br Breast cancer The interactions between

Breast cancer The interactions between 15-LOX and COX enzymes also affect the outcome of breast cancer. Indomethacin, a COX-1 and COX-2 inhibitor, decreased the growth of human breast cancer (BC) cells in nude mice, as well as slowed the rate of lung metastasis formation [41]. The levels of 12-HETE, but not 5- or 15-HETE, were elevated following indomethacin treatment, suggesting up-regulation of 12/15-LOX activity, and possibly a pro-tumorigenic role for this enzyme, in line with the stimulated metastatic growth rate induced by a high linoleic Istradefylline synthesis diet [41]. This accelerated metastatic rate was also achieved in a similar model by the addition of 12-HETE [42]. Other reports attributed pro-tumorigenic actions to 15-LOX metabolites in BC cells [43], possibly through epidermal growth factor (EGF)/transforming growth factor (TGF)-α regulation of 13-HODE production. 15-HPETE, on the other hand, was reported to have a cytotoxic effect on BC cells [44]. Also, treatment with EGF up-regulated both the activity and the expression of 12-LOX in a BC cell line [45]. A prospective study examined 120 human BC tumor biopsies for the expression of various LOX types using RT-PCR. The levels of 15-LOX-1 were shown to be reduced, whereas 5- and 12-LOX levels were increased [46]. Specifically, tissues from BC tumors with positive lymph node involvement showed a decreased 15-LOX-1 expression compared to lymph node-negative tumors. Moreover, 15-LOX-1 expression was reduced in patients who developed metastatic disease, local recurrence, or death, compared to patients with a more favorable outcome [46]. Interestingly, Western blotting showed increased expression of 15-LOX-2 in a BC cell line, in the absence of 15-LOX-1 [47]. Overexpression of 15-LOX-2 resulted in enhanced p38 MAPK phosphorylation in these cells following treatment with arachidonic acid [47]. Moreover, treatment with exogenous 15-HETE increased cell adhesion to collagen type IV, in keeping with previous reports on the importance of p38 MAPK in cell adhesion [47]. However, when tested in tumor biopsy samples, the levels of 15-LOX-2 were found to be reduced [46]. A thorough research into the effect of 15-LOX-1 on BC metastasis formation was published recently by Kerjaschki et al. [48]. To modulate lymphatic invasion by breast tumors an in vitro model was established using BC cell spheroid coculture in monolayers with lymphatic endothelial cells (LEC). Defects were documented in the organization of LEC monolayers cultured in proximity to BC spheroids, where 15-LOX, but not 12-LOX, expression was demonstrated [48]. Treatment with NDGA and baicalein, another pan-LOX inhibitor, inhibited the formation of these circular defects. Blocking 12-HETE or knocking down ALOX15 (the 15-LOX-1 gene) restored monolayer integrity, whereas knocking in ALOX12 (the 12-LOX gene) reestablished defect formation in ALOX15 knocked-down cells [48]. In the same study, 13 tumor samples were examined by tissue microarray and showed colocalization of both 15-LOX and 12-HETE to sentinel lymph nodes. Moreover, enzyme localization matched tumor stage. 12-LOX staining was not reported in tumor biopsies [48]. Taken together, the role of 15-LOX in BC has not been fully ascertained yet. While the deleterious effect of 12-HETE is consensual, it is not clear whether 15-LOX is in fact the enzyme responsible for its production in mammary tumor beds, or whether the culprit is 12-LOX.
Hematologic malignancies Examination of leukemic cells for various LOXs preceded much of the research on 15-LOX in solid tumors. This resulted from the expression of LOXs in human peripheral blood cells, both from erythroid and myeloid lineages, which are easily attainable. In an early report, bone marrow samples from chronic myelocytic leukemia (CML) were probed for the presence of LTB4 and 12-HETE using high-pressure liquid chromatography (HPLC). An increased production of LTB4 by CML bone marrow cells was found when compared to cells from healthy donors, which were skewed toward 12-HETE production [49]. Another early report suggested a role for 15-LOX in the maintenance of DNA synthesis in an erythroleukemia cell line [50]. Nonspecific inhibitors of LOXs blocked DNA synthesis, whereas 15-HETE increased it. Lipoxins also augmented DNA synthesis in the same cell line [51]. A contrasting anti-carcinogenic role for 12/15-LOX was implicated in a murine model of myeloproliferative neoplasm (MPN) progressing to leukemia. In 12/15-LOX-deficient mice, increased activation of the phosphatidylinositol 3 kinase (PI3K) pathway was demonstrated, as manifested by augmented Akt phosphorylation [52]. Elevated levels of the oncoprotein Bcl-2 were also demonstrated in 12/15-LOX-deficient mice, and these levels were reduced by PI3K inhibition. Moreover, 12/15-LOX overexpression suppressed the growth of a CML cell line [52]. Along these lines, treatment with 15-HPETE induced the generation of reactive oxygen species in a CML cell line, with subsequent apoptotic features [53].