Comparison of therapeutic potential of macrophage- or mesenchymal stem cell-derived exosomes in pancreatic cancer: An updated review

Abstract

Pancreatic cancer is known to have high metastatic potential and low survival rates due to the failure of the therapeutic agents to reach the cancer cells having the dense desmoplastic microenvironment. Exosomes are considered to be a promising therapeutic agent carrier due to their advantages such as low immunogenicity and easy targeting. More researches and future developments are needed, although exosome-based therapies need further research and development before they can be translated into clinical applications. In this review, we aimed to discuss comparatively two main exosome sources as mesenchymal stem cell (MSC)-derived and macrophage-derived exosomes on pancreatic cancer in terms of the therapeutic potential, advantages, disadvantages and also other comprehensive details. In vitro, in vivo and clinical phase studies examining the therapeutic potential of MSC-derived and macrophage-derived exosomes in pancreatic cancer will be discussed. We strongly believe that this review will guide the new investigations related to exosome-based targeted therapy in pancreatic cancer. In the meantime, we aimed to provide an overview of ongoing research on MSC and macrophage exosome-based therapies, focusing on their role in cancer treatment, particularly for pancreatic cancer. By examining current findings, this review will provide a broad perspective on the therapeutic potential and limitations of exosomes.

Key Words: Exosomes; Pancreatic cancer; Mesenchymal stem cell exosomes; Macrophage exosomes; Small extracellular vesicles

Core Tip: Pancreatic cancer has high metastatic potential and low survival rates due to its dense desmoplastic microenvironment, which limits drug delivery. Exosomes, with their low immunogenicity and targeting ability, are promising therapeutic carriers. Mesenchymal stem cell- and macrophage-derived exosomes show potential in pancreatic cancer treatment. This review compares their effects, summarizing in vitro, in vivo, and clinical studies while highlighting their advantages and disadvantages.

INTRODUCTION

Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer-related deaths in the United States. The low survival rate of this cancer type can be attributed to its poor prognosis, early systemic metastasis, and aggressive local growth[1]. In contrast to many other cancers, where early diagnosis and advances in oncological treatments have successfully improved survival rates, the vast majority of individuals affected by PDAC (more than 80%) present with end-stage cancer, resulting in a 5-year survival rate of only 11%[2]. Surgical resection at an early stage is currently the only effective treatment. Therefore, early diagnosis and timely surgical resection are critical to improving outcomes in pancreatic cancer patients[3]. Chemotherapy, radiotherapy, and immunotherapy can be considered treatment options for patients, who are not suitable candidates for surgical resection. However, their effectiveness has been unsatisfactory due to drug resistance and the desmoplastic microenvironment[4]. As a result, it is urgent to develop new, effective, and targeted therapies.

The failure of conventional therapies is primarily due to the inability of therapeutic agents to reach target cells because of the dense desmoplastic microenvironment in PDAC. Recent studies have shown that not only cancer cells but also the tumor microenvironment contribute to the aggressive prognosis of pancreatic cancer[1,4]. Approximately 90% of the pancreatic tumor mass consists of desmoplastic stroma, while tumor cells make up only 10% of the mass[5]. The microenvironment of pancreatic cancer comprises stromal cells, a dense extracellular matrix, and immune system cells. This stroma plays a critical role in regulating tumor growth, vascularization, drug response, immune structure, and metastasis[6]. Given this, the search for therapies that can both reach cells and reduce drug resistance while regulating the microenvironment continues. In this context, cell-based therapies are highly promising, though adverse immune reactions complicate their use. Recently, researchers have suggested that extracellular vesicles (EVs) secreted by different cells may play a therapeutic role[7].

EVs, which are double-layered lipid membrane structures, act as delivery vehicles to transport cellular cargo to recipient cells. Effector molecules, such as lipids, proteins, and nucleic acids, within EVs play an important role in intercellular signaling. There are three types of EVs recognized according to their intracellular origin: Apoptotic vesicles, microvesicles, and exosomes. Exosomes are defined as small EVs ranging in size from 40 to 100 nm and are secreted by all cell types[8]. The surface membrane of exosomes contains proteins such as CD63, CD81, CD82, CD53, CD37, and tetraspanins. They can carry a variety of biological components, including proteins, lipids, mRNAs, microRNAs (miRNAs), long non-coding RNA, and DNA fragments to target cells[9]. Almost all cell types, including endothelial cells, MSCs, T cells, B cells, macrophages, dendritic cells, and natural killer cells, can produce exosomes[10]. The delivered cargo can regulate specific genes and proteins in target cells, ultimately altering their properties[11]. Due to these properties, exosomes are used for the transport of drugs, delivery of tumor suppressor agents, immunomodulation, anti-inflammatory effects, and neuroregenerative properties. Additionally, exosomes have promising characteristics for cancer treatment, such as targeting, low immunogenicity, modification flexibility, and high permeability across the blood-brain barrier[12]. Studies have shown that sequential injections of exosomes do not have toxic effects on the body, that their small size allows them to pass through various vascular and capillary barriers, and that they possess immunocompatible and biocompatible properties suitable for therapeutic applications[13].

As can be understood, the direct use of exosomes for therapeutic applications in cancer is actively being studied. Exosomes are thought to be advantageous for the specific delivery of drugs to cancer cells because of natural structures with liposome-like properties, they are nanosized and remain largely stable in the blood. However, studies on donor cell type, exosome cargo content, loading technique and targeting methods are ongoing[13].

MSCs are multipotent stromal cells with significant potential for regeneration and therapeutic properties, including immunomodulatory, anti-apoptotic, pro-angiogenic, and chemoattractant effects[14]. MSCs are therapeutically used either allogeneically or autologously in conditions such as graft-vs-host-disease, autoimmune diseases, hematological malignancies, cardiovascular diseases, neurological disorders, organ transplants, diabetes, and regenerative medicine[15]. Recently, the therapeutic use of MSCs derived EVs in the acute tissue damage of various organs - such as the heart, brain, kidneys, lungs, and liver - along with their effects on tumor progression and potential in cancer treatment, has been actively investigated[16,17]. MSC-derived exosomes (MSC-Exos) have been reported to be non-cytotoxic and effectively reduce adverse side effects, including infusion-related toxicities[18]. Macrophages, which are immune system cells differentiated from monocytes, can phagocytose regulate inflammatory responses, and activate other immune system cells. Macrophages can exist in different activation and polarization states. While M1 macrophages exhibit anti-tumoral effects, M2 macrophages perform pro-tumorigenic actions that promote tumor growth[19]. Macrophage derived exosomes are also being explored for therapeutic use in cancer and other inflammation-related diseases, much like MSC-Exos[20]. Macrophage derived exosomes can serve as a therapeutic modality by affecting both tumor cells and the tumor microenvironment, indeed either directly or through modification[21].

In this review, we compare the two main sources of exosomes - MSC-derived and macrophage derived exosomes - in pancreatic cancer, focusing on their therapeutic potential, advantages, disadvantages, and other relevant details. We present an overview of in vitro, in vivo, and clinical studies examining the therapeutic potential of MSC-Exos and macrophage derived exosomes in pancreatic cancer. We believe that this review will help guide future exosome based research in the field of pancreatic cancer.

MSC-EXOS FOR THE MANAGEMENT OF PANCREATIC CANCER

Exosomes may contain membrane proteins, cytosolic and nuclear proteins, extracellular matrix proteins, cytokines, metabolites, and nucleic acids such as mRNA, non-coding RNA species, and DNA. Each molecule in their composition has an effect on cancer cells and is unique[22]. Both as a therapeutic candidate and as an important regulator in the tumor microenvironment, MSCs display both antitumor and protumor properties depending on their phenotype. MSCs act on cancer cells in the same microenvironment via secreting cytokines, chemokines, exosomes, or through direct contact. It is known that the exosomes produced by MSCs exhibit both tumor-inhibitory and tumor-promoting effects[23]. In cancer treatment, exosomes are used in two ways: In the first case, exosomes in their naive and intact forms are used, and in the second case, exosomes act as drug carriers. Moreover, the use of engineered exosomes, known as iExosomes, has increased in recent years. Exosomes containing loaded drugs, miRNAs, small interfering RNAs (siRNAs), and CRISPR/Cas system components are considered part of this therapeutic approach[24]. Exosomes are also manipulated by surface molecules to enhance therapeutic efficacy. For example, iExosomes can be designed to express a chemokine receptor to a greater extent, allowing them to migrate to the desired location in a targeted manner[25]. The promoting effects of naive MSC-Exos on cancer cells are also observed through different mechanisms, depending on their varying contents. However, exosomes seem to be more compatible with antitumor effects when used as carriers of the target agent or through manipulation of the MSCs.

MSC-exos in general effect cancer procession

It has been suggested that MSC-Exos, due to its tumor-inducing effects, may alter the functions of tumor cells by inducing ecto-5’-nucleotidase and matrix metalloproteinase-2 activity, thereby transforming the tumor microenvironment by increasing tumor heterogeneity[26]. Adipose-derived MSC-Exos have been shown to stimulate angiogenesis in endothelial cells via platelet-derived growth factor[27]. Umbilical cord-derived MSC-Exos have been shown to increase the proliferation, invasion, and metastatic potential of gastric cancer cells ex vivo by inducing the epithelial-mesenchymal transition (EMT) process and stimulating protein kinase B protein[28]. Bone marrow-derived MSC-Exos have been shown to stimulate tumor angiogenesis and cell proliferation in a gastric cancer model by increasing exosomes, extracellular signal-regulated kinase 1/2 signaling, and vascular endothelial growth factor expression[29]. MSC-Exos derived from hypoxic bone marrow contained miRNAs such as miR-193-3a, miR-5100, and miR-210-3p, which increased metastasis through signal transducer and activator of transcription 3-mediated EMT activation in advanced lung cancer cells[30]. It was observed that miR-15a was decreased in bone marrow MSC-Exos, and these exosomes supported clonal expansion in multiple myeloma cells[31]. Bone marrow MSC-derived EVs (MSC-EVs) have also been shown to promote the growth of osteosarcoma and gastric cancer cells by activating hedgehog signaling[32]. MSC-EVs in a hypoxic environment are reported to support the proliferation, survival, invasiveness, and EMT process of lung cancer cell lines. Furthermore, these EVs are thought to increase M2-type macrophage polarization, driven by the transfer of a miRNA, miR-21-5p[33]. It has been shown that exosomal circ_6790 derived MSCs can down-regulate S100A11 in PDAC cells and inhibit immune escape via CBX7-catalysed DNA hypermethylation[34]. The growth-promoting effects of MSC-EVs are more likely to be vary depending on the status of MSCs and the load carried by these EVs.

Once we evaluated the tumor-inhibitory effects of MSC-Exos, human umbilical cord MSC-Exos induced apoptosis by inhibiting proliferation in bladder tumor cells[35]. Wharton’s jelly MSC-Exos reduced migration in U87 glioblastoma multiforme cells and revealed that exosomes carried anti-tumorigenic miRNAs[36]. Xu et al[37] demonstrated that bone marrow MSC-Exos carrying miR-16-5p decreased tumor growth by inducing apoptosis through regulating integrin α2 in colorectal cancer. In chronic myeloid leukemia cells, it has been demonstrated that cord MSC-Exos support the inhibition of viability and apoptosis with a synergistic effect alongside imatinib[38]. The anticancer effects of bone marrow MSC-Exos carrying miR-124 were obtained in pancreatic cancer through inhibition of cell proliferation, EMT, and induction of chemotherapy sensitivity[39]. MSC-Exos containing hsa-miR-143-3p promoted apoptosis and suppressed cell growth and invasion in pancreatic cancer cells (PCCs)[40]. A systematic review showed that only 26% and 46% of the studies reported a tumor-suppressive effect for bone marrow MSC-Exos and adipose tissue MSC-Exos, respectively, whereas 88% confirmed a tumor-suppressive role for Wharton’s jelly MSC-Exos[41]. Even though MSC-Exos show tumor cell inhibitory properties, it has been reported in the literature that different MSC-Exos also have tumor-promoting effects in various cancer types[42]. It has been observed that exosomes with different contents are obtained from different cells. In the literature, Wharton’s jelly MSC-Exos are promising for future studies because of their antitumor effects allogenically.

MSC-derived exosomes for therapeutic agent delivery

MSCs-Exos can also be used as cell-free carriers for the delivery of therapeutic agents in cancer treatment and overcome the limitations of stem cell therapy[43]. The exosome-mediated delivery of anti-cancer drugs, such as gemcitabine (GEM) or paclitaxel (PTX), has been proven to be more efficient and less cardiotoxic compared to free drugs. Furthermore, when comparing exosomes with liposomes of the same size, their capacity to target cancer cells is about 10 times higher, mostly due to ligand-receptor interactions[44]. GEM is a first-line chemotherapeutic agent used for pancreatic cancer treatment. Autologous exosomes loaded with GEM (Exo-GEM) have been developed to reduce systemic side effects and prevent the development of chemotherapy resistance. Compared to GEM alone, the administration of Exo-GEM increases the apoptotic rate of tumor cells[45]. In another study, bone marrow MSC-Exos were loaded with GEMs and then treated with Panc-1 and MiaPaca-2 cells. The results showed that Exo-GEMs reduced cell viability more significantly than direct GEM and increased apoptotic cell death by approximately 15%[46]. Pascucci et al[47] demonstrated the strong anti-proliferative activity of MSCs-Exos coated with PTX against the human pancreatic cell line CFPAC-1. They showed that MSCs could encapsulate PTX and deliver the drug in vesicles, resulting in a 50% reduction in tumor growth. They also proved that exosomes, compared to other nanoparticles, fused more easily with the plasma membrane of cancer cells[47]. Dental pulp MSC-Exos is designed to express the suicide gene. The product of the suicide gene converts the non-toxic prodrug 5-fluorocytosine to the highly cytotoxic chemotherapeutic drug 5-fluorouracil in recipient cancer cells. High antiproliferative effects were observed as a result of this therapy applied to MiaPaCa-2 and Panc-1 cells. MSC-Exos has shown therapeutic potential to be designed for the successful delivery of chemotherapeutic drugs in combination with a prodrug suicide gene therapy system[48]. Osterman et al[49] studied the effect of curcumin via exosomal transport and found that curcumin up-regulated suppressor genes such as TP53 and down-regulated oncogenes. This led to upregulation of transcription factors involved in pancreatic cancer progression and resulted in a decrease of apoptosis inhibitors[49].

Drug efflux and chemoresistance can be modulated through miRNA delivery. Additionally, creating or inducing exosomes to express specific miRNAs presents another approach to alter cell phenotypes. Bone marrow MSC-Exos increased the chemosensitivity of glioblastoma multiforme cells against temozolomide with miR-9[50]. Kamerkar et al[51] demonstrated that exosomes containing oncogenic KRAS siRNAs significantly increased the survival rate of pancreatic tumors in mouse models. In another study, exosomes were used as DNA plasmid carriers for the CRISPR/Cas9 system to target KRAS G12D. CRISPR/Cas9-loaded exosomes can target the mutated Kras G12D oncogenic allele in PCC, thereby reducing the proliferative ability of cancer cells and suppressing tumor growth in both subcutaneous and orthotopic models. Therefore, exosomes can be used as promising carriers in pancreatic cancer gene therapy[52]. The overexpression of the p21-activated kinase 4 gene is associated with pancreatic cancer and increases tumor cell proliferation, survival, migration, and metastasis. In one study, exosomes derived from PCC were loaded with siRNA and applied to Panc-1 cells. The results showed that these exosomes reduced p21-activated kinase 4 expression, inhibited tumor growth, and increased survival in mouse models[53]. Exosomes containing hepatocyte growth factor siRNA have been shown to inhibit tumor growth and angiogenesis. Thus, they have been shown to be a target comparable to nanoparticles in tumor targeting[54]. Exosomes containing miR-145-5p derived from human umbilical cord MSCs suppressed proliferation and induced apoptosis in an in vivo PDAC model[55]. Bone marrow-derived MSC-Exos containing high levels of miR-1231 suppressed invasion and metastasis in pancreatic cancer both in vivo and in vitro[56]. Bone marrow MSC-Exos transferred with miR-128-3p inhibit the proliferation, invasion, and metastasis of pancreatic tumor cells and induce apoptosis both in vitro and in vivo by inhibiting a disintegrin and metalloproteinase domain 9 expression[57]. When the literature is evaluated, it is evident that MSC-Exos also show antitumor effects through varying mechanisms (Table 1).

Table 1 Impact of mesenchymal stem cell derived exosomes as a delivery agent in pancreatic cancer models.

Type of exosome	Therapeutic agent	Target	Effect	Ref.
Bone marrow MSC-Exos	Gemcitabine	Panc-1 and MiaPaca-2 cells	Decreased vitality. Induced apoptosis	[46]
Murine bone marrow stromal cell-Exos	Paclitaxel	CFPAC-1 cells	Decreased proliferation and growth	[47]
Dental pulp MSC-Exos	Suicide genes expression and gemcitabine treatment	Panc-1 and MiaPaca-2 cells	High antiproliferative activity	[48]
Fibroblast-like MSC-Exos	KRAS siRNA	Mouse model with KrasG12D mutation	Increased survival rates	[51]
Human umbilical cord MSC-Exos	Exogenous miR-145-5p	Xenograft mouse tumor model	Inhibited proliferation. Increased apoptosis	[55]
Bone marrow MSC-Exos	Exogenous miR-145-5p	Mouse model and PDAC cell lines	Suppressed invasion and metastasis	[56]
Bone marrow MSC-Exos	Exogenous miR-128-3p	Mouse model and PDAC cell lines	Inhibits metastasis. Induces apoptosis	[57]

MSC-Exos: Mesenchymal stem cell derived exosomes; Exos: Exosomes; siRNA: Small interfering RNA; PDAC: Pancreatic ductal adenocarcinoma.

MSC-exosomes in immunity

Exosomes can act as antigen carriers to stimulate both innate and adaptive immune responses and serve as immune modulators[58]. Exosomes containing indoleamine 2,3-dioxygenase 1 secreted by myeloid-derived suppressor cells have been shown to limit immune responses by reducing interferon-γ expression in dendritic cells and natural killer cells[59]. Additionally, MSCs-Exos have been shown to reduce immune responses by inducing interleukin (IL)-10 secretion and increasing the number of regulatory T cells[60]. Exosomes loaded with miR-10a from adipose-derived MSCs-Exos have been shown to stimulate T helper type 17 and regulatory T cells responses while decreasing T helper type 1 responses. Therefore, the use of anti-tumor exosomes holds promise for new therapeutic potentials in immunotherapeutic strategies[61]. The tumor microenvironment, initially pro-inflammatory in the early stages of the tumor, gradually transforms into an anti-inflammatory character based on the signals it receives over time. If this pro-inflammatory phenotype can be sustained, the immune system will remain active, and inhibitory effects on tumor cells will continue[62]. Tumor-associated macrophages change their phenotype from M1 to M2, allowing tumor cells to escape the immune system. However, through the delivery of miR-155 and miR-125b-2 via exosomes, these tumor-associated macrophages can be reprogrammed to the M1 phenotype, which exhibits anti-tumor immunity[63]. In PDAC and oxaliplatin induce immunogenic cell death, inhibit M2 macrophage polarization and the uptake of cytotoxic T lymphocytes, reverse the tumor’s immune microenvironment, and enhance the efficacy of immunotherapy[64]. The sudden increase in cytokine/chemokine release modulated by exosomes can either trigger anti-tumor immune responses or lead to immune suppressive effects. Therefore, exosomes, when not properly treated, can be both a blessing and a curse. For this reason, the targeted application of exosomes is expected to be more beneficial.

Tumor cells are not very immunogenic and are surrounded by an immunosuppressive environment characterized by a dense stroma (collagen, matrix proteins, and fibroblasts), which hinders the development of effective anti-cancer immunotherapies[65]. Therefore, combining immunostimulants (such as vaccines) with inhibitors of the immunosuppressive environment may be a promising approach to enhance anti-tumor immune responses and prevent metastasis. Immunotherapy strategies could involve the development of cancer vaccines for active immunization, indirect stimulation of the immune system, and the combination of pre-activated T-cells (via exosomes) with passive immunization, such as monoclonal antibodies. For example, it has been shown that catumaxomab, combined with activated T-cells, can eliminate pancreatic cancer stem cells[66].

MACROPHAGE-DERIVED EXOSOMES IN CANCERS, INCLUDING PANCREATIC CANCER

Exosomes can be derived from different cell types having the specific biological functions lipids, proteins, and genetic materials. Among the tumor microenvironment components, macrophages play key role in immune cells due to having the potential of polarization into M1 or M2 phenotypes in response to different stimuli. M1 macrophages lead to inhibit the tumor progression because of highly secreting IL-1β, tumor necrosis factor alpha α, IL-12, IL-18, and IL-23 as proinflammatory and immunostimulatory cytokines[19].

M1 macrophage-derived exosomes

M1 macrophage-derived exosomes (M1-Exos) can also secrete proinflammatory signals to stimulate tumor immune-microenvironment, as well as M1 macrophages, which makes them a therapeutic approach for cancer therapy. In addition to their therapeutic potential, M1-Exos are used as drug carriers to deliver several chemotherapeutics including, PTX cisplatin, GEM combined with deferasirox (DFX) into the tumor tissues.

Wang et al[67] demonstrated the application of exosomes from activated M1-type macrophages for the delivery of drugs to tumor cells. Upon co-culturing of breast cancer cells with M1 macrophage derived exosomes, M1 macrophages resulted in the inhibition of tumor progression due to the induction of apoptosis via enhanced caspase-3 expression and release of pro-inflammatory cytokines. When PTX was loaded into M1-Exos, its therapeutic effects were significantly improved. Apart from in vitro findings, M1-Exos based on chemotherapy increased the anti-tumor effects in tumor-bearing mice via regulating apoptosis in vivo[67].

Just as PTX, cisplatin-loaded M1 macrophage secreted-exosomes was also effectively shown to inhibit the proliferation of mouse Lewis lung cancer cells and induce apoptosis both in vitro and in vivo. Based on in vitro quantitative real-time polymerase chain reaction and Western blotting results, the decrease in proliferation rate of mouse Lewis lung cancer cells (P < 0.05) and increase in their apoptosis rate via up-regulated Bax and caspase-3 expressions (P < 0.01) were significantly observed in cisplatin-loaded M1-Exos group compared with only cisplatin treatment group. Additionally, owing to in vivo experiments, M1-Exos alone were also shown to suppress tumor growth, and that the carrier of M1-Exos could not only kill tumor cells, but also encapsulate cisplatin to enhance its anti-lung cancer effect as well[68].

M1-Exos were also proved as a drug carrier of co-delivery DFX and GEM for eliminating the drug resistance against GEM and enhancing its therapeutic potential in PCCs. M1-Exos based on co-delivery of DFX and GEM shined as a promising strategy for drug-resistant pancreatic cancer treatment because of the inhibitory effects on cell proliferation, metastasis, and chemoresistance by inhibition of ribonucleotide reductase subunit 2 expression via depleting iron in the GEM-resistant PANC-1/GEM cell line. M1Exos-GEM-DFX in nanoformulations using a 3D tumor spheroid model effectively inhibited the formation and growth of PANC-1/GEM tumor spheroids compared with free drugs[69].

M2 macrophage-derived exosomes

In contrast to M1-Exos, M2 macrophage derived exosomes (M2-Exos) are shown to promote tumor growth through several key mechanisms. They are shown to mediate the angiogenesis in mouse aortic endothelial cells in vitro and also the growth of subcutaneous tumors by increasing the vascular density of mice in vivo[70]. Additionally, M2-Exos mediate T-cell exhaustion in liver cancer, induce invasion in colon cancer, and regulate Brahma-related gene 1 expression in response to tumor microenvironment[71]. Zhang et al[71] demonstrated that exosome-free condition medium of M2 macrophages led to increase the proliferation, migration, invasion and glutamine uptake of PDAC SW1990 cells compared with the condition medium of M0 macrophages when co-culturing of macrophages and SW1990 cells. Because of the upregulated miR-193b-3p expression in plasma exosomes obtained from patients with pancreatic cancer, M2-Exos carrying miR-193b-3p were obtained to enhance the proliferation, migration, invasion, and glutamine uptake of SW1990 cells in vitro and in vivo[72]. M2-Exos have these tumor promoting effects by carrying oncogenic miRs. MiR-21-5p, miR-155-5p, miR-221-5p, and miR-501-3p were shown to induce the differentiation and activity of pancreatic cancer stem cells and the growth, angiogenesis, migration, and invasion of PCCs[24,70].

CLINICAL APPLICATIONS OF MSC AND MACROPHAGE-DERIVED EXOSOMES

Clinical trial studies in the literature involve the use of MSCs in their naive or modified forms. Some of these include NCT04087889, NCT04150042, and NCT01844661. These studies aim to evaluate the efficacy and safety of MSCs in the treatment of various diseases. MSC-based therapies, particularly MSC-Exos for drug delivery, have emerged as a promising approach. One of phase I clinical trials currently underway is investigating the efficacy of iExosomes loaded with KrasG12D siRNA in the treatment of pancreatic cancer with KrasG12D mutation, which has spread to other parts of the body (NCT03608631)[72].

To be able to widely use MSC-exos and macrophage-derived exosomes as clinical trial in cancer, several future challenges need to be addressed. These challenges are described into multiple headlines, which are immunogenicity and safety, mechanism of action ways, delivery and targeting, standardization and manufacturing, characterization and quality control. Because MSCs and macrophages can promote tumor growth under certain conditions and exosomes from immune cells, such as macrophages, may trigger unpredictable immune responses, their clinical usage has not been enough safe, yet. Additionally, exosomes contain diverse bioactive cargo (proteins, RNAs, lipids) which differ even within the from same cell type. Due to this heterogenicity, better characterization methods are needed to distinguish exosome subtypes and origins. There is also another risk related to delivery due to exosomes quickly degraded in circulation or accumulate in unintended tissues. To eliminate this challenge and find optimal dosage, engineering exosomes for targeted delivery is unfortunately still in early stages. Apart from all these challenges, the most important one is the ethical issues due to donor individuals. Use of primary cells from donors raises issues of consent, traceability, and infection screening.

Future studies investigating the clinical use of MSC-exos and macrophage-derived exosomes need to overcome these major challenges given above in detail. First of all, they are expected to mechanistically explain action ways, how exosomes interact with recipient cells at the molecular level, such as immunomodulation and angiogenesis and which specific RNAs, proteins, or lipids are responsible for therapeutic effects. Followed by mechanistical effects, their targeted delivery to specific tissues need to be guaranteed by modifying surfaces with ligands or antibodies. The further strategies are also required to improve crossing biological barriers like the blood-brain barrier. Thanks to more detail analysis of immune reactions in humans and animal models, the immunogenicity concerns and long-term safety effects will be revealed more clearly. The further investigations also will show that how long exosomes remain stable and active under various storage conditions.

CONCLUSION

Despite rapid advancements in the diagnosis and treatment of pancreatic cancer, the effectiveness of current treatment methods remains limited. Challenges associated with pancreatic cancer, such as malnutrition, immunosuppression, hypoxia, and desmoplastic features, contribute to the limited success of traditional treatments, including chemotherapy, targeted therapy, and immunotherapy. Therefore, there is an urgent need to explore alternative treatment pathways for pancreatic cancer. This review highlights the evolving role of exosomes derived from MSCs and macrophages in the treatment of pancreatic cancer (Figure 1). MSC-exosomes offer promising therapeutic options with properties such as regulating the tumor microenvironment, therapeutic delivery, and serving as biomarkers. Research shows that these soma naïve and engineered exosomes inhibit pancreatic tumor progression, migration, and invasion, while enhancing the efficacy of conventional therapies. However, further research and clinical trials are required for these therapies to reach their full potential.

Figure 1 The functions of mesenchymal stem cell and macrophage derived exosomes in cancer. MSC: Mesenchymal stem cell; siRNA: Small interfering RNA; EMT: Epithelial-mesenchymal transition.