TILORONE-INDUCED LYSOSOMAL LESIONS - THE BISBASIC CHARACTER OF THE DRUG IS ESSENTIAL FOR ITS HIGH POTENCY TO CAUSE STORAGE OF SULFATED GLYCOSAMINOGLYCANS

The immunomodulatory agent tilorone {2,7-[2-(diethyl-amino) ethoxy]flu oren-9-one} and congeners are potent inducers of lysosomal storage of sulphated glycosaminoglycans (GAGs) in animals and cultured fibroblast s of animals and man. All potent inducers of GAG storage hitherto desc ribed are bisbasic polycyclic aromatic compounds. They are accumulated in lysosomes and disturb the degradation of GAGs, mainly dermatan sul phate. It has been proposed that the drugs crosslink the polyanionic G AG chains giving rise to undegradable drug-GAG complexes. This hypothe sis implies that the bisbasic character of the drug molecules is essen tial for the side effect in question. In the present study, this was t ested by comparing tilorone and its monobasic derivative (MT) with res pect to (i) induction of GAG storage in cultured bovine corneal fibrob lasts and (ii) physicochemical interactions with GAGs in vitro. The in tralysosomal concentration of MT achieved after 1-3 days was of the sa me order of magnitude as previously shown for tilorone. Nevertheless, under conditions that did not enhance the secretion of a lysosomal enz yme (beta-hexosaminidase, EC 3.2.1.52), the ability of MT to cause sto rage of [S-35]GAGs was significantly lower than that of tilorone. Morp hological observations showed that MT was much more potent in causing lysosomal storage of polar lipids than of GAGs. CD spectroscopy with t ilorone revealed that the presence of GAGs caused the primarily achira l drug molecules to display CD. This suggested a helical orientation o f the tilorone molecules within GAG-drug complexes, and short intermol ecular distances which allowed electronic coupling of the aromatic rin g systems of adjacent drug molecules. In contrast, MT failed to displa y any induced optical activity, indicating the absence of highly order ed GAG-drug complexes. In conclusion, the present results show that th e substitution of the planar aromatic ring system with two basic side chains is essential for the high potency of tilorone in inducing lysos omal GAG storage. This is paralleled by, and presumably causally relat ed to, strong physicochemical interactions with GAGs.