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Updated: Jul 11, 2025
Cytotoxic Efficacy of Photodynamic Therapy in Osteosarcoma Cells In Vitro
Published on: March 18, 2014
In vitro and in vivo killing effects of methionine enkephalin on osteosarcoma
Hai Huang1, Xiaonan Wang2, Shuling Zhang3
1Department of Bone Oncology, the People's Hospital of Liaoning Province, Shenyang, Liaoning Province 110016, China.
Objective:
This study aimed to investigate the underlying regulatory effects of methionine enkephalin (MENK) on osteosarcoma.
Methods:
The Cell Counting Kit-8 assay, clone formation, wound healing, transwell assay, and flow cytometry were performed to measure the effects of MENK on the proliferation, migration, invasion, and apoptosis of MG-63 and Saos-2 cells. Opiate growth factor receptor expression (OGFr) in cells was stably knocked down using siRNA. A tumor model was established by inoculating MG-63 cells into mice. Flow cytometry was performed to identify alterations in mice bone marrow, spleen, and tumor tissue immune cells. The phenotype of tumor-associated macrophages was determined using immunohistochemistry. After OGFr knockdown or/and treatment with MENK, Bax, Bcl-2, caspase 3, caspase 9, and PARP expression levels were characterized using qRT-PCR, western blot, and WES, respectively.
Results:
MENK could significantly inhibit the proliferation, invasion, and migration of MG-63 and Saos-2, arrest the cell cycle in the G0/G1 phase, upregulate Bax, caspase 3, caspase 9, and PARP expression, and downregulate Bcl-2 expression. Tumor size and weight were lower in the MENK group than those in the control group. MENK-treated mice exhibited a reduced ratio of CD11b + Gr-1 + myeloid-derived suppressor cells. MENK increased the ratio of M1-type macrophages and decreased the proportion of M2-type macrophages in tumor tissue. Furthermore, the level of TNF-α significantly increased while that of IL-10 decreased in MENK-treated mice. The effect of MENK could be partly reversed by OGFr knockdown.
Conclusion:
MENK reduces the abundance of myeloid-derived suppressor cells, induces M1 polarization of macrophages, and exhibits an inhibitory effect on osteosarcoma.
Insights
Methionine enkephalin (MENK) inhibits osteosarcoma cell growth and migration. MENK also reduces immunosuppressive cells and promotes anti-tumor immunity in mouse models.
Area of Science:
- Oncology
- Immunology
- Molecular Biology
Background:
- Osteosarcoma is a primary bone malignancy with limited treatment options.
- Methionine enkephalin (MENK) is an endogenous opioid peptide with potential anti-cancer properties.
- Understanding MENK's regulatory effects is crucial for developing novel osteosarcoma therapies.
Purpose of the Study:
- To investigate the regulatory effects of methionine enkephalin (MENK) on osteosarcoma.
- To elucidate MENK's impact on osteosarcoma cell proliferation, migration, invasion, and apoptosis.
- To assess MENK's influence on the tumor immune microenvironment.
Main Methods:
- In vitro assays (CCK-8, clone formation, wound healing, Transwell, flow cytometry) were used to evaluate MENK's effects on MG-63 and Saos-2 cells.
- Opiate growth factor receptor (OGFr) knockdown was performed using siRNA.
- A mouse xenograft model was established to assess MENK's in vivo efficacy and immune modulation.
- Gene and protein expression (Bax, Bcl-2, caspases, PARP) were analyzed via qRT-PCR, Western blot, and WES.
Main Results:
- MENK significantly inhibited osteosarcoma cell proliferation, invasion, and migration, inducing G0/G1 cell cycle arrest.
- MENK treatment upregulated pro-apoptotic markers (Bax, caspase 3/9, PARP) and downregulated anti-apoptotic Bcl-2.
- In vivo, MENK reduced tumor growth, decreased myeloid-derived suppressor cells, and promoted M1 macrophage polarization, increasing TNF-α and decreasing IL-10.
- OGFr knockdown partially reversed MENK's effects, indicating its involvement in MENK's mechanism.
Conclusions:
- MENK exhibits significant anti-osteosarcoma activity by inhibiting tumor cell growth and metastasis.
- MENK modulates the tumor immune microenvironment by reducing suppressive myeloid cells and promoting M1 macrophage polarization.
- MENK's therapeutic potential in osteosarcoma warrants further investigation, potentially involving OGFr signaling.
