Pamela Kearns

The PARP inhibitor olaparib induces significant killing of ATM-deficient lymphoid tumor cells in vitro and in vivo

The Ataxia Telangiectasia Mutated (ATM) gene is frequently inactivated in lymphoid malignancies such as chronic lymphocytic leukemia (CLL), T-prolymphocytic leukemia (T-PLL), and mantle cell lymphoma (MCL) and is associated with defective apoptosis in response to alkylating agents and purine analogues. ATM mutant cells exhibit impaired DNA double strand break repair. Poly (ADP-ribose) polymerase (PARP) inhibition that imposes the requirement for DNA double strand break repair should selectively sensitize ATM-deficient tumor cells to killing. We investigated in vitro sensitivity to the poly (ADP-ribose) polymerase inhibitor olaparib (AZD2281) of 5 ATM mutant lymphoblastoid cell lines (LCL), an ATM mutant MCL cell line, an ATM knockdown PGA CLL cell line, and 9 ATM-deficient primary CLLs induced to cycle and observed differential killing compared with ATM wildtype counterparts. Pharmacologic inhibition of ATM and ATM knockdown confirmed the effect was ATM-dependent and mediated through mitotic catastrophe independently of apoptosis. A nonobese diabetic/severe combined immunodeficient (NOD/SCID) murine xenograft model of an ATM mutant MCL cell line demonstrated significantly reduced tumor load and an increased survival of animals after olaparib treatment in vivo. Addition of olaparib sensitized ATM null tumor cells to DNA-damaging agents. We suggest that olaparib would be an appropriate agent for treating refractory ATM mutant lymphoid tumors.

Expression of CD133 on leukemia-initiating cells in childhood ALL

Optimization of therapy for childhood acute lymphoblastic leukemia (ALL) requires a greater understanding of the cells that proliferate to maintain this malignancy because a significant number of cases relapse, resulting from failure to eradicate the disease. Putative ALL stem cells may be resistant to therapy and subsequent relapses may arise from these cells. We investigated expression of CD133, CD19, and CD38 in pediatric B-ALL. Cytogenetic and molecular analyses demonstrated that karyotypically aberrant cells were present in both CD133(+)/CD19(+) and CD133(+)/CD19(-) subfractions, as were most of the antigen receptor gene rearrangements. However, ALL cells capable of long-term proliferation in vitro and in vivo were derived from the CD133(+)/CD19(-) subfraction. Moreover, these CD133(+)/CD19(-) cells could self-renew to engraft serial nonobese diabetic-severe combined immunodeficient recipients and differentiate in vivo to produce leukemias with similar immunophenotypes and karyotypes to the diagnostic samples. Furthermore, these CD133(+)/CD19(-) ALL cells were more resistant to treatment with dexamethasone and vincristine, key components in childhood ALL therapy, than the bulk leukemia population. Similar results were obtained using cells sorted for CD133 and CD38, with only the CD133(+)/CD38(-) subfraction demonstrating xenograft repopulating capacity. These data suggest that leukemia-initiating cells in childhood B-ALL have a primitive CD133(+)/CD19(-) and CD38(-) phenotype.

The EBV oncogene LMP1 protects lymphoma cells from cell death through the collagen-mediated activation of DDR1

The malignant Hodgkin and Reed-Sternberg (HRS) cells of Hodgkin lymphoma are surrounded by a tumor microenvironment that is composed of a variety of cell types, as well as noncellular components such as collagen. Although HRS cells harbor oncogenic Epstein-Barr virus (EBV) in approximately 50% of cases, it is not known if the tumor microenvironment contributes to EBV-driven lymphomagenesis. We show that expression of the EBV-encoded latent membrane protein-1 (LMP1) in primary human germinal center B cells, the presumed progenitors of HRS cells, upregulates discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase activated by collagen. We also show that HRS cells intimately associated with collagen frequently overexpress DDR1 and that short-term exposure to collagen is sufficient to activate DDR1 in Hodgkin lymphoma-derived cell lines. The ectopic expression of DDR1 significantly increased the survival of collagen-treated DG75 Burkitt lymphoma cells, following etoposide treatment. Conversely, knockdown of DDR1 significantly decreased the survival of collagen-treated L428 Hodgkin lymphoma cells in the absence of specific apoptotic stimulus, suggesting that DDR1 also influences baseline survival. Our results identify a hitherto unknown function for collagen in protecting Hodgkin lymphoma cells from apoptosis and suggest an important contribution of the tumor microenvironment in promoting the oncogenic effects of EBV.

BET inhibition as a single or combined therapeutic approach in primary paediatric B-precursor acute lymphoblastic leukaemia

Paediatric B-precursor ALL is a highly curable disease, however, treatment resistance in some patients and the long-term toxic effects of current therapies pose the need for more targeted therapeutic approaches. We addressed the cytotoxic effect of JQ1, a highly selective inhibitor against the transcriptional regulators, bromodomain and extra-terminal (BET) family of proteins, in paediatric ALL. We showed a potent in vitro cytotoxic response of a panel of primary ALL to JQ1, independent of their prognostic features but dependent on high MYC expression and coupled with transcriptional downregulation of multiple pro-survival pathways. In agreement with earlier studies, JQ1 induced cell cycle arrest. Here we show that BET inhibition also reduced c-Myc protein stability and suppressed progression of DNA replication forks in ALL cells. Consistent with c-Myc depletion and downregulation of pro-survival pathways JQ1 sensitised primary ALL samples to the classic ALL therapeutic agent dexamethasone. Finally, we demonstrated that JQ1 reduces ALL growth in ALL xenograft models, both as a single agent and in combination with dexamethasone. We conclude that targeting BET proteins should be considered as a new therapeutic strategy for the treatment of paediatric ALL and particularly those cases that exhibit suboptimal responses to standard treatment.

Dasatinib in Children and Adolescents With Relapsed or Refractory Leukemia: Results of the CA180-018 Phase I Dose-Escalation Study of the Innovative Therapies for Children With Cancer Consortium

PURPOSE Dasatinib is a potent BCR-ABL inhibitor with proven efficacy in adults with newly diagnosed chronic myeloid leukemia (CML) in chronic phase (CP) and in imatinib-resistant/intolerant disease. This phase I study of the Innovative Therapies for Children with Cancer Consortium assessed dasatinib safety and efficacy in pediatric patients. PATIENTS AND METHODS Escalating once-daily dasatinib doses (60 to 120 mg/m(2)) were administered to children (n = 58) with (i) imatinib-pretreated CML or Philadelphia chromosome (Ph)-positive acute lymhoblastic leukemia (ALL) and (ii) treatment-refractory Ph-negative ALL or acute myeloid leukemia (AML). RESULTS Dasatinib safety and efficacy profiles compared favorably with those in adults. The most common drug-related nonhematologic adverse events were nausea (31%, all grades; 2%, grade 3 to 4), headache (22%, 3%), diarrhea (21%, 0%), and vomiting (17%, 2%). Of 17 patients with CML-CP, 14 (82%) achieved complete cytogenetic response (CCyR) and eight (47%) achieved major molecular response. After ≥ 24 months of follow-up, median complete hematologic response (CHR) and major cytogenetic response (MCyR) durations were not reached. Of 17 patients with advanced-phase CML or Ph-positive ALL, six (35%) achieved confirmed CHR and 11 (65%) achieved CCyR. Median MCyR duration was 4.6 months (95% CI, 2.1 to 17.4 months). No patient with Ph-negative ALL or AML responded. Dasatinib pediatric pharmacokinetic parameters were comparable with those in adult studies, showing rapid absorption (time to reach maximum concentration, 0.5 to 6.0 hours) and elimination (mean half-life, 3.0 to 4.4 hours). CONCLUSION Dasatinib 60 mg/m(2) and 80 mg/m(2) once-daily dosing were selected for phase II studies in children with Ph-positive leukemias.

Early UK experience in the use of clofarabine in the treatment of relapsed and refractory paediatric acute lymphoblastic leukaemia

Clofarabine is a second‐generation purine nucleoside analogue, which has shown promising activity in relapsed and refractory paediatric acute lymphoblastic leukaemia (ALL). This report summarizes the early United Kingdom experience of clofarabine for the treatment of paediatric ALL in 23 patients, outside of the context of a clinical trial. Our results demonstrated that clofarabine‐based chemotherapy regimes were effective and well‐tolerated in this heavily pre‐treated group, with an overall response rate of 67% when used in combination regimes. Responses were seen in both B and T cell disease and in patients with adverse cytogenetics.

The contribution of the Epstein-Barr virus to the pathogenesis of childhood lymphomas

The Epstein-Barr virus (EBV) is a lymphotropic herpes virus with oncogenetic properties which can lead to the development of lymphomas such as Burkitts lymphoma (BL), Hodgkins lymphoma (HL), or post-transplant lymphoma. This review discusses our current understanding of lymphomagenesis in relation to EBV and the potential for targeted therapies.

Gene expression profiling identifies different sub-types of retinoblastoma

Background:Mutation of the RB1 gene is necessary but not sufficient for the development of retinoblastoma. The nature of events occurring subsequent to RB1 mutation is unclear, as is the retinal cell-of-origin of this tumour.Methods:Gene expression profiling of 21 retinoblastomas was carried out to identify genetic events that contribute to tumorigenesis and to obtain information about tumour histogenesis.Results:Expression analysis showed a clear separation of retinoblastomas into two groups. Group 1 retinoblastomas express genes associated with a range of different retinal cell types, suggesting derivation from a retinal progenitor cell type. Recurrent chromosomal alterations typical of retinoblastoma, for example, chromosome 1q and 6p gain and 16q loss were also a feature of this group, and clinically they were characterised by an invasive pattern of tumour growth. In contrast, group 2 retinoblastomas were found to retain many characteristics of cone photoreceptor cells and appear to exploit the high metabolic capacity of this cell type in order to promote tumour proliferation.Conclusion:Retinoblastoma is a heterogeneous tumour with variable biology and clinical characteristics.

Diffuse intrinsic pontine glioma treated with prolonged temozolomide and radiotherapy--results of a United Kingdom phase II trial (CNS 2007 04).

Diffuse intrinsic pontine glioma (DIPG) has a dismal prognosis with no chemotherapy regimen so far resulting in any significant improvement over standard radiotherapy. In this trial, a prolonged regimen (21/28 d) of temozolomide was studied with the aim of overcoming O6-methylguanine methyltransferase (MGMT) mediated resistance. Forty-three patients with a defined clinico-radiological diagnosis of DIPG received radiotherapy and concomitant temozolomide (75 mg/m2) after which up to 12 courses of 21 d of adjuvant temozolomide (75–100 mg/m2) were given 4 weekly. The trial used a 2-stage design and passed interim analysis. At diagnosis median age was 8 years (2–20 years), 81% had cranial nerve abnormalities, 76% ataxia and 57% long tract signs. Median Karnofsky/Lansky score was 80 (10–100). Patients received a median of three courses of adjuvant temozolomide, five received all 12 courses and seven did not start adjuvant treatment. Three patients were withdrawn from study treatment due to haematological toxicity and 10 had a dose reduction. No other significant toxicity related to temozolomide was noted. Overall survival (OS) (95% confidence interval (CI)) was 56% (40%, 69%) at 9 months, 35% (21%, 49%) at 1 year and 17% (7%, 30%) at 2 years. Median survival was 9.5 months (range 7.5–11.4 months). There were five 2-year survivors with a median age of 13.6 years at diagnosis. This trial demonstrated no survival benefit of the addition of dose dense temozolomide, to standard radiotherapy in children with classical DIPG. However, a subgroup of adolescent DIPG patients did have a prolonged survival, which needs further exploration.

Novel therapies for children with acute myeloid leukaemia

Significant improvements in survival for children with acute myeloid leukaemia (AML) have been made over the past three decades, with overall survival rates now approximately 60–70%. However, these gains can be largely attributed to more intensive use of conventional cytotoxics made possible by advances in supportive care, and although over 90% of children achieve remission with frontline therapy, approximately one third in current protocols relapse. Furthermore, late effects of therapy cause significant morbidity for many survivors. Novel therapies are therefore desperately needed. Early-phase paediatric trials of several new agents such as clofarabine, sorafenib and gemtuzumab ozogamicin have shown encouraging results in recent years. Due to the relatively low incidence of AML in childhood, the success of paediatric early-phase clinical trials is largely dependent upon collaborative clinical trial design by international cooperative study groups. Successfully incorporating novel therapies into frontline therapy remains a challenge, but the potential for significant improvement in the duration and quality of survival for children with AML is high.