R-CHOP for non-Hodgkin lymphoma: Its effects on cancer cells, NK cell viability and cytotoxicity against B-lymphoma cell lines

Combining the anti-CD20 antibody rituximab with three chemotherapy drugs vincristine, doxorubicin, and cyclophosphamide plus the corticosteroid prednisone (R-CHOP) has been the standard first line-line therapy for many non-Hodgkin lymphomas including diffuse large B-cell lymphoma (DLBCL) during the last 20 years. Natural killer (NK) cells are believed to be the prime mediators of rituximab-induced antibody-dependent cellular cytotoxicity (ADCC). Whereas the toxicity of vincristine, doxorubicin, and cyclophosphamide against cancer cells is well-documented, little is known about their effects regarding NK cell viability and cytotoxicity against cancer cell lines. We have analyzed the effects of vincristine, doxorubicin, and cyclophosphamide plus rituximab against the DLBCL cancer cells TMD8, WSU-DLCL2, U-2932 and RI-1, and compared it with the toxicity against NK cells alone and in combinations. Furthermore, we have tested if NK cell cytotoxicity against TMD8 cells is influenced by the drugs. Vincristine, doxorubicin, and cyclophosphamide all eliminated the DLBCL cells lines in a dose-dependent manner at concentrations relevant for patients during therapy. They also decreased NK cell viability at similar concentrations. NK cytotoxicity against TMD8 cells was also reduced by all three drugs in a dose-dependent manner. Mafosfamide reduced cytotoxicity at all tested concentrations, doxorubicin at higher concentrations. NK cytotoxicity was not influenced by vincristine at or below 2 ng/ml but only at higher concentrations. Combinatorial experiments showed antagonisms between vincristine and doxorubicin but no significant synergisms, with 2 ng/ml vincristine alone being the favored in vitro condition with very efficient elimination of DLBCL cancer cells but only mild side effects on NK cell viability or cytotoxicity.