Tang Liu

Mesenchymal stem cells (MSCs) are multipotent stromal cells that can be obtained from various human tissues and organs. They can differentiate into a wide range of cell types, including osteoblasts, adipocytes and chondrocytes, thus exhibiting great potential in regenerative medicine. Numerous studies have indicated that MSCs play critical roles in cancer biology. The crosstalk between tumour cells and MSCs has been found to regulate many tumour behaviours, such as proliferation, metastasis and epithelial-mesenchymal transition (EMT). Multiple lines of evidence have demonstrated that MSCs can secrete exosomes that can modulate the tumour microenvironment and play important roles in tumour development. Notably, very recent works have shown that mesenchymal stem cell-derived exosomes (MSC-derived exosomes) are critically involved in cancer resistance to chemotherapy agents, targeted-therapy drugs, radiotherapy and immunotherapy. In this review, we systematically summarized the emerging roles and detailed molecular mechanisms of MSC-derived exosomes in mediating cancer therapy resistance, thus providing novel insights into the clinical applications of MSC-derived exosomes in cancer management.

Osteosarcoma is the most common primary bone malignancy in children and adolescents. Although improvements in therapeutic strategies were achieved, the outcome remains poor for most patients with metastatic or recurrent osteosarcoma. Therefore, it is imperative to identify novel and effective prognostic biomarker and therapeutic targets for the disease. Long noncoding RNAs (lncRNAs) are a novel class of RNA molecules defined as transcripts >200 nucleotides that lack protein coding potential. Many lncRNAs are deregulated in cancer and are important regulators for malignancies. Nine lncRNAs (91H, BCAR4, FGFR3-AS1, HIF2PUT, HOTTIP, HULC, MALAT-1, TUG1, UCA1) are upregulated and considered oncogenic for osteosarcoma. Loc285194 and MEG3 are two lncRNAs downregulated and as tumor suppressor for the disease. Moreover, the expressions of LINC00161 and ODRUL are associated with chemo-resistance of osteosarcoma. The mechanisms for these lncRNAs in regulating development of osteosarcoma are diverse, e.g. ceRNA, Wnt/β-catenin pathway, etc. The lncRNAs identified may serve as potential biomarkers or therapeutic targets for osteosarcoma.

The protein kinase Chk1 is required for cell cycle arrest in response to DNA damage. We have found that the 14-3-3 proteins Rad24 and Rad25 physically interact with Chk1 in fission yeast. Association of Chk1 with 14-3-3 proteins is stimulated in response to DNA damage. DNA damage results in phosphorylation of Chk1 and the 14-3-3 proteins bind preferentially to the phosphorylated form. Genetic analysis has independently implicated both Rad24 and Rad25 in the DNA-damage checkpoint pathway. We suggest that DNA damage-dependent association of phosphorylated Chk1 with 14-3-3 proteins mediates an important step along the DNA-damage checkpoint pathway, perhaps by directing Chk1 to a particular substrate or to a particular location within the cell. An additional role for 14-3-3 proteins in the DNA-damage checkpoint has been suggested based on the observation that human Chk1 can phosphorylate Cdc25C in vitro creating a 14-3-3 binding site. Our results suggest that in fission yeast the interaction between the 14-3-3 proteins and Cdc25 does not require Chk1 function and is unaffected by DNA damage, in sharp contrast to the interaction between the 14-3-3 proteins and Chk1.

Bone tissue has a strong ability to repair itself. When treated properly, most fractures will heal well. However, some fractures are difficult to heal. When a fracture does not heal, it is called nonunion. Approximately, 5% of all fracture patients have difficulty healing. Because of the continuous movement of the fracture site, bone nonunion is usually accompanied by pain, which greatly reduces the quality of life of patients. Bone marrow mesenchymal stem cells (BMSCs) play an important role in the process of nonunion. Circular RNAs (circRNAs) are a unique kind of noncoding RNA and represent the latest research hotspot in the RNA field. At present, no studies have reported a role of circRNAs in the development of nonunion. After isolation of BMSCs from patients with nonunion, the expression of circRNAs in these cells was detected by using a circRNA microarray. Alkaline phosphatase and Alizarin red staining were used to detect the regulation of osteogenic differentiation of BMSCs by hsa_circ_0074834. The target gene of hsa_circ_0074834 was detected by RNA pull-down and double-luciferase reporter assay. The ability of hsa_circ_0074834 to regulate the osteogenesis of BMSCs in vivo was tested by heterotopic osteogenesis and single cortical bone defect experiments. The results showed that the expression of hsa_circ_0074834 in BMSCs from patients with nonunion was decreased. Hsa_circ_0074834 acts as a ceRNA to regulate the expression of ZEB1 and VEGF through microRNA-942-5p. Hsa_circ_0074834 can promote osteogenic differentiation of BMSCs and the repair of bone defects. These results suggest that circRNAs may be a key target for the treatment of nonunion.

Photodynamic therapy (PDT) has achieved great success in cancer treatment. Despite its great promise, the efficacy of photodynamic immunotherapy can be limited by the hypoxia in solid tumors which is closely related to the abnormal tumor vasculature. These abnormal vasculatures are a hallmark of most solid tumors and facilitate immune evasion. Therefore, tumor vascular normalization is developed as a promising strategy to overcome tumor hypoxia, resulting in improved cancer therapy. Here, a NIR-II bio-degradable pseudo-conjugate polymer (PSP)-based photodynamic polymer is designed to deliver a vascular normalization agent, i.e., regorafenib (Reg) in nanoparticles (NP-PDT@Reg). NP-PDT@Reg under 808 nm laser irradiation (NP-PDT@Reg + L) can efficiently release Reg to improve the tumor hypoxia via vascular normalization, making more NP-PDT@Reg and oxygen enter the tumors. Moreover, NP-PDT@Reg + L can further result in generation of more reactive oxygen species (ROS) to eradicate tumor cells while inducing immunogenic cell death (ICD) to activate anti-tumor immune responses. In addition, Reg can reprogram TAM from a pro-tumor M2 phenotype to a tumor-killing M1 phenotype as well, thereby reversing the immunosuppressive tumor microenvironment. Taken together, the current study provides an innovative perspective on the development of novel nanomaterials to overcome the limitations in photodynamic immunotherapy.