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Quality of life is negatively affected in children with food allergy. Oral immunotherapy is an approach to food allergy that leads to patient desensitization by administering gradually increasing amounts of a given food allergen. The aim of this pilot study is to evaluate how oral immunotherapy affects quality of life in children allergic to cow milk proteins. Thirty children (aged 3–12 years) with cow milk allergy were recruited. Their parents were provided with a validated disease specific quality of life questionnaire (the food allergy quality of life questionnaire – parent form, FAQLQ-PF) before and again 2 months after completing an oral immunotherapy protocol with cow milk. A significant improvement in all the investigated domains - emotional impact, food anxiety and social and dietary limitations - was found. The separate analysis of the different age groups demonstrated that the emotional impact and the food-related anxiety improved in children older than 4, while the social domains improved in each age group. In this pilot experience, oral immunotherapy significantly improves quality of life in children with cow milk allergy. The improvement seems particularly evident in children over 4 years old, who are most likely to benefit from the oral immunotherapy approach. Further placebo-controlled studies are needed to confirm these preliminary results.

Intrinsic and acquired multidrug resistance (MDR) is an important problem in cancer therapy. MDR in human KB carcinoma cells selected for resistance to colchicine, vinblastine, or doxorubicin (former generic name adriamycin) is associated with overexpression of the "MDR1" gene, which encodes P-glycoprotein. We previously have isolated an overlapping set of cDNA clones for the human MDR1 gene from multidrug-resistant KB cells. Here we report the construction of a full-length cDNA for the human MDR1 gene and show that this reconstructed cDNA, when inserted into a retroviral expression vector containing the long terminal repeats of Moloney leukemia virus or Harvey sarcoma virus, functions in mouse NIH 3T3 and human KB cells to confer the complete multidrug-resistance phenotype. These results suggest that the human MDR1 gene may be used as a positive selectable marker to introduce genes into human cells and to transform human cells to multidrug resistance without introducing nonhuman antigens.

Considerable uncertainty surrounds the stoichiometry of coupling of ATP hydrolysis to drug pumping by P-glycoprotein, the multidrug transporter. To estimate relative turnovers for pumping of the drug vinblastine and ATP hydrolysis, we began by measuring the number of P-glycoprotein molecules on the surface of murine NIH3T3 cells expressing the human MDR1 gene. Fluorescence of cells treated with monoclonal antibody UIC2 was determined as a function of (i) amount of antibody at a fixed number of cells and (ii) increasing cell number at constant antibody. The two together gives 1.95 x 10(6) P-glycoprotein molecules/cell. Initial uptake rates of vinblastine +/- verapamil measure the ability of P-glycoprotein to extract vinblastine from the plasma membrane before it enters the cell. As a function of [vinblastine] at 37 degrees C, they give the maximum rate of this component of outward pumping as 2.1 x 10(6) molecules s-1 cell-1 or a turnover number of 1.1 s-1. Initial rates of one-way efflux as a function of [vinblastine] at 25 degrees C +/- glucose give the maximum rate of this component of pumping as 0.59 x 10(6) molecules s-1 cell-1. The ratio of ATPase activity of P-glycoprotein at 37 and 25 degrees C is 4.6. Appropriating this ratio for pumping, maximum one-way efflux at 37 degrees C is 4.6 x 0.59 = 2.7 x 10(6) molecules s-1 cell-1, a turnover number of 1.4 s-1. The vinblastine-stimulated ATPase activity of P-glycoprotein has a turnover number of 3.5 s-1 at 37 degrees C, giving 2.8 molecules of ATP hydrolyzed for every vinblastine molecule transported in a particular direction. These calculations involve several approximations, but turnover numbers for pumping of vinblastine and for vinblastine-stimulated ATP hydrolysis are comparable. Thus, ATP hydrolysis is probably directly linked to drug transport by P-glycoprotein.

We have established four cell lines derived from the human KB carcinoma cell line which express high-level multiple drug resistance. One of these lines was selected for resistance to colchicine, one was selected for resistance to colchicine in the presence of the tumor promoter, mezerein, one for resistance to vinblastine, and one for resistance to adriamycin. All of these cell lines are cross-resistant to the other selective agents. The development of multidrug resistance in these cultured human carcinoma cells is associated with a limited number of specific protein alterations revealed by high resolution two-dimensional gel electrophoresis and Western blot analysis. These protein alterations in multidrug-resistant lines include the decreased prevalence of members of a family of proteins of molecular mass 70,000 to 80,000 daltons, pI 4.8-5.0, the increased synthesis of a protein of molecular mass 21,000 daltons, pI 5.0, in the colchicine-resistant cell lines only, and the increased expression of a 170,000-dalton protein in membrane preparations from all of the resistant cells. The loss of the 70,000- to 80,000-dalton proteins in the multidrug-resistant lines, which can also be demonstrated by immunoprecipitation of these proteins with specific antisera, is associated with a loss of translatable mRNA for these proteins. These studies suggest that only a limited number of protein changes occur in multidrug-resistant cell lines.

To assess the role of phosphorylation of the human multidrug resistance MDR1 gene product P-glycoprotein for its drug transport activity, phosphorylation sites within its linker region were subjected to mutational analysis. We constructed a 5A mutant, in which serines at positions 661, 667, 671, 675, and 683 were replaced by nonphosphorylatable alanine residues, and a 5D mutant carrying aspartic acid residues at the respective positions to mimic permanently phosphorylated serine residues. Transfection studies revealed that both mutants were targeted properly to the cell surface and conferred multidrug resistance by diminishing drug accumulation. In contrast to wild-type P-glycoprotein, the overexpressed 5A and the 5D mutants exhibited no detectable levels of phosphorylation, either in vivo following metabolic labeling of cells with [32P]orthophosphate or in vitro in phosphorylation assays with protein kinase C, cAMP-dependent protein kinase, or a P-glyco-protein-specific protein kinase purified from multidrug-resistant KB-V1 cells. These results reconfirm that the major P-glycoprotein phosphorylation sites are located within the linker region. Furthermore, the first direct evidence is provided that phosphorylation/dephosphorylation mechanisms do not play an essential role in the establishment of the multidrug resistance phenotype mediated by human P-glycoprotein.

One form of multidrug resistance is due to the expression of a 170-kDa energy-dependent drug efflux pump called P-glycoprotein in the plasma membranes of human cancer cells. We have prepared conjugates of Pseudomonas toxin with the anti-P-glycoprotein monoclonal antibody MRK-16. These anti-P-glycoprotein-toxin conjugates specifically kill multidrug-resistant human KB cells. Similar conjugates could be useful in cancer therapy to reduce or eliminate multidrug-resistant tumor populations in tumors intrinsically resistant to chemotherapy or in populations that become resistant during combination chemotherapy.

An iodinated derivative of forskolin, 6-O-[[2-[3-(4-azido-3-[125I] iodophenyl)propionamido]ethyl]carbamyl]forskolin ([125I]6-AIPP-Fsk), photolabels the multidrug efflux pump P-glycoprotein in membranes prepared from the multidrug-resistant cell lines KB-V1 and KB-C1. The labeling site for [125I]6-AIPP-Fsk was localized by immunoprecipitation of tryptic fragments of P-glycoprotein labeled in KB-C1 membranes. A 6-kDa, photolabeled, tryptic fragment was immunoprecipitated by antiserum raised against residues 348-419 of P-glycoprotein, PEPG9, but not by antisera raised against flanking regions PEPG7 and PEPG11. A peptide that corresponds to residues 343-359 of P-glycoprotein inhibited immunoprecipitation of the 6-kDa fragment by antiserum against PEPG9 but had no effect on the immunoprecipitation of photolabeled fragments by antiserum against PEPG7. A second peptide, corresponding to residues 360-376, had no effect on the immunoprecipitation by antiserum against PEPG9. [125I]6-AIPP-Fsk labels the carboxyl-terminal half of P-glycoprotein, because low molecular mass tryptic fragments were immunoprecipitated by three carboxyl-terminal antisera. Therefore, [125I]6-AIPP-Fsk labels both halves of P-glycoprotein, and labeling in the amino-terminal half can be localized to residues 291-359, which span proposed transmembrane regions 5 and 6. KB-V1 membranes photolabeled with [125I]6-AIPP-Fsk and [125I]iodoarylazidoprazosin were digested with either Staphylococcus aureus V8 protease or chymotrypsin and had similar digestion patterns, suggesting that the two drugs label the same sites on P-glycoprotein.

A kinetic approach was used to analyze the mechanism by which a substitution of valine for glycine at position 185 in the multidrug transporter alters its substrate specificity so that colchicine and etoposide transport is increased, daunorubicin transport is unchanged, and vinblastine transport is decreased. Time courses for uptake and efflux of colchicine, vinblastine, etoposide, and daunorubicin for NIH/3T3 mouse cells transfected with wild-type (MDR1-G185) and mutant (MDR1-V185) strains of the human mdr1 gene were determined at room temperature in the presence and absence of an energy supply. The initial rate of vinblastine uptake was reduced approximately 5-fold by glucose feeding of ATP-depleted wild-type (MDR1-G185) cells but was only halved in MDR1-V185 transfectants. In contrast, glucose feeding decreased the initial rate of colchicine uptake approximately 4-fold in the MDR1-V185 (mutant) transfectant but not in the MDR1-G185 (wild-type) transfectant. Efflux of colchicine was accelerated > 5-fold in both the MDR1-V185 (mutant) and MDR1-G185 (wild-type) transfectants when glucose was given to raise ATP levels. The effects on initial rates of colchicine uptake accounted semiquantitatively for the increased colchicine resistance of MDR1-V185 (mutant) transfectants. Similar effects were found for etoposide in the MDR-V185 transfectants. Quinidine in the external medium greatly inhibited drug entry rates but had little effect on efflux, whereas verapamil inhibited both uptake and efflux. A possible interpretation of these data is that the multidrug transporter extracts drugs from the external and internal halves of the membrane bilayer by different paths, which are distinguishable by mutation and inhibitors.

Multidrug-resistant human tumor cells overexpress the MDR1 gene product P-glycoprotein, which is believed to function as an ATP-dependent efflux pump. In this study we demonstrate that the partially purified P-glycoprotein, when reconstituted in an artificial membrane, catalyzes drug-stimulated ATP hydrolysis. Plasma membrane proteins of a human multidrug-resistant cell line, KB-V1, were solubilized with 1.4% (wt/vol) octyl beta-D-glucopyranoside in the presence of 0.4% phospholipid and 20% (vol/vol) glycerol, and the crude detergent extract was chromatographed on DEAE-Sepharose CL-6B. The 0.1 M NaCl fraction, enriched in P-glycoprotein but devoid of Na,K-ATPase, was reconstituted by the detergent-dilution method. P-glycoprotein constituted 25-30% of the reconstituted protein in proteoliposomes. ATP hydrolysis by proteoliposomes was stimulated 3.5-fold by the addition of vinblastine but was unaffected by the hydrophobic antitumor agent camptothecin, which is not transported by P-glycoprotein. The stimulatory effect of vinblastine was observed only if the protein was reconstituted in proteoliposomes, suggesting that either the substrate binding site(s) was masked by detergent or that the conformation of the soluble P-glycoprotein might not be suitable for substrate-induced activation. Several other drugs that are known to be transported by P-glycoprotein enhanced the ATPase activity in a dose-dependent manner with relative potencies as follows: doxorubicin = vinblastine greater than daunomycin greater than actinomycin D greater than verapamil greater than colchicine. The basal and vinblastine-stimulated ATPase activities were inhibited by vanadate (50% inhibition observed at 7-10 microM) but were not affected by agents that inhibit other ATPases and phosphatases. These data indicate that the P-glycoprotein, similar to other ion-transporting ATPases, exhibits a high level of ATP hydrolysis (5-12 mumol per min per mg of protein).