The characteristics of the acetylation of dapsone (avlosulfon) were found to parallel those of isoniazid and sulfamethazine in 19 subjects, thereby establishing the genetic polymorphism for the acetylation of dapsone. This polymorphism was revealed by the distribution of the ratios of the plasma concentration of acetylated to parent drug. The acetylation capacity for dapsone was shown to be a reproducible, individual characteristic. Acetylation of dapsone and deacetylation of monoacetyl dapsone occurred concurrently. Constant plasma ratios of acetylated to parent drug characteristic for the individual were attained immediately after administration of dapsone but only after several hours following administration of monoacetyl dapsone. The available data suggest that acetylation rather than deacetylation is the primary determinant of these ratios. Rates of disappearance of dapsone and monoacetyl dapsone from the plasma were the same regardless of which of the two was administered or of the acetylator phenotype of the subject. After dapsone, no differences between rapid and slow acetylators were found in the 24 hour urinary excretion of dapsone and its conjugates hydrolyzed by mild or strong acid treatment. Rapid acetylators excreted significantly more monoacetyl dapsone and its acidlabile conjugates than slow acetylators. Because these compounds accounted for only a very small fraction of the dose, it was not possible to phenotype individuals by these measurements. More dapsone and acid‐hydrolyzable conjugates of dapsone were found in 120 hour urine collections after monoacetyl dapsone than after dapsone in both phenotypes.

Summary In this report, we investigate several examples of hypoxia-induced drug resistance and compare them with P-glycoprotein associated multidrug resistance (MDR). EMT6/Ro cells exposed to drugs in air immediately after hypoxic treatment developed resistance to adriamycin, 5-fluorouracil, and actinomycin D. However, these cells did not develop resistance to colchicine, vincristine or cisplatin. When the cells were returned to a normal oxygen environment, they lost resistance. There was no correlation between the content of adriamycin and the development of adriamycin resistance induced by hypoxia. There was no difference between the efflux of adriamycin from aerobic cells and that from hypoxia-treated cells. The mRNA for P-glycoprotein was not detected in the hypoxia-treated cells. These results suggest that hypoxia-induced drug resistance is different from P-glycoprotein associated multidrug resistance.As a tumour grows, heterogeneities of cellular microenvironments occur, such as the development of oxygen gradients in the tumour as a consequence of deficient vascularisation, and cause hypoxic cells that may be resistant to radiotherapy (Sutherland, 1988). Several studies using monolayer cultures (Smith et al., 1980;Teicher et al., 1981Teicher et al., , 1985 and the multicell spheroid system (Sutherland et al., 1979) Conditions of hypoxic exposure Before being gassed with N2, the cells were supplied with 5 ml of fresh complete medium and allowed to equilibrate in a humidified 37°C incubator. Cells undergoing hypoxic stress were isolated in specially designed hypoxic chambers at room temperature (Sutherland et al., 1982). The chambers were repeatedly evacuated and filled every 15 min for 2.25 h with the appropriate gas mixtures certified to contain less than 10 ppm 02. The sealed chambers were then removed to a warm room (37'C) at a time point, t, referred to hereafter as '0' hours of hypoxia.Preparation of drugs and conditions of drug exposure All drugs used were obtained from Sigma Chemical Company. Stock solutions of adriamycin (ADR), vincristine, and actinomycin D (ACTD) were prepared with phosphatebuffered saline (PBS). Solutions of 5-fluorouracil (5-FU), colchicine, and cisplatin were made before each experiment. The solvents used were PBS for ADR, ACTD and cisplatin and distilled water for 5-FU. Absolute ethanol was used as a solvent for colchicine in order to obtain a sufficiently high concentration for the experiments. The final concentration of alcohol in the medium was 1%. As a control for the alcohol solvent, we established that 1% of absolute ethanol in cultures for 2 h had no effect on plating efficiency. Drug treatment was started under aerobic conditions at 37'C in the incubator after culture dishes were removed from the chambers at the zero time. Exposure times for ADR, ACTD and cisplatin were 1 h. A 2 h exposure time was used for 5-FU, colchicine and vincristine to cause significant cell killing. Exposure times were limited to 1-2 h to avoid the effect of release from a ORPs-induced state,...

To enable investigations of the emerging roles of cell-to-cell shuttling of L-lactate, we have developed an intensiometric green fluorescent genetically encoded biosensor for extracellular L-lactate. We demonstrate that this biosensor, designated eLACCO1.1, enables minimally invasive cellular resolution imaging of extracellular L-lactate in cultured mammalian cells and brain tissue.

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3'-Deamino-3'-(4-morpholinyl)adriamycin (MRA) and 3'-deamino-3'(3-cyano-4-morpholinyl)adriamycin (MRA-CN) were compared with adriamycin (ADR) in ADR-sensitive (P388/S) and -resistant (P388/ADR) murine leukemia cell lines with respect to cytotoxicity and cellular accumulation. MRA is only two- to threefold more cytotoxic to P388/S in culture than ADR, whereas MRA-CN is 500-fold more cytotoxic than ADR to this cell line. Yet both MRA and MRA-CN retain their potency against P388/ADR in spite of a 150-fold decrease in potency for ADR. The observed noncross-resistance of both MRA and MRA-CN in P388/ADR correlates with their increased cellular uptake and retention relative to ADR and the inability of P388/ADR to exclude these analogs as readily as it does ADR. The decreased uptake of MRA and MRA-CN in P388/ADR relative to P388/S (1.5 to 2.0-fold), the increased efflux, and the ability of verapamil to enhance cellular uptake of these analogs in P388/ADR, as it does with ADR, all indicate that the mechanism of ADR-resistance effects ADR and the morpholino analogs in a similar manner but to far different extents. The potent cytotoxicity of MRA-CN appears to be related to strong cellular interactions of the drug with macromolecules that are characterized by its nonextraction from cells by chloroform: methanol or 10 M urea and may therefore represent covalent binding.

Plasma and tissue levels of doxorubicin (DXR) and doxorubicinol (DXR-OL) were measured fluorometrically after high-pressure liquid chromatography at 1, 3, and 24 h following one, nine, and 24 doses of 1.0 mg DXR/kg or one and eight doses of 4.0 mg DXR/kg, IP, to rats. Comparison of plasma levels of DXR found following single and multiple doses suggests significant build-up of DXR at 1 h with successive doses, but not at 3 h. Liver exhibited substantially higher levels of DXR (on a per gram of protein basis) than did plasma, and multiple doses did not produce higher levels than did a single dose. In contrast, the heart accumulated DXR slowly, attaining levels after multiple dosing in excess of those found in the liver. Skeletal muscle exhibited dose-related levels similar to those for heart but the absolute levels of DXR in muscle were only about one-tenth of those observed in heart. DXR-OL was at very low levels of less than or equal to 4% of the DXR levels in the tissues; it was, however, a major circulatory metabolite, attaining levels in the plasma as high as 85% of the concentration of DXR.