Phase III, multicenter, double-blind, randomized study of letrozole, an aromatase inhibitor, for advanced breast cancer versus megestrol acetate

PURPOSE

To compare two doses of letrozole (0.5 mg and 2.5 mg every day) and megestrol acetate (40 mg qid) as endocrine therapy in postmenopausal women with advanced breast cancer previously treated with antiestrogens.

PATIENTS AND METHODS

This double-blind, randomized, multicenter, multinational study enrolled 602 patients, all of whom were included in the primary analysis in the protocol. Patients had advanced or metastatic breast cancer with evidence of disease progression while receiving continuous adjuvant antiestrogen therapy, had experienced relapse within 12 months of stopping adjuvant antiestrogen therapy given for at least 6 months, or had experienced disease progression while receiving antiestrogen therapy for advanced disease. Tumors were required to be estrogen receptor- and/or progesterone receptor-positive or of unknown status. Confirmed objective response rate was the primary efficacy variable. Karnofsky Performance Status and European Organization for Research and Treatment of Cancer quality-of-life assessments were collected for 1 year.

RESULTS

There were no statistically significant differences among the three treatment groups for overall objective tumor response. Patients treated with letrozole 0.5 mg had improvements in disease progression (P =.044) and a decreased risk of treatment failure (P =.018), compared with patients treated with megestrol acetate. Letrozole 0.5 mg showed a trend (P =.053) for survival benefit when compared with megestrol acetate. Megestrol acetate was more likely to produce weight gain, dyspnea, and vaginal bleeding, and the letrozole groups were more likely to experience headache, hair thinning, and diarrhea.

CONCLUSION

Given a favorable tolerability profile, once-daily dosing, and evidence of clinically relevant benefit, letrozole is equivalent to megestrol acetate and should be considered for use as an alternative treatment of advanced breast cancer in postmenopausal women after treatment failure with antiestrogens.

Capsaicin receptor VR1 and ATP-gated ion channel P2X3 in human urinary bladder

OBJECTIVES

To determine the presence, distribution and molecular forms of the vanilloid receptor VR1, and confirm the presence and distribution of the ATP-gated ion channel P2X3 in the human urinary bladder. Materials and methods Normal urinary bladder tissues were obtained at postmortem from four subjects. Eight urinary bladder biopsies were also taken from patients with detrusor hyper-reflexia treated with intravesical resiniferatoxin. The specimens were studied using affinity-purified specific antibodies to VR1 and P2X3 by Western blotting and immunocytochemistry, and compared with immunostaining using antibodies to the pan-neuronal marker PGP 9.5 and Schwann cell marker S-100.

RESULTS

VR1- and P2X3-immunoreactive fine nerve fibres were scattered throughout the suburothelium of the normal bladder and cystoscopic biopsies, and traversed the muscle layer. They had a similar distribution to PGP 9.5-immunoreactive fibres, but there were fewer, suggesting localization in subsets of axons. Western blot studies showed an expected 100-kDa VR1 protein and a P2X3-immunoreactive 66-kDa protein. Conclusion VR1 and P2X3 are present in the human urinary bladder and may contribute to distinct pathophysiological states of bladder overactivity, in accord with their differential expression in sensory neurones. Intravesical vanilloids act via VR1 and are effective in the treatment of detrusor hyper-reflexia. P2X3 may represent a selective therapeutic target for other causes of overactive bladder.

Activation of hepatocyte growth factor (HGF) by endogenous HGF activator is required for metanephric kidney morphogenesis in vitro

The interaction of hepatocyte growth factor (HGF) with c-Met has been implicated in morphogenesis of the kidney, lung, mammary gland, liver, placenta, and limb bud. HGF is secreted as an inactive zymogen and must be cleaved by a serine protease to initiate Met signaling. We show here that a serine protease specific for HGF, HGF activator (HGFA), is expressed and activated by the ureteric bud of the developing kidney in vivo and in vitro. Inhibition of HGFA activity with serine protease inhibitors reduced ureteric bud branching and inhibited glomerulogenesis and nephrogenesis. Activated HGF rescued developing kidneys from the effects of inhibitors. HGFA was localized around the tips of the ureteric bud in developing kidneys, while HGF was expressed diffusely throughout the mesenchyme. These data show that expression of HGF is not sufficient for development, but that its activation is also required. The localization of HGFA to the ureteric bud and the mesenchyme immediately adjacent to it suggests that HGFA creates a gradient of HGF activity in the developing kidney. The creation and shape of gradients of activated HGF by the localized secretion of HGF activators could play an important role in pattern formation by HGF responsive tissues.

Asthma outcomes at an inner-city school-based health center

Childhood asthma has reached near-epidemic levels in the US cities. Innovative strategies to identify children with asthma and prevent asthma morbidity are needed. This study measured asthma outcomes after initiation of an inner-city elementary school health center with a schoolwide focus on asthma detection and treatment. The site was an inner-city elementary school in Minneapolis, Minn. The study design incorporated a pre and post comparison with a longitudinal cohort of children (n = 67) and a cross-sectional cohort of children before (n = 156) and after (n = 114) the intervention. Hospitalization rates for asthma decreased 75% to 80% over the study period. Outpatient visits for care in the absence of asthma symptoms doubled (p < .01), and the percentage of students seeing a specialist for asthma increased (p < .01). Use of peak flow meters, use of asthma care plans, and use of inhalers also improved (p < .01). While no change occurred in school absenteeism, parents reported that their children had less awakening with asthma and that asthma was less disruptive to family plans. This schoolwide intervention that included identification of children with asthma, education, family support, and clinical care using an elementary school health center was effective in improving asthma outcomes for children.

Biphasic behavior of the high-spin-->low-spin relaxation of [Fe(btpa)](PF6)2 in solution (btpa = N,N,N',N'-tetrakis(2-pyridylmethyl)-6,6'-bis(aminomethyl)-2,2'- bipyridine)

The light-induced high-spin-->low-spin relaxation for the Fe(II) spin-crossover compounds [Fe(btpa)](PF6)2 and [Fe(b(bdpa))](PF6)2 in solution, where btpa is the potentially octadentate ligand N,N,N',N'-tetrakis(2-pyridylmethyl)-6,6'-bis(aminomethyl)-2,2'-bipyridine and b(bdpa) is the analogous hexadentate ligand N,N'-bis(benzyl)-N,N'-bis(2-pyridylmethyl)-6,6'-bis(aminomethyl)-2,2'- bipyridine, respectively, has been studied by temperature-dependent laser flash photolysis. [Fe(b(bdpa))](PF6)2 shows single-exponential 5T2-->1A1 relaxation kinetics, whereas [Fe(btpa)](PF6)2 exhibits solvent-independent biphasic relaxation kinetics. The fast process of [Fe(btpa)](PF6)2 with a rate constant, kHL, of 2.5 x 10(7) s-1 at 295 K and an activation energy, Ea, of 1294(26) cm-1 in methanol can be assigned to the 5T2-->1A1 relaxation as well. The slow process with a kHL(295 K) of 3.7 x 10(5) s-1 and a Ea of 2297(32) cm-1 in methanol--which is the slowest light-induced relaxation process observed so far for an Fe(II) spin-crossover complex in solution--is assigned to a coupling of the 5T2-->1A1 relaxation process to a geometrical rearrangement within the pendent pyridyl arms.

Psychiatric inpatients and the MMPI-2: providing benchmarks

The second edition of the Minnesota Multiphasic Personality Inventory (MMPI-2: Butcher & Williams, 1992) has become the standard instrument for assessing individuals in a variety of settings, including inpatient psychiatric facilities (Piotrowski, 1997). This study reports on the responding of 516 adult psychiatric inpatients on an acute-care inpatient unit who were administered the MMPI-2 after they were referred for diagnostic testing. Base-rate responding, two-point code frequencies, and gender- and race-based responding are reported. Differences in gender and race responding are noted to coincide with differences in psychiatric diagnosis for those groups. The importance of having base rates for an inpatient sample is discussed. In particular, it is noted that the high levels of endorsement that are characteristic of this population can be difficult to interpret without access to inpatient comparison profiles.

Use of the MMPI-2's VRIN scale with severely disturbed populations: consistent responding may be more problematic than inconsistent responding

The Minnesota Multiphasic Personality Inventory--Second Edition includes a new validity scale, the VRIN scale, intended to detect random responding. High scores are viewed as casting suspicion on the validity of the profile. For the present study, the authors evaluated some of the complexities of the VRIN scale including its interaction with the F scale. In particular, we tested two hypotheses. First is that among psychotically disturbed test takers, some inconsistent responding is an integral and expected mode of responding to a self-report measure. That is, in an inpatient psychiatric population increased confused responding (high VRIN score) is related in predictable ways to increased endorsement of psychotic scales and two-point codes and to increased psychotic diagnoses. The second hypothesis is a corollary--that the absence of inconsistency (low VRIN) in a protocol indicating acute distress (high F) may indicate that a respondent is being too consistent in presenting self as having severe difficulties. In this case, the rest of the protocol may be an exaggerated description of the clinical presentation. A sample of 521 psychiatric inpatients was used to evaluate these hypotheses. Some support for both hypotheses is reported. Further studies are recommended to evaluate the hypotheses.

Fas ligand and Fas receptor are coexpressed in normal human esophageal epithelium: a potential mechanism of apoptotic epithelial turnover

Fas (CD95/Apo-1) receptor (FasR) is a cell-surface receptor that mediates apoptotic cell death upon triggering by Fas ligand (FasL). We sought to determine whether normal human esophageal epithelial cells express FasL and/or FasR and whether their localization is consistent with a role in the turnover of normal esophageal epithelium. Normal esophageal epithelium was immunohistochemically positive for FasL in upper prickle cell layers and in mature squamous cells, but the proliferative basal layer was negative. FasL mRNA was detected in the same epithelial cell layers by in situ hybridization. Co-localization of FasL mRNA and protein therefore confirmed that FasL expression is induced in esophageal epithelial cells as they reach terminal differentiation. FasR was immunohistochemically detected throughout the esophageal epithelium. Positive TUNEL (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling) staining confirmed cell death of the FasL and FasR coexpressing mature epithelial cells. CD45-positive immunocytes were notably absent from FasL-expressing upper epithelial layers. The findings are consistent with a contributory role for Fas-mediated autocrine suicide or paracrine fratricide in the apoptotic turnover of normal esophageal epithelium.

Expression of Fas ligand by human gastric adenocarcinomas: a potential mechanism of immune escape in stomach cancer

BACKGROUND

Despite being immunogenic, gastric cancers overcome antitumour immune responses by mechanisms that have yet to be fully elucidated. Fas ligand (FasL) is a molecule that induces Fas receptor mediated apoptosis of activated immunocytes, thereby mediating normal immune downregulatory roles including immune response termination, tolerance acquisition, and immune privilege. Colon cancer cell lines have previously been shown to express FasL and kill lymphoid cells by Fas mediated apoptosis in vitro. Many diverse tumours have since been found to express FasL suggesting that a "Fas counterattack" against antitumour immune effector cells may contribute to tumour immune escape.

AIM

To ascertain if human gastric tumours express FasL in vivo, as a potential mediator of immune escape in stomach cancer.

SPECIMENS

Thirty paraffin wax embedded human gastric adenocarcinomas.

METHODS

FasL protein was detected in gastric tumours using immunohistochemistry; FasL mRNA was detected in the tumours using in situ hybridisation. Cell death was detected in situ in tumour infiltrating lymphocytes using terminal deoxynucleotidyl transferase mediated dUTP nick end labelling (TUNEL).

RESULTS

Prevalent expression of FasL was detected in all 30 resected gastric adenocarcinomas examined. In the tumours, FasL protein and mRNA were co-localised to neoplastic gastric epithelial cells, confirming expression by the tumour cells. FasL expression was independent of tumour stage, suggesting that it may be expressed throughout gastric cancer progression. TUNEL staining disclosed a high level of cell death among lymphocytes infiltrating FasL positive areas of tumour.

CONCLUSIONS

Human gastric adenocarcinomas express the immune downregulatory molecule, FasL. The results suggest that FasL is a prevalent mediator of immune privilege in stomach cancer.

Definition of epitopes for monoclonal antibodies developed against purified sodium channel protein: implications for channel structure

To test sodium channel structural models, we defined the epitopes for nineteen independently cloned monoclonal antibodies previously generated against purified, detergent-solubilized, adult rat skeletal muscle sodium channel protein using channel proteolysis, synthetic peptides, and fusion proteins. All identified epitopes were continuous and unique to the skeletal muscle subtype alpha-subunit. Of the nineteen independent clones, seventeen had epitopes located either in the origin of the amino-terminus or in the interdomain 2-3 region while only two antibodies had epitopes located in the mid-portion of the interdomain 1-2 region. No immunogenic regions were identified on the alpha-subunit's extracellular regions, interdomain 3-4 segment, or carboxyl-terminus or on channel beta-subunits. While immune tolerance may explain the lack of immunogenicity of extracellular regions, the lack of immunogenicity of most of the channel's cytoplasmic mass may be due to segment inaccessibility from organization of these regions as globular domains, to insertion of parts of these regions into the membrane phase, or to interaction with other protein elements. The definition of monoclonal antibody epitopes allows us to reinterpret previously reported monoclonal antibody competition studies, providing independent support for our model of sodium channel cytoplasmic domain structure. In addition, these data suggest additional testable hypotheses concerning the interactions of the sodium channel amino- and carboxyl-termini with each other as well as with other protein elements.

The Fas counterattack in vivo: apoptotic depletion of tumor-infiltrating lymphocytes associated with Fas ligand expression by human esophageal carcinoma

Various cancer cell lines express Fas ligand (FasL) and can kill lymphoid cells by Fas-mediated apoptosis in vitro. FasL expression has been demonstrated in several human malignancies in vivo. We sought to determine whether human esophageal carcinomas express FasL, and whether FasL expression is associated with increased apoptosis of tumor-infiltrating lymphocytes (TIL) in vivo, thereby contributing to the immune privilege of the tumor. Using in situ hybridization and immunohistochemistry, respectively, FasL mRNA and protein were colocalized to neoplastic esophageal epithelial cells in all esophageal carcinomas (squamous, n = 6; adenocarcinoma, n = 2). The Extent of FasL expression was variable, with both FasL-positive and FasL-negative neoplastic regions occurring within tumors. TIL were detected by immunohistochemical staining for the leukocyte common Ag, CD45. FasL expression was associated with a mean fourfold depletion of TIL when compared with FasL-negative areas within the same tumors (range 1.6- to 12-fold, n = 6,p < 0.05). Cell death of TIL was detected by dual staining of CD45 (immunohistochemistry) and DNA strand breaks (TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling). There was a mean twofold increase in detectable cell death among TIL in FasL-positive areas compared with FasL-negative areas (range 1.6- to 2.4-fold, n = 6, p < 0.05). In conclusion, we demonstrate a statistically significant, quantitative reduction of TIL concomitant with significantly increased TIL apoptosis within FasL-expressing areas of esophageal tumors. Our findings suggest Fas-mediated apoptotic depletion of TIL in response to FasL expression by esophageal cancers, and provide the first direct, quantitative evidence to support the Fas counterattack as a mechanism of immune privilege in vivo in human cancer.

Letrozole (CGS 20267). A phase I study of a new potent oral aromatase inhibitor of breast cancer

BACKGROUND

Letrozole (CGS 20267), a triazole derivative, is a new, once-daily, oral nonsteroidal inhibitor of aromatase activity.

METHODS

In this Phase I trial, 23 heavily pretreated postmenopausal patients with metastatic breast cancer received letrozole at doses ranging from 0.1 to 5.0 mg once daily.

RESULTS

No hematologic, biochemical, or significant clinical toxicity was encountered. Serial steroid measurements were determined in 19 of these patients. Letrozole at all doses tested produced a marked suppression of plasma estrone, estradiol, estrone sulfate, and urine estrone and estradiol. This was observed within 24 hours of the initial dose of letrozole and resulted in a greater than 90% suppression of plasma and urinary estrogen levels within 2 weeks. Letrozole appears to be highly selective in its action and does not compromise glucocorticoid or mineralocorticoid production or thyroid function. Of the 21 evaluable patients, there were 2 with partial responses and 7 with stable disease.

CONCLUSIONS

Letrozole is a well tolerated, potent, and specific inhibitor of estrogen biosynthesis in postmenopausal patients with metastatic breast cancer.

Structure of the tomato Adh2 gene and Adh2 pseudogenes, and a study of Adh2 gene expression in fruit

A cDNA library was constructed from RNA from the pericarp of ripe tomato fruit and four cDNAs encoding ADH2 were isolated and characterized. The cDNAs encode a peptide 379 amino acids in length. They hybridized strongly with a 1.8 kb RNA species well represented in RNA from ripe, but not from mature, unripe fruit, and strongly to a similar RNA species present in hypoxic, but not in aerobic roots. Northern analysis showed that the mRNA for ADH2 in fruit increased in abundance through ripening, particularly during late ripening. In pericarp tissue of fruit, the Adh2 mRNA level increased to a maximum within 8-16 h of exposure to atmospheres with 3% (v/v) oxygen, and returned to the basal level within 16 h of a return to air. The mRNA level was sensitive to the oxygen level in the atmosphere, increasing 20-fold in 12% (v/v) oxygen and 100-fold in 3% oxygen. The homologous tomato Adh2 gene was isolated from a genomic library. The gene has an overall length of 2334 bp from transcription start site to poly(A) addition site and includes eight introns. Southern blot analysis of tomato genomic DNA identified multiple Adh2-related sequences. Two of these, PSA1 and PSA2, were cloned and found to have 94% similarity with each other and 77% similarity with the tomato Adh2 gene over a 1000 bp region. The homologous regions include introns and exons but the equivalent exons contain frame shifts, deletions and stop codons. The two regions are therefore presumptive pseudogenes.

Purification of three pectin esterases from ripe peach fruit

Three isoforms of pectin esterase (PE1-PE3) (pectin pectyl-hydrolase, EC 3.1.1.11.) were purified to homogeneity from ripe peach fruit (Prunus persica cv. Coronet). The three enzymes were basic proteins of M(r) 34,000 as determined by denaturing polyacrylamide gel electrophoresis but were separated by FPLC cation-exchange chromatography. The proteins were N-terminally blocked but amino acid sequences were obtained for peptides released from two of the three isoforms. The sequences revealed a threonine/lysine substitution in a comparison between isoform PE2/isoform PE3, and there were regions of sequence similarity with other plant pectin esterases. The proteins did not bind to concanavalin A and were not stained by the periodate-Schiff reagent suggesting a low or zero level of glycosylation. Polyclonal antisera to isoform PE3 also bound to isoforms PE1 and PE2. The study provides the enzyme protein sequence and immunological basis for an evaluation of the role of pectin esterases in normal and abnormal ripening of peach fruit.

Endo-1,4-[beta]-Glucanase, Xyloglucanase, and Xyloglucan Endo-Transglycosylase Activities Versus Potential Substrates in Ripening Tomatoes

In ripening fruits of tomato (Lycopersicon esculentum L. var 83-G-38), the amounts of cellulose and xyloglucan (XG) remained constant during tissue softening, but the relative molecular weight (Mr) of XG decreased markedly and the Mr of cellulose declined slightly. These changes could have been due to activities of non-specific endo-1,4-[beta]-glucanases and/or buffer-soluble XG endo-transglycosylase, both of which increased when tissue firmness declined most rapidly. Tomato extracts also reduced the viscosity of XG solutions, especially in the presence of added XG oligosac-charides. This depolymerizing (XGase) capacity differed from [beta]-glucanase and XG transglycosylase activity (a) by being almost entirely buffer insoluble, and (b) by declining precipitously during fruit softening. Although it disappeared from ripe fruit, XGase may have functioned in promoting wall loosening at earlier stages of fruit development when its activity was highest. By contrast, during aging of fruit in the ripening-inhibited mutant rin there was no change in Mr of XG or cellulose, and activities of [beta]-glucanases and XG transglycosylase were lower than in wild-type tomato. Nevertheless, some softening of the fruit did take place over time and XG amounts declined, possibly because high XGase activity was maintained in the mutant, unlike in wild-type fruit.

Effect of postharvest heat treatments on fruit quality, surface structure, and fungal disease in Valencia oranges

The effect of prestorage heat treatments on the quality of Valencia oranges and on postharvest disease was investigated during a 6-week storage trial. Fruit receiving a hot water immersion regime (45�C core temperature for 42 min) designed to disinfest against Queensland fruit fly lost significantly less moisture and remained firmer during storage than unheated control fruit. Disinfestation treatment also significantly reduced fruit acidity and number of viable spores of Colletotrichum gloeosporioides, Penicillium digitatum, and P. italicum. The gradual heating process involved with disinfestation was more successful in maintaining fruit quality than surface sterilisation by hot water immersion (12 min at 53�C), or conditioning in air (24 h at 30�C and 90% relative humidity). Heat-treated fruit showed enhanced colour development. Light and electron microscopy studies showed that heating had little effect on the structure of surface waxes; however, collapsed oil glands were observed after cool storage. Prestorage heat treatments could be a favourable alternative to chemicals for control of pests.

The efficacy of CGS 20267 in suppressing estrogen biosynthesis in patients with advanced stage breast cancer

The pharmacologic inhibition of aromatase activity has been the focus of clinical trials in patients with advanced stage breast cancer. Recent developments with imidazole compounds that inhibit aromatase activity suggest their clinical use as potent inhibitors of estrogen biosynthesis in postmenopausal breast cancer patients. In this Phase I, open-label, dose-range finding study, we examined the inhibitory potency of CGS 20267 on blood and urine levels of estradiol, estrone and estrone sulfate in 8 patients with metastatic breast cancer. Studies included evaluation of adrenal and thyroid function to look for evidence of general hydroxylase inhibition at dose levels effective for aromatase blockade. Patients were administered CGS 20267 at doses of 0.1 and 0.25 mg, once a day in ascending doses over a 12-week period. Preliminary data reveal that CGS 20267 elicits a striking suppression in plasma estradiol, estrone and estrone sulphate which was observed in some patients as quickly as within 24 h of the first dose. Estrogen suppression of over 90% was achieved within 2 weeks of therapy. No alterations in either baseline or ACTH (cortrosyn) stimulated cortisol and aldosterone levels were observed through the 12 weeks of therapy. In addition, 24 h urine sodium and potassium values were not appreciably altered during therapy. We conclude that CGS 20267 is a potent, specific inhibitor of estrogen biosynthesis in postmenopausal patients with metastatic breast cancer and effectively reduces blood and urine estrogens to undetectable levels.

Whiplash and temporomandibular joint dysfunction

This article examines the relationship between Temporomandibular joint dysfunction and rear-end (whiplash) motor vehicle accidents. The clinical and statistical evidence relating TMJ damage to whiplash is reviewed. The sequence of events regarding the head, neck and jaw movements which occur in these accidents is considered. The jaw movements are discussed in detail. An analysis of the forces resulting from these movements indicates that tensile, compressive and shear forces occur which challenge the integrity of the soft tissues of the Temporomandibular joint. An overview of the mechanisms whereby damage may occur is considered. A more detailed analysis of these mechanisms will be dealt with in further articles, to evaluate the precise magnitude and direction of forces in all phases of the accident.

The Florida breastfeeding promotion project: a coalition effort to improve hospital practices and policies

The Florida Healthy Mothers, Healthy Babies-Coalition initiated a breastfeeding promotion project. The Coalition focused on hospital policies because of their impact on breastfeeding success and because of the potential for working with other state efforts directed at pregnant women or new mothers. The Florida Healthy Mothers, Healthy Babies Coalition developed a three-part program. It consists of model hospital policies concerning breastfeeding, a lecture series which educates hospital nursing staff on the implementation of these model policies and a workshop through which trainers are prepared to present the educational program. Nurses' Association of the American College of Obstetrics and Gynecology (NAACOG), Special Supplemental Food Program for Women, Infants, and Children (WIC), and Florida Lactation Consultant Association (FLCA) all contributed to this project.

Emergency percutaneous dilatational cricothyroidostomy: use of modified nasal speculum

The authors devised a percutaneous dilatational method which they believe trained physicians and nonphysicians (emergency medical technicians and paramedics) can use with safety and speed. With one blade of a modified nasal speculum embedded in a tapered small pigtail-dilator catheter, the closed, flattened instrument is forced through the cricothyroid ligament, with a twisting motion, and then opened. Only the skin is incised 1 cm in length. Then a free flow of air via attached syringe is sought before any further penetration. This guarantees accurate and safe entry into the airway. The operator forces the J-tipped dilator and speculum inward as the needle is withdrawn. At the proper depth the speculum is opened transversely, and a cuffed tracheostomy tube with an internal diameter of 6 mm is inserted. The instrument is removed and immediate suctioning and active ventilation is possible. The authors developed the use of this instrument in trials on a mannequin and on 25 cadavers.

W mutant mice with mild or severe developmental defects contain distinct point mutations in the kinase domain of the c-kit receptor

Mutations at the mouse W/c-kit locus lead to intrinsic defects in stem cells of the melanocytic, hematopoietic, and germ cell lineages. W alleles vary in the overall severity of phenotype that they confer, and some alleles exhibit an independence of pleiotropic effects. To elucidate the molecular basis for these biological differences, we analyzed the c-kit locus and the c-kit-associated autophosphorylation activities in five different W mutants representative of a range of W phenotypes. Mast cell cultures derived from mice or embryos homozygous for each W allele were deficient in c-kit autophosphorylation activity, the extent of which paralleled the severity of phenotype conferred by a given W allele both in vivo and in an in vitro mast cell coculture assay. The mildly dominant, homozygous viable alleles W44 and W57 were found to express reduced levels of an apparently normal c-kit protein. In contrast, c-kit kinase defects conferred by the moderately dominant, homozygous viable alleles W41 or W55 or the homozygous lethal allele, W37, were attributed to single-point mutations within the kinase domain of the c-kit polypeptide, which result in point substitutions of amino acid residues highly conserved in the family of protein tyrosine kinases. The nature and location of these amino acid substitutions account for the relative severity of phenotypes conferred by these W alleles and demonstrate that the pleiotropic developmental defects associated with the W/c-kit locus arise as the result of dominant loss-of-function mutations in a transmembrane receptor tyrosine kinase.