More recently Serna Marquez and colleagues investigated LA i

More recently, Serna-Marquez and colleagues investigated LA-induced migration and invasion of MDA-MB-231 breast cancer cells. In this study, LA was shown to induce AKT-2 phosphorylation and cell invasion and migration in MDA cells. LA-induced cell migration was inhibited by siRNA that selectively targeted FFA4 as well as by treatment of 94 6 mg with the selective FFA4 antagonist AH7614 [79]. Meanwhile, LA-induced invasion was fully and partially blocked by FFA4 siRNA and AH7614, respectively. While the authors speculate that the intracellular mechanisms of these effects could be due to cross-talk with FFA1 or EGFR to activate downstream NF-KB activity and transcription, mechanistic studies on the specific role of FFA4 in this process was not investigated [79].
Bone cancer cell lines FFA4 has been shown to play a pivotal role in bone development, survival and function, where it suppresses RANKL-induced osteoclast differentiation as well as osteoclastogenesis, and accelerates osteoclast apoptosis and inhibition of bone resorption [84]. The same group that investigated the role of FFA1 and FFA4 on lung [63], pancreatic [64], and skin [68] cancer cells has also examined the role of the receptors in bone cancer derived cells. Expression of FFA4 and FFA1 in the MG-63 human bone osteosarcoma cell line was confirmed using RT-PCR, and the team generated MG-63 FFA4-KD cells with near full abrogation of FFA4 transcript expression for use in studies to characterize the role of both receptors. Cell migration of FFA4-KD cells was slightly lower than control cells, however, while GW9508 increased migration of control cells, it robustly inhibited migration in FFA4-KD cells [85]. These findings were confirmed in rat COS1NR osteosarcoma cells and suggest that FFA4 modulates migration of osteosarcoma cells [85]. The team also investigated the role of FFA4 in highly migratory MG-63 cells that were derived using an approach that utilized only migratory cells that were collected over seven migration cycles. FFA4 transcript expression was shown to be over two-fold higher in these highly migratory MG-63 cells compared to control MG-63 cells, whereas expression of FFA1 was unchanged [85]. While the proliferation of highly migratory MG-63 cells was significantly lower than control after 48 h in culture, cell migration was 200-fold greater in the highly migratory cells compared to control cells. Furthermore, the highly migratory cells showed 100-fold greater invasion through a matrigel extracellular matrix compared to control cells, an effect that was enhanced to nearly 200-fold by treatment with GW9508, which had no effect on invasion in control MG-63 cells [85]. Knockdown of FFA4 in highly migratory MG-63 cells showed significant abrogation to cell migration and invasion through the extracellular matrix, which was further reduced by GW9508 treatment. These results show that FFA1 and FFA4 play important, and contrasting, roles in migration and invasion of osteosarcoma cells. Whereas FFA1 seems to negatively regulate migration and invasion, FFA4 positively influences these affects. Intracellular signaling mechanisms weren’t addressed in this study, and no insight into the level of reduction of FFA4 in highly migratory cells was provided. Since these cells exhibited a 2-fold increase in expression of the receptor, the efficacy of FFA4 knockdown would provide a clearer picture into interpretations on the absolute role of agonism of the FFA receptors. Nonetheless, it is clear that FFA4 plays a role in influencing migratory taxis in osteosarcoma cells and will require further study.
Chemotherapy resistance A major barrier to effective cancer treatment is inducible resistance to chemotherapeutics, leading to pharmacotherapeutic failure and cancer relapse and progression. A seminal study in 2011 showed that chemotherapy with platinum-based agents such as cisplatin causes activation of mesenchymal stem cells (MSC) that facilitates chemotherapy resistance (i.e., chemoresistance) [86]. In MSC, platinum based chemotherapeutics were shown to induce signaling to cyclooxygenase-1 (COX1) and thromboxane synthase (TXAS) to produce two distinct PUFA, 12-S-hydroxy-5,8,10-heptadecatrienoic acid (12-S-HHT) and hexadeca-4,7,10,13-tetraenoic acid (16:4(n-3)), that in turn, directly mediate platinum-induced chemoresistance at picomolar concentrations [86] (Fig. 3). A follow up study by the same research team showed that dietary fish oils, particularly those obtained from mackerel and herring, but also those from salmon and tuna, contained physiologically relevant levels of 16:4(n-3), and that six commercial dietary fish oil supplements were found to contain substantial levels of 16:4(n-3), ranging in concentration from 0.2 to 5.7 μM [87]. Importantly, while fish oil monotherapy did not influence tumor size, even picomolar quantities of fish oil induced full cisplatin resistance in tumor bearing mice [87]. Finally, ingestion of recommended daily allowances of fish oil in 30 human volunteers facilitated observable levels of plasma 16:4(n-3), which was atypically higher than that found in the oral dose, suggesting metabolism of other fish oil fatty acids to 16:4(n-3) [87]. In an elegant and substantial study that sought to further characterize the molecular mechanisms of 12-S-HHT and 16:4(n-3) induced chemotherapy resistance, the same group showed that either splenectomy or clodronate-induced depletion of macrophages prevented the chemoresistance induced by the PUFA, demonstrating that the mechanism specifically involves splenic macrophages [88]. Further results showed that 12-S-HHT functions via activation of the low-affinity leukotriene B4 receptor-2 (BLT2) residing on splenic F4/80+/CD11blow macrophages to release lysophosphatidylcholines (LPC) that in turn, alter the ability of platinum-chemotherapeutics to induce DNA damage [88]. Notably, the other platinum-induced fatty acid, 16:4(n-3), was shown in this work to not engage BLT2, leaving its specific molecular target unresolved at that time.