Molecules linked to Ras signaling as therapeutic targets in cardiac pathologies

The Ras family of small Guanosine Triphosphate (GTP)-binding proteins (G proteins) represents one of the main components of intracellular signal transduction required for normal cardiac growth, but is also critically involved in the development of cardiac hypertrophy and heart failure. The present review provides an update on the role of the H-, K- and N-Ras genes and their related pathways in cardiac diseases. We focus on cardiac hypertrophy and heart failure, where Ras has been studied the most. We also review other cardiac diseases, like genetic disorders related to Ras. The scope of the review extends from fundamental concepts to therapeutic applications. Although the three Ras genes have a nearly identical primary structure, there are important functional differences between them: H-Ras mainly regulates cardiomyocyte size, whereas K-Ras regulates cardiomyocyte proliferation. N-Ras is the least studied in cardiac cells and is less associated to cardiac defects. Clinically, oncogenic H-Ras causes Costello syndrome and facio-cutaneous-skeletal syndromes with hypertrophic cardiomyopathy and arrhythmias. On the other hand, oncogenic K-Ras and alterations of other genes of the Ras-Mitogen-Activated Protein Kinase (MAPK) pathway, like Raf, cause Noonan syndrome and cardio-facio-cutaneous syndromes characterized by cardiac hypertrophy and septal defects. We further review the modulation by Ras of key signaling pathways in the cardiomyocyte, including: (i) the classical Ras-Raf-MAPK pathway, which leads to a more physiological form of cardiac hypertrophy; as well as other pathways associated with pathological cardiac hypertrophy, like (ii) The SAPK (stress activated protein kinase) pathways p38 and JNK; and (iii) The alternative pathway Raf-Calcineurin-Nuclear Factor of Activated T cells (NFAT). Genetic alterations of Ras isoforms or of genes in the Ras-MAPK pathway result in Ras-opathies, conditions frequently associated with cardiac hypertrophy or septal defects among other cardiac diseases. Several studies underline the potential role of H- and K-Ras as a hinge between physiological and pathological cardiac hypertrophy, and as potential therapeutic targets in cardiac hypertrophy and failure. Highlights - The Ras (Rat Sarcoma) gene family is a group of small G proteins - Ras is regulated by growth factors and neurohormones affecting cardiomyocyte growth and hypertrophy - Ras directly affects cardiomyocyte physiological and pathological hypertrophy - Genetic alterations of Ras and its pathways result in various cardiac phenotypes? - Ras and its pathway are differentially regulated in acquired heart disease - Ras modulation is a promising therapeutic target in various cardiac conditions.

Understanding the Molecular Basis of Juvenile Myelomonocytic Leukemia and Its Application for Novel Drugs Development / 임상소아혈액종양

To date, hematopoietic stem cell transplantation (HSCT) is the only choice of therapy for most patients with juvenile myelomonocytic leukemia (JMML). Relapse remains a major problem. Approximately 90% of patients carry either somatic or germline mutations of genes participating in RAS signal transduction such as PTPN11, CBL, K-RAS, N-RAS, or NF1 in their leukemic cells, allowing an understanding of the molecular pathophysiology of JMLL and the development of novel drugs. As these genetic aberrations are mutually exclusive, the genetic change observed in JMML helps us to establish the diagnosis of JMML. Furthermore, the genetic abnormalities of JMML are an important prognostic factor, as the type of abnormality may determine disease progression. Recent studies have revealed a strong association between hypermethylation of some genes and already known poor prognostic factors such as older age, elevated fetal hemoglobin at diagnosis, and somatic mutation of PTPN11. These molecular characteristics may be the basis for a guideline to determine the treatment, especially when to proceed with HSCT. Recently, novel drugs have been used based on these molecular characteristics. 5-Azacitidine, an inhibitor of DNA methyltransferase and tipifarnib, a selective farnesyl transferase inhibitor, have been used to improve the outcome of JMML. In addition, drugs which inhibit the RAS signal transduction have been developed, which are less toxic and will improve outcome in the near future.

Cytarabine Monotherapy as Bridging Treatment for Hematopoietic Stem Cell Transplantation in Children with Juvenile Myelomonocytic Leukemia / 임상소아혈액종양

BACKGROUND: Mutations leading to hyperactivation of the RAS pathway play a critical role in the pathogenesis of juvenile myelomonocytic leukemia (JMML). Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative therapy, and the role of anti-leukemic treatment prior to HSCT is still controversial. In this study, we analyzed the response of cytarabine monotherapy as a bridging therapy for HSCT in children recently diagnosed with JMML.METHODS: We retrospectively reviewed the medical records of patients with JMML at Seoul St. Mary's Hospital from December 2009 to April 2012.RESULTS: A total 7 patients with JMML were diagnosed and treated with chemotherapy and HSCT. At presentation, all patients showed hepatosplenomegaly and the median leukocyte count was 41.9x109/L (range, 34.3-85.0), median monocyte count was 5.6x109/L (range, 2.7-26.3) and median fetal hemoglobin (HbF) was 13.5% (range, 2.8-42.7). Karyotypic abnormalities in bone marrow cells were noted in 2 cases. Three patients had mutation of NRAS and 2 patients had mutation of NF1. One of the patients with NF1 mutations had characteristic clinical features and familial history of neurofibromatosis. All patients were treated with non-intensive sequential cytarabine chemotherapy (70 mg/m2/day, I.V., 4-12 days) before HSCT and achieved complete hematologic response. All patients underwent unrelated (N=2) or familial mismatched (N=5) HSCT, and all patients successfully engrafted. All patients, except one who relapsed, are alive with leukemia free, although the duration of follow-up is short.CONCLUSION: In our cohort of NRAS prevalent patients, non-intensive cytarabine monotherapy was effective as pre-transplant bridging treatment for JMML.

Cytarabine Monotherapy as Bridging Treatment for Hematopoietic Stem Cell Transplantation in Children with Juvenile Myelomonocytic Leukemia / 임상소아혈액종양

BACKGROUND: Mutations leading to hyperactivation of the RAS pathway play a critical role in the pathogenesis of juvenile myelomonocytic leukemia (JMML). Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative therapy, and the role of anti-leukemic treatment prior to HSCT is still controversial. In this study, we analyzed the response of cytarabine monotherapy as a bridging therapy for HSCT in children recently diagnosed with JMML. METHODS: We retrospectively reviewed the medical records of patients with JMML at Seoul St. Mary's Hospital from December 2009 to April 2012. RESULTS: A total 7 patients with JMML were diagnosed and treated with chemotherapy and HSCT. At presentation, all patients showed hepatosplenomegaly and the median leukocyte count was 41.9x109/L (range, 34.3-85.0), median monocyte count was 5.6x109/L (range, 2.7-26.3) and median fetal hemoglobin (HbF) was 13.5% (range, 2.8-42.7). Karyotypic abnormalities in bone marrow cells were noted in 2 cases. Three patients had mutation of NRAS and 2 patients had mutation of NF1. One of the patients with NF1 mutations had characteristic clinical features and familial history of neurofibromatosis. All patients were treated with non-intensive sequential cytarabine chemotherapy (70 mg/m2/day, I.V., 4-12 days) before HSCT and achieved complete hematologic response. All patients underwent unrelated (N=2) or familial mismatched (N=5) HSCT, and all patients successfully engrafted. All patients, except one who relapsed, are alive with leukemia free, although the duration of follow-up is short. CONCLUSION: In our cohort of NRAS prevalent patients, non-intensive cytarabine monotherapy was effective as pre-transplant bridging treatment for JMML.