BK-UM in patients with recurrent ovarian cancer or peritoneal cancer: a first-in-human phase-I study.

BACKGROUND: BK-UM (CRM197) is a mutant form of diphtheria toxin and a specific inhibitor of heparin-binding epidermal growth factor-like growth factor (HB-EGF). We assessed the safety, pharmacokinetics, recommended dose, and efficacy of BK-UM in patients with recurrent ovarian cancer (OC) or peritoneal cancer (PC), and measured HB-EGF levels in serum and abdominal fluid after BK-UM administration. METHODS: Eleven patients with advanced or recurrent OC or PC were enrolled and treated with BK-UM via the intraperitoneal route. The dose was escalated (1.0, 2.0, 3.3, and 5.0 mg/m2) using a 3 + 3 design. RESULTS: Eight of 11 patients completed treatment. No dose-limiting toxicity (DLT) was experienced at dose levels 1 (1.0 mg/m2) and 2 (2.0 mg/m2). Grade 3 transient hypotension as an adverse event (defined as a DLT in the present study) was observed in two of four patients at dose level 3 (3.3 mg/m2). Treatment with BK-UM was associated with decreases in HB-EGF levels in serum and abdominal fluid in seven of 11 patients and five of eight patients, respectively. Clinical outcomes included a partial response in one patient, stable disease in five patients, and progressive disease in five patients. CONCLUSIONS: BK-UM was well tolerated at doses of 1.0 and 2.0 mg/m2, with evidence for clinical efficacy in patients with recurrent OC or PC. A dose of 2.0 mg/m2 BK-UM is recommended for subsequent clinical trials. TRIAL REGISTRATION: This trial was prospectively performed as an investigator-initiated clinical trial. The trial numbers are UMIN000001002 and UMIN000001001, with registration dates of 1/30/2008 and 2/4/2008, respectively. UMIN000001001 was registered as a trial for the continuous administration of BK-UM after UMIN000001002 .

Humanized gene replacement in mice reveals the contribution of cancer stroma-derived HB-EGF to tumor growth.

Tumor progression is a complex process that involves the interaction of cancer cells with the cancer-surrounding stromal cells. The cancer stroma influences the cancer cell growth and metastatic potential. The EGF family growth factor HB-EGF is synthesized in cancer cells and plays pivotal roles in oncogenic transformation and tumor progression, but the contribution of HB-EGF expressed in tumor stromal cells to tumor growth remains unclear. In the present study, we found that HB-EGF was expressed in host-derived cancer stromal cells in xenograft and allograft mouse tumor models. CRM197 is a specific inhibitor of human HB-EGF that has no effect on mouse HB-EGF. To elucidate whether host-derived stromal HB-EGF contributes to tumor growth, we generated knock-in mice expressing a CRM197-inhibitable humanized mutant form of HB-EGF. Administration of CRM197 to humanized knock-in mice that were bearing tumors derived from human or mouse cancer cells revealed that inhibition of host-derived stromal HB-EGF by CRM197 significantly reduced tumor growth. These results suggest that HB-EGF in the cancer-associated stroma plays a significant role for tumor growth, and that the HB-EGF derived from the stroma, as well as that expressed by cancer cells, is a potential target for cancer therapy. The present results also suggest that the humanized HB-EGF knock-in mice could be utilized for pathophysiological studies of HB-EGF as well as the development of therapeutic strategies targeting HB-EGF.

Critical roles of Pten in B cell homeostasis and immunoglobulin class switch recombination.

Pten is a tumor suppressor gene mutated in human cancers. We used the Cre-loxP system to generate a B cell-specific mutation of Pten in mice (bPten(flox/flox)mice). bPten(flox/flox) mice showed elevated numbers of B1a cells and increased serum autoantibodies. Among B2 cells in bPten(flox/flox) spleens, numbers of marginal zone B (MZB) cells were significantly increased while those of follicular B (FOB) cells were correspondingly decreased. Pten-deficient B cells hyperproliferated, were resistant to apoptotic stimuli, and showed enhanced migration. The survival kinase PKB/Akt was highly activated in Pten-deficient splenic B cells. In addition, immunoglobulin class switch recombination was defective and induction of activation-induced cytidine deaminase (AID) was impaired. Thus, Pten plays a role in developmental fate determination of B cells and is an indispensable regulator of B cell homeostasis.

Diphtheria toxin mutant CRM197 possesses weak EF2-ADP-ribosyl activity that potentiates its anti-tumorigenic activity.

CRM197, a mutated diphtheria toxin (DT), has long been recognized to be a non-toxic protein. Based on its non-toxic feature, this protein has been utilized for various purposes, including as an inhibitor of heparin-binding EGF-like growth factor (HB-EGF) and as an immunological adjuvant for vaccination. Here we show evidence that CRM197 has a weak toxicity. This toxicity was observed in cells over-expressing the DT receptor/proHB-EGF, but not in parental cells, indicating that the toxicity was mediated through DT receptor. CRM197 did not show any toxicity toward DT-resistant cells, which have a mutation in elongation factor 2, and a cell-free assay revealed the existence of weak EF-2-ADP ribosylation activity in fragment A of CRM197. Thus, the present study indicates a requirement for specific care in the use of CRM197 at a high dosage, although the toxicity of CRM197 is about 10(6) times less than that of wild-type DT. We found that a monoclonal antibody to DT inhibited CRM197 toxicity, but did not affect the inhibitory activity of CRM197 toward HB-EGF-induced mitogenic activity. CRM197 strongly inhibits tumour growth in nude mice. The anti-DT monoclonal antibody administered with CRM197 reduced the anti- tumourigenic effect of CRM197, indicating that the toxicity of CRM197 potentiates its anti- tumourigenic effect.

Cytoplasmic domain phosphorylation of heparin-binding EGF-like growth factor.

Heparin-binding EGF-like growth factor (HB-EGF) is synthesized as a transmembrane precursor protein that is anchored to the plasma membrane. The extracellular EGF-like domain acts as a mitogen and motogen upon ectodomain shedding, but the functional roles of the transmembrane and cytoplasmic domains are largely unknown. We demonstrate here that cytoplasmic domain of HB-EGF is phosphorylated by external stimuli, and that the phosphorylation site is involved in HB-EGF-dependent tumorigenesis. Treatment of Vero cells overexpressing human HB-EGF with 12-O-tetradecanoylphorbol-13-acetate (TPA) caused ectodomain shedding of HB-EGF and generated two carboxyl (C)-terminal fragments with distinct electrophoretic mobilities. Mutation analysis showed that Ser207 in the cytoplasmic domain of HB-EGF is phosphorylated upon TPA stimulation, generating two C-terminal fragments with distinct phosphorylation states. Treatment of cells with lysophosphatidic acid, anisomycin, and calcium ionophore, all of which are known to induce ectodomain shedding, also caused phosphorylation of HB-EGF. Although ectodomain shedding and phosphorylation of HB-EGF occurred coordinately, Ala substitution of Ser207 had no effect on TPA-induced or constitutive ectodomain shedding. Injection of cells overexpressing HB-EGF into nude mice showed that Ala substitution of Ser207 reduced the tumorigenic activity of HB-EGF, even though the cell surface level and ectodomain shedding of HB-EGF were not affected by the mutation. Moreover, we found that the cytoplasmic domain of another EGFR ligand, transforming growth factor-alpha, is phosphorylated upon TPA stimulation. Thus, the present results suggest a novel role for the cytoplasmic domain of HB-EGF and other EGF family growth factors that is regulated by phosphorylation.

The Centre for Modeling Human Disease Gene Trap resource.

Gene trap mutagenesis of mouse embryonic stem cells generates random loss-of-function mutations, which can be identified by a sequence tag and can often report the endogenous expression of the mutated gene. The Centre for Modeling Human Disease is performing expression- and sequence-based screens of gene trap insertions to generate new mouse mutations as a resource for the scientific community. The gene trap insertions are screened using multiplexed in vitro differentiation and induction assays, and sequence tags are generated to complement expression profiles. Researchers may search for insertions in genes expressed in target cell lineages, under specific in vitro conditions, or based upon sequence identity via an online searchable database (http://www.cmhd.ca/sub/genetrap.asp). The clones are available as a resource to researchers worldwide to help to functionally annotate the mammalian genome and will serve as a source to test candidate loci identified by phenotype-driven mutagenesis screens.

Keratinocyte-specific Pten deficiency results in epidermal hyperplasia, accelerated hair follicle morphogenesis and tumor formation.

PTEN is a tumor suppressor gene mutated in many human cancers. We used the Cre-loxP system to generate a keratinocyte-specific null mutation of Pten in mice (k5Pten(flox/flox) mice). k5Pten(flox/flox) mice exhibit wrinkled skin because of epidermal hyperplasia and hyperkeratosis and ruffled, shaggy, and curly hair. Histological examination revealed that skin morphogenesis is accelerated in k5Pten(flox/flox) mice. Within 3 weeks of birth, 90% of k5Pten(flox/flox) mice die of malnutrition possibly caused by hyperkeratosis of the esophagus. All k5Pten(flox/flox) mice develop spontaneous tumors within 8.5 months of birth, and chemical treatment accelerates the onset of tumors. k5Pten(flox/flox) keratinocytes are hyperproliferative and resistant to apoptosis and show increased activation of the Pten downstream signaling mediators Akt/protein kinase B (PKB) and extracellular signal-regulated kinase. Pten is thus an important regulator of normal development and oncogenesis in the skin.

Prediction and testing of novel transcriptional networks regulating embryonic stem cell self-renewal and commitment.

Stem cell fate is governed by the integration of intrinsic and extrinsic positive and negative signals upon inherent transcriptional networks. To identify novel embryonic stem cell (ESC) regulators and assemble transcriptional networks controlling ESC fate, we performed temporal expression microarray analyses of ESCs after the initiation of commitment and integrated these data with known genome-wide transcription factor binding. Effects of forced under- or overexpression of predicted novel regulators, defined as differentially expressed genes with potential binding sites for known regulators of pluripotency, demonstrated greater than 90% correspondence with predicted function, as assessed by functional and high-content assays of self-renewal. We next assembled 43 theoretical transcriptional networks in ESCs, 82% (23 out of 28 tested) of which were supported by analysis of genome-wide expression in Oct4 knockdown cells. By using this integrative approach, we have formulated novel networks describing gene repression of key developmental regulators in undifferentiated ESCs and successfully predicted the outcomes of genetic manipulation of these networks.

BopB is a type III secreted protein in Bordetella bronchiseptica and is required for cytotoxicity against cultured mammalian cells.

The cytotoxicity of Bordetella bronchiseptica to infected cells is known to be dependent on a B. bronchiseptica type III secretion system. Although the precise mechanism of the type III secretion system is unknown, BopN, BopD and Bsp22 have been identified as type III secreted proteins. In order to identify other proteins secreted via the type III secretion machinery in Bordetella, a type III mutant was generated, and its secretion profile was compared with that of the wild-type strain. The results showed that the wild-type strain, but not the type III mutant, secreted a 40-kDa protein into the culture supernatant. This protein was identified as BopB by the analysis of its N-terminal amino acid sequence. Severe cytotoxicity such as necrosis was induced in L2 cells by infection with the wild-type B. bronchiseptica. In contrast, this effect was not observed by the BopB mutant infection. The haemolytic activity of the BopB mutant was greatly impaired compared with that of the wild-type strain. The results of a digitonin assay strongly suggested that BopB was translocated into HeLa cells infected with the wild-type strain. Taken together, our results demonstrate that Bordetella secretes BopB via a type III secretion system during infection. BopB may play a role in the formation of pores in the host plasma membrane which serve as a conduit for the translocation of effector proteins into host cells.