The
tyrosine kinase inhibitors PD 69896, 153717, and 158780, which belong to the chemical class 4-[ar(alk)ylamino]pyridopyrimidines, have been characterized with respect to enzymology, target specificity, and antiproliferative effects in
tumor cells. These compounds were competitive inhibitors with respect to
ATP against purified
epidermal growth factor (
EGF) receptor tyrosine kinase and inhibited
EGF receptor autophosphorylation in A431 human
epidermoid carcinoma with IC50 values of 2085, 110, and 13 nM, respectively. Onset of inhibition was immediate once cells were exposed to these compounds, whereas recovery of receptor autophosphorylation activity after the cells were washed free of the compound was dependent on inhibitory potency. Thus, full activity returned immediately after removal of
PD 69896 but required 8 hr after exposure to
PD 158780.
PD 158780 was highly specific for the
EGF receptor in Swiss 3T3 fibroblasts, inhibiting
EGF-dependent receptor autophosphorylation and
thymidine incorporation at low nanomolar concentrations while requiring micromolar levels for
platelet-derived growth factor- and
basic fibroblast growth factor-dependent processes.
PD 158780 inhibited
heregulin-stimulated phosphorylation in the SK-BR-3 and MDA-MB-453
breast carcinomas with IC50 values of 49 and 52 nM, respectively, suggesting that the compound was active against other members of the
EGF receptor family. The antiproliferative effects of this series of compounds against A431 cells correlated precisely with the inhibitory potency against
EGF receptor autophosphorylation.
PD 158780 reduced clone formation in soft
agar of fibroblasts transformed by
EGF,
EGF receptor, or the neu oncogene but not ras or raf, further demonstrating its high degree of specificity. Finally, this compound was active against clone formation in several
breast tumors having different expression patterns of the erbB family, indicating an anticancer utility in
tumors expressing these receptors.