Specific Targeting of Antiapoptotic Bcl-2 Proteins as a Radiosensitizing Approach in Solid Tumors

Area of Science:

• Oncology
• Molecular Biology
• Cancer Therapy

Background:

• Acquired resistance to radiotherapy, often due to the avoidance of therapy-induced apoptosis, remains a significant challenge in cancer treatment.
• The B-cell lymphoma 2 (Bcl-2) protein family, including Bcl-2, Mcl-1, and Bcl-x_L, plays a crucial role in regulating apoptosis, making them attractive therapeutic targets.

Purpose of the Study:

• To investigate the potential of specific inhibitors of Bcl-x_L (WEHI-539), Bcl-2 (ABT-199), and Mcl-1 (S63845) as radiosensitizers across various solid tumors.
• To evaluate the synergistic effects of these inhibitors combined with fractionated radiotherapy in Non-Small-Cell Lung Cancer (NSCLC), Head and Neck Squamous Cell Carcinoma (HNSCC), and synovial sarcoma cell lines.

Main Methods:

• Utilized Western blot to detect protein expression levels of Bcl-2 family members.
• Employed flow cytometry to quantify apoptosis and assess cell death.
• Exposed cancer cell lines (NSCLC, HNSCC, synovial sarcoma) to fractionated radiation with and without Bcl-2 protein inhibitors.

Main Results:

• High expression and upregulation of Bcl-x_L during radiotherapy indicated radioresistance in HNSCC and synovial sarcoma, but not in NSCLC.
• Combined therapy with Bcl-x_L inhibition synergistically enhanced radiotherapy effects in radioresistant cell lines across all tested entities.
• Mcl-1 inhibition significantly augmented radiotherapy in NSCLC cell lines, irrespective of Mcl-1 expression levels.

Conclusions:

• Targeting Bcl-x_L shows promise in overcoming radiotherapy resistance in HNSCC, synovial sarcoma, and NSCLC.
• Mcl-1 inhibition is a potentially valuable strategy for enhancing radiotherapy in NSCLC, warranting further investigation.