TARGETING OF SAPORIN TO HODGKINS LYMPHOMA-CELLS BY ANTI-CD30 AND ANTI-CD25 BISPECIFIC ANTIBODIES

CD25 and CD30 represent suitable target molecules for bispecific antib ody (bimAb)-driven toxin delivery to lymphoid tumour cells, We describ e two new anti-CD30/anti-saporin bimAbs (termed CD30 x sap1 and CD30 x sap2), produced by hybrid hybridomas, which react against non-cross-r eactive epitopes of the saporin molecule, and compared their effect wi th a bimAb reacting with saporin and with CD25 (CD25 x sap1). In a pro tein synthesis inhibition assay these bimAbs were able to enhance sapo rin toxicity (IC50 8.5 x 10(-9) M in the absence of mAbs) with a simil ar activity: in the presence of 10(-9) M CD30 x sap1 bimAb the IC50 wa s 2.75 x 10(-11) M, whereas with CD30 x sap2 bimAb the IC50 was 6.5 x 10(-11) M and CD25 x sapl bimAb displayed an IC50 Of 3 x 10(-11) M (as saporin). The combined use of the two anti-CD30 bimAbs further increa sed cytotoxicity by 100-fold, resulting in an IC50 of 1.9 x 10(-13) M. A Slightly less efficient improvement was obtained by combining the C D25 x sap1 bimAb with the CD30 x sap2 bimAb directed against a differe nt toxin epitope (saporin IC50 to 7 x 10-13 M). In contrast, no synerg istic effect was observed using the combination of the anti-CD25 bimAb with the anti-CD30 bimAb reacting with the same epitope of saporin (I C50 = 4.5 x 10(-11) M). Analysis of FITC-saporin binding to L540 cells by now cytometry demonstrated that the appropriate combinations of th e two anti-CD30/anti-saporin bimAbs or of the anti-CD30/anti-saporin a nd anti-CD25/anti-saporin bimAbs had a cooperative effect on the bindi ng of the ribosome-inactivating protein (RIP) to the cells, when compa red with single bimAbs.