The farnesyl protein transferase inhibitor SCH66336 is a potent inhibitor of MDR1 product P-glycoprotein.

P-glycoprotein (Pgp)-mediated drug efflux is a major factor contributing to the variance of absorption and distribution of many drugs, particularly cancer chemotherapeutics. Multidrug resistance (MDR) is caused largely by the efflux of therapeutics out of the tumor cell by Pgp, resulting in reduced efficacy of chemotherapy. SCH66336, a farnesyl transferase inhibitor in development for cancer therapy, was examined in the present study for its ability to inhibit Pgp. In a test system consisting of a NIH-G185 cell line presenting an overexpressed amount of the human transporter Pgp, known Pgp inhibitors, such as cyclosporin A, paclitaxel, verapamil, tamoxifen, and vinblastine, were demonstrated to inhibit the Pgp-mediated efflux of daunorubicin. SCH66336 significantly inhibited daunorubicin transport with an IC50 of about 3 microM and similarly affected the transport of rhodamine 123 with a potency similar to cyclosporin A. Additionally, by an ATP-hydrolysis assay, SCH66336 was shown to decrease Pgp-mediated ATP hydrolysis by >70% with a Km of 3 microM. This observation indicates that SCH66336 directly interacts with the substrate binding site of Pgp, a quality unique to SCH66336 and its analogues, although not inherent to farnesyl transferase inhibitors in general. Moreover, low concentrations of SCH66336 exhibit synergy with the Pgp substrate/inhibitors paclitaxel, tamoxifen, and vinblastine respectively by significantly potentiating their inhibition of Pgp. Treatment with SCH66336 would be predicted to be synergistic with coadministered cancer therapeutics that are substrates of Pgp. A further benefit of coadministration of SCH66336 could be reduced chemotherapy dosage, hence, lower exposure to normal cells and, therefore, less undesired toxicity.

Two transport binding sites of P-glycoprotein are unequal yet contingent: initial rate kinetic analysis by ATP hydrolysis demonstrates intersite dependence.

The ATP-dependent transport enzyme known as P-glycoprotein (P-gp) confers multidrug resistance (MDR) against many unrelated drugs and xenobiotics. To understand better the broad substrate specificity of the enzyme as well as the mechanism of substrate transport out of the cell, it is critical to characterize the substrate binding sites. Since approximately 1 ATP is hydrolyzed per transport event, phosphate release rate provides a steady-state kinetics assay. Notably, the substrate H33342 causes a decrease in the baseline hydrolysis of ATP (probably due to competition for transport with an endogenous membrane lipid substrate) providing an excellent tool for a comprehensive graphical kinetic analysis of the interaction of substrate pairs at the transport site(s) allowing the determination of inhibition type and hence characterization of transport binding sites. The substrate H33342 interacted with quinidine, progesterone, and propranolol in a non-competitive manner, indicating that binding of H33342 precludes active transport of these other substrates at a distinct site. Compounds such as TPP+ and verapamil, and perhaps also nicardipine, interacted with H33342 as mixed-type inhibitors. This type of interaction results from a reduced affinity at the opposing active site by a factor of alpha and sometimes a partial activity of a fraction beta. Indeed, H33342 binding caused a roughly four-fold reduced affinity for TPP+. Using this definitive approach to inhibition kinetics, we were able to establish traits of a second transport site in P-gp. Therefore, the sites are unequal; however, the performance at one site is contingent on the other being unoccupied, and transport is also sometimes mitigated when the other site is occupied.

Microleakage of Class I and II Composite Resin Restorations Using a Sonic-resin Placement System.

OBJECTIVES: To determine microleakage of posterior Class I and II restorations using the SonicFill composite resin system. METHODS AND MATERIALS: Eighty previously extracted third molars were randomly assigned to four preparation/restoration groups (n=20): Group A: Class I preparations restored with SonicFill system/bulk fill; Group B: Class II preparations restored with SonicFill system/bulk fill; Group C: Class I preparations restored with Herculite Ultra composite resin/incremental technique; and Group D: Class II preparations restored with Herculite Ultra composite resin/incremental technique. Class I preparations were approximately 3.0 mm in width buccolingually and 3.0 mm in depth. Class II preparations were approximately 3.0 mm in width buccolingually, 1.5 mm in axial depth, and 4.0 mm in gingival depth. In all groups, the enamel and dentin surfaces were conditioned with Kerr 37.5% phosphoric acid, followed by application of Optibond Solo Plus adhesive system. Following restoration, the specimens were thermocycled, immersed in methylene blue dye, and embedded in acrylic resin. Specimen blocks were sectioned in the mesiodistal direction, with marginal dye penetration (microleakage) examined using a 20× binocular microscope. Class I and II restoration microleakage was scored separately using a 0-3 ordinal ranking system. Statistical analyses were conducted using nonparametric testing at the p < 0.05 level of significance. RESULTS: Significantly less microleakage was associated with both Class I restorative groups (A and C), SonicFill bulk fill and Herculite Ultra incremental fill, compared to the Class II restorative groups (B and D), SonicFill/bulk fill and Herculite Ultra/incremental fill. CONCLUSIONS: According to the results of this study, the materials (SonicFill vs Herculite Ultra), C-factors, and insertion techniques (bulk vs incremental) did not appear to be significant influences with regard to marginal microleakage; however, the type of preparation cavity (Class I vs Class II) and the subsequent bonding surface (enamel vs dentin [cementum]) proved to be significant factors.

Total orthotopic small bowel allotransplantation in the dog. Features of atypical rejection and graft-versus-host reaction.

The critical histologic review of our experience with small bowel allotransplantation in the dog is presented. While "classical" rejection with dense small cell infiltration and mucosal destruction does occur, more common is the "atypical" rejection reaction in which cellular infiltration is sparse. This "atypical" rejection was characterized by a significant decrease of mucosal epithelial structures with increased mitotic figures in crypt cells and frequent vascular changes, including segmental fibrinoid necrosis and thrombosis with or without overlying mucosal destruction. Substantial regenerating capacity of bowel mucosa tends to compensate for the destruction, complicating the histology. The host lymph nodes and spleen present a histologic picture highly suggestive of GVH reaction. The reduction in host lymphocytes in these organs from karyorrhexis with replacement by histiocytes and subsequently by plasma cells is described. It is emphasized that rejection and GVH are not mutually exclusive and occur simultaneously. The decrease of functional mucosal mass could well account for the nutritional malsequelae. Also, the weakening of immune structures on the host and the graft side may predispose to catastrophic enterogenous infections, perhaps explaining the large number of animals that die without overt signs of rejection following small bowel transplantation.

Factors leading to delay in the diagnosis and affecting survival of children with head and neck rhabdomyosarcoma.

Rhabdomyosarcoma of the head and neck often presents with vague symptoms which mimic other disease conditions. These factors lead to undue delay in the establishment of the correct diagnosis and the delivery of acceptable therapy, including surgery, radiation therapy, and chemotherapy. There is, however, evidence of improved results of treatment of these tumors since the addition of multiple drug chemotherapy to surgery and radiotherapy.

Involvement of cytochrome P450, glutathione S-transferase, and epoxide hydrolase in the metabolism of aflatoxin B1 and relevance to risk of human liver cancer.

In recent years there has been considerable interest in the effect of variations in activities of xenobiotic-metabolizing enzymes on cancer incidence. This interest has accelerated with the development of methods for analyzing genetic polymorphisms. However, progress in epidemiology has been slow and the contributions of polymorphisms to risks from individual chemicals and mixtures are often controversial. A series of studies is presented to show the complexities encountered with a single chemical, aflatoxin B1 (AFB1). AFB1 is oxidized by human cytochrome P450 enzymes to several products. Only one of these, the 8,9-exo-epoxide, appears to be mutagenic and the others are detoxication products. P450 3A4, which can both activate and detoxicate AFB1, is found in the liver and the small intestine. In the small intestine, the first contact after oral exposure, epoxidation would not lead to liver cancer. The (nonenzymatic) half-life of the epoxide has been determined to be approximately 1 sec at 23 degrees C and neutral pH. Although the half-life is short, AFB1-8,9-exo-epoxide does react with DNA and glutathione S-transferase. Levels of these conjugates have been measured and combined with the rate of hydrolysis in a kinetic model to predict constants for binding of the epoxide with DNA and glutathione S-transferase. A role for epoxide hydrolase in alteration of AFB1 hepatocarcinogenesis has been proposed, although experimental evidence is lacking. Some inhibition of microsome-generated genotoxicity was observed with rat epoxide hydrolase; further information on the extent of contribution of this enzyme to AFB1 metabolism is not yet available.

Ultrastructure of malignant histiocytoma arising in the acromion.

The ultrastructural features of a malignant histiocytoma of the acromial process of the scapula were studied. Material was obtained from two surgical biopsy specimens and an amputation specimen from the tumor. Cells possessing characteristics of histiocytes, fibroblasts, xanthoma cells, and multinucleated giant cells were present throughout the tumor. Smaller numbers of undifferentiated cells and lymphocytes were also observed. Intimate cytoplasmic interdigitations between adjacent tumor cells were found, and instances of degenerating intracytoplasmic cells, possibly representing phagocytosis, were observed. Specimens stained with periodic acid-Schiff reagent with and without exposure to diastase, examined by light microscopy, showed that numerous cells contained phagocytized material consisting of degenerating cells rather than cytoplasmic glycogen. Intraumor lymphocytes apparently represented an inflammatory reaction to the tumor. The tumor giant cells and xanthoma cells were probably modified histiocytes. Results of the study were compared with previous reports of ultrastructural studies of malignant histiocytoma of soft tissues. Fundamental similarities between such studies and this one suggested that the progenitor cell is a histiocyte, whether arising in bone or in soft tissues, and that the progenitor cell is capable of differentiation in both histiocytic and fibroblastic directions.

Sarcomatous renal tumor of childhood. An electron microscopic study.

A review of 106 cases of Wilms' tumor revealed five examples of a distinctive, monomorphic, sarcomatous renal tumor. Electron microscopic studies suggested that such tumors have their origin from the blastemal cap cells of the developing metanephros. These variants of Wilms' tumor are more likely to metastasize to bone and have a poorer prognosis than the usual type of nephroblastoma.

Malignant "histiocytic" lymphoma in childhood.

Forty-one cases of childhood "histiocytic" lymphoma were studied morphologically and immunologically to determine whether this tumor type is composed of true histiocytic cells. Lysozyme and alpha-1-antichymotrypsin were used as markers for histiocytes, and cytoplasmic immunoglobulins were used as markers for B cells. Both indirect immunofluorescence and immunoperoxidase methods were used for functional characterization of tumor cells. Eight different subgroups were identified in the series, and only one case was proved to be true histiocytic lymphoma. When survival was evaluated for different subgroups, excluding convoluted lymphocytic, unclassified, and true histiocytic lymphomas, mixed follicular cell lymphoma had the most favorable prognosis; six of seven patients survived for at least one year. Immunoblastic lymphoma, by contrast, had an unfavorable prognosis; none of four patients were alive one year after diagnosis. The difference is statistically significant (P < 0.05) by chi-square analysis. Other groups of lymphoma (large cleaved, large noncleaved, and small noncleaved) had an intermediae prognosis (three of five, six of nine, and five of nine patients surviving at one year). Our results indicate that "histiocytic" lymphoma is a morphologically heterogeneous group of neoplasms, mostly not related to true histiocytes, and that morphologic subclassification may be useful in predicting prognosis.

Malignant fibrous histiocytoma arising from chronic ulcer.

A patient had malignant fibrous histiocytoma that developed in a chronic ulcer. Squamous cell carcinoma can develop on long-standing ulcers, but malignant fibrous histiocytoma developing in an ulcer is extremely rare.

Quantifying the cognitive trajectories of extrapolated movements.

Subjects' extrapolations of a piecewise constant-velocity trajectory and a constant-acceleration trajectory were mapped out over a sequence of trials that required only a button-press response. Without any performance feedback, subjects' extrapolations of both trajectories approximated an acceleration segment followed by a constant-velocity segment. With performance feedback, subjects' extrapolations of the constant-acceleration trajectory approached optimal performance. Subsequent withdrawal of the feedback shifted the entire extrapolated trajectory. These feedback-related changes in the extrapolated trajectory can be interpreted as changes in two parameters of a cognitive representation of the movement pattern.

Activation and detoxication of aflatoxin B1.

Aflatoxin B1 (AFB1) is a potent hepatocarcinogen in experimental animals and a hazard to human health in several parts of the world. Implementation of rational intervention plans requires understanding of aspects of the roles of individual chemical steps involved in its disposition. AFB1 is activated to AFB1 exo-8,9-epoxide primarily by cytochrome P450 (P450) enzymes, particularly P450 3A4. However, P450 3A4 and other P450s also oxidize AFB1 to less dangerous products. The exo-epoxide is unstable in H2O (t1/2 1 s at 25 degreesC, k=0.6 s-1) and the diol product undergoes base-catalyzed rearrangement to a dialdehyde that reacts with protein lysine residues. AFB1 exo-8, 9-epoxide reacts with DNA to give adducts in high yield (>98%). This interaction is characterized by a Kd of approximately 1.4 mM, intercalation between base pairs, and rapid reaction with the guanyl N7 atom (k approximately 40 s-1). A proton field on the periphery of DNA is postulated to catalyze hydrolysis and also conjugation. Rat and especially human epoxide hydrolase show very little rate acceleration of hydrolysis of AFB1 exo- or endo-8,9-epoxide. However, glutathione transferases (GSTs) can catalyze AFB1 exo-8,9-epoxide conjugation. Kinetic analysis indicates a range of ratios of kcat/Kd varying from 10 to 1700 s-1 M-1, with the polymorphic GST M1-1 having the highest activity of the human GSTs. Studies with human hepatocytes indicate a major role for GST M1-1 in AFB1 conjugation and that the model chemoprotective agent oltipraz can act by both inducing GSTs and inhibiting P450s.

Antimyosin and antirhabdomyoblast sera: their use for the diagnosis of childhood rhabdomyosarcoma.

Antisera against myosin of human normal skeletal muscle and against rhabdomyoblasts of autopsy-proved rhabdomyosarcoma were raised in white rabbits, purified, and assessed for their usefulness in the diagnosis of childhood rhabdomyosarcoma. The specificity of the antisera was tested by both immunofluorescence and immunoperoxidase methods in seven cases of autopsy-proved rhabdomyosarcoma, five of malignant lymphoma, three of neuroblastoma, and two of Ewing's sarcoma. Antimyosin serum tested positive for all cases of rhabdomyosarcoma and negative for other types of tumor. Antirhabdomyoblast serum was positive in all cases of rhabdomyosarcoma and cross-reacted with cases of neuroblastoma and Ewing's tumor, although the intensity of staining was much decreased. Our results indicate that antimyosin serum is specific for childhood rhabdomyosarcoma and can be used to differentiate this from other childhood "round cell" tumors.

Organ preservation injury in small bowel transplantation.

Histological features of preservation injury were studied in a dog model of total small bowel transplantation. It was remarkable that substantial microscopic injury was evident during cold ischemia, unlike in other organ systems. This was early in onset and was related to the duration of cold storage. There was further progression of injury during reperfusion, as expected. Nevertheless, the small bowel was noted to have substantial ability to recover from this storage- and reperfusion-related injury. Histological features of damage and recovery are described in detail.

Composite microfiller content and its effect on fracture toughness and diametral tensile strength.

Previous studies have examined the relationship between total filler content in hybrid restorative composites and some of their mechanical properties. This investigation evaluated the effect of varying the amount of microfiller in an experimental hybrid composite on fracture toughness (single edge-notch technique) and diametral tensile strength. The microfiller content in the experimental hybrid composite was varied from 0-44 wt% for seven specimen groups, while the total filler content ranged from 77-84 wt%. It was found that 9 wt% microfiller loading produced the highest mean fracture toughness (1.33 MPa.m(1/2)) and 44 wt% loading produced the lowest mean value (0.80 MPa.m(1/2)). Only the 9 wt% microfiller content group differed significantly in fracture toughness from the other specimen groups. The diametral tensile strength displayed only small differences for the range of microfiller content studied with mean values ranging from 42.1-49.6 MPa. Additional research on the viscoelastic properties of these heavily filled hybrid composites may provide some insight into the differences for the fracture toughness and diametral tensile strength results.

Treatment strategy for nodular renal blastema and nephroblastomatosis associated with Wilms' tumor.

Nodular renal blastema and nephroblastomatosis were present in 8 of 118 patients (6.8%) with Wilms' tumor. Five of these 8 patients (63%) had bilateral Wilms' tumors. Two had hemihypertrophy. Preoperative renal angiograms were accurate in detecting these metanephric anomalies. The surgical approach consisted of removal of the most diseased kidney and biopsy for diffuse tumors and wedge resections for localized tumors for the remaining kidney. Postoperatively, radiation was administered when tumor extended outside the kidney. Chemotherapy consisted of vincristine and dactinomycin for 18 mo and adriamycin for 6 mo. This method of management resulted in tumor-free survival of these 8 patients for 1--44 mo (median 24 mo). Nodular renal blastema and nephroblastomatosis may possibly develop into Wilms' tumor. All of these three conditions respond to surgery, chemotherapy, and radiation. When a Wilms' tumor is encountered, it is better to explore and possibly biopsy the opposite kidney. There is a place for second-look laparotomy in this spectrum of congenital anomalies.

P-glycoprotein-mediated efflux as a major factor in the variance of absorption and distribution of drugs: modulation of chemotherapy resistance.

Active efflux of many therapeutics and other xenobiotics from cells and tissues by P-glycoprotein (P-gp) can cause dramatic effects on bioavailability. This expulsion of compounds from cells is known as a major form of multiple drug resistance (MDR). Often a significant barrier to oral absorption at the intestine, P-gp also protects the liver, brain, placenta, testes, adrenal gland and other tissues from cytotoxic insult. Due to the wide tolerance of substrate recognition, P-gp can often be the mechanism for significant pharmacokinetic drug interactions when two or more drugs are competing for the P-gp transport site. P-gp levels are also inducible and can be even further elavated in cancer cells, thus contributing to the confounding pleiotropic resistance to chemotherapy and poor treatment prognosis. Consequently, a broad scope of research over 20 years has led to the evaluation of co-therapies intended to augment chemotherapy by inhibiting P-gp. This review includes a list of the currently known P-gp inhibiting adjuvant candidates described in the literature, with associated references and summary data. The summary catalogue of P-gp modulators illustrates the ardent pursuit to overcome this form of therapy resistance and gives examples of clinical success and failure.

Citric acid consumption and the human dentition.

The habitual and abusive use of fruits and foods containing citric acid can cause serious dissolution effects on human tooth enamel. Because these effects can occur so easily, this paper suggests that foods and fruits containing citric acid, as well as other acids, could be definite contributors to the many other forms of idiopathic erosion so often observed by the dentist. There is a need for continued research and study in this area.

Clinical performance of bonded amalgam restorations at 42 months.

BACKGROUND: Despite a lack of data based on clinical research, many positive characteristics have been attributed to the placement of amalgam restorations with an adhesive resin liner. METHODS: For 42 months, and authors followed two groups of subjects who had amalgam restorations placed in a previous study. In this double-blind study, these subjects had been randomly assigned to have amalgam restorations placed with an adhesive liner or with a copal varnish placed under all restorations and a bulk base of zinc phosphate cement for deeper lesions. The authors evaluated anatomical form, marginal adaptation, retention and the presence of secondary caries at six, 18, 30 and 42 months. RESULTS: At 42 months, the authors found that all restorations in both groups still were retained, were free of secondary caries and were rated clinically acceptable. No difference between the groups was found for any category (P > .05; analysis). CONCLUSIONS: Placement of amalgam restorations with adhesive liners was found to produce results equivalent to that of traditional methods over a 42-month period. CLINICAL IMPLICATIONS: Practitioners wary of using new methods that have not undergone thorough clinical testing can feel comfortable placing adhesive liners under amalgam restorations.

Reduction of postoperative pain: a double-blind, randomized clinical trial.

The authors investigated the capability of two commonly used basing techniques to reduce postoperative sensitivity. The authors measured the time it took the subjects to respond to a standardized stimulus of cold water (cold response measure, or CRM) at baseline and one week after treatment. The authors found no significant reduction in the mean CRM for the group receiving Amalgambond Plus (Parkell), but they did find a significant decrease in the mean CRM for the group receiving Copalite (Harry J. Bosworth Co.) with or without Vitrebond (3M). The authors concluded that the subjects in the Amalgambond Plus group experienced no more sensitivity to cold at one week postoperative than they did at baseline, while the subjects in the Copalite/Vitrebond group did.