Nature of interaction between basic fibroblast growth factor and the antiangiogenic drug 7,7-(carbonyl-bis[imino-N-methyl-4,2- pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino])bis-(1,3- naphthalene disulfonate)

PNU145156E (7,7-(carbonyl-bis[imino-N-methyl-4,2- pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino])bis-(1,3- naphthalene disulfonate)) is a naphthalene sulfonic distamycin A derivative that interacts with heparin-binding growth factors. Because PNU145156E inhibits tumor angiogenesis, it was selected for clinical development. Picosecond time-resolved fluorescence emission and anisotropy were used to characterize the binding of PNU145156E to the basic fibroblast growth factor (a protein associated with tumor angiogenesis). A decrease in PNU145156E fluorescence lifetime was observed as a function of human basic fibroblast growth factor (bFGF) concentration. Nonlinear least-squares fitting of the binding isotherm yielded K(d) = 145 nM for a single class of binding sites. Time-resolved anisotropy gave K(d) = 174 nM. K(d) = 150 nM was independently verified by quantitative high-performance affinity chromatography. The displaced volume of the complex, calculated from its rotational correlation time, fitted a sphere of 1:1 stoichiometry. These results account for the formation of a tight yet reversible PNU145156E:bFGF complex. An evaluation of PNU145156E fluorescence lifetimes in various solvents has highlighted the forces involved in stabilizing the complex. These are mostly electrostatic- hydrophobic in nature, with a relatively low contribution from hydrogen bonding. Both polar and nonpolar groups are involved on the protein-binding site within a largely hydrophobic cleft. A potential binding trajectory, based on a combination of these results with site-directed chemical modification and known bFGF x-ray structure, is suggested.