• Origin of blood cells and HSC production in the embryo.

      Costa, Guilherme; Kouskoff, Valerie; Lacaud, Georges; Cancer Research UK Stem Cell Hematopoiesis Group, Paterson Institute for Cancer Research, University of Manchester, Wilmslow Road, Manchester M20 4BX, UK; Graduate Program in Areas of Basic and Applied Biology (GABBA), University of Porto, Porto, Portugal. (2012-02-23)
      Hematopoietic stem cells (HSCs) are capable of self-renewal and differentiation into all blood cell types. During adult life, they reside in the bone marrow in a quiescent state. By contrast, in the growing embryo hematopoiesis is sequentially found in several developmental niches. This review provides an overview of the still controversial contribution of each of these embryonic sites to the final pool of adult HSCs and discusses new insights into the cellular origin and the molecular regulation implicated in the generation of blood progenitor cells. A better understanding of HSC development during ontogeny is essential to develop new strategies to amplify HSCs or to generate them from embryonic stem cells or by somatic cell reprogramming.
    • The origin of estrogen receptor alpha-positive and alpha-negative breast cancer.

      Clarke, Robert B; Sims, Andrew H; Howell, Anthony; Breast Biology Group, Division of Cancer Studies, University of Manchester Christie Hospital (NHS) Trust, Manchester, UK. (2008)
    • Origins of breast cancer subtypes and therapeutic implications.

      Sims, Andrew H; Howell, Anthony; Howell, Sacha J; Clarke, Robert B; Breast Biology Group, Paterson Institute for Cancer Research, University of Manchester, Manchester, UK. (2007-09)
      This Review summarizes and evaluates the current evidence for the cellular origins of breast cancer subtypes identified by different approaches such as histology, molecular pathology, genetic and gene-expression analysis. Emerging knowledge of the normal breast cell types has led to the hypothesis that the subtypes of breast cancer might arise from mutations or genetic rearrangements occurring in different populations of stem cells and progenitor cells. We describe the common distinguishing features of these breast cancer subtypes and explain how these features relate both to prognosis and to selection of the most appropriate therapy. Recent data indicate that breast tumors may originate from cancer stem cells. Consequently, inhibition of stem-cell self-renewal pathways should be explored because of the likelihood that residual stem cells might be resistant to current therapies.
    • Oropharyngeal cancer: United Kingdom National Multidisciplinary Guidelines

      Mehanna, H; Evans, M; Beasley, M; Chatterjee, S; Dilkes, M; Homer, Jarrod J; O'Hara, J; Robinson, M; Shaw, R; Sloan, P; et al. (2016-05-12)
      Abstract This is the official guideline endorsed by the specialty associations involved in the care of head and neck cancer patients in the UK. There has been significant debate in the management of oropharyngeal cancer in the last decade, especially in light of the increased incidence, clarity on the role of the human papilloma virus in this disease and the treatment responsiveness of the human papilloma virus positive cancers. This paper discusses the evidence base pertaining to the management of oropharyngeal cancer and provides recommendations on management for this group of patients receiving cancer care. Recommendations • Cross-sectional imaging is required in all cases to complete assessment and staging. (R) • Magnetic resonance imaging is recommended for primary site and computed tomography scan for neck and chest. (R) • Positron emission tomography combined with computed tomography scanning is recommended for the assessment of response after chemoradiotherapy, and has a role in assessing recurrence. (R) • Examination under anaesthetic is strongly recommended, but not mandatory. (R) • Histological diagnosis is mandatory in most cases, especially for patients receiving treatment with curative intent. (R) • Oropharyngeal carcinoma histopathology reports should be prepared according to The Royal College of Pathologists Guidelines. (G) • Human papilloma virus (HPV) testing should be carried out for all oropharyngeal squamous cell carcinomas as recommended in The Royal College of Pathologists Guidelines. (R) • Human papilloma virus testing for oropharyngeal cancer should be performed within a diagnostic service where the laboratory procedures and reporting standards are quality assured. (G) • Treatment options for T1–T2 N0 oropharyngeal squamous cell carcinoma include radical radiotherapy or transoral surgery and neck dissection (with post-operative (chemo)radiotherapy if there are adverse pathological features on histological examination). (R) • Transoral surgery is preferable to open techniques and is associated with good functional outcomes in retrospective series. (R) • If treated surgically, neck dissection should include levels II–IV and possibly level I. Level IIb can be omitted if there is no disease in level IIa. (R) • If treated with radiotherapy, levels II–IV should be included, and possibly level Ib in selected cases. (R) • Altering the modalities of treatment according to HPV status is currently controversial and should be undertaken only in clinical trials. (R) • Where possible, patients should be offered the opportunity to enrol in clinical trials in the field. (G)
    • Oropharyngeal squamous cell carcinoma treatment in the era of immune checkpoint inhibitors

      Stern, Peter L; Dalianis, T.; Manchester Cancer Research Centre, University of Manchester, Manchester M20 4GJ (2021)
      While head and neck squamous cell carcinomas (HNSCC) are marginally decreasing due to the reduction in exposure to the major risk factors, tobacco and alcohol, the incidence of high-risk human papillomavirus (HPV)-positive oropharynx squamous cell carcinomas (OPSCC), especially those in the tonsil and base of tongue subsites, are increasing. Patients with the latter are younger, display a longer overall survival, and show a lower recurrence rate after standard-of-care treatment than those with HPV-negative OPSCC. This may reflect an important role for immune surveillance and control during the natural history of the virally driven tumour development. Immune deviation through acquisition of immune-suppressive factors in the tumour microenvironment (TME) is discussed in relation to treatment response. Understanding how the different immune factors are integrated in the TME battleground offers opportunities for identifying prognostic biomarkers as well as novel therapeutic strategies. OPSCC generally receive surgery or radiotherapy for early-stage tumour treatment, but many patients present with locoregionally advanced disease requiring multimodality therapies which can involve considerable complications. This review focuses on the utilization of newly emerged immune checkpoint inhibitors (PD-1/PD-L1 pathway) for treatment of HNSCC, in particular HPV-positive OPSCC, since they could be less toxic and more efficacious. PD-1/PD-L1 expression in the TME has been extensively investigated as a biomarker of patient response but is yet to provide a really effective means for stratification of treatment. Extensive testing of combinations of therapeutic approaches by types and sequencing will fuel the next evolution of treatment for OPSCC.
    • Orphan macrodomain protein (human C6orf130) is an O-acyl-ADP-ribose deacylase: solution structure and catalytic properties.

      Peterson, F C; Chen, D; Lytle, B L; Rossi, Marianna N; Ahel, I; Denu, J M; Volkman, B F; Department of Biochemistry and Center for Eukaryotic Structural Genomics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA. (2011-10-14)
      Post-translational modification of proteins/histones by lysine acylation has profound effects on the physiological function of modified proteins. Deacylation by NAD(+)-dependent sirtuin reactions yields as a product O-acyl-ADP-ribose, which has been implicated as a signaling molecule in modulating cellular processes. Macrodomain-containing proteins are reported to bind NAD(+)-derived metabolites. Here, we describe the structure and function of an orphan macrodomain protein, human C6orf130. This unique 17-kDa protein is a stand-alone macrodomain protein that occupies a distinct branch in the phylogenic tree. We demonstrate that C6orf130 catalyzes the efficient deacylation of O-acetyl-ADP-ribose, O-propionyl-ADP-ribose, and O-butyryl-ADP-ribose to produce ADP-ribose (ADPr) and acetate, propionate, and butyrate, respectively. Using NMR spectroscopy, we solved the structure of C6orf130 in the presence and absence of ADPr. The structures showed a canonical fold with a deep ligand (ADPr)-binding cleft. Structural comparisons of apo-C6orf130 and the ADPr-C6orf130 complex revealed fluctuations of the β(5)-α(4) loop that covers the bound ADPr, suggesting that the β(5)-α(4) loop functions as a gate to sequester substrate and offer flexibility to accommodate alternative substrates. The ADPr-C6orf130 complex identified amino acid residues involved in substrate binding and suggested residues that function in catalysis. Site-specific mutagenesis and steady-state kinetic analyses revealed two critical catalytic residues, Ser-35 and Asp-125. We propose a catalytic mechanism for deacylation of O-acyl-ADP-ribose by C6orf130 and discuss the biological implications in the context of reversible protein acylation at lysine residues.
    • ORY-1001, a potent and selective covalent KDM1A inhibitor, for the treatment of acute leukemia.

      Maes, T; Mascaró, C; Tirapu, I; Estiarte, A; Ciceri, F; Lunardi, S; Guibourt, N; Perdones, A; Lufino, M; Somervaille, Tim C P; et al. (2018-03-12)
      The lysine-specific demethylase KDM1A is a key regulator of stem cell potential in acute myeloid leukemia (AML). ORY-1001 is a highly potent and selective KDM1A inhibitor that induces H3K4me2 accumulation on KDM1A target genes, blast differentiation, and reduction of leukemic stem cell capacity in AML. ORY-1001 exhibits potent synergy with standard-of-care drugs and selective epigenetic inhibitors, reduces growth of an AML xenograft model, and extends survival in a mouse PDX (patient-derived xenograft) model of T cell acute leukemia. Surrogate pharmacodynamic biomarkers developed based on expression changes in leukemia cell lines were translated to samples from patients treated with ORY-1001. ORY-1001 is a selective KDM1A inhibitor in clinical trials and is currently being evaluated in patients with leukemia and solid tumors.
    • Osteoblasts contribute to a protective niche that supports melanoma cell proliferation and survival

      Ferguson, J; Wilcock, DJ; McEntegart, S; Badrock, AP; Levesque, M; Dummer, R; Wellbrock, Claudia; Smith, M P; Manchester Cancer Research Centre, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester (2019)
      Melanoma is the deadliest form of skin cancer; a primary driver of this high level of morbidity is the propensity of melanoma cells to metastasize. When malignant tumours develop distant metastatic lesions the new local tissue niche is known to impact on the biology of the cancer cells. However, little is known about how different metastatic tissue sites impact on frontline targeted therapies. Intriguingly, melanoma bone lesions have significantly lower response to BRAF or MEK inhibitor therapies. Here, we have investigated how the cellular niche of the bone can support melanoma cells by stimulating growth and survival via paracrine signalling between osteoblasts and cancer cells. Melanoma cells can enhance the differentiation of osteoblasts leading to increased production of secreted ligands, including RANKL. Differentiated osteoblasts in turn can support melanoma cell proliferation and survival via the secretion of RANKL that elevates the levels of the transcription factor MITF, even in the presence of BRAF inhibitor. By blocking RANKL signalling, either via neutralizing antibodies, genetic alterations or the RANKL receptor inhibitor SPD304, the survival advantage provided by osteoblasts could be overcome.
    • The osteogenic capacity of bone narrow cells.

      Eaglesom, C; Ashton, B; Allen, Terence D; Owen, M; MRC Bone Research Laboratory, Nuffield Orthopaedic Centre, Oxford OX3 7LD, U.K. (1980)
    • Outcomes of patients with childhood B-cell precursor acute lymphoblastic leukaemia with late bone marrow relapses: long-term follow-up of the ALLR3 open-label randomised trial

      Parker, Catriona; Krishnan, Shekhar; Hamadeh, L; Irving, JAE; Kuiper, RP; Revesz, T; Hoogerbrugge, P; Hancock, J; Sutton, R; Moorman, AV; et al. (2019)
      BACKGROUND: The ALLR3 trial investigated outcomes of children with B-cell precursor acute lymphoblastic leukaemia who had late bone marrow relapses. We analysed long-term follow-up outcomes of these patients. METHODS: ALLR3 was an open-label randomised clinical trial that recruited children aged 1-18 years with B-cell precursor acute lymphoblastic leukaemia who had late bone marrow relapses. Eligible patients were recruited from centres in Australia, Ireland, the Netherlands, New Zealand, and the UK. Patients were randomly assigned from Jan 31, 2003, to Dec 31, 2007, and the trial closed to recruitment on Oct 31, 2013. Randomly assigned patients were allocated to receive either idarubicin or mitoxantrone in induction by stratified concealed randomisation; after randomisation stopped in Dec 31, 2007, all patients were allocated to receive mitoxantrone. After three blocks of therapy, patients with high minimal residual disease (?10-4 cells) at the end of induction were allocated to undergo allogeneic stem-cell transplantation and those with low minimal residual disease (<10-4 cells) at the end of induction were allocated to receive chemotherapy. Minimal residual disease level was measured by real-time quantitative PCR analysis of immunoglobulin and T-cell receptor gene rearrangements. The primary endpoint of the original ALLR3 clinical trial was progression-free survival of randomly assigned patients. The primary endpoint of this long-term follow-up analysis was progression-free survival of patients with late bone marrow relapses stratified by minimal residual disease level. Outcomes were correlated with age, site, time to recurrence, and genetic subtypes, and analysed by both intention to treat and actual treatment received. This trial is registered on the ISRCTN registry, number ISRCTN45724312, and on ClinicalTrials.gov, number NCT00967057. FINDINGS: Between Feb 2, 2003, and Oct 28, 2013, 228 patients with B-cell precursor acute lymphoblastic leukaemia and late bone marrow relapses were treated. After a median follow-up of 84 months (IQR 48-109), progression-free survival of all randomly assigned patients was 60% (95% CI 54-70). 220 patients achieved second complete remission, and minimal residual disease was evaluable in 192 (87%). 110 patients with late bone marrow relapses and high minimal residual disease at the end of induction were allocated to undergo stem-cell transplantation, and 82 patients with low minimal residual disease at the end of induction were allocated to receive chemotherapy. In the patients allocated to undergo stem-cell transplantation, four relapses and three deaths were reported before the procedure, and 11 patients were not transplanted. Of the 92 patients transplanted, 58 (63%) remained in second complete remission, 13 (14%) died of complications, and 21 (23%) relapsed after stem-cell transplantation. In patients allocated to receive chemotherapy, one early treatment-related death was reported and 11 patients were transplanted. Of the 70 patients who continued on chemotherapy, 49 (70%) remained in second complete remission, two (3%) died of complications, and 19 (27%) relapsed. Progression-free survival at 5 years was 56% (95% CI 46-65) in those with high minimal residual disease and 72% (60-81) in patients with low minimal residual disease (p=0·0078). Treatment-related serious adverse events were not analysed in the long-term follow-up. INTERPRETATION: Patients with B-cell precursor acute lymphoblastic leukaemia with late bone marrow relapses and low minimal residual disease at end of induction had favourable outcomes with chemotherapy without undergoing stem-cell transplantation. Patients with high minimal residual disease benefited from stem-cell transplantation, and targeted therapies might offer further improvements in outcomes for these patients. FUNDING: Bloodwise (Formerly Leukaemia and Lymphoma Research) UK, Cancer Research UK, Sporting Chance Cancer Foundation, National Health and Medical Research Council Australia, KindreneKankervrij Netherlands, European Union Seventh Framework Programme, India Alliance Wellcome DBT Margdarshi Fellowship.
    • Outstanding issues in radiation dose-fractionation studies.

      Hendry, Jolyon H; Mackay, Ranald I; Roberts, Stephen A; Slevin, Nicholas J; Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester, UK. (1998-04)
    • Ovarian cancer family and prophylactic choices.

      Evans, D Gareth R; Ribeiro, G; Warrell, D; Donnai, D; CRC Department of Cancer Genetics, Paterson Institute for Cancer Research, Christie Hospital, Manchester. (1992-06)
      A subject from a family with ovarian cancer who has developed bilateral medullary carcinoma of the breast at the age of 40 is presented. The family is consistent with dominant inheritance of ovarian cancer and 12 female family members at 12.5%, 25%, and 50% risk, including our case, have undergone bilateral prophylactic oophorectomy and been given hormone replacement therapy. Despite the risk of further primary tumours of the breast our patient chose to have treatment with wide excision and radiotherapy. The implications for screening, prophylaxis, and hormone replacement therapy for this family are discussed.
    • Ovarian failure following abdominal irradiation in childhood: the radiosensitivity of the human oocyte.

      Wallace, W Hamish B; Shalet, Stephen M; Hendry, Jolyon H; Morris-Jones, P H; Gattamaneni, Rao; Department of Endocrinology, Christie Hospital, Manchester. (1989-11)
      Ovarian function has been studied sequentially since 1975 in 19 patients treated in childhood for an intra-abdominal tumour with surgery and whole abdominal radiotherapy (total dose 30 Gy). Eleven patients received chemotherapeutic agents that are not known to cause gonadal dysfunction. All but one patient have developed ovarian failure with persistently elevated gonadotrophin levels (FSH and LH greater than 32 IU/litre) and low serum oestradiol values (less than 40 pmol/litre) before the age of 16 years. The majority (n = 12) did not progress beyond breast stage 1 without sex steroid replacement therapy. As the number of oocytes within the ovary declines exponentially by atresia from approximately 2,000,000 at birth to approximately 2000 at the menopause, we have been able to estimate that the LD50 for the human oocyte does not exceed 4 Gy.
    • Ovarian steroids and control of proliferation in the normal human breast.

      Anderson, Elizabeth; Clinical Research Department, Christie Hospital NHS Trust, Wilmslow Road, Manchester, UK. eanderson@picr.man.ac.uk (2001-08)
      Until recently, there has been considerable uncertainty as to how, or even which of the ovarian steroids influence human breast luminal epithelial cell proliferation. It is important that this is known because increased proliferative activity of this particular cell population is associated with increased risk of breast cancer. Review of the available literature suggests that while oestradiol is the major steroid mitogen in pre-menopausal women, the role of progesterone becomes more significant after the menopause when oestradiol levels are reduced. Moreover, recent studies have given new insights into the mechanisms by which oestradiol and progesterone exert their effects. This knowledge may allow development of new strategies for predicting breast cancer risk or preventing the disease.
    • Ovarian steroids and the human breast: regulation of stem cells and cell proliferation.

      Clarke, Robert B; Breast Biology Group, CR-UK Department of Medical Oncology, University of Manchester, Christie Hospital, Manchester, M20 4BX, UK. rclarke@picr.man.ac.uk (2006-07-20)
      Ovarian steroidal control of mammary gland proliferation and differentiation is not well defined in the human. We therefore developed the athymic nude mouse model in which intact normal human breast tissue is xenografted subcutaneously and treated with human physiological serum levels of oestrogen (E) and/or progesterone (P). We showed that: (i) E, and not P, is the major steroid hormone inducing proliferation of epithelial cells in the adult non-pregnant, non-lactating breast; (ii) E induces progesterone receptor (PR) expression; and (iii) PR expression is maximally induced at low E concentrations while a higher amount of E was required to induce proliferation. Using double label immuno-fluorescence, we demonstrated that cells expressing the oestrogen receptor-alpha (ER alpha) invariably contained the PR but that steroid receptor expression and cell proliferation (Ki67 antigen) were dissociated. Recently, we have demonstrated that some ER alpha/PR-positive epithelial cells are quiescent breast stem cells suggesting that they act as "steroid hormone sensors" that secrete paracrine factors to regulate the proliferative activity of adjacent ER alpha/PR-negative epithelial cells. The dissociation between steroid receptor expression and cell proliferation in normal epithelium was lost at an early stage in ER alpha/PR-positive breast tumour formation perhaps indicating that they arise from deregulation of the normally quiescent breast stem cells.
    • Ovarian tissue harvested from lymphoma patients to preserve fertility may be safe for autotransplantation.

      Kim, S Samuel; Radford, John A; Harris, Martin; Varley, Jennifer; Rutherford, Anthony J; Lieberman, Brian A; Shalet, Stephen M; Gosden, Roger; Centre for Reproduction, Growth and Development, University of Leeds, Leeds, UK. medssk@att.net (2001-10)
      BACKGROUND: Ovarian failure is a common sequel to chemo/radiotherapy in patients successfully treated for cancer. Harvesting, cryopreserving and subsequently re-implanting ovarian cortical grafts can be used to re-establish reproductive potential in women with cancer. The safety issue, however, is of great concern because residual disease in autografted ovarian tissues might cause recrudescence of disease. METHODS: A total of 30 non-obese diabetic severe combined immunodeficient (NOD/LtSz-SCID) mice were individually xenografted s.c. with frozen-thawed ovarian tissue from 18 patients with lymphoma [13 Hodgkin's lymphoma (HL) and 5 non-Hodgkin's lymphoma (NHL)]. The animals were autopsied at 16 weeks, or earlier if cachectic. The xenograft, liver, spleen, sternum, para-aortic lymph nodes and thymus were prepared for histology, immunohistochemistry and human DNA microsatellite analysis. RESULTS: None of the animals grafted with ovarian tissue from lymphoma patients developed disease. However, all 3 animals grafted with lymph node tissue from an NHL patient developed B-cell lymphomas that were confirmed as human in origin by DNA microsatellite analysis. CONCLUSION: Ovarian tissue harvested before high-dose chemotherapy for HL or NHL may not carry a risk of disease transmission by autotransplantation, although the possibility is difficult to exclude completely.
    • Overcoming resistance to BRAF inhibitors.

      Arozarena, I; Wellbrock, Claudia; Navarrabiomed-Fundacion Miguel Servet-Idisna, Complejo Hospitalario de Navarra, Pamplona, Spain (2017-10)
      The discovery of activating mutations in the serine/threonine (S/T) kinase BRAF followed by a wave of follow-up research manifested that the MAPK-pathway plays a critical role in melanoma initiation and progression. BRAF and MEK inhibitors produce an unparalleled response rate in melanoma, but it is now clear that most responses are transient, and while some patients show long lasting responses the majority progress within 1 year. In accordance with the key role played by the MAPK-pathway in BRAF mutant melanomas, disease progression is mostly due to the appearance of drug-resistance mechanisms leading to restoration of MAPK-pathway activity. In the present article we will review the development, application and clinical effects of BRAF and MEK inhibitors both, as single agent and in combination in the context of targeted therapy in melanoma. We will then describe the most prominent mechanisms of resistance found in patients progressed on these targeted therapies. Finally we will discuss strategies for further optimizing the use of MAPK inhibitors and will describe the potential of alternative combination therapies to either delay the onset of resistance to MAPK inhibitors or directly target specific mechanisms of resistance to BRAF/MEK inhibitors.
    • Overexpression of NAD(P)H:quinone oxidoreductase 1 in human reproductive system.

      Zappa, Francesco; Ward, Timothy H; Butler, John; Pedrinis, Ennio; McGown, Alan T; CRC Dept. of Drug Development, Paterson Institute for Cancer Research, Wilmslow Road, Manchester M20 4BX, United Kingdom. Fzappa@picr.man.ac.uk (2001-09)
      NAD(P)H:quinone oxidoreductase 1 (NQO1; DT-diaphorase; DTD) is a two-electron reductase that efficiently bioactivates compounds of the quinone family, such as mitomycin C. The observation that DTD is overexpressed in many cancerous tissues compared to normal tissues has provided us with a potentially selective target that can be exploited in the design of novel anticancer agents. Because of the relative lack of information on the cell-specific expression of DTD, the purpose of this study was to perform a body mapping of its normal distribution. Tissue samples from various components of the human reproductive system were analyzed by immunohistochemistry. We found strong expression of this enzyme in testicular stromal cells (Leydig cells) and in the epithelium of epididymis, ductuli efferentes, and Fallopian tube. These results suggest that DTD-bioactivated quinones could be responsible for a selective toxicity on these components of the reproductive system and cause clinical problems due to testosterone deficiency and infertility. This observation needs to be investigated in preclinical evaluation of new anticancer quinones and in patients treated with these compounds. (J Histochem Cytochem 49:1187-1188, 2001)
    • Oxaliplatin responses in colorectal cancer cells are modulated by CHK2 kinase inhibitors.

      Pires, I M; Ward, Timothy H; Dive, Caroline; Clinical and Experimental Pharmacology Group, Paterson Institute for Cancer Research, University of Manchester, Manchester, UK. (2010-03)
      BACKGROUND AND PURPOSE: Checkpoint kinase 2 (CHK2) is activated by DNA damage and can contribute to p53 stabilization, modulating growth arrest and/or apoptosis. We investigated the contribution of CHK2 to oxaliplatin-mediated toxicity in a colorectal cancer model. EXPERIMENTAL APPROACH: We evaluated the ability of CHK2 small molecule inhibitors to potentiate oxaliplatin-induced toxicity. The role of CHK2 in oxaliplatin-induced apoptosis was investigated in HCT116 cells that were wild-type (WT) or KO for CHK2. Small molecule inhibitors of CHK2 were used in combination studies with oxaliplatin in this cell model. KEY RESULTS: In oxaliplatin-treated CHK2 KO cells, accelerated apoptosis was accompanied by attenuated p53 stabilization and p21(WAF-1) up-regulation correlating with increased Bax expression, cytochrome c release and elevated caspase activity. The higher levels of apoptosis in CHK2 KO cells were restored to control (WT) levels when CHK2 was re-introduced. This 'uncoupling' of p53 stabilization and Bax up-regulation in CHK2 KO cells suggested oxaliplatin-induced apoptosis was due to a p53-independent response. Combination studies revealed that CHK2 inhibitor II or debromohymenialdisine antagonized the responses to oxaliplatin. This inhibitory effect correlated with decreases in apoptosis, p53 stabilization and DNA inter-strand cross-link formation, and was dependent on the presence (but not activity) of CHK2. CONCLUSIONS AND IMPLICATIONS: Combinations of CHK2 inhibitors with oxaliplatin should further sensitize cells to oxaliplatin treatment. However, these inhibitors produced an antagonistic effect on the response to oxaliplatin, which was reversed on the re-introduction of CHK2. These observations may have implications for the use of oxaliplatin in colorectal cancer therapy in combination with therapies targeting CHK2.