ABSTRACT MULTIDRUG RESISTANCE IN LOCALLY ADVANCED BREAST CANCER ATALAY, Mustafa Can Ph. D., Department of Biotechnology Supervisor: Prof. Dr. Ufuk G&Uuml / ND&Uuml / Z June 2004, 70 pages Breast cancer is the most frequently detected cancer among women. Early diagnosis leads to long term survival when the patients are treated with surgery, radiotherapy, chemotherapy, and hormone therapy. Unfortunately, advanced disease could still be encountered in some patients resulting in a poorer prognosis. The primary treatment modality is chemotherapy for this group of patients. Drug resistance is a serious problem resulting in the use of different drugs during chemotherapy and knowing the possibility of resistance before initiating first line chemotherapy may save time and money, and most importantly, may increase patient&rsquo / s survival. Therefore in this study, multidrug resistance is studied in locally advanced breast cancer patients. The breast tissues obtained from 25 patients both before and after chemotherapy were examined for drug resistance. Reverse transcriptase polymerase chain reaction was used for the detection of mdr1 and mrp1 gene expression. In addition, immunohistochemistry technique was used for P-glycoprotein and MRP1 detection. JSB-1 and QCRL-1 monoclonal antibodies were utilized to detect P-glycoprotein and MRP1, respectively. Five patients were unresponsive to chemotherapy. In four of these patients mdr1 gene expression was induced by chemotherapy where as the fifth patient initially had mdr1 gene expression. In addition, Pgp positivity was detected in 9 patients after chemotherapy. Both the induction of mdr1 gene expression (p&lt / 0.001) and Pgp positivity (p&lt / 0.001) during chemotherapy were significantly related with clinical response. On the other hand, mrp1 gene expression and MRP1 positivity were detected in 68% of the patients before the therapy. After chemotherapy, mrp1 expression increased to 84%. Although 80% of the clinically unresponsive patients had mrp1 gene expression, the relation between mrp1 expression and clinical drug response was not strong. Thus, it can be concluded that in locally advanced breast cancer mdr1 gene expression during chemotherapy contributed to clinical unresponsiveness. However, mrp1 gene expression did not correlate strongly with the clinical response. When RT-PCR and immunohistochemistry methods are compared in terms of detection of drug resistance, it seems that both methods gave similar and reliable results.

The development of resistance to chemotherapeutic drugs is the main obstacle to the successful treatment of many cancers, including childhood neuroblastoma, the most common solid tumour of infants. One factor that may play a role in determining response of neuroblastoma tumours to therapeutic agents is the p53 tumour suppressor gene. A number of previous studies have suggested that this tumour suppressor protein is inactive in neuroblastoma due to its cytoplasmic sequestration. This thesis therefore has examined the functionality of p53 and its role in determining drug response of neuroblastoma cells. An initial study was undertaken that characterised an unusually broad multidrug resistance (MDR) phenotype of a neuroblastoma cell line (IMR/KAT100). The results demonstrated that the MDR phenotype of the IMR/KAT100 cells was associated with the acquisition of mutant p53. To explore the role of p53 in drug resistance further, p53-deficient variants in cell lines with wild-type p53 were generated by transduction of p53-suppressive constructs encoding either shRNA or a dominant-negative p53 mutant. Analysis of these cells indicated that: (i) in contrast to previous reports, wild-type p53 was fully functional in all neuroblastoma lines tested, as evidenced by its activation and nuclear translocation in response to DNA damage, transactivation of target genes and control of cell cycle checkpoints; (ii) inactivation of p53 in neuroblastoma cells resulted in establishment of an MDR phenotype; (iii) knockdown of mutant p53 did not revert the drug resistance phenotype, suggesting it is determined by loss of wild-type function rather than gain of mutant function; (iv) p53-dependent cell senescence, the primary response of S-type neuroblastoma cells to DNA damage, is replaced, after p53 inactivation, by mitotic catastrophe and subsequent apoptosis. In contrast to neuroblastoma, p53 suppression had no effect or increased drug susceptibility in several other tumour cell types, indicating the importance of tissue context for p53- mediated modulation of tumour cell sensitivity to treatment. Taken together, these data provide strong evidence for p53 having a role in mediating drug resistance in neuroblastoma and suggest that p53 status may be an important prognostic marker of treatment response in this disease.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os enterococos estão amplamente distribuídos no ambiente. Nos seres humanos, compõem a microbiota do trato gastrintestinal, da cavidade oral e do trato geniturinário. Nas últimas décadas, esses microrganismos se tornaram importantes agentes etiológicos de infecções hospitalares. Uma característica marcante desses microrganismos é a resistência intrínseca a vários antimicrobianos utilizados habitualmente no tratamento de infecções, além de alguns fatores que tem sido relacionado à virulência de enterococos. Este estudo investigou a presença de enterococos em amostras de infecção e colonização de pacientes hospitalizados, profissionais de saúde, dietas hospitalares e manipuladores de alimentos. Foram analisadas 276 amostras de colonização, de quadros de infecção, dietas orais e manipuladores de alimento. Não foram recuperadas amostras dos profissionais de saúde. Todas as amostras foram submetidas a testes convencionais de caracterização do gênero e espécies. Testes de susceptibilidade aos antimicrobianos foram empregados pelo método de disco difusão, além da CIM para vancomicina e teicoplanina. A produção de biofilme e a expressão da gelatinase também foram avaliadas. Os genes de resistência a gentamicina, estreptomicina e vancomicina e os genes de virulência cylA, esp e fsr foram pesquisados pela técnica de PCR. O polimorfismo genético foi determinado por PFGE. A espécie E. faecalis foi a prevalente nas amostras isoladas de colonização e infecção (42,2% e 81,9%, respectivamente). E. casseliflavus (58,9%) foi a mais freqüente dentre as amostras das dietas hospitalares e E. faecium (46,7%) de manipuladores. Dentre as amostras de colonização as maiores taxas de resistência foram observadas para eritromicina (76,3%) e ciprofloxacina (53,9%). Dentre as amostras de infecção, >70% foram resistentes a eritromicina, ciprofloxacina e tetraciclina. Resistência a níveis elevados de gentamcina (HLR-GE) e estreptomicina (HLR-ST) foi detectada em 24,6% e 20,4% das amostras, respectivamente, e todas foram portadoras dos respectivos genes. A maioria das amostras de colonização (52,6%) e infecção (55,7%) foram multirresistentes. A taxa para resistência a níveis elevados de vancomicina foi de 5,2% e todas eram portadoras do gene vanA. Em relação a formação de biofilme, 70,2% foram produtoras, com uma maior freqüência dentre as de infecção. A expressão de gelatinase foi detectada em 28,9% e 44,3% das amostras de colonização e infecção, respectivamente. Nenhuma das amostras isoladas das dietas hospitalares e de manipuladores expressou gelatinase. Nas amostras pertencentes as espécies E. faecalis e E. faecium (n=109) 16,5%, 51,4% e 48,6% apresentaram produtos de amplificação referentes aos genes cylA, esp e fsr, respectivamente. A análise do polimorfismo genético revelou uma extensa diversidade dentre as amostras pertencentes as espécies E. faecalis e E. faecium, não acarretando um perfil eletroforético prevalente. Entretanto, foi observado um perfil único dentre as amostras de E. gallinarum resistentes a vancomicina (vanA). Este estudo mostrou que amostras de enterococos isoladas de diferentes fontes, não só de quadros infecciosos, podem representar um risco para a população, apontando para uma maior reflexão quanto ao papel desses microrganismos nas infecções humanas, particularmente no ambiente hospitalar. / Enterococci are widespread in the nature. In humans, as in the other animals, gastrointestinal tract, the oral cavity and the genitourinary tract. In recent decades, these microorganisms have emerged as one important of the most pathogen associated with nosocomial infections. They shows intrinsic resistance to several antimicrobial commonly used for treatment of the infections. Several potential virulence factors have been identified in enterococci, but none has been established as having a major contribution to virulence in humans, as well as some factors that has been linked to the virulence of enterococci. We analyzed 276 isolates obtained from colonization, infection, hospital diets and food handlers. The isolates were identified by conventional physiological tests for characterization at genus and species level. Antimicrobial susceptibilities were determined by the disk diffusion test method. CIM to vancomycin and teicoplanin were avayable by E-test. The biofilm production and the expression of gelatinase were also evaluated. The genes for resistance to gentamicin, vancomycin, streptomycin resistance genes as code as determinants virulence cylA, esp and fsr were investigated by PCR. The genetic polymorphism was determined by PFGE. E. faecalis was prevalent species recovered from colonization and infection (42.2% and 81.9%, respectively). E. casseliflavus (58.9%) was frequent species among the hospital diets samples. On the other hand, E. faecium (46.7%) was prevalent in food handlers. Among the colonization isolates the highest rates of resistance were observed to erythromycin (76.3%) and ciprofloxacin (53.9%). Although, >70% of infection isolates were resistant to erythromycin, tetracycline and ciprofloxacin. High level resistance to gentamicin (HLR-GE) and streptomycin (HLR-ST) were detected in 24.6% and 20.4% of the samples, respectively, and these isolates harboured the genes aac(6)-Ie-aph(2)-Ia and aph(2)-Ic. Most strains of colonization (52.6%) and infection (55.7%) were multidrug resistant. High level resistance to vancomycin were detected in 5.2% of isolates harbouring vanA gene. 70.2% of the isolates were biofilm producers, were greater frequency among of infection. The expression of gelatinase was detected in 28.9% and 44.3% of colonization and infection isolates, respectively. None of the isolates recovered from the hospital diets and food handlers expressed gelatinase. In E. faecalis and E. faecium strains (n = 109) 16.5%, 51.4% and 48.6% showed amplification products related cylA, esp and fsr genes, respectively. The analysis of genetic polymorphism showed a wide diversity among the isolates belonging to the E. faecalis and E. faecium species. None prevalent profile was observed. The E. gallinarum vanc1/vanA isolates showed identical PFGE profiles. This study showed that enterococci strains isolated from diferents sources, also represents a potential risk for population, particularly those in hospital environment.

Orientador: José Moacir Marin / Banca: Everlon Cid Rigobelo / Banca: Maria Cristina Monteiro de Souza-Gugelmin / Resumo: O objetivo deste estudo foi investigar a ocorrência de cepas de Escherichia coli produtoras de Shiga toxina (STEC) em queijos mussarela produzidos artesanalmente. Foram analisadas 59 amostras de queijo, produzidas no Vale do Jequitinhonha (Nordeste de Minas Gerais, Brasil). Isolando-se 147 cepas de E. coli e através da técnica de PCR, foram investigadas a presença dos genes da Shiga toxina (stx 1 e stx 2) e da intimina (eae). Dezesseis cepas bacterianas (10,8%) apresentaram o gene stx ( todas portavam o gene stx 1) e 13 delas também se mostraram eae positivas. Os isolados de E. coli foram também examinados para a detecção dos genes codificadores de adesinas (pap, sfa e afa). Não foram identificados nenhum desses genes.Todas as cepas STEC isoladas foram pesquisadas para resistência a 12 agentes antimicrobianos. As resistências predominantes detectadas foram de 37,5% para estreptomicina, 37,5% para a tetraciclina, 31,2% para a ampicilina e 31,2% para a amicacina. A resistência a múltiplas drogas foi encontrada em 5 cepas (31,2%). A presença dos genes codificadores dos fatores de virulência indica que o queijo mussarela produzido artesanalmente pode representar um risco à saúde dos consumidores. / Abstract: The aim of the present study was to investigate the occurrence of Escherichia coli strains presenting the Shiga toxin gene (probably STEC strains) in mussarela cheese produced by artesanal method in the Jequitinhonha Valey (Northeast of Minas Gerais State, Brazil). Fifty-nine cheese samples were analyzed and a hundred forty seven strains of E. coli were isolated. Using the PCR method the strains were screened for the Shiga toxin (stx 1 and stx 2) and the intimin (eae) genes. Sixteen isolates (10,8%) carried the stx gene (all of them showed the stx 1 gene ) and thirteen also presented the eae gene. Using the same method the strains were screened for the presence of pap, afa, and sfa genes, adhesin genes caracteristics of the E. coli extraintestinal pathogenic strains (ExPEC). None of them showed these adhesin genes and could not be classified as an ExPEC strains. The susceptibility of the probably STEC strains to twelve antimicrobial drugs were evaluated. The most important resistance was detected to the streptomycin (37,5%), tetracycline (37,5%), ampicillin (31,2%) and amikacin (31,2%). The multidrug resistance was detected in 5 isolates (31,2%). The presence of coding genes for virulence factors in the E. coli isolates recovered from mussarela cheese produced by artesanal method could represent a risk for the human health. / Mestre

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os enterococos estão amplamente distribuídos no ambiente. Nos seres humanos, compõem a microbiota do trato gastrintestinal, da cavidade oral e do trato geniturinário. Nas últimas décadas, esses microrganismos se tornaram importantes agentes etiológicos de infecções hospitalares. Uma característica marcante desses microrganismos é a resistência intrínseca a vários antimicrobianos utilizados habitualmente no tratamento de infecções, além de alguns fatores que tem sido relacionado à virulência de enterococos. Este estudo investigou a presença de enterococos em amostras de infecção e colonização de pacientes hospitalizados, profissionais de saúde, dietas hospitalares e manipuladores de alimentos. Foram analisadas 276 amostras de colonização, de quadros de infecção, dietas orais e manipuladores de alimento. Não foram recuperadas amostras dos profissionais de saúde. Todas as amostras foram submetidas a testes convencionais de caracterização do gênero e espécies. Testes de susceptibilidade aos antimicrobianos foram empregados pelo método de disco difusão, além da CIM para vancomicina e teicoplanina. A produção de biofilme e a expressão da gelatinase também foram avaliadas. Os genes de resistência a gentamicina, estreptomicina e vancomicina e os genes de virulência cylA, esp e fsr foram pesquisados pela técnica de PCR. O polimorfismo genético foi determinado por PFGE. A espécie E. faecalis foi a prevalente nas amostras isoladas de colonização e infecção (42,2% e 81,9%, respectivamente). E. casseliflavus (58,9%) foi a mais freqüente dentre as amostras das dietas hospitalares e E. faecium (46,7%) de manipuladores. Dentre as amostras de colonização as maiores taxas de resistência foram observadas para eritromicina (76,3%) e ciprofloxacina (53,9%). Dentre as amostras de infecção, >70% foram resistentes a eritromicina, ciprofloxacina e tetraciclina. Resistência a níveis elevados de gentamcina (HLR-GE) e estreptomicina (HLR-ST) foi detectada em 24,6% e 20,4% das amostras, respectivamente, e todas foram portadoras dos respectivos genes. A maioria das amostras de colonização (52,6%) e infecção (55,7%) foram multirresistentes. A taxa para resistência a níveis elevados de vancomicina foi de 5,2% e todas eram portadoras do gene vanA. Em relação a formação de biofilme, 70,2% foram produtoras, com uma maior freqüência dentre as de infecção. A expressão de gelatinase foi detectada em 28,9% e 44,3% das amostras de colonização e infecção, respectivamente. Nenhuma das amostras isoladas das dietas hospitalares e de manipuladores expressou gelatinase. Nas amostras pertencentes as espécies E. faecalis e E. faecium (n=109) 16,5%, 51,4% e 48,6% apresentaram produtos de amplificação referentes aos genes cylA, esp e fsr, respectivamente. A análise do polimorfismo genético revelou uma extensa diversidade dentre as amostras pertencentes as espécies E. faecalis e E. faecium, não acarretando um perfil eletroforético prevalente. Entretanto, foi observado um perfil único dentre as amostras de E. gallinarum resistentes a vancomicina (vanA). Este estudo mostrou que amostras de enterococos isoladas de diferentes fontes, não só de quadros infecciosos, podem representar um risco para a população, apontando para uma maior reflexão quanto ao papel desses microrganismos nas infecções humanas, particularmente no ambiente hospitalar. / Enterococci are widespread in the nature. In humans, as in the other animals, gastrointestinal tract, the oral cavity and the genitourinary tract. In recent decades, these microorganisms have emerged as one important of the most pathogen associated with nosocomial infections. They shows intrinsic resistance to several antimicrobial commonly used for treatment of the infections. Several potential virulence factors have been identified in enterococci, but none has been established as having a major contribution to virulence in humans, as well as some factors that has been linked to the virulence of enterococci. We analyzed 276 isolates obtained from colonization, infection, hospital diets and food handlers. The isolates were identified by conventional physiological tests for characterization at genus and species level. Antimicrobial susceptibilities were determined by the disk diffusion test method. CIM to vancomycin and teicoplanin were avayable by E-test. The biofilm production and the expression of gelatinase were also evaluated. The genes for resistance to gentamicin, vancomycin, streptomycin resistance genes as code as determinants virulence cylA, esp and fsr were investigated by PCR. The genetic polymorphism was determined by PFGE. E. faecalis was prevalent species recovered from colonization and infection (42.2% and 81.9%, respectively). E. casseliflavus (58.9%) was frequent species among the hospital diets samples. On the other hand, E. faecium (46.7%) was prevalent in food handlers. Among the colonization isolates the highest rates of resistance were observed to erythromycin (76.3%) and ciprofloxacin (53.9%). Although, >70% of infection isolates were resistant to erythromycin, tetracycline and ciprofloxacin. High level resistance to gentamicin (HLR-GE) and streptomycin (HLR-ST) were detected in 24.6% and 20.4% of the samples, respectively, and these isolates harboured the genes aac(6)-Ie-aph(2)-Ia and aph(2)-Ic. Most strains of colonization (52.6%) and infection (55.7%) were multidrug resistant. High level resistance to vancomycin were detected in 5.2% of isolates harbouring vanA gene. 70.2% of the isolates were biofilm producers, were greater frequency among of infection. The expression of gelatinase was detected in 28.9% and 44.3% of colonization and infection isolates, respectively. None of the isolates recovered from the hospital diets and food handlers expressed gelatinase. In E. faecalis and E. faecium strains (n = 109) 16.5%, 51.4% and 48.6% showed amplification products related cylA, esp and fsr genes, respectively. The analysis of genetic polymorphism showed a wide diversity among the isolates belonging to the E. faecalis and E. faecium species. None prevalent profile was observed. The E. gallinarum vanc1/vanA isolates showed identical PFGE profiles. This study showed that enterococci strains isolated from diferents sources, also represents a potential risk for population, particularly those in hospital environment.

La Multidrug resistance Protein 1 (MRP1) est impliquée dans le phénotype de résistance multiple aux médicaments (MDR) des cellules cancéreuses. Les substrats physiologiques de MRP1 comprennent notamment le glutathion (GSH). Certains médicaments anti-cancéreux tels que la doxorubicine sont co-transportés avec le glutathion. Pour contourner le phénotype MDR induit par MRP1, nous proposons une nouvelle stratégie thérapeutique basée sur la sensibilité collatérale (SC) des cellules résistantes surexprimant MRP1. Certains composés, comme le vérapamil, provoquent la mort sélective des cellules résistantes (les cellules témoins ne sont pas affectées) en stimulant l'efflux du glutathion médié par MRP1. La déplétion intracellulaire très rapide et très forte du glutathion induit probablement un stress oxydatif déclenchant la mort cellulaire. Nous avons identifié de nouveaux agents de sensibilité collatérale puissants in vitro et nous avons montré l'effet du meilleur composé sur la réduction de la croissance des tumeurs chimiorésistantes chez la souris. Nous avons étudié le mécanisme moléculaire d'action des agents de SC et identifié un résidu, localisé dans une région inattendue, impliqué dans la stimulation de l'efflux de glutathion induit par ces molécules / Multidrug resistance Protein 1 (MRP1) is involved in the multidrug resistance (MDR) phenotype of cancer cells. Physiological substrates of MRP1 include glutathione (GSH) and drugs such as doxorubicin are co-transported with glutathione. To circumvent the MDR phenotype induced by MRP1, we propose a new therapeutic strategy based on collateral sensitivity (CS) of resistant cell expressing MRP1, its overexpression becoming the Achilles heel of the cell. Some compounds, like verapamil, act as MRP1 modulators. They trigger selective death of resistant cells (control cells are not affected) by stimulating MRP1-mediated glutathione efflux. The fast and huge intracellular depletion of glutathione probably induces an oxidative stress triggering cell death. We identified new potent collateral sensitivity agents in vitro and we checked the effect of the strongest compound on reducing resistant tumor growth in nude mice. We studied the molecular mechanism of action of CS agents and identified an unexpected residue involved in the stimulation of glutathione efflux induced by these molecules

Magister Scientiae (Medical Bioscience) - MSc(MBS) / Staphylococcus aureus is a Gram-positive coccus belonging to the Stapylococcaeae family. S. aureus causes a wide range of infections that range from skin infections to lifethreatening infections such as pneumonia and endocarditis and is the major cause of hospital and community-acquired infections. Despite antibiotics being available for the treatment of S.aureus infections, resistance to a number of antibiotics has developed over the years due to their improper and continuous use. S. aureus develops resistance to various drugs via different mechanisms, one of which is the extrusion of the antibiotics through efflux pumps that play a role in its acquisition of multidrug resistance. The ability of methicillin-resistant S.aureus to develop resistance to a variety of antibiotics is causing global concern as treatment options are being limited. Various antimicrobial studies carried out on purified plant-based flavonoids have shown that flavonoids enhance the antibacterial effect of antibiotics. This study analysed antibacterial effects of the antibiotics; tetracycline, ampicillin, methicillin and vancomycin and three flavonoids; chrysin, naringenin and 7-hydroxyflavone, against methicillin-sensitive ATCC 25923 (MSSA) and methicillin-resistant ATCC 33591 (MRSA) S. aureus strains, using the Kirby-Bauer disk diffusion and microtitre microdilution assays. In the Kirby- Bauer assay, the antibiotics demonstrated inhibitory effects on the growth of MSSA ATCC 25923. However MRSA ATCC 33591 was only susceptible to vancomycin, with minimal inhibition zones observed with ampicillin. The flavonoids did not enhance or reduce the antibacterial activities of the antibiotics as the zones of inhibition sizes remained unchanged in the combination studies. Microtitre assay results revealed that naringenin enhanced the antibacterial activities of the antibiotics tetracycline and ampicillin, against MSSA ATCC 25923 and MRSA 33591. This was evident as calculated synergistic ratios by the Abbot formula showed that naringenin had an additive effect. The presence of the efflux pump genes in MSSA ATCC 25923 and MRSA ATCC 33591 was compared using polymerase chain reaction (PCR). The mepA and gyrA genes were identified in both strains whereas sepA was identified in MRSA ATCC 33591. The presence of efflux pump genes in both MSSA ATCC 25923 and MRSA ATCC 33591 also confirmed that the presence or absence of the genes may contribute to antibiotic resistance. The presence of sepA in the MRSA and not the MSSA confirmed that this gene plays a role in conferring drug resistance.

Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Multidrug resistance phosphoglycoprotein (MDR1/P-gp) and breast cancer resistance protein (BCRP) were first isolated in chemoresistant cancer cells and have since been found in a variety of normal tissue, including the placenta. The potential function of MDR1/P-gp and BCRP in the human placenta is to protect the fetus from maternally circulating endogenous steroids and hormones, therapeutic drugs and toxins. The objective of this study was to examine the role of maternal steroids in the regulation of MDR1/P-gp and BCRP in the human placenta. Trophoblast cells were isolated from term placenta tissues and immunohistochemistry, western blot analysis and transport studies were used to determine the effect of maternal steroids on MDR1/P-gp and BCRP regulation. Maternal steroids, present at high concentrations in maternal serum, did not have an effect on BCRP in human syncytiotrophoblast. Estrogen and progesterone did not alter MDR1/P-gp levels in human syncytiotrophoblast, but cortisol significantly decreased MDR1/P-gp levels.

The development of drug resistance during treatment is possibly the most important factor hampering the success of cancer therapy. In order to survive in the presence of chemotherapeutic drugs cells must quickly adapt to their altered environment. This may involve a collective stress response of interacting cells, whose mechanism is not yet clear. In the course of this work we interrogated the conceptual framework used to describe cancer and examined different aspects of drug resistance. While the main focus was on the role of ABC transporters in the rapid acquisition of drug resistance following a short period of drug treatment, the long-term adaptation to continuous drug treatment was also studied. As a tangent to this subject, the possible role of endocytosis in the process of adaptation to continuous presence of drug and subsequent resistance was also assessed. Cancer cell populations inexorably develop resistance to therapeutic treatment. In addition to selection of genetic variants, resistance may arise through two possible non-genetic mechanisms, (1) Darwinian selection of cells occupying (non-genetic) resistant microstates, or (2) Lamarckian instruction, in which cells adopt a resistant (treatment) induced phenotype. To examine the relative contribution of these two mechanisms we studied the population dynamics of leukemic cells (HL60 cell line) following treatment with the mitotic inhibitor vincristine. Single-cell analysis and mathematical modelling of state transition kinetics demonstrated that the appearance of multi-drug resistance phenotype within 24h was overwhelmingly the result of instruction. Transcriptome dynamics pointed towards a genome-wide state transition into a stress response state. Resistance induction correlated with Wnt pathway upregulation and was suppressed by beta-catenin knockdown, revealing a new opportunity for early therapeutic intervention against the development of drug resistance. By addressing the adaptation of the cell culture to prolonged drug treatment we observed that the survivor cells mounted a cellular response that neutralised the cytotoxic stress. That response involved the stabilisation of a transcriptome state that confers drug resistance. Our results suggested that the positive correlation between Wnt signalling and ABC transporters expression is important not only for the short-term survival but also for the enduring MDR phenotype. As we explored population heterogeneity we realised that the dead cells might also help the rest of the population to survive. Thus, our results support the need for examining the role of each population fraction, and ultimately each individual cell, in the overall story of cancer adaptation towards multidrug resistance. Subsequently we examined the differential endocytic behaviour between drug-sensitive and drug-resistant cells. By combining confocal time-lapse microscopy with flow cytometry we demonstrated that fluid-phase endocytosis was reduced in the resistant cells. The differences in the endocytic pathway only became noticeable after MDR1 expression has become constitutive, suggesting another protective role of the ABC transporters. All the results obtained support the idea that acquired drug resistance is not simply the passive selection of pre-existing mutants but can be accelerated by active adaptation. Cancer treatment is a double-edge sword: while the weakest cells die, the survivors cope cell-autonomously with the therapeutic perturbation.