In classical Hodgkin lymphoma, the malignant Reed–Sternberg cells express the cell surface marker CD30. Brentuximab vedotin is an antibody–drug conjugate (ADC) that selectively delivers a potent cytotoxic agent, monomethyl auristatin E (MMAE), to CD30-positive cells. Although brentuximab vedotin elicits a high response rate (75%) in relapsed/refractory Hodgkin lymphoma, most patients who respond to brentuximab vedotin eventually develop resistance.

We developed two brentuximab vedotin–resistant Hodgkin lymphoma cell line models using a pulsatile approach and observed that resistance to brentuximab vedotin is associated with an upregulation of multidrug resistance-1 (MDR1). We then conducted a phase I trial combining brentuximab vedotin and cyclosporine A (CsA) in patients with relapsed/refractory Hodgkin lymphoma.

Here, we show that competitive inhibition of MDR1 restored sensitivity to brentuximab vedotin in our brentuximab vedotin–resistant cell lines by increasing intracellular MMAE levels, and potentiated brentuximab vedotin activity in brentuximab vedotin–resistant Hodgkin lymphoma tumors in a human xenograft mouse model. In our phase I trial, the combination of brentuximab vedotin and CsA was tolerable and produced an overall and complete response rate of 75% and 42% in a population of patients who were nearly all refractory to brentuximab vedotin.

This study may provide a new therapeutic strategy to combat brentuximab vedotin resistance in Hodgkin lymphoma. This is the first study reporting an effect of multidrug resistance modulation on the therapeutic activity of an ADC in humans. The expansion phase of the trial is ongoing and enrolling patients who are refractory to brentuximab vedotin to confirm clinical activity in this population with unmet need.