Abstract: A method is provided for inhibiting growth of cancer cells comprising contacting said cells with an effective growth-inhibiting amount of a compound of the formula (II): ##STR1## or a physiologically acceptable salt thereof, wherein A.sup.1 and A.sup.2 are individually L-amino acid residues selected from the group consisting of Ala, Pro, Gly, Glu, Leu, Lys, Phe, Ser, Val, Ile, Arg, Tyr, Thr, Asp, Asn and Gly; R.sup.1 is C.sub.1 -C.sub.6 (alkyl) which is unsubstituted or is substituted with an aromatic substituent or one or more in-chain bivalent groups selected from the group consisting of --O--, --CO--, --S--, --NH--, --CONH--, CH.dbd.CH--, and --SO.sub.2 --; Y.sup.1 and Y.sup.2 are each H, or taken together from a moiety derived from a dihydroxy compound, and R.sup.1 is H or an N-terminal protecting group.