Selective FLT3 inhibition of FLT3-ITD+ acute myeloid leukaemia resulting in secondary D835Y mutation: a model for emerging clinical resistance patterns

Acquired resistance to selective FLT3 inhibitors, is an emerging clinical problem in the treatment of FLT3-ITD⁺ acute myeloid leukaemia (AML). The paucity of valid pre-clinical models has limited investigations to determine the mechanism of acquired therapeutic resistance, thereby limiting the development of effective treatments. We generated selective FLT3 inhibitor-resistant cells by treating the FLT3-ITD⁺ human AML cell line MOLM-13 in vitro with the FLT3-selective inhibitor MLN518, and validated the resistant phenotype in vivo and in vitro. The resistant cells, MOLM-13-RES, harboured a new D835Y tyrosine kinase domain (TKD) mutation on the FLT3-ITD⁺ allele. Acquired TKD mutations, including D835Y, have recently been identified in FLT3-ITD⁺ patients relapsing after treatment with the novel FLT3 inhibitor, AC220. Consistent with this clinical pattern of resistance, MOLM-13- RES cells displayed high relative resistance to AC220 and Sorafenib. Furthermore, treatment of MOLM-13-RES cells with AC220 lead to loss of the FLT3 wild type allele and duplication of the FLT3-ITD-D835Y allele. Our FLT3-Aurora kinase inhibitor, CCT137690, successfully inhibited growth of FLT3-ITD-D835Y cells in vitro and in vivo, suggesting that dual FLT3-Aurora inhibition may overcome selective FLT3 inhibitor resistance, in part due to inhibition of Aurora kinase, and may benefit patients with FLT3-mutated AML.

Derivation of male germ cells from induced pluripotent stem cells in vitro and in reconstituted seminiferous tubules

OBJECTIVES

Previous studies have demonstrated that mouse- and human-induced pluripotent stem (iPS) cells can differentiate into primordial germ cells in vitro. However, up to now it is not known whether iPS cells would be able to differentiate into male germ cells in vivo. The aim of this study was to explore differentiation potential of iPS cells to male germ cells in vitro and in vivo.

MATERIALS AND METHODS

In this study, approaches using in vitro retinoic acid induction and in vivo ectopic transplantation were combined to induce iPS cells to become male germ cells.

RESULTS

RT-PCR showed that expression of pre-meiotic and meiotic germ cell-specific genes was enhanced in iPS cell-derived embryoid bodies (EBs) compared to mRNA transcripts of iPS cells. Immunofluorescence analysis revealed that iPS cell-derived EBs positively expressed germ-cell markers VASA, c-Kit and SCP3. Furthermore, iPS cell-derived cells dissociated from EBs were injected with testicular cells into dorsal skin of mice. Histological examination showed that iPS cell-derived cells could reconstitute seminiferous tubules, and meanwhile, iPS cell-derived germ cells could settle at basement membranes of reconstituted tubules.

CONCLUSION

Our results suggest that iPS cells are able to differentiate into male germ cells in vitro and that reconstituted seminiferous tubules may provide a functional niche for exogenous iPS cell-derived male germ cells. Derivation of male germ cells from iPS cells has potential application for treating male infertility and provides an ideal platform for elucidating molecular mechanisms of male germ-cell development.

Fluxes, variability and sources of cadmium, lead, arsenic and mercury in dry atmospheric depositions in urban, suburban and rural areas

In China's largest city, Shanghai, dry deposition fluxes of Cd, Pb, As and Hg were 137, 19354, 2897 and 9.4 μgm(-2)a(-1), respectively in an urban area, intermediate in a suburban area, and 51.7, 5311, 1703 and 7.3 μgm(-2)a(-1), respectively in a rural area. Enrichment factors were Cd>Pb>As>Hg. Seasonal variations of metals differed: Pb and As were dominated by fossil fuel combustion, Cd was related to industrial pollution, and natural source controlled Hg levels.

454 EST analysis detects genes putatively involved in ginsenoside biosynthesis in Panax ginseng

Panax ginseng C.A. Meyer is one of the most highly valued medicinal plants in the world. To analyze the transcriptome of P. ginseng and discover the genes involved in ginsenoside biosynthesis, cDNAs derived from the total RNA of 11-year-old, wood-grown P. ginseng roots were analyzed by 454 sequencing. A total of 217,529 high quality reads (expressed sequence tags, ESTs), with an average length of 409 bases, were generated from a one-quarter run to yield 31,741 unique sequences. The majority (20,198; 63.6%) of the unique sequences were annotated using BLAST similarity searches. A total of 16,810 and 16,577 unique sequences were assigned to functional classifications and biochemical pathways based on Gene Ontology analysis and the Kyoto Encyclopedia of Genes and Genomes assignment, respectively. Nine genes involved in the biosynthesis of ginsenoside skeletons and many candidate genes putatively responsible for modification of the skeletons, including 133 cytochrome P450s and 235 glycosyltransferases, were identified. From these candidates, six transcripts encoding UDP-glycosyltransferases that were most likely to be involved in ginsenoside biosynthesis were selected. These results open a new avenue by which to explore and exploit biosynthetic and biochemical properties that may lead to drug improvement. These 454 ESTs will provide the foundation for further functional genomic research into the traditional herb P. ginseng or its closely related species.

Phosphatidylinositol 3-Kinase-C2β Inhibits Cisplatin-Mediated Apoptosis via the Akt Pathway in Oesophageal Squamous Cell Carcinoma

A major problem in treating oesophageal squamous cell carcinoma (ESCC) with cisplatin is the development of drug resistance. In order to determine whether phosphatidylinositol 3-kinase (PI3K)-C2β (encoded by the PIK3C2B gene) reduced the sensitivity of ESCC to cisplatin, transfected Eca109 cells that overexpressed PIK3C2B were produced. Additionally, PI3K-C2β-siRNA was used to silence endogenous PI3K-C2β in EC9706 cisplatin-resistant cells. The relationship between PIK3C2B expression and clinicopathological characteristics was also investigated in samples from 61 patients. The overexpression of PIK3C2B in Eca109 cells significantly inhibited cisplatin-induced apoptosis and cleavage of caspase-3. Knockdown of PI3K-C2β enhanced cisplatin-induced apoptosis in EC9706 cells. PIK3C2B expression was associated with an increased level of phosphorylated Akt. Based on the tumour samples, expression of PIK3C2B was associated with tumour metastasis and in vitro assay suggested that it mediated cell migration. These results indicated that PI3K-C2β, via the Akt signalling pathway, might play a key role in cisplatin resistance and that targeting this pathway might be useful in treating cisplatin-resistant tumours.

Limited-angle x-ray luminescence tomography: methodology and feasibility study

X-ray luminescence tomography (XLT) has recently been proposed as a new imaging modality for biological imaging applications. This modality utilizes phosphor nanoparticles which luminesce near-infrared light when excited by x-ray photons. The advantages of this modality are that it uniquely combines the high sensitivity of radioluminescent nanoparticles and the high spatial localization of collimated x-ray beams. Currently, XLT has been demonstrated using x-ray spatial encoding to resolve the imaging volume. However, there are applications where the x-ray excitation may be limited by geometry, where increased temporal resolution is desired, or where a lower dose is mandatory. This paper extends the utility of XLT to meet these requirements by incorporating a photon propagation model into the reconstruction algorithm in an x-ray limited-angle (LA) geometry. This enables such applications as image-guided surgery, where the ability to resolve lesions at depths of several centimeters can be the key to successful resection. The hybrid x-ray/diffuse optical model is first formulated and then demonstrated in a breast-sized phantom, simulating a breast lumpectomy geometry. Both numerical and experimental phantoms are tested, with lesion-simulating objects of various sizes and depths. Results show localization accuracy with median error of 2.2 mm, or 4% of object depth, for small 2-14 mm diameter lesions positioned from 1 to 4.5 cm in depth. This compares favorably with fluorescence optical imaging, which is not able to resolve such small objects at this depth. The recovered lesion size has lower size bias in the x-ray excitation direction than the optical direction, which is expected due to the increased optical scatter. However, the technique is shown to be quite invariant in recovered size with respect to depth, as the standard deviation is less than 2.5 mm. Sensitivity is a function of dose; radiological doses are found to provide sufficient recovery for µg ml(-1) concentrations, while therapy dosages provide recovery for ng ml(-1) concentrations. Experimental phantom results agree closely with the numerical results, with positional errors recovered within 8.6% of the effective depth for a 5 mm object, and within 5.2% of the depth for a 10 mm object. Object-size median error is within 2.3% and 2% for the 5 and 10 mm objects, respectively. For shallow-to-medium depth applications where optical and radio-emission imaging modalities are not ideal, such as in intra-operative procedures, LAXLT may be a useful tool to detect molecular signatures of disease.

SNP discovery, expression and cis-regulatory variation in the UGT2B genes

UGT2B enzymes metabolize multiple endogenous and exogenous molecules, including steroid hormones and clinical drugs. However, little is known about the inter-individual variation in gene expression and its determinants. We re-sequenced candidate regulatory regions and the partial coding regions (41.1 kb) of UGT2B genes and identified 332 genetic variants. We measured gene expression in normal breast and liver samples and observed different patterns. The expression levels varied greatly across individuals in both tissues and were significantly correlated with each other in liver. Genotyping of tagging single-nucleotide polymorphisms (SNPs) in the same samples and association tests between genotype and transcript levels identified 62 variants that were associated with at least one UGT2B mRNA levels in either tissue. Most of these cis-regulatory SNPs were not shared between tissues, suggesting that this gene family is regulated in a tissue-specific manner. Our results provide insight into studying the role of UGT2B variation in hormone-dependent cancers and drug response.