Ectopic expression of target genes may represent an inherent limitation of RT-PCR assays used for micrometastasis detection: studies on the epithelial glycoprotein gene EGP-2

Our objective was to develop and study the feasibility of a quantitative, nested reverse-transcription polymerase chain reaction (RT-PCR) assay for detection of micrometastatic, epithelial tumor cells using the epithelial glycoprotein EGP-2 gene as a target. Several carcinoma cell lines and peripheral blood samples of 10 healthy volunteers were screened for levels of EGP-2 mRNA. The assay included EGP-2 competitor molecules, carrying an internal deletion, that had been titrated by limiting dilution. Seven carcinoma cell lines showed a wide spectrum of EGP-2 mRNA expression levels, with the highest values (20-100 molecules/cell) seen in 3 breast-cancer cell lines. Unexpectedly, a consistent low level of EGP-2 mRNA expression (0.0004 molecules/cell) was observed in peripheral blood mononuclear cells, probably representing ectopic non-functional expression. Because of this background level, spiking experiments with T47D breast-carcinoma cells added to blood mononuclear cells exhibited a detection limit that was not better than approximately one tumor cell in 2 x 10(4) normal cells. Together with the considerable variation of EGP-2 transcript levels that is observed in different carcinoma cell lines, the extent of expression in normal blood cells would prevent a reliable estimation of low numbers of carcinoma cells in clinical samples. A similar situation might well apply for other target genes. This emphasizes the need for a critical evaluation of the different steps involved in the methods used for RT-PCR detection of micrometastatic tumor cells.

HMGIC, the gene for an architectural transcription factor, is amplified and rearranged in a subset of human sarcomas

Amplified segments of the long arm of chromosome 12 are frequently observed in human sarcomas. In most cases there are separate amplified regions around the MDM2 and CDK4 genes. Here we show recurrent amplification of a third region encompassing HMGIC, a human architectural transcription factor gene. Reduced amplification frequency of sequences flanking the gene was observed, indicating that inclusion of this third region in the amplicons is also selected for. In three samples only the 5' part of HMGIC was amplified, suggesting preferential loss of the 3' part of the gene preceding or during amplification. In several other samples rearrangement of the gene was observed. Expression analysis showed transcripts of aberrant sizes, lacking 3' sequences, and 3' RACE of one sample revealed replacement of exons 4 and 5 with ectopic sequences. This truncation of HMGIC resembles that reported for translocations of HMGIC in benign tumors, including lipomas, and it is striking that the gene was frequently amplified or rearranged in well differentiated liposarcomas, the malignant counterpart of lipomas. It seems conceivable that high levels of either full length or truncated hmgic could be relevant for the etiology of these tumors.

Zilascorb(2H), a new reversible protein synthesis inhibitor: clinical study of an oral preparation

The new anti-cancer drug zilascorb(2H) has shown promising activity in preclinical models. Its putative mechanism of action is reversible protein synthesis inhibition and long-term treatment is required. As a clinical treatment modality, long-term daily zilascorb(2H) infusions, as used in previous studies, are not regarded feasible. Therefore, an oral formulation of the drug was developed, and pharmacokinetic profile, toxicity and antitumor activity of zilascorb(2H) tablets were studied. Thirteen patients with advanced solid cancer not amenable to established therapy, but with adequate performance status and organ functions, were included. The treatment was given as a daily i.v. zilascorb(2H) infusion for 5 days, followed by zilascorb(2H) tablets twice daily for 3 months. Blood and urine sampling was performed when estimated plasma steady-state level was reached for each formulation, respectively. Analyses of drug concentrations in plasma and urine were performed by high performance liquid chromatography. Zilascorb(2H) in tablet formulation had a bioavailability of 32%, was quickly absorbed and slowly eliminated. Concomitant use of the H2-blocker ranitidine possibly enhanced bioavailability. Zilascorb(2H) was well tolerated. Two patients experienced drug-related fever, disturbing the treatment schedule for one of them. Moderate nausea was reported. One objective response was obtained. The bioavailability of zilascorb(2H) tablets was satisfactory. The principle of oral administration of zilascorb(2H) is feasible for long-term treatment and the side effects are acceptable. The mechanisms of action and the very low toxicity of the drug makes it a candidate for combination with other anticancer agents.

Immunobead filtration: a novel approach for the isolation and propagation of tumor cells

We have developed a method to facilitate the isolation and expansion of tumor cells from body fluids and tissue biopsies. Antibody-conjugated magnetic beads (immunobeads) were used to isolate tumor cells from blood, bone marrow, ascitic/pleural fluids, and enzyme-digested tissue biopsies. Filtration of the resulting cell suspension through a 20-micron nylon monofilament filter secured to the base of polystyrene 96-well strips purged the bead-rosetting cell fraction of contaminating normal cells and unbound beads. Tumor cells that bound the magnetic beads were retained on the membrane due to their increased size and concentrated into a small area (0.332 cm2), thus maintaining a high cell density. The filters provided a stable and uniform three-dimensional matrix for cell growth, with a total surface area of 1.42 cm2 available for cell attachment. The filters could be easily removed from the base of the 96-well strips to facilitate handling and transfer between culture vessels. Tumor cells grown on the filters could subsequently be harvested using trypsin/EDTA or left in situ for immunostaining with conventional immunohistochemical procedures. Filter-grown cells have shown extended passage in conventional cell culture in six cases. In two of five cases, the orthotopic implantation of confluent filters that contained approximately 10(4) cells/8 x 8 mm filter successfully produced tumors in nude mice after only 4 weeks. Our new approach may be of value in improving the success rate of generating long-term cultures from previously unproductive sources of tumor cells and thus may yield a greater variety of cell lines/strains for the study of malignant disease.

Cyclin kinase inhibitor p21WAF1/CIP1 in malignant melanoma: reduced expression in metastatic lesions

Immunohistochemical analysis of the expression of the cyclin kinase inhibitor p21WAF1/CIP1 in a panel of primary and metastatic human melanocytic tumors was performed. It was found that, independent of the p53 status, approximately 30% of the primary melanomas and 40% of the metastases completely lacked expression of this cell cycle inhibitor. Some tumors were also analyzed by Northern blotting, and in most of the cases a consistant correlation between mRNA and protein expression was observed. In four benign nevi studied, WAF1/CIP1 mRNA was expressed whereas the protein was not detected, suggesting a post-transcriptional regulation of the inhibitor in these cases. In superficial spreading melanomas, a significant correlation between protein expression and tumor thickness was found, with thin lesions showing low protein levels. Interestingly, by comparing primary and metastatic specimens obtained from the same patient, a reduction in p21WAF1/CIP1 antibody staining was observed in the latter, probably reflecting a more aggressive phenotype of the metastases. In conclusion, our results demonstrate the complexity in the relationship between p21WAF1/CIP1 expression and tumor phenotype and furthermore suggest that aberrant expression of the cyclin-dependent kinase inhibitor may be of importance in the development and progression of sporadic malignant melanoma.

Reversal of the in vivo metastatic phenotype of human tumor cells by an anti-CAPL (mts1) ribozyme

The putative role of the CAPL gene in enhancing the development of human cancer metastasis was examined by transfecting human high-expressing osteosarcoma cells with a hammerhead ribozyme directed against the gene transcript. The ability of the ribozyme to cleave target mRNA in intact cells was demonstrated in a 5'-rapid amplification of cDNA ends assay. In transfected cells, a suppression of the capacity to give skeletal metastases upon intracardial injection into nude rats was observed in cell clones with reduced expression of CAPL mRNA and protein, whereas in vitro and in vivo cell proliferation and tumorigenicity were unchanged. The results provide direct evidence that the expression level of the CAPL-encoded protein can determine the metastatic potential of osteosarcoma cells, and they demonstrate an association between reduced gene expression and proliferation-independent inhibition of the metastatic capacity of human tumor cells. The effects of the specific cleavage of CAPL mRNA indicate that the gene product is involved in key cellular functions associated with the metastatic process and suggest that therapeutic modulation of the protein function may represent a novel approach for inhibiting the metastatic spread of cancer cells.

Separate amplified regions encompassing CDK4 and MDM2 in human sarcomas

Amplification of MDM2 and CDK4 is observed frequently in human sarcomas. Although overexpression of these protooncogenes might inhibit growth regulation through the TP53- and retinoblastoma tumor suppressor protein (RB)-mediated pathways, neither gene was included consistently in all of the amplicons observed in our sarcoma panel. It was unclear whether both of these genes were selected for during amplification. Furthermore, in some samples without amplification of MDM2 or CDK4, comparative genomic hybridization showed amplification in the 12q13-15 region, suggesting that another selection mechanism might also be involved. To investigate the possibility that another target gene, which may be located between CDK4 and MDM2, could be the driving force, we characterized the involvement of 17 loci from this region in 12q13-15 amplicons that were detected previously in 21 sarcoma samples. The results showed discrete amplicons around MDM2 and CDK4 with reduced amplification of the intervening sequences. This suggests that there is separate selection for amplification of the two genes, and it makes the possibility of a common selective gene unlikely. Furthermore, D12S8, localized distal to MDM2, was amplified almost as frequently as MDM2 and was also amplified in one of the samples without MDM2 or CDK4 amplification. The data suggest that amplification of at least three different regions within the 12q13-15 segment may be selected for in tumor cells involving MDM2, CDK4, or a more distally located gene, possibly near D12S8.

Brain metastasis model in athymic nude mice using a novel MUC1-secreting human breast-cancer cell line, MA11

The MA11 human breast-cancer cell line was established with cells isolated from a bone-marrow sample using immunomagnetic beads conjugated to the anti-MUC1 antibody BM-2. The cell line showed a selective preference for metastasising to the brain in athymic nude mice. Following injection of MA11 cells into the left ventricle of the heart, brain metastases developed in 87% (20/23) animals, with a mean latency until development of neurological symptoms of 65 days. Necropsy and histological examination revealed tumour nodules of varying sizes throughout the brain, invading both grey and white matter of both hemispheres, and with extensive involvement of the cerebellum. MRI spin-echo images indicated brain lesions in some animals that were subsequently confirmed by histology. Three mice showed small tumour nodules (1-2 mm) in the lung, and 2 had solitary lesions (< 1 mm) within the spinal cord. Metastases were not detected in bone, liver, adrenal gland, kidney, spleen or heart. The human MUC1 mucin, as determined by a europium-based immunoradiometric assay, was detected in the serum of 9/11 animals that showed histological evidence of brain metastases. The mucin could not be found in mouse serum samples taken before day 46. The concentration range of MUC1 observed was from <1 to >50 U/ml, and did not appear to correlate with the size or number of tumours as determined from histological sections. This new model provides an opportunity to study the mechanisms of clinically relevant organ-selective metastases and may be of use in evaluating novel treatment for brain metastases in breast cancer.

Regulation of matrix metalloproteinase-1 and tissue inhibitor of metalloproteinase-1 in MCF-7 cells: comparison with regulatory mechanisms of pS2 expression

Regulation of two genes involved in tumor invasion, the matrix metalloproteinase (MMP)-1 and the tissue inhibitor of MMP (TIMP)-1, by activators of protein kinase C (PKC) or protein kinase A (PKA) was studied in MCF-7 mammary adenocarcinoma cells. The basal mRNA expression was undetectable for MMP-1 and low for TIMP-1. Treatment of MCF-7 cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) (100 nM) was associated with a high expression of MMP-1 mRNA, as well as an induction of the level of TIMP-1 mRNA (5- to 10-fold). In the presence of actinomycin D (AMD, 4.0 microM), an inhibitor of transcription, these stimulatory effects of TPA were abolished. Similar responses were observed when protein synthesis was inhibited by cycloheximide (CHX, 50 microM). In the presence of the cyclic AMP (cAMP) analogue N6-benzoyl (N6-Bzl)-cAMP (500 microM), the MMP-1 mRNA was unaffected and still below the level of detection, whereas a non-significant increase (< 2-fold) in TIMP-1 mRNA was observed. The level of pS2 mRNA, of which the induction by TPA in MCF-7 cells is a primary transcriptional event, was up-regulated (10- to 15-fold) by TPA (100 nM), whereas a much weaker increase (2- to 3-fold) was observed by treatment with N6-Bzl-cAMP (500 microM). Again, these stimulatory effects were counteracted by AMD (4.0 microM) and CHX (50 microM). These data suggest that activation of PKC but not of PKA may induce transcription of MMP-1 and TIMP-1, possibly by the synthesis of transcription factor(s), in transformed cells of epithelial origin.

Purging of tumor cells from leukapheresis products: experimental and clinical aspects

Peripheral blood progenitor cell autografts are being used increasingly in conjunction with high-dose therapy of cancer patients, in the belief that these products have a low probability of containing tumor cells. However, recent findings demonstrate that tumor cell involvement is frequent in leukapheresis products. Although the clinical value of purging has not been clinically established by prospective randomized trials, several studies indicate that contaminating tumor cells in autografts contribute to relapse of the disease in the recipients. We describe our experimental and clinical experience in purging tumor cells from leukapheresis products. Based on our work with purging of lymphoma cells from bone marrow by the use of anti-B cell and anti-T cell antibodies and immunobeads, a purging procedure to deplete leukapheresis products of lymphoma cells has been developed. Moreover, we present data showing that breast cancer cells can be efficiently removed from leukapheresis products using antibreast cancer antibodies, either in combination with immunobeads or as immunotoxins. Our experience with enrichment of CD34 cells employing immunobeads in leukaphresis products from patients with breast cancer and lymphomas shows high purity and yield of CD34 cells. In spite of this, contaminating tumor cells can be observed, strongly suggesting that a combination of CD34 cell enrichment and a purging procedure might be warranted.

Cysteine proteinase inhibitors reduce malignant melanoma cell invasion in vitro

Proteolytic enzymes are believed to be necessary for tumor cell invasion. We have studied the effects of the cysteine proteinase inhibitor E-64 and the serine and cysteine proteinase inhibitor leupeptin, on the ability of human malignant melanoma cells (LOX) to pass through an artificial basement membrane. Transwell chambers containing filters coated with the reconstituted basement membrane, Matrigel, were used. Nontoxic concentrations of the proteinase inhibitors reduced the invasion of LOX cells through Matrigel. E-64 (250 mumol/l) by 27% and leupepetin (250 micrograms/ml) by 46%. The proteinase inhibitors did not alter the growth rate of the tumor cells, their motility through uncoated filters, or their attachment to the Matrigel coated wells. Our results indicate that cysteine proteinases are involved in the degradation of basement membranes and thus contribute to the invasion of malignant melanoma cells.

Involvement of the pRb/p16/cdk4/cyclin D1 pathway in the tumorigenesis of sporadic malignant melanomas

Biopsies from 61 sporadic metastatic malignant melanomas and five melanoma cell lines were examined for homozygous deletions and mutations in the CDKN2 gene (p16). As the p16 protein is involved in a cell cycle regulatory pathway consisting of at least pRb, cdk4 and cyclin D1, the tumours were also screened for amplifications of the last two genes. Moreover, the transcript levels of the genes were determined and the results compared with the immunohistochemically assessed expression of pRb. Altogether, homozygous deletions of CDKN2 were found in seven tumours (11%) and two of five cell lines, whereas a mutation was detected in only one biopsy, indicating that in sporadic melanomas the former mechanism is predominant for inactivating this gene. Notably, in total 59% of the metastatic lesions lacked detectable expression of p16 mRNA, whereas all the biopsies were found to express pRb. In accordance with the postulated negative feedback loop between p16 and pRb, one melanoma cell line showed overexpression of CDKN2 mRNA together with very low levels of the Rb protein. Amplification of the other two genes may not be important in the tumorigenesis of melanomas, as only one CDK4 and no CCND1 amplification was observed. However, highly elevated CDK4 mRNA levels, compared with that seen in a panel of normal tissues, were observed in 76% of the tumours, accompanied in 71% of the cases by high expression of the CCND1 cyclin activator. Although a low frequency of CDKN2 DNA aberrations was observed, the high number of tumours that lacked CDKN2 expression but showed overexpression of CDK4 and/or CCND1, suggest that functional inactivation of pRb through this pathway may be involved in the development or progression of sporadic human melanomas.

Comparative antitumor activities of halichondrins and vinblastine against human tumor xenografts

Halichondrin B and homohalichondrin B are novel tubulin-interacting agents isolated from marine sponges. The in vivo antitumor activities of these compounds were examined in human tumor models in immunodeficient mice and rats. In nude mice, regression or pronounced delay of subcutaneous tumor growth was obtained with both halichondrins, at a maximum tolerable dose of 20 micrograms/kg Q2Dx5, in three of four vinblastine-sensitive tumors, including two melanomas and one osteosarcoma; one small-cell lung cancer line was resistant. The halichondrins as well as vinblastine showed only marginal activity against KM20L colon carcinoma xenografts. In a LOX melanoma lung colony formation assay in groups of six nude mice, all control animals were sacrificed because of respiratory symptoms 38 days after cell injection, and likewise one vinblastine-treated mouse after 53 days. All halichondrin-treated mice in the lung colony assay appeared healthy throughout an observation period of 112 days (p = 0.002). Upon necropsy all vinblastine-treated animals, and two of six mice in the halichondrin group, had macroscopic lung tumor colonies. In a nude rat model for LOX bone marrow metastases, the mean lifespan of untreated control animals was 15 days. Whereas vinblastine had only a marginal effect (17 days) in this model, halichondrin B prolonged the lifespan of the animals to 32 days, representing a significant (p = 0.0016) difference between the two compounds. In conclusion, the halichondrins, which comprise a subtype of tubulin-interactive anti-mitotic agents, showed distinct antitumor activity profiles in human tumor models, thereby encouraging their further preclinical development and possible clinical evaluation.

Comparative genomic hybridization analysis of human sarcomas: I. Occurrence of genomic imbalances and identification of a novel major amplicon at 1q21-q22 in soft tissue sarcomas

Comparative genomic hybridization (CGH) was recently developed as a tool to survey entire genomes for variations in DNA sequence copy numbers. We have applied this technique to detect and map amplified regions in 54 soft tissue sarcomas. Aberrations were detected by visual analysis of hybridizations or contrast-enhanced digital images, followed by quantitative digital ratio imaging of the aberrant chromosomes. Several tumors showed increased DNA sequence copy number at 12q14, as expected. However, CGH analysis detected amplification of 12q14 also in some tumors where neither MDM2 nor CDK4 was amplified, suggesting that another as yet unknown gene(s) may drive amplification of this region in sarcomas. Furthermore, a novel recurring amplicon was detected at 1q21-q22. DNA amplifications coinciding with this segment were as frequent as those observed for 12q14, indicating that 1q21-q22-linked gene(s) may also play an important role in the development and/or progression of human soft tissue sarcomas.

Comparative genomic hybridization analysis of human sarcomas: II. Identification of novel amplicons at 6p and 17p in osteosarcomas

Using comparative genomic hybridization (CGH), we have identified and mapped regions of DNA amplification in primary and metastatic osteosarcomas. Samples were obtained from four patients and ten independent xenografts. Sixty-four percent of the tumors showed increased DNA-sequence copy numbers, affecting 23 different chromosomal sites. Most of these regions were not previously associated with the development and/or progression of these tumors. Amplicons originating from 1q21-q23, 6p, 8q23-qter, and 17p11-p12 were observed most frequently. The 6p and 17p11-p12 amplicons seem to be specific for osteosarcomas, indicating that these regions may harbor genes relevant for the development of these tumors.

Homozygous deletion frequency and expression levels of the CDKN2 gene in human sarcomas--relationship to amplification and mRNA levels of CDK4 and CCND1

Homozygous deletions of the putative tumour-suppressor gene CDKN2, which encodes an inhibitor of cdk4, have been detected in a high percentage of cancer cell lines of various histological types. In the present study, 109 human sarcomas were examined for homozygous deletions and for mRNA expression levels of the CDKN2 gene. Altogether, deletions were found in only eight (7%) of the cases, but, interestingly, in two (of eight) malignant Schwannomas and in two (of five) rhabdomyosarcomas. In comparison, such deletions were seen in only one (of 21) osteosarcomas and in none of 20 MFHs and 21 liposarcomas. Notably, highly elevated CDKN2 mRNA levels were found in 33% of the sarcomas, whereas no detectable transcript was present in 12 normal tissues. Amplifications of CDK4 and CCND1 (cyclin D1) were observed in 11% and 4% of the sarcomas respectively, but never in tumours with CDKN2 deletions. The level of CDK4 mRNA expression was increased in nine tumours in addition to the 12 samples with CDK4 amplification. Increased levels of the cyclin D1 transcript was found in 37 cases, four with and 33 without amplification. The data indicate that aberrations of these functionally related genes, or in regulation of the expression of the kinase, the activator or the inhibitor, may participate in sarcoma development. Furthermore, the data suggest that homozygous CDKN2 deletions may be of dissimilar significance in different sarcoma subtypes.

Accumulation of p53 protein in human malignant melanoma. Relationship to clinical outcome

Paraffin-embedded tissue from the primary tumours of 116 patients with malignant melanoma, and in 40 cases also from corresponding metastases, were examined for accumulation of p53 protein. The fraction of tumours with positive p53 immunostaining was 13% in the least invasive and 36% in the most invasive primary lesions and 48% in the metastases. Where comparisons could be made, both the level and pattern of p53 immunoreactivity were the same in the primary and metastatic tumours. Nine (50%) patients with p53-positive and 34 (39%) with p53-negative primaries relapsed during the first 5 years, but no difference in disease-free period was observed between the two groups. However, an overall longer survival time was observed among patients with p53-positive primaries, especially for those with tumours less invasive than 3.0 mm. Notably, all 11 patients in this group were alive 5 years after diagnosis of the disease, whereas 15 out of 70 (21%) patients with p53-negative tumours died in same period. The results show that an increased level of p53 protein does not indicate increased degree of malignancy in melanoma, but rather suggests a more favourable disease progression.

In vitro and in vivo variation in transferrin receptor expression on a human medulloblastoma cell line

The poor prognosis associated with pediatric central nervous system tumors such as medulloblastoma has led to the development and investigation of a variety of new treatment techniques. Therapeutic agents include targeted-toxin conjugates or immunotoxins that show significant in vitro activity against many brain tumors. Transferrin receptors (TRs) are specific, cell-surface antigens that are expressed preferentially on brain tumors rather than on normal human brain tissue. This antigen has been successfully targeted in human and nonhuman brain tumors in vitro and in vivo. In this study, when TRs were used as a target in the DAOY human medulloblastoma-derived cell line in vitro, a significant level of expression was confirmed by testing the sensitivity to different immunotoxins. To ensure the relevance of the in vitro data to the in vivo situation, we also analyzed TR expression in DAOY tumors growing in athymic mice and rats. Immunocytochemistry, immunohistochemistry, immunobead binding, immunofluorescence, 125iodine-transferrin binding, and Northern blot analysis were used to compare TR expression in DAOY cells in vitro and in vivo. All in vitro assays demonstrated significant TR expression, whereas in vivo, the TR expression was negligible in the DAOY tissue. The results caution against extrapolating in vitro antigen and receptor expression data directly to the in vivo situation. Using a transferrin-toxin conjugate in a nude rat model of leptomeningeal carcinomatosis, we achieved therapeutic efficacy, despite demonstrating reduced TR expression on tumor tissue. With respect to clinical efficacy, the reduced expression of TR on DAOY medulloblastoma in vivo may be less significant than expected because of the extreme potency of immunotoxins observed in central nervous system tumors.

Endocrine and metabolic characteristics of polyoma large T transgenic mice that develop ACTH-producing pituitary tumors

The authors have analyzed several endocrine and metabolic parameters in polyoma large T transgenic mice (PyLT-1) that develop adrenocorticotropic hormone (ACTH)-immunoreactive pituitary tumors and in nontransgenic mice with tumor transplants. All clinically ill PyLT-1 mice (13 to 16 months of age) had pituitary macroadenomas and elevated plasma ACTH levels. Compared to PyLT-1 transgenic mice, the ACTH plasma concentrations in immunocompetent mice with transplant tumors were markedly raised. In these animals, a secondary effect of hypercorticotropism was documented by a moderate hyperglycemia. Furthermore, mice with transplant tumors had a pathological weight increase from the time the tumor was palpable. The present study supports and extends the authors' previous morphological documentation of the similarity between the ACTH-producing tumors in this mouse model and human Cushing's disease.

Semiquantitative polymerase chain reaction for t(14;18) in follicular lymphomas: a colorimetric approach

BACKGROUND

Autologous bone marrow transplantation is increasingly being used in the management of several types of cancer, and to avoid reintroduction of malignant cells, bone marrow purging is often performed. In such cases, sensitive quantitation methods are needed both to assess the efficacy of the purging and for surveillance of patients in remission. Polymerase chain reaction (PCR) has the necessary sensitivity for this application, but it requires that the cancer cells can be recognized by a defined genetic abnormality. In addition, PCR is in principle a qualitative technique and must be modified for quantitative purposes. In follicular non-Hodgkin's lymphomas, the translocation t(14;18) (q32;q21) is common and is used here for model experiments.

EXPERIMENTAL DESIGN

A PCR-based method for the quantitation of translocation-positive cells was developed on the basis of coamplification of cancer-specific target molecules with competitor molecules of known concentration. Gel electrophoresis was substituted by a colorimetric quantitation system to cope with patient PCR products of the same size as the competitor product and ease automation of the method at a later stage. Cell line Karpas 422, which contains the t(14;18) (q32;21) translocation, was used to validate the method. The method was used to assess the efficacy of a patient bone marrow purging where the initial infiltration levels were too low for traditional detection systems.

RESULTS

A reproducible and near linear response was obtained between 70 pg and 200 ng K422 DNA, equivalent to 10 K422 cells and 30,000 K422 cells, respectively. Bone marrow infiltration in one patient was 0.6 to 0.7% before malignant cell removal and 3 to 7 x 10(-4) after removal. The corresponding figures for the other patient were 2% and 3 to 7 x 10(-4), respectively.

CONCLUSIONS

The method presented has a sufficient dynamic range for applications like evaluation of bone marrow purging or monitoring of minimal residual disease. Adaptation of this method to other translocations is discussed.

The protooncogene CHOP/GADD153, involved in growth arrest and DNA damage response, is amplified in a subset of human sarcomas

The C/EBP-homologous transcription factor CHOP (GADD153) is inducible by growth inhibition or DNA damage, and has been shown to be oncogenically activated by the specific (12;16) translocation in human myxoid liposarcoma. We have now found CHOP amplification in two sarcoma cell lines with previously reported amplification of the nearby GLI gene. Among 98 other human sarcomas of various types, CHOP was amplified in a hemangiopericytoma, a liposarcoma, and two osteosarcoma. High constitutive expression levels of CHOP were observed in tumors with gene amplification, but also in some other samples. The nearby MDM2 gene, which codes for a protein that may inactivate wild-type p53, has previously been reported to be frequently amplified in sarcoma. In our sarcoma panel, MDM2 was amplified in 9 cases. MDM2 and CHOP were co-amplified in two of these, whereas the two osteosarcomas had amplified CHOP but not MDM2. CHOP was amplified in both cell lines with GLI amplification, and MDM2 only in one. No mutations in the TP53 gene have been found in samples with amplification of MDM2. In contrast, the cell line in which CHOP but not MDM2 was amplified had mutated TP53, suggesting that selection of this amplicon was not mediated through p53 inactivation.