RAS activation induces synthetic lethality of MEK inhibition with mitochondrial oxidative metabolism in acute myeloid leukemia.

Despite recent advances in acute myeloid leukemia (AML) molecular characterization and targeted therapies, a majority of AML cases still lack therapeutically actionable targets. In 127 AML cases with unmet therapeutic needs, as defined by the exclusion of ELN favorable cases and of FLT3-ITD mutations, we identified 51 (40%) cases with alterations in RAS pathway genes (RAS+, mostly NF1, NRAS, KRAS, and PTPN11 genes). In 79 homogeneously treated AML patients from this cohort, RAS+ status were associated with higher white blood cell count, higher LDH, and reduced survival. In AML models of oncogenic addiction to RAS-MEK signaling, the MEK inhibitor trametinib demonstrated antileukemic activity in vitro and in vivo. However, the efficacy of trametinib was heterogeneous in ex vivo cultures of primary RAS+ AML patient specimens. From repurposing drug screens in RAS-activated AML cells, we identified pyrvinium pamoate, an anti-helminthic agent efficiently inhibiting the growth of RAS+ primary AML cells ex vivo, preferentially in trametinib-resistant PTPN11- or KRAS-mutated samples. Metabolic and genetic complementarity between trametinib and pyrvinium pamoate translated into anti-AML synergy in vitro. Moreover, this combination inhibited the propagation of RA+ AML cells in vivo in mice, indicating a potential for future clinical development of this strategy in AML.

Loss of p19Arf in a Rag1(-/-) B-cell precursor population initiates acute B-lymphoblastic leukemia.

In human B-acute lymphoblastic leukemia (B-ALL), RAG1-induced genomic alterations are important for disease progression. However, given that biallelic loss of the RAG1 locus is observed in a subset of cases, RAG1's role in the development of B-ALL remains unclear. We chose a p19Arf(-/-)Rag1(-/-) mouse model to confirm the previously published results concerning the contribution of CDKN2A (p19ARF /INK4a) and RAG1 copy number alterations in precursor B cells to the initiation and/or progression to B-acute lymphoblastic leukemia (B-ALL). In this murine model, we identified a new, Rag1-independent leukemia-initiating mechanism originating from a Sca1(+)CD19(+) precursor cell population and showed that Notch1 expression accelerates the cells' self-renewal capacity in vitro. In human RAG1-deficient BM, a similar CD34(+)CD19(+) population expressed p19ARF. These findings suggest that combined loss of p19Arf and Rag1 results in B-cell precursor leukemia in mice and may contribute to the progression of precursor B-ALL in humans.

Characterization of sSMC by FISH and molecular techniques.

Small supernumerary marker chromosome (sSMC) is a structurally altered additional chromosome that may not be explicitly clarified by conventional karyotyping alone. About one third of sSMC carriers have abnormal phenotypes and its clinical correlation is difficult, especially in prenatal studies. The present study was aimed at characterizing 19 sSMC identified in 15 patients with dysmorphic features with or without multiple congenital anomalies, conspicuous family history, short stature and/or ambiguous genitalia. All the sSMC were primarily identified by routine cytogenetics studies (performed with banding techniques) from peripheral blood except in one patient, where amniotic fluid was used. All sSMCs were further characterized by array-CGH (using 44 K oligonucleotide probe) and/or fluorescence in situ hybridization (FISH) using multicolor banding (MCB), centromere specific multicolor FISH (cenM-FISH), subcentromere-specific multicolor FISH (subcenM-FISH), micro-dissection and/or reverse FISH. This report demonstrates the worth of advanced molecular (cyto)genetic techniques in characterizing sSMC, their utility in genotype-phenotype correlation and risk of clinical presentation.

Preimplantation genetic diagnosis: state of the art.

Preimplantation genetic diagnosis (PGD) is used to analyze embryos genetically before their transfer into the uterus. It was developed first in England in 1990, as part of progress in reproductive medicine, genetic and molecular biology. PGD offers couples at risk the chance to have an unaffected child, without facing termination of pregnancy. Embryos are obtained by in vitro fertilization with intracytoplasmic sperm injection (ICSI), and are biopsied mostly on day 3; blastocyst biopsy is mentioned as a possible alternative. The genetic analysis is performed on one or two blastomeres, by fluorescent in situ hybridization (FISH) for cytogenetic diagnosis, or polymerase chain reaction (PCR) for molecular diagnosis. Genetic analysis of the first or second polar body can be used to study maternal genetic contribution. Only unaffected embryos are transferred into the uterus. To improve the accuracy of the diagnosis, new technologies are emerging, with comparative genomic hybridization (CGH) and microarrays. In Europe, depending on national regulations, PGD is either prohibited, or allowed, or practiced in the absence of recommendations. The indications are chromosomal abnormalities, X-linked diseases or single gene disorders. The number of disorders being tested increases. In Europe, data collection from the year 2004 reports that globally 69.6% of cycles lead to embryo transfer and implantation rate is 17%. European results from the year 2004 show a clinical pregnancy rate of 18% per oocyte retrieval and 25% per embryo transfer, leading to 528 babies born. The cohort studies concerning the paediatric follow-up of PGD babies show developmental outcomes similar to children conceived after IVF-ICSI. Recent advances include human leucocyte antigen (HLA) typing for PGD embryos, when an elder sibling is affected with a genetic disorder and needs stem cell transplantation. The HLA-matched offspring resulting can give cord blood at birth. Preimplantation genetic screening (PGS) consists in euploid embryo selection; it could be used for advanced maternal age, repeated implantation failure, single embryo transfer or idiopathic recurrent pregnancy loss. These applications are controversial. PGD for inherited cancer predispositions is discussed and social sexing remains prohibited in Europe. PGD requires a close collaboration between obstetricians, fertility specialists, IVF laboratory and human geneticists. It needs intensive effort, expensive techniques and is demanding for the patients, but it offers tremendous opportunity for couples whose previous child has exhibited genetic abnormalities. The debate on certain indications is ongoing.

A 24-Mb deletion in 14q in a girl with corpus callosum hypoplasia.

Interstitial deletions of 14q including band 14q31 are uncommon. We report on a 3 year-old Tunisian girl who had a de novo interstitial deletion of the long arm of chromosome 14. The molecular cytogenetic study has identified the deletion as a del(14)(q24.3q32.2) covering nearly 24Mb. This abnormality was associated to phenotypic manifestations, mainly peculiar face, developmental delay and hypoplastic corpus callosum.

Five years' experience of preimplantation genetic diagnosis in the Parisian Center: outcome of the first 441 started cycles.

OBJECTIVE: To investigate the evolution of techniques and strategies and to evaluate the results of preimplantation genetic diagnosis (PGD) from January 2000 to December 2004 in chromosomal, monogenic and mitochondrial DNA disorders treated at our institution. DESIGN: Retrospective study. SETTING: Single French Parisian PGD center. PATIENT(S): Patients at risk of transmitting a serious genetic disorder to their offspring. INTERVENTION(S): 171 couples enrolled in the program undergoing stimulated and frozen embryo replacement cycles with PGD. MAIN OUTCOME MEASURE(S): Results of the 441 first PGD cycles performed for various genetic conditions. RESULT(S): During 5 years, 416 stimulation and 25 frozen embryo replacement cycles were started, among which 52 clinical and 47 ongoing pregnancies occurred. In stimulation cycles, the overall ongoing pregnancy rate was 24% per embryo transfer, 11% per started cycle, and 27% per couple. The implantation rate was 16%. CONCLUSION(S): These encouraging results demonstrate that PGD might be considered as a valid alternative to prenatal diagnosis. Nevertheless, couples referred for PGD must be selected and counseled appropriately, considering the complexity of the treatment and the relatively low take-home baby rate.