Exosomes as promising frontier approaches in future cancer therapy

Abstract

In this editorial, we will discuss the article by Tang et al published in the recent issue of the World Journal of Gastrointestinal Oncology. They explored an innovative approach to enhancing gemcitabine (GEM) delivery and efficacy using human bone marrow mesenchymal stem cells (HU-BMSCs)-derived exosomes. The manufacture of GEM-loaded HU-BMSCs-derived exosomes (Exo-GEM) has been optimized. The Tang et al’s study demonstrated that Exo-GEM exhibits enhanced cytotoxicity and apoptosis-inducing effects compared to free GEM, highlighting the potential of exosome-based drug delivery systems as a more effective and targeted approach to chemotherapy in pancreatic cancer. Additional in vivo studies are required to confirm the safety and effectiveness of Exo-GEM before it can be considered for clinical use.

Key Words: Mesenchymal stem cells; Exosomes; Gemcitabine; Pancreatic cancer; Apoptosis

Core Tip: The method of loading gemcitabine into exosomes is crucial for the effectiveness of the delivery system. The study ascertained that electroporation and sonication were more efficient than incubation in delivering gemcitabine into the human bone marrow mesenchymal stem cells-derived exosomes. Exosomes gemcitabine (Exo-GEM) demonstrated potent cytotoxicity against pancreatic cancer cells by enhancing GEM-induced apoptosis. Exo-GEM offers a promising strategy for targeted therapy in pancreatic cancer by harnessing the natural advantages of exosomes, such as high biocompatibility and the ability to navigate tumor microenvironments. Exo-GEM could deliver chemotherapy more precisely to cancer cells, reducing side effects in healthy cells.

INTRODUCTION

Pancreatic cancer is a malignant and aggressive disease characterized by invasion, rapid progression of the disease, and resistance to treatment. The most common type of pancreatic cancer is pancreatic ductal adenocarcinoma (PDAC), which accounts for about 90% of cases[1]. Typical symptoms in pancreatic cancer patients include abdominal pain, back pain, unexplained weight loss, jaundice, lightening of stool, darkening of urine, no hunger, etc., but there are usually no obvious symptoms in its early stage[2]. Due to the lack of an accurate early diagnostic test and specific symptoms, pancreatic cancer is usually diagnosed late or after it has metastasized to other organs[3].

At present, the main treatments for pancreatic cancer are surgery, radiation therapy, and chemotherapy. However, only around 20% of patients with pancreatic cancer are resectable, and the remaining 80% are not amenable to surgery. Gemcitabine (GEM) is sold under the brand name Gemzar and is the standard first-line treatment for metastatic pancreatic cancer patients[4]. However, its efficacy is often limited due to rapid metabolism, poor delivery efficiency, and the development of drug resistance.

Treatment efficacy is limited by strong biological barriers to drug/material transport into deep tissues, including macrophage uptake, fluid dynamics in blood vessels, and high intratumoral pressure[5]. Exosomes are natural biological nanoparticles secreted by cells (usually 30 nm-150 nm in diameter) and contain many biomolecules, including nucleic acids, proteins, and lipids. Exosomes act as novel mediators in intercellular communication, serving as messengers to mediate physiological and pathological processes[6]. Exosomes have been tested as drug delivery vehicles for cancer treatment due to their unique properties, such as size, innate stability, low immunogenicity, excellent tissue/cell penetration ability and ability to mimic synthetic liposomes in carrying various anticancer drugs/materials[7]. These nanoscale vesicles, i.e. exosomes, have garnered considerable interest in the fields of biology and medical sciences.

For example, Kamerkar et al[8] used inhibitory exosomes (iExosomes) derived from normal fibroblast-like mesenchymal cells containing RNA interference (RNAi) sequences designed to target KRAS^G12D. These iExosomes express cluster of differentiation 47 (CD47), which protects them from phagocytosis, ultimately enabling their enhanced efficacy to suppress cancer and increase survival in multiple mouse models of pancreatic cancer[8]. In addition to delivering RNAi to block the expression of KRAS in pancreatic cancer cells, exosomes can also carry clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) plasmid DNA for targeted gene deletion to replace the viral delivery system. McAndrews et al[9] used typical transfection protocols to effect the encapsulation of CRISPR/Cas9 plasmid DNA by non-autologous exosomes. The CRISPR/Cas9 DNA was designed to provoke targeted KRAS^G12D gene deletion in PDAC cells, proving that exosomes loaded with CRISPR/Cas9 can target mutated KRAS^G12D oncogenic alleles to suppress tumor growth in syngeneic subcutaneous and orthotopic models of pancreatic cancer[9].

Numerous studies have demonstrated that exosomes are potential carriers of therapeutic anti-cancer small molecules, including curcumin, paclitaxel, doxorubicin, and GEM[10-13]. Previous studies have revealed that exosomes gemcitabine (Exo-GEM) derived from tumors, M1 macrophages, and mesenchymal stem cells (MSCs) demonstrate a remarkable capacity to overcome drug resistance in pancreatic cancer[13-16]. However, the efficiency of Exo-GEM to specifically target pancreatic cancer cells has yet to be fully established. The study by Tang et al[17] in the recent issue of World Journal of Gastrointestinal Oncology has explored an innovative approach to improve GEM delivery and efficacy through the use of human bone marrow MSCs (HU-BMSCs)-derived exosomes[17].

CARGO LOADING AND EFFICACY OF EXOSOMES

Cargo, such as drugs and materials, can be loaded into or onto exosomes via three main approaches: (1) Biological methods, such as viral transduction[18] and incubation[19]; (2) Chemical methods, including saponin-assisted permeation[20], transfection by calcium phosphate[21], transfection using diethylaminoethyl-dextran[22], creating lipopolyplexes with polyethylenimine[23], merging liposomes with exosomes[24] etc.; and (3) Physical methods, e.g., sonication[25], extrusion[26], freeze-thaw cycles[27], electroporation[28], and dialysis[29] (Figure 1). It is important to note that while various methods can efficiently load different types of cargo into exosomes, these processes can potentially damage both exosomes and their cargo due to the destructive impact of the techniques. To ensure optimal loading, the ideal combination of key parameters, such as the intensity of physical interactions, operation time, cell type, and the concentration of reagents and exosomes should be carefully determined[7,30].

Figure 1 Schematic diagram of approaches for cargoes loading to exosomes. The scheme illustrates the approaches including biological, chemical, and physical methods, which are used to load cargoes, such as drugs, RNA interference, nucleotides, and proteins, into or onto the exosomes. RNAi: RNA interference; DEAE: Diethylaminoethyl; PEI: Polyethylenimine.

The recent study by Tang et al[17] compared three methods for loading GEM into the HU-BMSCs-derived exosomes: Electroporation, sonication, and incubation. Both electroporation and sonication showed significantly higher loading and encapsulation efficacy by approximately sixfold compared to incubation. Exo-GEM exhibited significantly higher cytotoxicity and induced more apoptosis against the human PDAC cell lines-Panc-1 and MiaPaca-2-than free GEM. The findings suggest that Exo-GEM may help overcome the challenges associated with conventional GEM chemotherapy, such as drug resistance and inadequate solubility[17]. Further modifications of the exosomes’ surface, such as conjugation with tumor-specific antibodies or ligands, might be considered for the next generation of Exo-GEM. Effectively delivering GEM by exosomes to the target cells could potentially improve the therapeutic outcomes of PDAC patients.

SAFETY AND ADMINISTRATION ROUTES OF EXOSOMES

Conventional administration of GEM by intravenous (IV) injection is associated with well-known toxicities, including hematological, gastrointestinal, and liver-related side effects[31]. Exosomes have the potential to enhance drug targeting, reduce systemic toxicity, and provide controlled release, thereby mitigating many of the adverse effects typically associated with conventional GEM treatment[32]. The IV administration of exosomes is the most common route and a convenient method for drug delivery, providing low immunogenicity and rapid therapeutic effects[33-35]. Intraperitoneal administration of exosomes could target organs affected by cancer within the peritoneal cavity, such as the ovaries[36]. Subcutaneous administration allows for a slower and more sustained release of exosomes[37,38].

Exo-GEM treatment significantly inhibited tumor growth and extended survival in tumor-bearing mice but caused minimal damage to normal tissues, suggesting exosomes are safe and effective carriers for the targeted delivery of GEM against pancreatic cancer[13]. Research on exosomes as therapeutic agents and drug delivery carriers has been predominantly carried out in animal models. Several clinical studies revealed no major toxicity or serious adverse events after administering dendritic cell-derived exosomes loaded with major histocompatibility complex class I or II peptides to enhance the immune response for the treatment of cancer patients[38-40]. Further clinical trials are essential to fully assess the long-term safety and efficacy of exosome-based therapies.

POTENTIAL CLINICAL APPLICATIONS

The study by Tang et al[17] opens new avenues for the clinical application of exosome-based drug delivery systems in the treatment of pancreatic cancer[17]. Exo-GEM could significantly impact the delivery of chemotherapy for pancreatic cancer patients. By enhancing the delivery and effectiveness of GEM, this approach may allow for lower dosages, leading to fewer side effects and an improved quality of life for pancreatic cancer patients. Additional in vivo studies are needed to validate the safety and effectiveness of Exo-GEM before it can be considered for clinical application. Several pilot clinical trials of exosome-based therapies have been launched, such as the curcumin-loaded plant exosomes for colon cancer, MSC-derived exosomes with KRAS^G12D siRNA (iExosomes) for metastatic pancreatic cancer, exosomes with antisense oligonucleotide-signal transducer and activator of transcription 6 (exoASO-STAT6)/(CDK-004) to target cancer-specific signaling pathways for patients with advanced hepatocellular carcinoma and patients with liver metastases, and vaccination with tumor antigen-loaded dendritic cell-derived exosomes (DEX2) for non-small cell lung cancer (Table 1).

Table 1 The clinical trials of cargoes for cancer therapy.

Study title	Conditions	Interventions	NCT number	Study status	Sponsor
Study investigating the ability of plant exosomes to deliver curcumin to normal and colon cancer tissue	Colon cancer	Dietary supplement: Curcumin conjugated with plant exosomes	NCT01294072	Recruiting	University of Louisville
Inhibitory exosomes in treating participants with metastatic pancreas cancer with KRASG12D mutation	KRAS NP004976.2: p.G12D; Metastatic Pancreatic Adenocarcinoma; Pancreatic ductal adenocarcinoma; Stage IV pancreatic cancer	Drug: Mesenchymal stromal cells-derived exosomes with KRASG12D siRNA	NCT03608631	Active; Not Recruiting	M.D. Anderson Cancer Center
A study of exoASO-STAT6 (CDK-004) in patients with advanced hepatocellular carcinoma and patients with liver metastases from either primary gastric cancer or colorectal cancer	Advanced hepatocellular carcinoma; Gastric cancer metastatic to liver; Colorectal cancer metastatic to liver	Drug: CDK-004	NCT05375604	Terminated	Codiak BioSciences
Trial of a vaccination with tumor antigen-loaded dendritic cell-derived exosomes	Non small cell lung cancer	Biological: DEX2	NCT01159288	Completed	Gustave Roussy, Cancer Campus, Grand Paris

Data collected from ClinicalTrials.gov accessed on August 20, 2024. exoASO-STAT6: Exosomes with antisense oligonucleotide-signal transducer and activator of transcription 6; CDK-004: Codiak BioSciences product-004; DEX: Dendritic cell-derived exosomes; NCT: National clinical trial.

CONCLUSION

The study by Tang et al[17] marks a significant advancement in cancer therapy, particularly in the treatment of pancreatic cancer. The fabrication of Exo-GEM has been optimized. By demonstrating the enhanced cytotoxicity and apoptosis-inducing effects of Exo-GEM compared to free GEM, the research highlights the potential of exosome-based drug delivery systems as a more effective and targeted approach to chemotherapy[17]. Although further research is necessary to validate these findings in vivo and explore their clinical applications, this study establishes a strong foundation for a promising new direction in cancer treatment. The use of HU-BMSCs-derived exosomes for drug delivery could potentially address some of the major challenges in current cancer therapies, offering renewed hope for patients facing this devastating disease.