A series of benzylidenemalononitrile derivatives previously synthesized by condensing aromatic
aldehydes with
malononitrile derivatives are known as
tyrphostins. In this study, 32
tyrphostins were synthesized, 19 of which are novel compounds. Both hydroxylated derivatives and compounds containing heteroaromatic moieties were prepared. We have confirmed and extended the observation that the
tyrphostins displayed an enhancement in their ability to inhibit the
epidermal growth factor (
EGF) receptor tyrosine kinase domain as the number of
hydroxyl groups on the aromatic portion was increased. IC50 values of 1-5 microM were readily achieved. Some inhibitory activity was seen with the heteroaromatic structures, with two compounds exhibiting IC50 values of 56 and 77 microM. However, these derivatives were poor inhibitors of the
EGF receptor tyrosine kinase activity as compared to the hydroxylated derivatives. The ability of the 32
tyrphostins synthesized in the present study to inhibit proliferation of a human breast
adenocarcinoma cell line (MCF-7) was determined using [3H]
thymidine incorporation as a measure of
DNA synthesis. Some of the compounds containing
pyridine,
imidazole or
thiophene portions displayed antiproliferative activity comparable to that of
tyrphostins prepared from
3,4,5-trihydroxybenzaldehyde. The lack of inhibitory effect of these heteroaromatic compounds on the
EGF receptor tyrosine kinase activity suggests that their antiproliferative activity is not related to inhibition of
EGF receptor function. As the growth of the MCF-7 cell line is governed by other factors, such as the
insulin-like growth factors (IGFs) and
oestradiol, it is also still to be established whether the antiproliferative activity of the hydroxylated
tyrphostins is directly related to inhibition of the
EGF receptor tyrosine kinase activity.