Non-lethal proteasome inhibition activates pro-tumorigenic pathways in multiple myeloma cells

Area of Science:

• Hematology
• Oncology
• Molecular Biology

Background:

• Multiple myeloma (MM) is a bone marrow cancer driven by plasma cell proliferation.
• Proteasome inhibitors (PIs) improve MM treatment outcomes but do not prevent relapse.
• Understanding MM cell survival mechanisms after PI therapy is crucial for overcoming resistance.

Purpose of the Study:

• To investigate molecular responses in MM cells after sub-lethal proteasome inhibition.
• To identify mechanisms by which MM cells survive and potentially cause relapse after PI treatment.

Main Methods:

• Treatment of MM cells with various proteasome inhibitors (bortezomib, epoxomicin, Rub999, PR671A, Rub1024) at non-lethal doses.
• Phosphoproteomic profiling to analyze protein phosphorylation changes.
• Cytokine and chemokine profiling to assess the secretory environment.

Main Results:

• Bortezomib and epoxomicin showed toxicity in MM cells at low concentrations.
• Non-lethal PI treatment induced cell-type-specific phosphoproteomic changes, activating STAT3 and STAT6.
• MM cells secreted increased immunosuppressive cytokines (IL6, IL8) and reduced T cell-attracting chemokines (CXCL10).

Conclusions:

• MM cells surviving PI therapy adapt by activating pro-tumorigenic signaling pathways (STAT3/6).
• These surviving cells create an immunosuppressive bone marrow microenvironment, fostering tumor growth and relapse.
• Targeting these adaptive mechanisms may offer new therapeutic strategies for relapsed multiple myeloma.