A comparative study of the anti-proliferative effects of calmodulin antagonists in cultured cells--W7 derivatives of improved cytostatic potential.

We have compared the effects of the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalene-sulphonamide (W7) and relatives of the parent compound, modified by substituting the 5-chloro- for an iodo-residue and increasing stepwise the length of the carbon chain from 6 to 12, for their ability to inhibit cell proliferation in tissue culture. These species showed improved specificity and potency, as determined against a calcium calmodulin-dependent beef heart phosphodiesterase in vitro, exhibited time courses of inhibition similar to the parent compound W7, but were more potent at inhibiting DNA synthesis in K562 human leukaemic cells cultured in serum-free medium. The elevation observed in the percentage of cells in G1 of the cell cycle following drug exposure indicated that these drugs, like W7, arrested growth by inhibiting entry of cells into and through S phase. Higher doses of all drugs were irreversibly cytotoxic as determined by the inability of the cells to recover DNA synthetic capacity and to form colonies in soft agar or to recover their normal cell cycle distribution. We also discuss the possible implications of extracellular calmodulin and antagonism thereof on cell proliferation.