PubMed Health⌕ Search

Biomedical subjects

R Mehta

Publications and source records attributed to R Mehta.

At least 37 records · Page 2Linked to original sources
PubMed1999

Pharmacokinetics and tissue disposition in monkeys of an antisense oligonucleotide inhibitor of Ha-ras encapsulated in stealth liposomes.

PURPOSE: This study examined the pharmacokinetics and tissue distribution of an antisense oligonucleotide ISIS 2503, formulated in stealth (pegylated) liposomes (encapsulated) or in phosphate-buffered saline (unencapsulated). METHODS: Encapsulated or unencapsulated ISIS 2503 was administered to rhesus monkeys by intravenous infusion. The concentrations of ISIS 2503 and metabolites in blood, plasma, and tissue samples were determined by capillary gel electrophoresis. RESULTS: Plasma concentrations of encapsulated ISIS 2503 decreased mono-exponentially after infusion with a mean half-life of 57.8 hours. In contrast, the concentration of unencapsulated ISIS 2503 in plasma decreased rapidly with a mean half-life of 1.07 hours. Both encapsulated and unencapsulated ISIS 2503 distributed widely into tissues. Encapsulated ISIS 2503 distributed primarily to the reticulo-endothelial system and there were few metabolites observed. In contrast, unencapsulated ISIS 2503 distributed rapidly to tissue with highest concentration seen in kidney and liver. Nuclease-mediated metabolism was extensive for unencapsulated oligonucleotide in plasma and tissues. CONCLUSIONS: The data suggest that stealth liposomes protect ISIS 2503 from nucleases in blood and tissues, slow tissue uptake, and slow the rate of clearance from the systemic circulation. These attributes may make these formulations attractive for delivering oligonucleotides to sites with increased vasculature permeability such as tumors or sites of inflammation.

Animals↗
PubMed1999

PD 098059, an inhibitor of ERK1 activation, attenuates the in vivo invasiveness of head and neck squamous cell carcinoma.

Increased mortality of patients with oral cancer largely reflects the local and regional spread of the disease. The invasiveness of these tumours requires hydrolases which are regulated through AP-1-dependent transcriptional mechanisms. Since the amount/activity of transcription factors bound to the AP-1 motif are regulated partly through the extracellular signal-regulated kinases (ERK1/ERK2), we determined the effect of PD 098059, an inhibitor of ERK1/ERK2 activation, on the in vivo invasiveness of a human squamous cell carcinoma cell line (UM-SCC-1) derived from the oral cavity. We utilized the floor of mouth musculature consisting of the mylohyoid, geniohyoid and genioglossus muscle (which are sequentially arranged), as a natural barrier to assess tumour spread in vivo in the nude mouse. Mice were inoculated with tumour cells superficial to the mylohyoid muscle. After 18 days, tumours were injected with either empty liposomes (control) or liposomes containing 5 microM PD 098059 and, after an additional 22 days, the jaws of mice examined histologically. Highly infiltrative tumours, which had penetrated the genioglossus muscle, were evident in 10/12 control mice. In contrast, in 9/12 mice in which the tumours were injected with PD 098059, tumours did not extend beyond the mylohyoid or geniohyoid muscles. Tumours penetrated bone nutrient canals in 7/12 control mice but in only 3/12 PD 098059-treated mice. Neurotropism, characteristic of aggressive oral squamous cell carcinoma, was evident in 6/12 control mice but was completely abolished (0/12 mice) in the PD 098059-treated mice. Using a staging system based on the muscle layer involved, neurotropism, as well as bone involvement, we found the inhibition of invasion to be statistically significant (P < 0.01). The reduced invasiveness of the PD 098059-liposome-treated oral cancers was associated with diminished 92-kDa type IV collagenase and ERK1/ERK2 activities but was not a consequence of a slower tumour growth rate. This is the first study to demonstrate reduced in vivo invasiveness of a malignancy brought about by an inhibitor of ERK1/ERK2 activation. These results raise the exciting possibility that second generation PD 098059 congeners may reduce the spread of the disease in patients afflicted with oral cancers.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

Comprehensive assessment of the components of energy expenditure in infants using a new infant respiratory chamber.

BACKGROUND: Current methods for energy expenditure (EE) measurements in term infants do not include simultaneous measurements of basal and sleeping metabolic rates (BMR and SMR) or a measure of physical activity (PA). Furthermore, prediction equations for calculating EE are not appropriate for use in infants with metabolic disorders. OBJECTIVE: To develop and utilize a new infant respiratory chamber for simultaneous measurements of EE (kJ/d), preprandial BMR (kJ/d), SMR (kJ/d) and an index of PA (oscillations/min/kg body weight) in infants with a variety of metabolic disorders, for up to four hours in a hospital setting, while allowing parental interaction in a comfortable environment. METHODS: We obtained simultaneous measurements of EE, BMR, SMR and PA in 21 infants (66+/-73 days of age, 4.5+/-1.7 kg body weight, 55+/-8 cm in length and 16+/-7% body fat) using our new infant respiratory chamber. Six of these infants were healthy, seven had thyroid dysfunction, five were HIV-exposed, one had AIDS, one had intrauterine and postnatal growth retardation and one was a hypothermic preterm infant. Energy expenditure, BMR and SMR were extrapolated for 24 hours. Body composition was estimated by skin-fold thickness, using age-appropriate formulae. Basal metabolic rate obtained with the infant respiratory chamber was compared to BMR that was calculated using the appropriate World Health Organization (WHO) equations. RESULTS: In all infants both extrapolated 24-hour EE and BMR correlated with fat-free mass (r = 0.89, p<0.01 and r = 0.88, p<0.01 respectively). Twenty-four hour EE also correlated with PA (r = 0.52, p<0.05). The HIV-exposed infants had higher BMR (p<0.05) than that calculated by the appropriate WHO equation. We found that the caloric requirements for the infant with growth retardation were underestimated based on the infant's weight and age. CONCLUSIONS: The infant respiratory chamber can measure all of the main components of EE. Some of the results obtained differed significantly from those obtained by the WHO equations; therefore, the new infant respiratory chamber is necessary for estimating EE in infants with metabolic and growth disorders.

Acquired Immunodeficiency Syndrome↗
PubMed1999

Resistance of HBL100 human breast epithelial cells to vitamin D action.

Vitamin D analogs are effective inhibitors of breast cancer cell growth, but many breast cancer cell lines show various degrees of resistance to the growth inhibitory effect of vitamin D. In this study, we investigated the mechanism of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] resistance of the human breast epithelial cell line HBL100, which had been immortalized by Simian virus 40 (SV40) large T antigen. We determined the expression, DNA binding and transactivation activity of vitamin D3 receptor (VDR) in HBL100 and a vitamin D-sensitive ZR75-1 breast cancer cell line. Western blot analysis revealed a comparable expression of VDR gene in both cell lines. However, gel retardation assays demonstrated nuclear proteins from ZR75-1 cells but not from HBL100; cells expressed a 9-fold increase in the binding activity with a vitamin D response element (VDRE). Using a transient transfection assay, we showed that the VDRE was activated by 8-fold in ZR75-1. However, in HBL100 cells there was no activation observed in response to 1,25(OH)2D3. On the other hand, co-transfection of a VDR expression vector could restore 1,25(OH)2D3-induced VDRE transcription in HBL100 cells. Moreover, stable expression of VDR in HBL100 cells resulted in enhanced sensitivity of the cells to the growth inhibitory effect of 1,25(OH)2D3. Since CV-1 cells express very little endogenous VDR, the interactions of VDR and large T antigen were carried out in these cells. By transient co-transfection, we observed that expression of the large T antigen strongly inhibited 1,25(OH)2D3-induced VDRE transcriptional activity in a dose-dependent fashion in CV-1 cells. At 120 ng VDR concentration, the inhibition was completely reversed. Thus the loss of the growth inhibitory effect of vitamin D3 in HBL100 cells may be caused by the expression of the large T antigen in the cells, and provide further evidence that VDR is required for efficient growth inhibition by vitamin D3.

Antigens, Polyomavirus Transforming↗
PubMed1999

Does treatment change the outcome of seizures and computerized tomographic lesions in intracranial granulomas?

In children, intracranial granuloma diagnosed on computerized tomography (CT) scan and presenting with seizures as the sole manifestation has traditionally been treated with antitubercular (ATB) therapy or albendazole (Alb) in addition to antiepileptic drugs (AED). This study was conducted to determine whether AED therapy alone or specific treatment (ATB + Alb) influences the outcome of seizures and the CT lesion. Sixty-eight children presenting with seizures along with intracranial granuloma on CT scan were selected for the study. They were randomly divided into two groups. Group A (n = 34) was treated with AED alone and group B (n = 34) received antitubercular therapy and albendazole in addition to AED. Seizure type was noted and electroencephalogram (EEG) and CT scan were done in all. They were followed up for a period of 2 to 9 years, during which a record of seizure count and type was maintained. CT scans were repeated at 3 monthly intervals and EEGs were repeated whenever indicated. Four patients in each group were lost to follow-up. Seizures persisted in four out of 30 in group A and six out of 30 in group B. There was no statistically significant difference (p > 0.05) in the outcome of seizures in the two groups. Taking the whole group together (n = 60), of the 13 who had presented with multiple seizures at onset, epilepsy was a sequela in five (p < 0.05); and of the 17 in whom the lesion had calcified, seizures persisted in seven (p < 0.05), irrespective of treatment modality. In conclusion, though specific treatment did not alter the outcome of seizures, children with multiple seizures at presentation and calcification of CT lesion had epilepsy as a sequela.

Adolescent↗
PubMed1998

Glutathione S-transferase-placental form expression and proliferation of hepatocytes in fumonisin B1-treated male and female Sprague-Dawley rats.

Fumonisin B1 (FB1), a mycotoxin produced by a common corn contaminant Fusarium moniliforme and a hepatocarcinogen in rats, has been previously suggested to act as a poor initiator, but a better promoter of gamma-glutamyltranspeptidase (GGT)-positive rat liver preneoplastic lesions. Using glutathione S-transferase-placental form (GSTP) as a more sensitive marker of initiation, we have further evaluated the initiating capacity of various doses of purified FB1 administered (a) intraperitoneally (i.p.) to male Sprague-Dawley (SD) rats for 4 days and (b) orally (PO) to male and female SD rats for 11 days. Compared to their respective controls, significant increases in GSTP-positive hepatocytes were observed in male rats administered FB1 i.p. at 10 mg/kg body weight/day for 4 days, as well as in male and female rats treated with 35 and 75 mg/kg body weight/day FB1 p.o. for 11 days. The percentage section area of liver occupied by GSTP-positive mini-foci comprising of three to 12 cells was increased significantly in male rats given 10 mg/kg FB1 i.p., or in p.o.-treated males and females with 75 mg/kg FB1. Both i.p. and p.o. FB1 treatments resulted in dose-related enhanced hepatocyte proliferation as measured by proliferating cell nuclear antigen (PCNA) labeling with significant increases in the number of PCNA-positive nuclei at the same i.p. and p.o. dose levels where the number of GSTP-positive cells were elevated. In all studies, enhanced PCNA and GSTP expression occurred at FB1 doses which, based on serum biochemical and histopathological data previously reported from our laboratory, were shown to be hepatotoxic. Therefore, our data suggest that in a manner similar to known genotoxic carcinogens, FB1 has the capacity to initiate GSTP-positive hepatocytes with their subsequent development into GSTP mini-foci at exposure levels that induce enhanced hepatocyte proliferation in response to liver toxicity. In SD rats, this occurs as early as within 4 days of i.p. treatment or 11 days of p.o. treatment.

Administration, Oral↗
PubMed1998

Microsomal enzyme activity, glutathione S-transferase-placental form expression, cell proliferation, and vitamin A stores in livers of rats consuming Great Lakes salmon.

Male and female Sprague-Dawley rats were fed diets incorporating lyophilized chinook salmon obtained from Lake Ontario and Lake Huron. After 70 days, females were bred and the progeny (F1) were reared on the same fish-based diets as the adults (F0). After 78-133 days on the diets, males and females of both generations were sacrificed and hepatic microsomal enzyme activities determined, along with glutathione S-transferase-placental form (GSTP) expression and hepatic cellular proliferation. Hepatic P450 enzyme activities (MROD, EROD, PROD, BROD, and aminopyrine) were increased significantly by fish diets from both sources. Increases in hepatic enzyme activity were greatest for fish caught from Lake Ontario and reflected the total levels of organochlorine contaminants in the fish. GSTP and cell proliferation rates did not show any diet-related or dose-related changes. Vitamin A stores were analyzed as the concentration of liver retinyl palmitate. In rats receiving the highest TEQ dose (i.e., 20% Lake Ontario fish diet), vitamin A stores were significantly lower in F0 adults, F1 weanlings, and F1 adult females.

Animal Feed↗
PubMed1998

Association of chronotropic incompetence with echocardiographic ischemia and prognosis.

OBJECTIVES: This study sought to examine the prognostic importance of chronotropic incompetence among patients referred for stress echocardiography. BACKGROUND: Although chronotropic incompetence has been shown to be predictive of an adverse prognosis, it is not clear if this association is independent of exercise-induced myocardial ischemia. METHODS: Consecutive patients (146 men and 85 women; mean age 57 years) who were not taking beta-adrenergic blocking agents and were referred for symptom-limited exercise echocardiography were followed for a mean of 41 months. Chronotropic incompetence was assessed in two ways: (1) failure to achieve 85% of the age-predicted maximum heart rate and (2) a low chronotropic index, a heart rate response measure that accounts for effects of age, resting heart rate and physical fitness. RESULTS: The primary end point, a composite of death, nonfatal myocardial infarction, unstable angina and late (>3 months after the exercise test) myocardial revascularization, occurred in 41 patients. Failure to achieve 85% of the age-predicted maximum heart rate was predictive of events (relative risk [RR] 2.47, 95% confidence interval [CI] 1.28 to 4.79, p=0.007); similarly, a low chronotropic index was predictive (RR 2.44, 95% CI 1.31 to 4.55, p=0.005). Even after adjusting for myocardial ischemia and other possible confounders, failure to achieve 85% of age-predicted maximum heart rate was predictive (adjusted RR 2.20, 95% CI 1.11 to 4.37, p=0.02). A low chronotropic index also remained predictive (adjusted RR 1.85, 95% CI 0.98 to 3.47, p=0.06). CONCLUSIONS: Chronotropic incompetence is predictive of an adverse cardiovascular prognosis even after adjusting for echocardiographic myocardial ischemia.

Echocardiography↗
PubMed1998

A pooled analysis of the Ottawa ankle rules used on adults in the ED.

A pooled analysis was conducted of the seven studies on the clinical diagnostic effectiveness of the Ottawa ankle rules when used with adult patients in the emergency department (ED). The seven studies, conducted in university and community hospital EDs, had examined the sensitivity, specificity, and positive and negative predictive values of the Ottawa ankle rules. ED physicians applied the Ottawa ankle rules with adult patients who had blunt ankle injuries. The gold standard was radiography. The combined sensitivity for the seven studies was 97% or higher for ankle/foot, original/refined Ottawa ankle rules and negative predictive value was greater than 99%. These results support the effectiveness of the Ottawa ankle rules for ruling out a fractured ankle or foot. Specificity was lower, ranging from 31% to 63%; positive predictive value was <20%. Thus, the Ottawa ankle rules should not be used for ruling in a fractured ankle or foot. This pooled analysis shows the Ottawa ankle rules to be effective as clinical practice guidelines for acute ankle and foot injuries in the adult ED patient. Patients with negative results when the rules are used are highly unlikely to have a fractured ankle or foot, but the diagnosis for positive patients is much less certain, suggesting the need for radiography.

Ankle Injuries↗
PubMed1997

Suppression of apoptosis by bcl-2 does not prevent p53-mediated control of experimental metastasis and anchorage dependence.

Mutations in the p53 tumor suppressor gene are frequently associated with the metastatic stage of tumor progression. Inactivation of p53 was shown to promote metastasis under experimental conditions. To determine the p53 functions that are involved in the control of tumor metastasis, we compared properties of three types of transformed mouse fibroblasts: with intact p53, with p53-mediated apoptosis suppressed by bcl-2 and with p53 inactivated by dominant negative mutants. Although expression of bcl-2 blocked apoptosis in detached cells and increased tumor cell survival in the blood circulation, it was insufficient to affect the ability of p53 to cause cell cycle arrest in detached cells and suppress experimental metastasis. For the suppression of metastasis complete inactivation of p53 was required. We conclude that the apoptotic function of p53 is dispensable for the p53-dependent suppression of experimental metastasis that is presumably achieved by controlling anchorage dependence. These data provide a possible explanation to dramatic differences in values of bcl-2 and mutant p53 as prognostic markers in human cancer.

Animals↗
PubMed1997

Cardiac outcomes in coronary patients with submaximum dobutamine stress echocardiography.

This study evaluated the prediction of cardiac events (cardiac death, myocardial infarction, unstable angina, or late myocardial revascularization) in patients with submaximum responses to dobutamine stress, defined by attainment of <85% age-predicted heart rate. Of 1,772 patients undergoing dobutamine echocardiography over a 2-year period, 425 had a submaximum heart rate response. After exclusion of patients treated with beta-adrenoceptor blocking agents, 255 patients formed the study group. In these patients, the test was terminated after administration of the maximum dose of 40 microg/kg/min of dobutamine with atropine (end of protocol, n = 186), severe angina, ischemic ST-segment changes, or intolerable side effects (n = 69). Dobutamine-induced changes (ischemia, viability, or both) were detected in 46 patients, involving ischemia in 133 segments, viability in 23, and ischemia and viability in 16 segments. Patients were followed for an interval of 28 +/- 17 months; 5 (1.2%) were lost to follow-up. Of the medically treated patients, cardiac events occurred in 73 of 228 (31%), including cardiac death in 25 (11%), nonfatal myocardial infarction in 11 (4.8%), severe unstable angina in 35 (15%), and late revascularization in 2 (0.9%). Cardiac events occurred in 11 of 30 (36%) with inducible abnormalities, and 62 of 198 without inducible abnormalities (31%, p = NS). Thus, cardiac event rates are high in patients with inadequate chronotropic responses to dobutamine stress, irrespective of whether stress-induced changes are detected. A negative dobutamine echocardiogram at submaximum heart rate should be considered nondiagnostic.

Aged↗
PubMed1997

Use of exercise echocardiography for prognostic evaluation of patients with known or suspected coronary artery disease.

OBJECTIVES: This study prospectively compared the incremental prognostic benefit of exercise echocardiography with that of exercise testing in a large cohort. BACKGROUND: Exercise echocardiography is widely accepted as a diagnostic tool, but the prognostic information provided by this test, incremental to clinical and stress testing evaluation, is ill-defined. METHODS: Clinical, exercise and echocardiographic variables were studied in a consecutive group of 500 patients undergoing exercise echocardiography. After exclusion of patients who underwent revascularization within 3 months of the stress test (n = 16, 3%) and those lost to follow-up (n = 21, 4%), the remaining 463 patients (mean [+/-SD] age 57 +/- 12 years, 302 men) were followed-up for 44 +/- 11 months. Outcome was related to the exercise and echocardiographic findings, and the incremental prognostic benefit of exercise echocardiography was compared with that of standard exercise testing. RESULTS: Cardiac events occurred in 81 patients (17%), including 33 (7%) with spontaneous events (cardiac death, myocardial infarction and unstable angina) and 48 with late revascularizations due to progressive symptoms. In a multivariate Cox proportional hazards model, the likelihood of any cardiac event was increased in the presence of ischemia (relative risk [RR] 5.06, 95% confidence interval [CI] 3.09 to 8.29, p < 0.001) and lessened by more maximal stress, measured as percent age-predicted maximal heart rate (RR per 5% increment 0.84, 95% CI 0.77 to 0.92, p < 0.001). Spontaneous events were more strongly predicted by ischemia (RR 8.20, 95% CI 3.41 to 19.71, p < 0.001) and percent age-predicted maximal heart rate (RR per 5% increment 0.78, 95% CI 0.67 to 0.91, p < 0.001). An interactive logistic regression model showed that the addition of echocardiographic to exercise and clinical data offered incremental predictive value. CONCLUSIONS: The presence of ischemia on the exercise echocardiogram can predict whether patients will experience an event. This relation is independent of, and incremental to, clinical and exercise data.

Aged↗
PubMed1997

Prognostic implications of exercise echocardiography in women with known or suspected coronary artery disease.

OBJECTIVES: The purpose of this study was to define the value of exercise echocardiography as an independent predictor of cardiac events in women with known or suspected coronary artery disease (CAD), incremental to the data provided by clinical evaluation and exercise testing. BACKGROUND: Exercise echocardiography is more accurate than exercise electrocardiography for the identification of CAD in women. However, the prognostic implications of exercise echocardiography, especially relative to exercise electrocardiography, are undefined. METHODS: Symptom-limited exercise echocardiography was performed in 549 consecutive women between 1989 and 1993. Echocardiography and electrocardiography were performed before and after treadmill exercise; an abnormal result on exercise electrocardiography was defined by ST segment depression > 0.1 mV, ischemia by exercise echocardiography as a new or worse wall motion abnormality after exercise and scar by akinesia or dyskinesia at rest. After exclusion of six patients with uninterpretable studies (1%) and 35 (6%) lost to follow-up, 508 women (mean [+/-SD] age 55 +/- 11 years) were followed up for 41 +/- 10 months for cardiac-related death, infarction or late revascularization. RESULTS: The group attained 92 +/- 10% of age-predicted maximal heart rate, with an exercise capacity of 7 +/- 2 metabolic equivalents. Of 420 women with an interpretable electrocardiogram, significant ST segment changes were present in 68 (16%). Results of exercise echocardiography were normal in 413 (81%) women, positive for ischemia in 66 (13%) and scar only in 29 (6%). No events occurred in 444 patients (89%), and 19 underwent primary revascularization (within 3 months of exercise test). Cardiac events occurred in 36 women (7%), including 17 who died of cardia causes and 19 who had a myocardial infarction or required late revascularization for progressive symptoms. On univariate analysis, the variables associated with cardiac mortality and total cardiac events were a history of CAD, diabetes, left ventricular hypertrophy, exercise capacity and echocardiographic evidence of myocardial ischemia and infarction. A Cox proportional hazards model showed the independent predictors of outcome to be known CAD (odds ratio [OR] 6.6, 95% confidence interval [CI] 3.2 to 13.7, p < 0.00001) and echocardiographic ischemia (OR 4.3, 95% CI 2.1 to 8.7, p < 0.0001). The prognostic value of exercise echocardiography incremental to clinical and exercise variables was demonstrated using sequential Cox models. CONCLUSIONS: In this large cohort of women, exercise echocardiography provided key prognostic information incremental to clinical and exercise testing data.

Coronary Disease↗
PubMed1996

Iodinated analogs of trimetoquinol as highly potent and selective beta 2-adrenoceptor ligands.

A series of trimetoquinol (1, TMQ) analogs were designed and synthesized based on the lead compound 2, a diiodinated analog of trimetoquinol which exhibits improved selectivity for beta 2-versus beta 1-adrenoceptors (AR). To determine the influence of 1-benzyl substituents of trimetoquinol on beta 2-AR binding affinity and selectivity, we replaced and/or removed the 3'-, 4'-, and 5'-methoxy substituents of trimetoquinol. Replacement of the 4'-methoxy group of 2 with an amino (21c) or acetamido (15) moiety did not significantly alter beta 2-AR and thromboxane A2/prostaglandin H2 (TP) receptor affinity. Substitution with a 4'-hydroxy (18) or -iodo (21b) group did not significantly alter beta 2-AR affinity, but greatly reduced TP receptor affinity (380- and 1200-fold, respectively). Further, the beta 2-AR can accommodate larger substituents such as a benzamide at the 4'-position (26b). Other monoiodo derivatives (24, 26a) have similar or slightly lower affinity to both beta 2-AR and TP receptor compared to their diiodo analogs. Interestingly, removal of the 4'-substituent of 3',5'-diiodo analogs increased beta 2-AR affinity with little or no effect on beta 1-AR and TP binding. Thus, analog 21a displayed highly potent (pKi 9.52) and selective (beta 2/beta 1 = 600) binding affinity for beta 2-AR. On the other hand, trifluoromethyl substituents at the 3'- and 5'-positions (27) essentially abolished binding affinity at beta 2-AR and TP receptors. The differential binding effects of the aforementioned trimetoquinol modifications on the receptor systems may reflect differences in the binding pocket that interacts with the benzyl portion of trimetoquinol analogs. Thus, manipulation of the 1-benzyl moiety of trimetoquinol (1) has resulted in analogs that exhibit potent beta 2-AR binding affinity and significantly lower beta 1-AR and TP receptor affinities.

Adrenergic beta-Agonists↗
PubMed1996

Use of in vitro assays to predict the efficacy of chemopreventive agents in whole animals.

Five in vitro assays have been applied to screen the efficacy of potential chemopreventive agents. These assays measure a) inhibition of morphological transformation in rat tracheal epithelial (RTE) cells, b) inhibition of anchorage independence in human lung tumor (A427) cells, c) inhibition of hyperplastic alveolar nodule formation in mouse mammary organ cultures (MMOC), d) inhibition of anchorage independence in mouse JB6 epidermal cells, and e) the inhibition of calcium tolerance in human foreskin epithelial cells. The efficacy of many of these same agents in whole animal studies of lung, colon, mammary gland, skin, and urinary bladder carcinogenesis has also been measured. The aim herein is to estimate the positive and negative predictive values of these in vitro assays against whole animal chemopreventive efficacy data using the same chemicals. For three of these assays--using RTE, A427 cells and mouse mammary organ culture (MMOC)-enough data are available to allow the estimate to be made. Such extrapolations of in vitro data to the in vivo situation are difficult at best. There are many dissimilarities between the two assay systems. The in vitro assays use respiratory and mammary epithelial cells, while the in vivo assays use respiratory, mammary, colon, bladder and skin cells. The in vitro assays use the carcinogens benzo(a)pyrene (B(a)P) and 7,12-dimethylbenz(a)anthracene (DMBA), while the in vivo assays use B(a)P, DMBA, N-methyl-N-nitrosourea (MNU), N,N'-diethylnitrosamine (DEN), azoxymethane (AOM), and N-butyl-N-(4-hydroxybutyl)nitrosoamine (OH-BBN). There are vast differences in pharmacodynamics and pharmacokinetics in vitro and in vivo, yet it is possible to rapidly screen chemicals in vitro for efficacy at one-tenth the cost and complete tests in weeks instead of months. A positive in vitro assay was defined as a 20% inhibition (compared with control) for the RTE and A427 assays and a 60% inhibition for the MMOC assay at nontoxic concentrations. For in vivo assays, the criterion for a positive result was a statistically significant inhibition of incidence, multiplicity or a significant increase in latency (mean time to first tumor). For an agent to be considered negative in animals, it required negative results in at least two different organ systems and no positive results. Using the battery of three in vitro tests, the positive predictive value for having one, two, or three positive in vitro assays and at least one positive whole animal test was 76%, 80%, and 83% respectively. The negative predictive values for one, two or all three in vitro assays was 25%, 27%, and 50%. From these data it is observed that in vitro assays give valuable positive predictive values and less valuable negative predictive values. The mechanisms of chemoprevention are not well understood. Seven categories of agents were examined for their cancer preventing both in vitro and in vivo: antiinflammatories, antioxidants, arachadonic acid metabolism inhibitors, GSH inducers, GST inducers, ODC inhibitors, and PKC inhibitors. Three or even five in vitro assays cannot be all-inclusive of the many mechanisms of cancer prevention. However, three assays help to predict whole animal efficacy with reasonable positive predictive values. Much work and development remains to be done to rapidly identify new chemopreventive drugs.

Animals↗