To measure ABCB1 function in tumors, we performed PET experiments using both [<sup>18</sup>F]AVT-011 and [<sup>18</sup>F]FDG in mice bearing orthotopic breast tumors (n = 7-10/group) expressing clinically relevant levels of ABCB1.
Reduced ABCB1 protein levels in breast tumors was associated with triple-negative subtype (adjusted odds ratio [OR<sub>adj</sub>] =0.24; 95% confidence interval [CI] =0.13-0.45), lymph node status < pN2 (OR<sub>adj</sub> =0.27; 95% CI =0.10-0.71), tumor size >2 cm (OR<sub>adj</sub> =0.55; 95% CI =0.32-0.93), and hypertensive status (OR<sub>adj</sub> =0.42; 95% CI =0.24-0.73), and it was significantly associated with shorter disease-free survival, either for all breast cancer patients (<i>p</i> log-rank =0.012; hazard ratio [HR] =3.46; 95% CI =1.21-9.91) or for those with triple-negative tumors (<i>p</i> log-rank =0.007; HR =11.41; 95% CI =1.29-100.67).
An important result of our study is the demonstration of a correlation between P-gp expression and patients with HER2-positive breast tumors that do not express steroid receptors.
The regulatory effect of Gal-1 on multidrug resistance (MDR) breast cancer cells is still unclear. qRT-PCR and western blot showed that Gal-1 and MDR gene 1 (MDR1) were both highly expressed in breast tumor tissues and cell lines.
Taken together, our data indicate that breast tumors with alveolar structures possess resistance to NAC, which is not related to high expression of MDR genes, whereas chemoresistance of tumors with trabecular structures can depend on the expression level of ABCB1.
The quantitative real-time polymerase chain reaction (Q-RT-PCR) technique was used to assess the MDR1 and MMP2 RNA expression levels in primary breast tumor and lymph nodal specimens.
Subsequently, there is a significant decrease in both MDR1 and Bcl-x(L) gene expression and an enhancement in caspase-3 activity and chemosensitivity in the breast tumor cells.
Determination of P-glycoprotein, MDR-related protein 1, breast cancer resistance protein, and lung-resistance protein expression in leukemic stem cells of acute myeloid leukemia.
Single nucleotide polymorphisms in the multidrug resistance gene 1 (ABCB1): effects on its expression and clinicopathological characteristics in breast cancer patients.
Hypermethylation of the ABCB1 downstream gene promoter accompanies ABCB1 gene amplification and increased expression in docetaxel-resistant MCF-7 breast tumor cells.
Production of P-glycoprotein from the MDR1 upstream promoter is insufficient to affect the response to first-line chemotherapy in advanced breast cancer.
Interleukin-6, multidrug resistance protein-1 expression and response to paclitaxel in women with metastatic breast cancer: results of cancer and leukemia group B trial 159806.
However, transcripts derived from the MDR1 USP were detected in some drug-resistant cell lines and a high proportion of primary breast tumors (71.6%; n = 61), whereas they were present at low frequency in normal breast tissue (10%; n = 10).