Levels of KLF4 can be manipulated by diverse agonists such as statins, resveratrol, bortezomib and dietary compounds, so these factors could be influential for TAM re-education.[130] Although still learn more preliminary, the association among c-Myc, STAT6 and M2 polarization has been proposed by recent studies. As reported, c-Myc up-regulated IL-4-mediated STAT6 activation and elevated the expression of 45% of the genes correlated with alternative activation of macrophages.[131] In contrast, c-Myc inhibition blocked the expression of some pro-tumoral genes.[131] Other proteins and signalling pathways known

to promote M2-like properties of macrophages are also the potential targets for tumour therapy. They include peroxisome Aurora Kinase inhibitor proliferator-activated receptor (PPARs), HIFs, Ets family member 2 (Ets2), Decoy receptor

(DcR3) and mammalian target of rapamycin (mTOR). First, PPAR-γ can promote M2 type differentiation of human macrophages by acting as a transcriptional inhibitor of NF-κB.[132] PPAR-α plays a role in macrophages by antagonizing M1 polarization and supporting M2 polarization.[133] As synthetic inhibitors of PPAR-α/γ have now been identified, the evaluation of their role in TAM-targeted therapy is essential. Second, HIFs are a hopeful target because of their over-expression in TAMs residing in the hypoxic tumour microenvironment and their ability to induce the production of angiogenic factors, including VEGF, platelet-derived growth factor-β, NOS2, fibroblast growth factor 2, IL-8 and cyclooxygenase-2.[134] In fact, macrophage-targeted depletion of HIF-1α reduced tumour

growth in mice.[135] Therefore, it would be interesting to see whether blocking HIFs could slow or halt tumour recovery. Third, Ets2 is a direct effector of the M-CSF signalling pathway, and so facilitates the formation of M2 macrophage. Zabuawala et al.[136] demonstrated that an Ets2-driven transcriptional program in TAMs could promote Montelukast Sodium the angiogenesis and metastasis of murine breast cancer. Interestingly, an Ets2-TAM gene signature consisting of 133 genes retrospectively predicted overall survival of breast cancer patients.[136] Investigations of DcR3 and mTOR are also interesting.[137, 138] Several anti-tumour drugs that are able to suppress M2 macrophages will be introduced as follows. (i) Histidine-rich glycoprotein (HRG): HRG can skew TAMs to M1 type by down-regulation of PIGF, a member of the VEGF family, and can combat tumour malignancy by enhancing immunity and vessel normalization.[26] Macrophages are a direct target of HRG; and re-education of TAMs is essential for HRG-mediated anticancer effects.[26, 139] (ii) Copper chelate (CuNG): A novel CuNG was demonstrated to modulate the cytokine profile of TAMs isolated from chemotherapy-resistant or radiotherapy-resistant cancer patients.