DRUG-INDUCED LYSOSOMAL STORAGE OF SULFATED GLYCOSAMINOGLYCANS - STUDIES ON THE UNDERLYING STRUCTURE-ACTIVITY-RELATIONSHIPS

Some immunomodulatory drugs have previously been shown to induce lysos omal storage of sulfated glycosaminoglycans (sGAG) in intact organisms and cultured cells. These compounds consist of a planary aromatic rin g system and two symmetric side chains each carrying a protonizable ni trogen. The purpose of this study was to test a larger collection of s uch compounds for their potencies to induce lysosomal storage of sGAG in cultured fibroblasts of rat cornea. The cells were exposed (72 h) t o various compounds differing with respect to the aromatic ring system or the side chains. Lysosomal sGAG-storage was demonstrated by select ive cytochemical staining with cuprolinic blue. The threshold concentr ation, i.e., the concentration necessary to induce cuprolinic blue-pos itive cytoplasmic inclusions in at least 1% of the cells, was determin ed for each compound. The threshold concentrations were distributed ov er a range of 0.3-30 mu M. It Should be emphasized that the threshold concentration of a given compound is not a constant, but depends on th e volume of cell culture medium per surface area of cell monolayer, si nce the lysosomal accumulation towers the initial drug concentration i n the medium. If the ratio of medium volume : cell monolayer surface i s increased as compared with standard cell culture conditions, the thr eshold concentration will be lowered. The compounds were ranked accord ing to their threshold concentrations as determined under standard con ditions. The following conclusions can be drawn from the ranking: the type of the central aromatic ring system and the distance between the ring system and the protonizable nitrogen atoms of the side chains inf luence the potency to induce lysomomal sGAG-storage. Regarding the rin g system, the potency decreases as follows: acridine similar to anthra chinone > fenfluorenone similar to fenfluorene > xanthenone; xanthene > dibenzofuran similar to dibenzothiophene. In intact organisms, these structure-activity relationships may be superimposed by drug metaboli sm and pharmacokinetic factors.