NEW MODULAR DELIVERY SYSTEM FOR DIAGNOSTIC AND THERAPEUTIC PRE-TARGETING USING TAUTOMER-SPECIFIC MONOCLONAL-ANTIBODY EM-6-47 AND 3-SUBSTITUTED ADENINES

We have developed a new modular affinity system for the 2-step deliver y of functional molecules to target cells. The system is based on the tautomer-specific monoclonal antibody (MAb) EM-6-47, which binds to 3- and 3,8-substituted adenines with high affinity (K-a > 10(9) l/mol) w ithout crossreacting with naturally occurring purine derivatives. This MAb serves as the hapten-specific fusion partner to produce bispecifi c MAbs (bs-MAbs) recognizing a target cell antigen and a low-m.w. hapt en as carrier molecule for, e.g., radionuclides. Either the C-8 or the N-3 position of adenines can be used for conjugation with effector mo lecules; the remaining position may be substituted with different moie ties to modulate the pharmacokinetics of the haptens. Different 3- and 3,8-substituted adenines conjugated to the chelates DOTA and DTPA or to the drug daunomycin were synthesized. Adenine-chelate derivatives w ere efficiently labeled with In-111 and Y-90, while high-affinity bind ing of 3-substituted adenines to MAb EM-6-47 remained almost unaffecte d by the conjugation to radiochelates. To confirm the validity of the delivery system, a prototype bs-MAb, EM-168-47, was generated by somat ic cell fusion of MAb EM-6-47 and MAb EM-168-2, the latter recognizing a surface antigen on canine hematopoietic cells. Two-step targeting a ssays in vitro verified the bs-MAb-mediated, dose-dependent delivery o f In-111-labeled adenine-chelate derivatives to myeloid cells. This sy stem represents a powerful tool for new pre-targeting approaches relyi ng on bs-MAbs and low-m.w. haptens. Suitable cellular antigens can be targeted by fusing the appropriate MAbs with hapten-specific MAb EM-6- 47, and tailor-made 3-substituted adenines may be labeled with diagnos tic or therapeutic: radionuclides, cytotoxic drugs or other functional molecules. Int. J. Cancer 77:610-619, 1998. (C) 1998 Wiley-Liss, Inc.