MSc Med, Clinical Microbiology and Infectious Diseases, Faculty of Health Sciences,University of the Witwatersrand, 2009 / Anaerobic bacteria cause serious life-threatening infections such as endocarditis, sepsis, intra abdominal, pleuro-pulmonary and central nervous systems infections. Most infections are polymicrobial and involve aerobes and anaerobes. Empiric therapy is generally based on the expected pathogens and the particular type of infection. Even when specimens are cultured and anaerobes identified, not all laboratories perform susceptibility testing. The clinician often relies on published surveillance data when selecting treatment regimens. Antimicrobial susceptibility of anaerobic bacteria is becoming increasingly unpredictable. Resistance can vary significantly and patterns differ geographically, and even within units of the same hospital. From June 2005 until February 2007, 180 consecutive anaerobes isolated from relevant, non- repetitive clinical specimens were tested routinely with the E test method for susceptibility to amoxicillin/ clavulanate (XL), clindamycin (Cm), metronidazole (Mz), penicillin (Pg), ertapenem (Etp), cefoxitin (Fx), ceftriaxone (Tx), chloramphenicol (Cl), and piperacillin/tazobactam (Ptc). The results were read after 48hr incubation in anaerobic conditions. Specimen distribution was as follows: abdominal fluid (3), abscess (7), abdominal abscess (4), aspirates (3), blood cultures (27), bone (3), breast (3), drainage fluid (2), empyema (1), fluids (36), other (4), placental (1), pleural fluid (2), pus (41), tissues (34), umbilicus (1) and unknown sites (8). Bacteroides fragilis was isolated from 81 (45%) clinically significant specimens, followed by Clostridium perfringens 23 (13%), Peptostreptococcus anaerobius 15 (8%) and Prevotella melaniniogenicus 15 (8%). B. fragilis demonstrated a 97.5% resistance to penicillin and 12.3% resistance to metronidazole. C. perfringens exhibited no resistance to penicillin and metronidazole while P. anaerobius had 40% resistance to penicillin and no resistance to metronidazole. P. melaninogenicus was resistant to penicillin in 60% and 6.7% to metronidazole. Overall, chloramphenicol, piperacillin/tazobactam, ertapenem and amoxicillin/clavulanate demonstrated the highest activity to anaerobic isolates, 100%, 99.4%, 97.2% and 96.7%, respectively. Among the 180 tested anaerobes a total of 8.9% resistance has been observed with metronidazole and 81.7% sensitivity with clindamycin. Periodic surveillance to monitor the susceptibility profile of the B. fragilis group and other anaerobic organisms is recommended to create empirical guidelines for appropriate use of antimicrobial agents.

A research report submitted to, the Faculty of Health Sciences, University of Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science in Population based field epidemiology March, 2013 / Introduction: Access to highly active antiretroviral therapy has dramatically increased worldwide since 2004. However, the emergence of HIV drug resistance presents huge obstacle in ART scale up as it contributes to treatment failure and poses a greater risk of disease progression and loss of treatment options. The study therefore investigated the risk factors and the association of HIV drug resistance, virological failure and CD4 cell count changes in patients on ART at Aurum Institute for Health Research in South Africa. Methods: A cohort of HIV infected patients who developed virological failure of their first HAART regimen was assessed. A genotypic resistance testing was performed using stored plasma on a subset of patients at first detection of virological failure. Data were collected prospectively on all registered patients using standardised forms. Clinical data was obtained from laboratory and pharmacy electronic records. Logistic regression and Cox proportional hazard models were used to assess factors associated with HIV drug resistance and virological failure respectively. Linear mixed-effects regression models were used to assess the changes in the CD4 cell count among patients who developed HIVDR. Results: Between January 2003 and December 2010, a total of 146 ART-treated patients who experienced virological failure were assessed. Of these, 108 (74%) developed HIVDR, of whom 80 (74%) were males; the median CD4 cell count at ART initiation was 121 cells/mm3 (interquartile range, 61-210). The most frequent NNRTI mutations patterns found were mutations leading to resistance to NNRTI agents with 33% having NNRTI resistance. The second most common resistance v pattern was resistance to lamivudine conferred by the M184V mutation (30%). The multivariable analysis showed that higher CD4 cell count at HIVDR detection was significantly associated with the reduced odds of developing HIV drug resistant mutation after adjusting for gender and age(adjusted OR=0.37, 95% CI 0.15–0.94). Similarly, there was significant association between age at ART initiation (adjusted HR=0.71, 95% CI 0.52–0.97) and CD4 cell count during follow-up (adjusted HR= 0.54 95% CI 0.36–0.81) with virological failure in those patients who developed HIVDR. The CD4 cell count slope on average increased by 10 cells per mL per year for the patients without any resistance (average annual change 9.89 cells per mL, 95% CI -6.90-26.69) and decreased by 10 cells per mL per year for patients who had any resistance (average annual change -9.61 cells per mL, 95% CI -19.41- 0.17). Conclusion and recommendation: HIV drug resistant virus was found in 74% of the South African patients who were accessing HIV care at Aurum Heath Institute and developed virological failure of first HAART regimen. Higher CD4 count at detection of HIVDR was significantly associated with lower risk of developing HIV drug resistant virus. Lower CD4 count and male gender were significantly associated with the development of virological failure. Patients with virological failure had significantly great CD4 count declines when any mutation and thymidine analog mutation (TAM) mutation were present. There is a great need therefore for multifaceted approach to target interventions that aim to increase patients CD4 cell counts. Patients should be either screened, possibly with HIVDR testing, prior to reinitiation of a first-line regimen

by Ho Iok Ieng Yolanda. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (p. 116-132). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Yeung Heung-fun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1987. / Includes bibliographical references.

by Yip Chi Wai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 70-87). / ABSTRACT --- p.i / ACKNOWLEDGEMENT --- p.iv / TABLE OF CONTENTS --- p.v / LIST OF TABLES --- p.ix / LIST OF FIGURES --- p.xiii / INTRODUCTION --- p.1 / LITERATURE REVIEW --- p.3 / Chapter I. --- Mycobacterial Infections --- p.3 / Chapter A. --- Mycobacterium tuberculosis --- p.3 / Chapter B. --- Atypical mycobacteria --- p.3 / Chapter II. --- Identification of Mycobacteria --- p.5 / Chapter A. --- Conventional methods --- p.6 / Chapter 1. --- Mycobacterium tuberculosis --- p.6 / Chapter 2. --- Atypical mycobacteria --- p.7 / Chapter B. --- Rapid identification methods --- p.8 / Chapter 1. --- Identification by fatty acid analysis --- p.8 / Chapter 2. --- Identification by mycolic acid analysis --- p.9 / Chapter III. --- In vitro Susceptibility Testing of Mycobacteria --- p.11 / Chapter A. --- Mycobacterium tuberculosis --- p.11 / Chapter 1. --- Principle --- p.12 / Chapter 2. --- Methods of susceptibility testing --- p.13 / Chapter a. --- The absolute concentration method --- p.13 / Chapter b. --- The resistance ratio method --- p.15 / Chapter c. --- The 1% proportion method --- p.16 / Chapter d. --- Radiometric method --- p.18 / Chapter e. --- Other methods --- p.19 / Chapter B. --- Atypical mycobacteria --- p.20 / Chapter IV. --- Plasmid Analysis in Mycobacteria --- p.22 / Chapter A. --- Discovery of plasmids in mycobacteria --- p.22 / Chapter B. --- Methodologies in the studies of mycobacterial plasmids --- p.23 / Chapter C. --- Possible roles of plasmid in epidemiology of mycobacteria --- p.24 / MATERIALS AND METHODS --- p.26 / Chapter I. --- Bacterial Strains and Strain Maintenance --- p.26 / Chapter A. --- Strains collection --- p.26 / Chapter B. --- Strains maintenance --- p.26 / Chapter II. --- Culture Media and Culture Conditions --- p.26 / Chapter III. --- Identification of Mycobacteria --- p.26 / Chapter A. --- Conventional methods --- p.26 / Chapter B. --- Fatty acid profile analysis --- p.27 / Chapter 1. --- Bacterial isolates --- p.27 / Chapter 2. --- Standards and reagents --- p.27 / Chapter 3. --- Preparation of methyl ester for GC/GC-MS --- p.28 / Chapter 4. --- Instrumentation --- p.28 / Chapter a. --- Gas chromatography-mass spectrometry (GC-MS) --- p.28 / Chapter b. --- Gas liquid chromatography (GLC) --- p.28 / Chapter 5. --- Fatty acid profile analysis --- p.29 / Chapter a. --- Calibration --- p.30 / Chapter b. --- Identification of mycobacterial fatty acids --- p.30 / Chapter c. --- Construction of mycobacterial fatty acid profiles --- p.30 / Chapter 6. --- Discriminant analysis --- p.31 / Chapter IV. --- In Vitro Drug Susceptibility Test --- p.31 / Chapter A. --- Test strains --- p.31 / Chapter B. --- Preparation of drug-containing media --- p.32 / Chapter C. --- Minmum inhibition concentration (MIC) determination --- p.32 / Chapter V. --- Heavy Metal Tolerance Test --- p.33 / Chapter A. --- Bacterial strains --- p.33 / Chapter B. --- Reagent and media preparation --- p.34 / Chapter 1. --- Heavy metal stock solution preparation --- p.34 / Chapter 2. --- Media preparation --- p.34 / Chapter C. --- Minimum inhibition concentration (MIC) determination --- p.34 / Chapter VI. --- Plasmid Analysis of Mycobacteria --- p.35 / Chapter A. --- Bacterial strains --- p.35 / Chapter B. --- Extraction procedures --- p.35 / Chapter 1. --- Modified Kado & Liu method --- p.35 / Chapter 2. --- French press procedure --- p.36 / Chapter 3. --- Spheroplasts preparation procedure --- p.37 / Chapter C. --- Electrophoresis procedure --- p.37 / Chapter D. --- Statistical analysis for correlation between plasmid and drug resistance or heavy metal tolerance --- p.38 / RESULTS --- p.39 / Chapter I. --- Identification of Mycobacteria --- p.39 / Chapter A. --- General characteristics of the chromatographic profile --- p.39 / Chapter B. --- Discriminant analysis --- p.40 / Chapter 1. --- Gas chromatography-mass spectrometry (GC-MS) --- p.40 / Chapter a. --- Slowly growing non-pigmented mycobacteria --- p.40 / Chapter b. --- Rapidly growing mycobacter-ia --- p.41 / Chapter c. --- Pigmented mycobacteria --- p.41 / Chapter 2. --- Gas liquid chromatography (GLC) --- p.41 / Chapter a. --- Slowly growing non-pigmented mycobacteria --- p.42 / Chapter b. --- Rapidly growing mycobacteria --- p.42 / Chapter c. --- Pigmented mycobacteria --- p.43 / Chapter II. --- Vitro Drug Susceptibility Test --- p.43 / Chapter A. --- Mycobacterium tuberculosis --- p.43 / Chapter B. --- Atypical mycobacteria --- p.45 / Chapter 1. --- General characteristics --- p.45 / Chapter 2. --- Sensitivity pattern of different species --- p.46 / Chapter a. --- Mycobacterium kansasii --- p.46 / Chapter b. --- Mycobacterium avium- intracellulare complex --- p.46 / Chapter c. --- Mycobacterium scrofulaceum --- p.47 / Chapter d. --- Mycobacterium terrae complex --- p.47 / Chapter e. --- Mycobacterium fortuitum --- p.47 / Chapter f. --- Mycobacterium chelonae --- p.48 / Chapter III. --- Heavy Metal Tolerance Test --- p.48 / Chapter IV. --- Plasmid in Mycobacteria --- p.48 / Chapter A. --- Mycobacterium tuberculosis --- p.48 / Chapter B. --- Atypical mycobacteria --- p.49 / Chapter 1. --- General characteristics --- p.49 / Chapter 2. --- Correlation between drug resistance and plasmid --- p.50 / Chapter 3. --- Correlation between heavy metal tolerance and plasmid --- p.50 / DISCUSSION --- p.52 / Chapter I. --- Identification of Mycobacteria --- p.52 / Chapter II. --- In Vitro Drug Susceptibility Test --- p.56 / Chapter A. --- Mycobacterium tuberculosis --- p.56 / Chapter B. --- Atypical mycobacteria --- p.60 / Chapter 1. --- Mycobacterium kansasii --- p.61 / Chapter 2. --- Mycobacterium avium- intracellulare complex --- p.61 / Chapter 3. --- Mycobacterium scrofulaceum --- p.62 / Chapter 4. --- Mycobacterium terrae complex --- p.62 / Chapter 5. --- Mycobacterium fortuitum --- p.63 / Chapter 6. --- Mycobacterium chelonae --- p.64 / Chapter III. --- Plasmid Analysis in Mycobacteria --- p.64 / Chapter A. --- Mycobacterium tuberculosis --- p.64 / Chapter B. --- Atypical mycobacteria --- p.66 / SUMMARYS AND CONCLUSIONS --- p.68 / LITERATURE CITED --- p.70 / Chapter APPENDIX - --- Tables --- p.88 / Figures --- p.144

No description available.

Recent whole-exome sequencing studies of hundreds of high-risk neuroblastoma (hNB) patients have identified Anaplastic Lymphoma Kinase (ALK) as the only directly ‘druggable’ target with a significant mutation rate (9%). ALK is a receptor tyrosine kinase whose dysregulation has been implicated as the driver lesion in a variety of cancer types, including Non-Small Cell Lung Cancer (NSCLC) and various paediatric malignancies. As a kinase normally only expressed during early development in the foetal brain, ALK is an ideal therapeutic target and it has proven relatively simple to target therapeutically. However, resistance to ALK-targeted therapy, particularly in ALK+ NSCLC patients has frequently been observed. The majority of the acquired resistance mechanisms noted in NSCLC patients rely on bypass signalling pathways, which are tissue-context dependent. To proactively identify and develop strategies to counter these varied yet expected resistance mechanisms in other ALK-driven tumours, we must gain a better insight of the bypass-track mechanism(s) in a tumour-specific manner. The present study aimed to functionally identify putative resistance mechanisms against ALK inhibitors via extensive CRISPR/Cas9-based genome-wide knockout (GeCKO) or overexpression screens (SAM) in the human neuroblastoma cell line, SHSY-5Y, to develop novel therapeutic strategies for ALK mutant NBs. The GeCKO screen identified a total of 39 genes and miRNAs, and the SAM overexpression screen identified 25 genes that induce resistance to ALK inhibitors. These putative resistance-inducing candidates were then aligned with a publicly available expression dataset of hNB patients (n = 476) to identify those with prognostic significance (Kaplan-Meier event-free survival analysis), specifically those that are indicative of relapse risk. Furthermore, all candidates identified from the screen were individually validated in vitro. Two of the candidates, one from each of the knockout and overexpression screens, were further investigated. Inhibition of hsa-miR-1304-5p, identified from GeCKO screen, induced resistance to ALK inhibitors. Interestingly, interference of has-miR-1304-5p, in the absence of ALK inhibitors, also enabled enhanced cell viability whilst the transfection of its mimic led to a significant reduction of viability across 17 distinct NB cell lines. Through genome-wide cDNA microarrays, in silico predictions, and UTR-luciferase assays, this study identified hsa-miR-1304-5p to be a major regulator of the Ras/MAP Kinase pathway. Overexpression of PIM1, identified from the SAM screen, in NB cell lines induced resistance to ALK inhibitors and this phenotype could be reversed on transducing cells with RNAi against PIM1. Interestingly, inhibition of PIM1 in wild-type cell lines via RNAi or pharmacological compounds led to substantially enhanced potency of ALK inhibitors suggesting PIM1 inhibitors as combinatorial agents with ALK inhibitors for the therapy of treatment-naive hNB. Through protein analysis of all identified downstream targets of PIM1, this study revealed NB-specific actions of the PIM1 oncoprotein that include the inactivation of the pro-apoptotic protein BAD. In summary, this study has identified mechanisms of resistance to ALK inhibitors as well as novel front-line therapeutic strategies for hNB patients that should be implemented clinically.

Wong Pak Cheung Ronald. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 121-142). / Abstracts in English and Chinese. / Acknowledgement --- p.I / Abstract --- p.II / Abbreviation --- p.VI / List of figures --- p.IX / List of tables --- p.XI / Content --- p.XII / Content / Chapter Chapter 1: --- General Introduction --- p.1 / Chapter 1.1 --- The p53 tumor suppressor gene --- p.2 / Chapter 1.1.1 --- Structure and function --- p.2 / Chapter 1.1.2 --- Regulation of p53 stability and activity --- p.3 / Chapter 1.1.3 --- p53 and cell cycle arrest --- p.4 / Chapter 1.1.4 --- p53 and apoptosis --- p.4 / Chapter 1.2 --- Mutation in p53 gene --- p.9 / Chapter 1.2.1 --- Loss of function through dominant negative effect --- p.9 / Chapter 1.2.2 --- Gain-of-function through transactivation by mutant p53 --- p.10 / Chapter 1.2.3 --- Mutation in p53 and resistance to cancer therapy --- p.10 / Chapter 1.3 --- Objective of the study --- p.14 / Chapter Chapter 2: --- Mutant p53 induced interferon resistance and its regulation of the Jak/Stat pathway --- p.15 / Chapter 2.1 --- Introduction --- p.16 / Chapter 2.1.1 --- IFN classification and biological activities --- p.16 / Chapter 2.1.2 --- IFN signaling --- p.17 / Chapter 2.1.3 --- IFN direct antitumor effect: cell cycle arrest and apoptosis --- p.18 / Chapter 2.1.4 --- IFN in immunotherapy --- p.20 / Chapter 2.1.5 --- Resistance to IFN therapy --- p.21 / Chapter 2.2 --- Materials and Methods --- p.24 / Chapter 2.2.1 --- Cell lines --- p.24 / Chapter 2.2.2 --- Drugs and antibodies --- p.24 / Chapter 2.2.3 --- Cell Proliferation assay- MTT assay --- p.24 / Chapter 2.2.4 --- Cell cycle analysis --- p.25 / Chapter 2.2.5 --- DNA fragmentation assay --- p.25 / Chapter 2.2.6 --- Western blot analysis --- p.26 / Chapter 2.2.7 --- "Combined treatment of IFNs and Jak inhibitors in MTT assay, DNA fragmentation assay and Western blot analysis" --- p.26 / Chapter 2.3 --- Results --- p.27 / Chapter 2.3.1 --- Mutant p53-V143A and p53-R273H induced IFN resistance: the role of IFN induced apoptosis and cell cycle arrest --- p.27 / Chapter 2.3.2 --- IFN induction of apoptosis: a p53-independent and caspase-dependent pathway --- p.28 / Chapter 2.3.3 --- Mutant p53 regulation of Jak/Stat pathway --- p.36 / Chapter 2.3.4 --- Janus kinases (Jaks) and IFN-alpha sensitivity in Saos-2 cells --- p.41 / Chapter 2.3.5 --- Janus kinases (Jaks) and IFN-gamma sensitivity --- p.49 / Chapter 2.4 --- Discussion --- p.56 / Chapter 2.4.1 --- Mutant p53-V143 and p53-R273H induced IFN resistance in Saos-2 cells --- p.56 / Chapter 2.4.2 --- Role of Jaks in IFN sensitivity in Saos-2 cells --- p.57 / Chapter 2.4.3 --- IFN signaling in Saos-2 cells --- p.57 / Chapter 2.4.4 --- Jak2 and IFN induced apoptosis --- p.58 / Chapter Chapter 3: --- Mutant p53 induced drug resistance --- p.60 / Chapter 3.1 --- Introduction --- p.61 / Chapter 3.1.1 --- The multidrug resistance (MDR) --- p.61 / Chapter 3.1.2 --- Anticancer drugs used in the study: action mechanisms and resistance --- p.67 / Chapter 3.1.3 --- Jak/Stat pathway and MDR --- p.68 / Chapter 3 .2 --- Materials and Methods --- p.72 / Chapter 3.2.1 --- Cell lines --- p.72 / Chapter 3.2.2 --- Drugs and antibodies --- p.72 / Chapter 3.2.3 --- Caspase 3 activity assay --- p.72 / Chapter 3.2.4 --- Cell Proliferation assay- MTT assay --- p.73 / Chapter 3.2.5 --- Cell cycle analysis --- p.73 / Chapter 3.2.6 --- DNA fragmentation assay --- p.73 / Chapter 3.2.7 --- Reverse transcription polymerase chain reaction --- p.73 / Chapter 3.2.8 --- Western blot analysis --- p.74 / Chapter 3.2.9 --- "Combined treatment of IFNs and Jak inhibitors in MTT assay, DNA fragmentation assay and Western blot analysis" --- p.74 / Chapter 3.3 --- Results --- p.75 / Chapter 3.3.1 --- Mutant p53 and drug sensitivity --- p.75 / Chapter 3.3.2 --- Mutant p53 and drug induced apoptosis and cell cycle arrest --- p.75 / Chapter 3.3.3 --- Classical drug resistance factors in mutant p53 induced drug resistance --- p.87 / Chapter 3.3.4 --- The role of Jaks in drug sensitivity of Saos-2 cells --- p.89 / Chapter 3.3.5 --- The role of Jaks in drug induced DNA fragmentationin Saos-2 cells --- p.89 / Chapter 3.3.6 --- Jak signaling and caspase activation in MTX induced apoptosis in Saos-2 cells --- p.100 / Chapter 3.3 --- Discussion --- p.108 / Chapter 3.3.1 --- Mutant p53-V143A and p53-R273H induced drug resistance in Saos-2 cells --- p.108 / Chapter 3.3.2 --- Role of Jaks in drug sensitivity in Saos-2 cells --- p.109 / Chapter 3.3.3 --- Jak/Stat signaling in Saos-2 cells --- p.109 / Chapter 3.3.4 --- Jak2 and MTX induced apoptosis --- p.110 / Chapter Chapter 4: --- General discussion --- p.112 / Chapter 4.1 --- Mutant p53 induced immunotherapy and chemotherapy resistance --- p.113 / Chapter 4.2 --- Gain of new function of mutant p53-V143A and p53-R273H in regulating Jak/Stat pathway leading to resistance to IFN and chemotherapeutic drugs --- p.114 / Chapter 4.3 --- The role of Jaks in MTX sensitivity --- p.114 / Chapter 4.4 --- Future work --- p.115 / Chapter 4.5 --- Perspective --- p.120 / References --- p.121

by Timothy W.L. Wong. / "July 2000." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (p. 200-238). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

The ability of low, clinically relevant levels of the chemotherapeutic drugs epirubicin and vinblastine to induce drug resistance was examined in the K562. U937, KG-la and HEL human leukaemia cell lines. Treatment with epirubicin and vinblastine induced the MDR phenotype and P-glycoprotein expression in K562 and U937 cells. However this treatment had no effect on drug resistance in the P-glycoprotein expressing KG-la and HEL cells. In the U937 cells, drug resistant cells were not only MDR but were also resistant to other drugs including cisplatinum and chlorambucil which are not normally associated with MDR. The drug resistant U937 sublines were also sensitised to doxorubicin, cisplatinum and chlorambucil by buthionine sulphoximine (BSO), suggesting that glutathione-related mechanisms also contributed to resistance in these sublines. The U937 sublines also had an increased DNA content and an increased ability to recover from DNA damage, as determined by cell cycle analysis, indicating that the broad cross-resistance exhibited by these cells was due to the co-existence of multiple resistance mechanisms. Drug treatment induced changes in expression of differentiation associated antigens in all four cell lines. Treatment with inducers of differentiation (TPA, sodium butyrate, granulocyte-macrophage colony-stimulating factor; GM-CSF). Treatment of K562 and K562/E15B cells with TPA induced megakaryocytic differentiation, with increases in drug resistance, and increased P-glycoprotein expression in the K562/E15B subline. TPA induced monocytic differentiation in the U937 cells but not the U937/EIS subline, with increased P-glycoprotein expression and function in the U937/E15 cells but not the U937 cells. Staurosporine, an inhibitor of PKC, inhibited differentiation in these cell lines, but did not inhibit increases in P-glycoprotein expression, suggesting drug resistance was not mediated by PKC. Sodium butyrate induced erythroid differentiation, and increased P-glycoprotein expression in the K562/E15B cells. However at a higher concentration (15 mM) this was not accompanied by increased drug resistance. Granulocyte monocyte colony stimulating factor (GM-CSF) did not induce differentiation in the K562 cells or K562/E15B subline, although the K562/E15B cells became more drug resistant after treatment with GM-CSF. Treatment with GM-CSF induced differentiation in the U937/E15 subline but did not change drug resistance in either the U937 cells or the U937/EI5 subline. Therefore the P-glycoprotein expressing K562/E15B and U937/E15 sublines were more responsive to inducers of differentiation than the parental cell lines. Induction of differentiation therefore induced increases in P-glycoprotein expression and drug resistance, suggesting that expression of P-glycoprotein or a multidrug resistance phenotype was associated with differentiation.