Protection by various deoxynucleosides against deoxyadenosine-induced DNA damage in adenosine deaminase-inactivated lymphocytes

Adenosine deaminase deficiency is an inborn error resulting in immunodeficiency. The pathogenesis of the lymphopenia is not fully understood. Intracellular increases in dATP in the absence of deamination retard DNA repair in human resting lymphocytes and results in the slow accumulation of DNA strand breaks. We focused on the relationship between DNA damage and DNA precursor pools in cultures of deoxycoformycin-treated, ADA-inhibited resting lymphocytes. The addition of 10 microM deoxyadenosine led to a substantial number of DNA strand breaks within 12 h, breaks equivalent to those which occur with about 190 rad irradiation. Addition of any of the other deoxynucleosides used partially prevented this dAdo-induced DNA damage and promoted DNA repair. However, the preventive effects did not correlate inversely with intracellular dATP levels. Resting lymphocytes have very small dNTP pools. Treatment with dAdo slightly reduced dTTP and dCTP. Three kinds of deoxynucleosides, other than dAdo, restored or raised the corresponding dNTP level but the pool imbalance was only minimally corrected. Regarding the toxic effects of dAdo in ADA deficiency, not only dATP levels but also dNTP pool balance has a crucial role in the pathogenesis. Pool sizes of dTTP, dCTP, and possibly dGTP must be maintained at normal levels, if dAdo-induced DNA damage is to be avoided.

Clonal analysis of gliomas

In malignant gliomas, the characteristically heterogeneous features and frequent diffuse spread within the brain have raised the question of whether malignant gliomas arise monoclonally from a single precursor cell or polyclonally from multiple transformed cells forming confluent clones. Although monoclonality has been shown in surgically resected tissues, these may not include the full spectrum of patterns seen on autopsy material. Little is known about the clonality of low-grade gliomas from which malignant gliomas may sometimes arise. We sought to investigate the clonality of low-grade and malignant gliomas by using and comparing surgical and autopsy material with a Polymerase chain reaction (PCR)-based assay for nonrandom X chromosome inactivation. For that, purpose, archival surgical and autopsy material from 15 female patients (group A) (age 4 to 73 years; median, 45) with malignant gliomas (12 glioblastomas, one gliosarcoma, one anaplastic oligoastrocytoma, one gliomatosis cerebri), surgical material only from 21 female patients (group S) (age 6 to 78 years; median, 60) with low-grade and malignant gliomas (four low-grade astrocytomas, three oligoastrocytomas, two anaplastic astrocytomas, one gemistocytic astrocytoma, four oligodendrogliomas, seven glioblastomas) were analyzed. In group A, representative areas (mean = 5/patient; median = 7) were microdissected from tissue sections and assayed by PCR amplification of a highly polymorphic microsatellite marker locus of the human androgen receptor gene (HUMARA) in the presence of alpha32P with and without predigestion with a methylation-sensitive restriction enzyme (HhaI). Products were resolved by denaturing gel electrophoresis and autoradiographed. In group S, selected tumor areas were used for the assay. Each patient's normal brain tissue was used for control. The band intensity of alleles were measured by densitometric scanning. In group A, 13 of 15 cases were informative (heterozygous). The same pattern of nonrandom X chromosome inactivation was present in all areas of solid dense and moderate tumor infiltration in eight including all components of the gliosarcoma. Two of eight also showed focal loss of heterozygosity (LOH). One of 13 presented global LOH. Two of 13 showed microsatellite instability, one of which in a patient with Turcot syndrome, the other in gliomatosis cerebri. Opposite skewing patterns were seen in distant areas of gliomatosis cerebri consistent with oligoclonal derivation. Clonality remained indeterminate in one glioblastoma and in the anaplastic oligoastrocytoma because of skewed lyonization in the normal control. In group S, 19 of 21 cases were informative. Fifteen of 19 were monoclonal (four low-grade astrocytomas, one anaplastic astrocytoma, one gemistocytic astrocytoma, two oligodendrogliomas, one oligoastrocytoma, six glioblastomas). Four of 19 were indeterminate. We conclude that (1) Low-grade and malignant gliomas are usually monoclonal tumors, and extensively infiltrating tumors must result from migration of tumor cells (2) Gliomatosis cerebri may initiate as an oligoclonal process or result from collision gliomas (3) Biphasic gliomas likely arise from a single precursor cell. (4) LOH at the HUMARA locus is probably related to partial or complete deletion of an X-chromosome, which occurs in malignant gliomas during clonal evolution.

Correlation between p53 immunostaining patterns and gene sequence mutations in breast carcinoma

We performed p53 immunostaining in 82 invasive breast carcinomas by using two commercially available antibodies, one of which (DO7) was employed in formalin-fixed paraffin-embedded sections. The other antibody (PAb1801) was evaluated in corresponding acetone-fixed cryostat sections. A greater percent of cases were immunostained with DO7 compared to PAb1801 (52% vs 33%); however, the staining was more often heterogeneous (6-50% cells positive) or focal (< or = 5% cells positive) with DO7 (9% vs 31%). To investigate the genetic relevance of p53 immunostaining, single-strand conformational polymorphism (SSCP) analysis and DNA sequencing were performed on exons 2-11 by using archival tissue samples of 18 cases that were selected on the basis of certain immunostaining patterns. Two (33%) of six tumors with negative staining for DO7 had gene sequence mutations; however, one of these mutations was a base-pair deletion that caused a reading-frame shift and the other was a base-pair insertion that resulted in a stop codon. Both of these tumors exhibited immunostaining with PAb1801, although it was weak and cytoplasmic in one case. Conversely, three (30%) of 10 tumors showing immunoreactivity in 6-100% of cells with both reagents lacked a gene sequence mutation. Of the remaining seven tumors that were positive by SSCP, six contained a point mutation resulting in a base-pair substitution. Despite repeat analyses, one of the cases positive by SSCP failed to demonstrate a mutation in the sequenced exons. Four (80%) of five cases with heterogeneous DO7 immunoreactivity (that is, 6-50% of nuclei positive) were positive for gene sequence mutation. Neither of two cases showing focal DO7 nuclear staining in < 5% of tumor cells contained a mutation in the sequenced exons, and neither of these cases was strongly positive with PAb1801. Staining for either antibody was significantly associated with adverse outcome, as determined by disease recurrence at 52 months median follow-up (DO7, p = 0.01; and PAb1801 p = 0.002, chi-squared test). We conclude that a variety of factors may account for discrepancies when immunohistology is used to evaluate p53 status. These include fixation artifacts, differing epitope specificities of monoclonal reagents, presence of immunohistologically "silent" mutations and, possibly, aberrant overexpression of wild-type protein.