Macrophages, which have functions of engulfing and digesting foreign substances, can clear away harmful matter, including cellular debris and tumor cells. Based on the condition of the internal environment, circulating monocytes give rise to mature macrophages, and when they are recruited into the tumor microenvironment and in suitable conditions, they are converted into tumor-associated macrophages (TAMs). Generally, macrophages grow into two main groups called classically activated macrophages (M1) and alternatively activated macrophages (M2). M2 and a small fraction of M1 cells, also known as TAMs, not only lack the function of phagocytizing tumor cells but also help these tumor cells escape from being killed and help them spread to other tissues and organs. In this review, we introduce several mechanisms by which macrophages play a role in the immune regulation of tumor cells, including both killing factors and promoting effects. Furthermore, the targeted therapy for treating tumors based on macrophages is also referred to in our review. We confirm that further studies of macrophage-focused therapeutic strategies and their use in clinical practice are needed to verify their superior efficacy and potential in cancer treatment.

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The synthesis and characterization, including crystallographic analysis, of the bifunctional boranes RCHdC[B(C 6 F 5 ) 2 ] 2 (R ) t-C 4 H 9 , 1a; C 6 H 5 , 1b; C 6 F 5 , 1c) by regioselective hydroboration of the corresponding 1-boraalkynes using HB(C 6 F 5 ) 2 are reported herein. Compounds 1a and 1b have been screened as cocatalysts for ethylene polymerization in the presence of Cp 2 ZrMe 2 (3) under a variety of conditions. NMR spectroscopic studies indicate that Cp 2 -Zr[η 2 -Bu t CtCB(C 6 F 5 ) 2 ] (4a), Cp 2 ZrMe(C 6 F 5 ), the organoborane Me 2 BC 6 F 5 , and methane gas are the final products formed from reaction of 1a with 3 in toluene solution at room temperature. The stoichiometric mechanism for this transformation has been elucidated through variable-temperature NMR studies. Complex 4a and MeB(C 6 F 5 ) 2 (7) were prepared independently and screened as ethylene polymerization catalysts and cocatalysts, respectively. Compound 4a is inactive for ethylene polymerization, either alone or in the presence of additional 1a. However, the combination of Cp 2 ZrMe 2 and 7 gives rise to the species [Cp 2 ZrMe] + [Me 2 B(C 6 F 5 ) 2 ] -(8), which although unstable at room temperature in solution (decomposing over a period of 60 min to give Cp 2 ZrMe(C 6 F 5 ) and the organoborane Me 2 -BC 6 F 5 ), is active for ethylene polymerization. From a comparison of activity and MW data, it is concluded that the putative ion pairs formed from 1a (or 1b) and 3 lack sufficient thermal stability at conventional polymerization temperatures and that the polymerization activity observed can be interpreted as arising from species 8.