Specific activation of the prodrug mitomycin phosphate by a bispecific anti-CD30/anti-alkaline phosphatase monoclonal antibody.

The bispecific monoclonal antibody (Bi-MAb) HRS-3/AP-1 was developed by somatic hybridization of the 2 mouse hybridoma cell lines HRS-3 and AP-1, which produce monoclonal antibodies with reactivity against the Hodgkin's- and Reed-Sternberg cell-associated CD30 antigen and alkaline phosphatase, respectively. After an active incubation with alkaline phosphatase, respectively. After an active incubation with alkaline phosphatase, purified whole immunoglobulin molecules and F(ab')2 fragments of the Bi-MAb were equally effective in converting a relatively noncytotoxic prodrug, mitomycin phosphate (MOP), into mitomycin alcohol, which was 100 times more toxic to the Hodgkin's- and Reed-Sternberg cell line L540 (CD30+) than MOP. The cytotoxic activity of MOP was unaffected when the cells were pretreated with either the Bi-MAb or the enzyme alone. The Bi-MAb HRS-3/AP-1 did not bind to HPB-ALL cells (CD30-) and was not able to activate MOP on these cells. In cocultivation experiments with HPB-ALL and L540 cells, the activation of MOP by the Bi-MAb HRS-3/AP-1 and alkaline phosphatase led to considerable cytotoxicity against the antigen-negative bystander cells. Thus, this immunotherapeutic approach might be effective in tumors in which not all the tumor cells express the respective tumor antigen.