Genetics of ABCB1 in Cancer

ABCB1, also known as MDR1, is a gene that encodes P-glycoprotein (P-gp), a membrane-associated ATP-dependent transporter. P-gp is widely expressed in many healthy tissues-in the gastrointestinal tract, liver, kidney, and at the blood-brain barrier. P-gp works to pump xenobiotics such as toxins and drugs out of cells. P-gp is also commonly upregulated across multiple cancer types such as ovarian, breast, and lung. Overexpression of ABCB1 has been linked to the development of chemotherapy resistance across these cancers. In vitro work across a wide range of drug-sensitive and -resistant cancer cell lines has shown that upon treatment with chemotherapeutic agents such as doxorubicin, cisplatin, and paclitaxel, ABCB1 is upregulated. This upregulation is caused in part by a variety of genetic and epigenetic mechanisms. This includes single-nucleotide variants that lead to enhanced P-gp ATPase activity without increasing ABCB1 RNA and protein levels. In this review, we summarize current knowledge of genetic and epigenetic mechanisms leading to ABCB1 upregulation and P-gp-enhanced ATPase activity in the setting of chemotherapy resistance across a variety of cancers.

Epidemiologic Study of Gastric Cancer in Iran: A Systematic Review

BACKGROUND

Gastric cancer (GC) is one of the most common cancers in Iran. Knowledge of the epidemiology of the disease is essential in planning for prevention. So this study aimed to investigate the epidemiological aspects of gastric cancer including prevalence, incidence, mortality, and risk factors of Iran.

METHODS

This systematic review study was based on articles published in both English and Persian languages during the years of 1970-2020 in international databases (PubMed, Web of Science, Scopus) and national databases (including SID, Magiran, and IranDoc). Papers related to epidemiological aspects of the disease including mortality, prevalence, incidence, and risk entered the final review.

RESULTS

According to the studies, the minimum and maximum prevalence of gastric cancer in northwestern Iran (Ardabil) is between 0.2 and 100 per 100,000. Also, the death rate per 100,000 people ranged from 10.6 to 15.72 and the ASMR ranged from 4.2 to 32.2%. On the other hand, the incidence of GC was higher in men than in women (74.9 vs 4.6%). The GC risk ratio was 8-times higher in the elderly than in the other age groups (HR=8.0, 2.7-23.5). The incidence of gastric cancer in patients with H. pylori infection was 18-times and that of smokers 2-times higher than other populations. Low level of economic situation and food insecurity increased the odds of GC by 2.42- and 2.57-times, respectively. It should be noted that there was a direct relationship between consumption of processed red meat, dairy products, fruit juice, smoked and salty fish and legumes, strong and hot tea, and consumption of salt and gastric cancer incidence. There was also an inverse relationship between citrus consumption, fresh fruit, garlic, and gastric cancer. In addition, the mRNA genes are the most GC-related genes.

CONCLUSION

Given the high incidence of GC in Iran, changing lifestyle and decreasing consumption of preservatives in food, increasing consumption of fruits and vegetables, and improving the lifestyle can be effective in reducing the incidence of this disease.

Interleukin-6 Genetic Variation and Susceptibility to Gastric Cancer in an Iranian Population

Background:

Despite recent decrease in the incidence of gastric cancer, it is still a common type of cancer in the north of Iran. Many evaluations have shown that polymorphisms of cytokine genes like that for interleukin 6 (IL-6), which play important roles in regulation of the immune response, can increase the risk of gastric cancer. This study examined the role of the IL-6-174 gene polymorphism in susceptibility in an Iranian population.

Method:

Genomic DNA was extracted from peripheral whole blood of 100 patients and 361 healthy controls. Genotyping was accomplished by the sequence-specific primer-polymerase chain reaction (SSP-PCR) method and statistical analyses were carried out using Fisher’s exact test. Frequencies of the IL-6-174 G/C genotypes were determined under co-dominant, dominant, and recessive genetic models.

Results:

An association between the polymorphism of IL-6 -174 G/C and susceptibility to gastric cancer was observed. The frequency of G allele was higher in patients (78%) than in controls (70.5 %) (OR=1.48, 95% CI=1.01-2.20, P=0.04).

Conclusions:

The high G allele and G/G genotype frequency in patients compared to control subjects suggests that the IL-6 -174 G/C polymorphism may influence the susceptibility to gastric cancer. In addition, the demographic information showed that most of the subjects were male (69.0%) that gastric cancer is related to environmental factors.

Hypoxia Induces Multidrug Resistance via Enhancement of Epidermal Growth Factor-Like Domain 7 Expression in Non-Small Lung Cancer Cells

Chemotherapy is widely used in non-small cell lung cancer (NSCLC) treatment, yet multidrug resistance (MDR) is a major chemotherapeutic obstacle in both resectable and advanced NSCLC. Epidermal growth factor-like domain 7 (EGFL7), also known as vascular endothelial stain, is an endothelial cell-derived secreted factor that regulates vascular tube formulation. The aim of this study was to investigate the potential relationships between EGFL7 and MDR in NSCLC cells. We first obtained the CDDP-based MDR phenotype cell line A549/CDDP by repeated exposure to a proper concentration of CDDP (cisplatin) from original A549 cells. These A549/CDDP cells, which maintained relative high levels of EGFL7 and P-glycoprotein (P-gp), were resistant to other chemotherapy drugs, such as carboplatin (CBP), paclitaxel (TAX), and gemcitabine (GEM) (p < 0.05). We also found that hypoxia significantly reduced the chemosensitivity of NSCLC cells, and hypoxia-induced MDR was mediated by P-gp and EGFL7 (p < 0.05). EGFL7 was veryy relevant to NSCLC cell MDR, and downregulation of EGFL7 could significantly increase the chemosensitivity of NSCLC cells (p < 0.05). Thus, our findings first indicate that hypoxia induced NSCLC cell MDR at least partly by enhancing the expression of EGFL7 protein. EGFL7 might be a feasible target for reversing hypoxia-mediated MDR in NSCLC cells and a promising biomarker for predicting the development of MDR in NSCLC patients on chemotherapy.