Introduction

Canine multicentric lymphoma is commonly treated with CHOP (cyclophosphamide, hydroxydaunorubicin, vincristine [oncovin], prednisone) combination cytotoxic chemotherapy. Proteasome inhibitors are employed clinically in combination with CHOP for the treatment of human hematological malignancies, including lymphoma. The aim of this study was to determine the effect of proteasome inhibitors bortezomib and ixazomib on a canine B cell lymphoma cell line (CLBL-1) cell viability, and to investigate whether they sensitize cells to CHOP chemotherapy agents. We hypothesized that proteasome inhibitors will reduce CLBL-1 viability and will be synergistic with CHOP compounds.

Methods

The effects of proteasome inhibitors and CHOP on CLBL-1 viability were determined using a resazurin assay. Drugs were combined over a range of doses that maintained a IC50:IC50 ratio as well as a clinically relevant Cmax:Cmax ratio.

Results

After 48 hr exposure, the IC50 of bortezomib was 15.1 nM and of ixazomib was 59.14 nM. The IC50 after 48 hr exposure to the CHOP compounds cyclophosphamide (as 4-HC), hydroxydaunorubicin, and vincristine were 1.623 µM, 111.5 nM, and 156.1 nM, respectively. Proteasome inhibitors plus hydroxydaunorubicin had a synergistic effect on CLBL-1 viability after IC50:IC50 co-treatment. Vincristine had an antagonistic effect at the same respective dose ratio, but when combined using a Cmax:Cmax ratio, proteosome inhibitors synergized with vincristine. We are currently investigating CLBL-1 responses to cyclophosphamide and prednisone in combination with proteasome inhibition.

Conclusion

These results may have clinical utility, as proteasome inhibition could potentially be used with a synergizing CHOP compound to improve CHOP responsiveness for canine lymphoma patients.

Funding Information

OVC Pet Trust