Targeting of M2-like tumor-associated macrophages with a melittin-based pro-apoptotic peptide

Abstract

Background Tumor-associated macrophages (TAMs) are the major component of tumor-infiltrating immune cells. Macrophages are broadly categorized as M1 or M2 types, and TAMs have been shown to express an M2-like phenotype. TAMs promote tumor progression and contribute to resistance to chemotherapies. Therefore, M2-like TAMs are potential targets for the cancer immunotherapy. In this study, we targeted M2-like TAMs using a hybrid peptide, MEL-dKLA, composed of melittin (MEL), which binds preferentially to M2-like TAMs, and the pro-apoptotic peptide d (KLAKLAK) 2 (dKLA), which induces mitochondrial death after cell membrane penetration. Methods The M1 or M2-differentiated RAW264.7 cells were used for mitochondrial colocalization and apoptosis test in vitro. For in vivo study, the murine Lewis lung carcinoma cells were inoculated subcutaneously in the right flank of mouse. The dKLA, MEL and MEL-dKLA peptides were intraperitoneally injected at 175 nmol/kg every 3 days. Flow cytometry analysis of tumor-associated macrophages and immunofluorescence staining were performed to investigate the immunotherapeutic effects of MEL-dKLA. Results We showed that MEL-dKLA induced selective cell death of M2 macrophages in vitro, whereas MEL did not disrupt the mitochondrial membrane. We also showed that MEL-dKLA selectively targeted M2-like TAMs without affecting other leukocytes, such as T cells and dendritic cells, in vivo. These features resulted in lower tumor growth rates, tumor weights, and angiogenesis in vivo. Importantly, although both MEL and MEL-dKLA reduced numbers of CD206 + M2-like TAMs in tumors, only MEL-dKLA induced apoptosis in CD206 + M2-like TAMs, and MEL did not induce cell death. Conclusion Taken together, our study demonstrated that MEL-dKLA could be used to target M2-like TAMs as a promising cancer therapeutic agent.

Galectin-3 as a Next-Generation Biomarker for Detecting Early Stage of Various Diseases

“…Macrophages are the most abundant immune cell population present in tumor tissue, and these cells are called tumor-associated macrophages (TAMs) [133,134]. The density of TAMs is reported to be associated with a poor prognosis and positively correlated with tumor progression in several studies.…”

“…Macrophages are generally categorized as M1 or M2 types, and the majority of TAMs have been shown to exhibit M2-like phenotype in the tumor microenvironment [134]. As a rule, M1 macrophages are considered to have inflammatory and cytotoxic function, whereas M2 macrophages are anti-inflammatory and promoting wound healing.…”

“…Furthermore, the parasite-infected brain shows abundant Gal-3 expression in M2 macrophages, and the Gal-3 in M2 macrophages plays a central role in protective function by clearance of neutrophils accumulated in the brain. However, in tumor microenvironment, M2 macrophages which are major component of TAMs promote tumor progression and contribute to resistance to chemotherapies [133,134].…”

P2X7R promotes angiogenesis and tumor-associated macrophage recruitment by regulating the NF-κB signaling pathway in colorectal cancer cells

“…Angiogenesis and the ability to metastasize involve tumor-associated macrophages (TAMs) in CRC (6,7). M1 and M2 are the major classes of TAMs that display polar effects on tumors (8,9). The former class is activated classically by lipopolysaccharide (LPS) and interferon-γ (IFN-γ) to secrete interleukin-12 (IL-12), IL-1β and cytotoxic inducible nitric oxide synthase (iNOS), among other factors (10,11).…”

Aging interacts with tumor biology to produce major changes in the immune tumor microenvironment

“…Previous studies have suggested 17 that old age alters macrophage polarization such that the same signals that would produce 18 polarization in younger individuals do not produce differentiated macrophages with all the 19 characteristics generally ascribed to M1 and M2 subtypes (Mahbub et al, 2012). Thus, these 20 results must be interpreted carefully, but an increase in tumor infiltrating macrophages still 21 appears to be a poor survival prognostic in older individuals, which suggests that therapeutics 22 being developed to target the generally negative effects of tumor-associated macrophages 23 (Chanmee et al, 2014), (Poh and Ernst, 2018), (Lee et al, 2019) may be of particular impact in 24 patients of advanced age. 25 A further observation of note is that we find a significant increase in NK cell abundance in GTEx, 1 which we do not identify in TCGA tumor data.…”