Cancer research
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Infection with hepadnaviruses and exposure to dietary aflatoxin are considered major risk factors in the development of hepatocellular carcinoma (HCC) both in humans and in animals. Recently, a broad range of mutations in the p53 tumor suppressor gene has been reported in human HCCs, predominantly from hepatitis B virus carriers in areas with either high or low levels of exposure to dietary aflatoxin. To determine whether p53 mutations are common to HCCs of hosts infected with related hepadnaviruses with and without treatment with aflatoxin, we studied the occurrence of mutations in the p53 gene in HCCs of ground squirrels and woodchucks with history of infection with ground squirrel hepatitis virus (GSHV) and woodchuck hepatitis virus, respectively. ⋯ Mutation was caused by a G to T transversion in the second position of the codon, resulting in the replacement of cysteine with phenylalanine, and was accompanied by a tumor-specific loss of heterozygosity. p53 allelic amino acid variation with sequences coding for aspartic acid or asparagine was present in codon 61 in the variable region of exon 4 in both HCCs and nonneoplastic tissues of ground squirrels. In view of the considerably lower apparent rate of mutations in comparison to human HCCs, we suggest a less important role for aflatoxin in the induction of p53 mutations in HCCs of ground squirrels. Alternatively, etiological factors other than p53 mutations may be of greater significance in the development of HCC in ground squirrels and woodchucks.
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We present a physiological pharmacokinetic model that describes the plasma and cerebrospinal fluid (CSF) concentrations of topotecan [(S)-9-dimethylaminomethyl-10-hydroxyamptothecin hydrochloride, SK&F 104864-A, NSC 609699] following i.v. and intraventricular administrations in monkeys. The model consists of three physical spaces: the CSF, the plasma, and a body compartment. The model incorporates such processes as reversible conversion of topotecan lactone to an inactive hydroxy acid form, microvascular exchange between CSF and plasma, bulk CSF flow, exchange between plasma and body compartments, and elimination of drug from the plasma compartment. ⋯ The forward and reverse rate constants for the lactone-to-hydroxy acid conversion were 1.0 and 0.29 h-1, respectively. Comparison of the clearances (normalized to body surface area) with values reported for mice and humans shows reasonable similarity across species. This pharmacokinetic model may help guide future development and refinement of clinical protocols, especially in the treatment of diseases of the central nervous system.