Hypoxia-mimetic by CoCl2 increases SLC7A5 expression in breast cancer cells in vitro.

OBJECTIVE: Increased expression of the amino acid transporter solute Carrier Family 7 Member 5 (SLC7A5) has been observed in neoplastic cells during hypoxic conditions in vitro, indicating an adaptation for cell survival. To further explore this, we evaluated hypoxia-mimetic by CoCl2 as a model for hypoxia in breast cancer cell lines and the effect on SLC257A5 expression. Four different breast cancer cell lines (MCF7, T-47D, BT-474 and ZR-75-1) were exposed to 100 µM CoCl2 for 48 h. Subsequently, cell viability, gene- and protein expression analyses were performed. RESULTS: The gene expression of VEGF, a marker of hypoxia, was significantly elevated in all four cell lines compared to the control (p < 0.0001), indicating that CoCl2 exposure generates a hypoxic response. Moreover, CoCl2 exposure significantly upregulated SLC7A5 gene expression in T-47D (p < 0.001), BT-474 (p < 0.0001) and ZR-75-1 (p < 0.0001) cells, as compared to vehicle control. Immunofluorescence staining showed increased SLC7A5 protein expression in MCF7, T-47D and BT-474 cells compared to vehicle control. This report suggests that hypoxia-mimetic by CoCl2 can be used as a simple model for inducing hypoxia in breast cancer cell lines and in fact influence SLC7A5 gene and protein expression in vitro.

Improved plasmablast response after repeated pneumococcal revaccinations following primary immunization with 13-valent pneumococcal conjugate vaccine or 23-valent pneumococcal polysaccharide vaccine in patients with chronic lymphocytic leukemia.

BACKGROUND: Patients with chronic lymphocytic leukemia (CLL) show an immune dysfunction with increased risk of infections and poor response to vaccination. Streptococcus pneumoniae is a common cause of morbidity and mortality in CLL patients. In a previous randomized clinical trial, we found a superior immune response in CLL patients receiving conjugated pneumococcal vaccine compared to non-conjugated vaccine. The response to revaccination in CLL patients is scarcely studied. In this study, early humoral response to repeated revaccinations with pneumococcal vaccines was evaluated, by determination of B cell subsets and plasmablast dynamics in peripheral blood. METHOD: CLL patients (n = 14) and immunocompetent controls (n = 31) were revaccinated with a 13-valent pneumococcal conjugate vaccine (PCV13) after previous primary immunization (3-6 years ago) with PCV13 or a 23-valent pneumococcal polysaccharide vaccine (PPSV23). Eight weeks after the first revaccination, all CLL patients received a second revaccination with PCV13 or PPSV23. B cell subsets including plasmablasts were analyzed in peripheral blood by flow cytometry, before and after the first and the second revaccination. RESULTS: None of the CLL patients, but all controls, had detectable plasmablasts at baseline (p < 0.001). After the first revaccination with PCV13, the plasmablast proportions did not increase in CLL patients (p = 0.13), while increases were seen in controls (p < 0.001). However, after a second revaccination with PCV13 or PPSV23, plasmablasts increased compared to baseline also in CLL patients (p < 0.01). If no response was evident after first revaccination, only a second revaccination with PCV13 increased plasmablasts in contrast to PPSV23 revaccination. Patients with hypogammaglobulinemia and ongoing/previous CLL specific treatment responded poorly, also to a second revaccination. CONCLUSION: In CLL patients, pneumococcal revaccination induced minor early plasmablast response compared to controls, but the response improved using a strategy of repeated doses with of conjugated T cell dependent pneumococcal vaccine.

SLC7A5 is linked to increased expression of genes related to proliferation and hypoxia in estrogen­receptor­positive breast cancer.

The amino acid transporter named solute carrier family 7 member 5 (SLC7A5) is suggested to play a part in altered cell metabolism and proliferative signaling and has been reported to be overexpressed in various types of cancer, including breast cancer. Estrogen­receptor­positive (ER+) breast cancers constitute the most common type of breast malignancies and are often treated with anti­estrogenic therapies. In this group of patients, endocrine resistance is a challenging problem that could lead to recurrent disease. To overcome this, additional prognostic biomarkers are needed. The present study aimed therefore to determine whether SLC7A5 may be considered as a possible prognostic marker in ER+ breast cancer and to investigate its relation with certain cancer­related genes. We used a local breast cancer cohort (n=154) and immunohistochemistry to analyze the expression of SLC7A5 in association with clinicopathological characteristics and patient outcome. In addition, gene expression analysis was performed on 80 of these tumors. Furthermore, the METABRIC dataset was used for correlation analyses between expression of SLC7A5 and several genes related to breast cancer biology. The results demonstrated that overexpression of SLC7A5 was significantly associated with histopathological grade in patients with breast cancer, and that SLC7A5 mRNA expression was positively correlated with the expression of marker of proliferation Ki­67 and hypoxia inducible factor 1 subunit alpha. Overexpression of SLC7A5 may therefore play a role in the biology of endocrinologically­driven disease. However, when further assessing SLC7A5 using the METABRIC dataset, SLC7A5 mRNA expression level was more significantly increased in ER­ subgroups compared with ER+ disease. All breast cancer subtypes included, SLC7A5 mRNA expression was correlated with a higher number of cancer­related genes than in estrogen receptor positive tumors alone. The present study suggested that SLC7A5 expression may be of importance for breast cancer cell proliferation and survival. In order to further establish the biological and clinical role of SLC7A5 in breast cancer, further investigation using different breast cancer subgroups is required.

Evaluation of SPP1/osteopontin expression as predictor of recurrence in tamoxifen treated breast cancer.

Breast cancer patients treated with tamoxifen may experience recurrence due to endocrine resistance, which highlights the need for additional predictive and prognostic biomarkers. The glyco-phosphoprotein osteopontin (OPN), encoded by the SPP1 gene, has previously shown to be associated with poor prognosis in breast cancer. However, studies on the predictive value of OPN are inconclusive. In the present study, we evaluated tissue SPP1 mRNA and OPN protein expression as markers of recurrence in estrogen receptor- positive (ER+) breast cancer tissue. Tamoxifen- treated patients with recurrence or non-recurrence were selected using a matched case-control design. SPP1 mRNA expression was analysed using qPCR (n = 100) and OPN protein by immunohistochemistry (n = 116) using different antibodies. Odds ratios were estimated with conditional logistic regression. The SPP1 expression increased the risk of recurrence with an odds ratio (OR) of 2.50 (95% confidence interval [CI]; 1.30-4.82), after adjustment for tumour grade, HER 2 status and other treatments to OR 3.62 (95% CI; 1.45-9.07). However, OPN protein expression was not associated with risk of recurrence or with SPP1-gene expression, suggesting SPP1 mRNA a stronger prognostic marker candidate compared to tumor tissue OPN protein.

Effect of lidocaine and ropivacaine on primary (SW480) and metastatic (SW620) colon cancer cell lines.

Regional anesthesia may prolong survival following surgery for different types of cancers. The mechanisms behind this are unclear but direct effects on cancer cells by local anesthetics (LA) have been suggested. The aim of this study was to investigate if lidocaine or ropivacaine have a dose-dependent effect on the cell viability and proliferation of a primary and a secondary colon carcinoma cell line in vitro. The colon cancer cell lines SW480 derived from primary tumor and SW620 from a metastatic site in the same patient were exposed to increasing concentrations of lidocaine and ropivacaine (5-1,000 µM). Cell viability was measured using CellTiter-Blue® and cell proliferation by PKH67 after exposure for up to 72 h. Cell viability was significantly reduced by ropivacaine at the highest concentration (1,000 µM) after 48 and 72 h in the cell line SW480 and at 72 h in SW620. Exposure to lidocaine did not show any significant reduction in cell viability. Notably, low concentrations of both lidocaine and ropivacaine significantly increased cell viability after 48 and 72 h in SW620. Cell proliferation was significantly reduced by 1,000 µM lidocaine in SW480 and by 1,000 µM ropivacaine in SW620. In summary, both lidocaine and ropivacaine showed an anti-proliferative effect in the colon cancer cell lines at high concentrations and after prolonged exposure to LA in vitro. Our findings also indicate that lower concentrations promote cell viability in the metastatic cell line.

Dynamics of monocytic HLA-DR expression differs between bacterial etiologies during the course of bloodstream infection.

OBJECTIVE: In the pathogenesis of sepsis, activation of both pro- and anti-inflammatory responses are key components, but knowledge is lacking on the association between bacterial etiology and development of dysregulated responses with sustained immunosuppression. The aim of this study was to evaluate how the immunosupression marker HLA-DR on monocytes (mHLA-DR) is associated with bacterial etiology and markers of inflammation during the clinical trajectory of bloodstream infection (BSI). METHODS: Ninety-one adults, predominantly non-ICU patients, with BSI caused by Streptococcus pneumoniae (n = 27), Staphylococcus aureus (n = 22), Escherichia coli/Klebsiella pneumoniae (n = 23), and other species (n = 19) were prospectively included, and sampled on admission (day 0) and on days 1-2, 3, 7±1, 14±2, and 28±4. RESULTS: The dynamics of mHLA-DR, measured by flow cytometry, differed significantly between etiology groups (p<0.001). Patients with S. pneumoniae and S. aureus BSI demonstrated low initial mHLA-DR, with the S. aureus group showing delayed recovery over time. Eleven patients (55% S. aureus) had negative outcome (secondary bacteremia or death) and they demonstrated sustained C-reactive protein elevation, neutrophilia, lymphocytopenia, and loss of mHLA-DR. CONCLUSIONS: Dynamics of mHLA-DR varied according to the bacterial etiology of infection, with delayed recovery in patients with S. aureus BSI. Patients with negative outcome showed sustained CRP elevation, neutrophilia, lymphocytopenia, and low levels of mHLA-DR, supporting the theory of a dysregulated host response with persistent inflammation and immunosuppression in late stages of deleterious sepsis.

Decreased expression of the mitochondrial solute carrier SLC25A43 in basal cell carcinoma compared with healthy skin.

Basal cell carcinoma is the most common type of cancer in fair-skinned individuals, and its incidence is rapidly increasing. The aim of the present study was to investigate the gene and protein expression of the mitochondrial solute carrier family 25 member 43 (SLC25A43) in basal cell carcinoma. SLC25A43 has previously been identified to be genetically altered and associated with cell proliferation in human epidermal growth factor receptor 2-positive breast cancer. However, the knowledge about SLC25A43 is limited, and its role in other cancers is unknown. The SLC25A43 gene and protein expression was analysed in 14 basal cell carcinomas and healthy skin samples from the same individuals by quantitative polymerase chain reaction and immunohistochemistry, respectively. The results demonstrated a significantly lower (≥50%) SLC25A43 gene expression in all carcinomas compared with that in healthy skin. In addition, SLC25A43 protein expression was absent in >90% of all visual fields in the basal cell carcinomas, and the H-score was significantly lower in tumours compared with the adjacent epidermis. These results demonstrate that SLC25A43 expression is altered at the gene and protein levels in basal cell carcinoma. The underlying mechanisms and the clinical relevance of these data must be elucidated in additional experimental and clinical studies.

Quantitative Real-Time Polymerase Chain Reaction Measurement of HLA-DRA Gene Expression in Whole Blood Is Highly Reproducible and Shows Changes That Reflect Dynamic Shifts in Monocyte Surface HLA-DR Expression during the Course of Sepsis.

INTRODUCTION: A decrease in the expression of monocyte surface protein HLA-DR (mHLA-DR), measured by flow cytometry (FCM), has been suggested as a marker of immunosuppression and negative outcome in severe sepsis. However, FCM is not always available due to sample preparation that limits its use to laboratory operational hours. In this prospective study we evaluated dynamic changes in mHLA-DR expression during sepsis in relation to changes in HLA-DRA gene expression and Class II transactivator (CIITA), measured by quantitative Real-Time Polymerase Chain Reaction (qRT-PCR). AIMS: The aims of this study were: 1. to validate the robustness of qRT-PCR measurement of HLA-DRA- and CIITA-mRNA expression, in terms of reproducibility; and 2. to see if changes in expression of these genes reflect changes in mHLA-DR expression during the course of severe and non-severe bacteraemic sepsis. METHODS AND FINDINGS: Blood samples were collected from 60 patients with bacteraemic sepsis on up to five occasions during Days 1-28 after hospital admission. We found the reproducibility of the qRT-PCR method to be high by demonstrating low threshold variations (<0.11 standard deviation (SD)) of the qRT-PCR system, low intra-assay variation of Ct-values within triplicates (≤0.15 SD) and low inter-assay variations (12%) of the calculated target gene ratios. Our results also revealed dynamic HLA-DRA expression patterns during the course of sepsis that reflected those of mHLA-DR measured by FCM. Furthermore, HLA-DRA and mHLA-DR recovery slopes in patients with non-severe sepsis differed from those in patients with severe sepsis, shown by mixed model for repeated measurements (p<0.05). However, during the first seven days of sepsis, PCR-measurements showed a higher magnitude of difference between the two sepsis groups. Mean differences (95% CI) between severe sepsis (n = 20) and non-severe sepsis (n = 40) were; on day 1-2, HLA-DRA 0.40 (0.28-0.59) p<0.001, CIITA 0.48 (0.32-0.72) p = 0.005, mHLA-DR 0.63 (0.45-1.00) p = 0.04, day 7 HLA-DRA 0.59 (0.46-0.77) p<0.001, CIITA 0.56 (0.41-0.76) p<0.001, mHLA-DR 0.81 (0.66-1.00) p = 0.28. CONCLUSION: We conclude that qRT-PCR measurement of HLA-DRA expression is robust, and that this method appears to be preferable to FCM in identifying patients with severe sepsis that may benefit from immunostimulation.

Mitochondrial regulation of cell cycle progression through SLC25A43.

An increasing body of evidence is pointing towards mitochondrial regulation of the cell cycle. In a previous study of HER2-positive tumours we could demonstrate a common loss in the gene encoding for the mitochondrial transporter SLC25A43 and also a significant relation between SLC25A43 protein expression and S-phase fraction. Here, we investigated the consequence of suppressed SLC25A43 expression on cell cycle progression and proliferation in breast epithelial cells. In the present study, we suppressed SLC25A43 using siRNA in immortalised non-cancerous breast epithelial MCF10A cells and HER2-positive breast cancer cells BT-474. Viability, apoptosis, cell proliferation rate, cell cycle phase distribution, and nuclear Ki-67 and p21, were assessed by flow cytometry. Cell cycle related gene expressions were analysed using real-time PCR. We found that SLC25A43 knockdown in MCF10A cells significantly inhibited cell cycle progression during G1-to-S transition, thus significantly reducing the proliferation rate and fraction of Ki-67 positive MCF10A cells. In contrast, suppressed SLC25A43 expression in BT-474 cells resulted in a significantly increased proliferation rate together with an enhanced G1-to-S transition. This was reflected by an increased fraction of Ki-67 positive cells and reduced level of nuclear p21. In line with our previous results, we show a role for SLC25A43 as a regulator of cell cycle progression and proliferation through a putative mitochondrial checkpoint. These novel data further strengthen the connection between mitochondrial function and the cell cycle, both in non-malignant and in cancer cells.

HER4 tumor expression in breast cancer patients randomized to treatment with or without tamoxifen.

The human epidermal growth factor receptor (HER) 4 is a relative of HER2 and has been associated to endocrine breast cancer and prediction of tamoxifen response. In addition to PI3K/Akt and MAPK pathway activation, ligand binding to HER4 triggers proteolytic cleavage and release of an intracellular receptor domain (4ICD) with signaling properties. The aim of the present study was to analyze HER4 protein expression and intracellular localization in breast cancer tissue from patients randomized to treatment with or without adjuvant tamoxifen. To investigate HER4 expression and localization in response to estradiol (E2) and 4-hydroxytamoxifen (4-OHT) exposure, we also performed in vitro studies. Cytoplasmic, nuclear and membrane expression of HER4 protein was evaluated by immunohistochemical staining in tumor tissue from 912 breast cancer patients. Three different breast epithelia cancer cell lines were exposed to E2 and 4-OHT and mRNA expression was analyzed using qPCR. Further, nuclear and cytoplasmic proteins were separated and analyzed with western blotting. We found an association between nuclear HER4 protein expression and ER-positivity (P=0.004). Furthermore, significant association was found between cytoplasmic HER4 and ER-negativity (P<0.0005), PgR-negativity (P<0.0005), tumor size >20 mm (P=0.001) and HER2-negativity (P=0.008). However, no overall significance of HER4 on recurrence-free survival was found. After E2 exposure, HER4 mRNA and protein expression had decreased in two cell lines in vitro yet no changes in nuclear or cytoplasmic protein fractions were seen. In conclusion, nuclear HER4 seem to be co-located with ER, however, we did not find support for overall HER4 expression in independently predicting response of tamoxifen treatment. The possible influence of separate isoforms was not tested and future studies may further evaluate HER4 significance.

Preliminary results in quantitation of HLA-DRA by real-time PCR: a promising approach to identify immunosuppression in sepsis.

INTRODUCTION: Reduced monocyte human leukocyte antigen (mHLA)-DR surface expression in the late phase of sepsis is postulated as a general biomarker of sepsis-induced immunosuppression and an independent predictor of nosocomial infections. METHODS: Fifty-nine patients with sepsis and blood culture growing pathogenic bacteria were studied. Blood samples were collected at day 1 or 2 after admission, for measurement of mHLA-DR by flow cytometry and mRNA expression of HLA-DRA and class II transactivator (CIITA) by qRT-PCR. Blood samples from blood donors were used as controls (n = 30). RESULTS: A significant reduced expression of mHLA-DR, HLA-DRA, and CIITA was seen in septic patients compared with controls. HLA-DRA mRNA level in whole blood was highly correlated with surface expression of mHLA-DR. CONCLUSIONS: Patients with sepsis display a diminished expression of HLA-DR at the monocyte surface as well as in the gene expression at the mRNA level. The mRNA expression level of HLA-DRA monitored by qRT-PCR correlates highly with surface expression of HLA-DR and appears to be a possible future biomarker for evaluation of immunosuppression in sepsis.

The mitochondrial transport protein SLC25A43 affects drug efficacy and drug-induced cell cycle arrest in breast cancer cell lines.

The mitochondria have been identified as key players of apoptosis, cell proliferation and cell cycle regulation. However, the role of mitochondria in breast cancer and treatment failure remains unclear. We have previously shown a common deletion of the gene SLC25A43 in human epidermal growth factor receptor 2 (HER2)-positive breast cancer. This gene is coding for a mitochondrial inner membrane transporter and, to date, little is known about the function of this protein. We have also found that low protein expression of SLC25A43 significantly correlates with a lower S phase fraction in HER2-positive breast cancer. The aim of this study was to investigate whether knockdown (KD) of SLC25A43 could have an effect on the cytotoxicity of different cytostatic drugs using MCF10A, MCF7 and BT-474 cells. Following siRNA-mediated KD of SLC25A43, one non-malignant and two breast cancer cell lines were exposed to the anthracycline epirubicin or the taxane paclitaxel. The HER2-positive breast cancer cells were also exposed to the targeted therapy trastuzumab and dual exposure to trastuzumab and paclitaxel. We found that KD of SLC25A43 resulted in a decreased cytotoxic effect of paclitaxel in the two cancer cell lines (P<0.05). Further analysis of cell cycle phase distribution showed that KD increased the paclitaxel-induced G2/M block in these two cell lines (P<0.05). KD of SLC25A43 also reduced the inhibitory effect of trastuzumab on cell proliferation in the HER2-positive cancer cell line BT-474 (P<0.05), and the drug-induced G0/G1 block (P<0.05). Moreover, SLC25A43 influenced the percentage of Ki-67-positive cells. Our findings demonstrate that the mitochondrial protein SLC25A43 affects drug efficacy and cell cycle regulation following drug exposure in breast cancer cell lines.

The mitochondrial transporter SLC25A43 is frequently deleted and may influence cell proliferation in HER2-positive breast tumors.

BACKGROUND: Overexpression of the human epidermal growth factor receptor (HER) 2 is associated with poor prognosis and shortened survival in breast cancer patients. HER2 is a potent activator of several signaling pathways that support cell survival, proliferation and metabolism. In HER2-positive breast cancer there are most likely unexplored proteins that act directly or indirectly downstream of well established pathways and take part in tumor development and treatment response. METHODS: In order to identify novel copy number variations (CNVs) in HER2-positive breast cancer whole-genome single nucleotide polymorphism (SNP) arrays were used. A PCR-based loss of heterozygosis (LOH) assay was conducted to verify presence of deletion in HER2-positive breast cancer cases but also in HER2 negative breast cancers, cervical cancers and lung cancers. Screening for mutations was performed using single-strand conformation polymorphism (SSCP) followed by PCR sequencing. Protein expression was evaluated with immunohistochemistry (IHC). RESULTS: A common deletion at chromosome Xq24 was found in 80% of the cases. This locus harbors the gene solute carrier (SLC) family 25A member 43 (SLC25A43) encoding for a mitochondrial transport protein. The LOH assay revealed presence of SLC25A43 deletion in HER2-positive (48%), HER2-negative (9%), cervical (42%) and lung (67%) cancers. HER2-positive tumors with negative or low SLC25A43 protein expression had significantly lower S-phase fraction compared to tumors with medium or high expression (P = 0.024). CONCLUSIONS: We have found deletion in the SLC25A43 gene to be a common event in HER2-positive breast cancer as well as in other cancers. In addition, the SLC25A43 protein expression was shown to be related to S-phase fraction in HER2-positive breast cancer. Our results indicate a possible role of SLC25A43 in HER2-positive breast cancer and support the hypothesis of altered mitochondrial function in cancer.

Topoisomerase IIalpha expression in acute myeloid leukaemia cells that survive after exposure to daunorubicin or ara-C.

Patients diagnosed with acute myeloid leukaemia are often treated with a combination of daunorubicin and 1-beta-D-arabinofuranosylcytosine (ara-C). Both daunorubicin and ara-C exert their effects in the cell nucleus but by different mechanisms, i.e. daunorubicin causes double stranded DNA breaks by inhibition of the nuclear enzyme, topoisomerase (topo) IIalpha, whereas ara-C is an anti-metabolite that integrates with DNA during DNA synthesis and causes cell cycle arrest. Despite the initial efficacy of these drugs, resistance often develops in the clinical setting. The mechanisms underlying clinical resistance to these drugs are poorly understood, but may be associated with an increase in the proportion of topo IIalpha negative cells. Therefore, the aim of this study was to determine whether daunorubicin treatment results in increased numbers of topo IIalpha negative subpopulations in vitro. Acute myeloid leukaemia cells isolated from 12 consenting patients were treated for 24 h with increasing concentrations of daunorubicin or ara-C and the proportion of topo IIalpha-negative cells in surviving cell populations determined by flow cytometry. Treatment with daunorubicin, but not ara-C, resulted in a significant increase in the proportion of topo IIalpha negative cells (p=0.0023). These results suggest that daunorubicin may act by cell cycle arrest and/or by selection of pre-existing topo IIalpha negative subpopulations. Both of these mechanisms can theoretically contribute to a reduced efficacy of a second dose of daunorubicin. The clinical relevance of these interactions should be further elucidated in experimental and clinical studies.

Rapid induction of P-glycoprotein mRNA and protein expression by cytarabine in HL-60 cells.

BACKGROUND: Overexpression of P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and glutathione-S-transferase pi (GSTpi) is associated with drug resistance in acute myeloid leukemia (AML). The short-term effects of drug exposure on their expression levels were investigated. MATERIALS AND METHODS: HL-60 cells and drug-resistant sublines were cultured with or without daunorubicin (DNR) and cytarabine (Ara-C). At several time-points the expression levels of P-gp, BCRP and GSTpi were determined. RESULTS: After exposure to Ara-C, P-gp mRNA rapidly increased in all the cell lines. P-gp protein was detected in the sensitive cells after 8 h exposure to Ara-C. GSTpi mRNA increased in the resistant cells, but no change in BCRP mRNA was observed. Exposure to DNR revealed rapidly increased P-gp and GSTpi mRNA in the resistant cells. CONCLUSION: Ara-C rapidly increases P-gp mRNA and protein expression in sensitive and resistant cells, and GSTpi mRNA in resistant cells, in vitro. This may be of clinical importance during AML induction chemotherapy.

Topoisomerase IIalpha mRNA and protein expression vs. in vitro drug resistance and clinical outcome in acute leukaemia.

The objective of this study was to correlate the expression of topoisomerase (topo) IIalpha to in vitro drug sensitivity and to the clinical outcome in patients with acute leukaemia. Leukaemic cells were isolated from bone marrow or blood from 94 patients. Topo IIalpha mRNA (n=58) and protein (n=60) expression was determined by real-time RT-PCR and flow cytometry, respectively. In both groups, chemosensitivity testing by a bioluminescence ATP assay was performed to a variable extent for both topo IIalpha poisons and non-topo IIalpha targeting drugs. Topo IIalpha mRNA expression varied with relative values ranging from 0.03 to 14.20 (median 1.10). The median value for topo IIalpha protein-positive cells was 23% (range 0-99%). Cell samples from patients with a high (>median value) percentage of topo IIalpha-positive cells were significantly more sensitive to the topo IIalpha active drugs etoposide and daunorubicin, and showed a borderline value for idarubicin (p=0.08), while there was no difference for non-topo IIalpha targeting drugs. However, we did not find any significant differences in mRNA expression or the percentage of topo IIalpha-positive cells in patients who achieved complete remission after at most two induction courses compared with those who did not, nor did we find any difference in survival when patients with high mRNA expression/percentage of topo IIalpha-positive cells were compared with patients with low values. We conclude that expression of topo IIalpha, determined as percentage of topo IIalpha-positive cells, in leukaemic cells correlates to chemosensitivity in vitro against topoisomerase poisons but that it does not predict clinical outcome in acute leukaemia.