An Application of Tumor-Associated Macrophages as Immunotherapy Targets: Sialic Acid-Modified EPI-Loaded Liposomes Inhibit Breast Cancer Metastasis.

Breast cancer metastasis is an important cause of death in patients with breast cancer and is closely related to circulating tumor cells (CTCs) and the metastatic microenvironment. As the most infiltrating immune cells in the tumor microenvironment (TME), tumor-associated macrophages (TAMs), which highly express sialic acid (SA) receptor (Siglec-1), are closely linked to tumor progression and metastasis. Furthermore, the surface of CTCs also highly expressed receptor (Selectin) for SA. A targeting ligand (SA-CH), composed of SA and cholesterol, was synthesized and modified on the surface of epirubicin (EPI)-loaded liposomes (EPI-SL) as an effective targeting delivery system. Liposomes were evaluated for characteristics, stability, in vitro release, cytotoxicity, cellular uptake, pharmacokinetics, tumor targeting, and pharmacodynamics. In vivo and in vitro experiments showed that EPI-SL enhanced EPI uptake by TAMs. In addition, cellular experiments showed that EPI-SL could also enhance the uptake of EPI by 4T1 cells, resulting in cytotoxicity second only to that of EPI solution. Pharmacodynamic experiments have shown that EPI-SL has optimal tumor inhibition with minimal toxicity, which can be ascribed to the fact that EPI-SL can deliver drugs to tumor based on TAMs and regulate TME through the depletion of TAMs. Our study demonstrated the significant potential of SA-modified liposomes in antitumor metastasis. Schematic diagram of the role of SA-CH modified EPI-loaded liposomes in the model of breast cancer metastasis.

Meng X ，Wang M ，Zhang K ，Sui D ，Chen M ，Xu Z ，Guo T ，Liu X ，Deng Y ，Song Y ... -  《AAPS PHARMSCITECH》

Targeted delivery of epirubicin to tumor-associated macrophages by sialic acid-cholesterol conjugate modified liposomes with improved antitumor activity.

With the knowledge that the receptors of sialic acid are overexpressed on the surface of tumor-associated macrophages (TAMs), which play a crucial role in the tumor's progression and metastasis, a sialic acid-cholesterol conjugate (SA-CH) was synthesized and modified on the surface of epirubicin (EPI)-loaded liposomes (EPI-SAL) to improve the delivery of EPI to the TAMs. The liposomes were developed using remote loading technology via a pH gradient. The liposomes were evaluated for particle size, encapsulation efficiency, in vitro release, stability, in vitro cytotoxicity and pharmacokinetics. And the in vitro and in vivo cellular uptake studies demonstrated EPI-SAL achieved enhanced accumulation of EPI into TAMs. The antitumor studies indicated that EPI-SAL provided the strongest antitumor activity compared with the other formulations (EPI-S, EPI-CL and EPI-PL represent EPI solution, conventional liposomal EPI, PEGylated liposomal EPI, respectively), and the survival percent of tumor-bearing mice was 83.3%. The superior antitumor efficacy was probably attributed to the killing of TAMs by EPI-SAL, and modulating the tumor microenvironment with the depletion of TAMs. These findings suggested that SA-CH decorated EPI-loaded liposomes may present an effective strategy to eradicate TAMs, which may be a promising approach for cancer therapy.

Zhou S ，Zhang T ，Peng B ，Luo X ，Liu X ，Hu L ，Liu Y ，Di D ，Song Y ，Deng Y ... -  《-》

Sialic acid conjugate-modified liposomes enable tumor homing of epirubicin via neutrophil/monocyte infiltration for tumor therapy.

Neutrophils and monocytes (N/Ms) are potential candidates for the delivery of therapeutic agents to the tumor microenvironment (TME) because of their tumor-accumulating nature. L-selectin and Siglec-1, receptors for sialic acid (SA), are highly expressed in circulating neutrophils and monocytes, respectively, in tumor-bearing mice, and N/Ms are recruited to tumors in response to inflammatory cytokines secreted by the TME, promoting tumor growth and invasion. Therefore, we constructed a drug delivery nano-platform using N/Ms as vehicles. SA-stearic acid conjugate was synthesized and utilized to modify epirubicin-loaded liposomes (EPI-SL) for enhanced endocytosis of liposomes by circulating N/Ms. Cellular uptake studies showed that SA modification improved the accumulation of EPI in N/Ms and did not alter the inherent chemotaxis of N/Ms. In tumor-bearing mice, EPI-SL significantly improved the tumor-targeting efficiency and therapeutic efficacy of EPI compared to other preparations and even eradicated tumors because of the tumor-accumulating and inhibitory effects of N/Ms containing EPI-SL. Our research showed, for the first time, that as an N/M-based drug delivery platform, EPI-SL remedied the limited tumor targeting in the conventional EPR effect-based treatment strategy, contributing to the exploitation of a new drug delivery platform for cancer treatment. STATEMENT OF SIGNIFICANCE: Tumor-associated neutrophils (TANs) and macrophages (TAMs) are closely associated with tumor growth and invasion, and therefore the development of therapeutic strategies targeting TANs and TAMs is crucial for tumor treatment. Given that most TANs and TAMs are derived from peripheral blood neutrophils and monocytes (N/Ms), respectively, we synthesized sialic acid-stearic acid conjugates that specifically bind N/Ms for the surface modification of liposomal epirubicin (EPI-SL). The N/Ms loaded with EPI-SL maintained their inherent chemotaxis toward the tumor. Additionally, EPI-SL significantly improved the survival of tumor-bearing mice and even eradicated tumors. These findings suggested that EPI-SL has substantial potential for clinical application by compensating for the previous low efficacy of ex vivo transformed cell infusion and improving the tumor-targeting efficiency.

Ding J ，Sui D ，Liu M ，Su Y ，Wang Y ，Liu M ，Luo X ，Liu X ，Deng Y ，Song Y ... -  《-》

Sialic acid-decorated liposomes enhance the anti-cancer efficacy of docetaxel in tumor-associated macrophages.

Tumor-associated macrophages (TAMs) in the tumor microenvironment potentially enhance tumor growth and invasion through various mechanisms and are thus an essential factor in tumor immunity. The highly expressed siglec-1 receptors on the surfaces of TAMs are potential targets for cancer drug delivery systems. Sialic acid (SA) is a specific ligand for siglec-1. In this study, the sialic acid-polyethylene glycol conjugate (DSPE-PEG2000-SA) was synthesized to modify the surface of liposomes and target TAMs by interacting with the siglec-1 receptor. Three docetaxel (DTX)-loaded liposomes, conventional (DTX-CL), DSPE-PEG2000-coated (DTX-PL), and DSPE-PEG2000-SA-coated (DTX-SAPL) liposomes, were prepared, with a particle size of <100 nm, uniform polydispersity index (PDI) values, negative zeta potential, and % encapsulation efficiency (EE) exceeding 95 %. Liposomes showed high stability after 3 months of storage at 4 °C without significant changes in particle size, PDI, zeta potential, or % EE. DTX was released from liposomes according to the Weibull model, and DTX-SAPL exhibited more rapid drug release than other liposomes. In vitro studies demonstrated that DTX-SAPL liposome exhibited a higher uptake and cytotoxicity on RAW 264.7 cells (TAM model) and lower toxicity on NIH3T3 cells (normal cell model) than other formulations. The high cell uptake ability was demonstrated by the role of the SA-SA receptor. Biodistribution studies indicated a high tumor accumulation of surface-modified liposomal formulations, particularly SA-modified liposomes, showing high signal accumulation at the tumor periphery, where TAMs were highly concentrated. Ex vivo imaging showed a significantly higher accumulation of SA-modified liposomes in the tumor, kidney, and heart than conventional liposomes. In the anti-cancer efficacy study, DTX-SAPL liposomes showed effective inhibition of tumor growth and relatively low systemic toxicity, as evidenced by the tumor volume, tumor weight, body weight values, and histopathological analysis. Therefore, DSPE-PEG2000-SA-coated liposomes could be promising carriers for DTX delivery targeting TAMs in cancer therapy.

Tran NP ，Tran P ，Yoo SY ，Tangchang W ，Lee S ，Lee JY ，Son HY ，Park JS ... -  《-》

Terminating the renewal of tumor-associated macrophages: A sialic acid-based targeted delivery strategy for cancer immunotherapy.

Mononuclear phagocytes are efficient drug delivery targets for cancers owing to their cancerous tissue-accumulating nature. As receptors of sialic acid, Siglecs (sialic acid-binding immunoglobulin-type lectins) are noticeably found on peripheral blood monocytes (PBMs) and tumor-associated macrophages (TAMs), which renew by the differentiation of recruited PBMs at the tumor site and positively correlate with tumor growth. Given this, a sialic acid-octadecylamine conjugate (SA-ODA) was synthesized and then modified on the surface of liposomal epirubicin (EPI-SAL) as a potent tumor-targeting delivery strategy. A cellular uptake assay indicated that SA-modified liposomes provided improved distribution of the drug in both PBMs and TAMs. Pharmacodynamic tests demonstrated that the antitumor efficacy of the EPI-SAL group was better than that of the other groups, owing to both inhibition of TAMs by EPI-SAL, and high-efficiency targeting of PBMs by EPI-SAL, after which PBMs containing EPI-SAL were recruited to the tumor site and then killed by EPI. Thus, an SA-based targeted delivery strategy effectively interdicted the generation of TAMs. Our research provides the feasibility of the SA-ODA decorated liposome as an active carrier for cancer immunotherapy.

Ding J ，Zhao D ，Hu Y ，Liu M ，Liao X ，Zhao B ，Liu X ，Deng Y ，Song Y ... -  《-》