A therapeutic method comprising inhibiting vascular smooth muscle cell proliferation comprising administering to a mammal an effective cytostatic antiproliferative amount of a compound of formula (I): ##STR6## wherein Z is a covalent bond; Y is H or O(C1 -C4)alkyl, R1 and R2 are individually (C1 -C4)alkyl or together with N are a saturated heterocyclic group, R3 is ethyl or chloroethyl, R4 is H or