Academic Research Report: MCL1 Copy Number Gain as a Therapeutic Target for Osteosarcoma

Academic Background

Osteosarcoma (OS) is a primary malignant bone tumor that predominantly affects children and adolescents. Although the treatment regimen combining surgery with chemotherapy was established in the 1970s and remains the standard therapy, progress in the treatment of osteosarcoma has been limited, especially for patients with metastatic or recurrent osteosarcoma, whose five-year survival rate is only 20%-30%. Recent clinical trials have shown poor efficacy of immune checkpoint inhibitors in osteosarcoma treatment, further highlighting the urgent need for new therapeutic strategies.

The genomic characteristics of osteosarcoma are marked by widespread copy number variations (CNVs) and structural variations (SVs), which may drive disease progression and malignant transformation. Although mutations in the TP53 and RB1 pathways are common in osteosarcoma, the specific driver gene mutations and fusion genes have not been fully elucidated. Therefore, identifying actionable oncogenic drivers in osteosarcoma is a current research focus.

MCL1 (Myeloid Cell Leukemia 1) is an anti-apoptotic protein belonging to the Bcl-2 family, and its overexpression in various cancers is closely associated with apoptosis evasion in tumor cells. MCL1 expression is regulated by multiple mechanisms, including activation of the PI3K/AKT/mTOR pathway. In recent years, BH3 mimetics targeting Bcl-2 family proteins (such as Venetoclax) have achieved significant clinical success, but the application of MCL1 inhibitors remains under investigation.

Source of the Paper

This paper was authored by Satoshi Takagi, Mikako Nakajima, and colleagues from the Japanese Foundation for Cancer Research (JFCR) and the University of Tokyo, and published in the journal Oncogene in 2024. The primary objective of the paper is to explore the frequency of MCL1 copy number gain in osteosarcoma and its potential as a therapeutic target.

Research Process and Results

1. High Frequency of MCL1 Copy Number Gain in Osteosarcoma

The research team first analyzed 41 osteosarcoma patient specimens using fluorescence in situ hybridization (FISH) and found that 46.3% of patients exhibited MCL1 gene amplification. Further genomic DNA quantitative PCR (qPCR) analysis revealed that 45.5% of osteosarcoma cell lines (⁵⁄₁₁) had MCL1 copy number gain. Immunoblotting analysis showed that MCL1 was widely expressed in all osteosarcoma cell lines, while Bcl-2 expression levels were low.

2. Correlation Between MCL1 Copy Number Gain and Sensitivity to MCL1 Inhibitors

To validate whether MCL1 copy number gain correlates with sensitivity to MCL1 inhibitors, the research team treated osteosarcoma cell lines with several Bcl-2 family inhibitors (such as Mik665 and Azd5991). The results showed that cell lines with MCL1 copy number gain were more sensitive to MCL1 inhibitors. Pearson correlation analysis revealed that MCL1 copy number variations (rather than mRNA levels) were significantly correlated with sensitivity to MCL1 inhibitors.

3. Synergistic Effect of MCL1 Inhibitors and IGF-1R Inhibitors

The research team further discovered that the combination of MCL1 inhibitors and IGF-1R inhibitors (such as Osi906) significantly enhanced apoptosis in osteosarcoma cells. The IGF-1R signaling pathway plays an important role in the pathogenesis of osteosarcoma, and the 1q21.2-3 region, where MCL1 is located, also contains multiple genes related to the IGF-1R/PI3K pathway (such as PIP5K1A, TARS2, OTUD7B, and ENSA), which also exhibited copy number gain in MCL1-amplified osteosarcoma cells. Immunoblotting analysis confirmed the expression of IGF-1R and IR in osteosarcoma cell lines, and IGF-1 treatment rapidly increased MCL1 expression.

4. In Vivo Validation of Combination Therapy Efficacy

The research team validated the therapeutic efficacy of combining MCL1 inhibitors with IGF-1R inhibitors in mouse xenograft models. The results showed that the MCL1 inhibitor Mik665 significantly inhibited tumor growth in MCL1-amplified osteosarcoma, and the combination with Osi906 further enhanced this effect. In models with lower MCL1 copy numbers, the combination therapy showed relatively weaker but still significant anti-tumor activity.

5. MCL1 Copy Number Gain in Patient Specimens

Through FISH and immunohistochemical (IHC) analysis of 41 osteosarcoma patient specimens, the research team found that 14.6% of patients had high-level MCL1 copy number gain, while 31.7% had low-level gain. IHC staining further confirmed high expression of MCL1 protein in specimens with MCL1 amplification.

Conclusions and Significance

This study demonstrates that MCL1 copy number gain frequently occurs in osteosarcoma and is closely associated with sensitivity to MCL1 inhibitors. The combination of MCL1 inhibitors and IGF-1R inhibitors significantly enhances apoptosis in osteosarcoma cells and inhibits tumor growth in vivo. These findings provide a new therapeutic strategy for osteosarcoma patients with MCL1 amplification, and MCL1 copy number gain can serve as a predictive biomarker for the efficacy of combination therapy.

Research Highlights

1. High Frequency of MCL1 Copy Number Gain: The study found that approximately 46.3% of osteosarcoma patients have MCL1 copy number gain, providing a theoretical basis for the clinical application of MCL1 inhibitors.
2. Synergistic Effect of MCL1 Inhibitors and IGF-1R Inhibitors: The combination of MCL1 inhibitors and IGF-1R inhibitors significantly enhances apoptosis in osteosarcoma cells, overcoming drug resistance.
3. In Vivo Validation: Mouse xenograft models confirmed the significant efficacy of combination therapy in inhibiting osteosarcoma tumor growth, providing strong support for clinical trials.
4. Discovery of Biomarkers: MCL1 copy number gain can be detected via FISH and IHC, offering a new biomarker for personalized treatment in osteosarcoma patients.

Other Valuable Information

The research team also found that the 1q21.2-3 region, where MCL1 is located, frequently undergoes structural variations in various cancers, suggesting that gene amplification in this region may have significant biological implications in other cancers. Additionally, the team developed a FISH-based detection method for rapid diagnosis of MCL1 copy number gain, providing technical support for clinical application.

Summary

The findings of this study offer new insights into the treatment of osteosarcoma, particularly for patients with MCL1 amplification. The combination therapy of MCL1 inhibitors and IGF-1R inhibitors not only demonstrates significant anti-tumor effects but also provides a new biomarker for personalized treatment in osteosarcoma. Future research will further validate the clinical application prospects of this therapeutic strategy.