leukemogenesis mechanisms caused by deregulated epigenome/metabolic abnormality
A great deal of effort for comprehensive mutation analysis has revealed various types of genetic alterations in AML (Acute Myeloid Leukemia) such as chromosomal translocation and mutation. Some of those mutations are found in specific genes associated with epigenetic and metabolic regulations. To achieve the complete cure of AML, we have focused on and studied about how these genetic alterations affect the epigenetic and metabolic pathways to drive leukemia.
Epigenetic regulators MOZ and MLL, which are histone acetyltransferase and methyltansferase respectively, often form leukemogenic fusion proteins because of chromosomal translocation. Those fusion proteins disturb the epigenetic status and constitutively activate CSF1R and HOXA cluster genes, resulting in the development of AML (Aikawa Y. et al.,Nat. Med., 2010, Aikawa Y. et al., Caner Sci., 2015). Nuclear pore complex protein Nup98 also form leukemogenic fusion proteins. We showed that NUP98-fusion protein interacts and cooperates with MLL to constitutively activate HOXA cluster genes, resulting in AML development. Based on these our results, we are working on the development of medication by targeting the epigenetic abnormality.
NPM mutation is one of the most frequently mutated genes in AML and often accompanied by the mutation in IDH and/or DNMT3A gene. To clarify the detailed mechanisms of NPM-mutated AML, we have developed the mouse model of NPM-mutated AML, and clearly demonstrated that although NPM mutation alone could not effectively induce AML, it could cause a typical type of NPM-mutated AML through the cooperation with IDH and DNMT3A mutations. Intriguingly, IDH mutant protein gains cancer-specific altered enzymatic activity to produce cancer-specific metabolite 2-hydroxyglutarate from alpha-ketoglutarate. We showed that IDH mutant is crucial for maintenance of the leukemic stem cell of NPM-mutated-AML (Ogawara Y. et al., Cancer Res., 2015). Therefore, we are developing drug specifically targeting IDH mutant protein to treat NPM-mutated AML. Also, in leukemia cells associated with NUP98-fusion proteins, it appeared that the fatty acid synthesis pathway is deregulated. So, we are working on to verify whether the fatty acid synthesis pathway can be a target of cancer therapy.
Thus, in Division of Hematological Malignancy, we study about the molecular basis of AML development from the various biological viewpoints and are trying to apply these results to therapeutic application.
the mechanisms of cancer stem cell regulation
MLL fusion genes and MOZ fusion genes, which are generated from chromosomal translocations, induce acute myeloid leukemia (AML). These types of AML are classified as FAB-M4 or FAB-M5 and has poor prognosis. One of the reasons making it difficult to treat the leukemia is that the existing chemotherapy cannot completely eradicate leukemia-initiating cells (LSCs, cancer stem cells). Therefore, we are trying to develop molecular targeted drugs to remove the LSCs.
To target the LSCs, we tried to identify the LSCs in MLL fusion genes- and MOZ fusion genes-expressing leukemia cells. We found that M-CSF receptor (MCSFR) is expressed highly in the LSCs. And we also identified that MCSFR depletion results in complete inhibition of leukemogenesis (Aikawa Y. et al., Nat. Med., 2010, Aikawa Y. et al., Caner Sci., 2015). These results indicate that MCSFR is a good target for therapy. Now we are developing monoclonal antibodies specific for human MCSFR to target and kill the LSCs.
We are also investigating the molecular mechanisms of transcriptional activation by MLL fusion protein and MOZ fusion protein to find the novel molecular targets for the therapy. In this study, we identified that TIP60 and MOZ, which are histone acetylases, play important roles in the transcriptional activation. We think that the inhibitors against these proteins would be useful for the eradication of leukemic cells including LSCs. Therefore, we are developing the inhibitors cooperatively with domestic pharmaceutical companies.
Recently, it has been reported that polycomb complex 2 (PRC2) is essential for the LSCs. EZH1 and EZH2 are the catalytic subunits of PRC2. We found that both EZH1 and EZH2 deletion results in complete inhibition of AML. The deletion accelerates cell cycle of LSCs, result in loss of stemness activity. Based on this finding, we are developing the dual inhibitor against EZH1 and EZH2 cooperatively with the domestic pharmaceutical company. We also identified that RING1A and RING1B, which are the subunits of polycomb complex 1 (PRC1), are essential for the LSCs. Therefore, the inhibitors against not only EZH1 and EZH2 but also RING1A and RING1B would be useful for AML therapy.
Development of molecular targeted agents
We are actively trying to translate the achievements of our basic research to bed-side through the collaboration with Japanese pharmaceutical companies, introducing several novel molecular-targeted agents to preclinical or clinical trials. Indeed, we have successfully delivered a novel agent; EZH1/2 dual inhibitor to phase1 clinical trial in our institution and are going to launch another clinical trial for mutated-IDH inhibitor within a few years.
Our EZH1/2 dual inhibitor is a bioavailable first-in-class drug inhibiting both of EZH1 and EZH2. Our preclinical research showed that our compound effectively eradicates chemo-resistant and quiescent AML LSCs to impair its stemness. EZH1/2 inhibitor is now under phase1 clinical trial for malignant lymphoma in our hospital, and we are going to begin the clinical trial for AML in near future. Furthermore, our drug shows the excellent effectiveness even for multiple myeloma. We are currently aiming toward the further expansion of application for several types of hematological malignancy.
Our mutated-IDH1 inhibitor effectively impairs the progression of several IDH-mutation carrying diseases including AML, brain tumor and chondrosarcoma, in our preclinical animal models. We previously reported that mutated IDH is a crucial factor in the maintenance of stemness of AML LSCs, and suggested that inhibition of mutated IDH delivers favorable changes in epigenetic or metabolic status for tumor regression (Ogawara Y. et al., Cancer Res., 2015). We are currently performing the drug efficacy study for this novel compound using metabolic analysis, epigenetic analysis and in vivo imaging, as a preclinical study.