Progress in cancer research on the regulator of phagocytosis CD47, which determines the fate of tumor cells (Review)

Cluster of differentiation 47 (CD47) is a transmembrane protein that is widely and moderately expressed on the surface of various cells and can have an essential role in mediating cell proliferation, migration, phagocytosis, apoptosis, immune homeostasis and other related responses by binding to its ligands, integrins, thrombospondin-1 and signal regulatory protein α. The poor prognosis of cancer patients is closely associated with high expression of CD47 in glioblastoma, ovarian cancer, breast cancer, bladder cancer, colon cancer and hepatocellular carcinoma. Upregulation of CD47 expression facilitates the growth of numerous types of tumor cells, while downregulation of its expression promotes phagocytosis of tumor cells by macrophages, thereby limiting tumor growth. In addition, blocking CD47 activates the cyclic GMP-AMP (cGAMP) synthase/cGAMP/interferon gene stimulating factor signaling pathway and initiates an adaptive immune response that kills tumor cells. The present review describes the structure, function and interactions of CD47 with its ligands, as well as its regulation of phagocytosis and tumor cell fate. It summarizes the therapeutics, mechanisms of action, research advances and challenges of targeting CD47. In addition, this paper provides an overview of the latest therapeutic options for targeting CD47, such as chimeric antigen receptor (CAR) T-cells, CAR macrophages and nanotechnology-based delivery systems, which are essential for future clinical research on targeting CD47.

A Novel Anti-CD47 Nanobody Tetramer for Cancer Therapy

CD47 acts as a defense mechanism for tumor cells by sending a "don't eat me" signal via its bond with SIRPα. With CD47's overexpression linked to poor cancer outcomes, its pathway has become a target in cancer immunotherapy. Though monoclonal antibodies offer specificity, they have limitations like the large size and production costs. Nanobodies, due to their small size and unique properties, present a promising therapeutic alternative. In our study, a high-affinity anti-CD47 nanobody was engineered from an immunized alpaca. We isolated a specific VHH from the phage library, which has nanomolar affinity to SIRPα, and constructed a streptavidin-based tetramer. The efficacy of the nanobody and its derivative was evaluated using various assays. The new nanobody demonstrated higher affinity than the monoclonal anti-CD47 antibody, B6H12.2. The nanobody and its derivatives also stimulated substantial phagocytosis of tumor cell lines and induced apoptosis in U937 cells, a response confirmed in both in vitro and in vivo settings. Our results underscore the potential of the engineered anti-CD47 nanobody as a promising candidate for cancer immunotherapy. The derived nanobody could offer a more effective, cost-efficient alternative to conventional antibodies in disrupting the CD47-SIRPα axis, opening doors for its standalone or combinatorial therapeutic applications in oncology.

Genetically Engineered-Cell-Membrane Nanovesicles for Cancer Immunotherapy

The advent of immunotherapy has marked a new era in cancer treatment, offering significant clinical benefits. Cell membrane as drug delivery materials has played a crucial role in enhancing cancer therapy because of their inherent biocompatibility and negligible immunogenicity. Different cell membranes are prepared into cell membrane nanovesicles (CMNs), but CMNs have limitations such as inefficient targeting ability, low efficacy, and unpredictable side effects. Genetic engineering has deepened the critical role of CMNs in cancer immunotherapy, enabling genetically engineered-CMN (GCMN)-based therapeutics. To date, CMNs that are surface modified by various functional proteins have been developed through genetic engineering. Herein, a brief overview of surface engineering strategies for CMNs and the features of various membrane sources is discussed, followed by a description of GCMN preparation methods. The application of GCMNs in cancer immunotherapy directed at different immune targets is addressed as are the challenges and prospects of GCMNs in clinical translation.

High-affinity decoy protein, nFD164, with an inactive Fc region as a potential therapeutic drug targeting CD47

CD47, as an innate immune checkpoint molecule, is an important target of cancer immunotherapy. We previously reported that a high-affinity SIRPα variant FD164 fused with IgG1 subtype Fc showed a better antitumor effect than wild-type SIRPα in an immunodeficient tumor-bearing model. However, CD47 is widely expressed in blood cells, and the drugs targeting CD47 may cause potential hematological toxicity. Herein, we modified the FD164 molecule by Fc mutation (N²⁹⁷A) to inactivate the Fc-related effector function and named it nFD164. Moreover, we further studied the potential of nFD164 as a candidate drug targeting CD47, including the stability, in vitro activity, antitumor activity of single or combined drugs in vivo, and hematological toxicity in humanized CD47/SIRPα transgenic mouse model. The results show that nFD164 maintains strong binding activity to CD47 on tumor cells, but has weak binding activity with red blood cells or white blood cells, and nFD164 has good drug stability under accelerated conditions (high temperature, bright light and freeze-thaw cycles). More importantly, in the immunodeficient or humanized CD47/SIRPα transgenic mice bearing tumor model, the combination of nFD164 and anti-CD20 antibody or anti-mPD-1 antibody had a synergistic antitumor effect. Especially in transgenic mouse models, nFD164 combined with anti-mPD-1 significantly enhanced tumor suppressive activity compared with anti-mPD-1 (P < 0.01) or nFD164 (P < 0.01) as a single drug and had fewer hematology-related side effects than FD164 or Hu5F9-G4. When these factors are taken together, nFD164 is a promising high-affinity CD47-targeting drug candidate with better stability, potential antitumor activity, and improved safety profile.

The expression profiles of CD47 in the tumor microenvironment of salivary gland cancers: a next step in histology-driven immunotherapy

BACKGROUND

Salivary gland carcinomas (SGC) are extremely rare malignancies with only limited treatment options for the metastatic phase of the disease. Treatment with anti-CD47 antibodies could represent a potent therapy for SGCs by promoting the phagocytic clearance of tumor cells through various mechanisms. However, the efficacy of anti-CD47 therapy is largely dependent on the expression of CD47 within the tumor microenvironment (TME).

MATERIALS AND METHODS

In 43 patients with SGC, we were the first to investigate the CD47 expression in both tumor cells and tumor-infiltrating immune cells (TIIC) in the center and periphery of primary tumors. We also correlated the data with the clinicopathological variables of the patients and offered novel insights into the potential effectiveness of anti-CD47 therapy in SGCs.

RESULTS

We observed that the CD47⁺ tumor cells are outnumbered by CD47⁺ TIICs in mucoepidermoid carcinoma. In the tumor center, the proportion of CD47⁺ tumor cells was comparable to the proportion of CD47⁺ TIICs in most histological subtypes. In low-grade tumors, significantly higher expression of CD47 was observed in TIICs in the periphery of the tumor as compared to the center of the tumor.

CONCLUSION

The reason for a high expression of 'don't eat me' signals in TIICs in the tumor periphery is unclear. However, we hypothesize that in the tumor periphery, upregulation of CD47 in TIICs could be a mechanism to protect newly recruited leukocytes from macrophage-mediated phagocytosis, while also allowing the removal of old or exhausted leukocytes in the tumor center.

Overcoming Immunotherapeutic Resistance in PDAC: SIRPα-CD47 blockade

A daily increase in the number of new cases of pancreatic ductal adenocarcinoma remains an issue of contention in cancer research. The data revealed that a global cumulated case of about 500, 000 have been reported. This has made PDAC the fourteenth most occurring tumor case in cancer research. Furthermore, PDAC is responsible for about 466,003 deaths annually, representing the seventh prevalent type of cancer mortality. PDAC has no salient symptoms in its early stages. This has exasperated several attempts to produce a perfect therapeutic agent against PDAC. Recently, immunotherapeutic research has shifted focus to the blockade of checkpoint proteins in the management and of some cancers. Investigations have centrally focused on developing therapeutic agents that could at least to a significant extent block the SIRPα-CD47 signaling cascade (a cascade which prevent phagocytosis of tumors by dendritic cells, via the deactivation of innate immunity and subsequently resulting in tumor regression) with minimal side effects. The concept on the blockade of this interaction as a possible mechanism for inhibiting the progression of PDAC is currently being debated. This review examined the structure--function activity of SIRPα-CD47 interaction while discussing in detail the mechanism of tumor resistance in PDAC. Further, this review details how the blockade of SIRPα-CD47 interaction serve as a therapeutic option in the management of PDAC.

The regulation of CD47-SIRPα signaling axis by microRNAs in combination with conventional cytotoxic drugs together with the help of nano-delivery: a choice for therapy?

CD47, a member of the immunoglobulin superfamily, is an important "Don't Eat-Me" signal in phagocytosis process [clearance of apoptotic cells] as well as a regulator of the adaptive immune response. The lower level of CD47 on the cell surface leads to the clearance of apoptotic cells. Dysregulation of CD47 plays a critical role in the development of disorders, particularly cancers. In cancers, recognition of CD47 overexpression on the surface of cancer cells by its receptor, SIRPα on the phagocytic cells, inhibits phagocytosis of cancer cells. Thus, blocking of CD47-SIRPα signaling axis might be as a promising therapeutic target, which promotes phagocytosis of cancer cells, antigen-presenting cell function as well as adaptive T cell-mediated anti-cancer immunity. In this respect, it has been reported that CD47 expression can be regulated by microRNAs (miRNAs). MiRNAs can regulate phagocytosis of macrophages apoptotic process, drug resistance, relapse of disease, radio-sensitivity, and suppress cell proliferation, migration, and invasion through post-transcriptional regulation of CD47-SIRPα signaling axis. Moreover, the regulation of CD47 expression by miRNAs and combination with conventional cytotoxic drugs together with the help of nano-delivery represent a valuable opportunity for effective cancer treatment. In this review, we review studies that evaluate the role of miRNAs in the regulation of CD47-SIRPα in disorders to achieve a novel preventive, diagnostic, and therapeutic strategy.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Also, kindly confirm the details in the metadata are correct. Confirmed.Journal standard instruction requires a structured abstract; however, none was provided. Please supply an Abstract with subsections..Not confirmed. This is a review article. According to submission guidelines: "The abstract should be presented divided into subheadings (unless it is a mini or full review article)". Kindly check and confirm whether the corresponding authors and mail ID are correctly identified. Confirmed.

Macrophage-Mediated Tumor Cell Phagocytosis: Opportunity for Nanomedicine Intervention

Macrophages are one of the most abundant non-malignant cells in the tumor microenvironment, playing critical roles in mediating tumor immunity. As important innate immune cells, macrophages possess the potential to engulf tumor cells and present tumor-specific antigens for adaptive antitumor immunity induction, leading to growing interest in targeting macrophage phagocytosis for cancer immunotherapy. Nevertheless, live tumor cells have evolved to evade phagocytosis by macrophages via the extensive expression of anti-phagocytic molecules, such as CD47. In addition, macrophages also rapidly recognize and engulf apoptotic cells (efferocytosis) in the tumor microenvironment, which inhibits inflammatory responses and facilitates immune escape of tumor cells. Thus, intervention of macrophage phagocytosis by blocking anti-phagocytic signals on live tumor cells or inhibiting tumor efferocytosis presents a promising strategy for the development of cancer immunotherapies. Here, the regulation of macrophage-mediated tumor cell phagocytosis is first summarized, followed by an overview of strategies targeting macrophage phagocytosis for the development of antitumor therapies. Given the potential off-target effects associated with the administration of traditional therapeutics (for example, monoclonal antibodies, small molecule inhibitors), we highlight the opportunity for nanomedicine in macrophage phagocytosis intervention.

Molecular functions of SIRPα and its role in cancer

Signal regulatory protein α (SIRPα), also known as cluster of differentiation (CD)172a or Src homology 2 domain-containing phosphatase substrate-1, is a cell surface receptor expressed on myeloid and hematopoietic stem cells and neurons. Accumulating data suggests an important role of SIRPα in cell signaling as a negative regulator of the phosphatidylinositol 3-kinase signaling and mitogen-activated protein kinase pathways. In various cancers, including prostate, breast and liver, as well as astrocytoma and myeloid malignancies, downregulation of SIRPα is frequently observed, resulting in activation of these downstream signaling pathways. In turn, cell proliferation, transformation, migration and invasion may occur. Recently, it has been reported that blocking CD47, an anti-phagocytic signal expressed on tumor cells and an SIRPα ligand, may serve as a promising therapeutic approach, particular for the treatment of acute myeloid leukemia. In the present review, the current findings on SIRPα are summarized, with particular focus on its role in cancer.