Oncogene amplification and chromosomal abnormalities in small cell lung cancer

Molecular biology of lung cancer: clinical implications

Lung cancer is a heterogeneous disease clinically, biologically, histologically, and molecularly. Understanding the molecular causes of this heterogeneity, which might reflect changes occurring in different classes of epithelial cells or different molecular changes occurring in the same target lung epithelial cells, is the focus of current research. Identifying the genes and pathways involved, determining how they relate to the biological behavior of lung cancer, and their utility as diagnostic and therapeutic targets are important basic and translational research issues. This article reviews current information on the key molecular steps in lung cancer pathogenesis, their timing, and clinical implications.

Fractionated irradiation of H69 small-cell lung cancer cells causes stable radiation and drug resistance with increased MRP1, MRP2, and topoisomerase IIalpha expression

PURPOSE

After standard treatment with chemotherapy and radiotherapy, small-cell lung cancer (SCLC) often develops resistance to both treatments. Our aims were to establish if fractionated radiation treatment alone would induce radiation and drug resistance in the H69 SCLC cell line, and to determine the mechanisms of resistance.

METHODS AND MATERIALS

H69 SCLC cells were treated with fractionated X-rays to an accumulated dose of 37.5 Gy over 8 months to produce the H69/R38 subline. Drug and radiation resistance was determined using the MTT (3,-4,5 dimethylthiazol-2,5 diphenyltetrazolium bromide) cell viability assay. Protein expression was analyzed by Western blot.

RESULTS

The H69/R38 subline was resistant to radiation (2.0 +/- 0.2-fold, p < 0.0001), cisplatin (14 +/- 7-fold, p < 0.001), daunorubicin (6 +/- 3-fold, p < 0.05), and navelbine (1.7 +/- 0.15-fold, p < 0.02). This was associated with increased expression of the multidrug resistance-associated proteins, MRP1 and MRP2, and topoisomerase IIalpha and decreased expression of glutathione-S-transferase pi (GSTpi) and bcl-2 and decreased cisplatin accumulation. Treatment with 4 Gy of X-rays produced a 66% decrease in MRP2 in the H69 cells with no change in the H69/R38 cells. This treatment also caused a 5-fold increase in topoisomerase IIalpha in the H69/R38 cells compared with a 1.5-fold increase in the H69 cells.

CONCLUSIONS

Fractionated radiation alone can lead to the development of stable radiation and drug resistance and an altered response to radiation in SCLC cells.

Advances in the analysis of chromosome alterations in human lung carcinomas

A review of chromosomal analyses of human lung carcinomas is presented. Karyotypic studies have revealed multiple cytogenetic changes in most small cell lung carcinomas (SCLCs) and non-small cell lung carcinomas (NSCLCs). In SCLCs, losses from 3p, 5q, 13q, and 17p predominate; double minutes associated with amplification of members of the MYC oncogene family may be common late in disease. In NSCLCs, deletions of 3p, 9p, and 17p, +7, i(5)(p10), and i(8)(q10) often are reported. The recurrent deletions encompass sites of tumor suppressor genes commonly inactivated in lung carcinomas, such as CDKN2 (9p21), RB1 (13q14), and TP53 (17p13). Despite technical advances in cell culture, the rate of successful karyotypic analysis of lung carcinomas has remained low. Alternative molecular cytogenetic methods to assess chromosome changes in lung cancer, particularly comparative genomic hybridization (CGH) analysis, are discussed. Initial CGH studies confirm the existence of many of the karyotypic imbalances identified earlier in lung cancer and have revealed several recurrent abnormalities, such as 10q- in SCLC, that had not been recognized previously. The further application of such molecular cytogenetic approaches should enable investigators to define more precisely the spectrum and clinical implications of chromosome alterations in lung cancer.

Molecular events in lung cancer

The observation that genes contributing to the process of malignant transformation are altered forms of genes normally present in eukaryotic cells initiated many of the advances that have increased our understanding of lung carcinogenesis at the molecular level. The gene families implicated in carcinogenesis include dominant oncogenes and tumor suppressor genes. Proto-oncogenes (normal homologue of the oncogene) participate in critical cell functions, including signal transduction and transcription. Only a single mutant allele is required for malignant transformation. Primary modifications in the dominant oncogenes that confer gain of transforming function include point mutations, amplification, translocations, and rearrangements. A second recently described gene family is the tumor suppressor genes. Tumor suppressor genes appear to require homozygous loss of function either by mutation, deletion, or a combination of these. Some tumor suppressor genes appear to play a role in the governance of proliferation by regulation of transcription. The identification of specific genes that contribute to the development of the cancer cell presents an opportunity to use these genes and their products as prevention and treatment targets.

Secretion of atrial natriuretic peptide and vasopressin by small cell lung cancer

BACKGROUND

Hyponatremia in patients with small cell lung cancer (SCLC) is a common clinical problem usually attributed to tumor secretion of arginine vasopressin (AVP). It recently was shown that some SCLC cell lines produce atrial natriuretic peptide (ANP). The purpose of this investigation was to determine the frequency and clinical consequences of secretion of ANP by SCLC and the relative contribution of ANP and AVP to the hyponatremia associated with this disease.

METHODS

Levels of ANP and AVP were measured in 23 SCLC cell lines and 23 other human tumor cell lines. Also, ANP and AVP levels were determined in plasma samples from 69 patients with active small cell carcinomas.

RESULTS

Of the 23 SCLC lines, 16 (70%) had elevated ANP levels. Only two (8.7%) had elevated AVP levels, and these two also had elevated ANP levels. One of the ANP-producing cell lines was derived from a hyponatremic patient with no other apparent explanation for a low sodium level. However, the four cell lines with the highest levels of ANP were derived from patients who were not hyponatremic. Two other human tumor lines also produced ANP. Of the 69 patients with SCLC, 21 (30.4%) had elevated ANP levels, whereas 4 (6%) had elevated AVP levels. Fifteen of these patients were hyponatremic during their clinical course (21.7%). Of the eight patients who were hyponatremic when samples were collected, two had elevated ANP levels, and only one had elevated AVP levels. Six patients (8.7%) had symptoms of postural hypotension, possibly attributable in some cases of tumor secretion of ANP.

CONCLUSIONS

The majority of SCLC lines produce ANP, and a minority produce AVP. Secretion of ANP may result in hyponatremia and/or postural hypotension. However, secretion of either or both of these peptides does not account for all cases of hyponatremia in patients with SCLC and does not necessarily cause clinical manifestations.

Detailed deletion mapping of the short arm of chromosome 3 in small cell and non-small cell carcinoma of the lung

We constructed a detailed deletion map of the short arm of chromosome 3 (3p) for 55 lung cancer cases by using 17 restriction fragment length polymorphism (RFLP) probes. Initially, we examined 40 small cell lung cancer (SCLC) cases and found three regions of deletion at 3p25-26, 3p21.3 and 3p14-cen, suggesting the possibility of at least three different tumor-suppressor genes on 3p. In order to obtain more detailed deletion area, and to compare the pattern of 3p deletion, we also examined 15 non-small cell lung cancer (NSCLC) cases. Compared to NSCLC cases, most of SCLC cases have widespread deletion on 3p, suggesting multiple tumor-suppressor genes on 3p may be inactivated in this type of cancer. In 3p21.3 area, minimum overlapping area of deletion lays between two probes which are close to each other. These data will be useful to isolate the putative tumor-suppressor genes located on the chromosome 3p.

Do glutathione and related enzymes play a role in drug resistance in small cell lung cancer cell lines?

Small cell lung cancer (SCLC) is treated primarily with combination chemotherapy. Despite high initial response rates, most patients eventually die with drug resistant disease. In some tumours, resistance to multiple chemotherapeutic agents is attributed to overexpression of P-glycoprotein (P-gp). However, this does not appear to be a frequent occurrence in drug resistant SCLC. Increased levels of glutathione (GSH) and related enzymes may play a role in resistance to alkylating agents as well as natural product drugs. We measured levels of GSH, glutathione S-transferase (GST), glutathione reductase (GSH Red), glutathione peroxidase (GSH Px), and gamma-glutamyl transpeptidase (gamma-GT) in a panel of 20 SCLC cell lines. Most of these lines were established from patients treated at this centre. Each cell line had a characteristic and reproducible profile of GSH and related enzyme levels. Immunoblot analysis indicated that the predominant GST in the cell lines was the anionic pi isoenzyme. The relative sensitivity of each of these cell lines to 16 different chemotherapeutic agents was measured using a modified MTT assay. Spearman rank correlation analysis was used to determine the relationships between the relative chemosensitivity of these cell lines and the levels of GSH and related enzymes. The number of positive correlations was no greater than expected by chance alone. Furthermore, there was no correlation with the treatment history of the patients from whom the cell lines were derived. These data suggest that alterations in glutathione metabolism do not play a major role in resistance to chemotherapeutic agents in these human SCLC cell lines.

Oncogene activation: c-raf-1 gene mutations in experimental and naturally occurring tumors

We demonstrate here consistent point mutations of the c-raf-1 proto-oncogene, within a small region of the kinase domain, in a mouse model for chemical tumor induction. This is the first demonstration of point mutated raf genes in vivo, and the first isolation of activating in vivo point mutations in the kinase domain of a proto-oncogene. The specific region where these mutations are clustered also has biological significance. This is precisely the region where 5/5 independently generated monoclonal antibodies raised against Raf-1 map to [29], and predictions based upon the crystal structure of A kinase identify this as the substrate pocket. The tumors examined show a selective specificity for Raf-1 mutations in that another family of genes, the ras proto-oncogenes which are frequently activated by point mutation in both animal and human tumors [15-21,26], is not involved. Our consistent finding of Raf-1 mutations in a mouse tumor model also has consequences for further evaluation of the role of Raf-1 in human tumor development, as it emphasizes the need to examine c-raf-1 at the sequence level. In fact preliminary screening of human lung tumors indicates point mutations at amino acid 533 (John Lyons, personal communication). Finally, the cumulative data on the critical role of Raf-1 in signal transduction and the occurrence of oncogenic Raf-1 in tumors [32-41] highlight this enzyme as an attractive target for development of novel anticancer regimens.

Molecular cloning of IGFBP-5 from SCLC cell lines and expression of IGFBP-4, IGFBP-5 and IGFBP-6 in lung cancer cell lines and primary tumours

We showed recently that insulin-like growth factor binding protein (IGFBP)-1, -2 and -3 are differentially expressed in lung cancer and permanent lung cancer cell lines. Elevated levels of IGF binding capacity in serum of lung cancer patients were also reported. The function and tissue specificity of IGFBP are still obscure but they are probably local regulators of IGF action. Here we show the expression of IGFBP-4 transcripts in 11/11 small cell lung cancer (SCLC) cell lines, in nine out of 11 non-small cell lung cancer (NSCLC) cell lines, in 11/11 lung tumour specimens (10 derived from patients with NSCLC and one from SCLC origin) and in normal lung. In addition we isolated IGFBP-5 cDNA from lambda gt10 libraries of SCLC cell lines. With this IGFBP-5 cDNA we detected transcripts of different lengths in seven out of 11 SCLC cell lines, in 11/11 lung cancer specimens but only in one out of 11 NSCLC cell lines and in normal lung. IGFBP-6 was not detected in northern analysis of any tested SCLC cell line but it was expressed in nine out of 11 NSCLC cell lines and in nine out of 11 human lung cancer specimens and in normal lung.

Establishment and characterization of a panel of human lung cancer cell lines

The establishment and characterization of 11 human lung cancer cell lines are described in this article. Nine of these cell lines were established over a 5-year period, from 1983 to 1988, from patients treated at the Kingston Regional Cancer Centre. These include eight definite or probable small cell lung cancer (SCLC) lines and one adenocarcinoma line. In addition, two other SCLC cell lines were characterized. All of the lines have been in continuous culture for more than 2 years. The clinical histories of the patients from whom the cell lines were derived are outlined here. Several features of the cell lines are presented, including the following: (1) a comparison of the histologic features of the cell lines with the original biopsy specimens; (2) the expression of various markers, including cytokeratin, carcinoembryonic antigen, calcitonin, and neuron-specific enolase; (3) activities of the enzymes l-dopa decarboxylase and the brain isoenzyme of creatine kinase; (4) growth characteristics; (5) cloning efficiency in soft agar; (6) tumorigenicity in nude mice; and (7) cytogenetic studies. These cell lines, obtained directly from patients with a spectrum of drug-sensitive and drug-resistant tumors, will be valuable in vitro models of sensitivity and resistance to chemotherapy in lung cancer.

Differential expression of insulin-like growth factor binding proteins in human non-small cell lung cancer cell lines

The possible expression and secretion of insulin-like growth factor binding proteins (IGFBPs) by non-small cell lung cancer (NSCLC) cell lines was investigated and compared with possible IGFBP expression by primary NSCLC tumours. Cells growing under serum-free conditions released binding proteins with apparent molecular masses of 26-43 kD when analysed by a ligand blotting method under non-reducing conditions. Additionally, northern blot analysis of total RNA from NSCLC cell lines and tumours was performed using cDNAs coding for each of IGFBP-1, IGFBP-2, and IGFBP-3. This analysis revealed expression of all three mRNAs to varying degrees by all cell lines. In contrast all primary tumours analysed expressed predominantly IGFBP-2 and IGFBP-3 and none showed any evident expression of IGFBP-1. Both NSCLC cell lines and tumours synthesise IGFBPs but the pattern of expression differs significantly between cell lines and primary tumours.

Characterization of ligand binding and processing by gastrin-releasing peptide receptors in a small-cell lung cancer cell line

The ligand-binding properties of the gastrin-releasing peptide (GRP) receptor and the cellular processing of GRP have been studied in the small-cell lung cancer (SCLC) cell line COR-L42. Scatchard analysis of GRP receptor expression indicated a single class of high-affinity receptors (Kd 1.5 nM) and approx. 6700 receptors/cell. GRP bound to its receptor with a Ki of 2.4 nM. The bombesin-related peptides neuromedin B (NMB) and phyllolitorin also bound to GRP receptors with Ki values of 22.7 and 59.1 nM respectively. Binding of 125I-GRP to COR-L42 cells increased rapidly at 37 degrees, achieved a maximum at 10 min and declined rapidly thereafter. At 4 degrees C, maximum binding was achieved at 30 min and the subsequent decline in cell-associated radioactivity was slower than that seen at 37 degrees C. Acid/salt extraction, to separate surface-bound ligand from internalized GRP, indicated that after receptor binding 125I-GRP was rapidly internalized. To determine the pathway of 125I-GRP degradation, binding studies were carried out with the lysosomotropic agent chloroquine (5 mM), and with phosphoramidon (10 microM), an inhibitor of the membrane-bound enzyme (EC 3.4.24.11). Both agents markedly inhibited the degradation of GRP, indicating that this process involves a lysosomal pathway and a phosphoramidon-sensitive pathway, possibly involving the EC 3.4.24.11 enzyme. GRP receptor down-regulation was observed following a 10 min exposure to 100 nM-GRP. With longer pretreatment times the number of binding sites recovered to 80% of control values. Treatment with 5 mM-chloroquine plus GRP or cycloheximide (10 micrograms/ml) plus GRP demonstrated that the majority of GRP receptors are recycled. NMB and phyllolitorin pretreatment did not influence the subsequent binding of 125I-GRP, suggesting that these peptides do not down-regulate GRP receptors.

Involvement of the RAF1 locus, at band 3p25, in the 3p deletion of small-cell lung cancer

The ability to establish long-term cell lines of small-cell lung cancer (SCLC) has provided an in vitro model for the disease. We report on the characterization of 10 new human SCLC cell lines established from 34 cytopathologically positive specimens. Based on morphologic and biochemical characterization, growth properties, and expression of MYC and neuroendocrine properties, eight cell lines were categorized as "classic" and two cell lines as "variant". Cytogenetic examination revealed loss of all or part of 3p in all nine SCLC cell lines analyzed. The smallest deletion in common was found at 3p21-3p25. Restriction fragment length polymorphism (RFLP) analyses with probes for 3p were performed for correlation with karyotypic data and supported the cytogenetic findings. In 21 SCLC specimens (cell lines and tumor tissue) with normal DNA, used for comparison, we observed loss of heterozygosity at RAF1 (3p25) in ten of ten informative pairs by using two RFLPs from the RAF1 locus. In addition, loss of heterozygosity was noted in nine of 10 pairs examined with DNF15S2 (3p21) and four of four with D3S3 (3p14). Analysis of cell lines and tumor specimens that lacked paired normal tissue showed a homozygous pattern with the RAF1 probes in all 18 cases. Northern blots revealed significant expression of RAF1 in all cell lines tested. The transcript size was normal. The cytogenetic and RFLP data suggest that the RAF1 locus at 3p25 is involved in the chromosomal deletion of SCLC.

Multidrug resistance-associated antigens on drug-sensitive and -resistant human tumour cell lines

In this paper the biochemical properties of the antigens detected by six murine monoclonal antibodies (MAbs) are described. These MAbs react selectively with the multidrug-resistant small cell lung cancer (SCLC) cell line, H69AR, compared to its sensitive parent cell line, H69 (Mirski & Cole, 1989). Because H69AR cells do not overexpress P-glycoprotein, the antigens detected by these MAbs may be markers for non-P-glycoprotein-mediated mechanisms of resistance. We found that the 36 kDa protein precipitated by MAb 3.186 is phosphorylated and has a pI of approximately 6.7. The 55 kDa protein precipitated by MAb 3.50 is also phosphorylated and has a pI of approximately 5.7. Several observations suggest that MAbs 3.80, 3.177 and 3.187 recognise the same 47 kDa molecule and hence only MAb 3.187 was characterised further. This MAb precipitates an acidic protein which runs as a streak on isoelectric focusing gels. The 25 and 22.5 kDa cell surface proteins precipitated by MAb 2.54 both have a pI of approximately 7.6. Treatment of immunoprecipitates with glycosidase F indicated that none of the proteins detected by MAbs 2.54, 3.187, 3.50 and 3.186 have large N-linked carbohydrates. The peptide nature of the epitopes detected by MAbs 2.54 and 3.186 was unequivocally demonstrated by precipitation from in vitro translation products of H69AR RNA. The antigens detected by MAbs 3.50 and 3.187 were not detectable in immunoprecipitates of translation products but the epitopes are probably peptides because they were destroyed by boiling in sodium dodecyl sulphate. When the reaction of the MAbs with a panel of 15 paired drug-sensitive and -resistant cell lines was examined in a cell enzyme-linked immunosorbent assay, only a few resistance associated reactions were observed. Most of the reactions were either negative or not resistance-associated. When tested with three SCLC cell lines, MAb 3.187 reacted in a manner consistent with the relative resistance of the cell lines. Antigens that had similar electrophoretic mobility to those from H69AR cells were precipitated from extracts of five human cell lines of various tumour types. These data indicate that the cross-reactivities of the MAbs are due to antigens shared among the cell lines and not just the expression of common epitopes on different proteins. Resistance-associated proteins with the biochemical properties of the antigens described in this paper have not been reported previously and they remain potential markers for the as yet to be determined mechanisms of drug resistance in SCLC and other human malignancies.

Insulin-like growth factor binding protein expression in human small cell lung cancer cell lines

Insulin-like growth factor binding proteins (IGF-BP) are secreted by several human small cell lung cancer cell lines (SCLC). In order to identify the IGF-BPs from SCLC cell lines the RNA from 10 different SCLC cell lines was analyzed by Northern blot analysis with the probes for three different IGF-BPs, IGFBP-1, IGFBP-2, and IGFBP-3. No hybridization signal could be detected with the probes encoding for IGFBP-1 and IGFBP-3. The hybridization with different IGFBP-2-specific oligodeoxynucleotide probes and with the corresponding full-length cDNA showed that all SCLC cell lines which secreted IGF-BPs express IGFBP-2.

Chemosensitivity testing of small cell lung cancer using the MTT assay

A simple colorimetric test, the MTT assay, has been adapted for chemosensitivity testing of human small cell lung cancer cell lines, and fresh tumour samples. Optimal conditions for clinical chemosensitivity testing were determined using established SCLC lines. Nineteen different chemotherapeutic agents were tested, and sixteen of them were found to be cytotoxic in this assay system. The drug sensitivity of a panel of 16 SCLC cell lines was measured and compared. There was very little intraexperiment variation, but the interexperiment variation was significant. Cell lines which were derived from patients who had not received chemotherapy at the time the cell line was established were more sensitive (to all but one of the drugs) than lines derived from treated patients, and the differences were statistically significant for two of the drugs. One cell line, NCI-H209, which was derived from an untreated patient, stood out as being the most sensitive or among the most sensitive to all of the drugs tested. Another cell line, H69AR, which is a multidrug resistant subline of the cell line NCI-H69, was the most resistant to many of the natural product drugs tested. Multiple drug chemosensitivity testing was performed on eight fresh tumour samples from SCLC patients (five pleural effusions, one lymph node, and two primary tumours). It was possible to perform chemosensitivity testing on all of the clinical samples in which sufficient tumour cells were available. The drug sensitivity of the clinical samples was, in most cases, within the same range as for the cell lines. Since this assay is very rapid and simple to perform, it may have practical applications in clinical drug sensitivity testing of human tumours.

An unusually proximal deletion on the short arm of chromosome 3 in a patient with small cell lung cancer

The tumors of patients with small cell lung carcinoma (SCLC) frequently exhibit the loss of alleles at polymorphic loci on the short arm of chromosome 3. We report the genotype analysis of six SCLC patients obtained using 15 chromosome 3 probes that identified 19 restriction fragment length polymorphisms (RFLPs). Five of the six patients were reduced to homozygosity in the tumor DNA at every informative 3p locus, and thus did not serve to delineate the deletion. However, the RFLP analysis of the tumor DNA of the sixth patient demonstrated both heterozygous and hemizygous loci on 3p and allowed the definition of an interstitial deletion that extends proximal to the D3S2 locus at 3p14.2-p21 to include at least 3p13-p14. The exclusion of the D3F15S2 locus from the deleted region, observed in this patient, is an uncharacteristic feature of SCLC deletions. This deletion includes the location of D3S30 and D3S4, and thus serves to map these loci within the proximal half of chromosome 3.

A submicroscopic homozygous deletion at the D3S3 locus in a cell line isolated from a small cell lung carcinoma

We have used 14 DNA probes, which detect 19 different restriction enzyme length polymorphisms, to search for heterozygosity on chromosome 3 in five cell lines isolated from patients with small cell lung carcinoma. The cell lines on karyotype analysis did not show the deletion in chromosome 3 characteristic of this disease. Our objective was to determine if allelic loss had occurred by some chromosomal mechanism other than deletion. Two of the cell lines are consistent with allelic loss having occurred by whole chromosome loss and reduplication. The third may have lost only the short arm due to i(3q) formation. The fourth cell line has an i(3q) chromosome, together with a translocation product involving the distal portion of the short arm of chromosome 3. Lack of evidence of heterozygosity for this distal portion of 3p suggests that a copy of the 3p homologue is involved in the translocation and therefore does not explain allelic loss of of the other homologue. The fifth, while also likely to have lost one chromosome homologue, has a submicroscopic deletion on all chromosome 3s, only detectable by RFLP analysis. Such homozygous deletions have recently proved useful in the isolation of tumour suppressor genes.

Molecular mapping of deletion sites in the short arm of chromosome 3 in human lung cancer

We used 10 restriction fragment length polymorphism (RFLP) probes spanning the length of the short arm of chromosome 3 (3p) to map deletion sites in human lung cancer. Two approaches were used. 1) When a patient's tumor and normal tissue were available, loci with allelic heterozygosity in the normal tissue were tested for loss of alleles at 3p. 2) When the corresponding normal tissue was not available, the frequency of heterozygosity at each locus in a panel of tumors was compared to the corresponding published frequencies in nontumor tissue of healthy individuals or patients with lung cancer. In 14 small cell lung carcinomas (SCLC) with normal DNA for comparison, allele loss was found at all heterozygous loci, with one exception at a locus near the 3p centromere (D3S4). In the total of 53 SCLCs, which included tumors without paired normal tissue, frequency of heterozygosity was significantly reduced in all 10 3p loci. Three loci, DNF 15S2, RAF1, and D3S18, were homozygous in all tumors in the SCLC panel. These loci, which are in regions 3p21 and 3p25, may thus be involved in the origin or evolution of SCLC. We also investigated 24 non-SCLC tumors. In this panel, frequency of heterozygosity was significantly reduced at seven of the 10 loci tested. Comparison of the results shows that the pattern of allele loss on 3p is different in SCLC and non-SCLC, suggesting a difference in pathogenesis at the genetic level.

Frequency and extent of allelic loss in the short arm of chromosome 3 in nonsmall-cell lung cancer

DNA was prepared from tumour and normal tissue from 48 patients representing all common histological types of nonsmall-cell lung cancer. Using eight DNA probes, which detect nine restriction enzyme fragment length polymorphisms (RFLP) on chromosome 3, we established that among the 44 informative patients 32 had lost alleles on the short arm of one of their copies of chromosome 3. Of these 32, at least 13 had also lost alleles on the long arm of chromosome 3, suggesting that the whole chromosome might be lost. For one patient, cytogenetic analysis indicated that the mechanism of allelic loss was reciprocal translocation followed by chromosomal loss of one of the reciprocal products. Two patients with allelic loss distal to the D3S3 locus (which maps to 3p13-14) retained heterozygosity at that locus. These results indicate that loss of alleles on the short arm of chromosome 3 is a common event in lung tumours of the nonsmall-cell type, that this loss occurs by a variety of chromosomal mechanisms, and that the minimally deleted region is 3p13-14----3pter.

Relative tumorigenicities of hybrid cells with and without HSR-bearing chromosomes from a human melanoma cell line

Some cell types within the human melanoma cell line MeWo contain homogeneously staining regions (HSRs) consisting of repetitive DNA sequences and ribosomal RNA (rRNA) genes derived from chromosome 15. To further examine the association between enhanced tumorigenicity and the presence of HSR-bearing chromosomes, hybrid cell lines were constructed by fusing X-HSR-containing MeWo cells with ouabain-resistant, HPRT-deficient Chinese hamster ovary cells and culturing in HAT medium containing ouabain. A hybrid containing the X-HSR chromosome and several MeWo chromosomes was more tumorigenic in BALB/c nude mice than derivative cells lacking the X-HSR and human chromosome 18. However, since this enhanced tumorigenicity could be due to sequences on either the X-HSR or chromosome 18, a second series of hybrids was constructed by micro-cell fusion. In this case, the tumorigenicity of hybrid cells containing 2 copies of the X-HSR as the only MeWo chromosome was similar to that of derivative cells lacking these chromosomes. Cytogenetic analysis revealed that the nucleolar organizer regions (NORs) on the HSR were inactive in the hybrid cells. Our data indicate that DNA sequences amplified on MeWo HSRs do not enhance tumorigenicity under experimental conditions in which rRNA genes are not expressed. As the only active NORs in MeWo HSR-containing cells are on the HSRs, we suggest that expression of these amplified rRNA genes is responsible for the selective growth advantage of these cell types in nude mice. Our data also indicate that the enhanced tumorigenicity of MeWo HSR-containing cells is not due to co-amplification of a dominant oncogene.

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.

Cytogenetic abnormalities in human small cell lung carcinoma: cell lines characterized for myc gene amplification

Nine cell lines established from various malignant tissues of patients with small cell lung carcinoma (SCLC) were examined for chromosomal abnormalities and myc gene amplification. Cytogenetic studies revealed that all cell lines were aneuploid, often with a bimodal distribution with modal concentrations in the hypodiploid and hypertriploid range. With respect to chromosome #3, deletions of 3p were confined to six of nine SCLC "classic" lines. The region of overlap of the observed 3p deletions lies within 3p21-3p24 which is in agreement with previous assignments. Six of the nine lines tested with c-, N-, and L-myc probes showed an increase of between ten- and 100 fold in myc gene copy number. Coamplification of two or more of these genes was not observed in any cell line. Five of the six lines with myc gene amplification had cytogenetic markers of gene amplification either in the form of homogeneously staining regions (HSR) or double minutes (DM). Our results confirm that cytogenetically visible deletions of 3p are often present in cell lines established from patients with SCLC, and that mutually exclusive c-, L-, or N-myc gene amplification is also a common event in SCLC cell lines.

Loss of heterozygosity of chromosome 3p markers in small-cell lung cancer

Specific chromosomal deletions sometimes associated with tumours such as retinoblastoma (chromosome 13q14) and Wilm's tumour (chromosome 11p13) have led to the hypothesis that recessive genes may be involved in tumorigenesis. This hypothesis is supported by demonstration of allele loss specific for these regions using polymorphic DNA markers and by the isolation of a complementary DNA clone for the retinoblastoma gene. A cytogenetic deletion in chromosome 3 (p14-p23) was reported in small-cell lung cancer (SCLC) by Whang-Peng et al. At least one homologue of chromosome 3 was affected in the majority of SCLC tumours; however, the multiple chromosomal changes seen presented the possibility that chromosome 3 was rearranged, not deleted. We used polymorphic DNA probes for chromosome 3p and compared tumour and constitutional genotypes of nine SCLC patients. Our data show loss of alleles of chromosome 3p markers in tumour DNA of all nine patients supporting the hypothesis that this region contributes to tumorigenesis in SCLC.