Drug Chemosensitivity Research Articles

Demethylating agent 5-aza-2-deoxycytidine enhances susceptibility of breast cancer cells to anticancer agents

DNA methylation plays an important role in regulation of gene expression and is increasingly being recognized as a determinant of chemosensitivity of human cancers. With the aim of improving the chemotherapeutic efficacy of breast carcinoma, the effect of DNA methyltransferase inhibitor, 5-Aza-2'-deoxycytidine (5-aza-CdR), on the chemosensitivity of anticancer drugs was investigated. The cytotoxicity of paclitaxel (PTX), adriamycin (ADR), and 5-fluorouracil (5-FU) was analyzed against human breast cancer cell lines, MDA MB 231 and MCF 7 cell lines using the MTT assay, and the synergy of 5-aza-CdR and these agents was determined by Drewinko's fraction method. The effects of each single agent or the combined treatment on cell cycle arrest were analyzed by flow cytometric analysis. We also investigated the effect of each single agent or the combined treatment of anticancer drugs with 5-aza-CdR on the methylation status of the selected genes by methylation specific PCR. In MDA MB 231 cells, a synergistic antiproliferative effect was observed with a combination of 10 microM 5-aza-CdR and these three anticancer drugs, while in MCF 7 cells, a semiadditive effect was observed. Treatment with 5-aza-CdR and anticancer drug resulted in partial demethylation of a panel of genes including RARbeta2, Slit2, GSTP1, and MGMT. Based on these findings, we propose that 5-aza-CdR enhances the chemosensitivity of anticancer drugs in breast cancer cells and may be a promising approach for increasing the chemotherapeutic potential of these anticancer agents for more effective management of breast carcinomas.

Abstract B24: Establishment of human primary non-small cell lung cancer xenograft models to test anticancer drugs

Abstract Background: Human xenograft tumor models established by transplantation of human tumor cell lines into immunodifficient mice have been routinely used for preclinical test of anticancer agents. But such tumor models have a relatively low transplantability and limited correlation with clinical findings. Recently, we have developed human non-small lung cancer (NSCLC) xenograft models by transplanting human fresh lung cancer tissues into nude mice, which have been employed for test of clinically used chemotherapeutical drugs and are under way for new drug chemosensitivity in vivo screening. Methods: The fresh lung cancer samples were collected from local hospitals. The tumor fragments of 1–2 mm3 were subcutaneously implanted in the flanks of the Balb/c nude mice by trocar needle. Sixteen tumor fragments were grafted into four mice from one patient tumor tissue (passage 1). In the first passage, tumors derived from male patients were implanted into male mice, and tumors from women were inoculated into female mice. All therapeutic efficacy experiments used female mice. The drugs tested were clinically used drugs for NSCLC including cisplatin (4 mg/kg, q3d x 4), paclitaxel (15 mg/kg, q3d x 4), vinorelbine (2.5 mg/kg, q4d x 4), gemcitabine (120 mg/kg, q4d x 4), and the epidermal growth factor receptor (EGFR) inhibitor erlotinib (50 mg/kg/daily x 14, po). Results: A total of 42 NSCLC samples were implanted, and 13 tumor models were established (tumor taking rate 31%) for the first passage. The tumor taking rates were higher in the second and third passages (80–100%). Cisplatin, paclitaxel, vinorelbine, and gemcitatbine produced tumor growth inhibition rates of 48–55% regardless of the EGFR mutation status. While erlotinib demonstrated a significant antitumor activity only in the tumors bearing EGFR, which were consistent with their clinical findings. The tumor xenografts' architecture, the cell and histopathological morphology from the three generations mirrored the original patient cancers. Conclusions: These results suggest that human primary tumor xenograft models provide a unique renewable source of tumor material for test of novel anticancer agents. They may predict more relevant clinical response rates and higher correlation with clinical findings than use of xenograft models established from in vitro long-term cultured cancer cell lines, especially for test of target-oriented therapeutics in new drugs development programs. Citation Information: Clin Cancer Res 2010;16(7 Suppl):B24

The p53 Family Protein p73 Provides New Insights into Cancer Chemosensitivity and Targeting

The p53 tumor suppressor is part of a small family of related proteins that includes two other members, p73 and p63. Interest in the p53 family members, their functions and their complex interactions and regulation, has steadily grown over recent years and does not show signs of waning. p73 is a major determinant of chemosensitivity in humans, and mutant p53 proteins carrying specific polymorphisms can induce drug resistance by inhibiting TAp73. Cooperation between TA (transactivating, proapoptotic, antiproliferative) and Delta N (truncated, antiapoptotic, pro-proliferative) p73 isoforms and among the three family members guarantees equilibrium between proliferation, differentiation, and cell death, thus creating a harmony that is lost in several human cancers. In this article, we review our current knowledge of the role of p73 in cancer chemosensitivity and the real prospect of therapy targeting this molecule. We also draw attention to the crucial role of specific phosphorylation and acetylation events for p73-induced apoptosis and drug chemosensitivity.

Impedance studies of bio-behavior and chemosensitivity of cancer cells by micro-electrode arrays

Impedimetric analysis on adherently growing cells by micro-electrodes provides information related to cell number, cell adhesion and cellular morphology. In this study, cell-based biosensor with micro-electrode arrays (MEAs) was used to monitor the culture behavior of mammalian cancer cells and evaluate the chemosensitivity of anti-cancer drugs using electrochemical impedance spectroscopy. The platinum electrode arrays were fabricated by semiconductor technology to a 10 × 10 pattern, with diameter of 80 μm of each electrode. The human oesophageal cancer cell lines (KYSE 30) were cultured on the surface of the electrodes with the pre-coated fibronectin, the connecting protein for tumor cells metastasis and adhesion in extracellular matrix. Morphology changes during cells adhesion, spreading, and proliferation can be detected by impedimetric analysis in a real time and non-invasive way. Cisplatin was added to cells for potential drug screening applications. The experimental results show that this well-known anti-cancer drug has characteristic chemosensitivity effects on KYSE 30 cells which can be detected by MEA. Thus, this cell-based chip provides a useful analytical method for cancer research.

Laser microdissection and primary cell cultures improve pharmacogenetic analysis in pancreatic adenocarcinoma

A key focus of research on pancreatic ductal adenocarcinoma (PDAC) is identifying new techniques to tailor gemcitabine and 5-fluorouracil treatments. Availability of tumor tissue is critical for the accurate assessment of gene expression, and laser microdissection (LMD) and primary cell cultures may be useful tools to separate tumor cells from the stromal reaction. The aim of this study was (1) to address the genetic profile relevant to drug activity and (2) to evaluate differences between microdissected and non-microdissected tumors, normal tissues, and primary cell cultures. Quantitative PCR of seven key genes was performed on mRNA from 113 microdissected and 28 non-microdissected tumors, a pool of normal tissues and four established primary cell lines. Protein expression was evaluated by western blot and immunocytochemistry and cytotoxicity by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. LMD allowed the analysis of 110 samples and revealed significant differences in mRNA levels between microdissected tumors and normal tissues, as well as between non-microdissected and microdissected tumors from the same patients. In contrast, primary cell lines showed similar expression profiles with respect to their respective microdissected tumors. In particular, expression levels of human equilibrative nucleoside transporter-1 and thymydilate synthase were significantly related to gemcitabine and 5-fluorouracil cytotoxicity. We conclude that LMD is a reliable technique for mRNA extraction, and allows detection of significant differences in the expression of specific target genes when compared to non-microdissected specimens and normal tissues. Moreover, expression levels in microdissected tumors are similar to those observed in primary tumor cell cultures, both at mRNA and protein level, and are related to drug chemosensitivity. The use of these ex vivo techniques for molecular analysis of tumors therefore appears to be of some value in implementing the clinical management of PDAC.

Response projected clustering for direct association with physiological and clinical response data

BackgroundMicroarray gene expression data are often analyzed together with corresponding physiological response and clinical metadata of biological subjects, e.g. patients' residual tumor sizes after chemotherapy or glucose levels at various stages of diabetic patients. Current clustering analysis cannot directly incorporate such quantitative metadata into the clustering heatmap of gene expression. It will be quite useful if these clinical response data can be effectively summarized in the high-dimensional clustering display so that important groups of genes can be intuitively discovered with different degrees of relevance to target disease phenotypes.ResultsWe introduced a novel clustering analysis approach, response projected clustering (RPC), which uses a high-dimensional geometrical projection of response data to the gene expression space. The projected response vector, which becomes the origin in the projected space, is then clustered together with the projected gene vectors based on their different degrees of association with the response vector. A bootstrap-counting based RPC analysis is also performed to evaluate statistical tightness of identified gene clusters. Our RPC analysis was applied to the in vitro growth-inhibition and microarray profiling data on the NCI-60 cancer cell lines and the microarray gene expression study of macrophage differentiation in atherogenesis. These RPC applications enabled us to identify many known and novel gene factors and their potential pathway associations which are highly relevant to the drug's chemosensitivity activities and atherogenesis.ConclusionWe have shown that RPC can effectively discover gene networks with different degrees of association with clinical metadata. Performed on each gene's response projected vector based on its degree of association with the response data, RPC effectively summarizes individual genes' association with metadata as well as their own expression patterns. Thus, RPC greatly enhances the utility of clustering analysis on investigating high-dimensional microarray gene expression data with quantitative metadata.

Time and Dose Dependent Study of Doxorubicin Induced DU-145 Cytotoxicity

Doxorubicin is one of the most effective anti-tumour agent. To clarify whether a single dose produces its effects soon after dosing or only after hours or days and whether the effects are brief or prolonged, time-dose relationships were explored by calculating lethal time (LT(50)) values which is a statistical estimate of the time from dosage to death of 50% of the organisms/ or cells in a very large population subjected to a toxicant under specific conditions. This was achieved by the log-time log-dose curve which may be used to predict the proper doses to be used in long-term studies. Drug chemosensitivity using DU-145 cell lines have been investigated for this purpose. The results shows that the effects of doxorubicin started only after 24 hrs; however, resistance was developed, 40 hrs was the time required to kill 50% of cells , and post-incubation with fresh media (F.M.) exhibited more cell damages. It is concluded that doxorubicin is effective only after 24 hrs with resistance developed and post-incubation with F.M after treating cells with doxorubicin causes more damage than continuous incubation with the drug.

The feasibility of antitumor drugs chemosensitivity testing by flow cytometry

Objective To investigate the feasibility of chemosensitivity testing of antitumor drugs by flow cytometry in clinical applications so as to provide experimental and theoretical basis for the establishment of a novel antitumor drugs sensitivity testing and the screening of particular antitumor drugs.

Alterations of Cell Signaling Pathways in Pediatric B-ALL Patients.

The outcome for children with Acute Lymphoblastic Leukemia (ALL) has improved in the last few decades with current therapy resulting in an event free survival exceeding 75%. Despite of this, 25% of patients still relapse or resist to conventional therapies. Proteomics, in particular the Reverse Phase Protein Arrays (RPA), offers a new approach to study both the potential molecular mechanisms of drugs chemosensitivity versus resistance, and identify new drug targets in the patients that do not respond to therapy. RPA, which can quantitatively measure dozens to hundreds of phosphorylated kinase substrates from only a few thousand cells, can be used to profile the working state of cellular signaling pathways in a manner not possible with gene microarrays, since post-translational modifications cannot be accurately portrayed by global gene expression patterns alone. We employed RPA to study the phosphorylated cellular pathways in bone marrow aspirate samples collected prior to treatment. The phosphorylation status of 95 key signaling proteins, including pro-survival, pro-apoptotic and those involved in cell cycle control were analyzed from 120 pediatric B-ALL specimens collected at the Pediatric Oncohematology Laboratory (University of Padova) over the past 15 years. Molecular network analysis and phosphoprotein profiling were performed using commercially available software. Our results indicate that there may be a difference between the molecular networks of activated kinase substrates within leukemic patients depending on disease state, genotype, or response therapy. The discovery of the molecular mechanisms related to drug resistance could play an important role for individualizing therapy and may reveal new strategies to improve treatment outcome.

Flavonoid Dimers as Bivalent Modulators for P-Glycoprotein-Based Multidrug Resistance: Synthetic Apigenin Homodimers Linked with Defined-Length Poly(ethylene glycol) Spacers Increase Drug Retention and Enhance Chemosensitivity in Resistant Cancer Cells

Much effort has been spent on searching for better P-glycoprotein- (P-gp-) based multidrug resistance (MDR) modulators. Our approach was to target the binding sites of P-gp using dimers of dietary flavonoids. A series of apigenin-based flavonoid dimers, linked by poly(ethylene glycol) chains of various lengths, have been synthesized. These flavonoid dimers modulate drug chemosensitivity and retention in breast and leukemic MDR cells with the optimal number of ethylene glycol units equal to 2-4. Compound 9d bearing four ethylene glycol units increased drug accumulation in drug-resistant cells and enhanced cytotoxicity of paclitaxel, doxorubicin, daunomycin, vincristine, and vinblastine in drug-resistant breast cancer and leukemia cells in vitro, resulting in reduction of IC50 by 5-50 times. This compound also stimulated P-gp's ATPase activity by 3.3-fold. Its modulating activity was presumably by binding to the substrate binding sites of P-gp and disrupting drug efflux.

Potential Use of the Adenosine Triphosphate Cell Viability Assay in Endometrial Cancer

Adenosine triphosphate cell viability assay (ATP-CVA) was used previously to evaluate chemotherapy in uterine cancer cell lines. In this study, we have performed the ATP-CVA on endometrial cancer patients to study the feasibility of using ATP-CVA in endometrial cancer to determine the intrinsic chemosensitivity of the cytotoxic drugs. Thirty-three patients with endometrial adenocarcinoma who presented for a staging operation were recruited. Endometrial cancer samples were obtained at the time of operation. In vitro ATP-CVA and chemosensitivity testing was performed using cisplatin, carboplatin, paclitaxel, etoposide, doxorubicin, 4-epidoxorubicin, and topotecan. Thirty-two of the 33 endometrial cancer samples were evaluable for SF50 (survival fraction at 50% of the peak plasma concentration [PPC]) using ATP-CVA. The median SF50 of carboplatin (0.33) was significantly less than the median SF50 of cisplatin (0.71), topotecan (0.93), paclitaxel (0.68), doxorubicin (1.0), etoposide (0.70), or 4-epidoxorubicin (0.88) (Wilcoxon signed rank test, P <.001). This study showed the feasibility of using the ATP-CVA in endometrial cancer to determine the intrinsic chemosensitivity of cytotoxic drugs.

Histone deacetylase inhibitor, trichostatin A, increases the chemosensitivity of anticancer drugs in gastric cancer cell lines

Epigenetic alterations of the histone acetylation play an important role in the regulation of gene expression associated with cell cycles and apoptosis that may affect the chemosensitivity of gastric carcinomas. Recently, a histone deacetylase inhibitor, trichostatin A (TSA), was proven to be a chemo-sensitizer on human erythroleukemia cells. With the aim of improving the chemotherapeutic efficacy of gastric carcinoma, the effect of TSA on the chemosensitivity of several anticancer drugs in gastric carcinoma cells was investigated. Human gastric cancer cell lines, OCUM-8 and MKN-74, and 5 anticancer drugs, 5-fluorouracil (5-FU), paclitaxel (PTX), oxaliplatin (OXA), irinotecan (SN38) and gemcitabine (GEM) were used. In both gastric cancer cell lines, a synergistic anti-proliferative effect by the combination of TSA (30 ng/ml) with 5-FU, PTX or SN38 showed a synergistic anti-proliferative effect in OCUM-8 and MKN-74 cells. TSA increases the expression of p21, p53, DAPK-1 and the DAPK-2 gene in both OCUM-8 and MKN-74 cells. In conclusion, TSA is a promising chemotherapeutical agent in combination with anticancer drugs of 5-FU, PTX and SN38 in gastric cancer cell lines. The up-regulation of p53, p21, DAPK-1 and DAPK-2 might be associated with the synergistic effect of TSA.

The anti-hepatitis drug DDB chemosensitizes multidrug resistant cancer cells in vitro and in vivo by inhibiting P-gp and enhancing apoptosis

DDB (dimethyl-4,4'-dimethoxy-5,6,5'6'-dimethylene dioxybiphenyl-2,2'-dicarboxylate) is a synthetic hepatoprotectant which has been widely used to treat chronic viral hepatitis B patients in China for more than 20 years. In this study, we evaluated DDB as a multidrug resistance (MDR) chemosensitizing agent. A panel of sensitive and resistant cancer cell lines were treated with various concentration of DDB, and the effect on chemosensitivity and accumulation of anticancer drugs; promotion of apoptosis and P-glycoprotein (P-gp) expression were determined by MTT (Dimethyl thiazolyl-2,5-diphenyltetrazolium bromide) assay, fluorospectrometry and flow cytometry respectively. Drug resistance reversal activity of DDB was also examined in BALB/c nude mice bearing both acquired MDR human nasopharyngeal carcinoma KBv200 and parental KB xenografts. The effect of DDB on the pharmacokinetics of Dox and hematological toxicity induced by Dox was measured in ICR and C(57)/BL mice, respectively. DDB at nontoxic concentrations of 12.5, 25 and 50 microM partly reversed the resistance to vincristine, doxorubicin, paclitaxel in acquired MDR breast carcinoma MCF-7/Adr cells, KBv200 and intrinsic MDR human hepatocarcinoma Bel(7402) cells, whereas no chemosensitizing effect of DDB was observed in sensitive KB and MCF-7 cells. DDB increased the intracellular accumulation of doxorubicin and inhibited surface P-gp expression in MCF-7/Adr cells. Furthermore, it was found that DDB promoted doxorubicin-induced apoptosis of Bel(7402) cells through enhanced caspase-3 activation. Co-administration of DDB at 300 and 500 mg/kg orally to nude mice increased the antitumor activity of vincristine to KBv200 xenografts without a significant increase in toxicity. In contrast, Co-administration of DDB did not inhibit the growth of KB xenografts. DDB also markedly reduced the decrease of leukocytes in doxorubicin-treated C(57)/BL mice. Co-administration of DDB increased Dox concentration in ICR mice bearing S180 sarcoma, but no pharmacokinetical interaction with Dox was observed. These results indicate that DDB has MDR reversal activity by inhibiting P-gp and when used in combination with anti-cancer drugs, it could potentially be used as a clinical treatment for P-gp-mediated MDR cancers.

P-044 Alteration of drug chemosensitivity caused by p73 Gene inhuman lung adenocarcinoma cells A549

P-044 Alteration of drug chemosensitivity caused by p73 Gene inhuman lung adenocarcinoma cells A549

Cellular and Pharmacogenetics Foundation of Synergistic Interaction of Pemetrexed and Gemcitabine in Human Non–Small-Cell Lung Cancer Cells

Gemcitabine and pemetrexed are effective agents in the treatment of non-small-cell lung cancer (NSCLC), and the present study investigates cellular and genetic aspects of their interaction against A549, Calu-1, and Calu-6 cells. Cells were treated with pemetrexed and gemcitabine, and their interaction was assessed using the combination index. The role of drug metabolism in gemcitabine cytotoxicity was examined with inhibitors of deoxycytidine kinase (dCK), 5'-nucleotidase, and cytidine deaminase, whereas the role of pemetrexed targets, thymidylate synthase (TS), dihydrofolate reductase (DHFR), and glycinamide ribonucleotide formyltransferase (GARFT) in drug chemosensitivity was analyzed in cytotoxicity rescue studies. The effect of gemcitabine and pemetrexed on Akt phosphorylation was investigated with enzyme-linked immunosorbent assay, whereas quantitative polymerase chain reaction (PCR) was used to study target gene-expression profiles and its modulation by each drug. Synergistic cytotoxicity was demonstrated, and pemetrexed significantly decreased the amount of phosphorylated Akt, enhanced apoptosis, and increased the expression of dCK in A549 and Calu-6 cells, as well as the expression of the human nucleoside equilibrative transporter 1 (hENT1) in all cell lines. PCR demonstrated a correlation between dCK expression and gemcitabine sensitivity, whereas expression of TS, DHFR, and GARFT was predictive of pemetrexed chemosensitivity. These data demonstrated that 1) gemcitabine and pemetrexed synergistically interact against NSCLC cells through the suppression of Akt phosphorylation and induction of apoptosis; 2) the gene expression profile of critical genes may predict for drug chemosensitivity; and 3) pemetrexed enhances dCK and hENT1 expression, thus suggesting the role of gene-expression modulation for rational development of chemotherapy combinations.

Experimental study on the chemosensitivity of peripheral blood lymphocytes and tumor cells of lung cancer in vitro

To study chemosensitivity of anticancer drugs in the peripheral blood lymphocytes(PBL) of lung cancer patients and evaluate the correlation of chemosensitivity of tumor cells and peripheral blood lymphocytes in vitro. The sensitive rate of 15 kinds of anticancer drugs in the peripheral blood lymphocytes and the tumor cells of 74 cases of lung cancer in vitro were tested by the MTT method. There was no significant difference in the sensitivity of 12 anticancer drugs between PBL and tumor cells of patients with lung cancer (P > 0.05). The chemosensitive test of the peripheral blood lymphocytes is valuable for reference of selecting anti-cancer drugs in clinic for lung cancer.

Chemosensitivity Assessed by Collagen Gel Droplet Embedded Culture Drug Sensitivity Test, and MDR1, MRP1, and MRP2 mRNA Expression in Human Colorectal Adenocarcinomas

To evaluate chemosensitivity and its correlation with expression levels of the multidrug resistant transporter (MDR1) and the multidrug resistance-associated proteins 1 and 2 (MRP1, MRP2) mRNA in human colorectal adenocarcinomas. Colorectal adenocarcinomas were obtained as surgical samples from 25 patients. The chemosensitivity of 12 anticancer drugs was assessed by the collagen gel droplet embedded culture drug sensitivity test (CD-DST). The expression levels of MDR1, MRP1, and MRP2 mRNA in colorectal adenocarcinomas were also evaluated by real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). The chemosensitivity was successfully evaluated for 16 of 25 patients, and the anticancer drugs were effective against the samples showing a relatively high growth rate. Gemcitabine hydrochloride was found to be more promising than those often prescribed for the treatment of colorectal adenocarcinoma. There was no correlation of the mRNA expression levels of MDR1 and MRP1 with the chemosensitivity of any anticancer drugs tested, but mitomycin C was found to be more effective for the colorectal adenocarcinoma with relatively high expression of MRP2 mRNA.

Chemosensitivity assay in mice prostate tumor: Preliminary report of flow cytometry, DNA fragmentation, ion ratiometric methods of anti-neoplastic drug monitoring

Flow cytometry, DNA fragmentation, ion ratiomateric analysis and NMR peaks characterized drug chemosensitivity of antineoplastic drugs. Hypotheses were: 1. The chemosensitive effect of different cancer cell lines is characteristic; 2. DNA fragmentation, ion ratiometric analysis suggest apoptosis status of tumor cells.MethodsPC-3 cell lines were compared with DU-145, LNCaP cell lines in culture for the [Na]i and [Ca]i ion sensing dyes, cell death, NMR peaks and apoptosis staining for chemotherapeutic action of different drugs.ResultsDNA fragmentation, ratiometric ions and fluorescence endlabelling plots were characteristic for cell lines and drug response. 31P-23Na NMR spectra showed characteristic high phospho-choline and sodium peaks.ConclusionFlow cytometry, DNA fragmentation, ion ratiometric methods and NMR peaks indicated apoptosis and offered in vivo drug monitoring method.

Drug-sensitivity pattern analysis for study of functional relationship between gene products

We have developed a method that we call ‘drug-sensitivity pattern analysis’, or DSPA, for analysis of protein function. Cells are transfected with cDNA of the test molecule, followed by analysis of the sensitivity of the transfected cells to multiple growth-inhibitory drugs. If two cDNA products have similar functions, their transfected cells should show similar drug-sensitivity patterns. The cDNAs of some signaling molecules were transfected into NIH3T3 or Ha- ras-transformed NIH3T3 (ras-NIH) cells and stable transfectants, which expressed high amounts of the gene product, were isolated. Chemosensitivity of the transfected clone was compared with the parental cells by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide method using more than 40 drugs. The chemosensitivity changes caused by the transfected gene were calculated and expressed numerically as ‘drug chemosensitivity index’ (DCI). When the DCI values were analyzed by regression analysis, a significant positive relationship between IκBα superrepressor and dominant-negative IKKβ and an inverse relationship between p53 and Mdm2 were consistent with previous reports. Thus, the DSPA method is useful for identifying functional similarities between gene products.

Appraisal of the MTT-based Assay as a Useful Tool for Predicting Drug Chemosensitivity in Leukemia

The MTT-based assay relies upon the cellular reduction of tetrazolium salts to their intensely colored formazans. The test is easy to perform in hematological malignancies and is adaptable for high throughput of samples, although there are some minor limitations in its application resulting from metabolic interference. This class of assays are highly accurate for predicting drug resistance, whereas their predictive value for drug sensitivity depends on the type of disease and drug or drug combination used. They have been found to predict clinical response to fludarabine FLD in B-CLL and were useful for predetermining clinical potential of a single drug or drug combination in AML patients. Extensive studies with ALL patients have supported their advantage for selecting effective drug treatment of the disease. To conclude, pretreatment chemosensitivity assays may help in the selection of chemotherapeutic drugs with the greatest likelihood for clinical effectiveness, and in the exclusion of uneffective therapy. This can lead to improved disease management, response, survival and use of financial resources.