2) The protein presence of MDR1 and BCRP in MDR tumors was also significantly higher than those in the control group in vivo and in clinical specimens.
265/F4 may thus be used to distinguish between the murine P-glycoprotein isoforms so revealing differences between tumour cell lines in cellular localisation and in the time of appearance of mdr1a and mdr1b P-glycoprotein following drug exposure.
Tumors with an allelic loss of the chromosomal 1p region showed significant (P<0.05) lower MDR1 gene expression (MDR1: 50+/-29, n=4) than tumors without (MDR1: 117+/-81, P<0.05, n=36).
Tumor specimens prior to and following neoadjuvant chemotherapy from 29 cases of high grade soft tissue sarcoma were analyzed with 2 monoclonal antibodies (C494 and JSB-1) that recognize different epitopes of P-glycoprotein.
Tumours with bimodal DNA distribution showed median values of P-glycoprotein expression of their hyperdiploid cell clones significantly higher than those of their diploid clones and of the tumours with unimodal DNA distribution (P less than 0.005).
Tumors with higher tumor margin scores were more strongly associated with the doxorubicin resistance transcriptional program and had a greater prevalence of venous invasion and worse stage.
P-Glycoprotein expression in the tumor tissue was determined immunohistochemically and by measuring mRNA expression of the multidrug resistance-1 gene.
MDR1 and GST-pi expression, which is known to be a marker for adriamycin resistance, was detected in six (66.7%) and seven (77.8%) of the nine clinically resistant tumors, respectively.
MDR1 gene expression was found to be increased in 5 out of 29 tumor samples at onset (17%) and in 1 out of 3 at relapse, but none of them expressed both MDR1 and N-myc genes simultaneously.
MDR1 was hypomethylated in 47% tumors and 44% paired sera of IDC patients and correlated significantly with increased tumor size and advanced tumor stage.
P-glycoprotein (P-gp, ABCB1) is a highly efficient drug efflux pump expressed in brain, liver, and small intestine, but also in tumor cells, that affects pharmacokinetics and confers therapy resistance for many anticancer drugs.
MDR1 and MRP1 expression levels have been shown to be independent of tumor size, histological grade and the status of progesterone or estrogen receptor.
ABCB1 mRNA levels were highest in the healthy individuals and significantly lower in mild/moderate and severe dysplasia tissue (P<0.05 for both), morphologically normal tissues close to the tumour (P<0.05), morphologically normal tissue at a distance from the tumour (P<0.05) and CRC tissue (P<0.001).
ABCB1 immunoreactivity was detected in a number of tumor cells in human melanomas, and in particular in clusters at the invasive front of the primary tumors.