Multidrug resistance and stem cells in acute myeloid leukemia.
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ADP-ribosyl Cyclase 1↗
Biomedical subjects
Branimir I Sikic
Publications and source records attributed to Branimir I Sikic.
Regional activation of chromosomal arm 7q with and without gene amplification in taxane-selected human ovarian cancer cell lines.
Taxanes are important drugs in the treatment of ovarian and other cancers, but their efficacy is limited by intrinsic and acquired drug resistance. Expression of the multidrug transporter P-glycoprotein, encoded by the MDR1 (ABCB1) gene, is one of the causes of clinical drug resistance to taxanes. To study the mechanisms of MDR1 activation related to taxanes, we established 11 multidrug-resistant variants from six ovarian cancer cell lines by continuous exposure to either paclitaxel or docetaxel. We profiled gene expression and gene copy number alterations in these cell lines using cDNA microarrays and identified a cluster of genes coactivated with MDR1 in 7q21.11-13. Regional activation was evident in nine resistant variants displaying a coexpression pattern of up to 22 genes over an 8-Mb area, including SRI, MGC4175, CLDN12, CROT, and CDK6. In six of these variants, regional activation was driven by gene copy number alterations, with low-level gains or high-level amplifications spanning the involved region. However, three variants displayed regional increases in gene expression even without concomitant gene copy number changes. These results suggest that regional gene activation may be a fundamental mechanism for acquired drug resistance, with or without changes in gene dosage. In addition to numerical and structural chromosomal changes driven by genome instability in cancer cells, other mechanisms might be involved in MDR1 regional activation, such as chromatin remodeling and DNA or histone modifications of the 7q21 region.
Cell Line, Tumor↗
Phase I study of gefitinib, oxaliplatin, 5-fluorouracil, and leucovorin (IFOX) in patients with advanced solid malignancies.
PURPOSE: Aphase 1 study of gefitinib in combination with oxaliplatin, 5-fluorouracil and leucovorin (IFOX)was conducted to evaluate the safety and feasibility of this regimen. PATIENTS AND METHODS: Patients with advanced solid malignancies were treated with escalating doses of gefitinib (250 mg or 500 mg once daily) in combination with FOLFOX (oxaliplatin, 5-fluorouracil, and leucovorin). The initial dose of oxaliplatin was 70 mg/m2 with sequential dose escalation to 85 mg/m2. RESULTS: Sixteen patients received a total of 138 14-day courses of daily gefitinib in combination with FOLFOX. Escalation of gefitinib from 250 mg/d to 500 mg/d with FOLFOX was well-tolerated. In addition, no severe toxicities precluded subsequent dose escalation of oxaliplatin from 70 mg/m2 to 85 mg/m2 at which no dose-limiting toxicity was seen. No further dose escalation was performed as this represented the oxaliplatin dose administered in the standard FOLFOX-4 regimen. The most predominant toxicity was diarrhea, which was well controlled with oral antidiarrheal agents. Four partial remissions occurred in patients with metastatic colorectal cancer. CONCLUSIONS: Gefitinib as a 500 mg daily continuous dose was well tolerated in combination with full doses of FOLFOX-4.
Adult↗
A pilot phase II trial of valspodar modulation of multidrug resistance to paclitaxel in the treatment of metastatic carcinoma of the breast (E1195): a trial of the Eastern Cooperative Oncology Group.
BACKGROUND: To assess the activity and toxicity of valspodar (PSC-833) in combination with paclitaxel in women with anthracycline refractory, metastatic breast cancer. PATIENTS AND METHODS: Limited, multi-institutional, Phase II trial of valspodar at 5 mg/kg/dose orally every 6 hours for 12 doses in combination with paclitaxel 70 mg/m2 administered intravenously as a 3-hour infusion beginning 4 hours after the fifth dose of valspodar, every 3 weeks. Eligible patients had bi-dimensionally measurable metastatic carcinoma of the breast, prior anthracycline therapy or a medical contraindication to anthracycline therapy, no more than one prior chemotherapy for recurrent or metastatic breast cancer, and adequate organ function. Treatment was continued until disease progression or unacceptable toxicity. RESULTS: Thirty-four patients are evaluable for response and 37 for toxicity. Two (6 percent) patients achieved a complete response and 5 (15 percent) a partial response for an objective response rate of 21 percent (95 percent confidence interval of 9 to 38 percent). Median duration of response was 9.7 months (95 percent confidence interval 8.0-17.2 months), median time to progression was 3.3 months (95 percent confidence interval 2.0-4.2 months), and median survival was 12 months (95 percent confidence interval 8.1-17.3 months). The toxicity experienced was acceptable. CONCLUSIONS: Combination valspodar plus paclitaxel is an active regimen and has acceptable toxicity. The combination is not clearly more active than single agent paclitaxel.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Tumor necrosis factor-alpha-induced protein 3 as a putative regulator of nuclear factor-kappaB-mediated resistance to O6-alkylating agents in human glioblastomas.
PURPOSE: Pre-existing and acquired drug resistance are major obstacles to the successful treatment of glioblastomas. METHODS: We used an integrated resistance model and genomics tools to globally explore molecular factors and cellular pathways mediating resistance to O6-alkylating agents in glioblastoma cells. RESULTS: We identified a transcriptomic signature that predicts a common in vitro and in vivo resistance phenotype to these agents, a proportion of which is imprinted recurrently by gene dosage changes in the resistant glioblastoma genome. This signature was highly enriched for genes with functions in cell death, compromise, and survival. Modularity was a predominant organizational principle of the signature, with functions being carried out by groups of interacting molecules in overlapping networks. A highly significant network was built around nuclear factor-kappaB (NF-kappaB), which included the persistent alterations of various NF-kappaB pathway elements. Tumor necrosis factor-alpha-induced protein 3 (TNFAIP3) was identified as a new regulatory component of a putative cytoplasmic signaling cascade that mediates NF-kappaB activation in response to DNA damage caused by O6-alkylating agents. Expression of the corresponding zinc finger protein A20 closely mirrored the expression of the TNFAIP3 transcript, and was inversely related to NF-kappaB activation status in the resistant cells. A prediction model based on the resistance signature enabled the subclassification of an independent, validation cohort of 31 glioblastomas into two outcome groups (P = .037) and revealed TNFAIP3 as part of an optimized four-gene predictor associated significantly with patient survival (P = .022). CONCLUSION: Our results offer strong evidence for TNFAIP3 as a key regulator of the cytoplasmic signaling to activate NF-kappaB en route to O6-alkylating agent resistance in glioblastoma cells. This pathway may be an attractive target for therapeutic modulation of glioblastomas.
Antineoplastic Agents, Alkylating↗
Gene expression profiling differentiates germ cell tumors from other cancers and defines subtype-specific signatures.
Germ cell tumors (GCTs) of the testis are the predominant cancer among young men. We analyzed gene expression profiles of 50 GCTs of various subtypes, and we compared them with 443 other common malignant tumors of epithelial, mesenchymal, and lymphoid origins. Significant differences in gene expression were found among major histological subtypes of GCTs, and between them and other malignancies. We identified 511 genes, belonging to several critical functional groups such as cell cycle progression, cell proliferation, and apoptosis, to be significantly differentially expressed in GCTs compared with other tumor types. Sixty-five genes were sufficient for the construction of a GCT class predictor of high predictive accuracy (100% training set, 96% test set), which might be useful in the diagnosis of tumors of unknown primary origin. Previously described diagnostic and prognostic markers were found to be expressed by the appropriate GCT subtype (AFP, POU5F1, POV1, CCND2, and KIT). Several additional differentially expressed genes were identified in teratomas (EGR1 and MMP7), yolk sac tumors (PTPN13 and FN1), and seminomas (NR6A1, DPPA4, and IRX1). Dynamic computation of interaction networks and mapping to existing pathways knowledge databases revealed a potential role of EGR1 in p21-induced cell cycle arrest and intrinsic chemotherapy resistance of mature teratomas.
Chromosomes, Human↗
Genetic and epigenetic modeling of the origins of multidrug-resistant cells in a human sarcoma cell line.
The origin of drug-resistant cells in human cancers has been a fundamental problem of cancer pharmacology. Two major contrasting hypotheses (genetics versus epigenetics) have been proposed to elucidate the mechanisms of acquired drug resistance. In this study, we answer these fundamental questions through investigation of the genetic and epigenetic pathways that control the origin of ABCB1 (MDR1) gene activation with acquired multidrug resistance in drug-sensitive human sarcoma (MES-SA cells). The genetic and epigenetic bases of this selected activation involve the initiation of transcription at a site 112 kb upstream of the ABCB1 proximal promoter (P1) in the drug-resistant cells. This activation was associated with a chromatin-remodeling process characterized by an increase in acetylated histone H3 within a 968-bp region 5' of the ABCB1 upstream promoter. These alterations provide both genetic and epigenetic susceptibility for ABCB1 expression in drug-resistant cells. Complete activation of the ABCB1 gene through the coding region was proposed by interactions of selected trans-alterations or epigenetic changes on the ABCB1 proximal promoter, which occurred during initial drug exposure. Thus, our data provide evidence for a major genomic alteration that changes the chromatin structure of the ABCB1 upstream promoter via acetylation of histone H3 initiating ABCB1 activation, further elucidating the genetic and epigenetic bases that determine chemotherapeutic response in drug-resistant derivatives of MES-SA cells.
Acetylation↗
Functional network analysis reveals extended gliomagenesis pathway maps and three novel MYC-interacting genes in human gliomas.
Gene expression profiling has proven useful in subclassification and outcome prognostication for human glial brain tumors. The analysis of biological significance of the hundreds or thousands of alterations in gene expression found in genomic profiling remains a major challenge. Moreover, it is increasingly evident that genes do not act as individual units but collaborate in overlapping networks, the deregulation of which is a hallmark of cancer. Thus, we have here applied refined network knowledge to the analysis of key functions and pathways associated with gliomagenesis in a set of 50 human gliomas of various histogenesis, using cDNA microarrays, inferential and descriptive statistics, and dynamic mapping of gene expression data into a functional annotation database. Highest-significance networks were assembled around the myc oncogene in gliomagenesis and around the integrin signaling pathway in the glioblastoma subtype, which is paradigmatic for its strong migratory and invasive behavior. Three novel MYC-interacting genes (UBE2C, EMP1, and FBXW7) with cancer-related functions were identified as network constituents differentially expressed in gliomas, as was CD151 as a new component of a network that mediates glioblastoma cell invasion. Complementary, unsupervised relevance network analysis showed a conserved self-organization of modules of interconnected genes with functions in cell cycle regulation in human gliomas. This approach has extended existing knowledge about the organizational pattern of gene expression in human gliomas and identified potential novel targets for future therapeutic development.
Adult↗
Phase II study of gefitinib, fluorouracil, leucovorin, and oxaliplatin therapy in previously treated patients with metastatic colorectal cancer.
PURPOSE: To investigate the gefitinib, fluorouracil (FU), leucovorin, and oxaliplatin regimen (IFOX) in previously treated patients with metastatic colorectal cancer. PATIENTS AND METHODS: Eligible patients had stage IV colorectal adenocarcinoma and had demonstrated progression or intolerance to a prior chemotherapy regimen not including oxaliplatin. Each cycle consisted of 14 days. Cycle 1 consisted of oxaliplatin 85 mg/m2 intravenously (IV) during 2 hours on day 1, hours 0 to 2; leucovorin 200 mg/m2 IV on days 1 and 2, hours 0 to 2; FU 400 mg/m2 IV push on days 1 and 2; and FU 600 mg/m2 IV on days 1 and 2, hours 2 to 24 (FOLFOX-4). All subsequent cycles consisted of FOLFOX-4 with gefitinib at 500 mg/d administered orally throughout the 14-day cycle. RESULTS: Twenty-seven patients were enrolled onto the study. The median number of prior chemotherapy regimens was two, and 74% of all patients received prior irinotecan. Nine of the 27 patients (33%) and six of the 20 patients (30%) who had prior FU and irinotecan had a partial response by Response Evaluation Criteria in Solid Tumors Group criteria. Median overall survival was 12.0 months. Median event-free survival was 5.4 months. Grade 3 to 4 toxicities included neutropenia (48%), diarrhea (48%), nausea (22%), and vomiting (15%). CONCLUSION: IFOX is an active regimen in patients with previously treated metastatic colorectal adenocarcinoma, demonstrating higher response rates than those reported with FOLFOX-4 alone in a similar patient population.
Adenocarcinoma↗
High-resolution genome-wide mapping of genetic alterations in human glial brain tumors.
High-resolution genome-wide mapping of exact boundaries of chromosomal alterations should facilitate the localization and identification of genes involved in gliomagenesis and may characterize genetic subgroups of glial brain tumors. We have done such mapping using cDNA microarray-based comparative genomic hybridization technology to profile copy number alterations across 42,000 mapped human cDNA clones, in a series of 54 gliomas of varying histogenesis and tumor grade. This gene-by-gene approach permitted the precise sizing of critical amplicons and deletions and the detection of multiple new genetic aberrations. It has also revealed recurrent patterns of occurrence of distinct chromosomal aberrations as well as their interrelationships and showed that gliomas can be clustered into distinct genetic subgroups. A subset of detected alterations was shown predominantly associated with either astrocytic or oligodendrocytic tumor phenotype. Finally, five novel minimally deleted regions were identified in a subset of tumors, containing putative candidate tumor suppressor genes (TOPORS, FANCG, RAD51, TP53BP1, and BIK) that could have a role in gliomagenesis.
Brain Neoplasms↗
A phase I trial of aprinocarsen (ISIS 3521/LY900003), an antisense inhibitor of protein kinase C-alpha administered as a 24-hour weekly infusion schedule in patients with advanced cancer.
PURPOSE: A phase I study was performed to determine the maximum tolerated dose (MTD), safety profile and pharmacology of aprinocarsen (ISIS 3521), an antisense oligonucleotide to protein kinase C-alpha, in patients with refractory solid tumors. EXPERIMENTAL DESIGN: Fourteen patients were treated in sequential cohorts of aprinocarsen by 24-hour continuous infusion (CIV), weekly, at doses of 6, 12, 18 and 24 mg/kg. RESULTS: One grade 4 toxicity was observed, transient grade 4 neutropenia at 18 mg/kg. Grade 3 toxicities included neutropenia at 12 mg/kg, fever and hemorrhage at 18 mg/kg, and neutropenia, nausea, and chills at 24 mg/kg. Grade 2 toxicities included thrombocytopenia myalgias, chills, headache, fatigue, fever and nausea/vomiting. Mean prothrombin times and activated partial thromboplastin times (aPTT) increased by 10% and 29% from baseline (p = 0.006 and 0.005). Mean complement split products (Bb and C3a) increased 1.6-fold and 3.6-fold (from p = 0.014 and 0.004, respectively). These changes correlated with dose and were transient with recovery to baseline by day 7. Steady state plasma concentrations (Css) of aprinocarsen were achieved within four hours. Css better described changes in aPTT than dose. Clinical evidence of complement activation was not observed. CONCLUSIONS: In contrast to 21-day protracted infusion schedules, delivery of aprinocarsen over a 24-hour infusion schedule showed concentration-dependent effects on coagulation and complement, which are consistent with nonclinical toxicology studies performed in the phosphorothioate DNA antisense drug class. These coagulation and complement changes resulted in a maximum tolerated dose 24 mg/kg.
Adult↗
Amplification of whole tumor genomes and gene-by-gene mapping of genomic aberrations from limited sources of fresh-frozen and paraffin-embedded DNA.
Sufficient quantity of genomic DNA can be a bottleneck in genome-wide analysis of clinical tissue samples. DNA polymerase Phi29 can be used for the random-primed amplification of whole genomes, although the amplification may introduce bias in gene dosage. We have performed a detailed investigation of this technique in archival fresh-frozen and formalin-fixed/paraffin-embedded tumor DNA by using cDNA microarray-based comparative genomic hybridization. Phi29 amplified DNA from matched pairs of fresh-frozen and formalin-fixed/paraffin-embedded tumor samples with similar efficiency. The distortion in gene dosage representation in the amplified DNA was nonrandom and reproducibly involved distinct genomic loci. Regional amplification efficiency was significantly linked to regional GC content of the template genome. The biased gene representation in amplified tumor DNA could be effectively normalized by using amplified reference DNA. Our data suggest that genome-wide gene dosage alterations in clinical tumor samples can be reliably assessed from a few hundred tumor cells. Therefore, this amplification method should lend itself to high-throughput genetic analyses of limited sources of tumor, such as fine-needle biopsies, laser-microdissected tissue, and small paraffin-embedded specimens.
Chromosome Aberrations↗
Activity of novel cytotoxic agents in lung cancer: epothilones and topoisomerase I inhibitors.
The treatment of lung cancer--small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC)--is a significant challenge in oncology. The best reported median survival remains near 1 year in advanced NSCLC despite several decades of steady improvement and extensive research with traditional chemotherapy drugs and novel compounds targeted to different aspects of tumor cell growth and function (such as the epidermal growth factor receptor). Extensive-stage SCLC survival is only slightly better. Novel "targeted" therapeutic agents hold promise, but cytotoxic therapy remains the backbone of treatment. Many new cytotoxic agents are currently in development. In this review, we will focus on 2 classes of cytotoxins: epothilones and topoisomerase I inhibitors. Epothilones are microtubule stabilizers with a mechanism of action similar to that of the taxanes, with preclinical activity superior to that of the taxanes. Phase I trials have been completed for patupilone and ixabepilone, and there are encouraging phase II data with ixabepilone in NSCLC. A phase II trial of patupilone is ongoing. The camptothecins, which are topoisomerase I inhibitors, have a long history in the treatment of lung cancer, but the currently available drugs, topotecan and irinotecan, have limitations. Gimatecan and other novel camptothecins have superior preclinical activity and promising phase I/II data in NSCLC and SCLC.
Antineoplastic Agents↗
A method for detecting and correcting feature misidentification on expression microarrays.
BACKGROUND: Much of the microarray data published at Stanford is based on mouse and human arrays produced under controlled and monitored conditions at the Brown and Botstein laboratories and at the Stanford Functional Genomics Facility (SFGF). Nevertheless, as large datasets based on the Stanford Human array began to accumulate, a small but significant number of discrepancies were detected that required a serious attempt to track down the original source of error. Due to a controlled process environment, sufficient data was available to accurately track the entire process leading to up to the final expression data. In this paper, we describe our statistical methods to detect the inconsistencies in microarray data that arise from process errors, and discuss our technique to locate and fix these errors. RESULTS: To date, the Brown and Botstein laboratories and the Stanford Functional Genomics Facility have together produced 40,000 large-scale (10-50,000 feature) cDNA microarrays. By applying the heuristic described here, we have been able to check most of these arrays for misidentified features, and have been able to confidently apply fixes to the data where needed. Out of the 265 million features checked in our database, problems were detected and corrected on 1.3 million of them. CONCLUSION: Process errors in any genome scale high throughput production regime can lead to subsequent errors in data analysis. We show the value of tracking multi-step high throughput operations by using this knowledge to detect and correct misidentified data on gene expression microarrays.
Animals↗
Gene expression profiles at diagnosis in de novo childhood AML patients identify FLT3 mutations with good clinical outcomes.
Fms-like tyrosine kinase 3 (FLT3) mutations are associated with unfavorable outcomes in children with acute myeloid leukemia (AML). We used DNA microarrays to identify gene expression profiles related to FLT3 status and outcome in childhood AML. Among 81 diagnostic specimens, 36 had FLT3 mutations (FLT3-MUs), 24 with internal tandem duplications (ITDs) and 12 with activating loop mutations (ALMs). In addition, 8 of 19 specimens from patients with relapses had FLT3-MUs. Predictive analysis of microarrays (PAM) identified genes that differentiated FLT3-ITD from FLT3-ALM and FLT3 wild-type (FLT3-WT) cases. Among the 42 specimens with FLT3-MUs, PAM identified 128 genes that correlated with clinical outcome. Event-free survival (EFS) in FLT3-MU patients with a favorable signature was 45% versus 5% for those with an unfavorable signature (P = .018). Among FLT3-MU specimens, high expression of the RUNX3 gene and low expression of the ATRX gene were associated with inferior outcome. The ratio of RUNX3 to ATRX expression was used to classify FLT3-MU cases into 3 EFS groups: 70%, 37%, and 0% for low, intermediate, and high ratios, respectively (P < .0001). Thus, gene expression profiling identified AML patients with divergent prognoses within the FLT3-MU group, and the RUNX3 to ATRX expression ratio should be a useful prognostic indicator in these patients.
Acute Disease↗
Mitoxantrone, etoposide, and cytarabine with or without valspodar in patients with relapsed or refractory acute myeloid leukemia and high-risk myelodysplastic syndrome: a phase III trial (E2995).
PURPOSE: To determine whether adding the multidrug resistance gene-1 (MDR-1) modulator valspodar (PSC 833; Novartis Pharmaceuticals, Hanover, NJ) to chemotherapy provided clinical benefit to patients with poor-risk acute myeloid leukemia (AML) and high-risk myelodysplastic syndrome (MDS). PATIENTS AND METHODS: A phase III randomized study was performed using valspodar plus mitoxantrone, etoposide, and cytarabine (PSC-MEC; n=66) versus MEC (n=63) to treat patients with relapsed or refractory AML and high-risk MDS. RESULTS: For the PSC-MEC versus MEC arms, complete response (CR) was achieved in 17% versus 25% of patients, respectively (P=not significant). For patients who had not received prior intensive chemotherapy (ie, with secondary AML or high-risk MDS), the CR rate was increased--35% versus 15% for the remaining patients (P=.018); CR rates did not differ between treatment arms. The median disease-free survival in those achieving CR was similar in the two arms (10 versus 9.3 months) as was the patients' overall survival (4.6 versus 5.4 months). The CR rates in MDR+ (69% of patients) versus MDR- patients were similar for those receiving either chemotherapy regimen (16% versus 24%). The CR rate for unfavorable cytogenetic patients (45% of patients) was 13% compared to the remainder, 28% (P=.09). Population pharmacokinetic analysis demonstrated that the clearances of mitoxantrone and etoposide were decreased by 59% and 50%, respectively, supporting the empiric dose reductions in the PSC-MEC arm designed in anticipation of drug interactions between valspodar and the chemotherapeutic agents. CONCLUSION: CR rates and overall survival were not improved by using PSC-MEC compared to MEC chemotherapy alone in patients with poor-risk AML or high-risk MDS.
Adolescent↗
A Phase II trial of aprinocarsen, an antisense oligonucleotide inhibitor of protein kinase C alpha, administered as a 21-day infusion to patients with advanced ovarian carcinoma.
BACKGROUND: It has been postulated that protein kinase C alpha (PKC-alpha) plays a pivotal role in signal transduction in tumor cancer cells. Aprinocarsen, a 20-base antisense oligonucleotide, has shown ability to inhibit PKC-alpha protein expression and inhibit tumor growth in human xenograft models. In a previous Phase I trial, the authors demonstrated the safety and some evidence of activity in ovarian carcinoma of aprinocarsen administered as a 21-day, continuous, intravenous infusion. METHODS: In this Phase II trial, 36 patients with advanced ovarian carcinoma were treated with aprinocarsen at a dose of 2 mg/kg per day delivered as a 21-day, continuous, intravenous infusion. The primary objective was to determine the antitumor response, and the secondary objectives were to evaluate toxicity and to evaluate effects on quality of life (QOL). RESULTS: Between September 1997 and December 1999, 36 patients (median age, 58 years) were enrolled in this trial. Patients were stratified into 2 groups: a platinum-sensitive group (n = 12 patients) and a platinum-resistant group (n = 24 patients). All 36 patients were evaluable for toxicity, and 27 patients were fully assessable for antitumor response after 2 cycles of therapy. All patients had received prior treatments. No objective responses were noted in the platinum-sensitive group. In the platinum-resistant group, 1 patient had some evidence of antitumor activity indicated by a decrease in serum CA 125 and stable disease on imaging studies for 8 months. No changes were noted in overall patient ratings for any of the five QOL domains. CONCLUSIONS: When it was administered as a single agent, aprinocarsen did not have significant clinical activity in patients with advanced ovarian carcinoma. Further study may be warranted in combination with platinum-based regimens.
Aged↗
Genomics-based hypothesis generation: a novel approach to unravelling drug resistance in brain tumours?
No currently available chemotherapy seems likely to substantially improve outcome in most patients with brain tumours. Several resistance-associated cellular factors, which were discovered in other cancer models, have also been identified in brain tumours. Although these mechanisms play some part in resistance in brain tumours, they are not sufficient to explain the poor clinical response to chemotherapy. There could be other brain-tumour-specific genetic profiles that are associated with tumour sensitivity to chemotherapy. There is increasing awareness that drug resistance in brain tumours is not a result of changes in single molecular pathways but is likely to involve a complex network of regulatory dynamics. Further insights into chemoresistance in brain tumours could come with comprehensive characterisation of their gene expression, as well as the genetic changes occurring in response to chemotherapy. Recent progress in high-throughput bioanalytical methods for genome-wide studies has made possible a novel research model of initial hypothesis generation followed by functional testing of the generated hypothesis.
Brain Neoplasms↗