Detection of P-glycoprotein in squamous cell carcinomas of the head and neck

Differential gene expression in a paclitaxel-resistant clone of a head and neck cancer cell line

The anti-neoplastic drug paclitaxel (taxol), which is known to block cells in the G2/M phase of the cell cycle through stabilization of microtubules, is meanwhile commonly used for chemotherapy of advanced head and neck cancer. Chemotherapy is primarily used in order to preserve laryngeal and/or pharyngeal structures. Although paclitaxel generally seems to be a powerful agent, it failed to reach a loco-regional tumor control in a sufficient percentage of patients. In order to investigate molecular resistance mechanisms, we have established a paclitaxel-resistant subline originating from the larynx carcinoma cell line HLaC79, which seemed to be partially dependent on taxol. The original and the descendant cell line were characterized by growth inhibition assays. We used western blotting and the cDNA subtraction (SSH) technique to identify genes differentially expressed in the taxol-resistant cell clone. cDNA subtraction revealed increased expression of six genes, including clathrin heavy chain, alpha3-tubulin, a neuroblastoma-specific Thymosin beta, the ribosomal protein L7a, HLA-B associated transcript 3 and collagen IIIalpha1 in the taxol-resistant cell line. Furthermore, western blots showed an overexpression of MDR-1 in the taxol-resistant clone, while alpha- and beta-tubulins and p48/IRF9 were expressed in equal amounts in both cell lines.

Immunolocalisation of an ABC transporter, P-glycoprotein, in the eggshells and cuticles of free-living and parasitic stages of Haemonchus contortus

Recent data have suggested that P-glycoprotein (Pgp), working as membrane efflux "pumps", plays a major role in the transport of anthelmintic drugs in parasitic nematodes of ruminants. Flow cytometry analyses has shown that active Pgp is probably present in the external layers of Haemonchus contortus eggshells, following staining with the mouse monoclonal anti-human MDR1 antibody UIC2, which binds to Pgp in its active conformation. We evaluated the presence and distribution of this protein in the envelopes (eggshells and cuticles) of H. contortus and compared the various stages (eggs, L1-L2 larvae, L3 larvae, adult male and female worms). Electrophoresis revealed a 170-kDa band, corresponding to the molecular weight of Pgp in all stages. Indirect immunofluorescence staining with UIC2 showed Pgp to be located in the external layer of eggshells or cuticles. Transmission electron microscopy was used to localise Pgp more accurately in the three layers of the eggshells and cuticles. The conformation and biological functions of this protein, which we did not expect to find in such structures, remain to be determined.

Multidrug resistance gene 1 expression in salivary gland adenocarcinomas and oral squamous-cell carcinomas

In combined chemotherapy for head-and-neck cancer (HNC), salivary gland-cell adenocarcinoma (SGA) shows insufficient clinical outcome, and it has been suggested that the sensitivity and/or the mechanism of resistance to anti-cancer drugs are different between SGA and oral squamous-cell carcinoma (SCC). The aim of our study was to clarify whether P-glycoprotein (P-gp) expression is associated with multidrug resistance (MDR) in HNC and the difference in the process of its development between SGA and SCC. In immunohistochemical analysis, P-gp expression was found in the ductal cells of salivary glands but not in oral mucosal epithelium. In cancer tissues, a few SCC cells in 12 of 37 and most cells in all SGAs expressed P-gp. The intensive P-gp expression was significantly found in SGA compared with SCC. In an in vivo chemotherapeutic model using tumor-bearing nude mice, P-gp expression in counterparts was observed in only a few cells of the HSY line, while no P-gp expression was observed in Hepd cells. However, P-gp expression was developed in both HSY and Hepd cell lines after vincristine (VCR) treatment. RT-PCR showed that the mean ratios of mdr1 mRNA expression levels in HSY clones were 3.7-fold higher than those in Hepd clones after VCR treatment, while each cell line exhibited both induction and activated production of P-gp. These results suggest that P-gp-related MDR in SGA is an inherent phenotype caused by both high levels of P-gp induction and activated P-gp production during VCR treatment, while that in SCC is an acquired phenotype chiefly caused by induction of P-gp.

Expression of drug resistance-related genes in head and neck squamous cell carcinomas and normal mucosa

We examined the expression levels of mRNA for multidrug resistance 1 (MDR1), multidrug resistance-associated protein (MRP), human canalicular multispecific organic anion transporter (cMOAT), lung resistance-related protein (LRP), topoisomerase IIalpha, beta (Topo IIalpha, beta) and topoisomerase I (Topo I) genes in human head and neck squamous cell carcinoma (HNSCC) specimens and mucosa (HNM) specimens, to elucidate their roles in relation to the biological characteristics and drug resistance in vivo. Fifty-eight samples (45 head and neck carcinomas and 13 head and neck mucosa) obtained during surgical resection or biopsy from 38 patients were analyzed using the quantitative reverse transcription-polymerase chain reaction (RT-PCR) method. MDR1, MRP, LRP, Topo IIalpha, Topo IIbeta, and Topo I gene transcripts were detected in all the samples tested, but cMOAT mRNA was not detected in them. Comparisons of the expression levels in HNSCC with those in HNM showed that the Topo IIalpha gene expression level was higher in HNSCC than in HNM (P=0.0298). Moreover, the Topo IIalpha mRNA level was significantly higher in metastatic lymph node samples of HNSCC than in HNM samples (P=0.0205). There were no significant differences in the six genes' expression levels between samples exposed to platinum drugs and those not exposed to platinum drugs. These results suggest that it may be effective in anticancer therapy to use topoisomerase-targetting drugs against HNSCC, especially metastatic neck tumors, and that the expression of these genes in HNSCC is not associated with platinum drug exposure.

Role of glutathione, glutathione S-transferases and multidrug resistance-related proteins in cisplatin sensitivity of head and neck cancer cell lines

Resistance to chemotherapy is a major problem in the treatment of patients with head and neck squamous cell carcinoma (HNSCC). Important factors involved are drug detoxification by glutathione (GSH) and reduced drug accumulation due to active transport out of the cell by so-called 'multidrug resistance-related proteins'. We have studied a panel of eight HNSCC cell lines showing differences in sensitivity to the anti-cancer drug cisplatin. Our previous studies indicated that the IC50 values were inversely correlated with the intracellular accumulation of platinum (Pt). In the present study, cellular GSH levels were found not to be related to the IC50 values. The expression levels of the enzymes glutathione S-transferase (GST) alpha, mu, and pi, the multidrug resistance-related proteins P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP) and the lung resistance protein (LRP) were determined semiquantitatively by means of immunocytochemistry. The levels of the GSTs, P-gp and LRP were not found to be correlated with the IC50 values of the HNSCC cell lines. Surprisingly, however, an inverse correlation was found between MRP levels and IC50 values. The MRP expression levels were in agreement with the results of the MRP functional assay, based on the transport of calcein across the cell membrane as performed for two of the cell lines. Further studies should prove whether other pump mechanisms or DNA repair are involved in the cisplatin accumulation and the subsequent HNSCC cell growth inhibition.

No evidence of significant activity of the multidrug resistance gene product in primary human breast cancer

BACKGROUND

The discovery of the multidrug resistance (MDR1) gene product P-glycoprotein (P-gp) has been widely seen as an important milestone in our understanding of the mechanisms underlying the clinical phenomenon of the emergence of resistant cells. MDR1 expression has been shown for numerous solid tumors and for virtually all hematologic malignancies. Nevertheless, results regarding MDR1/P-gp expression in human breast cancer have been controversial and the results of clinical trials on modulation of P-gp activity have not been encouraging.

PATIENTS AND METHODS

MDR1/P-gp expression and the function of the P-gp pump were investigated in 61 tumor samples from patients with primary breast cancers by multiparameter analysis using MDR1-RT-PCR, immunohistochemistry with two MAbs (UIC2 and MRK16) and the rhodamine 123 (Rh123) efflux assay. The cellular composition of the tumor cell suspension was analyzed by using specific MAbs against the P-gp expressing lymphocyte subsets CD4, CD8 and CD56, as well as against the HER-2/neu gene product, which was used to identify breast carcinoma cells.

RESULTS

UIC2 and MRK16 revealed a staining positivity in 72% and 75% of samples, respectively. A positive MDR1-RT-PCR signal was detected in 62% of the samples. Nevertheless, no correlation between immunohistochemistry and RT-PCR could be established. Furthermore, there was no correlation between HER-2/neu expression and MDR1-RT-PCR or P-gp immunohistochemical assays. A contamination by CD8+ and CD4+ lymphocytes was established in 100% and 84% of tumor cell suspensions, respectively. As assessed by the Rh123 efflux assay CD8+ and the CD4+ lymphocytes exhibited marked P-glycoprotein activity, whereas such activity was not detectable in a single instance for the breast carcinoma cells. In MDR1-RT-PCR positive samples, contamination by CD8 lymphocytes averaged 4.3%, while the contamination of CDS cells in the MDR1 mRNA-negative samples was only 2.4% (P = 0.007). This signal vanished after elimination of the lymphocyte subpopulations by T-cell rosetting.

CONCLUSIONS

In primary breast cancer detection of MDR1 gene expression by means of RT-PCR or immunohistochemical assays is not indicative for the MDR phenotype, since there is no evidence of significant activity of the P-gp pump.

Expression of P-glycoprotein and p53 in advanced hepatocellular carcinoma treated by single agent chemotherapy: clinical correlation

Hepatocellular carcinoma (HCC), a chemoresistant tumour, is the most common fatal cancer in Taiwan. Hepatocellular carcinoma frequently expresses a high level of P-glycoprotein (P-gp), which is a specific phenotype of a multidrug-resistance gene, and harbours mutations of the tumour suppressor gene p53. A modulatory relationship between p53 and P-gp has been reported. In this study, we analysed the expression of P-gp in relation to chemotherapeutic response and p5353 protein expression in advanced HCC. Prechemotherapeutic tumour samples were obtained from 25 patients with HCC which had been treated with either etoposide (VP-16) or doxorubicin. P-glycoprotein and p53 in HCC were visualized by immunohistochemical staining using the monoclonal antibodies JSB-1 and DO1, respectively. We investigated the correlation of P-gp expression with chemotherapeutic responses, clinicopathological features and p53 protein expression. In our study, seven cases achieved partial remission, and the remaining 18 cases had a poor response to chemotherapy. Expression of P-gp was observed in 13 tumours (52%). Positive P-gp protein expression was significantly associated with non-responders (8% or 1/13 vs 50% or 6/12, P = 0.03). Thus, P-gp expression inversely correlated with chemotherapeutic response. Expression of p53 protein was seen in 12 cases and did not correlate with chemosensitivity or P-gp expression. In summary, P-gp expression correlates with the chemosensitivity of HCC that has been treated with VP-16 or doxorubicin and p 53 mutations do not appear to be a major determinant of P-gp expression in advanced HCC.

P-glycoprotein expression in the squamous cell carcinoma of the tongue base

P-glycoprotein (PGP), which is a product of the multidrug resistance gene (MDR1), is an active transmembrane efflux pump responsible for detoxifying normal cells as well as rendering tumor cells resistant to chemotherapy. It has also been implicated to be expressed by more aggressive cancers. It has not been well described in squamous cell carcinoma of the head and neck. In this investigation, an attempt was made to characterize advanced squamous cell carcinoma of the base of tongue with respect to expression of PGP. Using immunohistochemical techniques two anti-PGP monoclonal antibodies (JSB1 and C494) were used to detect PGP in these lesions, and an attempt was made to correlate levels of PGP staining and various tumor parameters. Usefulness of PGP in predicting survival and time to recurrence was also examined for these advanced lesions. All 33 base of tongue lesions showed staining for PGP with these monoclonal antibodies. This was the first study examining utility of C494 in detecting PGP in squamous cell carcinoma at this site. Increased level of PGP expression was seen in better-differentiated tumors as well as in tumors with diploid DNA. A trend of higher PGP expression and decreased survival emerged. This may represent a true relationship, but inherent heterogeneity of PGP expression within cells cannot be excluded. Both antibodies examined appear to be useful in the investigations of PGP distribution in squamous cell carcinomas of the head and neck sites by immunohistochemical techniques. Prognostic value of the level of PGP expression remains to be seen.

P-glycoprotein: clinical significance and methods of analysis

Multidrug resistance (MDR) is responsible for a decrease in sensitivity of tumor cells tumor cells to unrelated, naturally occurring anticancer drugs. This resistance is correlated with expression and activity of a membrane protein, P-gp 170, functioning as a drug-extruding pump. It has been well described in in vitro situations; however, the clinical detection and implications are not yet clear. Multiple detection assays have been developed based on the discovery of the MDR gene family and the corresponding protein. Southern, Northern, or Western blot analysis, S1 nuclease protection or PCR-based assays, immunohistochemical detection or functionality tests by flow cytometry have been used extensively. However, by use of these techniques on clinical material, both normal and malignant, contradictory results have emerged. The sensitivity and specificity of a certain technique are always limited by unavoidable parameters, for example, skill of the technician. Moreover, the complexity of the development of resistance against anticancer agents (external determinants), such as the diversity of tumor tissues, the simultaneous presence of other resistance mechanisms, and the low expression level, make MDR detection equivocal and can lead to contradictory results. Previous treatment influencing the MDR profile and inappropriate timing of the test make a possible correlation between MDR expression and chemotherapeutic resistance difficult to establish and can lead to discordant results. In this review, the need for proper criteria is stressed. No single detection technique provides the ideal test to detect MDR. Tandem testing could give more certainty, although small sample size limit this application. Formulation of a standard assay with better definition of a positivity is essential before clinical trials are started.

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.