MDM2 inhibition enhances proteasome inhibitor activity even in TP53-mutant multiple myeloma models
Background: Targeting proteasome inhibitor resistance
A preclinical study published in Cells found that combining an MDM2 inhibitor with a proteasome inhibitor can reduce cancer cell viability even in multiple myeloma models with TP53 mutations. The findings were observed in cell lines and patient-derived samples; this was not a clinical trial evaluating patients’ treatment responses or survival benefit.
Multiple myeloma is a cancer of plasma cells in the bone marrow. Because cancer cells must continually process proteins to sustain proliferation and immunoglobulin production, they are vulnerable to proteasome inhibitors (PIs), which block protein degradation. Resistance can emerge during treatment, prompting research into factors that modulate drug response.
The researchers performed a genome-wide CRISPR activation (CRISPRa) screen, which increases gene expression, in the carfilzomib (CFZ)-sensitive AMO-1 cell line. Separately, they tested 320 inhibitors in combination with CFZ in PI-resistant U266 cells. Both approaches identified MDM2, an E3 ubiquitin ligase that attaches ubiquitin to proteins, as a shared candidate.
Key findings: Combination effects in cell lines and patient samples
AMO-1 cells with increased MDM2 expression had higher viability upon CFZ exposure and recovered faster than controls after treatment at a lethal concentration. This supports a role for MDM2 in helping cells withstand CFZ-induced proteotoxic stress.
Conversely, combining the MDM2 inhibitor NVP-CGM097 with CFZ or bortezomib reduced viability compared with single-agent treatment in six PI-sensitive and four PI-resistant cell lines. The effect was observed regardless of TP53 mutation status in the cell lines tested. In resistant U266 cells treated with 20 nM CFZ and 10 μM NVP-CGM097, Excess over Bliss (EOB), a measure of how much the observed effect exceeds that predicted by the Bliss independence model, exceeded 0.5, supporting synergy. These concentrations were conditions used in this cell experiment, not patient doses.
Mechanistic analyses showed increased levels of the cell-cycle regulator p21, G1-phase arrest, and reduced c-MYC. In TP53-mutant models, the researchers also observed increased DNA damage markers and reduced phosphorylation of the damage-response proteins ATR and BRCA1. Genetically lowering MDM2 expression likewise increased p21 and enhanced CFZ sensitivity, supporting the target’s role.
The combination effect persisted throughout the 10-day observation period in co-culture with bone marrow stromal cells. In 13 patient-derived samples, the proportion of CD138-positive plasma cells decreased compared with single-agent treatment. An effect was also observed in samples with del(17p), a deletion of the short arm of chromosome 17 associated with TP53 loss.
Implications and outlook: Questions to address before clinical use
These findings support the possibility that the effect of combining MDM2 inhibition with a PI does not depend solely on normal p53 function. However, the extent to which c-MYC reduction contributes to synergy remains unresolved, as does whether suppression of the DNA damage response precedes cell death.
Most patient samples came from people with asymptomatic or newly diagnosed multiple myeloma. The findings therefore do not establish that the combination overcomes resistance in patients with relapsed or refractory disease. No in vivo validation was performed, and it is uncertain whether the concentrations used in vitro correspond to drug exposures achievable in patients.
In peripheral blood mononuclear cells (PBMCs) from eight healthy donors, viability decreased only modestly at the highest concentration tested. Results in mature blood cells, however, cannot establish bone marrow safety. Given the known hematologic toxicity of MDM2 inhibitors, hematopoietic progenitor cells and bone marrow function require separate assessment.
The study design, results, and limitations are available in the full paper.
Proteasome inhibitors (PIs) are central to multiple myeloma (MM) therapy; however, resistance remains a major clinical challenge, particularly in relapsed/refractory disease. To identify functional mediators of carfilzomib (CFZ) resistance, we performed complementary gain-of-function CRISPR activation and pharmacological screening approaches. These unbiased strategies converged on the E3 ubiquitin ligase MDM2 as a modulator of PI response. MDM2 transactivation enhanced MM cell survival and accelerated recovery following CFZ exposure, supporting a causal role in proteotoxic stress tolerance. Pharmacologic inhibition of MDM2 with NVP-CGM097 synergized with CFZ across multiple PI-sensitive and PI-resistant MM cell lines, irrespective of
This study presents MDM2 as a functional regulator of proteasome inhibitor resistance and adds evidence to support further development of a strategy that inhibits both targets. Possible next steps include reproducing the effects in samples from patients with relapsed or refractory disease, including those with TP53 abnormalities, and evaluating tumor suppression, drug exposure, and bone marrow toxicity together in animal models. Comparing the exposure range associated with combination effects against damage to hematopoietic progenitor cells could help assess whether clinical evaluation is feasible. The current findings alone cannot justify changing patients’ treatment choices and do not guarantee efficacy or safety in patients with del(17p).