Studies on lysosomes. 13. Effects of stilbamidine and hydroxystilbamidine on in vitro and in vivo systems

Fluoro-Gold: composition, and mechanism of uptake

Determining the mechanism by which fluorescent retrograde neuronal tracers are taken up requires knowledge of their composition. It has been claimed that Fluoro-Gold, a retrogradely transported fluorescent neuronal tracer, is 2-hydroxy-4,4'-diamidinostilbene (hydroxystilbamidine), an amidine antibiotic. However, this appears questionable, since the fluorescence spectrograms reported for Fluoro-Gold differ markedly from the spectrograms previously reported for purified hydroxystilbamidine. To help clarify the mechanism by which Fluoro-Gold might be taken up, it was decided to examine its composition and determine whether hydroxystilbamidine was its active agent. Fluoro-Gold was found by mass spectrometry to contain a component with a molecular weight of 280 Da (identical to that of hydroxystilbamidine), and fluorescence spectroscopy demonstrated the existence of a substance with a fluorescence spectrum similar to that of purified hydroxystilbamidine. Although a major fluorescent impurity was also observed, chromatographic separation of different fluorescent components of Fluoro-Gold suggested that the fraction resembling hydroxystilbamidine was responsible for its retrograde labeling of cells. It is concluded that hydroxystilbamidine is the active constituent of Fluoro-Gold. Chemically, hydroxystilbamidine is a weak base. In this respect it resembles True blue, DAPI, Granular blue, bis-benzimide, Nuclear yellow, and several other retrogradely transported molecules. It is suggested that these agents cross cell membranes in their uncharged form and are trapped in lysosomes and endosomes by a favorable pH gradient. Thus, the uptake of this type of retrograde tracer may be an example of a well-understood process occurring widely throughout biological systems: the trapping of weak bases in acidic cellular compartments.

Chloroquine, hydroxystilbamidine, and dapsone inhibit resorption of fetal rat bone in organ culture

Three potential inhibitors of lysosomal enzyme release, chloroquine, hydroxystilbamidine, and dapsone were tested for their effects on the release of previously incorporated 45Ca and beta (beta)-glucuronidase from fetal rat long bones cultured in a chemically defined medium. At concentrations of 10(-5) to 10(-8)M, all three agents were able to inhibit the stimulation of bone resorption by parathyroid hormone (PTH) or prostaglandin E2 (PGE2). Inhibition was seen at concentrations which did not alter the uptake of (3H)-2-deoxy-glucose or the incorporation of (3H)-thymidine in bone. While the inhibitors blocked the stimulation of beta-glucuronidase release by PTH and PGE2, they could also cause a direct increase in total beta-glucuronidase content and release. Hence the usual strong correlation between the release of beta-glucuronidase and 45Ca was no longer seen in the presence of inhibitors. These data indicate that chloroquine, hydroxystilbamidine, and dapsone are potent inhibitors of bone resorption which may act by blocking the release of lysosomal enzymes in cells stimulated by PTH or PGE2, but may have a different effect on other cell populations.

Inhibition of respiratory syncytial virus-host cell interactions by mono- and diamidines

Several aromatic mono- and diamidines were found to block cell fusion induced by respiratory syncytial virus. The best inhibitors were able to achieve complete suppression of syncytium formation at a concentration of 1.0 microM. Inhibition occurred in respiratory syncytial virus-infected HEp-2 and CV-1 cells, but the same inhibitors were ineffective in preventing fusion induced by parainfluenza virus type 3. The fusion inhibitors did not reduce single-cycle virus yields, but did reduce multiple-cycle yields. In addition, the active compounds caused a significant retardation of respiratory syncytial virus penetration. The mechanism by which amidines interfere with respiratory syncytial virus-host cell interactions is unknown, but parallels can be drawn between antiviral activity and the ability of the compounds to inhibit certain trypsin-like proteases.

Isolation of giant silk fibroin polysomes and fibroin mRNP particles using a novel ribonuclease inhibitor, hydroxystilbamidine

Hydroxystilbamidine isethionate, a dye capable of binding to both DNA and RNA, has been found to be a powerful inhibitor of cellular ribonucleases. A procedure has been developed that, with the aid of this compound, permits the preparative isolation of giant silk fibroin polyribosomes from the posterior silk gland of Bombyx mori. The polyribosomes contain approximately 45-112 ribosomal particles, as judged by electron microscopy. Treatment of giant fibroin polyribosomes with EDTA releases a particle that sediments at 125S. This mRNP particle contains biologically active silk fibroin mRNA, as judged by cell-free translation in an mRNA-dependent reticulocyte cell-free system.

Immunosuppression by hydroxystilbamidine isethionate, a lysosome-stabilizing, anti-proteolytic, antifungal drug

Hydroxystilbamidine (HSB) is a potent suppressor of the plaque-forming cell response of mice injected with heterologous erythrocytes. HSB, given in varying doses and injection schedules, suppressed both the primary and secondary immune responses to bovine serum albumin. Apparently the effect is not simply a toxic effect on spleen cells, because there was no appreciable difference in cell numbers between control and HSB-treated mice. The effect of HSB was most apparent in the early phase of the immune respone.