Elisabeth Ersvær

Histone Deacetylase Inhibitors in Cancer Treatment: A Review of the Clinical Toxicity and the Modulation of Gene Expression in Cancer Cells

Characterization of epigenetic events in carcinogenesis has led to the discovery of a new class of oncogenes and thereby a new class of therapeutic targets. Among the new therapeutic approaches are modulation of protein lysine acetylation through inhibition of histone deacetylases (HDACs). HDACs deacetylate histones as well as transcription factors and can modulate gene expression through both these mechanisms in normal and malignant cells. Furthermore, acetylation is an important posttranslational modulation of several proteins involved in the regulation of cell proliferation, differentiation and apoptosis in normal as well as cancer cells. Even though several HDAC inhibitors have been characterized in vitro, only a limited number of these agents are in clinical trials. Various HDAC inhibitors differ in their toxicity profile when comparing the side effects described in the available clinical studies of HDAC inhibition in the treatment of cancer. These drugs may also affect normal hematopoiesis; hematologic toxicity is common to many drugs but stimulation of hematopoiesis seems to occur for others. HDAC inhibitors usually affect < 10% of the genes in cancer cells. Divergent effects of HDAC inhibition on the global gene expression profiles have been described when testing various cancer cells, and this is further complicated by altered HDAC expression induced by HDAC inhibitors. However, increased p21 expression seems to be a common characteristic for most studies, suggesting an important role of this molecule during HDAC inhibitory treatment. Even though the initial studies are encouraging, additional in vitro and in vivo pharmacological characterization is definitely needed.

The proteasome inhibitors bortezomib and PR-171 have antiproliferative and proapoptotic effects on primary human acute myeloid leukaemia cells.

Proteasome inhibitors represent a new class of antineoplastic drugs that are considered in the treatment of haematological malignancies. We compared the effects of the reversible proteasome inhibitor bortezomib (Velcade®) and the epoxomicin derivative PR‐171, an irreversible inhibitor, on primary human acute myeloid leukaemia (AML) cells. Both drugs inhibited autocrine‐ and cytokine‐dependent proliferation of primary AML blasts when tested at nanomolar levels (0·1–100 nmol/l). The antiproliferative effect was independent of basal chymotrypsin‐like proteasome activity (showing a 20‐fold variation between patients), genetic abnormalities, morphological differentiation and CD34 expression when testing a large group of consecutive patients (n = 54). The effect was retained in cocultures with bone marrow stromal cells. In addition, both drugs enhanced apoptosis. The effect of PR‐171 could be detected at lower concentrations than for bortezomib, especially when testing the influence on clonogenic AML cell proliferation. Both drugs had divergent effects on AML cells’ constitutive cytokine release. Furthermore, both drugs caused a decrease in proliferation and viability when tested in combination with idarubicin or cytarabine. An antiproliferative effect on primary human acute lymphoblastic leukaemia cells was also detected. We conclude that nanomolar levels of the proteasome inhibitors tested had dose‐dependent antiproliferative and proapoptotic effects on primary AML cells in vitro.

Heat shock protein 90 - a potential target in the treatment of human acute myelogenous leukemia.

Heat shock proteins (HSPs) are molecular chaperones that stabilize folding and conformation of normal as well as oncogenic proteins. These chaperones thereby prevent the formation of protein aggregates. HSPs are often overexpressed in human malignancies, including AML. HSP90 is the main chaperon required for the stabilization of multiple oncogenic kinases involved in the development of acute myelogenous leukemia (AML). HSP90 client proteins are involved in the regulation of apoptosis, proliferation, autophagy and cell cycle progression; several of these proteins are in addition considered as possible therapeutic targets for the treatment of AML. HSP90 inhibition thereby offers the possibility to modulate several intracellular regulatory pathways through targeting of a single molecule. Several direct inhibitors of HSP90 have been developed, and they are classified into four groups: benzoquinon ansamycines and their derivatives, radicicol and its derivates, small synthetic inhibitors and a final group of other inhibitors. The HSP90 activity is regulated by posttranscriptional modulation; HSP90 inhibition can thereby be indirectly achieved through increased acetylation caused by histone deacetylase inhibitors. Many of these agents have entered phase I/II clinical trials, and the results from these initial studies have documented that HSP90 inhibition can mediate antileukemic effects in vivo. However, one would expect immunosuppressive side effects because HSP90 inhibitors have both direct and indirect inhibitory effects on T cell activation. Thus, future clinical studies are needed to clarify the efficiency and toxicity of HSP90 inhibitors in the treatment of human AML, including studies where HSP90 inhibitors are combined with conventional chemotherapy.

Primary human acute myeloid leukaemia cells increase the proliferation of microvascular endothelial cells through the release of soluble mediators

Bone marrow angiogenesis is suggested to play a role in the pathogenesis of acute myeloid leukaemia (AML) and endothelial cells may mediate chemosensitivity. This study investigated in vitro endothelial effects of coculture of microvascular endothelial cells (MVEC) with AML cells derived from 33 consecutive AML patients. A proliferation assay showed that (i) AML cells from the majority of patients examined increased endothelial cell proliferation, while cytokine neutralizing experiments had divergent effects on proliferation and (ii) the angiopoietin/Tie2 system was important for growth of AML cells, and angiopoietin‐1 induced phosphorylation of signal transducers and activators of transcription (STAT) proteins in AML cells. Finally, gene expression profiling of MVEC cocultured with AML cells was conducted in non‐contact cultures. Microarray analysis revealed that the majority of significantly expressed genes could be categorized into gene ontology terms involved in transcription, cellular organization and intracellular signalling. Our study indicates a role for the leukaemic‐endothelium crosstalk in leukaemogenesis with enhancement of endothelial cell growth and increased AML cell proliferation possibly mediated by angiopoietin‐1 and the STAT signalling pathway.

The Protein Kinase C Agonist PEP005 (Ingenol 3-Angelate) in the Treatment of Human Cancer: A Balance between Efficacy and Toxicity

The diterpene ester ingenol-3-angelate (referred to as PEP005) is derived from the plant Euphorbia peplus. Crude euphorbia extract causes local toxicity and transient inflammation when applied topically and has been used in the treatment of warts, skin keratoses and skin cancer. PEP005 is a broad range activator of the classical (α, β, γ) and novel (δ, ε, η, θ) protein kinase C isoenzymes. Direct pro-apoptotic effects of this drug have been demonstrated in several malignant cells, including melanoma cell lines and primary human acute myelogenous leukemia cells. At micromolar concentrations required to kill melanoma cells this agent causes PKC-independent secondary necrosis. In contrast, the killing of leukemic cells occurs in the nanomolar range, requires activation of protein kinase C δ (PKCδ) and is specifically associated with translocation of PKCδ from the cytoplasm to the nuclear membrane. However, in addition to this pro-apoptotic effect the agent seems to have immunostimulatory effects, including: (i) increased chemokine release by malignant cells; (ii) a general increase in proliferation and cytokine release by activated T cells, including T cells derived from patients with chemotherapy-induced lymphopenia; (iii) local infiltration of neutrophils after topical application with increased antibody-dependent cytotoxicity; and (iv) development of specific anti-cancer immune responses by CD8+ T cells in animal models. Published studies mainly describe effects from in vitro investigations or after topical application of the agent, and careful evaluation of the toxicity after systemic administration is required before the possible use of this agent in the treatment of malignancies other than skin cancers.

The combination of valproic acid, all-trans retinoic acid and low-dose cytarabine as disease-stabilizing treatment in acute myeloid leukemia

BackgroundA large proportion of patients with acute myeloid leukemia (AML) are not fit for intensive and potentially curative therapy due to advanced age or comorbidity. Previous studies have demonstrated that a subset of these patients can benefit from disease-stabilizing therapy based on all-trans retinoic acid (ATRA) and valproic acid. Even though complete hematological remission is only achieved for exceptional patients, a relatively large subset of patients respond to this treatment with stabilization of normal peripheral blood cell counts.MethodsIn this clinical study we investigated the efficiency and safety of combining (i) continuous administration of valproic acid with (ii) intermittent oral ATRA treatment (21.5 mg/m2 twice daily) for 14 days and low-dose cytarabine (10 mg/m2 daily) for 10 days administered subcutaneously. If cytarabine could not control hyperleukocytosis it was replaced by hydroxyurea or 6-mercaptopurin to keep the peripheral blood blast count below 50 × 109/L.ResultsThe study included 36 AML patients (median age 77 years, range 48 to 90 years) unfit for conventional intensive chemotherapy; 11 patients responded to the treatment according to the myelodysplastic syndrome (MDS) response criteria and two of these responders achieved complete hematological remission. The most common response to treatment was increased and stabilized platelet counts. The responder patients had a median survival of 171 days (range 102 to > 574 days) and they could spend most of this time outside hospital, whereas the nonresponders had a median survival of 33 days (range 8 to 149 days). The valproic acid serum levels did not differ between responder and nonresponder patients and the treatment was associated with a decrease in the level of circulating regulatory T cells.ConclusionTreatment with continuous valproic acid and intermittent ATRA plus low-dose cytarabine has a low frequency of side effects and complete hematological remission is seen for a small minority of patients. However, disease stabilization is seen for a subset of AML patients unfit for conventional intensive chemotherapy.

Targeting the angiopoietin (Ang)/Tie-2 pathway in the crosstalk between acute myeloid leukaemia and endothelial cells: studies of Tie-2 blocking antibodies, exogenous Ang-2 and inhibition of constitutive agonistic Ang-1 release.

Background: The Tie-2 receptor can bind its agonistic ligand Angiopoietin-1 (Ang-1) and the potential antagonist Ang-2. Tie-2 can be expressed both by primary human acute myeloid leukaemia (AML) cells and endothelial cells, and Tie-2-blocking antibodies are now being evaluated in clinical trials for cancer treatment. Design and methods: We investigated the effects of Tie-2-blocking antibodies, exogenous Ang-2 and pharmacological agents on AML cell proliferation and the release of angioregulatory mediators. Results: Tie-2-blocking antibodies had a growth inhibitory effect on human AML cells co-cultured with microvascular endothelial cells, but this inhibition was not observed when leukaemic cells were co-cultured with fibroblasts or osteoblasts. AML cell viability in co-cultures was not altered by anti-Tie-2. Furthermore, anti-Tie-2 decreased hepatocyte growth factor (HGF) levels and increased CXCL8 levels in co-cultures, whereas the levels of endocan (a proteoglycan released by endothelial cells) were not altered. The only significant effects of exogenous Ang-2 were decreased levels of HGF and endocan. Constitutive AML cell release of agonistic Ang-1 was decreased by the proteasomal inhibitor bortezomib and the specific IκB-kinase/NFκB inhibitor BMS-345541. Conclusion: We conclude that various strategies for inhibition of Tie-2-mediated signalling should be considered in AML therapy, possibly in combination with other antiangiogenic strategies.

Combination of intensive chemotherapy and anticancer vaccines in the treatment of human malignancies: the hematological experience.

In vitro studies have demonstrated that cancer-specific T cell cytotoxicity can be induced both ex vivo and in vivo, but this therapeutic strategy should probably be used as an integrated part of a cancer treatment regimen. Initial chemotherapy should be administered to reduce the cancer cell burden and disease-induced immune defects. This could be followed by autologous stem cell transplantation that is a safe procedure including both high-dose disease-directed chemotherapy and the possibility for ex vivo enrichment of the immunocompetent graft cells. The most intensive conventional chemotherapy and stem cell transplantation are used especially in the treatment of aggressive hematologic malignancies; both strategies induce T cell defects that may last for several months but cancer-specific T cell reactivity is maintained after both procedures. Enhancement of anticancer T cell cytotoxicity is possible but posttransplant vaccination therapy should probably be combined with optimalisation of immunoregulatory networks. Such combinatory regimens should be suitable for patients with aggressive hematological malignancies and probably also for other cancer patients.

Expression profile of heat shock proteins in acute myeloid leukaemia patients reveals a distinct signature strongly associated with FLT3 mutation status – consequences and potentials for pharmacological intervention

Heat shock proteins (HSPs) are molecular chaperones that assist proteins in their folding to native structures. HSPs are regarded as possible therapeutic targets in acute myeloid leukaemia (AML). We used bioinformatical approaches to characterize the HSP profile in AML cells from 75 consecutive patients, in addition to the effect of the HSP90 inhibitor 17‐DMAG. Patients harbouring a FLT3‐internal tandem duplication (FLT3‐ITD) were extensively overrepresented in the cluster with high HSP levels, indicating a strong dependence of HSPs in stabilizing FLT3‐ITD encoded oncoproteins. FLT3 ligation further increased the levels of HSP90 and its co‐chaperone HSP70. HSP90 inhibition had a stronger pro‐apoptotic effect for AML cells with FLT3‐ITD than for cells with wild‐type FLT3, whereas the anti‐proliferative effect of HSP90 inhibition was similar for the two patient subsets. HSP90 inhibition altered the constitutive cytokine release profile in an anti‐angiogenic direction independent of FLT3 mutational status: (i) pro‐angiogenic CXCL8, MMP‐2 and MMP‐9 showed a stronger decrease than anti‐angiogenic CXCL9–11, (ii) the Tie‐2 agonist Ang‐1 showed a stronger decrease than the potentially antagonistic Ang‐2, and (iii) VEGF and HGF levels were decreased. Finally, HSP90 inhibition counteracted the leukaemia‐stimulating effect of endothelial cells. Our studies demonstrate that HSP90 inhibition mediates anti‐leukaemic effects through both direct and indirect activity.

Long‐term cryopreservation of autologous stem cell grafts: a clinical and experimental study of hematopoietic and immunocompetent cells

BACKGROUND: Autologous stem cell transplantation (ASCT) is used in the treatment of several malignancies. Harvesting sufficient peripheral blood progenitor cells (PBPCs) for a potential second autotransplantation at the time of relapse several years after diagnosis is becoming an increasingly common practice.