Flow cytometric analysis of multidrug-resistance-associated antigen (P-glycoprotein) and DNA ploidy in human colon cancer

Stage-specific frequency and prognostic significance of aneuploidy in patients with sporadic colorectal cancer--a meta-analysis and current overview

PURPOSE

Aneuploidy has long been suggested as an independent prognostic marker for colorectal cancer (CRC) patients and could thus aid for individualized medicine. However, due to a large spectrum of deviating studies, expert panels do not recommend ploidy assessment. In order to clarify a potential bias of stage-specific frequency of aneuploidy, we now conducted a meta-analysis combined with a systematic review regarding aneuploidy and prognosis.

METHODS

A systematic, web-based search process retrieved 1935 studies published in English between 1990 and 2011. The defined endpoint for the meta-analysis was an increase in aneuploidy frequency between early- (Dukes A, B and UICC I, II; n = 3632 samples) and late-stage (Dukes C, D and UICC III, IV; n = 3440 samples) colorectal carcinomas.

RESULTS

Of 1935 studies initially identified, 17 image (2130 patients) and 20 (7023 patients) flow cytometric studies were analyzed in detail. The meta-analysis (7072 patients) revealed late-stage CRC to be more frequently aneuploid than early-stage CRC (odds ratio 1.51, 95 % CI 1.37-1.67; p = 0.0007). Independent of tumor stage, the overall range of aneuploidy was 39 to 81 % (median 58 %), and altogether, 21 (54.1 %) studies described a significant prognostic impact of aneuploidy for overall, disease-specific, and recurrence-free survival, respectively.

CONCLUSIONS

A substantial number of studies showed a prognostic importance of aneuploidy in CRC. Furthermore, the higher frequency of aneuploidy in late-stage CRC implies an increase in genomic instability with CRC progression, indicating aneuploidy to be also a stage-specific prognostic marker.

Multidrug resistance-associated protein (MRP1) is overexpressed in DNA aneuploid carcinomatous cells in non-small cell lung cancer (NSCLC)

Resistance to chemotherapy is intrinsically present in most nonsmall-cell lung carcinomas (NSCLC). No parameter has yet been determined to predict the response to chemotherapy. However, MRP1 (multidrug resistance-associated protein) is suspected to play an important role in resistance to treatment. The genetic basis for this resistance is not clearly understood, but it could result from chromosome reassortments catalyzed by aneuploidy. The aim of this study was to investigate MRP1 expression concurrently to DNA ploidy analysis in order to evaluate the link between MRP1 expression and chromosome 16 (MRP1 gene location) aberrations in NSCLC before treatment. Eighty-four surgical tumor specimens, 18 selected samples containing more than 80% of carcinomatous cells and 11 samples from normal bronchial epithelium were studied. Samples were stained by MRP1 FITC indirect staining and propidium iodide and analyzed by Flow Cytometry. Fifty tumors contained at least 1 DNA-aneuploid clone and the percentage of MRP1-positive cells was higher in DNA-aneuploid cells (p = 0.0003). All tumors expressed MRP1, but the level of expression was 3-fold higher in DNA-aneuploid cells than in DNA-diploid cells (normal bronchial cells as well as carcinomatous cells) (p < 0.0001). FISH analysis of 24 tumor imprints using a chromosome 16 alpha-satellite centromere probe demonstrated significantly more frequent gain of chromosome 16 in DNA-aneuploid tumors. These results suggest that MRP1 overexpression in NSCLC could be a consequence of chromosome 16 reassortments catalyzed by aneuploidy and that DNA-aneuploid tumors could require different treatment modalities from those applied to DNA-diploid tumors.

P-glycoprotein is not expressed in a majority of colorectal carcinomas and is not regulated by mutant p53 in vivo

Overexpression of the MDR1 product, P-glycoprotein (Pgp), has been shown to be one of the mechanisms underlying the development of multidrug resistance (MDR). Recently, one mutant p53 has been shown to stimulate the MDR1 gene promoter in vitro, whereas wild-type p53 repressed this activity. We measured Pgp and p53 expression by immunoblotting in 34 colorectal tumours, and performed mutation analyses on the p53-positive tumours to confirm the presence of mutant p53 protein. Tumour DNA indices (DIs) were also measured using flow cytometry. Pgp was detected in 44% (15/34) of the tumours and in 100% (13/13) of the normal mucosas (P = 0.0005), with highest levels of expression seen in normal mucosa, suggesting that initial drug resistance in colorectal tumours is not caused by Pgp. Highly DNA aneuploid tumours demonstrated the lowest levels of Pgp expression relative to moderately aneuploid and diploid colorectal tumours. p53 protein was detected in 53% (18/34) of the tumours, and 12 of 14 p53-positive tumours had p53 gene mutations, p53-negative tumours had approximately twice the level of Pgp expression of p53-positive tumours. Pgp expression was not associated with either p53 expression (P = 0.73) or incidence of p53 gene mutation (P = 0.70), suggesting that mutant p53 does not induce Pgp overexpression in colorectal carcinomas.

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.

Multidrug resistance in cancer chemotherapy

Resistance to chemotherapy is the single most important reason for treatment failure in cancer patients. Over the past 15 years, we have gained significant insight into one of the mechanisms responsible for this process: multidrug resistance (MDR). Far from being a phenomenon limited to the laboratory, multidrug resistance has been identified in a wide variety of newly diagnosed and recurrent human tumors. A number of compounds can block p-glycoprotein and overcome MDR in vitro and in vivo. Current strategies to block MDR are discussed in this review. Future research in this area will focus on the identification of more selective and potent MDR reversing agents and the development of entirely new approaches to overcoming multidrug resistance such as monoclonal antibodies, immunotoxins, and gene therapy.

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.