PHYSICAL MAPPING OF HUMAN INSULIN-LIKE GROWTH-FACTOR-I USING SPECIFICMONOCLONAL-ANTIBODIES

The primary structure of recombinant human (h) insulin-like growth fac tor-I (IGF-I) epitopes recognized by a panel of 28 monoclonal antibodi es (mAbs) is characterized. Pairwise mAb epitope mapping defines eight 'epitopic clusters' (I-VIII) which cover nearly the entire solvent-ex posed IGF-I surface. Monoclonal antibody reactivity with 32 overlappin g synthetic peptides and with IGF-I mutants is used to associate these epitopic clusters with the probable primary IGF-I sequences recognize d. Epitopic cluster I involves residues in the C-domain and the first alpha-helix of the A-domain; clusters II, V and VII involve principall y the B-domain; clusters III and TV map to amino acid sequences (55-70 ) and (1-13) respectively; cluster VI includes the A- and B-domains; a nd cluster VIII involves mainly the C-terminal part of the B-domain. D ata indicate that this mAb panel defines 14 distinct IGF-I epitopes. T he specific inhibition of HEL 92.1.7 IGF-I-promoted proliferation by t hese mAbs was explored. Direct correlation between mAb affinity and in hibitory activity was observed except in the case of clusters III- and VII-specific mAbs. Finally, the combination of epitopic cluster I and II mAbs detect 0.5-10 ng/ml hIGF-I in a sandwich immunoassay, with no IGF-Tr crossreactivity. These anti-IGF-I mAbs are, therefore, useful for both the inhibition of IGF-I mitogenic activity and for the quanti fication of this growth factor. The potential use of this mAb panel in tumor cell growth control is discussed.