Breast cancer (BC) is considered the most common cancer
affecting women worldwide and the second leading cause of death in
them. Each year, 1.3 million new cases of breast cancer are diagnosed
worldwide, and account for almost 15% of all cancer-related deaths. In Egypt, breast cancer is the most frequent cancer among Egyptian females. It represents about 38% of all reported cancer cases in Egyptian females.
Wide variability in the response of individuals to breast cancer treatment at the same doses may occur and not all breast cancer patients were benefited from treatment. It may be a result of inter-individual genetic differences.
Resistance to anticancer agents is one of the most important
problems in cancer treatment. Although breast cancer is one of the most sensitive solid tumors to anticancer agents, after a successful course of treatment, most patients show different degrees of drug resistance. Despite various treatment regimens used for breast cancer, the complete response to treatment is considerably varied between patients.
Multidrug resistance (MDR) is a complex phenomenon which is affected by many genetic and environmental factors. It is considered a major cause for treatment failure in breast cancer. Identification of prognostic markers of treatment resistance which can be targeted effectively to reverse the resistance would represent a significant advance in treatment for breast carcinoma.
Considerable attention has been dedicated to the role of the multi-drug resistance1 (MDR1) gene in breast cancer. The MDR1 gene encodes for a glycosylated protein, called P-glycoprotein (p-gp). P-gp is a key player in the multidrug-resistant phenotype in cancer. Genetic variations affecting function and expression of P-gp have a role in resistance to many anti-cancer drugs including anthracyclines and taxanes.
CYP2D6 enzyme (CYP2D6 gene product) is responsible for the metabolism of about 20-25% of commonly prescribed drugs. CYP2D6 is the main enzyme that catalyzes the rate-limited step in the metabolism of tamoxifen to its potent metabolite, endoxifen. Tamoxifen is heavily metabolized by several of the cytochrome P450 drug metabolizing enzymes.
According to CCR5 gene, it was found that CCR5/CCL5 axis has an important role in tumor development, progression and invasiveness through multiple mechanisms: acting as growth factors, modulating the extracellular matrix, stimulating angiogenesis, inducing the additional stromal and inflammatory cells, and taking part in immune evasion mechanisms. CCR5 and its ligand CCL5 is also involved in drug resistance.
The aim of our study is to clarify the role of MDR1, CYP2D6 and CCR5 polymorphisms in breast cancer patients and provide a better insight into the association between these genes and prediction of response/ resistance to breast cancer treatment.
Our study was performed on 40 breast cancer patients and 20 cancer- free controls. We subdivided the breast cancer group according to treatment response into two groups, the first included responders patients (either complete response or partial response), and the other included
non-responders (either static disease or progressive disease). The breast cancer patients were treated by surgical resection and drug therapy in the form FAC (5- fluorouracil + Adriamycin + cyclophosphamide) ± tamoxifen.
Blood samples (3 ml) were put on EDTA for mutation detection of MDR1, CYP2D6 and CCR5 genes based on the reverse hybridization principle using (HVD strip kit). The mutation detection assay covered 5 polymorphic loci: MDR1 3435 C>T, CYP2D6 1795delT (2D6*6), CYP2D6 1934 G>A (2D6*4), CYP2D6 2637delA (2D6*3), CCR5 32bp deletion.
The steps included: DNA isolation (using 100 µl blood sample for extraction), PCR amplification (in a multiplex reaction using biotinylated primers) and hybridization of amplified products to a test strip containing allele-specific oligonucleotide probes immobilized as an array of parallel lines, bound biotinylated sequences were detected using streptavidin-alkaline phosphatase and color substrates and interpretation of results.
The data analysis of MDR1 C3435T gene revealed a significant increase in the frequency of mutant (T) allele and heterozygous mutant (CT) genotype of in breast cancer patients and interestingly, mutant (T) allele and mutant genotypes (CT & TT) are associated with increase response to treatment.
Moreover, the results obtained for the gene CYP2D6 demonstrated that the homozygous genotype (CYP2D6 *4/*4), mutant CYP2D6 *4 allele and (CYP2D6-PM) phenotype are significantly associated with the breast cancer development and worse treatment response.
In addition, the results showed absence of the CCR5 mutant allele (CCR5-Δ32) in our study.
In conclusion, the results obtained in this study support the association between MDR1 gene, CYP2D6 gene polymorphisms to breast cancer risk and treatment response among a group of Egyptian patients in Qalyubia governorate. A large scale study in Egypt is recommended to confirm the role of the MDR1 gene, CYP2D6 gene polymorphisms in breast cancer development and response to treatment. This may help to get more insights into the mechanism of the disease and provide novel diagnostic and therapeutic strategies.
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