Targetable Vulnerabilities in MYC-Driven B Cell Lymphomas Resistant to BCR Extinction.

Area of Science:

• Oncology
• Immunology
• Pharmacology

Background:

• Polatuzumab vedotin, a CD79B-targeting antibody-drug conjugate (ADC), shows promise in diffuse large B cell lymphoma (DLBCL) and high-grade B cell lymphoma (HGBCL).
• MYC-driven B cell lymphomas, especially those with MYC/BCL2 rearrangements, often downregulate surface B cell receptor (BCR)/CD79B, limiting ADC efficacy.
• New therapeutic strategies are needed to overcome BCR extinction in aggressive B cell lymphomas.

Purpose of the Study:

• To identify small-molecule drug vulnerabilities in BCR-extinguished aggressive B cell lymphomas.
• To explore complementary treatments for CD79B-directed ADCs in MYC-driven lymphomas.
• To investigate the mechanisms underlying drug sensitivity in BCR-negative lymphomas.

Main Methods:

• Conditional ablation of surface BCR expression in a λ-MYC mouse B cell lymphoma model.
• Screening of 1475 small-molecule compounds, including approved agents, against syngenic BCR-positive and BCR-negative tumor cells.
• Mechanistic studies involving mTOR and CDK4/6 pathways, protein synthesis, and Cyclin D3 levels.

Main Results:

• Compounds with activity against both BCR-positive and BCR-negative cells were identified.
• Inhibitors of mTORC1/2 and CDK4/6 demonstrated potent efficacy against BCR-negative lymphoma cells.
• BCR loss was linked to impaired mTOR-dependent anabolism and increased sensitivity to CDK4/6 inhibitors.

Conclusions:

• Targetable vulnerabilities exist in MYC-driven B cell lymphomas that silence BCR expression.
• mTOR and CDK4/6 inhibitors show promise as complementary therapies for aggressive B cell lymphomas.
• Combining CD79B-directed ADCs with mTOR or CDK4/6 inhibitors may overcome treatment resistance.