P-TEFb promotes cell survival upon p53 activation by suppressing intrinsic apoptosis pathway

Area of Science:

• Oncology
• Molecular Biology
• Cancer Therapeutics

Background:

• Positive transcription elongation factor b (P-TEFb) is critical for RNA polymerase II (Pol II) pause release and a potential cancer target.
• Single-agent therapies often lack durable clinical responses, suggesting combination strategies are needed.

Purpose of the Study:

• To identify synergistic drug combinations targeting P-TEFb for colorectal cancer treatment.
• To elucidate the mechanisms by which P-TEFb inhibition interacts with antimetabolites and MDM2 inhibitors.

Main Methods:

• Screening of a comprehensive oncology library for compounds synergistic with P-TEFb inhibitors.
• Assessment of cancer cell death, cell-cycle arrest, and apoptosis induction.
• Analysis of gene expression related to p53, PI3K-AKT signaling, and apoptosis pathways.
• Evaluation of combination treatments on colorectal cancer cell spheroids.

Main Results:

• Antimetabolites (e.g., 5-fluorouracil) and MDM2 inhibitors (e.g., Nutlin-3a) showed synergy with P-TEFb inhibitors in eliciting p53-dependent colorectal cancer cell death.
• P-TEFb inhibition augmented 5-fluorouracil-induced apoptosis.
• Nutlin-3a combined with P-TEFb inhibition shifted cancer cells from cell-cycle arrest to apoptosis.
• This fate switching involved p53-dependent gene induction, repression of P-TEFb-dependent pro-survival genes, and activation of the intrinsic apoptosis pathway.
• Combination treatments induced apoptosis in cancer cell spheroids.

Conclusions:

• Co-targeting P-TEFb with antimetabolites or MDM2 inhibitors is a promising strategy for colorectal cancer.
• The combination therapy modulates key signaling pathways to promote cancer cell apoptosis.
• This approach offers a potential new avenue for eliminating cancer cells, particularly in combination with targeting intrinsic apoptosis suppressors.