Isolation from a human MDR lung cell line of multiple clonal subpopulations which exhibit significantly different drug resistance

The heterogeneous nature of an adriamycin-selected human MDR squamous lung cell line, DLKP-A, was investigated by isolating and characterising 9 of its clonal subpopulations. The DLKP-A cell line exhibits resistance to the classical MDR drugs, overexpresses P-glycoprotein and displays reduced topoisomerase II amounts. The clonal cell lines exhibit a wide range of resistance extents, with the most resistant clone displaying 9 times the extent of adriamycin resistance observed in the least resistant clone. A number of clones exhibit sensitivity to the concentration of adriamycin in which the parental cell line was selected, possibly indicating cooperation between the more and less resistant cells. Detailed analysis of 4 of the clonal subpopulations revealed broadly similar drug resistance mechanisms. Alterations in expression of the MDR-associated genes MDR1 and Topo IIalpha were observed, with no detectable changes in the expression of MDR3, MRP, GSTpi, Topo IIbeta, Topo I and CYP1A1 noted. However, each clonal cell line displayed a distinct extent of expression of MDR1 and Topo IIalpha and further characterisation of the clones indicated that other modes of drug resistance may exist in at least one of the cell lines. In particular, 2 of the clones (DLKPA6B and DLKPA11B) which have almost identical drug resistance profiles appear to have quite different mechanisms of resistance. The clonal subpopulations possess individual growth rates, amounts of adriamycin accumulation and susceptibility to toxicity-enhancement by MDR-modulating agents. It was possible to generate a cell line with a drug toxicity profile similar to DLKP-A by mixing some of the clonal subpopulations. Our results provide evidence of heterogeneity within an MDR human cell population with respect to resistance and expression of MDR-associated genes.

The multidrug-resistant human lung tumour cell line, DLKP-A10, expresses novel drug accumulation and sequestration systems

Drug accumulation studies with the anticancer agents adriamycin and vincristine were carried out on the MDR variant of the human lung cell lines DLKP, DLKP-A10 which overexpresses the MDR associated P-glycoprotein efflux pump. Reduced cellular accumulation of both agents was observed in the resistant variant. The subsequent addition of verapamil and cyclosporin A resulted in partial restoration of cellular accumulation of both drugs in the DLKP-A10 resistant variant while complete restoration of cellular drug levels was observed in the SKMES-1/ADR cell line. These results suggested that the accumulation defect observed in the SKMES-1/ADR cell line was P-glycoprotein mediated and that accordingly, the cells exhibited characteristics consistent with the classical MDR phenotype. In contrast, while P-glycoprotein also appears to mediate a reduction in cellular drug accumulation in the DLKP-A10 cells, an alternative transport mechanism may also be present. No significant increase in the expression of either the MRP or LRP transport proteins was observed in the resistant cells. Metabolic inhibition by antimycin A (but not sodium azide or 2-deoxy-D-glucose) resulted in complete restoration of drug accumulation suggesting the presence of an alternative energy dependent transport mechanism. Fluorescent microscopy studies indicated different cellular localisation of the drug within the parental and resistant cells despite equivalent intracellular concentrations. These studies also revealed the presence of an ATP-dependent, vesicular sequestration mechanism which may be involved in the reduction of nuclear adriamycin accumulation in the DLKP-A10 cell line. This was indicated by observation of the disruption of cytoplasmic vesicles by antimycin A and also inhibition of cytoplasmic drug sequestration by the carboxylic ionophores, monensin and nigericin, accompanied by increased adriamycin accumulation and redistribution of the drug from the cytoplasm to the nucleus.

Membrane changes associated with the early stages of apoptosis in HEp-2 cells decrease susceptibility to adherence by Candida albicans

The aim of the present work was to establish whether apoptotic HEp-2 cells demonstrated an altered susceptibility to adherence by the pathogenic yeast Candida albicans. Cultures of HEp-2 cells were treated with concentrations of three chemotherapeutic agents sufficient to induce cell death by apoptosis and this was confirmed by microscopic examination and by the loss of membrane asymmetry (as indicated by phosphatidylserine externalization) and the fragmentation of nuclear DNA into distinct subunits. Cells in the early stages of apoptosis demonstrated a reduced susceptibility to adherence by a number of strains of C. albicans. A correlation between the decrease in yeast adherence and the loss of membrane asymmetry, associated with the early stages of apoptosis, was established.

Co-expression of MDR-associated markers, including P-170, MRP and LRP and cytoskeletal proteins, in three resistant variants of the human ovarian carcinoma cell line, OAW42

Variants of the human ovarian carcinoma cell line, OAW42, exhibiting low-level intrinsic resistance (OAW42-SR) and drug-induced higher-level resistance (OAW42-A1 & OAW42-A), were studied along with a sensitive clonal population (OAW42-S) which was isolated from OAW42-SR. Expression of the MDR-associated protein P-170, the more recently discovered LRP (lung resistance-related protein) and MRP (multidrug resistance-associated protein), topoisomerase II alpha and beta, GST pi and the cytoskeletal proteins, cytokeratin 8 and vimentin, were studied (using immunocytochemistry and Western blotting techniques) in conjunction with drug (doxorubicin) accumulation and subcellular distribution. Expression of mRNA for P-170, MRP, topoisomerase 11 alpha and beta and GST pi was studied using RT-PCR (reverse transcriptase polymerase chain reaction). Results indicate differential co-expression of four MDR-associated parameters (P-170, MRP, LRP and reduced topoisomerase II alpha and beta) in the OAW42-SR and OAW42-A1 variants, whereas resistance in the OAW42-A variant appeared to be mainly P-170 mediated. Comparable amounts of MRP and greater amounts of LRP were detected in the OAW42-S cells compared to the OAW42-SR variant (which showed increased resistance compared to the OAW42-S cells), but all cell lines expressed similar low-level amounts of MRP mRNA (by RT-PCR). GST pi levels did not differ markedly between variants. Increased levels of the cytoskeletal proteins were observed with increasing levels of resistance. The relative resistance of the variants, OAW42-SR and OAW42-A1, compared with OAW42-S was seen to change during increased serial passaging of the cells. There was greater drug accumulation by the sensitive OAW42-S cell line compared with that of the resistant variants, particularly the most highly resistant OAW42-A cells. Both verapamil and cyclosporin A effectively restored the accumulation defects seen in the resistant variants, cyclosporin A being the more effective of the two. Sub-cellular location of drug was predominantly in the nucleus with maximum levels seen in the sensitive OAW42-S variant and minimum levels in the most resistant OAW42-A clone.

Multidrug resistance in ocular melanoma

AIMS/BACKGROUND

Metastatic disease in patients with ocular melanoma is resistant to chemotherapy. One of the main mechanisms of modulating multidrug resistance is the expression of the multidrug resistance gene 1 (MDR1) product (p-glycoprotein) by tumour cells. The purpose of this study was to evaluate the frequency of expression of the MDR1 gene in ocular melanoma whose primary treatment was surgical excision or enucleation.

METHODS

Twelve recent ocular melanomas were received fresh, snap frozen and cryostat sections of tumour were analysed for expression of MDR1 by immunohistochemistry using a well characterised monoclonal antibody to MDR1. Tumour explants were established in short term tissue culture from four tumours and cell blocks were examined by immunohistochemistry.

RESULTS

MDR1 expression was present in five of 12 ocular melanomas. Upregulation of protein expression was found in four cell lines established in short term culture from tumour explants. A recurrent tumour, initially treated by local excision and radioactive plaque, showed overexpression of MDR1 mRNA.

CONCLUSIONS

These results suggest that significant level of MDR1 may be intrinsically present in ocular melanomas before exposure to drugs involved in multidrug resistance, and indicate the possible importance of MDR1 in modulating chemoresistance in ocular melanoma. Chemosensitisation may be of potential value in planning adjuvant chemotherapy for patients with metastatic disease.

Behavior of a novel monoclonal antibody for investigation of ovarian cancer and with possible involvement in multiple drug resistance

Monoclonal antibodies (MAbs) were raised to an ovarian cancer cell line, OAW42, derived from a patient with a histology of serous cystadenocarcinoma of the ovary, in an attempt to identify novel antigens with a possible role in cancer medicine. One antibody P1H10, subclass IgG1, with a high titer was isolated and shown to recognize an antigen of 48 kDa. Enzyme-linked immunosorbent assay and immunocytochemical studies showed the presence of the target antigen in a number of carcinoma cell lines, including lung and breast, and in two out of three frozen breast tissue specimens. The antigen was not detected in normal human lymphocytes and there was minimal binding of the antibody to normal buccal cells. The antigen was not secreted by the OAW42 or the HepG2 cell lines and was not detected in the sera of a number of ovarian cancer patients. Indirect immunofluorescence studies confirmed the localization of the antigen to be intracellular. The binding of the antibody P1H10 to a number of multidrug resistant variants of the OAW42 cell line showed that the presence and the localization of the antigen in the drug-sensitive parental line and resistant variant cell lines was distinctly different and varied with the degree of drug resistance. The relative specificity of the antibody suggests it may be a possible diagnostic agent in human cancer. A possible role of the antigen in multiple drug resistance (MDR) is also suggested.

Absence of correlation between chemo- and radioresistance in a range of human tumour cell lines

The correlation between cellular resistance to radiation and to chemotherapeutic drugs has been investigated in a number of solid tumour cell lines, and preliminary results indicate no direct relationship. The acquisition of a multidrug resistance (MDR) profile by adriamycin-selected variants of a human squamous lung carcinoma, an ovarian carcinoma, a cervical carcinoma and by a colchicine-selected variant of a Chinese hamster ovarian carcinoma resulted in alterations to their radiosensitivity. However, the degree of change in the radiosensitivity of the MDR cell lines could not be predicted from their level of resistance to adriamycin. Clonal populations derived from DLKP-A, an adriamycin-selected MDR variant of the human lung carcinoma cell line DLKP, exhibited individual radiosensitivity profiles, which did not correlate with their chemoresistance. Exposure of DLKP to consecutive increasing doses of radiation did not confer cross-resistance to chemotherapeutic drugs.

Multiple drug resistance-related messenger RNA expression in archival formalin-fixed paraffin-embedded human breast tumour tissue

A method is described by which RNA, suitable for reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, can be extracted from formalin-fixed paraffin-embedded (FFPE) tissues and subsequently used for detecting the expression of several genes. Using this technique, RNA can be extracted from specimens, quantified, reverse transcribed and regions of interest amplified and analysed within 36 h. The tissue specimens included in this study were from human breast carcinoma, investigating a range of genes associated with the development and/or maintenance of multiple drug resistance (MDR). This technique, applied to archival tissues, offers great potential for increasing our understanding of alterations in expression levels of genes associated with MDR. The method developed is also applicable to studies on expression of other genes in paraffin-embedded tissues.

mdr1 ribozyme mediated reversal of the multi-drug resistant phenotype in human lung cell lines

An mdr1 hammerhead was introduced into two adriamycin-selected multi-drug resistant human lung cell lines both of which over-express p-glycoprotein. Expression of the ribozyme resulted in a decrease in mdr1 mRNA expression and an increase in drug sensitivity in both cell lines. This would suggest that the use of specific ribozymes may represent an effective and specific approach in order to restore cellular sensitivity towards anti-cancer drugs.

Microstructural musical linguistics: composers' pulses are liked most by the best musicians

Western music is a combination of notated structure plus microstructure. Composers' pulses, as precise microstructural functions, were tested with five groups of subjects of graded musical proficiency: (1) 10 famous artists including Vladimir Ashkenazy, Yehudi Menuhin, Paul Badura-Skoda and others; (2) 14 Julliard School of Music graduate students; (3) 19 Manhattan School of Music graduate students; (4) 51 Australian conservatory students; and (5) 41 non-music students (total, 135 subjects). Composers' pulses consist of combined amplitude and timing warps specific to each composer--the composer's pulse matrix. Each subject listened to and scored 40 versions of 10 short music examples (not selected by the author) of eight bars each, composed by Beethoven, Mozart, Haydn and Schubert, performed by computer, in which composers' pulses, as developed by Clynes (1983, 1985a,b, 1986, 1987), were incorporated in a two-level hierarchic pulse configuration, and interchanged. Each example was heard with the pulses of those four composers in turn, in quasi-random sequence, one performance thus incorporating the "right" pulse and three the "wrong" ones. Results show dramatically that the greater the musical proficiency, the more marked the preference for the "right" pulse (p < .0001). Non-musicians as a group showed a similar tendency of preference, but typically to a considerably less pronounced degree. Further studies suggest that longer excerpts (32 bars) and repeated hearing would help non-musicians also to better understand composers' pulses. A theory of music as a double stream is introduced. The results suggest that the composers' pulse matrices posited by Clynes as a first approximation are in fact appropriately meaningful. Brain function aspects of the meaningful discrimination of such tiny time differences are discussed.

Multiple drug-resistance in variant of a human non-small cell lung carcinoma cell line, DLKP-A

A 300-fold adriamycin resistant variant (DLKP-A) of the human lung squamous cell carcinoma line DLKP was established by stepwise selection in increasing concentrations of adriamycin. Different levels of cross-resistance were observed towards VP-16, VM-26, colchicine, vincristine and, somewhat unexpectedly, cis-platin. Resistance was stable for at least 3 months in culture in the absence of drug. P-glycoprotein overexpression was detected by immunofluorescence and Western Blotting, and a direct causal role for P-glycoprotein overexpression in the resistant phenotype was established by transfection with an mdr1 specific antisense oligonucleotide. A modified cryopreservation procedure was necessary for the resistant variant line. The resistant population displays clonal heterogeneity with respect to resistance level. A higher frequency of double minute chromosomes was observed in DLKP-A when compared with the parental cell line.

Production of autostimulatory growth factors by the human carcinoma line, RPMI 2650

The human carcinoma line RPMI 2650 produces autocrine factors; they are detected by the ability of RPMI 2650 conditioned medium (CM) to stimulate growth in soft agar of RPMI 2650 cells plated at low density. The autocrine activity in crude CM can be fractionated by ultrafiltration into a lower molecular weight (MW) fraction (R1-30), which concentrates molecules in the 1000-30,000 Da range; and a higher MW fraction (R30) with molecules greater than 30,000 Da in a more concentrated form. R1-30 is labile to acid, base, and heat treatment, whereas R30 is stable to (and sometimes activated by) these treatments. Boiling of R30, however, renders it labile to acid, base, and trypsin treatments. CM can be separated into a weakly heparin-binding fraction (with stability properties similar, but not identical, to R1-30), and a non-heparin binding fraction (with stability properties similar to R30). RPMI 2650 cells secrete transforming growth factor (TGF)alpha- and TGF beta-like molecules, but the R1-30 fraction can be distinguished from these TGFs, and from most other known growth factors, by its unusual combination of acid lability and weak affinity for heparin. Since the R30/non-heparin binding fraction is rendered labile by boiling or acid treatment, it may represent a bound or conformationally stable form of a growth factor.

Comparison of 5 microplate colorimetric assays for in vitro cytotoxicity testing and cell proliferation assays

This paper describes a critical comparative evaluation of 5 miniaturised colorimetric assays applicable to cytotoxicity testing of anti-tumour drugs (and other toxins) in vitro. Each assay shows a different linear range for optical density versus cell number, a different sensitivity to change in cell number and a different minimum detectable cell number; the values of these parameters vary with experimental conditions and with cell line used. All the methods gave good correlation with viable cell number (determined by colony forming efficiency) in toxicity assays after 3 or 4 days of treatment, but they underestimated cell death after 2 days. Toxicity levels for individual chemicals (in a standard 6-day assay) are similar for the different assays, irrespective of the mechanism of action of the chemical being tested. Two of the more recently developed assays (APNaOH and SRB) were found to be very sensitive under the conditions examined.

Human cell lines as models for multidrug resistance in solid tumours

In spite of our expanding knowledge on the molecular biology of cancer, relatively little progress has been made in improving therapy for the solid tumours which are major killers, e.g., lung, colon, breast. Significant advances over the past 10-15 years in chemotherapy of some tumours such as testicular cancer and some leukaemias indicates that, in spite of the undesirable side-effects, chemotherapy has the potential to effect cure in the majority of patients with certain types of cancer. Multidrug resistance, inherent or acquired, is one important limiting factor in extending this success to most solid tumours. In vitro studies described in this review are now uncovering a diversity of possible mechanisms of cross-resistance to different types of drug. Sensitive methods such as immunocytochemistry, RT-PCR or in situ RNA hybridisation may be necessary to identify corresponding changes in clinical material. Only by classifying individual tumours according to their specific resistance mechanisms will it be possible to define the multidrug resistance problem properly. Such rigorous definition is a prerequisite to design (and choice on an individual basis) of specific therapies suited to individual patients. Since a much larger proportion of cancer biopsies should be susceptible to accurate analysis by the immunochemical and molecular biological techniques described above than to direct assessment of drug response, it seems reasonable to hope that this approach will succeed in improving results for cancer chemotherapy of solid tumours where other approaches such as individualised in vitro chemosensitivity testing have essentially failed. Results from clinical trials using cyclosporin A or verapamil are encouraging, but these agents are far from ideal, and reverse resistance in only a subset of resistant tumours. Proper definition of the other mechanisms of MDR, and how to antagonize them, is an urgent research priority.

Multiple drug resistance in the human ovarian carcinoma cell line OAW42-A

A new multidrug-resistant variant (OAW42-A) of a human ovarian carcinoma line has been selected by exposure to increasing concentrations of doxorubicin. The variant is resistant to doxorubicin, vincristine (but surprisingly not to colchicine), etoposide, tenoposide and also to cisplatin (a drug not usually involved in classical multidrug resistance), but not to 5-fluorouracil. Overexpression of P-glycoprotein in the resistant line was demonstrated by immunofluorescence and western blotting. Direct evidence for P-glycoprotein as a determinant of resistance was provided by transfection with a specific antisense oligonucleotide. Reversal was incomplete and this, along with the pattern of cross-resistance observed, suggests that additional mechanisms of resistance may also be involved. Substantial clonal variation in resistance exists within the cell line.

The use of reverse transcriptase-polymerase chain reaction (RT-PCR) to investigate specific gene expression in multidrug-resistant cells

Expression of specific genes at the level of mRNA can be studied using techniques such as Northern blot, slot/dot blot, RNase protection assay, in situ hybridisation and RT-PCR. In this article these methods of analysis are compared; RT-PCR offers higher levels of specificity and sensitivity than traditional methods of RNA analysis and as such has become the method of choice for the study of gene expression. The RT-PCR technique is described in detail with sections dealing with RNA extraction, choice of primers (including the use of cDNA sequence data bases), PCR and RT-PCR protocols in addition to the limitations of the method. The study of one particular mRNA transcript (MDR1) using RT-PCR is discussed in detail. Recently described methods for quantitation of PCR products are discussed. Quantitative PCR would appear to offer a method of studying gene expression in a more extensive way than has been possible to date.

Cytogenetic comparison of two poorly differentiated human lung squamous cell carcinoma lines

This paper presents a cytogenetic analysis of two established but early-passage (passages 5 and 18) cell lines derived from histologically similar, poorly differentiated lymph node metastases of squamous cell carcinoma of the lung. The cell lines showed 3 shared marker chromosomes, del(1)(q11), del(2)(p11.1) and del(2)(q11.1). One of the lines (DLKP) had 8 additional markers including structural rearrangements such as translocations and isochromosomes. Five additional markers (including two deletions of chromosome 3) were found in DLRP. A notable feature of DLRP was the high incidence of telomeric association evident in the majority of metaphase plates. Over-representation of chromosome 7 was a characteristic feature of metaphases derived from DLKP, and identification of i(21q) in this cell line was an unusual finding. The results indicate significant cytogenetic heterogeneity between these early-passage cell lines derived from two apparently histologically similar tumors.