Takefumi Komiya

t(11;19)(q21;p13) translocation in mucoepidermoid carcinoma creates a novel fusion product that disrupts a Notch signaling pathway

Truncation of Notch1 has been shown to cause a subtype of acute leukemia, and activation of Notch4 has been associated with mammary and salivary gland carcinomas of mice. Here we identify a new mechanism for disrupting Notch signaling in human tumorigenesis, characterized by altered function of a new ortholog of the Drosophila melanogaster Notch co-activator molecule Mastermind. We cloned the t(11;19) translocation that underlies the most common type of human malignant salivary gland tumor. This rearrangement fuses exon 1 from a novel gene of unknown function at 19p13, termed mucoepidermoid carcinoma translocated 1 (MECT1), with exons 2–5 of a novel member of the Mastermind-like gene family (MAML2) at 11q21 (ref. 3). Similar to D. melanogaster Mastermind and MAML1 (refs. 4,5), full-length MAML2 functioned as a CSL (CBF-1, suppressor of hairless and Lag-1)-dependent transcriptional co-activator for ligand-stimulated Notch. In contrast, MECT1–MAML2 activated transcription of the Notch target gene HES1 independently of both Notch ligand and CSL binding sites. MECT1–MAML2 induced foci formation in RK3E epithelial cells, confirming a biological effect for the fusion product. These data suggest a new mechanism to disrupt the function of a Notch co-activator in a common type of malignant salivary gland tumor.

Germline PTEN Mutation Cowden Syndrome: An Underappreciated Form of Hereditary Kidney Cancer

PURPOSEnCowden syndrome is a hereditary cancer syndrome associated with a germline mutation in PTEN. Patients are predisposed to multiple malignancies including renal cell carcinoma.nnnMATERIALS AND METHODSnPatients with Cowden syndrome were evaluated as part of a clinical protocol. Those with a history of renal cell carcinoma underwent review of clinical features, tumor characteristics and family history. Renal tumors were evaluated for loss of heterozygosity.nnnRESULTSnAmong 24 patients with Cowden syndrome 4 were identified with renal cell carcinoma (16.7%). Three patients had solitary tumors, 2 with papillary type I histology and 1 with clear cell histology. The fourth patient had bilateral, synchronous chromophobe tumors. No patients had a prior family history of renal cell carcinoma. All patients with renal cell carcinoma had dermatologic manifestations of Cowden syndrome and had macrocephaly. Loss of heterozygosity at the PTEN mutation was identified in 4 tumors (80%). No genotype-phenotype association was found, as the same mutation was identified in different renal cell carcinoma histologies.nnnCONCLUSIONSnRenal cell carcinoma is an underappreciated feature of Cowden syndrome. As most patients lack a prior family history or a distinctive renal cell carcinoma histology, recognition of the associated nonrenal features should target referral for genetic counseling. PTEN loss of heterozygosity is common in Cowden syndrome renal tumors. Because loss of PTEN can activate mTOR and mTOR inhibitors are Food and Drug Administration approved to treat renal cell carcinoma, these agents have clinical potential in renal cell carcinoma associated with Cowden syndrome.

Ritterazine B, a new cytotoxic natural compound, induces apoptosis in cancer cells

PurposeRitterazinexa0B, one of the ritterazine analogues extracted from Ritterella tokioka, has been shown to be chemically similar to cephalostatin 1, and among the ritterazine derivatives is the most cytotoxic to P388 murine leukemia cells. The objective of this study was to determine the cytotoxicity of ritterazinexa0B to non-small-cell lung cancer (NSCLC) cells in vitro and its effects on the cell cycle and apoptosis.MethodsThe cytotoxicity of ritterazinexa0B against PC14 NSCLC cells was investigated using a 4-day MTT assay. Morphological changes in cells after exposure to this compound were evaluated by phase-contrast microscopy. The effects on the cell cycle of HL-60 leukemia cells and PC14 cells were elucidated by flow cytometry and an in vitro CDK/cyclin kinase assay. Induction of apoptosis in HL-60 cells was assessed using the TUNEL assay and Hoechst 33342 staining. In addition, molecules involved in apoptosis were evaluated by Western blotting.ResultsRitterazinexa0B exerted strong cytotoxic effects against PC14 cells with a mean GI50 of 75.1xa0nM. Cell cycle analysis showed that ritterazinexa0B caused accumulation of HL-60 and PC14 cells at the G2/M checkpoint. Furthermore, ritterazinexa0B-treated HL-60 cells became multinucleated, and at a concentration of 20xa0nM this resulted in the onset of apoptosis. Neither cleavage of caspase target molecules nor phosphorylation of bcl-2 were observed in ritterazinexa0B-treated HL-60 cells.ConclusionsThese results indicate that ritterazinexa0B might be a potent inducer of apoptosis acting via a novel antimitotic mechanism.

Low-penetrant RB allele in small-cell cancer shows geldanamycin instability and discordant expression with mutant ras.

Certain kindreds with low-penetrant (lp) retinoblastoma carry mutant alleles which retain partial tumor suppressor activity and we previously showed that these alleles exhibit defective, temperature-sensitive binding in yeast. To investigate the molecular basis for incomplete penetrance, we studied three recurrent lp alleles and observed approximately 50% of wildtype activity measured by i) phosphorylation at key regulatory sites, S780, S795, S807/S811, ii) transcriptional co-activation, and iii) ‘flat-cell’ differentiation in mammalian cells in vivo. In addition, we studied a small-cell carcinoma that is homozygous for the R661W allele providing the first analysis of the effect of a naturally occurring lp allele in a human tumor. While we detected abundant expression of the R661W protein, we noted marked instability of both endogenous and recombinant R661W following treatment in vivo with the Hsp90 inhibitor, geldanamycin, and stabilization of R661W following heat shock. In addition, we observed a discordant phenotype in the tumor cells with induction of p16 and loss of cyclin D1 consistent with a null RB status combined with homozygous expression of mutant ras which had not been reported previously for RB (-) small-cell cancer. These findings show that a recurrent missense lp allele retains greater functional activity in vivo than predicted from earlier in vitro assays, proposing a role for stabilizing chaperone-like activity in vivo. In addition, these data suggest that reversible protein instability and the requirement for a cooperating mutation may provide a stochastic explanation for the molecular basis of incomplete penetrance in kindreds carrying these alleles.

Abstract 2927: Rapamycin decreases expression of thymidylate synthase and enhances the response to pemetrexed in preclinical studies and a Phase I/II clinical study of subjects with non-small cell lung cancer

Non-small-cell lung cancer (NSCLC) accounts for 80-85% of lung cancers and almost half of patients with newly diagnosed NSCLC have metastatic disease. Platinum-based chemotherapy regimens given as first-line treatment for advanced NSCLC patients with metastasis are standard but have modest response rates. Pemetrexed is well tolerated and inhibits several folate-dependent enzymes including thymidylate synthase, TS. Increased expression of TS confers resistance to pemetrexed in vitro and is a predictive factor for poor response to pemetrexed. Rapamycin is a mTOR inhibitor and suppresses protein synthesis. Here, we show that rapamycin decreases endogenous expression of TS in NSCLC cells. The combination of rapamycin and pemetrexed synergistically inhibits NSCLC cell proliferation and enhances the inhibition of 4E-binding protein 1 (4E-BP1) activation that is regulated by mTOR. Although pemetrexed as a single agent upregulated expression of TS, pretreatment with rapamycin suppressed pemetrexed-upregulated TS expression. In vivo, the combination of rapamycin and pemetrexed inhibited the growth of NSCLC xenografts, which correlated with decreased mTOR activity and inhibition of pemetrexed-induced upregulated expression of TS. Based on these preclinical data, we have conducted a Phase I/II clinical trial combining rapamycin and pemetrexed in subjects with relapsed NSCLC. This regimen was well tolerated, and resulted in a 22% partial response rate that is above what is expected for response to single agent pemetrexed (9%). In biomarker analyses, pretreatment with rapamycin decreased the expression of TS in peripheral blood mononuclear cells, which correlated with increased progression free survival. Collectively, these studies identify rapamycin and pemetrexed as an effective combination in NSCLC, and suggest that rapamycin enhances the efficacy of pemetrexed by suppressing TS expression. Citation Format: Shigeru Kawabata, Chun-Te Chiang, Regan M. Memmott, Takefumi Komiya, Joell J. Gills, Phillip A. Dennis. Rapamycin decreases expression of thymidylate synthase and enhances the response to pemetrexed in preclinical studies and a Phase I/II clinical study of subjects with non-small cell lung cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2927. doi:10.1158/1538-7445.AM2014-2927