TORC1 and class I HDAC inhibitors synergize to suppress mature B cell neoplasms

Area of Science:

• Oncology
• Molecular Biology
• Pharmacology

Background:

• Cancer progression involves enhanced proliferative signaling and loss of cell cycle regulation.
• Activation of the mTOR pathway and deregulation of the Cyclin D/retinoblastoma (Rb) pathway are common in lymphoid malignancies like multiple myeloma (MM).

Purpose of the Study:

• To evaluate the synergistic effects of combining the mTOR inhibitor sirolimus with the histone deacetylase inhibitor entinostat.
• To assess the efficacy of this combination in various lymphoid malignancy models and patient samples.

Main Methods:

• A dose-matrix screening approach was used to test the drug combination in human MM cell lines.
• In vitro and ex vivo testing was performed on mouse plasmacytoma (PCT), human Burkitt's lymphoma (BL), mantle cell lymphoma (MCL) cell lines, and primary MM patient samples.
• Co-culture systems were used to simulate the tumor microenvironment.

Main Results:

• The combination of sirolimus and entinostat demonstrated high activity and synergy in a panel of human MM cell lines.
• Synergistic activity was observed in mouse PCT, human BL, and MCL cell lines, as well as in primary MM patient samples.
• The combination enhanced cell cycle arrest and apoptosis, with minimal effects on healthy donor cells.
• Molecular analysis revealed increased expression of cell cycle negative regulators (CDKN1A, CDKN2A) and decreased expression of growth/survival effectors (Cyclin D, BCL-XL, BIRC5, MAPK).

Conclusions:

• The combination of sirolimus and entinostat represents a promising synergistic therapeutic strategy for lymphoid malignancies.
• This combination effectively targets key cancer pathways, induces cell death, and shows efficacy across diverse models and patient samples.
• The drug combination maintains activity in the presence of protective tumor microenvironment interactions and spares healthy cells.