Elena Kleymenova

Characterization of an Akt Kinase Inhibitor with Potent Pharmacodynamic and Antitumor Activity

Akt kinases 1, 2, and 3 are important regulators of cell survival and have been shown to be constitutively active in a variety of human tumors. GSK690693 is a novel ATP-competitive, low-nanomolar pan-Akt kinase inhibitor. It is selective for the Akt isoforms versus the majority of kinases in other families; however, it does inhibit additional members of the AGC kinase family. It causes dose-dependent reductions in the phosphorylation state of multiple proteins downstream of Akt, including GSK3 beta, PRAS40, and Forkhead. GSK690693 inhibited proliferation and induced apoptosis in a subset of tumor cells with potency consistent with intracellular inhibition of Akt kinase activity. In immune-compromised mice implanted with human BT474 breast carcinoma xenografts, a single i.p. administration of GSK690693 inhibited GSK3 beta phosphorylation in a dose- and time-dependent manner. After a single dose of GSK690693, >3 micromol/L drug concentration in BT474 tumor xenografts correlated with a sustained decrease in GSK3 beta phosphorylation. Consistent with the role of Akt in insulin signaling, treatment with GSK690693 resulted in acute and transient increases in blood glucose level. Daily administration of GSK690693 produced significant antitumor activity in mice bearing established human SKOV-3 ovarian, LNCaP prostate, and BT474 and HCC-1954 breast carcinoma xenografts. Immunohistochemical analysis of tumor xenografts after repeat dosing with GSK690693 showed reductions in phosphorylated Akt substrates in vivo. These results support further evaluation of GSK690693 as an anticancer agent.

Tuberin-Dependent Membrane Localization of Polycystin-1: A Functional Link between Polycystic Kidney Disease and the TSC2 Tumor Suppressor Gene

The PKD1 gene accounts for 85% of autosomal dominant polycystic kidney disease (ADPKD), the most common human genetic disorder. Rats with a germline inactivation of one allele of the Tsc2 tumor suppressor gene developed early onset severe bilateral polycystic kidney disease, with similarities to the human contiguous gene syndrome caused by germline codeletion of PKD1 and TSC2 genes. Polycystic rat renal cells retained two normal Pkd1 alleles but were null for Tsc2 and exhibited loss of lateral membrane-localized polycystin-1. In tuberin-deficient cells, intracellular trafficking of polycystin-1 was disrupted, resulting in sequestration of polycystin-1 within the Golgi and reexpression of Tsc2 restored correct polycystin-1 membrane localization. These data identify tuberin as a determinant of polycystin-1 functional localization and, potentially, ADPKD severity.

Exposure In Utero to Di(n-Butyl) Phthalate Alters the Vimentin Cytoskeleton of Fetal Rat Sertoli Cells and Disrupts Sertoli Cell-Gonocyte Contact

Abstract Di(n-butyl) phthalate (DBP) is commonly used in personal care products and as a plasticizer to soften consumer plastic products. Male rats exposed to DBP in utero have malformations of the male reproductive tract and testicular atrophy characterized by degeneration of seminiferous epithelium and decreased sperm production. In the fetal testis, in utero exposure to DBP reportedly resulted in reduced testosterone levels, Leydig cell aggregates, and multinucleated gonocytes (MNG). We investigated whether exposure in utero to DBP affects rat fetal Sertoli cells and compromises interactions between Sertoli and germ cells in the developing testis. Histological examination showed that MNG occurred at low frequency in the normal fetal rat testis. Exposure in utero at the dose level of DBP above estimated environmental or occupational human exposure levels significantly increased the number of these abnormal germ cells. Postnatally, MNG exhibited aberrant mitoses and were detected at the basal lamina. MNG were not apoptotic in the fetal and postnatal rat testes, as indicated by TUNEL. Sertoli cells in DBP-exposed fetal testis had retracted apical processes, altered organization of the vimentin cytoskeleton, and abnormal cell-cell contacts with gonocytes. The effect of DBP on Sertoli cell morphology at the level of light microscopy was reversed after birth and cessation of exposure. Our data indicate that fetal Sertoli cells are targeted by exposure in utero to DBP and suggest that abnormal interactions between Sertoli and germ cells during fetal life play a role in the development of MNG.

Dose-dependent effects on cell proliferation, seminiferous tubules, and male germ cells in the fetal rat testis following exposure to di (n-butyl) phthalate

Adult male rats gestationally exposed to di(n‐butyl)phthalate (DBP) have dysgenetic testes characterized by seminiferous epithelial degeneration, clustering of Leydig cells, and decreased spermatogenesis. Cell proliferation and apoptosis are key processes regulating development of the testis, and alterations in these processes may underlie testicular dysgenesis. Objective: To determine whether gestational exposure to DBP affects cell proliferation and apoptosis in the developing rat testis. Design: Pregnant dams were exposed to different dose levels of DBP in mid‐gestation and cellular outcomes in fetal and early postnatal testes were assayed by histological and morphometric approaches. Results: Gestational exposure to high dose DBP inhibited proliferation of fetal testicular somatic cells but did not affect apoptosis. Exposed fetal testes had a smaller volume and decreased cell numbers, with decreases in both the tubular and interstitial cell populations. A reduction was observed in the testis volume and altered seminiferous tubule morphometry at ≥50 mg/kg/d, and a decreased testicular cell number at ≥30 mg/kg/d DBP. The number of multinucleated gonocytes in DBP‐exposed fetal testes increased after exposure to ≥100 mg/kg/d. The number of proliferating cells in the DBP‐exposed testis rapidly rose after birth (when exposure stopped), and the testis volume and the total cell number was comparable to control by postnatal day 2. Conclusion: DBP reversibly inhibits proliferation of somatic cells in the fetal rat testis. Decreased proliferation, rather than increased apoptosis, is the underlying mechanism of altered fetal development of DBP‐exposed seminiferous tubules contributing to testicular dysgenesis. Microsc. Res. Tech., 2009.

Determination of loss of heterozygosity in frozen and paraffin embedded tumors by denaturating high-performance liquid chromatography (DHPLC).

Spontaneous renal cell carcinoma (RCC) occurs with a high frequency in Eker rats carrying a germline alteration of the tuberous sclerosis-2 (Tsc-2) tumor suppressor gene. To determine the frequency with which the wild-type allele of the Tsc-2 gene is lost in RCC and the ability of DHPLC to detect loss of heterozygosity (LOH) at this gene locus, fresh-frozen and paraffin-embedded formalin-fixed tumors from heterozygous Eker rats (Tsc-2(Ek/+)) were examined for LOH at the Tsc-2 locus. LOH was determined by quantitation of peak areas of PCR products specific for the mutant and wild-type Tsc-2 alleles. For normal DNA isolated from heterozygous animals, the allele ratio (AR) of mutant to wild-type PCR products was empirically determined to be 1.5+/-0.3 (n=30) and LOH was defined as >2 standard deviations away from this mean, i.e. any AR >2.1. Analysis of 15 spontaneous frozen RCC samples showed LOH in 10/15 samples (66%). Carcinogen-induced tumors exhibited an even higher frequency of LOH, with 6/6 paraffin-embedded, formalin-fixed tumors exhibiting LOH. 100% concordance was observed between the results obtained by DHPLC and traditional methodologies. Therefore, LOH appears to occur with a high frequency in both spontaneous and carcinogen-induced RCC in this animal model and DHPLC is a sensitive and high throughput methodology for detecting this type of genetic alteration.

Identification of a tumor-specific methylation site in the Wilms tumor suppressor gene.

Malignant mesothelioma is one of the very few extra-renal neoplasms in which the Wilms tumor suppressor gene (wt1) is expressed. We examined wt1 for alterations in rat mesotheliomas, a well characterized animal model for the human disease. Southern analysis revealed a 3.5 kb EcoRI wt1 fragment readily detectable in majority of mesothelioma cell lines and primary mesotheliomas but not in normal rat tissues. Cloning and sequencing of this fragment revealed that the presence of this EcoRI fragment resulted from an in-ability of this enzyme to cut at a EcoRI site in intron 1 of wt1. This site contains potential motifs for cytosine methylation and treatment of mesothelioma cells with 5-azadeoxycytosine restored the normal EcoRI digestion pattern of wt1 in these cells indicating that cleavage was inhibited by methylation at this site. Southern analysis using HpaII/MspI digestion revealed no differences in methylation between mesothelioma cell lines and normal mesothelium at other CpG sites in wt1 5′ region. Renal cell carcinoma lines which did not express wt1 were also methylated at this EcoRI site. Our identification of a site frequently methylated in malignant cells, independent of gene expression, provides a new model system to study determinants of site-specific methylation in tumors.

Retention of membrane‐localized β‐catenin in cells lacking functional polycystin‐1 and tuberin

The tuberous sclerosis (TSC) 2 tumor suppressor gene encodes the protein tuberin, which has recently been shown to play a crucial role in the intracellular trafficking of polycystin‐1, the product of the polycystic kidney disease (PDK) 1 gene. PKD1 is responsible for most cases of autosomal dominant polycystic kidney disease, which has been described as “neoplasia in disguise.” Polycystin‐1 is a membrane protein localized to adherens junctions in a complex containing E‐cadherin and α‐, β‐, and γ‐catenins. To determine whether loss of membrane localization of polycystin‐1 and E‐cadherin affects the function of β‐catenin, β‐catenin localization and signaling were characterized in tuberin‐null EKT2 and ERC15 cells and in tuberin‐positive TRKE2 cells derived from polycystic, neoplastic, and normal rat kidney epithelial cells, respectively. EKT2 cells lacking tuberin because of inactivation of the Tsc2 gene fail to localize polycystin‐1 and E‐cadherin appropriately to these junctions. However, β‐catenin was retained at lateral cell membranes in both tuberin‐null and tuberin‐positive cells. Moreover, gene transcription mediated by β‐catenin T‐cell–specific transcription factor complexes showed no differences among EKT2, ERC15, and TRKE2 cells. Thus, β‐catenin was stably retained at the lateral cell membrane in tuberin‐null renal cells lacking membrane‐localized polycystin‐1 and E‐cadherin. These data suggest that, although loss of Tsc2 tumor suppressor gene function disrupts normal polycystin‐1 function and membrane localization of E‐cadherin, normal β‐catenin signaling is retained in tuberin‐null cells.

Polycystic Kidney Disease as a Result of Loss of the Tuberous Sclerosis 2 Tumor Suppressor Gene During Development

Somatic loss of function of the tuberous sclerosis 2 (TSC2) tumor suppressor gene leads to the development of benign and malignant lesions of the kidney, brain, uterus, spleen, and liver and germline loss of function of this tumor suppressor gene is embryonic lethal. In addition, the gene product of TSC2, tuberin, is necessary for normal function of the polycystic kidney disease 1 (PKD1) gene product, polycystin-1, which is required for normal cell-cell and cell-matrix interactions. We report here the development of severe polycystic kidney disease in three cases of young Eker rats carrying a germline inactivation of one allele of the Tsc2 gene. Extrarenal tumors were also noted in the spleen and uterus of these animals, which was remarkable given their young age and in the case of the spleen, diffuse involvement of the affected organ. A cell line (EKT2) was established from an affected kidney of one of these animals and used in conjunction with tissues from affected animals to elucidate the defect responsible for the development of these lesions. Affected cells were determined to have lost the wild-type Tsc2 allele while retaining two copies of chromosome 10 containing the mutant Tsc2 allele along with two normal copies of the Pkd1 gene. The genetic data, bilateral nature of the observed kidney disease, and extent of involvement of the spleen and kidney indicate that, in affected animals, loss of the wild-type Tsc2 allele occurred during embryogenesis, probably as a result of chromosome nondisjunction, with affected animals being mosaics for loss of Tsc2 gene function.

CHARACTERIZATION OF THE RAT NEUROFIBROMATOSIS 2 GENE AND ITS INVOLVEMENT IN ASBESTOS-INDUCED MESOTHELIOMA

The neurofibromatosis 2 (NF2) tumor suppressor gene was recently implicated in the genesis of human mesothelioma. To investigate the role of this tumor suppressor gene in rat asbestos‐induced mesothelioma, a commonly used model for the human disease, we characterized the rat homologue of NF2 and examined rat chrysotile‐induced primary mesotheliomas and cell lines derived from chrysotile‐ and crocidolite‐induced mesotheliomas for alterations in this gene. The coding sequence obtained for the rat NF2 gene had 90% nucleotide homology with the human NF2 gene. The rat NF2 gene was ubiquitously expressed as a 4.4‐kb transcript in normal rat tissues as well as in rat mesothelioma cell lines. Reverse transcription‐polymerase chain reaction analysis to examine splicing of NF2 exons in mesothelioma cells indicated that the exon splicing pattern was similar in normal and neoplastic cells. To determine if mutations had occurred in the NF2 coding region in rat mesotheliomas, single‐strand conformation polymorphism analysis and direct sequencing were used to screen 10 primary tumors and six tumor cell lines. No DNA sequence alterations were observed in any of the rat mesothelioma samples examined. These findings contrast with data reported previously for human mesotheliomas, in which the NF2 gene was found to be mutated in 40% of cases. Taken together, these data suggest that the role of NF2 in the development of rodent asbestos‐induced mesothelioma may differ significantly from the role in the human disease. Mol. Carcinog. 18:54–60, 1997.

Tissue-specific Expression and Splicing of the Rat Polycystic Kidney Disease 1 Gene

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic potentially lethal human disorder and the polycystic kidney disease 1 (Pkdl) gene is accounted for 85-90% of these cases. We have obtained rat Pkdl cDNA sequence and characterized splicing of Pkdl RNA transcripts in normal rat tissues. Our sequence data revealed a high conservation of the Pkdl gene between rat and other species and mapped rat Pkdl to chromosome 10 in “tail-to-tail” orientation to the tuberous sclerosis 2 (Tsc2) gene. Pkdl was found ubiquitously expressed in the normal rat tissues and the brain had a complex pattern of exon 12 splicing. A novel splicing variant lacking entire exon 31, which occurs in rat and mouse but not in humans, was also identified. As the rat appears to be a valuable model for investigating polycystic kidney disease, the characterization of the rat Pkdl gene will help facilitate future studies to elucidate the molecular mechanisms of cystogenesis in this animal model.