Drug resistance mechanisms in cancers:Execution of prosurvival strategies

One of the quintessential challenges in cancer treatment is drug resistance.Several mechanisms of drug resistance have been described to date,and new modes of drug resistance continue to be discovered.The phenomenon of cancer drug resistance is now widespread,with approximately 90% of cancer-related deaths associated with drug resistance.Despite significant advances in the drug discovery process,the emergence of innate and acquired mechanisms of drug resistance has impeded the progress in cancer therapy.Therefore,understanding the mechanisms of drug resistance and the various pathways involved is integral to treatment modalities.In the present review,I discuss the different mechanisms of drug resistance in cancer cells,including DNA damage repair,epithelial to mesenchymal transition,inhibition of cell death,alteration of drug targets,inactivation of drugs,deregulation of cellular energetics,immune evasion,tumor-promoting inflammation,genome instability,and other contributing epigenetic factors.Furthermore,I highlight available treatment options and conclude with future directions.

Role of targeting ferroptosis as a component of combination therapy in combating drug resistance in colorectal cancer

Colorectal cancer(CRC)is a form of cancer that is often resistant to chemotherapy,targeted therapy,radiotherapy,and immunotherapy due to its genomic instability and inflammatory tumor microenvironment.Ferroptosis,a type of non-apoptotic cell death,is characterized by the accumulation of iron and the oxidation of lipids.Studies have revealed that the levels of reactive oxygen species and glutathione in CRC cells are significantly lower than those in healthy colon cells.Erastin has emerged as a promising candidate for CRC treatment by diminishing stemness and chemoresistance.Moreover,the gut,responsible for regulating iron absorption and release,could influence CRC susceptibility through iron metabolism modulation.Investigation into ferroptosis offers new insights into CRC pathogenesis and clinical management,potentially revolutionizing treatment approaches for therapy-resistant cancers.

Research progress in tumor angiogenesis and drug resistance in breast cancer

Angiogenesis is considered a hallmark pathophysiological process in tumor development. Aberrant vasculature resulting from tumor angiogenesis plays a critical role in the development of resistance to breast cancer treatments, via exacerbation of tumor hypoxia, decreased effective drug concentrations within tumors, and immune-related mechanisms. Antiangiogenic therapy can counteract these breast cancer resistance factors by promoting tumor vascular normalization. The combination of antiangiogenic therapy with chemotherapy, targeted therapy, or immunotherapy has emerged as a promising approach for overcoming drug resistance in breast cancer. This review examines the mechanisms associated with angiogenesis and the interactions among tumor angiogenesis, the hypoxic tumor microenvironment, drug distribution, and immune mechanisms in breast cancer. Furthermore, this review provides a comprehensive summary of specific antiangiogenic drugs, and relevant studies assessing the reversal of drug resistance in breast cancer. The potential mechanisms underlying these interventions are discussed, and prospects for the clinical application of antiangiogenic therapy to overcome breast cancer treatment resistance are highlighted.

MATHEMATICAL MODELING AND BIFURCATION ANALYSIS FOR A BIOLOGICAL MECHANISM OF CANCER DRUG RESISTANCE

Drug resistance is one of the most intractable issues in targeted therapy for cancer diseases.It has also been demonstrated to be related to cancer heterogeneity,which promotes the emergence of treatment-refractory cancer cell populations.Focusing on how cancer cells develop resistance during the encounter with targeted drugs and the immune system,we propose a mathematical model for studying the dynamics of drug resistance in a conjoint heterogeneous tumor-immune setting.We analyze the local geometric properties of the equilibria of the model.Numerical simulations show that the selectively targeted removal of sensitive cancer cells may cause the initially heterogeneous population to become a more resistant population.Moreover,the decline of immune recruitment is a stronger determinant of cancer escape from immune surveillance or targeted therapy than the decay in immune predation strength.Sensitivity analysis of model parameters provides insight into the roles of the immune system combined with targeted therapy in determining treatment outcomes.

Inferring Mycobacterium Tuberculosis Drug Resistance and Transmission using Whole-genome Sequencing in a High TB-burden Setting in China

Objective China is among the 30 countries with a high burden of tuberculosis(TB)worldwide,and TB remains a public health concern.Kashgar Prefecture in the southern Xinjiang Autonomous Region is considered as one of the highest TB burden regions in China.However,molecular epidemiological studies of Kashgar are lacking.Methods A population-based retrospective study was conducted using whole-genome sequencing(WGS)to determine the characteristics of drug resistance and the transmission patterns.Results A total of 1,668 isolates collected in 2020 were classified into lineages 2(46.0%),3(27.5%),and 4(26.5%).The drug resistance rates revealed by WGS showed that the top three drugs in terms of the resistance rate were isoniazid(7.4%,124/1,668),streptomycin(6.0%,100/1,668),and rifampicin(3.3%,55/1,668).The rate of rifampicin resistance was 1.8%(23/1,290)in the new cases and 9.4%(32/340)in the previously treated cases.Known resistance mutations were detected more frequently in lineage 2 strains than in lineage 3 or 4 strains,respectively:18.6%vs.8.7 or 9%,P<0.001.The estimated proportion of recent transmissions was 25.9%(432/1,668).Multivariate logistic analyses indicated that sex,age,occupation,lineage,and drug resistance were the risk factors for recent transmission.Despite the low rate of drug resistance,drug-resistant strains had a higher risk of recent transmission than the susceptible strains(adjusted odds ratio,1.414;95%CI,1.023–1.954;P=0.036).Among all patients with drug-resistant tuberculosis(DR-TB),78.4%(171/218)were attributed to the transmission of DR-TB strains.Conclusion Our results suggest that drug-resistant strains are more transmissible than susceptible strains and that transmission is the major driving force of the current DR-TB epidemic in Kashgar.

Prox1 Suppresses Proliferation and Drug Resistance of Retinoblastoma Cells via Targeting Notch1

Objective Retinoblastoma(RB)is a prevalent type of eye cancer in youngsters.Prospero homeobox 1(Prox1)is a homeobox transcriptional repressor and downstream target of the proneural gene that is relevant in lymphatic,hepatocyte,pancreatic,heart,lens,retinal,and cancer cells.The goal of this study was to investigate the role of Prox1 in RB cell proliferation and drug resistance,as well as to explore the underlying Notch1 mechanism.Methods Human RB cell lines(SO-RB50 and Y79)and a primary human retinal microvascular endothelial cell line(ACBRI-181)were used in this study.The expression of Prox1 and Notch1 mRNA and protein in RB cells was detected using quantitative real time-polymerase chain reaction(RT-qPCR)and Western blotting.Cell proliferation was assessed after Prox1 overexpression using the Cell Counting Kit-8 and the MTS assay.Drug-resistant cell lines(SO-RB50/vincristine)were generated and treated with Prox1 to investigate the role of Prox1 in drug resistance.We employed pcDNA-Notch1 to overexpress Notch1 to confirm the role of Notch1 in the protective function of Prox1.Finally,a xenograft model was constructed to assess the effect of Prox1 on RB in vivo.Results Prox1 was significantly downregulated in RB cells.Overexpression of Prox1 effectively decreased RB cell growth while increasing the sensitivity of drug-resistant cells to vincristine.Notch1 was involved in Prox1’s regulatory effects.Notch1 was identified as a target gene of Prox1,which was found to be upregulated in RB cells and repressed by increased Prox1 expression.When pcDNA-Notch1 was transfected,the effect of Prox1 overexpression on RB was removed.Furthermore,by downregulating Notch1,Prox1 overexpression slowed tumor development and increased vincristine sensitivity in vivo.Conclusion These data show that Prox1 decreased RB cell proliferation and drug resistance by targeting Notch1,implying that Prox1 could be a potential therapeutic target for RB.

PHLDA2 reshapes the immune microenvironment and induces drug resistance in hepatocellular carcinoma

Hepatocellular carcinoma(HCC)is a malignancy known for its unfavorable prognosis.The dysregulation of the tumor microenvironment(TME)can affect the sensitivity to immunotherapy or chemotherapy,leading to treatment failure.The elucidation of PHLDA2’s involvement in HCC is imperative,and the clinical value of PHLDA2 is also underestimated.Here,bioinformatics analysis was performed in multiple cohorts to explore the phenotype and mechanism through which PHLDA2 may affect the progression of HCC.Then,the expression and function of PHLDA2 were examined via the qRT-PCR,Western Blot,and MTT assays.Our findings indicate a substantial upregulation of PHLDA2 in HCC,correlated with a poorer prognosis.The methylation levels of PHLDA2 were found to be lower in HCC tissues compared to normal liver tissues.Besides,noteworthy associations were observed between PHLDA2 expression and immune infiltration in HCC.In addition,PHLDA2 upregulation is closely associated with stemness features and immunotherapy or chemotherapy resistance in HCC.In vitro experiments showed that sorafenib or cisplatin significantly up-regulated PHLDA2 mRNA levels,and PHLDA2 knockdown markedly decreased the sensitivity of HCC cells to chemotherapy drugs.Meanwhile,we found that TGF-βinduced the expression of PHLDA2 in vitro.The GSEA and in vitro experiment indicated that PHLDA2 may promote the HCC progression via activating the AKT signaling pathway.Our study revealed the novel role of PHLDA2 as an independent prognostic factor,which plays an essential role in TME remodeling and treatment resistance in HCC.

Deciphering resistancemechanisms and novel strategies to overcome drug resistance in ovarian cancer:a comprehensive review

Ovarian cancer is among the most lethal gynecological cancers,primarily due to the lack of specific symptoms leading to an advanced-stage diagnosis and resistance to chemotherapy.Drug resistance(DR)poses the most significant challenge in treating patients with existing drugs.The Food and Drug Administration(FDA)has recently approved three new therapeutic drugs,including two poly(ADP-ribose)polymerase(PARP)inhibitors(olaparib and niraparib)and one vascular endothelial growth factor(VEGF)inhibitor(bevacizumab)for maintenance therapy.However,resistance to these new drugs has emerged.Therefore,understanding the mechanisms of DR and exploring new approaches to overcome them is crucial for effective management.In this review,we summarize the major molecular mechanisms of DR and discuss novel strategies to combat DR.

The superiority of PMFs on reversing drug resistance of colon cancer and the effect on aerobic glycolysis-ROS-autophagy signaling axis

Background:Polymethoxylatedflavones(PMFs)are compounds present in citrus peels and other Rutaceae plants,which exhibit diverse biological activities,including robust antitumor and antioxidant effects.However,the mechanism of PMFs in reversing drug resistance to colon cancer remains unknown.In the present study,we aimed to investigate the potential connection between the aerobic glycolysis-ROS-autophagy signaling axis and the reversal of PTX resistance in colon cancer by PMFs.Methods:MTT Cell viability assay and colony formation assay were used to investigate the effect of PMFs combined with PTX in reversing HCT8/T cell resistance ex vivo;the mRNA and protein levels of the target were detected by SDS-PAGE(sodium dodecyl sulfate-polyacrylamide gel electrophoresis),quantitative real-timefluorescence polymerase chain reaction(qRT-PCR)and Western blot protein immunoblotting(WB);An HCT8/T cell xenograft model was established to investigate the MDR reversal activity of PMFs in vivo;The extracellular acidification rate(ECAR)and the oxygen consumption rate(OCR)were detected to assess the cellular oxygen consumption rate and glycolytic process.Results:HCT8/T cells demonstrated significant resistance to PTX,up-regulating the expression levels of ABCB1 mRNA,P-gp,LC3-I,and LC3-II protein,and increasing intracellular reactive oxygen species(ROS)content.PMFs mainly contain two active ingredients,nobiletin,and tangeretin,which were able to reverse drug resistance in HCT8/T cells in a concentration-dependent manner.PMFs exhibited high tolerance in the HCT8/T nude mouse model while increasing the sensitivity of PTX-resistant cells and suppressing tumor growth significantly.PMFs combined with PTX reduced extracellular acidification rate(ECAR)and oxygen consumption rate(OCR)in HCT8/T cells.Additionally,PMFs reduced intracellular ROS content,down-regulated the expression levels of autophagy-related proteins LC3-I,LC3-II,Beclin1,and ATG7,and significantly reduced the number of autophagosomes in HCT8/T cells.Conclusions:The present study demonstrated that PMFs could potentially reverse PTX resistance in colon cancer by regulating the aerobic glycolysis-ROS-autophagy signaling axis,which indicated that PMFs would be potential potentiators for future chemotherapeutic agents in colon cancer.

Analysis of The Correlation Between inhA Gene Mutation and Resistance to Protionamide in Drug-Resistant Mycobacterium Tuberculosis

Objective: To investigate the characteristics of katG and inhA gene mutations in multidrug-resistant tuberculosis (MDR-TB), pre-extensively drug-resistant tuberculosis (preXDR-TB), and their correlation with resistance to protionamide (Pto). Methods: A total of 229 patients with MDR-TB and pre-XDR-TB diagnosed in the Eighth Affiliated Hospital of Xinjiang Medical University from January 2020 to February 2024 were selected to analyze the characteristics of katG and inhA mutations in MTB clinical isolates and their correlation with Pto resistance. Results: The mutation rate of katG (with or without inhA mutation) was 85.2%. The mutation rates in MDR-TB and pre-XDR-TB were 87.4% (125/143) and 81.4% (70/86), respectively. The mutation rate of inhA (including katG mutation) was 14.8% (34/229), which was 12.6% (18/143) and 18.6% (16/86) in MDR-TB and pre-XDR-MTB, respectively. There was no difference in mutation (P > 0.05). Conclusion: The total resistance rate to Pto in 229 strains was 8.7% (20/229), which was 8.4% (12/143) and 9.3% (8/86) in MDR-TB and pre-XDR-TB, respectively. Among the inhA mutant strains, 13 were resistant to the Pto phenotype, and the resistance rate was 65% (13/20). In MDR-TB and pre-XDR-TB strains resistant to Pto, inhA gene mutations occurred in 66.7% (6/9) and 63.6% (7/11), respectively. The resistance rates of MDR-MTB and pre-XDR-TB strains without inhA gene mutation to Pto were 2.4% (3/125) and 5.7% (4/70), respectively.

Isolation and Drug Resistance Analysis of Swine Salmonella

In this study, 68 fresh pork samples were collected from several major wholesale markets in Dalian City of Liaoning Province to isolate Salmonella using SS agar medium as selective medium. Salmonella isolates were identified with colony morphology observation and PCR method. The resistance of Salmonella iso- lates to 15 antibiotics was analyzed by broth microdilution susceptibility test. Accord- ing to the result, 12 Salmonella strains were isolated from 68 fresh pork samples, indicating a detection rate of 17.64%; 83.33% of Salmonella strains isolated from fresh pork samples could at least resist one antibiotic; Salmonella strains exhibited the strongest resistance to florfenicol （75.0%）, sarafloxacin hydrochloride （66.7%）, neomycin sulfate （66.7%） and doxycycline hydrochloride （66.7%）, followed by oxyte- tracycline （58.3%）, gentamicin sulphate （58.3%） and mequindox （58.3%）; Salmonella strains exhibited relatively low resistance to ciprofloxacin lactate （50.0%）, en- rofloxacin （50.0%）, ciprofloxacin hydrochloride （50.0%）, amoxicillin （16.7%） and col- istin sulphate （16.7%）. Salmonella in fresh pork samples from wholesale markets in Dalian Economic ＆ Technological Development Zone exhibited a high detection rate, and the isolated Salmonella strains showed extremely high resistance to various an- tibiotics. The strong drug-resistance of Salmonella can also be transmitted through the food chain from the food to the people, which should attract sufficient attention.

Study on Drug Resistance and Relative Mechanisms of Chlamydia Trachomatis

Chlamydia Trachomatis (C.T.) is one of the most common pathogens of human sexually transmitted diseases. Treatment of C.T. infection primarily depends on Tetracyclines, Macrolides and Quinolones, but with the wide use of antibiotics an increasing number of drug-resistant Chlamydia trachomatis cases have been reported. This review summarizes the resistant conditions and the possible resistance mechanisms of C.T..

Prevalence and evolution of drug resistance HIV-1 variants in Henan, China

To understand the prevalence and evolution of drug resistant HIV strains in Henan China after the implementation of free antiretroviral therapy for AIDS patients. 45 drug naive AIDS patients, 118 AIDS patients who received three months antiretroviral therapy and 124 AIDS patients who received six months antiretroviral treatment were recruited in the southern part of Henan province. Information on general condition, antiretroviral medicines, adherence and clinical syndromes were collected by face to face interview. Meanwhile, 14ml EDTA anticoagulant blood was drawn. CD4/CD8 T cell count, viral load and genotypic drug resistance were tested. The rates of clinical improvement were 55.1% and 50.8% respectively three months and six months after antiretroviral therapy. The mean CD4 cell count after antiretroviral therapy was significantly higher than in drug naive patients. The prevalence rate of drug resistant HIV strains were 13.9%, 45.4% and 62.7% in drug naive patients, three month treatment patients and six month treatment patients, respectively. The number of resistance mutation codons and the frequency of mutations increased significantly with continued antiretroviral therapy. The mutation sites were primarily at the 103, 106 and 215 codons in the three-month treatment group and they increased to 15 codon mutations in the six-month treatment group. From this result, the evolution of drug resistant strains was inferred to begin with the high level NNRTI resistant strain, and then develop low level resistant strains to NRTIs. The HIV strains with high level resistance to NVP and low level resistance to AZT and DDI were highly prevalent because of the AZT＋DDI＋NVP combination therapy. These HIV strains were also cross resistant to DLV, EFV, DDC and D4T. Poor adherence to therapy was believed to be the main reason for the emergence and prevalence of drug resistant HIV strains. The prevalence of drug resistant HIV strains was increased with the continuation of antiretroviral therapy in the southern part of Henan province. Measures, that could promote high level adherence, provide new drugs and change ART regimens in failing patients, should be implemented as soon as possible.

Effects of Taxotere on invasive potential and multidrug resistance phenotype in pancreatic carcinoma cell line SUIT-2

INTRODUCTIONDevelopment of drug-resistance to chemotherapyand subsequent metastasis of tumor are primarilyresponsible for treatment failure and the death fromcancer. There have been many previous studies onthe relationship between expression of multidrugresistance (MDR) phenotype P-glycoprotein (P-gp)and the malignant properties of tumors, but theresults are often conflicting[1-8]. The difference intumor types or MDR phenotype induced by specificagents might account for this discrepancy. Taxotere(TXT), a member of the family of taxanes, hasantitumor activity through its effect of promotingthe polymerization of tubulin[9,10].

New strategies against drug resistance to herpes simplex virus

Herpes simplex virus （HSV）, a member of the Herpesviridae family, is a significant human pathogen that results in mucocutaneous lesions in the oral cavity or genital infections. Acyclovir （ACV） and related nucleoside analogues can successfully treat HSV infections, but the emergence of drug resistance to ACV has created a barrier for the treatment of HSV infections, especially in immunocompromised patients. There is an urgent need to explore new and effective tactics to circumvent drug resistance to HSV. This review summarises the current strategies in the development of new targets （the DNA helicase/primase （H/P） complex）, new types of molecules （nature products） and new antiviral mechanisms （lethal mutagenesis of Janus-type nucleosides） to fight the drug resistance of HSV.

Drug sensitivity and drug resistance profiles of human intrahepatic cholangiocarcinoma cell lines

AIM: To study the effect of a number of chemotherapeutic drugs on five human intrahepatic cholangiocarcinoma (CCA) cell lines. The expressions of genes that have been proposed to influence the resistance of chemotherapeutic drugs including thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), glutathione-S-transferase PI (GSTP1), multidrug resistance protein (MDR1) and multidrug resistance-associated proteins (MRPs) were also determined. METHODS: Five human CCA cell lines (KKU-100, KKU-M055, KKU-M156, KKU-M214 and KKU-OCA17) were treated with various chemotherapeutic drugs and growth inhibition was determined by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay. Semi-quantitative levels of gene expression were determined by a reverse transcriptase polymerase chain reaction (RT-PCR). Results of IC_(50) values and the ratios of gene expression were analyzed by linear regression to predict their relationship. RESULTS: Among five CCA cell lines, KKU-M055 was the most sensitive cell line towards all chemotherapeutic drugs investigated, particularly taxane derivatives with IC_(50) values of 0.02-3 nmol/L, whereas KKU-100 was apparently the least sensitive cell line. When compared to other chemotherapeutic agents, doxorubicin and pirarubicin showed the lowest IC_(50) values (＜5 μmol/L) in all five CCA cell lines. Results from RT-PCR showed that TS, MRP1, MRP3 and GSTP1 were highly expressed in these five CCA cell lines while DPD and MRP2 were only moderately expressed. It should be noted that MDR1 expression was detected only in KKU-OCA17 cell lines. A strong correlation was only found between the level of MRP3 expression and the IC_(50) values of etoposide, doxorubicin and pirarubicin (r=0.86-0.98, P＜0.05). CONCLUSION: Sensitivity to chemotherapeutic agents is not associated with the histological type of CCA. Choosing of the appropriate chemotherapeutic regimen for the treatment of CCA requires knowledge of drug sensitivity. MRP3 was correlated with resistance of CCA cell lines to etoposide, doxorubicin and pirarubicin, whereas other chemotherapeutic drugs showed no association. The role of this multidrug resistance-associated protein, MRP3, in chemotherapeutic resistance in CCA patients needs to be further investigated.

The crosstalk between autophagy and ferroptosis:what can we learn to target drug resistance in cancer?

Autophagy is a conserved intracellular degradation system that plays a dual role in cell death;thus,therapies targeting autophagy in cancer are somewhat controversial.Ferroptosis is a new form of regulated cell death featured with the iron-dependent accumulation of lethal lipid ROS.This pathway is morphologically,biochemically and genetically distinct from other forms of cell death.Accumulating studies have revealed crosstalk between autophagy and ferroptosis at the molecular level.In this review,we summarize the mechanisms of ferroptosis and autophagy,and more importantly,their roles in the drug resistance of cancer.Numerous connections between ferroptosis and autophagy have been revealed,and a strong causal relationship exists wherein one process controls the other and can be utilized as potential therapeutic targets for cancer.The elucidation of when and how to modulate their crosstalk using therapeutic strategies depends on an understanding of the fine-tuned switch between ferroptosis and autophagy,and approaches designed to manipulate the intensity of autophagy might be the key.

Dynamic changes and surveillance function of prion protein expression in gastric cancer drug resistance

AIM:To explore the dynamic changes of prion protein (PrPc) in the process of gastric cancer drug resistance and the role of PrPc expression in the prognosis of gastric cancer patients receiving chemotherapy.METHODS:A series of gastric cancer cell lines resistant to different concentrations of adriamycin was established,and the expression of PrPc,Bcl-2 and Bax was detected in these cells.Apoptosis was determined using Annexin V staining.Western blotting and immunohisto-chemistry were performed to detect the expression of PrPc in patients receiving chemotherapy and to explore the role of PrPc expression in predicting the chemosensitivity and the outcome of gastric cancer patients receiving chemotherapy.Follow-up was performed for 2 years.RESULTS:PrPc expression was increased with the increase in drug resistance.Bcl-2,together with PrPc,increased the level of anti-apoptosis of cancer cells.Increased PrPc expression predicted the enhanced level of anti-apoptosis and resistance to anticancer drugs.PrPc expression could be used as a marker for predicting the efficacy of chemotherapy and the prognosis of gastric cancer.Increased PrPc expression predicted both poor chemosensitivity and a low 2-year survival rate.Contrarily,low PrPc expression predicted favorable chemosensitivity and a relatively high 2-year survival rate.CONCLUSION:PrPc expression is associated with histological types and differentiation of gastric cancer cells;The PrPc expression level might be a valuable marker in predicting the efficacy of chemotherapy and the prognosis of gastric cancer patients receiving chemotherapy.

Use of arrays to investigate the contribution of ATP-binding cassette transporters to drug resistance in cancer chemotherapy and prediction of chemosensitivity

Multidrug resistance （MDR） is a major problem in cancer chemotherapy. One of the best known mechanisms of MDR is the elevated expression of ATP-binding cassette （ABC） transporters. While some members of human ABC transporters have been shown to cause drug resistance with elevated expression, it is not yet known whether the over-expression of other members could also contribute to drug resistance in many model cancer cell lines and clinics. The recent development ofmicroarrays and quantitative PCR arrays for expression profiling analysis of ABC transporters has helped address these issues. In this article, various arrays with limited or full list of ABC transporter genes and their use in identifying ABC transporter genes in drug resistance and chemo-sensitivity prediction will be reviewed.

Effects of multidrug resistance, antisense RNA on the chemosensitivity of hepatocellular carcinoma cells

BACKGROUND: Multidrug resistance is a major obstacle in cancer chemotherapy. We examined whether the antisense RNA of multidrug resistance gene 1 (mdr1) could reverse multidrug resistance in the human hepatocellular carcinoma (HCC) cell line SMMC7721/ADM. METHODS: The recombinant adenoviruses pAdEasy- GFP-ASmdr1 product was produced by the adenoviral vector AdEasy system, which can express antisense RNA against the mdr1 gene. Following that, the recombinant adenovirus was transfected into the P-glycoprotein- producing multidrug resistance cell line, SMMC7721/ADM human HCC cells resistant to adriamycin (ADM) and daunorubicin (DNR). In order to investigate the reversal of multidrug resistance phenotype, we measured the expression of mdr1 mRNA by RT-PCR and the production of P-glycoprotein by flow cytometry. The sensitivities for ADM and DNR SMMC7721/ADM cells were examined by [3-(4, 5-dimethylthi-azol-2-yl)-2,5 diphenyl-terazolium bromide] (MTT) analysis. RESULTS: The low-level expression of mdr1 mRNA and P-glycoprotein production were observed in parental sensitive cells SMMC/7721 in addition to the overexpressionof mdr1 mRNA and P-glycoprotein in SMMC7721/ADM cells. The transfection of antisense-RNA into SMMC7721/ ADM cells resulted in decreases of mdr1 mRNA and P-glycoprotein, but increase of drug sensitivities. The sensitivities of transfected SMMC7721/ADM cells to ADM and DNR in IC50 reduced by 31.25% and 62.96% respectively. CONCLUSIONS: Mdr1 antisense RNA can increase the sensitivities of SMMC7721/ADM cells to anticancer drug by decreasing the expression of the mdr1 gene and inhibiting P-glycoprotein expression. This strategy may be applicable to cancer patients with P-glycoportein mediated multidrug resistance.