Rachael A Papa

Publications (7)35.54 Total impact

• Source

  Available from: PubMed Central

  Article: Validation of a mouse xenograft model system for gene expression analysis of human acute lymphoblastic leukaemia.

  Amy L Samuels, Violet K Peeva, Rachael A Papa, Marin J Firth, Richard W Francis, Alex H Beesley, Richard B Lock, Ursula R Kees
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  ABSTRACT: Pre-clinical models that effectively recapitulate human disease are critical for expanding our knowledge of cancer biology and drug resistance mechanisms. For haematological malignancies, the non-obese diabetic/severe combined immunodeficient (NOD/SCID) mouse is one of the most successful models to study paediatric acute lymphoblastic leukaemia (ALL). However, for this model to be effective for studying engraftment and therapy responses at the whole genome level, careful molecular characterisation is essential. Here, we sought to validate species-specific gene expression profiling in the high engraftment continuous ALL NOD/SCID xenograft. Using the human Affymetrix whole transcript platform we analysed transcriptional profiles from engrafted tissues without prior cell separation of mouse cells and found it to return highly reproducible profiles in xenografts from individual mice. The model was further tested with experimental mixtures of human and mouse cells, demonstrating that the presence of mouse cells does not significantly skew expression profiles when xenografts contain 90% or more human cells. In addition, we present a novel in silico and experimental masking approach to identify probes and transcript clusters susceptible to cross-species hybridisation. We demonstrate species-specific transcriptional profiles can be obtained from xenografts when high levels of engraftment are achieved or with the application of transcript cluster masks. Importantly, this masking approach can be applied and adapted to other xenograft models where human tissue infiltration is lower. This model provides a powerful platform for identifying genes and pathways associated with ALL disease progression and response to therapy in vivo.
  BMC Genomics 01/2010; 11:256. · 4.07 Impact Factor
• Article: Methotrexate and aminopterin exhibit similar in vitro and in vivo preclinical activity against acute lymphoblastic leukaemia and lymphoma.

  Min H Kang, Narine Harutyunyan, Connor P Hall, Rachael A Papa, Richard B Lock
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  ABSTRACT: Due to the development of neurological toxicity and resistance to methotrexate (MTX), other antifolates have been evaluated for its potential replacement in the treatment of childhood acute lymphoblastic leukaemia (ALL). Aminopterin (AMT) has been suggested to provide clinical advantages over MTX and other antifolates. AMT activity, compared with MTX, was evaluated in ALL and lymphoma preclinical models. The minimum survival fraction at the range of concentrations tested was lower with AMT than with MTX in 3 out of 15 cell lines. Both AMT and MTX significantly extended the event-free survival of mice bearing 3 out of 4 xenografts with equivalent activity.
  British Journal of Haematology 03/2009; 145(3):389-93. · 4.94 Impact Factor
• Article: A xenograft model of infant leukaemia reveals a complex MLL translocation.

  Michelle J Henderson, Seoyeon Choi, Alex H Beesley, David L Baker, Dale Wright, Rachael A Papa, Ashleigh Murch, Lynda J Campbell, Richard B Lock, Murray D Norris, Michelle Haber, Ursula R Kees
  British Journal of Haematology 04/2008; 140(6):716-9. · 4.94 Impact Factor
• Article: A role for altered microtubule polymer levels in vincristine resistance of childhood acute lymphoblastic leukemia xenografts.

  Vivienna Ong, Natalia L M Liem, Michael A Schmid, Nicole M Verrills, Rachael A Papa, Glenn M Marshall, Karen L Mackenzie, Maria Kavallaris, Richard B Lock
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  ABSTRACT: The microtubule-depolymerizing drug, vincristine, is effective in the treatment of acute lymphoblastic leukemia (ALL). Although vincristine resistance mechanisms have been extensively characterized in cell lines, their clinical relevance is poorly understood. The aim of the current study was to define clinically relevant mechanisms of vincristine resistance in a panel of childhood ALL xenografts established in immune-deficient (nonobese diabetic/severe combined immunodeficient) mice. We also studied two independent xenograft sublines that were selected by in vivo vincristine exposure. In vitro vincristine sensitivity determined by a stromal coculture, murine bone marrow stromal cell line (MS-5), assay, but not methyl-thiazolyl-tetrazolium metabolic activity assay, significantly correlated (P = 0.05) with the length of the patients' first remission. Investigations into mechanisms of resistance revealed no association with steady-state vincristine accumulation or increased activity and/or expression of ATP-binding cassette transporters, although increased intracellular levels of polymerized tubulin significantly correlated with resistance (r = 0.85; P = 0.0019). Two xenograft sublines selected by in vivo vincristine exposure exhibited a 2-fold increase in polymerized tubulin levels compared with the parental subline (P < 0.05), reflecting their in vivo vincristine resistance. In this study, a vincristine-resistant xenograft with high levels of polymerized tubulin was relatively sensitive to the microtubule-polymerizing drug paclitaxel. These results indicate that the balance between polymerized and nonpolymerized tubulin may be an important determinant of response to Vinca alkaloid-based chemotherapy regimens in childhood ALL.
  Journal of Pharmacology and Experimental Therapeutics 02/2008; 324(2):434-42. · 3.83 Impact Factor
• Article: Divergent mechanisms of glucocorticoid resistance in experimental models of pediatric acute lymphoblastic leukemia.

  Petra S Bachmann, Rosemary Gorman, Rachael A Papa, Jane E Bardell, Jette Ford, Ursula R Kees, Glenn M Marshall, Richard B Lock
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  ABSTRACT: Cell line models of glucocorticoid resistance in childhood acute lymphoblastic leukemia (ALL) almost invariably exhibit altered glucocorticoid receptor (GR) function. However, these findings are incongruous with those using specimens derived directly from leukemia patients, in which GR alterations are rarely found. Consequently, mechanisms of glucocorticoid resistance in the clinical setting remain largely unresolved. We present a novel paradigm of glucocorticoid resistance in childhood ALL, in which patient biopsies have been directly established as continuous xenografts in immune-deficient mice, without prior in vitro culture. We show that the GRs from six highly dexamethasone-resistant xenografts (in vitro IC(50) >10 micromol/L) exhibit no defects in ligand-induced nuclear translocation and binding to a consensus glucocorticoid response element (GRE). This finding contrasts with five commonly used leukemia cell lines, all of which exhibited defective GRE binding. Moreover, whereas the GRs of dexamethasone-resistant xenografts were transcriptionally active, as assessed by the ability to induce the glucocorticoid-induced leucine zipper (GILZ) gene, resistance was associated with failure to induce the bim gene, which encodes a proapoptotic BH3-only protein. Furthermore, the receptor tyrosine kinase inhibitor, SU11657, completely reversed dexamethasone resistance in a xenograft expressing functional GR, indicating that pharmacologic reversal of glucocorticoid resistance in childhood ALL is achievable.
  Cancer Research 06/2007; 67(9):4482-90. · 7.86 Impact Factor
• Article: Preclinical testing of antileukemic drugs using an in vivo model of systemic disease.

  Richard B Lock, Natalia L Liem, Rachael A Papa
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  ABSTRACT: Acute lymphoblastic leukemia (ALL) is predominantly a disease of the bone marrow that disseminates to multiple organ sites throughout the body and, without aggressive treatment, eventually results in multiorgan failure and death. Experimental models that mimic the dissemination of ALL have been difficult to establish, principally due to the poor engraftment efficiency of normal and malignant human hematopoietic cells in various strains of immune-deficient mice. The recent availability of mouse strains that are even more immunocompromised than established strains such as the nude (nu/nu) or severe combined immunodeficient (SCID) mouse has presented opportunities to establish improved experimental models of human leukemia. In this chapter we outline the methodology to (1) establish continuous xenografts from primary childhood ALL biopsies in nonobese diabetic/SCID (NOD/SCID) mice and (2) utilize these xenograft models of systemic disease to test established and experimental drugs while monitoring leukemia progression in "real time" by serial monitoring of murine peripheral blood. These experimental models will be useful for the preclinical evaluation of novel therapies.
  Methods in molecular medicine 02/2005; 111:323-34.
• Article: Characterization of childhood acute lymphoblastic leukemia xenograft models for the preclinical evaluation of new therapies.

  Natalia L M Liem, Rachael A Papa, Christopher G Milross, Michael A Schmid, Mayamin Tajbakhsh, Seoyeon Choi, Carole D Ramirez, Alison M Rice, Michelle Haber, Murray D Norris, Karen L MacKenzie, Richard B Lock
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  ABSTRACT: Continuous xenografts from 10 children with acute lymphoblastic leukemia (ALL) were established in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. Relative to primary engrafted cells, negligible changes in growth rates and immunophenotype were observed at second and third passage. Analysis of clonal antigen receptor gene rearrangements in 2 xenografts from patients at diagnosis showed that the pattern of clonal variation observed following tertiary transplantation in mice exactly reflected that in bone marrow samples at the time of clinical relapse. Patients experienced diverse treatment outcomes, including 5 who died of disease (median, 13 months; range, 11-76 months, from date of diagnosis), and 5 who remain alive (median, 103 months; range, 56-131 months, following diagnosis). When stratified according to patient outcome, the in vivo sensitivity of xenografts to vincristine and dexamethasone, but not methotrexate, differed significantly (P =.028, P =.029, and P =.56, respectively). The in vitro sensitivity of xenografts to dexamethasone, but not vincristine, correlated significantly with in vivo responses and patient outcome. This study shows, for the first time, that the biologic and genetic characteristics, and patterns of chemosensitivity, of childhood ALL xenografts accurately reflect the clinical disease. As such, they provide powerful experimental models to prioritize new therapeutic strategies for future clinical trials.
  Blood 06/2004; 103(10):3905-14. · 9.90 Impact Factor