Despite significant therapeutic advances, multiple myeloma (MM) remains incurable in most patients due to frequent tumor relapse. A major contributor to relapse is clonal heterogeneity, where subclones exhibit distinct mechanisms of therapy resistance, along with the presence of drug-resistant dormant cells. Eliminating these distinct populations, which often coexist in the tumor niche, is clinically challenging. Identifying survival mechanisms shared by drug-resistant proliferating and dormant cells holds potential for the simultaneous elimination of different tumor-repopulating clones.

To identify shared mechanisms of therapeutic resistance, we analyzed clinical databases and drug-resistant myeloma cell lines. We employed pharmacologic approaches to target common candidates identified in our analysis and assessed their impact on tumor progression and survival in preclinical mouse models containing both therapy-resistant and dormant cells.

We identified upregulation of several components of the Notch signaling pathway in both dormant and drug-resistant MM cells, which correlated with poor clinical outcomes in newly diagnosed MM patients. Selective blockade of NOTCH3 with a neutralizing antibody or pan-Notch inhibition with a bone-targeted inhibitor reduced tumor burden and eliminated coexisting dormant and bortezomib-resistant cells in clinically relevant models of MM disease.

Our findings reveal that NOTCH3-dependent survival programs represent a shared vulnerability in both cells refractory to therapy and dormant cells. These programs can be exploited to overcome the diverse mechanisms by which cancer cells evade therapy, potentially preventing disease relapse and extending remission in patients with MM.