M Corbo

University College London, Londinium, England, United Kingdom

Are you M Corbo?

Claim your profile

Publications (8)88.57 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Robust quantitative estimation of average whole cell mitochondrial dysfunction is a useful tool for assessing sensitivity to apoptotic stimuli induced either by novel agents, or following manipulation of apoptotic threshold by pharmacological or functional genomics approaches. We have mathematically modelled the kinetics of whole cell mitochondrial membrane potential depolarisation within a population of cells as a Bernouli transition. An exponential distribution enables the median latency preceding mitochondrial membrane potential dissipation to be derived. The kinetic model can be fitted to in vitro single cell resolution data derived from kinetic flow cytometric studies by non-linear regression. We propose that kinetic determination of cumulative frequency distributions provides a useful approach for estimating apoptosis sensitivity across cell populations over short time-frames.
    APOPTOSIS 04/2005; 10(2):447-52. DOI:10.1007/s10495-005-0818-2 · 3.61 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cholangiocarcinoma cells express high levels of the antiapoptotic proteins Bcl-X(L) and Mcl-1 and are markedly chemo- and radioresistant. Mitochondria have emerged as central players in apoptosis. Antiapoptotic members of the Bcl-2 protein family localise to the outer mitochondrial membrane and regulate mitochondrial release of apoptogenic proteins. Mitochondrial benzodiazepine receptor (mBzR) ligands have been shown to reverse Bcl-2 action and facilitate apoptosis. We evaluated the ability of the mBzR antagonist Pk11195 to overcome preapoptotic mitochondrial dysfunction in Egi-1 and Tfk-1, two human cholangiocarcinoma cell lines expressing high levels of Bcl-X(L) and Mcl-1. Cells growing in culture were used to perform in vitro experiments over 48-96 hours following treatment. The cytotoxic agents used were 5 fluorouracil 10 microM and etoposide (Vp16) 10 microM, together with ultraviolet and 0.5-1 Gy x ray irradiation with or without 75 microM Pk11195. Apoptosis and mitochondrial dysfunction were measured at single cell resolution by flow cytometry using the mitochondrial fluorochrome DiOC6(3). Severe combined immunodeficient non-obese diabetic (SCID-NOD) mice with subcutaneous xenografts using the Egi-1 and Tfk-1 cell lines were treated with etoposide with or without addition of Pk11195 over a 72 hour period during which time the xenograft growth patterns were monitored. In vitro, the effect of Pk11195 on induction of apoptosis in cholangiocarcinoma cells following stimulation by chemotherapy or radiotherapy was found to be both time and dose dependent, with Pk11195 increasing rates of apoptosis by 50-95%. Intraperitoneal administration of Pk11195 in combination with Vp16 was found to increase the growth inhibiting effects of Vp16 on xenografts during the treatment phase. PK11195 75 microM on its own had no intrinsic cytotoxic efficacy. This is the first study to demonstrate that functional antagonism of coexpressed Bcl-X(L) and Mcl-1 proteins using the mBzR antagonist Pk11195 can facilitate apoptosis in cholangiocarcinoma following chemotherapy and radiotherapy.
    Gut 11/2002; 51(4):556-61. · 13.32 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The expression of MRP1 (multidrug resistance protein-1) is associated with chemoresistance and poor prognosis in neuroblastoma. MRP1 antisense oligonucleotides were used in an in vivo mouse-human xenograft model of neuroblastoma to downregulate MRP1. The MRP1 ASO reduced protein levels of MRP1 to an average of 40% of the nil treated controls (p = 0.007). There was significant chemosensitisation to single-agent chemotherapy, VP16 (etoposide), at 1 microg/mL (p = 0.035) and 10 microg/mL (p = 0.02) in comparison to tumours not receiving oligonucleotides. In contrast, MDR1-ASO produced significant chemosensitisation only at 10 microg/mL of VP16 (p = 0.029). No significant chemosensitisation was seen following nonsense oligonucleotides. The downregulation of MRP1 was also associated with an increase in tumour cell death (79% increase in apoptosis index p = 0.0313) and a reduction in cell turnover (42% reduction in mitotic index p = 0.0313), which was not seen with any other oligonucleotide. This new and novel perspective of MRP1 function, which is an apparent involvement in apoptosis and cell cycle progression in neuroblasts, presents a fresh avenue for investigation of the biologic consequences of MRP1 expression that occurs in many tumour cell types. Our work is the first to concurrently explore the effects of downregulation of MRP1 and MDR1 by antisense oligonucleotides in a neuroblastoma xenograft model. It provides rationale for the investigation of therapy adjuvants such as antisense oligonucleotides in the treatment of this malignancy.
    International Journal of Cancer 03/2002; 98(1):128-33. DOI:10.1002/ijc.10159 · 5.01 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Resistance to apoptosis is a major obstacle preventing effective therapy for malignancy. Mitochondria localized anti-death proteins of the Bcl-2 family play a central role in inhibiting apoptosis and therefore present valid targets for novel therapy. The peripheral benzodiazepine receptor (PBR) shares a close physical association with the permeability transition pore complex (PTPC), a pivotal regulator of cell death located at mitochondrial contact sites. In this study we investigated the cytotoxicity of the PBR ligand, PK11195, in the micromolar concentration range. PK11195 induced antioxidant inhibitable collapse of the inner mitochondrial membrane potential (DeltaPsi(m)) and mitochondrial swelling in HL60 human leukaemia cells, but not in SUDHL4 lymphoma cells (which exhibited a higher level of reduced glutathione and relative tolerance to chemotherapy or pro-oxidant induced DeltaPsi(m)dissipation). PK11195 induced the production of hydrogen peroxide that was not inhibited by Bcl-2 transfection, nor depletion of mitochondrial DNA. ROS production was however blocked by protonophore, implicating a requirement for DeltaPsi(m). Our findings suggest that PK11195-induced cytotoxicity relies upon Bcl-2 resistant generation of oxidative stress; a process only observed at concentrations several orders of magnitude higher that required to saturate its receptor.
    British Journal of Cancer 06/2001; 84(10):1397-404. DOI:10.1054/bjoc.2001.1788 · 4.82 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Bcl-XL, a member of the Bcl-2-related anti-apoptosis protein family, antagonizes a diverse range of apoptosis-inducing stimuli by preventing mitochondrial permeability transition, release of apoptogenic factors including cytochrome C, and caspase activation. We have tested the hypothesis that the susceptibility of Bcl-XL-expressing leukaemic cells to apoptosis induced by VP16 (etoposide) can be enhanced by pharmacological downregulation of Bcl-XLin vivo. Two subcutaneous xenograft models of B-cell leukaemia-employing SEMK-2 and BV173 cell lines were established in severe combined immunodeficient/non-obese diabetic mice followed by 14 d of continuous subcutaneous administration of Bcl-XL-specific second generation oligonucleotides ISIS 16009 or ISIS 15999. Tumours were disaggregated, enabling investigation of Bcl-XL expression and apoptosis susceptibility at single-cell resolution using cytofluorimetry. Marked sequence-specific reduction of Bcl-XL was associated with sequence-specific enhancement of VP16-induced mitochondrial permeability transition, caspase-3 activation and loss of membrane asymmetry. A negative correlation between Bcl-XL expression and apoptosis susceptibility was observed, together with a positive correlation with respect to a reduced redox state. Bcl-XL downregulation reduces the threshold for VP16-induced apoptosis by potentiating mitochondrial dysfunction and its sequelae, and therefore presents a novel therapeutic strategy for reversing chemoresistance.
    British Journal of Haematology 02/2001; 112(3):706 - 713. DOI:10.1046/j.1365-2141.2001.02603.x · 4.96 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Chronic myelogenous leukemia is characterized by a clonal expansion of abnormal hematopoietic cells, which eventually replaces normal hematopoiesis. We wanted to test the hypothesis that the growth kinetics of CML and normal hematopoietic cells are different. We compared the growth kinetics and the phenotype of engraftment of chronic phase CML and normal human CD34(+) precursor cells in the bone marrow of immune deficient mice. High levels of engraftment of normal precursors occurred early and consisted of myeloid, erythroid, megakaryocytic, and lymphoid elements. This level and pattern of engraftment were maintained at later assessments. The level of CML cell engraftment was initially much lower, but it increased progressively at late time-points with no indication of a plateau in growth. Early engraftment of CML cells consisted almost entirely of myeloid and mast cells but soon after only mast cells were detectable. Conversely mast cells were infrequent in mice engrafted with normal progenitors. We conclude that in contrast to normal cell engraftment, engraftment of CML cells in NOD/SCID mice is characterized by a slow but progressive myeloid infiltration, which eventually consists almost entirely of mast cells.
    The Hematology Journal 02/2000; 1(5):307-15. DOI:10.1038/sj/thj/6200051 · 1.86 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In vitro studies have provided little consensus on the kinetic abnormality underlying the myeloid expansion of chronic myelogenous leukemia (CML). Transplantation of human CML cells into non-obese diabetic mice with severe immunodeficiency disease (NOD/SCID mice) may therefore be a useful model. A CML cell line (BV173) and peripheral blood cells collected from CML patients in chronic phase (CP), accelerated phase (AP), or blastic phase (BP) were injected into preirradiated NOD/SCID mice. Animals were killed at serial intervals; cell suspensions and/or tissue sections from different organs were studied by immunohistochemistry and/or flow cytometry using antihuman CD45 monoclonal antibodies (MoAbs), and by fluorescence in situ hybridization (FISH) for the BCR-ABL fusion gene. One hour after injection, cells were sequestered in the lungs and liver, but 2 weeks later they were no longer detectable in either site. Similar short-term kinetics were observed using 51Cr-labeled cells. The first signs of engraftment for BV173, AP, and BP cells were detected in the bone marrow (BM) at 4 weeks. At 8 weeks the median percentages of human cells in murine marrow were 4% (range, 1 to 9) for CP, 11% (range, 5 to 36) for AP, 38.5% (range, 18 to 79) for BP, and 54% (range, 31 to 69) for BV173. CP cells progressively infiltrated BM (21%) and spleen (6%) by 18 to 20 weeks; no animals injected with the cell line or BP cells survived beyond 12 weeks. The rate of increase in human cell numbers was higher for BP (7.3%/week) as compared with CP (0.9%/week) and AP (0. 5%/week). FISH analysis with BCR and ABL probes showed that some of the human cells engrafting after injection of CP cells lacked a BCR-ABL gene and were presumably normal. We conclude that CML cells proliferate in NOD/SCID mice with kinetics that recapitulate the phase of the donor's disease, thus providing an in vivo model of CML biology.
    Blood 09/1998; 92(4):1390-6. · 10.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Overexpression of BCL-2 is common in non-Hodgkin lymphoma and leads to resistance to programmed cell death (apoptosis) and promotes tumorigenesis. Antisense oligonucleotides targeted at the open reading frame of the BCL-2 mRNA cause a specific down-regulation of BCL-2 expression which leads to increased apoptosis. Lymphoma grown in laboratory animals responds to BCL-2 antisense oligonucleotides with few toxic effects. We report the first study of BCL-2 antisense therapy in human beings. A daily subcutaneous infusion of 18-base, fully phosporothioated antisense oligonucleotide was administered for 2 weeks to nine patients who had BCL-2-positive relapsed non-Hodgkin lymphoma. Toxicity was scored by the common toxicity criteria, and tumour response was assessed by computed tomography scan. Efficacy was also assessed by quantification of BCL-2 expression; BCL-2 protein levels were measured by flow cytometry in samples from patients. During the course of the study, the daily dose of BCL-2 antisense was increased incrementally from 4.6 mg/m2 to 73.6 mg/m2. No treatment-related toxic effects occurred, apart from local inflammation at the infusion site. In two patients, computed tomography scans showed a reduction in tumour size (one minor, one complete response). In two patients, the number of circulating lymphoma cells decreased during treatment. In four patients, serum concentrations of lactate dehydrogenase fell, and in two of these patients symptoms improved. We were able to measure BCL-2 levels by flow cytometry in the samples of five patients, two of whom had reduced levels of BCL-2 protein. In patients with relapsing non-Hodgkin lymphoma, BCL-2 antisense therapy led to an improvement in symptoms, objective biochemical and radiological evidence of tumour response, and down-regulation of the BCL-2 protein in some patients. Our findings are encouraging and warrant further investigations of BCL-2 antisense therapy in cancer treatment.
    The Lancet 05/1997; 349(9059):1137-41. DOI:10.1016/S0140-6736(96)11103-X · 45.22 Impact Factor

Publication Stats

569 Citations
88.57 Total Impact Points

Institutions

  • 2002
    • University College London
      • Institute of Child Health
      Londinium, England, United Kingdom
  • 1997
    • Institute for Child Health Policy (ICHP)
      • Institute of Child Health
      London, Ohio, United States