Loss of imprinting in hepatoblastoma

We and others have described loss of imprinting (LOI) of the insulin-like growth factor II (IGF2) gene in 70% of Wilms' tumors (WT), an embryonal kidney tumor, and we have also found LOI of the H19 gene in 29% of WTs. In WT, LOI of IGF2 is coupled to down-regulation of H19. LOI of IGF2 has subsequently been described in a second embryonal neoplasm, rhabdomyosarcoma. However, the hypothesis that LOI is a general feature of embryonal tumors is challenged by a report of absence of LOI in three hepatoblastomas (S. M. Davies, Cancer Res., 53: 4781-4783, 1993). We identified five hepatoblastomas informative for a transcribed polymorphism of the IGF2 gene. One tumor showed LOI of IGF2, in contrast to the previous report. That tumor also showed LOI of H19, further documenting a role for this gene in imprinting disturbances in cancer. However, in contrast to WT, LOI in hepatoblastoma was not associated with down-regulation of H19. Thus, IGF2 and H19 expression can be uncoupled in tumors with LOI.

Loss of imprinting of IGF2 is linked to reduced expression and abnormal methylation of H19 in Wilms' tumour

The insulin-like growth factor-II (IGF2) and H19 genes are imprinted in mouse and human, with expression of the paternal IGF2 and maternal H19 alleles. IGF2 undergoes loss of imprinting (LOI) in most Wilms' tumours (WT). We now show that: (i) LOI of IGF2 is associated with a 80-fold down regulation of H19 expression; (ii) these changes are associated with alterations in parental-origin-specific, tissue-independent sites of DNA methylation in the H19 promoter; and (iii) loss of heterozygosity is also associated with loss of H19 expression. Thus, imprinting of a large domain of the maternal chromosome results in a reversal to a paternal epigenotype. These data also suggest an epigenetic mechanism for inactivation of H19 as a tumour suppressor gene.

Simple purification of human chromosomes to homogeneity using muntjac hybrid cells

Chromosome sorting from hybrid cells offers enormous advantages for gene mapping and cloning, but purification of most chromosomes has been largely hindered by their similarity in size to other chromosomes. We have developed a novel cell line and strategy that allows simple, mass purification of mammalian chromosomes, permitting significant target genome enrichment. This strategy takes advantage of the small number of giant chromosomes (1,2,X) of the female Indian muntjac, a barking deer, avoiding the problem of size similarity. We introduced human chromosomes into a cell line derived from a muntjac and purified them to homogeneity using a relatively simple technique. This strategy should facilitate the isolation of chromosomes from species other than human for which hybrid cells are not available currently.

Epigenetic effects in eukaryotic gene expression

In the broadest terms, epigenetic phenomena in eukaryotes depend on the interaction of alleles or repeated sequences or on the mitotic inheritance of chromatin states or methylation patterns. One of the most exciting aspects of the study of epigenetic phenomena is the insight that can be gained into the structure and assembly of higher-order chromatin structures, an important subject that has proved refractory to current biochemical methodologies. Rapid progress in the study of gene inactivation in fungi, plants, and invertebrates will provide new hypotheses to be tested in mammals.

A developmental context for multiple genetic alterations in Wilms' tumor

Wilms' tumor has served as an example of Knudson's two-hit hypothesis of recessive tumor genes, but the genetics has proven to be surprisingly complex. WT1, a tumor suppressor gene on 11p13, is mutated in only a small fraction of Wilms' tumors, and a second chromosomal region, 11p15, harbors a second Wilms' tumor gene also involved in other cancers. In addition, loss of genomic imprinting, or parental origin-specific gene expression of at least two genes, appears to be an early step in Wilms' tumorigenesis and common cancers. Finally, genes on other chromosomes also play a role. I propose a model of Wilms' tumorigenesis in which multiple genetic alterations act within a specific developmental context, accounting for the epidemiological and pathological heterogeneity of Wilms' tumor, as well as the tissue specificity of the tumor types arising from alterations in these genes.

Parental imprinting of human chromosome region 11p15.3-pter involved in the Beckwith-Wiedemann syndrome and various human neoplasia

Cytogenetic and DNA analyses of patients with the Beckwith-Wiedemann syndrome (BWS) enabled us to refine the localization of the syndrome at 11p15.3-pter to two distinct regions. One chromosome region (BWSCR1) is near the insulin (INS) and insulin-like growth factor 2 (IGF2) genes. The other region (BWSCR2) is more proximal near two sequences with zinc-binding finger motifs and a number of known and putative genes. This latter region, at least, seems to be associated with the development of childhood tumors. Our results strongly support the proposed involvement of parental imprinting in the etiology of BWS since all balanced chromosomal abnormalities in these patients were maternally transmitted while the mothers were phenotypically normal. We demonstrate that such an autosomal balanced rearrangement can lead to a specific maternal hypomethylation of the INS/IGF2 genes localized distal to the breakpoint. This underlines the role of these genes in the etiology of the syndrome.

Relaxation of imprinted genes in human cancer

Genomic imprinting, or parental allele-specific expression of genes, has been demonstrated at the molecular level in insects and mice but not in man. Imprinting as a potential mechanism of human disease is suggested by paternal uniparental disomy of 11p15 in Beckwith-Wiedemann syndrome and by maternal uniparental disomy of 15q11-12 in Prader-Willi syndrome. Beckwith-Wiedemann syndrome is characterized by multiorgan overgrowth and predisposition to embryonal tumours such as Wilms' tumour of the kidney. A loss of heterozygosity of 11p15 is also frequently found in a wide variety of tumours, including Wilms' tumour and lung, bladder, ovarian, liver and breast cancers; 11p15 also directly suppresses tumour growth in vitro. Two genes in this band, H19 and insulin-like growth factor-II (IGF2) undergo reciprocal imprinting in the mouse, with maternal expression of H19 (ref. 13) and paternal expression of IGF2 (ref. 14). Here we find that both of these genes show monoallelic expression in human tissues and, as in mouse, H19 is expressed from the maternal allele and IGF2 from the paternal allele. In contrast, 69% of Wilms' tumours not undergoing loss of heterozygosity at 11p showed biallelic expression of one or both genes, suggesting that relaxation or loss of imprinting could represent a new epigenetic mutational mechanism in carcinogenesis.

Tumor cell growth arrest caused by subchromosomal transferable DNA fragments from chromosome 11

A fundamental problem in the identification and isolation of tumor suppressor and other growth-inhibiting genes is the loss of power of genetic complementation at the subchromosomal level. A direct genetic strategy was developed to isolate subchromosomal transferable fragments (STFs) from any chromosome, each containing a selectable marker within the human DNA, that could be transferred to any mammalian cell. As a test of the method, several overlapping STFs from 11p15 were shown to cause in vitro growth arrest of rhabdomyosarcoma cells. This activity mapped between the beta-globin and insulin genes.

A novel general strategy for cloning tumor suppressor genes using radiation-reduced chromosomal superfragments

To identify the tumor suppressor gene on human chromosome 11p15, we generated mouse microcell hybrids containing small transferable chromosome 11p15 fragments, which we have termed "DNA superfragments". These hybrids will be used to identify which fragments contain a tumor suppressor gene by direct transfer of the fragments to tumor cells via microcell fusion.

Multiple tumor suppressor genes in multistep carcinogenesis

One of the most exciting areas of molecular oncology is the convergence of two independent lines of evidence suggesting involvement of multiple tumor suppressor genes in a given type of cancer. First, epidemiology and somatic cell genetics indicate the presence of multiple tumor suppressor genes in each of several malignancies. Second, cancers often lose multiple chromosomal regions during tumor progression. We will use two tumors, colorectal cancer and Wilms tumor, to illustrate the questions that multiple tumor suppressor genes raise.

A third Wilms' tumor locus on chromosome 16q

Loss of heterozygosity studies have been used to identify chromosomal regions which are frequently deleted and thus indicate areas which may harbor tumor suppressor genes. As a result, both the WT1 gene located in chromosome 11p13 and an unidentified gene(s) within chromosome 11p15 have been implicated in Wilms' tumorigenesis. Cytogenetic and linkage studies suggest that additional non-chromosome 11 sites are involved in Wilms' tumor. Because these sites may also involve loss of heterozygosity, loci on 33 autosomal arms were screened for allele loss in a series of Wilms' tumors. We found that in addition to loss on chromosome 11p (11 of 25 informative tumors) there was significant loss on chromosome 16q (9 of 45 informative tumors), while the total frequency of allele loss excluding these loci was low (9 of 426 total informative loci). These data indicate that losses of both chromosome 11p and 16q alleles are nonrandom events and suggest that 16q is the location of a third tumor suppressor gene underlying Wilms' tumorigenesis. The parental origin of the lost chromosome 16q allele was determined in eight sporadic tumors. Alleles of paternal and of maternal origin were each lost in four sporadic tumors indicating that, unlike chromosome 11p, alleles of either parental origin are lost on 16q.

Molecular analysis of retroviral transduction in chronic myelogenous leukemia

We have developed a polymerase chain reaction (PCR) assay for detection of integrated retroviral transgenomes containing the neo G418 resistance gene in colonies (40 cells or more) grown in G418 selection after exposure to the neo-positive retrovirus LNL6. This assay also provides for simultaneous characterization of these colonies as belonging to a chronic myelogenous leukemic (bcr-abl positive) or nonleukemic population (bcr-abl negative). Using these techniques, we assessed transduction of the LNL6 retrovirus into the normal and leukemic cells of a blast-crisis chronic myelogenous leukemia (CML) patient. This work was designed to support the use of the LNL6 retroviral marker to help identify the origin of relapse after autologous marrow infusion. The data from these experiments show that the majority of CML blast crisis cells that, following exposure to the LNL6 virus, produce colonies under rigorous G418 selection are indeed transduced by the virus, as shown by the presence of the neo retroviral gene. Most of these colonies are also shown to be leukemic by PCR detection of the bcr-abl RNA. This demonstrates the feasibility of the study of CML marrow for retroviral marking. These procedures will be of use in establishing if relapse arises from leukemic blasts which contaminate purged autologous bone marrow infused following intensive therapy for leukemia.

Interferon-alpha restores the deficient expression of the cytoadhesion molecule lymphocyte function antigen-3 by chronic myelogenous leukemia progenitor cells

Hematopoietic cells from the malignant clone in chronic myelogenous leukemia (CML) maintain and expand a proliferative advantage over normal hematopoietic cells within the bone marrow. This advantage is often ameliorated or reversed in vivo by IFN alpha. Based upon earlier studies suggesting decreased adhesiveness of CML progenitor cells, we asked whether CML progenitor cells are deficient in their expression of the cytoadhesion molecule lymphocyte function antigen-3 (LFA-3, CD58) which is normally expressed on hematopoietic progenitors. Progenitor cells from untreated CML patients showed greatly reduced or absent LFA-3 expression, whereas progenitors from patients treated with IFN alpha in vivo or in vitro expressed surface LFA-3 at more normal levels. LFA-3-deficient CML progenitor cells were unable to stimulate normal regulatory proliferative responses in autologous T cells. We hypothesize that IFN alpha-sensitive LFA-3 deficiency reflects a cell surface cytoadhesion defect which may help explain adhesive abnormalities of CML progenitor cells in vitro and clonal proliferation in vivo.

Tissue, developmental, and tumor-specific expression of divergent transcripts in Wilms tumor

The Wilms tumor locus on chromosome 11p13 has been mapped to a region defined by overlapping, tumor-specific deletions. Complementary DNA clones representing transcripts of 2.5 (WIT-1) and 3.5 kb (WIT-2) mapping to this region were isolated from a kidney complementary DNA library. Expression of WIT-1 and WIT-2 was restricted to kidney and spleen. RNase protection revealed divergent transcription of WIT-1 and WIT-2, originating from a DNA region of less than 600 bp. Both transcripts were present at high concentrations in fetal kidney and at much reduced amounts in 5-year-old and adult kidneys. Eleven of 12 Wilms tumors classified as histopathologically heterogeneous exhibited absent or reduced expression of WIT-2, whereas only 4 of 14 histopathologically homogeneous tumors showed reduced expression. These data demonstrate a molecular basis for the pathogenetic heterogeneity in Wilms tumorigenesis.

Multiple genetic alterations in distal and proximal colorectal cancer

Multiple genetic alterations were investigated in colorectal cancer, including changes in DNA content, mutations in ras oncogenes, and deletions involving chromosomes 5, 17, and 18. A non-random association of deletions and mitotic abnormalities by site was seen, with both types of alterations occurring significantly more frequently in distal tumours. In contrast, the frequency of c-Ki-ras mutations did not differ between proximal and distal cancers. In addition, deletions were significantly associated with each other and with change in DNA content. The data provide strong support for the hypothesis that proximal and distal colon carcinoma might differ in the genetic mechanisms in their initiation and/or progression.

Genetic linkage of Beckwith-Wiedemann syndrome to 11p15

Beckwith-Wiedemann syndrome (BWS), characterized by multiorgan developmental abnormalities and predisposition to cancer, usually occurs sporadically, but small apparently dominant pedigrees have been described. Since rare patients show varying karyotypic abnormalities on the short arm of chromosome 11, it has been suggested that BWS may be related to the Wilms tumor gene on 11p13 or, alternatively, to growth factor genes on 11p15. We performed genetic linkage analysis on two BWS kindreds, using RFLPs for loci on 11p. BWS was linked to the insulin gene (11p15.5), with an overall maximum lod score of 3.60 (recombination fraction = .00). Linkage to D11S16 (11p13) could be excluded for recombination fractions less than or equal to .03. These results suggest that BWS defines a tumor-predisposition gene on 11p15.

Loss of allelic heterozygosity at a second locus on chromosome 11 in sporadic Wilms' tumor cells

Children with associated Wilms' tumor, aniridia, genitourinary malformations, and mental retardation (WAGR syndrome) frequently have a cytogenetically visible germ line deletion of chromosomal band 11p13. In accordance with the Knudson hypothesis of two-hit carcinogenesis, the absence of this chromosomal band suggests that loss of both alleles of a gene at 11p13 causes Wilms' tumor. Consistent with this model, chromosomes from sporadically occurring Wilms' tumor cells frequently show loss of allelic heterozygosity at polymorphic 11p15 loci, and therefore it has been assumed that allelic loss extends proximally to include 11p13. We report here that in samples from five sporadic Wilms' tumors, allelic loss occurred distal to the WAGR locus on 11p13. In cells from one tumor, mitotic recombination occurred distal to the gamma-globin gene on 11p15.5. Thus, allelic loss in sporadic Wilms' tumor cells may involve a second locus on 11p.

Capture and characterization of 5-aza-2'-deoxycytidine-treated C3H/10T1/2 cells prior to transformation

A model system was developed to capture phenotypically normal cells committed to transformation to address two fundamental questions in cancer biology: (i) what are the earliest events in transformation; and (ii) what is the role of DNA methylation in carcinogenesis? Individual C3H/10T1/2 cells were treated with 5-aza-2'-deoxycytidine, which causes hypomethylation of DNA. Cells were grown to subconfluence, and individual microcolonies were trypsinized into two fractions. One fraction was cryopreserved, and the other was replated and maintained in culture. Ten percent of these replated colonies became morphologically transformed after 4-6 weeks. The cryopreserved ancestral cells of both transformed and nontransformed microcolonies were then cultured and compared to each other and to the transformants for phenotypic properties of cellular transformation. Pretransformed and nonpretransformed ancestral cells were initially morphologically indistinguishable, their early growth curves did not differ significantly, and they did not form colonies in soft agar. On continued growth in culture, however, the pretransformants displayed all of the phenotypic characteristics of transformation. Furthermore, transformation occurred in a given pretransformant in most or all of the cells of that clone. Thus, cells committed to transformation could be isolated in this way prior to phenotypic transformation. Studies of these pretransformed cells will permit examination of the earliest events in carcinogenesis and the role of DNA methylation in transformation.

Concerted nonsyntenic allelic loss in human colorectal carcinoma

Familial polyposis coli (FPC) is caused by an autosomal dominant gene on chromosome 5, and it has been proposed that colorectal cancer in the general population arises from loss or inactivation of the FPC gene, analogous to recessive tumor genes in retinoblastoma and Wilms' tumor. Since allelic loss can be erroneously scored in nonhomogeneous samples, tumor cell populations were first microdissected from 24 colorectal carcinomas, an additional nine cancers were engrafted in nude mice, and nuclei were flow-sorted from an additional two. Of 31 cancers informative for chromosome 5 markers, only 6 (19%) showed loss of heterozygosity of chromosome 5 alleles, compared to 19 of 34 (56%) on chromosome 17, and 17 of 33 (52%) on chromosome 18. Therefore, it appears that (i) FPC is a true dominant for adenomatosis but not a common recessive gene for colon cancer; and (ii) simple Mendelian models involving loss of alleles at a single locus may be inappropriate for understanding common human solid tumors.

Reduced genomic 5-methylcytosine content in human colonic neoplasia

DNA methylation appears to play an important role in both physiological and experimentally modified gene expression, and alterations in DNA methylation have been described in animal tumor models and in transformed cells and tumor cell lines. However, there have been comparatively few reports on DNA methylation in primary human malignancies, and these reports are somewhat contradictory. While individual genes have shown hypomethylation in colon cancer and premalignant adenomas as well as in lung cancer, other genes have shown increased methylation, and absolute measures of 5-methylcytosine content have shown decreases in malignancies but not in premalignant adenomas. We have used a sensitive quantitative measurement of 5-methylcytosine content by high performance liquid chromatography revealing an unequivocal hypomethylation of tumor DNA. An average of 8 and 10% reduction in genomic 5-methylcytosine content was seen in apparently all colon adenomas and adenocarcinomas, respectively, and there was no significant difference between benign and malignant tumors. This is a substantial quantitative alteration and suggests a pervasive abnormality in the control of DNA methylation. Surprisingly, three patients with the highest 5-methylcytosine content in their normal colon appear to have a germline predisposition to cancer (Lynch syndrome).

Alterations in DNA methylation in human colon neoplasia

A review of studies on DNA methylation in colonic neoplasia is presented. Hypomethylation of a wide variety of genes from throughout the genome was seen in all colon cancers studied. These changes preceded malignancy because benign adenomas were also affected.

Evidence for rearrangement, amplification, and expression of c-myc in a human glioblastoma

Amplified cellular genes are frequently manifested in one of two cytologically recognizable forms, double minutes or homogeneously staining regions. Additionally, evidence is accumulating that aberrant expression of cellular genes (including oncogenes) may be mediated by gene amplification. We now describe the amplification and expression of the cellular oncogene c-myc in double-minute-containing cells from a patient with glioblastoma multiforme, and we have shown that the amplification is associated with rearrangement of the c-myc gene. This finding further supports the common association of the myc gene family in neurogenic tumors and provides evidence of myc gene amplification in human brain cancer.

Loss of genes on the short arm of chromosome 11 in bladder cancer

Recent studies have shown that normal cellular sequences on chromosome 13 are lost during the development of retinoblastomas and that sequences on chromosome 11 are similarly lost during the development of Wilms' kidney tumours and embryonal tumours. Cells from these tumors have been found to contain either the paternal or maternal copies of loci on the affected chromosome, but not both. Thus, the somatic loss of heterozygosity for sequences on chromosome 13 or 11 is hypothesized to result in homozygosity for a recessive mutant allele on these chromosomes, and in this way the chromosomal loss may contribute to the development of these tumours. We sought to investigate whether similar losses of heterozygosity for chromosome 11 sequences occurred in a common adult tumour. We chose to analyse bladder cancers, since such cancers are common in the adult population and are derived from urogenital tissue, as are Wilms' tumours. We examined constitutional and tumour genotypes at loci on the short arm of chromosome 11 (11p) in 12 patients with transitional cell carcinomas. In five tumours, we observed the somatic loss of genes on 11p resulting in homozygosity or hemizygosity of the non-deleted alleles in the tumour cells. Our results show that the frequency of loss of 11p sequences in bladder cancer approaches that seen in Wilms' tumour (42% compared with 55%), and suggest that recessive genetic changes involving sequences on 11p may contribute to the development of bladder neoplasms.

Hypomethylation of DNA from benign and malignant human colon neoplasms

The methylation state of DNA from human colon tissue displaying neoplastic growth was determined by means of restriction endonuclease analysis. When compared to DNA from adjacent normal tissue, DNA from both benign colon polyps and malignant carcinomas was substantially hypomethylated. With the use of probes for growth hormone, gamma-globin, alpha-chorionic gonadotropin, and gamma-crystallin, methylation changes were detected in all 23 neoplastic growths examined. Benign polyps were hypomethylated to a degree similar to that in malignant tissue. These results indicate that hypomethylation is a consistent biochemical characteristic of human colonic tumors and is an alteration in the DNA that precedes malignancy.

Use of restriction fragment length polymorphisms to determine the clonal origin of human tumors

A novel strategy to determine the clonal origin of human tumors has been devised. The strategy involves the use of a cloned polymorphic X-chromosomal gene and two restriction endonucleases. The first endonuclease distinguishes the paternal and maternal copies of the gene through a DNA polymorphism of restriction fragment length. The second endonuclease distinguishes active from inactive copies of this gene through changes in DNA methylation. As illustrations of this strategy, three human cancers were each shown to be monoclonal. The analysis described should have a wide variety of clinical and experimental applications.

Metabolic competition studies of 2'-fluoro-5-iodo-1-beta-d-arabinofuranosylcytosine in vero cells and herpes simplex type 1-infected vero cells

2'-Fluoro-5-iodo-1-beta-D-arabinofuranosylcytosine (FIAC) is a potent antiviral agent with minimal cytotoxicity. In Vero cells, incorporation of labeled dCyd and dThd into the acid-insoluble DNA fraction was, respectively, competitively and noncompetitively inhibited by FIAC. In herpes simplex type 1 (HSV-1) infected Vero cells, these inhibition patterns became noncompetitive. The inhibition constants of FIAC on dThd and dCyd incorporation into the acid-insoluble fraction during a 15-min period were greater than 30 microM which were much higher than the antiviral concentration of FIAC (ED90 = 0.003-0.013 microM) for continuous exposure. Incorporation of dUrd into acid-insoluble DNA was inhibited by 10 microM FIAC in HSV-1-infected Vero cells, but not in uninfected cells. The radioactivity of [2-14C]FIAC was incorporated into the acid-insoluble DNA fraction, and this incorporation in uninfected cells was strongly inhibited by 10 microM dCyd but not by dThd. By contrast, the incorporation in HSV-1-infected Vero cells was strongly inhibited by 10 microM dThd but not by dCyd. These data indicate that FIAC behaves metabolically like dThd, dUrd, or 5-iodo-dUrd in HSV-1-infected cells but like dCyd in noninfected cells. Thus, combined use of dCyd and FIAC may reduce cytotoxicity of FIAC or incorporation of FIAC into host cell DNA without affecting its antiviral activity. This finding is of significance since, for practical reasons, incorporation of FIAC into host cell DNA needs to be reduced as much as possible.

Detection by high-performance liquid chromatography of methotrexate and its metabolites in tumor tissue from osteosarcoma patients treated with high-dose methotrexate/leucovorin rescue

Methotrexate (MTX) polyglutamates were detected in osteogenic sarcoma tumor samples obtained from patients 24 or 48 h after receiving high-dose MTX/leucovorin rescue therapy. Tumor samples were assayed by high-performance liquid chromatography, and polyglutamyl metabolites, along with MTX, were quantitated using both direct u.v. absorption at 313 nm and an enzyme titration assay. Good agreement between these two methods was found although the more sensitive enzyme assay detected peaks in some samples not detected by u.v. absorbance. A wide variation in MTX:MTX polyglutamate levels (1:1 to 25:1) was found among the six clinical samples studied. Also, no correlation between the extent of polyglutamate formation and plasma levels (determined at the time of tumor sampling) was observed. High intracellular levels of a derivative which appears to be the 7-hydroxy metabolite of MTX were also detected in four of six samples. This material coeluted with authentic standard, showed spectral properties like standard 7-OH-MTX, and did not inhibit dihydrofolate reductase.

Somatic deletion and duplication of genes on chromosome 11 in Wilms' tumours

One of the most provocative findings in tumour biology is the relationship between chromosomal changes and embryonal cancers in children. For example, children with the rare paediatric syndrome AGR triad (aniridia, genito-urinary abnormalities and mental retardation) often develop Wilms' tumours at a very early age and carry a germ-line deletion on the short arm of chromosome 11 (11p13). It has been suggested that the germ-line deletion 11p is the first of two or more steps to cancer in AGR children. If this were true, one might expect a similar deletion to arise somatically in the far more common isolated Wilms' tumours of children without AGR, as suggested by Knudson from epidemiological data. However, a chromosomal deletion on 11p was observed in only two of five such cases, while it was absent or seen inconsistently in others. We have now used a molecular genetic approach to determine whether Wilms' tumour cells possess somatic alterations at 11p loci. We have found somatic deletions of specific genes in four of six Wilms' tumours. Surprisingly, in all four cases, the deletions were associated with duplications leading to homozygosity of the non-deleted alleles in the tumour cells. As analogous observations were recently reported in retinoblastoma, the genetic events reported here may underlie the development of many such embryonal tumours in children.

A technique for radiolabeling DNA restriction endonuclease fragments to high specific activity

A technique for conveniently radiolabeling DNA restriction endonuclease fragments to high specific activity is described. DNA fragments are purified from agarose gels directly by ethanol precipitation and are then denatured and labeled with the large fragment of DNA polymerase I, using random oligonucleotides as primers. Over 70% of the precursor triphosphate is routinely incorporated into complementary DNA, and specific activities of over 10(9) dpm/microgram of DNA can be obtained using relatively small amounts of precursor. These "oligolabeled" DNA fragments serve as efficient probes in filter hybridization experiments.

Uptake, initial effects, and chemotherapeutic efficacy of harringtonine in murine leukemic cells sensitive and resistant to vincristine and other chemotherapeutic agents

[3H]Harringtonine was shown to be taken up rapidly by L1210/0 cells using a fast-mixing, fast-separating technique and was retained with a slow rate of limited release to the medium. Cells resistant to vincristine (L1210/VCR) showed impaired capability to take up the drug at 20 degrees. Its initial uptake in L1210 sublines in vitro was: L1210/0 greater than L1210/cyclophosphamide, L1210/1-beta-D-arabinofuranosylcytosine, L1210/6-mercaptopurine greater than L1210/5-fluorouracil, L1210/Adriamycin greater than L1210/VCR. In [3H]harringtonine-preloaded cells, L1210/0 retained significantly more radioactivity than did L1210/VCR cells after repeated washing with fresh medium at 37 degrees. The radioactivity appeared to be predominantly bound to the microsomal fractions. [3H]Leucine incorporation into protein in L1210/0 cells was inhibited 90% within 15 min by harringtonine (0.5 micrograms/ml); incorporation of [3H]thymidine into DNA and [3H]cytidine into RNA was much less inhibited and showed an apparent lag of onset for 5 and 10 min, respectively. The relative potency of harringtonine to inhibit [3H]leucine incorporation in the above sublines in vitro follows an order similar to their rates of uptake of harringtonine by these sublines of cells. The efficacy of harringtonine, 2.4 or 3.6 mg/kg i.p., in increasing the life span of C57BL/6 X DBA/2 F1 mice bearing the sublines of leukemic cells, on the average, was: L1210/0 greater than L1210/cyclophosphamide, L1210/6-mercaptopurine greater than L1210/1-beta-D-arabinofuranosylcytosine, L1210/5-fluorouracil greater than L1210/Adriamycin, L1210/VCR. These results suggest that: (a) protein synthesis is the major initial target for the effect of harringtonine; (b) harringtonine bound more tightly to the cellular components of VCR-sensitive leukemic cells than to VCR-resistant cells; and (c) cellular uptake of harringtonine and the relative potency of inhibiting protein synthesis in sublines have a rank order similar to the chemotherapeutic efficacy of harringtonine in these cells.

Mutation affecting the 12th amino acid of the c-Ha-ras oncogene product occurs infrequently in human cancer

A point mutation alters the 12th amino acid of the c-Ha-ras oncogene product p21 in a human bladder cancer cell line. This is, at present, the only mutation known to result in a human transforming gene. This mutation may therefore represent a possible target for mutagenesis leading to carcinogenesis in humans. By means of restriction enzyme analysis, 29 human cancers, including 20 primary tumor tissues, derived from organs commonly exposed to environmental carcinogens, were tested for the presence of this mutation. None of ten primary bladder carcinomas exhibited the mutation; nor did nine colon carcinomas or ten carcinomas of the lung. Thus the point mutation affecting the 12th amino acid of the c-Ha-ras gene product, while a valuable model for carcinogenesis, does not appear to play a role in the development of most human epithelial cancers of the bladder, colon, or lung.

Hypomethylation of ras oncogenes in primary human cancers

We have examined the methylation status of two cellular oncogenes, c-Ha-ras and c-Ki-ras, in primary human carcinomas and the adjacent analogous normal tissues from which the tumors derived. The c-Ha-ras gene was hypomethylated in six of eight carcinomas, including five colonic adenocarcinomas and one small cell lung carcinoma, when compared to adjacent normal tissues. The c-Ki-ras gene was hypomethylated to a lesser extent in two colonic adenocarcinomas. This is the first demonstration of alterations in methylation of cellular oncogenes in human cancer.

Hypomethylation distinguishes genes of some human cancers from their normal counterparts

It has been suggested that cancer represents an alteration in DNA, heritable by progeny cells, that leads to abnormally regulated expression of normal cellular genes; DNA alterations such as mutations, rearrangements and changes in methylation have been proposed to have such a role. Because of increasing evidence that DNA methylation is important in gene expression (for review see refs 7, 9-11), several investigators have studied DNA methylation in animal tumours, transformed cells and leukaemia cells in culture. The results of these studies have varied; depending on the techniques and systems used, an increase, decrease, or no change in the degree of methylation has been reported. To our knowledge, however, primary human tumour tissues have not been used in such studies. We have now examined DNA methylation in human cancer with three considerations in mind: (1) the methylation pattern of specific genes, rather than total levels of methylation, was determined; (2) human cancers and adjacent analogous normal tissues, unconditioned by culture media, were analysed; and (3) the cancers were taken from patients who had received neither radiation nor chemotherapy. In four of five patients studied, representing two histological types of cancer, substantial hypomethylation was found in genes of cancer cells compared with their normal counterparts. This hypomethylation was progressive in a metastasis from one of the patients.

Organ site specificity for cancer in chromosomal instability disorders

DNA rearrangement rather than point mutation is an emerging hypothesis for human carcinogenesis. Although there is no direct evidence for this hypothesis, indirect evidence is provided by cancer cytogenetics and genetics. It has been suggested that patients with Bloom's syndrome, a disorder of spontaneous chromosomal rearrangement, develop the common fatal internal cancers and thus that genetic rearrangements, rather than chemical mutagens, cause most internal human cancers. To test this observation, we have derived age- and sex-adjusted cancer incidence rate ratios for specific organ sites in patients with three chromosomal instability disorders (Bloom's syndrome, xeroderma pigmentosum, and dyskeratosis congenita) and have found that the increased incidence of cancer in all three disorders is limited to specific and often uncommon organ sites. We conclude that chromosomal instability disorders do not predispose patients to the common fatal internal cancers. Although DNA rearrangement remains a promising concept in human carcinogenesis, the organ site specificity of cancers associated with Bloom's syndrome, xeroderma pigmentosum, and dyskeratosis congenita cannot be used as evidence to implicate this mechanism.

Incorporation of metabolites of 2'-fluoro-5-iodo-1-beta-D-arabinofuranosylcytosine into deoxyribonucleic acid of neoplastic and normal mammalian tissues

The radioactivity of 14C-labeled 2'-fluoro-5-iodo-1-beta-D-arabinofuranosylcytosine ([2-14C]-FIAC), a new and potent antiherpetic agent, was shown previously to be incorporated into the DNA fractions of mammalian and neoplastic tissues. The present work was undertaken to learn the nature of the incorporated moieties. Enzyme degradation of highly purified DNA from the small intestine of mice treated with [2-14C]FIAC and analysis of the resulting nucleosides failed to reveal the presence of unchanged FIAC. Rather, three metabolites were found, namely, the 2'-fluoro-1-beta-D-arabinofuranosyl nucleosides of cytosine (FAC), thymine (FMAU) and 5-iodouracil (FIAU). Labeled metabolites of FIAC were also found in the DNA isolated from P815 leukemic cells in mice given [2-14C]FIAC. It is of interest to note that FMAU, FIAU and FAC are, like FIAC, potent antiherpetic agents.

Segregation of pre-stalk and pre-spore cells of Dictyostelium discoideum: observations consistent with selective cell cohesion

Aggregating Dictyostelium discoideum cells were dissociated and separated into two populations, pre-stalk and pre-spore cells, by centrifugation in a Percoll gradient. After harvesting, one population of cells was labeled with fluorescein isothiocyanate and the other with tetramethylrhodamine isothiocyanate. Equal numbers of the two cell populations were then mixed and observed while they aggregated and differentiated to form fruiting bodies. Within minutes after mixing, the two populations showed evidence of segregation and tended to form separate streams of cells as they migrated toward aggregation centers. Many separate clusters of tetramethylrhodamine isothiocyanate-labeled or fluorescein isothiocyanate-labeled cells were found within an aggregation center. Thereafter there was further segregation. The denser cells from the gradient tended to assume the position of stalk cells whereas the lighter cells migrated to the position characteristic of spore cells. The patterns of segregation suggest that selective cohesiveness of one or both cell types plays a role in morphogenesis.

Duodenal leiomyoma as a cause of gastrointestinal hemorrhage

A case report and review of the problem of duodenal leiomyoma are presented. Although these lesions are rare and usually asymptomatic, they can present with symptoms of hemorrhage, obstruction, pain, and perforation. Barium roentgenographic examination may show filling defects of compressive lesions. Angiography shows a hypervascular, encapsulated lesion. Endoscopy may reveal a submucosal mass with central depression. At operation, it is important to distinguish the benign leiomyoma from leiomyosarcoma.

The opiate receptor: a model explaining structure-activity relationships of opiate agonists and antagonists

A model of the opiate receptor is proposed which explains structure-activity relationships of opiate drugs, including (i) the unique potency of certain opiates such as etonitazene, fentanyl, phenazocine, and oripavines; (ii) the role of N-allyl substituents in conferring antagonist properties; and (iii) chemical features that afford "pure" antagonists. The model indicates mlecular mechanisms for interconversion of the opiate receptor between respective states that bind agonists or antagonists with high affinity.

Focal dermal hypoplasia (Goltz syndrome) in a male. A case report

A 3-year-old boy presented with the clinical and histological features of focal dermal hypoplasia. Radiological examination showed the longitudinal parallel striations of osteopathia striata. As far as can be ascertained this is the fifth recorded case in a male patient.