# c-FOS Confers Stem Cell-like Features to Multiple Myeloma Cells in a Bone Marrow Microenvironment

## TL;DR

The study shows that c-FOS helps multiple myeloma cells survive in the bone marrow and act like stem cells, suggesting that blocking c-FOS could improve treatment outcomes.

## Contribution

This study is the first to show that c-FOS gives multiple myeloma cells stem cell-like traits in the bone marrow environment.

## Key findings

- c-FOS upregulation is linked to poor prognosis and drug resistance in multiple myeloma cells.
- Inhibiting c-FOS with T-5224 reduces the regeneration of myeloma cells in a mouse model.

## Abstract

Multiple myeloma (MM) is the second most common hematologic malignancy and has a poor prognosis. Although the outcomes of MM have markedly improved with the approval of novel agents, the high incidence of relapse means that MM remains incurable. The bone marrow microenvironment (BMME) contributes to drug resistance and minimal residual disease (MRD), which is a major source of relapse in patients with MM. However, the underlying molecular mechanisms are not fully understood. We have previously shown that the upregulation of the AP-1 transcription factor c-FOS confers lenalidomide resistance by maintaining IRF4 expression in MM cells. In this study, we show that upregulated expression of c-FOS confers a poor prognosis and cancer stem cell-like features, including drug resistance, within BMME, both in vitro and in vivo, via IRF4 upregulation; and that inhibition of c-FOS by the AP-1 inhibitor, T-5224, prevents regeneration of MM cells via IRF4 downregulation in a murine serial transplantation assay. These results suggest a functional role for c-FOS in conferring cancer stem cell-like features to MM cells in the BMME for the first time. Therefore, c-FOS inhibition may be an effective treatment strategy for improving the outcomes of patients with MM by eliminating drug-resistant cancer stem cell-like MM cells in MRD.