Hematological toxicity studies

The association between low TPMT activity and excessive hematological toxicity has been recognized [31, 35, 37]. Molecular analysis of the TPMT genotype is able to identify patients at risk for acute toxicity from thiopurines. A recent study involving 180 children identified that the TPMT genotype plays an important role in a patients tolerance to 6-MP therapy [51]. Two of the patients, who were TPMT-de-... 

The traditional acute, subchronic, and chronic toxicity studies performed in rodents and other species also can be considered to constitute multiple endpoint screens. Although the numerically measured continuous variables (body weight, food consumption, hematology values) generally can be statistically evaluated individually by traditional means, the same concerns of loss of information present in the interrelationship of such variables apply. Generally, traditional multivariate methods are not available, efficient, sensitive, or practical (Young, 1985). 

Wise, L.D., Clark, R.L., Minsker, D.H. and Robertson, R.T. (1988). Use of hematology and serum biochemistry data in developmental toxicity studies. Teratology 37 502-503. 

Approximately 10% of new chemical entities (NCEs) show serious adverse drug reactions (ADRs) after market launch. Such events usually result in new black box warnings by the US Food and Drug Administration (FDA), label change or market withdrawal. The most common causes for these actions are hepatic toxicity, hematologic toxicity and cardiovascular toxicity [2], Reasons for such ADRs, which are identified only after NCEs are launched on the market, include the narrow spectrum of clinical disorders and participating patient profiles in clinical studies as well as the fact that serious ADRs are often rare and that the number of patient exposures required to identify such occurrences sometimes may range over a few millions [3],... 

In one study, 68 patients with rheumatic disease on AZA (2 to 3 mg/kg/d) were genotyped for TPMT and TPMT3A alleles. All patients were assessed for side effects from AZA, such as leukopenia, liver function abnormalities, and GI intolerance. Of these patients, 6 (9%) patients were heterozygous for TPMT3A, of whom 5 discontinued AZA within 4 weeks of starting the medication because of hematologic toxicity (48). In another study, 40 RA patients on AZA (0.7 to 1.4 mg/ kg/d) were genotyped for the TPMT alleles. Of the 40 patients, 6 discontinued... 

Other stndies have examined the association between the activity of TPMT and other enzymes in the pnrine pathway and AZA toxicity. In one stndy, TPMT, HPRT, 5 -nncleotidase, and pnrine nncleoside phosphorylase activity in the RBCs of 33 RA patients on AZA (dose of approximately 2mg/kg/d) and 66 controls was meas-nred. Compared to patients with normal TPMT activity, 14 RA patients with low (p = 0.004) and 7 patients with intermediate TPMT activity (RR 3.1) developed AZA toxicity(4d). None of the patients were genotyped. Another study measured TPMT activity in 3 RA patients who had experienced AZA-induced hematologic toxicity and 16 RA patients withont AZA toxicity. In this study, 2 patients with AZA-indnced hematologic toxicity were TPMT deficient, one partial and the other complete (50). Patients were not genotyped in either of these studies. 

Thiopurine methyltransferase methylates 6-mercaptopurine, a commonly used treatment for childhood acute lymphocytic leukemia, reducing its conversion to the active form of the drug. Approximately 10% of patients have intermediate enzyme activity, and 0.3% are deficient for TPMT activity. Intermediate activity patients have a greater incidence of thiopurine toxicity, whereas TPMT-deficient patients have severe or fatal hematological toxicity from 6-mercaptopurine therapy. In one study, patients deficient for TPMT tolerated only 7% of a 2.5-yr mercaptopurine treatment regimen. Patients with intermediate TPMT activity tolerated 65% of total weeks of therapy and patients with normal TPMT activity tolerated 84% of total weeks of therapy (3). 

A number of developmental toxicity studies have been conducted on EEA. In rabbits, inhalation exposure to 100-3 00 ppm resulted in maternal toxicity, including clinical signs and alterations in hematology (reduced hemoglobin). Developmental toxicity was seen as an increased incidence of totally resorbed litters above 2 00 ppm and an increase in non-viable fetuses at 3 00 ppm fetal ossification was observed above 100 ppm, and the incidence of total malformations was 100% at 300ppm. Similar effects were observed in rats, with maternal and developmental toxicity at 100-300 ppm and teratogenic effects at 200-300 ppm. 

Other potential radiation sensitizers for cervical cancer are being explored in phase I and II trials. Paclitaxel has been combined with cisplatin in several small phase I studies. Pignata et al. (29) found that 50 mg/m2 per week of paclitaxel could be combined with weekly cisplatin (30 mg/m2) and radiation therapy with acceptable toxicity, although 10 of 18 patients in their study had grade 3-4 hematologic toxicity. Chen etal. (30) also were able to give weekly paclitaxel at a dose of 50 mg/m2 (in this case combined with 50 mg/m2 of cisplatin every three weeks) with tolerable toxicity and minimal delay in planned radiation therapy. In both studies, the dose-limiting side effect appeared to be diarrhea. It should be noted that the total dose of cisplatin delivered in these trials was lower than that used in the most successful prospective trials of cisplatin or cisplatin and fluorouracil (Table 3). 

Most studies in leukemia patients have used RBC as a surrogate tissue for phenotyping TPMT activity, and several of them have shown that childhood leukemia patients with TPMT /TPMT " phenotypes are at high risk of developing severe hematologic toxicity after treatment with standard doses of thiopurines (196,197,198). Thus, dose adjustment... 

In Study 103, 30 patients were enrolled and treated with doses up to 62.2 mg/ m2 [19]. The MTD was 46.8 mg/m2, with the DLT being neutropenia. Other non-hematologic toxicities included nausea and vomiting, diarrhea and fatigue, all of which were mild to moderate in severity, and manageable. In terms of response, one patient with metastatic non-small lung carcinoma experienced a minor response, and one patient with hepatocellular carcinoma had stable disease lasting 11 months. 

Toxicity studies consist of acute, subacute, and chronic phases, which come under preclinical evaluation in species to asses the extent of toxicity by using various parameters (e.g., hematology, biochemical, histopathologic, body weight, food intake, water intake, general behavior). General requirements of a toxicity study are given in Appendixes I and II. 

Subchronic and toxicity study results may be summarized in tabular form. In addition to the aspects indicated under acute oral toxicity, details of food and water intake, body growth rate, clinical symptoms of toxicity and mortality rate, after different test chemical doses may be included. Results also should include dose-related changes in hematology, clinical enzymes, and macroscopic and microscopic changes found in the vital organs of animals. 

Clinical Examination and Pathology The clinical examination of the test animals may be made as described for subchronic oral toxicity. These, include ophthalmologic examination, hematology, and clinical biochemistry. Gross necropsy and histopathology of all vital organs may be recorded as described for subchronic oral toxicity study. All observed results, quantitative and incidental, should be evaluated by an appropriate statistical method. 

In the EU and the USA, two week studies are the minimum duration. In Japan, 2 week non-rodent and 4 week non-rodent studies are needed. In the USA, as an alternative to 2-week studies, single dose toxicity studies with extended examinations (hematology, clinical chemistry, urinalysis, macroscopic and microscopic pathology) can support single dose human trials. 

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