An open-label, phase 2 study evaluating the efficacy and safety of the anti-IGF-1R antibody cixutumumab in patients with previously treated advanced or metastatic soft-tissue sarcoma or Ewing family of tumours.

BACKGROUND: Cixutumumab (IMC-A12), a fully human immunoglobulin G1 (IgG1) monoclonal antibody, exerts preclinical activity in several sarcoma models and may be effective for the treatment of these tumours. METHODS: In this open-label, multicentre, phase 2 study, patients with previously treated advanced or metastatic rhabdomyosarcoma, leiomyosarcoma, adipocytic sarcoma, synovial sarcoma or Ewing family of tumours received intravenous cixutumumab (10mg/kg) for 1h every other week until disease progression or discontinuation. The primary end-point was the progression-free survival rate (PFR), defined as stable disease or better at 12 weeks. In each tier of disease histology, Simon's optimum 2-stage design was applied (PFR at 12 weeks P0=20%, P1=40%, α=0.10, ß=0.10). Stage 1 enrolled 17 patients in each disease group/tier, with at least four patients with stable disease or better required at 12 weeks to proceed to stage 2. RESULTS: A total of 113 patients were enrolled; all tiers except adipocytic sarcoma were closed after stage 1 due to futility. The 12-week PFR was 12% for rhabdomyosarcoma (n=17), 14% for leiomyosarcoma (n=22), 32% for adipocytic sarcoma (n=37), 18% for synovial sarcoma (n=17) and 11% for Ewing family of tumours (n=18). Median progression-free survival (weeks) was 6.1 for rhabdomyosarcoma, 6.0 for leiomyosarcoma, 12.1 for adipocytic sarcoma, 6.4 for synovial sarcoma and 6.4 for Ewing family of tumours. Among all patients, the most frequent treatment-emergent adverse events (AEs) were nausea (26%), fatigue (23%), diarrhoea (23%) and hyperglycaemia (20%). CONCLUSIONS: Patients with adipocytic sarcoma may benefit from treatment with cixutumumab. Cixutumumab treatment was well tolerated, with limited gastrointestinal AEs, fatigue and hyperglycaemia.

Correction of cross-linker sensitivity of Fanconi anemia group F cells by CD33-mediated protein transfer.

Studies have previously described the feasibility of receptor-mediated protein transfer in a cell culture model of Fanconi anemia (FA) group C. This study explores the versatility of this approach by using an antibody single-chain fusion protein to correct the phenotypic defect in FA group F cells. A 68.5-kd chimeric protein (His-M195FANCF) was expressed, consisting of a His tag, a single-chain antibody to the myeloid antigen CD33, and the FANCF protein, as well as a 43-kd His-FANCF fusion protein lacking the antibody motif, in Escherichia coli. The nickel-agarose-purified His-M195FANCF protein bound specifically to the surface of HeLa cells transfected with CD33 and internalized through vesicular structures. The fusion protein, but not CD33, sorted to the nucleus, consistent with the known nuclear localization of FANCF. No similar binding or internalization was observed with His-FANCF. Pretreatment of the transfected cells with chloroquine abolished nuclear accumulation, but there was little change with brefeldin A, indicating a minimal if any role for the Golgi apparatus in mediating transport from endosomes to the cytosol and the nucleus. The intracellular half-life of His-M195FANCF was approximately 160 minutes. Treatment of CD33-transfected FA group F lymphoblastoid cells with 0.1 mg/mL His-M195FANCF conferred resistance to mitomycin C. No similar protection was noted in CD33(-) parental cells or CD33(+) FA cells belonging to groups A and C. These results demonstrate that antibody-directed, receptor-mediated protein transfer is a versatile method for the delivery of biologically active proteins into hematopoietic cells.

Fanconi anemia group C protein prevents apoptosis in hematopoietic cells through redox regulation of GSTP1.

The Fanconi anemia group C protein (FANCC) plays an important role in hematopoiesis by ensuring the survival of hematopoietic progenitor cells through an unknown mechanism. We investigated the function of FANCC by identifying FANCC-binding proteins in hematopoietic cells. Here we show that glutathione S-transferase P1-1 (GSTP1) interacts with FANCC, and that overexpression of both proteins in a myeloid progenitor cell line prevents apoptosis following factor deprivation. FANCC increases GSTP1 activity after the induction of apoptosis. GSTP1 is an enzyme that catalyzes the detoxification of xenobiotics and by-products of oxidative stress, and it is frequently upregulated in neoplastic cells. Although FANCC lacks homology with conventional disulfide reductases, it functions by preventing the formation of inactivating disulfide bonds within GSTP1 during apoptosis. The prevention of protein oxidation by FANCC reveals a novel mechanism of enzyme regulation during apoptosis and has implications for the treatment of degenerative diseases with thiol reducing agents.

Functional analysis of the putative peroxidase domain of FANCA, the Fanconi anemia complementation group A protein.

Fanconi anemia (FA) is an autosomal recessive disorder manifested by chromosomal breakage, birth defects, and susceptibility to bone marrow failure and cancer. At least seven complementation groups have been identified, and the genes defective in four groups have been cloned. The most common subtype is complementation group A. Although the normal functions of the gene products defective in FA cells are not completely understood, a clue to the function of the FA group A gene product (FANCA) was provided by the detection of limited homology in the amino terminal region to a class of heme peroxidases. We evaluated this hypothesis by mutagenesis and functional complementation studies. We substituted alanine residues for the most conserved FANCA residues in the putative peroxidase domain and tested their effects on known biochemical and cellular functions of FANCA. While the substitution mutants were comparable to wild-type FANCA with regard to their stability, subcellular localization, and interaction with FANCG, only the Trp(183)-to-Ala substitution (W183A) abolished the ability of FANCA to complement the sensitivity of FA group A cells to mitomycin C. By contrast, TUNEL assays for apoptosis after exposure to H2O2 showed no differences between parental FA group A cells, cells complemented with wild-type FANCA, and cells complemented with the W183A of FANCA. Moreover, semiquantitative RT-PCR analysis for the expression of the peroxide-sensitive heme oxygenase gene showed appropriate induction after H2O2 exposure. Thus, W183A appears to be essential for the in vivo activity of FANCA in a manner independent of its interaction with FANCG. Moreover, neither wild-type FANCA nor the W183A mutation appears to alter the peroxide-induced apoptosisor peroxide-sensing ability of FA group A cells.

Cancer predisposition caused by elevated mitotic recombination in Bloom mice.

Bloom syndrome is a disorder associated with genomic instability that causes affected people to be prone to cancer. Bloom cell lines show increased sister chromatid exchange, yet are proficient in the repair of various DNA lesions. The underlying cause of this disease are mutations in a gene encoding a RECQ DNA helicase. Using embryonic stem cell technology, we have generated viable Bloom mice that are prone to a wide variety of cancers. Cell lines from these mice show elevations in the rates of mitotic recombination. We demonstrate that the increased rate of loss of heterozygosity (LOH) resulting from mitotic recombination in vivo constitutes the underlying mechanism causing tumour susceptibility in these mice.

Localization of the Bloom syndrome helicase to punctate nuclear structures and the nuclear matrix and regulation during the cell cycle: comparison with the Werner's syndrome helicase.

The Bloom (BLM) and Werner's (WRN) syndrome proteins may regulate recombination and DNA repair. Using a novel polyclonal antibody to human BLM, we detected the 170-kda BLM antigen in wild-type but not Bloom syndrome cells. BLM was localized to punctate nuclear structures. The level of BLM but not WRN was 3.6 fold-higher in G(1)/S-synchronized fibroblasts than in G(0)-synchronized fibroblasts. BLM-positive cells invariably expressed topoisomerase IIalpha, whereas topoisomerase IIbeta was expressed constitutively. Transfections of BLM deletion mutants demonstrated that the C-terminal domain of BLM mediated nuclear entry and the central helicase domain was necessary for producing the punctate pattern. By subcellular fractionation, BLM was found primarily in high-salt extracts of the nucleoplasm and the nuclear matrix and was enriched in G(1)/S-synchronized cells compared with G(0)-synchronized cells. There was no interaction between BLM and WRN or topoisomerases IIalpha and IIbeta in fibroblasts. These results demonstrate that BLM is targeted to specific nuclear structures and that its expression is enhanced during cell growth. The known nucleolar localization of WRN, its invariant expression during the cell cycle, and the lack of interaction between BLM and WRN suggest distinct roles for BLM and WRN in processes such as DNA repair and recombination.

Targeting of a heterologous protein to a regulated secretion pathway in cultured endothelial cells.

The stimulation of regulated exocytosis in vascular endothelial cells (EC) by a variety of naturally occurring agonists contributes to the interrelated processes of inflammation, thrombosis, and fibrinolysis. The Weibel-Palade body (WPB) is a well-described secretory granule in EC that contains both von Willebrand factor (vWF) and P-selectin, but the mechanisms responsible for the targeting of these proteins into this organelle remain poorly understood. Through adenoviral transduction, we have expressed human growth hormone (GH) as a model of regulated secretory protein sorting in EC. Immunofluorescence microscopy of EC infected with GH-containing recombinant adenovirus (GHrAd) demonstrated a granular distribution of GH that colocalized with vWF. In contrast, EC infected with an rAd expressing the IgG(1) heavy chain (IG), a constitutively secreted protein, did not demonstrate colocalization of IG and vWF. In response to phorbol ester, GH as well as endogenously synthesized vWF were rapidly released from GHrAd-infected EC. By immunofluorescence microscopy, granular colocalization of GH with endogenous tissue-type plasminogen activator (tPA) was also demonstrated, and most of the tPA colocalized with vWF. These data indicate that EC are capable of selectively targeting heterologous proteins, such as GH, to the regulated secretory pathway, which suggests that EC and neuroendocrine cells share common protein targeting recognition signals or receptors.

A physical complex of the Fanconi anemia proteins FANCG/XRCC9 and FANCA.

Fanconi anemia (FA) is a recessively inherited disease characterized at the cellular level by spontaneous chromosomal instability and specific hypersensitivity to cross-linking agents. FA is genetically heterogeneous, comprising at least eight complementation groups (A-H). We report that the protein encoded by the gene mutated in complementation group G (FANCG) localizes to the cytoplasm and nucleus of the cell and assembles in a molecular complex with the FANCA protein, both in vivo and in vitro. Endogenous FANCA/FANCG complex was detected in both non-FA cells and in FA cells from groups D and E. By contrast, no complex was detected in specific cell lines belonging to groups A and G, whereas reduced levels were found in cells from groups B, C, F, and H. Wild-type levels of FANCA/FANCG complex were restored upon correction of the cellular phenotype by transfection or cell fusion experiments, suggesting that this complex is of functional significance in the FA pathway. These results indicate that the cellular FA phenotype can be connected to three biochemical subtypes based on the levels of FANCA/FANCG complex. Disruption of the complex may provide an experimental strategy for chemosensitization of neoplastic cells.

Protein replacement by receptor-mediated endocytosis corrects the sensitivity of Fanconi anemia group C cells to mitomycin C.

Current methods for direct gene transfer into hematopoietic cells are inefficient. Here we show that functional complementation of Fanconi anemia (FA) group C cells by protein replacement can be as efficacious as by transfection with wild-type FAC cDNA. We expressed a chimeric protein (called His-ILFAC) consisting of the mature coding portion of gibbon interleukin-3 (IL-3) and full-length FAC in Escherichia coli. The purified bacterial protein is internalized by hematopoietic cells via IL-3 receptors. The intracellular half-life of His-ILFAC is approximately 60 minutes, which is comparable to that of the transgene-encoded FAC protein. In this cell-culture model His-ILFAC completely corrects the sensitivity of FA group C cells to mitomycin C, but it has no effect on FA cells that belong to complementation groups A and B. We suggest that receptor-mediated endocytosis of cytokine-fusion proteins may be of general use to deliver macromolecules into hematopoietic progenitor cells.

Analysis of epitope-tagged forms of the dyskeratosis congenital protein (dyskerin): identification of a nuclear localization signal.

The X-linked form of the bone marrow failure syndrome Dyskeratosis congenital is caused by mutations in dyskerin, a 514 amino acid protein that is presumed to play a role in ribosome biogenesis. Here we report that dyskerin tagged with the human immunoglobulin epitope localizes to nuclei of transfected HeLa and COS-1 cells. A carboxyl-terminal domain consisting of amino acids 467-475 and encoding KKEKKKSKK is both necessary and sufficient to mediate nuclear entry. Immunoglobulin-tagged dyskerin did not interact with the Fanconi anemia group A protein, FANCA. These results suggest a nuclear role for dyskerin. Moreover, hematopoietic failure observed in both Dyskeratosis congenital and the most common type of Fanconi anemia is unlikely to have a common mechanism resulting from abnormal physical interactions between the respective gene products of these disorders.

The Fanconi anemia proteins FAA and FAC function in different cellular compartments to protect against cross-linking agent cytotoxicity.

Fanconi anemia (FA) is an autosomal recessive disease characterized by chromosomal instability, bone marrow failure, and a high risk of developing malignancies. Although the disorder is genetically heterogeneous, all FA cells are defined by their sensitivity to the apoptosis-inducing effect of cross-linking agents, such as mitomycin C (MMC). The cloned FA disease genes, FAC and FAA, encode proteins with no homology to each other or to any known protein. We generated a highly specific antibody against FAA and found the protein in both the cytoplasm and nucleus of mammalian cells. By subcellular fractionation, FAA is also associated with intracellular membranes. To identify the subcellular compartment that is relevant for FAA activity, we appended nuclear export and nuclear localization signals to the carboxy terminus of FAA and enriched its localization in either the cytoplasm or the nucleus. Nuclear localization of FAA was both necessary and sufficient to correct MMC sensitivity in FA-A cells. In addition, we found no evidence for an interaction between FAA and FAC either in vivo or in vitro. Together with a previous finding that FAC is active in the cytoplasm but not in the nucleus, our results indicate that FAA and FAC function in separate subcellular compartments. Thus, FAA and FAC, if functionally linked, are more likely to be in a linear pathway rather than form a macromolecular complex to protect against cross-linker cytotoxicity.

Overexpression of the fanconi anemia group C gene (FAC) protects hematopoietic progenitors from death induced by Fas-mediated apoptosis.

Fanconi anemia is a rare, inherited disorder characterized by bone marrow failure, congenital malformations, and cancer susceptibility. The group C Fanconi anemia gene, FAC, identified by expression cloning methods, encodes a protein of unknown function that may be involved in the response to apoptotic stimuli. Hematopoietic progenitor cells from Fac knock-out mice are hypersensitive to IFN-gamma, a molecule that can induce apoptosis through up-regulation of the Fas death receptor. In this study, we used FAC-overexpressing transgenic mice to examine the relationship between FAC and Fas-triggered cell death. Hematopoietic progenitors from FAC-transgenic mice were up to 10-fold less sensitive to the cytolytic effect of Fas-ligation. Our experiments implicate FAC in the regulation of apoptosis mediated by the Fas death receptor.

Werner helicase is localized to transcriptionally active nucleoli of cycling cells.

Mutations at the Werner helicase locus (WRN) are responsible for the Werner syndrome (WS), a "caricature of aging." We have localized the Werner protein (WRNp) to the nucleoli of replicating mammalian cells, where its appearance is associated with transcriptional activity. A dramatic reduction of the nucleolar signal and of [3H]uridine incorporation occurred when cultures were made quiescent or were exposed to 4-nitroquinoline-1-oxide (4NQO), to which WS cells are particularly susceptible. Total cellular levels of WRNp, however, did not change, and virtually all WRNp was in the nuclear fractions, consistent with translocation to the nucleoplasm and/or masking of the epitopes. The 4NQO-induced altered state of WRNp was prevented by Na3VO4, but not by okadaic acid, suggesting that WRNp localization/function is partially regulated by kinases/phosphatases for Tyr substrates on WRNp or interacting proteins. The repression of rDNA transcription by 4NQO was not reversed by Na3VO4. We suggest that physiological states and genotoxic agents modulate the interaction of WRNp with rDNA, consistent with a role of WRNp in rDNA transcription.

Cytoplasmic localization of a functionally active Fanconi anemia group A-green fluorescent protein chimera in human 293 cells.

Hypersensitivity to cross-linking agents and predisposition to malignancy are characteristic of the genetically heterogeneous inherited bone marrow failure syndrome, Fanconi anemia (FA). The protein encoded by the recently cloned FA complementation group A gene, FAA, has been expected to localize in the nucleus as based on the presence of sequences homologous to a bipartite nuclear localization signal (NLS) and a leucine repeat motif. In contrast to this expectation, we show here that a functionally active FAA-green fluorescent protein (GFP) hybrid resides in the cytoplasmic compartment of human kidney 293 cells. In accordance with this finding, disruption of the putative NLS by site-directed mutagenesis failed to affect both subcellular localization and the capacity to complement hypersensitivity to the cross-linking agent mitomycin C in FA-A lymphoblasts. Furthermore, the N-terminal part of FAA with the putative NLS at amino acid position 18 to 35 showed no nuclear translocation activity when fused to GFP, while the first 115 N-terminal amino acids appeared to be indispensable for the complementing activity in FA-A cells. Similarly, mutagenesis studies of the putative leucine repeat showed that, even though this region of the protein is important for complementing activity, this activity does not depend on an intact leucine zipper motif. Finally, fusion of the NLS motif derived from the SV40 large T antigen to FAA could not direct the hybrid protein into the nucleus of 293 cells, suggesting that FAA is somehow maintained in the cytoplasm via currently unknown mechanisms. Thus, like the first identified FA protein, FAC, FAA seems to exert its function in the cytoplasmic compartment suggesting FA proteins to be active in a yet to be elucidated cytoplasmic pathway that governs hematopoiesis and protects against genomic instability.

MxA overexpression reveals a common genetic link in four Fanconi anemia complementation groups.

Fanconi anemia (FA) consists of a group of at least five autosomal recessive disorders that share both clinical (e.g., birth defects and hematopoietic failure) and cellular (e.g., sensitivity to cross-linking agents and predisposition to apoptosis) features with each other. However, a common pathogenetic link among these groups has not been established. To identify genetic pathways that are altered in FA and characterize shared molecular defects, we used mRNA differential display to isolate genes that have altered expression patterns in FA cells. Here, we report that the expression of an interferon-inducible gene, MxA, is highly upregulated in cells of FA complementation groups A, B, C, and D, but it is suppressed in FA group C cells complemented with wild-type FAC cDNA as well as in non-FA cells. A posttranscriptional mechanism rather than transcriptional induction appears to account for MxA overexpression. Forced expression of MxA in Hep3B cells enhances their sensitivity to mitomycin C and induces apoptosis, similar to the FA phenotype. Thus, MxA is a downstream target of FAC and is the first genetic marker to be identified among multiple FA complementation groups. These data suggest that FA subtypes converge onto a final common pathway, which is intimately related to the interferon signaling mechanism. Constitutive activity of this pathway may explain a number of the phenotypic features of FA, particularly the pathogenesis of bone marrow failure.

Suppression of apoptosis in hematopoietic factor-dependent progenitor cell lines by expression of the FAC gene.

Fanconi anemia (FA) is a genetically heterogeneous, inherited blood disorder characterized by bone marrow failure, congenital malformations, and a predisposition to leukemias. Because FA cells are hypersensitive to DNA cross-linking agents and have chromosomal instability, FA has been viewed as a disorder of DNA repair. However, the exact cellular defect in FA cells has not been identified. Sequence analysis of the gene defective in group C patients (FAC) has shown no significant homologies to other known genes. The FAC protein has been localized to the cytoplasm, indicating that FAC may either play an indirect role in DNA repair or is involved in a different cellular pathway. Recent evidence has indicated that FA cells may be predisposed to apoptosis, especially after treatment with DNA cross-linking agents. The demonstration that genes can suppress apoptosis has been accomplished by overexpression of such genes in growth factor-dependent cell lines that die by apoptosis after factor withdrawal. Using retroviral-mediated gene transfer, we present evidence that expression of FAC in the hematopoietic factor-dependent progenitor cell lines 32D and MO7e can suppress apoptosis induced by growth factor withdrawal. Flow cytometry and morphologic analysis of propidium iodide stained cells showed significantly lower levels of apoptosis in FAC-retroviral transduced cells after growth factor deprivation. Expression of FAC in both cell lines promoted increased viability rather than proliferation, which is consistent with other apoptosis-inhibiting genes such as Bcl-2. These findings imply that FAC may act as a mediator of an apoptotic pathway initiated by growth factor withdrawal. Furthermore, the congenital malformations and hematologic abnormalities characterizing FA may be related to an increased predisposition of FA progenitor cells to undergo apoptosis, particularly in the absence of extracellular signals.

Cytoplasmic localization of FAC is essential for the correction of a prerepair defect in Fanconi anemia group C cells.

Mutations in the gene defective in Fanconi anemia complementation group C, FAC, are responsible for a subset of Fanconi anemia, a group of autosomal recessive disorders characterized by chromosomal instability, hypersensitivity to cross-linking agents, and cancer susceptibility. Although abnormalities in DNA repair have been suspected, localization of the FAC gene product to the cytoplasm has cast doubt on such a mechanism. Monitoring of interstrand DNA cross-linking shows that the predominant defect in group C cells is in the initial induction of cross-links, not in repair synthesis. Both the cross-linking defect and the enhanced cytotoxicity of cross-linkers on Fanconi anemia group C cells are corrected completely by cytoplasmic isoforms of the FAC protein, but not by an isoform targeted to the nucleus. The ability of FAC to correct these phenotypic abnormalities reaches a maximum threshold despite overexpression leading to higher levels of cytosolic protein. These results demonstrate that cytoplasmic localization is essential for the intracellular activity of the FAC protein. It is proposed that this activity is coupled to a cytoplasmic defense mechanism against a specific class of genotoxic agents.