), 47 providing yet another example of tumor lipid metabolism effecting the tumor micro- and possibly also macroenvironment. A large multicenter study revealed a positive association between serum palmitic acid with a high relative risk of 1.90 for prostate cancer and an inverse association with stearic acid, respectively 48 .…”

Human fetal intestinal epithelial cells metabolize and incorporate branched chain fatty acids in a structure specific manner

“…As no normal (straight chain FA) controls were run, the effect may be due to high free fatty acid concentrations taken up by cells as intact lipid laden microparticles and may not be completely specific to the tested BCFA, isopentadecanoic acid (13-methyl tetradecanoic acid, 13-MTD). Indeed, unbound FA mediated cellular signaling events are reversed by the addition of albumin [20, 21]. BSA has seven binding sites with high to moderate affinity for fatty acids, 2–3 of which are high affinity with equilibrium constants on the order of 10 8 M −1 for palmitate [22].…”

Unbound Free Fatty Acids from Preterm Infants Treated with Intralipid Decouples Unbound from Total Bilirubin Potentially Making Phototherapy Ineffective

“…1 and No. 5 interferes with a variety of cellular functions including immune and cardiac functions [19,20]. Limiting Intralipid may therefore reduce acute bilirubin encephalopathy as well as FFA u -mediated toxicity.…”