Historical Perspective and Current Trends in Anticancer Drug Development.

Cancer is considered one of the leading causes of death in the 21st century. The intensive search for new anticancer drugs has been actively pursued by chemists and pharmacologists for decades, focusing either on the isolation of compounds with cytotoxic properties from plants or on screening thousands of synthetic molecules. Compounds that could potentially become candidates for new anticancer drugs must have the ability to inhibit proliferation and/or induce apoptosis in cancer cells without causing too much damage to normal cells. Some anticancer compounds were discovered by accident, others as a result of long-term research. In this review, we have presented a brief history of the development of the most important groups of anticancer drugs, pointing to the fact that they all have many side effects.

Anticancer Properties of 3-Dietoxyphosphorylfuroquinoline-4,9-dione.

Herein, the antitumor activity of a novel synthetic analog with 5,8-quinolinedione scaffold, diethyl (2-(2-chlorophenyl)-4,9-dioxo-4,9-dihydrofuro [3,2-g]quinolin-3-yl)phosphonate (AJ-418) was investigated on two breast cancer cell lines. This analog was selected from a small library of synthetic quinolinediones on the basis of its strong antiproliferative activity against MCF-7 and MDA-MB-231 cells and 4-5-fold lower cytotoxicity towards healthy MCF-10A cells. The morphology of MCF-7 and MDA-MB-231 cancer cells treated with AJ-418 changed drastically, while non-tumorigenic MCF-10A cells remained unaffected. In MCF-7 cells, after 24 h incubation, the increased number of apoptotic cells coincided with a decrease in proliferation and cell viability. The 24 h treatment of MDA-MB-231 cells with the tested compound reduced their cell viability and proliferation rate; however, a significant pro-apoptotic effect was visible only after longer incubation times (48 h and 72 h). Then, the maximum tolerated dose (MTD) of compound AJ-418 in C3H mice after subcutaneous administration was determined to be 160 mg/kg, showing that this analog was well tolerated and can be further evaluated to assess its potential therapeutic effect in tumor-bearing mice.

Prognostic Significance of HMGA1 Expression in Lung Cancer Based on Bioinformatics Analysis.

High-mobility group protein 1 (HMGA1) participates in the processes of DNA transcription, replication, recombination, and repair. The HMGA1 gene is expressed abundantly during embryogenesis and is reactivated during carcinogenesis. HMGA1 gene expression has been associated with a high degree of malignancy, metastatic tendency, and poor survival in breast, colon, ovary, and pancreatic cancers. However, its prognostic significance in lung cancer remains unclear. Using publicly available data, HMGA1 was shown to be overexpressed in both small and non-small lung tumors, with higher expression compared to both the adjacent non-malignant lung tissues and non-tumor lung tissues of healthy individuals. Elevated HMGA1 expression could result from lowered HMGA1 methylation and was connected with some clinicopathological features like sex, age, and stage of the disease. The high HMGA1 expression level was connected with shorter overall and first progression survival time among lung adenocarcinoma patients, but not lung squamous cell carcinoma patients. HMGA1 could interact with proteins involved in cellular senescence and cell cycle control (TP53, RB1, RPS6KB1, and CDK1), transcription regulation (EP400 and HMGA2), chromatin assembly and remodeling (LMNB1), and cholesterol and isoprene biosynthesis (HMGCR and INSIG1). Taken together, HMGA1 overexpression could be an essential element of lung carcinogenesis and a prognostic feature in lung cancer.

Changes in the expression of membrane type-matrix metalloproteinases genes (MMP14, MMP15, MMP16, MMP24) during treatment and their potential impact on the survival of patients with non-small cell lung cancer (NSCLC).

The analysis concerned the comparison of the expression of membrane type matrix metalloproteinases genes in the blood and tissue of NSCLC patients during the course of the disease and comparison to the control group. Blood and neoplastic tissue taken from 45 patients diagnosed with non-small cell lung cancer was a research material. The expression level of MMP14, MMP15, MMP16 and MMP24 was evaluated by qPCR and the results were compared with controls. The expression of MMP14 and MMP24 before tumor removal surgery and 100 days after was lower than in the control group. Interestingly, one year after surgery the levels of expression of these genes were identical to those in the control group. This suggests that the expression of metalloproteinase genes changes in the course of cancer and that effective treatment results in the normalization of gene expression. Lower expression of MMP15 in the blood of patients with more advanced cancer disease was observed, confirming the suppressive nature of changes in the blood. It has also been demonstrated that higher expression of MMP14 and MMP15 in the tissue is associated with more advanced stage of disease development or more invasive nature of the lesion. There is a noticeable increase of expression level in the environment surrounding the tumor, while a lower can be observed in the blood. This may indicate that changes in the expression of metalloproteinases in cancer are much more complex than merely the tumor tissue, which may also account for the inadequacies of metalloproteinase inhibitors.

Importance of Altered Gene Expression of Metalloproteinases 2, 9, and 16 in Acute Myeloid Leukemia: Preliminary Study.

Acute myeloid leukemia is a group of hematological neoplasms characterized by a heterogeneous course and high mortality. The important factor in the neoplastic process is metalloproteinases, proteolytic enzymes capable of degrading various components of the extracellular matrix, which take an active part in modifying the functioning of the cell, including transformation to cancer cell. They interact with numerous signaling pathways responsible for the process of cell growth, proliferation, or apoptosis. In the present study, changes in the expression of MMP2, MMP9, and MMP16 genes between patients with AML and people without cancer were examined. The impact of cytogenetic changes in neoplastic cells on the expression level of MMP2, MMP9, and MMP16 was also assessed, as well as the impact of the altered expression on the effectiveness of the first cycle of remission-inducing therapy. To evaluate the expression of all studied genes MMP2, MMP9, and MMP16, SYBR Green-based real-time PCR method was used; the reference gene was GAPDH. For two investigated genes MMP2 and MMP16, the lower expression level was observed in patients with AML when compared to healthy people. The MMP9 gene expression level did not differ between patients with AML and healthy individuals which may indicate a different regulation of gene expression in acute myeloid leukemia. However, no correlation was observed between the genes' expression of all tested metalloproteinases and the result of cytoreductive treatment or the presence of cytogenetic changes. The obtained results show that the expression of MMP2 and MMP16 genes is reduced while the expression of MMP9 is unchanged in patients with acute myeloid leukemia. This may indicate a different regulation of the expression of these genes, and possible disruptions in gene transcription or posttranscriptional mechanisms in the MMP2 and MMP16 genes, however, do not affect the level of MMP9 expression. Obtained results in AML patients are in contrary to various types of solid tumors where increased expression is usually observed.

The impact of ABCB1 gene polymorphism and its expression on non-small-cell lung cancer development, progression and therapy - preliminary report.

The ABCB1 gene belongs to ATP binding cassette (ABC) transporter genes that has been previously implicated in cancer progression and drug response. This study aimed to evaluate the association between the SNP 3435 and the expression of the ABCB1 gene in lung cancer patients in the Polish population in comparison to clinicopathological parameters and treatment. 150 RNA and 47 DNA samples were isolated from 49 lung cancer cases including both tissue samples and blood taken from the same patients at three time points: diagnosis, 100 days and one year after the surgical intervention. Qualitative and real-time PCR analysis of expression were done, also genotyping by PCR-RFLP. Mutant homozygous TT and allele T are present statistically significantly more frequently in the group of patients with lung cancer. There is no difference with expression level in lung cancer tissue and blood sample taken from the same patients before surgical treatment. On the basis of blood samples analysis it was observed that the expression level of ABCB1 mRNA was growing in time. Higher levels were marked after 100 days and one year after the surgical intervention. The complementary pharmacological treatment induced higher expression levels of ABCB1. The presented data suggest an important role of ABCB1 in lung cancer, the increasing level of ABCB1 mRNA which can be connected with induction of multidrug resistance mechanism is also significant, that observation must be confirmed in further analysis.

Synthesis of 2,2,6-Trisubstituted 5-Methylidene-tetrahydropyran-4-ones with Anticancer Activity.

In our continuous search for new, relatively simple 2-alkylidene-1-oxoheterocycles as promising anticancer drug candidates, herein we report an efficient synthesis of 2,2,6-trisubstituted 5-methylidenetetrahydropyran-4-ones. These compounds were obtained in a four step reaction sequence, in which starting diethyl 2-oxopropylphosphonate was transformed into 2,2-disubstituted 5-diethoxyphosphoryldihydropyran-4-ones, followed by Michael addition of various Grignard reagents and Horner-Wadsworth-Emmons reaction of the obtained adducts with formaldehyde. Stereochemistry of the intermediate Michael adducts is also discussed. Final 5-methylidenetetrahydropyran-4-ones were tested for their possible antiproliferative effect against three cancer cell lines and 6-isopropyl-2,2-dimethyl-5-methylidenetetrahydropyran-4-one (11c), which showed very high cytotoxic activity against HL-60 human leukemia cells and was three times more active than known anticancer drug carboplatin, was selected for further biological evaluation, in order to disclose its mechanism of action. The obtained results indicated that 11c induced apoptosis in HL-60 cells and caused the arrest of the cell cycle in the G2/M phase, which may suggest its cytotoxic and cytostatic activity.

New Uracil Analogs with Exocyclic Methylidene Group as Potential Anticancer Agents.

BACKGROUND: Hybrid molecules combining uracil skeleton with methylidene exo-cyclic group were designed in the search for novel anticancer drug candidates. OBJECTIVE: Two series of racemic 5-methylidenedihydrouracils, either 1,3-disubstituted or 1,3,6-trisubstituted were synthesized and tested for their possible cytotoxic activity against two cancer cell lines (HL-60 and MCF-7) and two healthy cell lines (HUVEC and MCF-10A). The most cytotoxic analogs were re-synthesized as pure enantiomers. The analog designated as U-332 [(R)-3-(4-bromophenyl)-1-ethyl-5-methylidene-6-phenyldihydrouracil], which had a very low IC50 value in HL-60 cell line (0.77µM) and was the most selective towards cancer cells was chosen for further experiments on HL-60 cell line, in order to determine the possible mechanism involved in its antineoplastic action. METHODS: Cytotoxic activities of compound was assessed by the MTT assay. In order to explore the mechanism of U-332 activity, we performed quantitative real-time PCR analysis of p53 and p21 genes. Apoptosis, cell proliferation and DNA damage in HL-60 cells were determined using the flow cytometry. The ability of U-332 to determine GADD45ɑ protein level in HL-60 cells incubated with U-332 was analyzed by ELISA test. RESULTS: U-332 was shown to generate excessive DNA damage (70% of the cell population), leading to p53 activation, resulting in p21 down-regulation and a significant increase of GADD45α protein, responsible for the cell cycle arrest in G2/M phase. CONCLUSION: U-332 can be used as a potential lead compound in the further development of novel uracil analogs as anticancer agents.

Estimation of CYP3A4*1B single nucleotide polymorphism in patients with recurrent Major Depressive Disorder.

BACKGROUND: Major depression is the most common mental illness in the world. Failures in treatment may occur due to the presence of a subtype of depression called TRD (Treatment- Resistant Depression). CYP3A4 polymorphism (rs2740574) can increase the activity of Cytochrome P450 3A4, contributing to faster metabolism of xenobiotics and reduced response to treatment. The aim of the study was to assess the distribution of CYP3A4*1B in study and control group and to estimate the influence of particular genotypes on parameters such as: age at onset, severity of symptoms before treatment and on the effectiveness of therapy. METHODS: Total of 192 patients were enrolled in this study (102 patients suffering from recurrent Major Depression Disorder, 90 healthy blood donors). PCR Restriction Fragment Length Polymorphism method with MboII enzyme was performed. The presence of CYP3A4*1B allele was evaluated on the basis of agarose gel electrophoresis. RESULTS: There was a tendency in frequency of genotypes distribution in the study group in comparison with the control group (p = 0.050). There were no statistically significant differences in the distribution mutant allele among these two groups, but there was a tendency for mutant allele to occur more often in the study group (p = 0.050). No significant correlations were found between the specific genotype and the studied parameters: age at onset (p = 0.232), severity of the symptoms (p = 0.946), and efficacy of treatment (p = 0.882). CONCLUSION: The study suggests that CYP3A4*1B polymorphism have no influence on the predisposition to depression, the severity of depressive symptoms and the efficiency of antidepressant therapy.

CYP2C19*2 polymorphism in Polish peptic ulcer patients.

BACKGROUND: CYP2C19 isoenzyme of cytochrome P450 in the liver catabolises proton pump inhibitors, one of the therapeutics utilized in Helicobacter pylori eradication therapy, and in this way could influence the eradication effectiveness. The isoensyme contributes also to metabolism of endogenous substances, which derivatives are involved in the pathogenesis of peptic ulceration. CYP2C19*2 polymorphism (rs4244285) changing the CYP2C19 function could be relevant in the predisposition to peptic ulcer disease. METHODS: CYP2C19*2 polymorphism in 197 peptic ulcer patients and 107 healthy subjects of Polish origin by PCR-RFLP method was investigated. RESULTS: There were no statistically significant differences in genotypes and alleles frequencies for investigated polymorphism between peptic ulcer patients and healthy individuals. No associations between frequencies of particular CYP2C19 genotypes and alleles and the presence of H. pylori infection in peptic ulcer patients were stated. However, significant association between CYP2C19*2 and gender in H. pylori-infected but not -uninfected peptic ulcer individuals was found. CONCLUSIONS: Investigated polymorphism is not a risk factor for peptic ulcer in Polish population. Obtained results could suggested there is some interaction between gender, CYP2C19*2 polymorphism, and pathogenesis of H. pylori infection development. However, this hypothesis should be verified in the further studies.

The contribution of ABCG2 G34A and C421A polymorphisms to multiple myeloma susceptibility.

BACKGROUND: Breast cancer resistance protein BCRP, belonging to superfamily G of the adenosine triphosphate-binding cassette (ABC) transporters, is an efflux pump and plays a critical role in protecting cells against xenobiotics and toxic compounds including (pro)carcinogens. BCRP is expressed in many tissues, including hematopoietic stem cells. Genetic variants such as single nucleotide polymorphisms (SNPs) can change the gene expression and/or reduce their products' activity which may affect an individual's susceptibility to xenobiotics and the development of carcinoma. These changes may affect the exposure of blood cells to toxic compounds, which increases the risk of multiple myeloma. The aim of this study was to determine polymorphisms at positions G34A and C421A of the ABCG2 gene in multiple myeloma in the Polish population for the first time. MATERIALS AND METHODS: Material for the study included DNA isolated from nucleus of cells of peripheral blood of patients diagnosed with multiple myeloma (investigated group N=181) and from healthy people (control group N=97). Research into the polymorphisms was conducted using the polymerase chain reaction-restriction fragment length polymorphism technique. RESULTS: The present study showed a statistically significant association between SNP C421A of the ABCG2 gene and the risk of developing multiple myeloma (P=0.0218). No statistically significant relationship was found for the other parameters analyzed, such as age, gender, or type of secreted immunoglobulin. CONCLUSION: Preliminary studies indicate that SNP C421A may become a potential predictor for the development of multiple myeloma.

Decreased MMP1 gene expression in acute myeloid leukaemia.

Acute myeloid leukaemia (AML) is a heterogeneous disorder of haematopoietic stem cells or progenitor cells. Metalloproteinases (MMPs) are proteolytic enzymes whose activity is increased in different types of solid tumours. These enzymes regulate many processes associated with tumour progression. In haematological malignancy, the role of MMPs seems to be underestimated, and only metalloproteinase 2 (MMP2) and metalloproteinase 9 (MMP9) have been widely examined so far. In this work, differences in metalloproteinase 1 (MMP1) gene expression between patients with AML and healthy individuals were assessed. The relative expression level of the MMP1 gene was obtained by a real time PCR method preceded by reverse transcription. The relative level of MMP1 gene expression in patients with AML was decreased when compared to that of the control group. The role of MMP1 in AML could be different from that in solid tumours. Decreased MMP1 gene expression in AML similar to that of MMP9, shows a greater role for MMP1 in normal haematopoiesis than in the development of leukaemic cells.

Synthesis of 3-Methylidene-1-tosyl-2,3-dihydroquinolin-4(1H)-ones as Potent Cytotoxic Agents.

An efficient synthetic strategy to 3-methylidene-2,3-dihydroquinolin-4(1H)-ones variously substituted in position 2 has been developed. The title compounds were synthesized in the reaction sequence involving reaction of diethyl methylphosphonate with methyl 2-(tosylamino)benzoate, condensation of thus formed diethyl 2-oxo-2-(2-N-tosylphenyl)ethylphosphonate with various aldehydes followed by successful application of the obtained 3-(diethoxyphosphoryl)-1,2-dihydroquinolin-4-ols as Horner-Wadsworth-Emmons reagents for the olefination of formaldehyde. Also, enantioselective approach to the target compounds has been evaluated using 3-dimenthoxyphosphoryl group as a chiral auxiliary. Single X-ray crystal analysis of (2S)-3-(dimenthoxyphosphoryl)-2-phenyl-1-tosyldihydroquinolin-4-ol revealed the presence of strong resonance-assisted hydrogen bond (RAHB). The obtained 3-methylidene-2,3-dihydroquinolin-4(1H)-ones were then tested for their cytotoxic activity against two leukemia cell lines NALM-6 and HL-60 and a breast cancer MCF-7 cell line. All compounds showed very high cytotoxic activity with the IC50 values mostly below 1 µm in all three cancer cell lines. The selected analogs were also tested on human umbilical vein endothelial cells (HUVEC) and on human mammary gland/breast cells (MCF-10A) to evaluate their influence on normal cells. Since one of the most serious problems in cancer chemotherapy is the development of drug resistance, the mRNA levels and activity of ABCB1 transporter considered to be the most important factor engaged in drug resistance, were evaluated in MCF-7 cells treated with two selected analogs. Both compounds were strong ABCB1 transporter inhibitors that could prevent efflux of anticancer drugs from cancer cells.

Association of ABCB1 T-129C polymorphism and multiple myeloma risk in Polish population.

The possible interaction between gene polymorphism and cancer risk development is a very interesting issue. The genetic variants of the ATP-binding cassette superfamily B member 1 (ABCB1) are known to be involved in developing cancer risk and individual differences in chemotherapeutic response. Polymorphisms may affect the reduction of the activity and/or expression of important protective cellular proteins. The increased exposure to toxic compounds, including carcinogens is associated with an increased risk of developing cancers. The present study was aimed to evaluate the possible effect of ABCB1 T-129C single nucleotide polymorphism in risk of cancer development in Polish patients diagnosed with multiple myeloma. 91 multiple myeloma patients and 94 healthy controls were enrolled in this case-control study. The ABCB1 T-129C genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism method (PCR-RFLP). The distribution of particular genotypes between multiple myeloma patients and controls group was not significantly different for T-129C SNP (p = 0.4297). The studied polymorphism does not seem to affect the increased risk of multiple myeloma development.

The effect of hydrazine derivatives of 3-formylchromones on angiogenic basic fibroblast growth factor and fibroblast growth factor receptor-1 in human melanoma cell line WM-115.

The hydrazine derivatives of benzopyrones remain an unexplored group of chemical compounds. This preliminary study investigates the influence of A-5, CH-3 and K-2 derivatives at concentrations of 1, 10, 100 nM and 1 µM on selected biochemical factors of a melanoma cell line WM-115, with regard to their potential angiogenic properties. The studied compounds were found to influence cell proliferation, as well as total protein, bFGF and FGFR1 concentration.

Synthesis of 4,4-Disubstituted 3-Methylidenechroman-2-ones as Potent Anticancer Agents.

The synthesis of a new library of 4,4-disubstituted 3-methylidene-3,4-dihydro-2H-chroman-2-ones applying Horner-Wadsworth-Emmons methodology for the construction of an exo-methylidene moiety is reported. Corresponding 3-diethoxyphosphorylchroman-2-ones were synthesized in a three-step reaction sequence consisting of O-methylation of ethyl 2-diethoxyphosphoryl-3-oxoalkanoates, followed by reaction of the obtained 2-diethoxyphosphoryl-3-methoxy-2-alkenoates with phenols or 1-naphthol. The resulting 3-diethoxyphosphorylochromen-2-ones proved to be effective Michael acceptors in reactions with various Grignard reagents. Preliminary biological evaluations showed that many of the synthesized 3-methylidenechroman-2-ones possess very high cytotoxic activity against NALM-6 and HL-60 cancer cell lines (IC50 <1.0 µm) as well as high activity against the MCF-7 cancer cell line (IC50 <10 µm). Furthermore, two of the highly active 3-methylidenechroman-2-ones with geminal methyl and ethyl substituents at position 4 showed promising therapeutic indexes of 10 and 13 in tests against human umbilical vein endothelial cells (HUVECs).

Anticancer properties of new synthetic hybrid molecules combining naphtho[2,3-b]furan-4,9-dione or benzo[f]indole-4,9-dione motif with phosphonate subunit.

In this paper we report an efficient and general synthesis of substituted 3-diethoxyphosphorylnaphtho [2,3-b]furan-4,9-diones and 3-diethoxyphosphorylbenzo [f]indole-4,9-diones which integrate the natural 1,4-naphtalenedione scaffold, present in several anticancer agents with the phosphonate moiety. The cytotoxicity of such hybrid molecules was tested against two leukemia cell lines, HL-60 and NALM-6 and against a breast adenocarcinoma MCF-7 cell line. Selected compounds were also tested on normal human cells: HUVEC and MCF-10A. In general, naphthofuran-4,9-diones showed much higher cytotoxic activity (IC50 values below 10 µM) than benzoindole-4,9-diones. The most promising 2-(2-chlorophenyl)-3-diethoxyphosphorylnaphtho [2,3-b]furan-4,9-dione, with the highest cytotoxic activity in the MTT test, was chosen for further evaluation of its anticancer potential. This compound, tested on HL-60 and MCF-7 cells inhibited cell proliferation, generated DNA damage and induced apoptosis. The suggested mechanism of its cytotoxic activity was the generation of intracellular reactive oxygen species and the induction of mitochondrial membrane potential dissipation.

Assessment of TNFA polymorphisms at positions -857 and -863 in Polish peptic ulcer patients.

PURPOSE: Peptic ulceration connected with chronic inflammation in gastrointestinal mucosa could be induced by Helicobacter pylori infection. Tumor necrosis factor alpha (TNF-α) encoded by TNFA gene is a key mediator in the inflammation process. There are several polymorphisms in the promoter of TNFA influencing its transcriptional activity. -857C>T (rs1799724) and -863C>A (rs1800630) substitutions may be responsible for increased TNFA transcription and TNF-α production. The association of these two polymorphisms with peptic ulceration and the development of H. pylori infection in peptic ulcer patients in Poles were evaluated. MATERIAL AND METHODS: Polymorphisms were assessed by PCR-RFLP in 203 peptic ulcer patients. H. pylori infection was confirmed by rapid urease test. The results of genotyping were compared with those obtained for 248 healthy Polish individuals. RESULTS: There were no significant differences in genotype and allele frequencies for both investigated polymorphisms between peptic ulcer patients and healthy individuals. No associations between frequencies of particular genotypes and alleles for both SNPs and the presence of H. pylori infection in peptic ulcer patients and in subgroups of peptic ulcer women and men were confirmed. CONCLUSIONS: The investigated SNPs are not risk factors for peptic ulcer development. They are not risk factors for H. pylori infection in ulcer patients.

ABCG2 in peptic ulcer: gene expression and mutation analysis.

The aim of this study was to evaluate the participation of polymorphism at position C421A and mRNA expression of the ABCG2 gene in the development of peptic ulcers, which is a very common and severe disease. ABCG2, encoded by the ABCG2 gene, has been found inter alia in the gastrointestinal tract, where it plays a protective role eliminating xenobiotics from cells into the extracellular environment. The materials for the study were biopsies of gastric mucosa taken during a routine endoscopy. For genotyping by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) at position C421A, DNA was isolated from 201 samples, while for the mRNA expression level by real-time PCR, RNA was isolated from 60 patients. The control group of healthy individuals consisted of 97 blood donors. The dominant genotype in the group of peptic ulcer patients and healthy individuals was homozygous CC. No statistically significant differences between healthy individuals and the whole group of peptic ulcer patients and, likewise, between the subgroups of peptic ulcer patients (infected and uninfected with Helicobacter pylori) were found. ABCG2 expression relative to GAPDH expression was found in 38 of the 60 gastric mucosa samples. The expression level of the gene varies greatly among cases. The statistically significant differences between the intensity (p = 0.0375) of H. pylori infection and ABCG2 gene expression have been shown. It was observed that the more intense the infection, the higher the level of ABCG2 expression.

The Influence of C3435T Polymorphism of the ABCB1 Gene on Genetic Susceptibility to Depression and Treatment Response in Polish Population - Preliminary Report.

BACKGROUND: Despite the high prevalence of depression, the mechanism of the origin of this disease as well as the causes of resistance to therapy in some patients are still not fully understood. Increasingly, the possible role of genetic factors is considered. One of them is polymorphisms in the ABCB1 (MDR1) gene which encodes P-glycoprotein, responsible for the transport of xenobiotics, including antidepressant drugs, through the blood-brain barrier. METHODS: C3435T was evaluated in 90 patients with recurrent depressive disorders (rDD). Genotyping was performed using a polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). RESULTS: The obtained results indicate that the TT genotype occurred more frequently among patients with rDD than in healthy volunteers (p=0.0441). Also, at least one C allele was present significantly less frequent in the study group than in healthy individuals (p=0.0300). The severity of depressive symptoms was higher among patient with the CC genotype in comparison with the other genotypes (p=0.0106) but treatment response to antidepressants was better in this group than among patients with CT or TT genotypes (p=0.0301). Likewise, patients with the T allele have a significantly lower severity of symptoms (p=0.0026) and decreased therapy effectiveness (p=0.0142) than C allele carriers. CONCLUSIONS: This study suggests that C3435T polymorphisms in the ABCB1 gene are strongly associated with a predisposition to depression development, the severity of depressive symptoms and the effectiveness of therapy with using different groups of antidepressant agents.