- Email: [email protected]
29 In vitro basis for treatment with hypomethylating agents and HDAC inhibitors: Can epigenetic changes be used to monitor treatment?
S24
Invited Lectures
with post-transplant complications, such as mucositis, bacteraemia, and number of febrile days. This association, apparent in earlier autologous studies, became more obvious in the large retrospective analysis performed by the Dana Farber Institute Group on 543 recipients of allogeneic HSCT. This analysis showed a strong association between pretransplantation serum ferritin levels and a lower overall rate of survival, especially in patients with MDS and AML. Strikingly, the median serum ferritin level in this group was 930 mg/L. The percentage of patients with elevated serum ferritin levels varied greatly, from 25% in chronic myeloid leukemia (CML) to 70% in non-Hodgkin lymphoma (NHL), 88% in MDS, and 97% in AML. The question arises as to what can be done to prevent iron overload-related toxicity. The approach should be multifactorial, because iron overload cannot be solely attributed to the number of units of blood transfused – other factors play a role as well. In a post-mortem study, the iron content of 10 patients who died soon after HSCT was in a range similar to that of patients with haemachromatosis, even though on average only 48 transfusions were given from diagnosis to death. In the pre-transplant period vigorous iron chelation may be important, but prospective studies should prove a clear survival benefit. During the transplant period therapies, including various iron-chelating agents, glutamine, and the angiotensin-converting enzyme (ACE)-inhibitor captopril, may be considered, but at present clinical experience is limited to anecdotal observations. During the conditioning and early post-transplant period, innocuous glutathione-depleting agents like acetaminophen should be avoided. Finally, in the post-transplant period phlebotomy, sometimes combined with erythropoietin, has been successfully applied after HSCT in thalassaemic patients. For those patients who cannot be phlebotomized, iron chelation therapy can be considered as well. In conclusion, iron toxicity is likely to be an underestimated cause of HSCT treatment-related mortality. We need to know more about the pathogenesis, diagnosis, and monitoring of iron-induced organ damage. Prevention of ironinduced toxicity will require a multidisciplinary approach involving biochemists, pathologists, transfusionists, and clinicians. It is clear that we need well-designed prospective studies, not only with regard to interventions prior to HSCT, but also after it. 29 In vitro basis for treatment with hypomethylating agents and HDAC inhibitors: Can epigenetic changes be used to monitor treatment? S.D. Gore ° . Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD, USA The discovery of the activity of the azanucleosides analogues 5-azacytidine (5AC) and 2 -deoxy-5-azacytidine (DAC) for the treatment of myelodysplastic syndromes
(MDS) came from empiric observations; early trials focused on the use of these drugs to induce terminal differentiation. The ability of these compounds to reverse DNA methylation through incorporation into DNA and formation of inactive adducts with DNA methyltransferases (DNMT) required for de novo and maintenance DNA methylation has been known for over twenty years. The importance of DNA methylation in mediating the transcriptional silencing of genes has been recognized more recently. Thus, the azanucleosides DNMT inhibitors were developed empirically without pharmacodynamic guidance. Re-expression of genes silenced through methylation of their promoters using azanucleosides can be augmented synergistically by the subsequent addition of histone deacetylase inhibitors (HDAC inhibitors). A variety of early phase trials have combined 5AC and/or DAC with sodium phenylbutyrate, valproic acid, entinostat, vorinostat, and belinostat. Ongoing randomized trials compare 5AC alone and with entinostat, and DAC alone and with valproic acid. Despite the marked clinical activity of the azanucleosides − including survival benefit for 5AC in high risk MDS − the connection between clinical response and underlying epigenetic reprogramming remains uncertain. Reversal of methylation of non-coding elements of DNA and specific gene promoters as well as re-expression of epigenetically silenced genes has been demonstrated in samples from blood and bone marrow from patients undergoing treatment with these drugs. Studies vary considerably in terms of association between methylation reversal or gene reexpression and clinical response. A strong correlation has not yet emerged in any study. While a variety of variables in these complex clinical experiments could explain such ambiguous outcomes, the possibility that these drugs exert their clinical activity through other mechanisms must be considered. Both the aza nucleosides and HDAC inhibitors can induce reactive oxygen species and both classes of drugs induce double stranded breaks in DNA. Evidence of such DNA damage can be found in blood and bone marrow cells from patients treated with 5AC, DAC, and HDAC inhibitors. Those HDAC inhibitors which inhibit Class II HDACs may induce acetylation of important non-histone proteins including p53 and HSP90, and can impact NFkappaB signaling. At this point, no epigenetic markers exist which can predict responders to azanucleosides analogues, with or without HDAC inhibitors. Further exploration of the mechanism of action of both classes of drugs remains imperative for future drug development, patient selection, and patient monitoring.
31 Decitabine in the treatment of higher-risk MDS D.P. Steensma ° . Mayo Clinic, Rochester, MN, USA Decitabine − 5-aza-2 -deoxycytidine − is a cytosine analog that is a potent inhibitor of DNA methyltransferase, resulting
Invited Lectures
with post-transplant complications, such as mucositis, bacteraemia, and number of febrile days. This association, apparent in earlier autologous studies, became more obvious in the large retrospective analysis performed by the Dana Farber Institute Group on 543 recipients of allogeneic HSCT. This analysis showed a strong association between pretransplantation serum ferritin levels and a lower overall rate of survival, especially in patients with MDS and AML. Strikingly, the median serum ferritin level in this group was 930 mg/L. The percentage of patients with elevated serum ferritin levels varied greatly, from 25% in chronic myeloid leukemia (CML) to 70% in non-Hodgkin lymphoma (NHL), 88% in MDS, and 97% in AML. The question arises as to what can be done to prevent iron overload-related toxicity. The approach should be multifactorial, because iron overload cannot be solely attributed to the number of units of blood transfused – other factors play a role as well. In a post-mortem study, the iron content of 10 patients who died soon after HSCT was in a range similar to that of patients with haemachromatosis, even though on average only 48 transfusions were given from diagnosis to death. In the pre-transplant period vigorous iron chelation may be important, but prospective studies should prove a clear survival benefit. During the transplant period therapies, including various iron-chelating agents, glutamine, and the angiotensin-converting enzyme (ACE)-inhibitor captopril, may be considered, but at present clinical experience is limited to anecdotal observations. During the conditioning and early post-transplant period, innocuous glutathione-depleting agents like acetaminophen should be avoided. Finally, in the post-transplant period phlebotomy, sometimes combined with erythropoietin, has been successfully applied after HSCT in thalassaemic patients. For those patients who cannot be phlebotomized, iron chelation therapy can be considered as well. In conclusion, iron toxicity is likely to be an underestimated cause of HSCT treatment-related mortality. We need to know more about the pathogenesis, diagnosis, and monitoring of iron-induced organ damage. Prevention of ironinduced toxicity will require a multidisciplinary approach involving biochemists, pathologists, transfusionists, and clinicians. It is clear that we need well-designed prospective studies, not only with regard to interventions prior to HSCT, but also after it. 29 In vitro basis for treatment with hypomethylating agents and HDAC inhibitors: Can epigenetic changes be used to monitor treatment? S.D. Gore ° . Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD, USA The discovery of the activity of the azanucleosides analogues 5-azacytidine (5AC) and 2 -deoxy-5-azacytidine (DAC) for the treatment of myelodysplastic syndromes
(MDS) came from empiric observations; early trials focused on the use of these drugs to induce terminal differentiation. The ability of these compounds to reverse DNA methylation through incorporation into DNA and formation of inactive adducts with DNA methyltransferases (DNMT) required for de novo and maintenance DNA methylation has been known for over twenty years. The importance of DNA methylation in mediating the transcriptional silencing of genes has been recognized more recently. Thus, the azanucleosides DNMT inhibitors were developed empirically without pharmacodynamic guidance. Re-expression of genes silenced through methylation of their promoters using azanucleosides can be augmented synergistically by the subsequent addition of histone deacetylase inhibitors (HDAC inhibitors). A variety of early phase trials have combined 5AC and/or DAC with sodium phenylbutyrate, valproic acid, entinostat, vorinostat, and belinostat. Ongoing randomized trials compare 5AC alone and with entinostat, and DAC alone and with valproic acid. Despite the marked clinical activity of the azanucleosides − including survival benefit for 5AC in high risk MDS − the connection between clinical response and underlying epigenetic reprogramming remains uncertain. Reversal of methylation of non-coding elements of DNA and specific gene promoters as well as re-expression of epigenetically silenced genes has been demonstrated in samples from blood and bone marrow from patients undergoing treatment with these drugs. Studies vary considerably in terms of association between methylation reversal or gene reexpression and clinical response. A strong correlation has not yet emerged in any study. While a variety of variables in these complex clinical experiments could explain such ambiguous outcomes, the possibility that these drugs exert their clinical activity through other mechanisms must be considered. Both the aza nucleosides and HDAC inhibitors can induce reactive oxygen species and both classes of drugs induce double stranded breaks in DNA. Evidence of such DNA damage can be found in blood and bone marrow cells from patients treated with 5AC, DAC, and HDAC inhibitors. Those HDAC inhibitors which inhibit Class II HDACs may induce acetylation of important non-histone proteins including p53 and HSP90, and can impact NFkappaB signaling. At this point, no epigenetic markers exist which can predict responders to azanucleosides analogues, with or without HDAC inhibitors. Further exploration of the mechanism of action of both classes of drugs remains imperative for future drug development, patient selection, and patient monitoring.
31 Decitabine in the treatment of higher-risk MDS D.P. Steensma ° . Mayo Clinic, Rochester, MN, USA Decitabine − 5-aza-2 -deoxycytidine − is a cytosine analog that is a potent inhibitor of DNA methyltransferase, resulting