c-Ki-ras amplification in human lung cancer

KRAS and HRAS mutations confer resistance to MET targeting in preclinical models of MET-expressing tumor cells

The MET receptor tyrosine kinase is often deregulated in human cancers and several MET inhibitors are evaluated in clinical trials. Similarly to EGFR, MET signals through the RAS-RAF-ERK/MAPK pathway which plays key roles in cell proliferation and survival. Mutations of genes encoding for RAS proteins, particularly in KRAS, are commonly found in various tumors and are associated with constitutive activation of the MAPK pathway. It was shown for EGFR, that KRAS mutations render upstream EGFR inhibition ineffective in EGFR-positive colorectal cancers. Currently, there are no clinical studies evaluating MET inhibition impairment due to RAS mutations. To test the impact of RAS mutations on MET targeting, we generated tumor cells responsive to the MET inhibitor EMD1214063 that express KRAS G12V, G12D, G13D and HRAS G12V variants. We demonstrate that these MAPK-activating RAS mutations differentially interfere with MET-mediated biological effects of MET inhibition. We report increased residual ERK1/2 phosphorylation indicating that the downstream pathway remains active in presence of MET inhibition. Consequently, RAS variants counteracted MET inhibition-induced morphological changes as well as anti-proliferative and anchorage-independent growth effects. The effect of RAS mutants was reversed when MET inhibition was combined with MEK inhibitors AZD6244 and UO126. In an in vivo mouse xenograft model, MET-driven tumors harboring mutated RAS displayed resistance to MET inhibition. Taken together, our results demonstrate for the first time in details the role of KRAS and HRAS mutations in resistance to MET inhibition and suggest targeting both MET and MEK as an effective strategy when both oncogenic drivers are expressed.

Human lung epithelial cells progressed to malignancy through specific oncogenic manipulations

We used CDK4/hTERT-immortalized normal human bronchial epithelial cells (HBEC) from several individuals to study lung cancer pathogenesis by introducing combinations of common lung cancer oncogenic changes (p53, KRAS, and MYC) and followed the stepwise transformation of HBECs to full malignancy. This model showed that: (i) the combination of five genetic alterations (CDK4, hTERT, sh-p53, KRAS(V12), and c-MYC) is sufficient for full tumorigenic conversion of HBECs; (ii) genetically identical clones of transformed HBECs exhibit pronounced differences in tumor growth, histology, and differentiation; (iii) HBECs from different individuals vary in their sensitivity to transformation by these oncogenic manipulations; (iv) high levels of KRAS(V12) are required for full malignant transformation of HBECs, however, prior loss of p53 function is required to prevent oncogene-induced senescence; (v) overexpression of c-MYC greatly enhances malignancy but only in the context of sh-p53+KRAS(V12); (vi) growth of parental HBECs in serum-containing medium induces differentiation, whereas growth of oncogenically manipulated HBECs in serum increases in vivo tumorigenicity, decreases tumor latency, produces more undifferentiated tumors, and induces epithelial-to-mesenchymal transition (EMT); (vii) oncogenic transformation of HBECs leads to increased sensitivity to standard chemotherapy doublets; (viii) an mRNA signature derived by comparing tumorigenic versus nontumorigenic clones was predictive of outcome in patients with lung cancer. Collectively, our findings show that this HBEC model system can be used to study the effect of oncogenic mutations, their expression levels, and serum-derived environmental effects in malignant transformation, while also providing clinically translatable applications such as development of prognostic signatures and drug response phenotypes.

Ras in cancer and developmental diseases

Somatic, gain-of-function mutations in ras genes were the first specific genetic alterations identified in human cancer about 3 decades ago. Studies during the last quarter century have characterized the Ras proteins as essential components of signaling networks controlling cellular proliferation, differentiation, or survival. The oncogenic mutations of the H-ras, N-ras, or K-ras genes frequently found in human tumors are known to throw off balance the normal outcome of those signaling pathways, thus leading to tumor development. Oncogenic mutations in a number of other upstream or downstream components of Ras signaling pathways (including membrane RTKs or cytosolic kinases) have been detected more recently in association with a variety of cancers. Interestingly, the oncogenic Ras mutations and the mutations in other components of Ras/MAPK signaling pathways appear to be mutually exclusive events in most tumors, indicating that deregulation of Ras-dependent signaling is the essential requirement for tumorigenesis. In contrast to sporadic tumors, separate studies have identified germline mutations in Ras and various other components of Ras signaling pathways that occur in specific association with a number of different familial, developmental syndromes frequently sharing common phenotypic cardiofaciocutaneous features. Finally, even without being a causative force, defective Ras signaling has been cited as a contributing factor to many other human illnesses, including diabetes and immunological and inflammatory disorders. We aim this review at summarizing and updating current knowledge on the contribution of Ras mutations and altered Ras signaling to development of various tumoral and nontumoral pathologies.

ras oncogene mutations in diethylnitrosamine-induced hepatic tumors in medaka (Oryzias latipes), a teleost fish

Medaka fish are an established non-mammalian research model for the study of liver carcinogenesis and exposure to environmental pollutants. Studies have emphasized the development of hepatic neoplasms in medaka following exposure to model carcinogens. To date however, little information is known regarding the mechanisms underlying initiation of hepatic tumors in this species. The aim of this study was to relate our understanding of diethylnitrosamine (DEN)-induced tumor formation to ras gene activation in hepatic neoplasms of exposed medaka. Initial studies were conducted to identify medaka ras exons 1 and 2 by reverse transcriptase polymerase chain reaction (RT-PCR). Amplification of ras exons 1 and 2 from untreated medaka liver resulted in the identification of three polymorphic ras sequence variants exhibiting a high degree of homology to other teleost and mammalian ras genes. Exposure of medaka to 159 ppm of DEN resulted in a wide range of hepatic neoplasms including: hepatocellular adenomas, hepatocellular carcinomas, cholangiomas, and mixed hepatocholangiocellular carcinomas. Individual liver tumors were examined for oncogenically activating ras mutations by probing genomic DNA with probes specific for activating point mutations or by direct cloning and sequencing of ras transcripts using RT-PCR. Using allele-specific oligonucleotide (ASO) analysis, a single point mutation was detected in codon 12 position two in 8/25 (32%) tumors examined. Mutated ras alleles were additionally detected in 12 of 39 (30%) medaka liver tumors by sequence analysis. Ten of the 12 mutations identified contained a single point mutation at codon 12 resulting in a Gly to Asp amino acid substitution. Two unique mutations were identified at codon 16 resulting in either Lys to Asn or Lys to Thr amino acid substitutions. Our results show that ras mutations are induced by DEN and are present in over 30% of the fish that developed tumors. A ras mutation incidence of 30% is similar to that reported in mammalian species exposed to DEN. While mutations at codon 12 have previously been reported, the present study is the first in vivo report of ras point mutations at codon 16.

Detailed genomic mapping and expression analyses of 12p amplifications in pancreatic carcinomas reveal a 3.5-Mb target region for amplification

Previous cytogenetic and comparative genomic hybridization (CGH) analyses have shown that the gain of chromosome arm 12p is frequent in pancreatic carcinomas. We investigated 15 pancreatic carcinoma cell lines using CGH, fluorescence in situ hybridization (FISH), and semiquantitative polymerase chain reaction (PCR) to characterize 12p amplifications in detail. The CGH analysis revealed gains of 12p in four of the cell lines and local amplification within 12p11-12 in six cell lines. By FISH analysis, using precisely mapped YAC clones, the commonly amplified region was found to be approximately 5 Mb. The amplified segment extended from YAC 753f12, covering the KRAS2 locus, to YAC 891f1, close to the centromere. A semiquantitative PCR methodology was used to estimate genomic copy numbers of 14 precisely mapped expressed sequence tags (ESTs) and sequence-tagged sites, located within this interval. The level of amplification ranged from two- to 12-fold. The produced gene copy profiles revealed a 3.5-Mb segment with various local amplifications. This region includes KRAS2 and ranges from D12S1617 to sts-N38796. Two of the cell lines (primary and metastatic tumor from the same patient) showed amplification peaks within the distal region of this segment, two had peaks within the proximal region, one showed subpeaks in both regions, and one displayed amplification of the entire region. Chromosome segment-specific cDNA array analysis of 29 expressed sequences within the whole interval between D12S1617 and sts-N38796 indicated overexpression of four ESTs, two corresponding to DEC2 and PPFIBP1, and two to ESTs with unknown function. Expression analysis of these and of KRAS2 showed specific overexpression in the six cell lines with local 12p amplifications. These findings indicate two target regions within the 3.5-Mb segment in 12p11-12, one proximal including PPFIBP1, and one distal including KRAS2.

Wildtype Kras2 can inhibit lung carcinogenesis in mice

Although the ras genes have long been established as proto-oncogenes, the dominant role of activated ras in cell transformation has been questioned. Previous studies have shown frequent loss of the wildtype Kras2 allele in both mouse and human lung adenocarcinomas. To address the possible tumor suppressor role of wildtype Kras2 in lung tumorigenesis, we have carried out a lung tumor bioassay in heterozygous Kras2-deficient mice. Mice with a heterozygous Kras2 deficiency were highly susceptible to the chemical induction of lung tumors when compared to wildtype mice. Activating Kras2 mutations were detected in all chemically induced lung tumors obtained from both wildtype and heterozygous Kras2-deficient mice. Furthermore, wildtype Kras2 inhibited colony formation and tumor development by transformed NIH/3T3 cells and a mouse lung tumor cell line containing an activated Kras2 allele. Allelic loss of wildtype Kras2 was found in 67% to 100% of chemically induced mouse lung adenocarcinomas that harbor a mutant Kras2 allele. Finally, an inverse correlation between the level of wildtype Kras2 expression and extracellular signal-regulated kinase (ERK) activity was observed in these cells. These data strongly suggest that wildtype Kras2 has tumor suppressor activity and is frequently lost during lung tumor progression.

Analysis of p53, K-ras-2, and C-raf-1 in pulmonary neuroendocrine tumors. Correlation with histological subtype and clinical outcome

Neuroendocrine tumors of lung, including typical carcinoid (TC), atypical carcinoid (AC), large cell neuroendocrine carcinoma (LCNEC), and small cell lung carcinoma (SCLC) constitute a spectrum of malignancies in which the pathologist at times has difficulty in discerning tumor subtype and aggressiveness in a reproducible fashion. Therefore, 59 primary neuroendocrine lung tumors including 10 TCs, 26 ACs, 15 LCNECs, and 8 SCLCs were selected from cases collected from 1976 to 1988 and immunostained for p53 protein. All of these tumors were also genotyped for specific point mutational damage affecting p53 (exons 5, 7, and 8; with ACs additionally sequenced for p53 exon 6); 13 tumors for K-ras-2 (exon 1); and 31 tumors for c-raf-1 (exon 15) growth-regulatory genes. Genotyping was performed on topographically selected, minute tumor samples removed from unstained formalin-fixed, paraffin-embedded tissue sections (topographic genotyping) using polymerase chain reaction and direct sequencing. The distribution of p53 immunohistochemical staining had four patterns: negative in TCs, one-half of ACs, 3 of 15 LCNECs, and 1 of 8 SCLCs; less than 10% but more than five tumor cells per 10 high power fields (focal) in a subset (7 of 26) of aggressive ACs; 10 to 49% of tumor cells (patchy) in a subset (6 of 26) of ACs with a higher grade of aggressiveness; and 50 to 100% of tumor cells (diffuse), exclusively seen in LCNECs (12 of 15) and SCLCs (7 of 8). Three patterns of immunohistochemical staining intensity of p53 protein were seen: negative, weak or mild, and moderate to marked. SCLCs and LCNECs accounted for cases of moderate to marked staining and were the only ones to have mutations in p53 exons 5, 7, or 8. No mutations were found in AC and TC, showing absent to weak staining and no staining, respectively. The difference in distribution and staining intensities between LCNEC and SCLC compared with AC and TC was statistically significant (P < 0.001). Patients having AC with patchy p53 immunostaining usually had survival limited to 3 years, whereas those having AC with focal p53 immunostaining subsequently developed metastatic or recurrence of AC disease (P < 0.05). The absence of point mutations in cases with patchy or focal immunostaining suggests increased expression of wild-type p53 tumor suppressor protein likely in response to growth deregulation in a more aggressive subtype of AC. A novel hypothesis is presented in regard to these findings. K-ras-2 and c-raf-1 gene sequence analysis showed no evidence of point mutational change in any of the tumors studied. The TC and AC categories are therefore genetically distinct from the higher grade neuroendocrine SCLC and LCNEC. Immunohistochemistry for p53 on AC lung tumors may be helpful to delineate cases at higher risk for aggressive behavior. Additionally, although LCNEC is categorized as a non-small-cell carcinoma, it is more akin genetically and immunohistochemically to SCLC.

Neuroendocrine neoplasms of the lung are not associated with point mutations at codon 12 of the Ki-ras gene

The most prominent abnormality of ras proto-oncogenes in human lung tumours has involved point mutations at codon 12 of the Ki-ras gene. We have analysed 35 tumour samples of neuroendocrine lung neoplasms (ten carcinoid tumours, ten well-differentiated neuroendocrine carcinomas, and 15 intermediate/small cell neuroendocrine carcinomas) for a point mutation at this site. For this purpose, formalin-fixed and paraffin-embedded tissue sections were microdissected to remove non-tumours areas. DNA in the remaining tumour tissue was amplified in vitro by the polymerase chain reaction (PCR) and double-stranded PCR products were subjected to sequence analysis. Neither point mutations at codon 12 nor additional structural alterations at codons 1-32 were detected in Ki-ras gene. Our results suggest that point mutations at codon 12 of the Ki-ras gene do not seem to be involved in the pathogenesis of pulmonary neuroendocrine neoplasms.

Hypomethylation of ras oncogenes in chemically induced and spontaneous B6C3F1 mouse liver tumors

The male hybrid B6C3F1 mouse exhibits a 30% spontaneous hepatoma incidence, and both males and females of this strain are sensitive to chemical induction of liver tumors. The Ha-ras, Ki-ras, and myc oncogenes have been implicated in a variety of solid tumors. Specifically, Ha- and, less frequently Ki-ras have been reported to be activated in B6C3F1 mouse liver tumors, and such activated oncogenes frequently contain a particular point mutation. In light of indications that the transforming capacity of some oncogenes is directly related to the level of the gene product, we hypothesized that transcriptional control of Ha-ras, Ki-ras, and myc is compromised in B6C3F1 mouse liver tumors. A positive correlation has been established between gene expression and hypomethylation. Therefore, the methylation states of these genes were examined in spontaneous liver tumors and in tumors induced by two diverse hepatocarcinogens: phenobarbital and chloroform. Ha-ras was found to be hypomethylated in all tumors examined, whereas Ki-ras was sometimes hypomethylated; such hypomethylation might play a role in the promotion stage of carcinogenesis. The methylation state of myc was unaltered, although this gene appeared to be amplified in tumors. These results suggest that a component of the mechanism by which these oncogenes are activated in B6C3F1 mouse liver tumors involves loss of stringent control of expression, via hypomethylation of the ras oncogenes and, possibly, amplification of myc. These results support the assertion that tumors induced by different classes of carcinogens or arising spontaneously share common biochemical pathways of oncogene activation during tumorigenesis.

Allele-specific detection of K-ras oncogene expression in human non-small-cell lung carcinomas

Point mutations in codon 12 of the K-ras oncogene are frequent in human lung adenocarcinomas. To study the expression of the K-ras gene in these tumors we have developed a mRNA detection technique based on the polymerase chain reaction (PCR). By this technique, K-ras expression can be detected semi-quantitatively in samples of less than 100 ng total RNA. Hybridization of the amplified cDNA sequences with mutation-specific oligonucleotides allows separate quantification of the expression of normal and point-mutated alleles in a single sample. RNA samples from 24 human non-small-cell lung carcinomas (NSCLC), from 2 lung metastases of colonic adenocarcinomas, from 3 human lung adenocarcinoma cell lines, and from normal lung tissue were analyzed. In most tumors, expression of K-ras was detected at levels equal to or several times higher than those found in normal lung tissue. A lung metastasis from a colon adenocarcinoma, known to contain an amplified K-ras gene, highly over-expressed the K-ras gene. In those tumors in which the K-ras oncogene was activated by a point mutation, both alleles of the gene were expressed. Our results show that a high over-expression of K-ras is a rare event in human lung carcinomas, but that a certain degree of over-expression of the mutated allele can be demonstrated in tumors with an activated K-ras gene. With the technique we describe here, adequate estimation of the expression of specific genes in minimal amounts of tumor cells becomes possible.

Application of automated image analysis to demonstrate the correlation between ras p21 expression and severity of gliomas

We found a direct correlation between increasing ras p21 protein immunopositivity and severity of human glioma using computer-assisted, digital-image processing to quantify the amount of p21 immunoreactive to the monoclonal antibody RAP-5. We determined that there was a significant difference in reactivity between glioblastoma multiformes and more-differentiated astrocytomas (experiment-wise error less than 0.05). This result confirmed the conclusions made on the same tumors using standard light microscopy and visual examination. Immunohistochemistry quantized by automated image analysis may be a useful adjunct to current histopathological strategies since it decreases assay subjectivity and variation.

Biochemical and immunological characterizations of antigens recognised by human monoclonal antibodies

The lymphocytes from lymph nodes of six patients with metastatic mammary carcinomas were hybridised by fusion with a non-secreting variant of murine myeloma cells. Hybrid cells producing human immunoglobulin were detected by screening of culture supernatants using a solid-phase enzyme-linked immunosorbent assay for human IgG or IgM. Reactivity of human immunoglobulins to breast tumour cells was assessed by an indirect immunoperoxidase staining of fresh-frozen breast carcinoma sections. In the initial screening, the tissues used were those removed from the patients who acted as source of lymphocytes for fusion. The hybrid-cells, after repeated cloning, were stable for secretion of immunoglobulins. A total of 14 immunoglobulin G and 51 immunoglobulin M human monoclonal antibodies, showing variable reactivity to mammary carcinoma cells in tissue sections by an indirect immunoperoxidase staining method, were obtained. Two immunoglobulin G monoclonal antibodies (designated HMA-29 and HMA-31) were selected on the basis of their strong reactivity to the tumour cells and utilised to identify their corresponding antigens. The antibodies quantitatively discriminated, as expressed by the degree of staining, malignant from normal or benign mammary epithelia in freshly frozen or formalin-fixed breast tissues. The antibodies also showed reactivity to malignant cells of colon, stomach and lung and to normal cells lining the renal tubules and surface epithelium of colon. As revealed by blocking experiments, the epitopes recognised by these antibodies were not expressed on carcinoembryonic antigens, erythrocytes, lymphocytes, glycoproteins from milk-fat-globule membrane or keratins. The antibody HMA-29 immunoprecipitated a phosphoprotein (Mr = 29,000), and antibody HMA-31 two protein components (Mr = 31,000 and 34,000), from lysates of intrinsically labelled human mammary carcinoma cell line (MCF7). Neither of these proteins were present in detectable amounts in an intrinsically labelled melanoma cell line. Immunoblocking and immunoprecipitation experiments suggested that epitopes recognised by these two antibodies are dissimilar and are expressed on different molecules. The antibodies appear to be useful for functional characterisation of those antigens which are present in elevated levels in malignant compared with normal mammary epithelia.

Cellular protoonocogenes are infrequently amplified in untreated non-small cell lung cancer

To examine a potential contribution of protooncogene abnormalities other than point-mutational activation of the K-ras protooncogene in the classification of non-small cell lung cancer, amplification of cellular protooncogenes was studied in 47 lung tumour specimens obtained at thoracotomy and in four lung tumour cell lines. The primary tumours included 21 adenocarcinomas, nine large-cell carcinomas, 13 epidermoid carcinomas, one carcinoid and three metastases of primaries outside the lung. The copy numbers per haploid genome of 11 protooncogenes in every tumour sample were determined: H-ras, K-ras, N-ras, c-myc, N-myc, L-myc, erbB, mos, myb, ncu (erbB-2) and ral amplifications. The c-myc gene was amplified 5-7-fold in two adenocarcinomas, the H-ras gene 3 5-fold in one adenocarcinoma, while the K-ras and the neu gene were amplified in lung metastases from a colorectal and a breast cancer primary respectively. None of the tumours with an amplified protooncogene simultaneously harboured a mutationally activated K-ras gene. We conclude that amplification of the investigated protooncogenes is a rare event in non-small cell lung cancer. In view of the two c-myc amplifications detected, a systematic study of c-myc expression levels in non-small cell lung cancers appears worthwhile.

Immunohistochemical analysis of normal and mutated ras oncogene p21 expression in human pulmonary and pleural neoplasms

In this study we examined 214 cases of primary human pulmonary neoplasms for the expression of a mutated form of the ras oncogene p21 product, recognized by the monoclonal antibody (MCA) DWP. Adjacent serial sections from these same cases had previously been used to demonstrate the frequency of ras p21 expression using the broadly reactive anti-ras p21 MCA RAP-5. Confirmation of the increased expression of p21 was accomplished using MCA Y13-259. The use of adjacent tissue sections from these cases allows the direct comparison of the expression of the mutated and non-mutated forms of ras p21. If reactivity with DWP would prove to be significantly more restrictive than that of the "pan" ras MCAs, RAP-5 and Y13-259, it would lend support to the possibility that DWP (and similar MCAs which detect other specific mutations) could be used to define subsets of these neoplasms based on their specific ras p21 phenotype. Since one would anticipate that the valine/cysteine substitution at position 12 of the ras p21 would occur at only low frequencies in human tumors, our results with DWP are consistent with this hypothesis. As previously reported, RAP-5 reacted with a high proportion of lung tumors (100/214 or 47%). In this report, we demonstrate the selective expression of the mutation recognized by the MCA DWP in only 5% of these same tumors (13/214), and that the expression of this mutated form is not restricted to any of the conventional histological subclasses of pulmonary neoplasms.

Characterization of the state of differentiation of six newly established human non-small-cell lung cancer cell lines

Six new non-small-cell lung cancer (NSCLC) cell lines were established directly from human tissue or indirectly via nude mouse xenografts in serum-supplemented media with success rates of 8% and 13%, respectively. They comprised one adenocarcinoma (ADLC-5M2), two squamous cell carcinomas (EPLC-32M1, EPLC-65H), two large cell carcinomas (LCLC-97TM1, LCLC-103H), and one malignant biphasic mesothelioma (MSTO-211H). All cell lines grew adherent to culture vessels with population doubling times (PDT) of 16-40 h, formed colonies in soft agarose with efficiencies of 0.1%-5.1%, and all grew in athymic nude mice. Xenograft histologies appeared as follows: (a) undifferentiated carcinomas with feeble resemblance to the original tumors in the case of adenocarcinomas and squamous cell carcinomas; (b) large cell carcinoma with high resemblance to the original tumor; (c) an undifferentiated tumor with predominance of large epithelial cells and few fibrous cells in the case of mesothelioma. Human chorionic gonadotropin (HCG) was found by radioimmunoassay and high-affinity binding sites for epidermal growth factor (EGF) by radio-receptor assay in 4/4 cell lines. A very low activity of L-DOPA decarboxylase (DDC) was detectable only in the adenocarcinoma cell line. All cell lines overexpressed the c-myc protooncogene, and no gene rearrangement or amplification was observed. Chromosome analysis revealed modal chromosome numbers of 70-73 in ADLC-5M2, EPLC-32M1, EPLC-65H, and MSTO-211H. Cell lines derived from large cell carcinoma had modal values of 65 and 170 and a wider chromosome distribution than all other cell lines. A NSCLC specific chromosomal aberration has been undetectable until now. These cell lines may aid in elucidating the biology of NSCLC and its interrelationship to other lung tumors.

Mutational activation of the K-ras oncogene. A possible pathogenetic factor in adenocarcinoma of the lung

To define the role of cellular oncogenes in human cancers, we studied the prevalence of mutational activation of ras oncogenes in untreated non-small-cell lung cancer. Genomic DNA was extracted from 39 tumor specimens obtained by thoracotomy and was examined for activating point mutations in codons 12, 13, and 61 of the H-ras, K-ras, and N-ras genes. A novel, highly sensitive assay based on oligonucleotide hybridization following an in vitro amplification step was employed. The K-ras gene was found to be activated by point mutations in codon 12 in 5 of 10 adenocarcinomas. Two of these tumors were less than 2 cm in size and had not metastasized. No ras gene mutations were observed in 15 squamous-cell carcinomas, 10 large-cell carcinomas, 1 carcinoid, 2 metastatic adenocarcinomas from primary tumors outside the lung, and 1 small-cell carcinoma. An approximately 20-fold amplification of the unmutated K-ras gene was observed in a tumor that proved to be a solitary lung metastasis of a rectal carcinoma. We conclude that mutational K-ras activation may be an important early event in the pathogenesis of adenocarcinoma of the lung but that amplification of ras genes or mutational activation of H-ras or N-ras does not play a major part in non-small-cell lung cancer.

Epidermal growth factor receptors in lung tumours

Immunocytochemical analysis of epidermal growth factor (EGF) receptor expression was carried out on frozen sections of 109 primary lung tumours resected at the Brompton Hospital from February 1984 to May 1985. Tumours with detectable levels of this proto-oncogene protein were significantly more frequent among squamous cell carcinomas than among other types of lung tumour. No truncated EGF receptors were detected in the tumours using two monoclonal antibodies (Mabs) directed against different portions of the receptor (EGFR1 and F4). Mab F4 is the first antibody to the EGF receptor to show reactivity in paraffin sections. Southern blot analysis of a subset of the tumours detected amplification of the EGF receptor gene in squamous cell carcinomas but not in adenocarcinomas. The one carcinosarcoma examined had a re-arranged and amplified EGF receptor gene. Measurement of EGF receptor expression in lung tumours can be of diagnostic value and may prove to be useful in the development of antibody-directed therapy.

Isolation of a human genomic fragment, co-amplified with c-Ki-ras, that affects plasmid supercoiling in E. coli

Amplification of cellular proto-oncogenes has been implicated in the development of human malignancies. A library was constructed from genomic DNA extracted from a lung tumour, previously shown to carry an amplified c-Ki-ras 2 gene. Using a v-Ki-ras probe, a fragment with ras homology was isolated and shown to be amplified in the original tumour DNA to the same level as c-Ki-ras. Studies with human hamster hybrids demonstrated that it is normally located on human chromosome 12 (as is c-Ki-ras). The restriction map of the fragment is different from that of the known Ha, Ki or N-ras genes and its sequence shows evolutionary conservation, as demonstrated by hybridisation to the genomic DNA of several mammalian species. A pUC19 subclone (pK42), carrying a 1.3kb insert, shows supercoil heterogeneity in plasmid preparations, as does a second compatible plasmid introduced into the same bacterial host with pK42. It appears therefore that the subclone is encoding a product that affects DNA topoisomerase activity in E. coli.

Anonymous genomic fragment co-amplified with c-Ki-ras 2 detects frequent polymorphism (pK42)

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Genetic predisposition to human lung cancer

The influence of polymorphic variants of the human c-Ha-ras gene on predisposition to lung cancer has been investigated. The human c-Ha-ras gene has been shown to reside on a polymorphic BamH1 restriction fragment. This restriction fragment length polymorphism (RFLP) results from variation in the size of a region of repetitive DNA 3' to the gene. An attempt has been made to characterise and compare the c-Ha-ras RFLP's in a normal population and in a group of cancer patients. DNA was extracted from the white blood cells of 101 normal donors and four common Ha-ras alleles identified, with occasional rare alleles of various sizes. The allele frequencies were examined in 132 lung cancer patients, comprising 66 individuals with small cell carcinoma of the lung (SCCL) and 66 with non-small cell carcinoma of the lung (non-SCCL). An abnormal allele distribution was found in individuals with non-SCCL compared to both control and SCCL values suggesting a degree of genetic pre-position to non-SCCL. In addition, analysis of the Ha-ras RFLP's in solid samples inferred a deletion of material from the short arm of chromosome 11 in two of 16 informative samples.