Lamellarin 14, a derivative of marine alkaloids, inhibits the T790M/C797S mutant epidermal growth factor receptor.

The emergence of acquired resistance is a major concern associated with molecularly targeted kinase inhibitors. The C797S mutation in the epidermal growth factor receptor (EGFR) confers resistance to osimertinib, a third-generation EGFR-tyrosine kinase inhibitor (EGFR-TKI). We report that the derivatization of the marine alkaloid topoisomerase inhibitor lamellarin N provides a structurally new class of EGFR-TKIs. One of these, lamellarin 14, is effective against the C797S mutant EGFR. Bioinformatic analyses revealed that the derivatization transformed the topoisomerase inhibitor-like biological activity of lamellarin N into kinase inhibitor-like activity. Ba/F3 and PC-9 cells expressing the EGFR in-frame deletion within exon 19 (del ex19)/T790M/C797S triple-mutant were sensitive to lamellarin 14 in a dose range similar to the effective dose for cells expressing EGFR del ex19 or del ex19/T790M. Lamellarin 14 decreased the autophosphorylation of EGFR and the downstream signaling in the triple-mutant EGFR PC-9 cells. Furthermore, intraperitoneal administration of 10 mg/kg lamellarin 14 for 17 days suppressed tumor growth of the triple-mutant EGFR PC-9 cells in a mouse xenograft model using BALB/c nu/nu mice. Thus, lamellarin 14 serves as a novel structural backbone for an EGFR-TKI that prevents the development of cross-resistance against known drugs in this class.

IMU1003, an atrarate derivative, inhibits Wnt/ß-catenin signaling.

Aberrant activation of the canonical Wnt/ß-catenin signaling pathway triggers tumorigenesis in various tissues. This study identified an atrarate compound, IMU14, derived from filamentous fungi as an inhibitor of Wnt/ß-catenin signaling in phenotypic chemical inhibitor screening of the zebrafish eyeless phenotype. Its derivatization resulted in synthesis of IMU1003 with enhanced Wnt inhibitory activity. IMU1003 inhibited ß-catenin/TCF-dependent transcriptional activation and decreased nuclear ß-catenin level. In addition, IMU1003 selectively decreased viability and target gene products of the Wnt/ß-catenin signaling pathway in human non-colorectal cancer cell lines harboring intact APC and ß-catenin. Therefore, atrarate derivatives inhibit Wnt/ß-catenin signaling and show anticancer potential, and we developed a new class of chemical backbones for Wnt/ß-catenin signaling inhibitors.

Clotrimazole inhibits the Wnt/ß-catenin pathway by activating two eIF2α kinases: The heme-regulated translational inhibitor and the double-stranded RNA-induced protein kinase.

The Wnt/ß-catenin signaling pathway controls cell proliferation and differentiation, and therefore, when this pathway is excessively activated, it causes tumorigenesis. Our chemical suppressor screening in zebrafish embryos identified antifungal azoles including clotrimazole, miconazole, and itraconazole, as Wnt/ß-catenin signaling inhibitors. Here we show the mechanism underlying the Wnt/ß-catenin pathway inhibition by antifungal azoles. Clotrimazole reduced ß-catenin revels in a proteasome-independent fashion. By gene knockdown of two translational regulators, heme-regulated translational inhibitor and double-stranded RNA-induced protein kinase, we show that they mediate the clotrimazole-induced inhibition of the Wnt/ß-catenin pathway. Thus, clotrimazole inhibits the Wnt/ß-catenin pathway by decreasing ß-catenin protein levels through translational regulation. Antifungal azoles represent genuine candidate compounds for anticancer drugs or chemopreventive agents that reduce adenomatous polyps.

DNA damage-induced modulation of GLUT3 expression is mediated through p53-independent extracellular signal-regulated kinase signaling in HeLa cells.

Many cancer cells exhibit increased rates of uptake and metabolism of glucose compared with normal cells. Glucose uptake in mammalian cells is mediated by the glucose transporter (GLUT) family. Here, we report that DNA-damaging anticancer agents such as Adriamycin and etoposide suppressed the expression of GLUT3, but not GLUT1, in HeLa cells and a tumorigenic HeLa cell hybrid. Suppression of GLUT3 expression determined by the real-time PCR was also evident with another DNA-damaging agent, camptothecin, which reduced the promoter's activity as determined with a luciferase-linked assay. The suppression by these agents seemed to be induced independently of p53, and it was evident when wild-type p53 was overproduced in these cells. In contrast, the mitogen-activated protein kinase/extracellular signal regulated kinase (MAPK/ERK) kinase (MEK) inhibitor U0126 (but not the phosphoinositide 3-kinase inhibitor LY294002) prevented the drug-induced suppression as determined by reverse transcription-PCR and promoter assays. Furthermore, overexpression of GLUT3 in HeLa cell hybrids increased resistance to these drugs, whereas depletion of the gene by small interfering RNA rendered the cells more sensitive to the drugs, decreasing glucose consumption. The results suggest that DNA-damaging agents reduce GLUT3 expression in cancer cells through activation of the MEK-ERK pathway independently of p53, leading to cell death or apoptosis. The findings may contribute to the development of new chemotherapeutic drugs based on the GLUT3-dependent metabolism of glucose.

The intrinsic structure of glucose transporter isoforms Glut1 and Glut3 regulates their differential distribution to detergent-resistant membrane domains in nonpolarized mammalian cells.

The hexose transporter family, which mediates facilitated uptake in mammalian cells, consists of more than 10 members containing 12 membrane-spanning segments with a single N-glycosylation site. We previously demonstrated that glucose transporter 1 is organized into a raft-like detergent-resistant membrane domain but that glucose transporter 3 distributes to fluid membrane domains in nonpolarized mammalian cells. In this study, we further examined the structural basis responsible for the distribution by using a series of chimeric constructs. Glucose transporter 1 and glucose transporter 3 with a FLAG-tagged N-terminus were expressed in detergent-resistant membranes and non-detergent-resistant membranes of CHO-K1 cells, respectively. Replacement of either the C-terminal or N-terminal cytosolic portion of FLAG-tagged glucose transporter 1 and glucose transporter 3 did not affect the membrane distribution. However, a critical sorting signal may exist within the N-terminal half of the isoforms without affecting transport activity and its inhibition by cytochalasin B. Further shortening of these regions altered the critical distribution, suggesting that a large proportion or several parts of the intrinsic structure, including the N-terminus of each isoform, are involved in the regulation.

Differential localization of glucose transporter isoforms in non-polarized mammalian cells: distribution of GLUT1 but not GLUT3 to detergent-resistant membrane domains.

The hexose transporter family, which mediates a facilitated uptake in mammalian cells, consists of more than 10 members containing 12 membrane-spanning segments with a single N-glycosylation site. However, it remains unknown how these isoforms are functionally organized in the membrane domains. In this report, we describe a differential distribution of the glucose transporter isoforms GLUT1 and GLUT3 to detergent-resistant membrane domains (DRMs) in non-polarized mammalian cells. Whereas more than 80% of cellular proteins containing GLUT3 in HeLa cell lines was solubilized by a non-ionic detergent (either Triton X-100 or Lubrol WX) at 4 degrees C, GLUT1 remained insoluble together with the DRM-associated proteins, such as caveolin-1 and intestinal alkaline phosphatase (IAP). These DRM-associated proteins and the ganglioside GM1 were shown to float to the upper fractions when Triton X-100-solubilized cell extracts were centrifuged on a density gradient. In contrast, GLUT3 as well as most soluble proteins remained in the lower layers. Furthermore, perturbations of DRMs due to depletion of cholesterol by methyl-beta-cyclodextrin (m beta CD) rendered GLUT1 soluble in Triton X-100. Immunostaining patterns for these isoforms detected by confocal laser scanning microscopy in a living cell were also distinctive. These results suggest that in non-polarized mammalian cells, GLUT1 can be organized into a raft-like DRM domain but GLUT3 may distribute to fluid membrane domains. This differential distribution may occur irrespective of the N-glycosylation state or cell type.