Glucose-induced insulin secretion is potentiated by a new imidazoline compound.

Sulfonylureas stimulate insulin secretion independent of the blood glucose concentration. This can lead to hypoglycaemia in type 2 diabetic patients. Over the last years a number of imidazoline derivatives have been identified that stimulate insulin secretion in a more glucose-dependent way. In agreement with this, our aim was to generate imidazoline derivatives with a potential for the treatment of type 2 diabetic patients. We developed the compound 2-[4-(4-chlorophenyl)-3-(2-methoxyethoxy)-2-naphthalenyl]-4,5-dihydro-1-H-imidazole monohydrochloride (LY389382) with an imidazoline moiety and investigated its effects on glucose-dependent insulin secretion in a beta-cell line, isolated rat islets and in vivo. We could demonstrate that LY389382 induces insulin secretion in MIN6 cells and rat islets in a glucose-dependent manner (EC50=1.1 microM and 0.3 microM, respectively). Furthermore during hyperglycaemia LY389382 increased insulin secretion in a dose-dependent manner in healthy rats, whereas the compound had no effect at euglycemia in a tenfold higher dosage. After 7 days of treatment of Zucker Diabetic Fatty [ZDF/ (Gmi/fa)] rats with LY389382 with a dose of 15 mg/kg twice daily the blood glucose concentration was reduced from 22.7 +/- 1.7 mM to 16.6 +/- 2.3 mM. During the same time period the glucose concentration increased from 21.7+/-1.7 mM to 28.9 +/- 1.3 mM in the vehicle-treated group (P<0.05). The drop of the insulin level was also inhibited by LY389382 in ZDF rats. In contrast to other well-characterised imidazolines that have been shown to induce a glucose-dependent insulin secretion only within a limited range of concentrations, LY389382 stimulates insulin secretion over a concentration range of at least two log units in a glucose-dependent manner. These data suggest that this imidazoline compound has a potential for the treatment of type 2 diabetes.

Activated MEK stimulates expression of AP-1 components independently of phosphatidylinositol 3-kinase (PI3-kinase) but requires a PI3-kinase signal To stimulate DNA synthesis.

To investigate the contribution that ERK/mitogen-activated protein kinase signalling makes to cell cycle progression and gene expression, we have constructed cell lines to express an inducible version of activated MEK1. Using these cells, we show that activation of MEK leads to the expression of Fra-1 and Fra-2 but not c-Fos. Treatment of Ras-transformed cells with the MEK inhibitor PD098059 blocks expression of Fra-1 and Fra-2, showing that in Ras transformation ERK signalling is responsible for Fra-1 and Fra-2 expression. Activation of MEK1 in growth-arrested cells leads to DNA synthesis; however, ERK activation alone is insufficient because the induction of DNA synthesis is blocked by inhibition of phosphatidylinositol 3-kinase (PI3-kinase). Activation of PI3-kinase is indirect, perhaps through autocrine growth factors, and is required for the induction of cyclin D1.

Development of transforming function during transduction of proto-ras into Harvey sarcoma virus.

Oncogenic retroviruses are generated by transduction of the coding region of a protooncogene and acquire genetic changes during subsequent replication. Critical genetic events which occurred during and after transduction of rat proto-ras-1Ha into Harvey sarcoma virus were identified by evaluating the transforming activity of plausible synthetic progenitor proviruses encompassing the complete proto-ras genomic region with or without various 5' deletions. All progenitor proviruses induced phenotypic transformation of mouse NIH 3T3 cells, although with a 5- to 10-fold lower frequency than Harvey sarcoma provirus. Although no tumor formation was observed in vivo after inoculation in the absence of helper murine retrovirus, both wild-type and progenitor viruses inoculated in the presence of helper virus induced tumors in newborn BALB/c mice. No critical alterations of the p21ras coding region and no deletion of 5' genomic elements were detected in a progenitor virus encompassing the complete proto-ras genomic region that had been isolated from tumors. However, one progenitor virus that included all proto-ras exons induced tumors with a decreased latency. This virus contained a mutation in codon 12 (glycine to valine), which had apparently been selected during tumorigenesis in vivo. During the genesis of Harvey sarcoma virus, critical steps conferring transforming function are therefore transduction of coding proto-ras exons and enhancement of their transforming function by specific amino acid changes in p21ras.