## 5 Studies and Mechanism about n-3 PUFAs and Melanoma
### In Vivo Studies  
Nevertheless, in spite of the increasing evidence supporting the benefits of n-3 PUFA, experimental findings suggest that the ability of n-3 PUFAs to inhibit cancer growth is contingent not only on their quantity but also on the baseline levels of n-6 PUFAs. Additionally, research has demonstrated that the therapeutic advantage of dietary n-3 PUFAs is most pronounced when their proportion significantly surpasses that of n-6 PUFAs. Studies showed that endogenously increased levels of n-3 PUFAs in the tumor tissues of Fat-1 transgenic mice was associated with a reduction in the growth rate of melanoma [161, 162]. In these studies, the researchers implant melanoma cells with a higher metastatic potential in the Fat-1 and wild type (WT) mice and examine different outcomes. [PERSON] et al. demonstrated reduction of melanoma formation and growth in Fat-1 transgenic mice. The level of n-3 PUFA and their metabolite prostaglandin PGE3 were much higher (but the n-6/n-3 ratio is much lower) in the tumor and surrounding tissues of Fat-1 mice than of WT animals and the amounts of PGE2 in the tumor and surrounding tissues of Fat-1 transgenic mice are lower than those of WT mice. Moreover, in this study the phosphatase and tensin (PTEN) homologue deleted on chromosome 10 was upregulated in the Fat-1 mice. PTEN is a classical tumor suppressor gene through its action as a negative regulator of the PI3K signaling pathway and plays a role in the homeostatic maintenance of the PI3K/AKT cascade by decreasing downstream AKT activity and cell cycle progression is arrested at the G1/S phase [163] (Figure 5). In in vitro experiments, it was observed that the introduction of n-3 PUFA or PGE3 suppressed the proliferation of melanoma cells and heightened the expression of PTEN (Figure 5). This effect was found to be partially diminished when the production of PGE3 was inhibited. These findings suggest an anti-melanoma impact of n-3 PUFA, potentially attributed to the activation of the PTEN pathway facilitated by PGE3. In this study, the incidence of tumor formation and growth rate was much slower in the Fat-1 transgenic mice when compared to the WT mice, showing that the modification of the tissue n-6/n-3 PUFA ratio by increasing n-3 PUFA and decreasing n-6 PUFA could potentially serve as an efficacious therapeutic strategy, as it has the potential to not only decrease the cancer-promoting eicosanoids derived from AA but also enhance the production of anti-tumor eicosanoids derived from n-3 PUFA, resulting in a dual effect [161]. [PERSON] et al. reported comparable findings, revealing that the naturally elevated levels of n-3 PUFAs in tumor tissues of transgenic Fat-1 mice were linked to a decrease in the growth rate of melanoma xenografts. Moreover, they also showed that the protein expression levels of E-cadherin and N-cadherin were markedly upregulated and downregulated in the tumor tissues of at-1 mice compared with those of the WT controls, respectively. On the other hand, the levels of NF-kB and phosphorylated NF-kB protein expression levels were lower in Fat-1 mouse tumor tissues than those from WT mice as well as signal transducer and activator of transcription 3 levels, suggesting that both may be involving in modulating E-cadherin expression. Furthermore, Fat-1 tumor tissues exhibited a marked decrease in the expression levels of \(\beta\)-catenin and c-Myc, a known transcriptional target of \(\beta\)-catenin, compared with those from WT mice, and the study reveals that the EGFR/AKT/GSK-3\(\beta\) signaling pathway may be involved in controlling endogenous n-3 PUFA-induced \(\beta\)-catenin degradation and also shows that the tumor growth inhibition was not related to n-3 PUFA-induced oxidative stress after VitE administration. However, Fat-1 mice exhibited decreased tumor growth compared with WT-mice, suggesting that VitE enhances the antitumor effects of n-3 PUFAs [162] (Table 1).