Design of a novel small peptide targeted against a tumor-specific receptor

EGFRvIII is the most common deletion variant of the epidermal growth factor receptor and is found in cancers of the brain, breast, ovary, and lung. The complete absence of the receptor in healthy tissues makes it an ideal tumor marker. We sought to design a peptide ligand against EGFRvIII for development as a diagnostic imaging agent. We used the concept of hydropathic complementarity to search for sequences whose amino acid sidechains display a reciprocal pattern of hydropathicity to those of the deletion junction of EGFRvIII. The resulting peptide (PEPHC1) was synthesized and tested for binding to EGFRvIII and EGFR. In in vitro assays, PEPHC1 bound the recombinant EGFRvIII extracellular domain or full-length EGFRvIII solubilized from cell membranes in preference to native EGFR. These results demonstrate the utility of hydropathic complementarity as a basis for the design of highly specific ligands that may prove useful as tumor-targeting agents.

Molecular characterization of the human delta opioid receptor in lung cancer

A variety of neuropeptide receptors have been detected in human lung cancer. They are thought to play a role in autocrine/paracrine regulation of cell growth, and may be clinically useful as diagnostic, prognostic or therapeutic targets. The current study characterizes the molecular structure of the delta opioid receptor and its gene expression level in lung cancer cell lines relative to normal human lung using a sensitive RT-PCR approach. The goals of this investigation were a) to define the correlation between receptor binding and gene expression in lung cancer cell lines, and b) to determine the cDNA sequence integrity of this receptor in comparison to the receptor recently found in human brain. Five small cell lung cancer (SCLC) cell lines revealed size-matched RT-PCR products which strongly hybridized to the human brain delta opioid receptor probe. One of three non-small cell lung cancer (NSCLC) cell lines (NCI-H23), known to be negative by binding analysis, demonstrated low level expression. No gene expression was found in normal human lung. RT-PCR products from two SCLC cell lines (SCLC-22H and 16HC) as well as the low level expressing NSCLC cell line (NCI-23) were subjected to bidirectional DNA sequence analysis and the receptor ends were resolved using a 3'-end RACE and 5'-end gene-specific approach. The isolated cDNA sequences proved to be identical to the published human brain delta opioid receptor sequence. These data show that lung cancers with neuroendocrine features express human brain delta opioid receptors in contrast to normal lung, and that the delta opioid receptor mRNA in lung cancer is not mutated. This unique feature of lung cancer may be exploitable for diagnostic, prognostic, and therapeutic strategies.

Purification, cDNA sequence, and tissue distribution of rat uroguanylin

Guanylin, a peptide purified from rat jejunum, is thought to regulate water and electrolyte balance in the intestine. We show here, using a combination of Northern blots, Western blots, and functional assays, that guanylin and its receptor (GCC) are not distributed in parallel within the rat intestine. To investigate the possibility that there might be a second intestinal peptide that serves as a ligand for GCC, we assayed tissue extracts for the ability to stimulate cyclic GMP synthesis in a GCC-expression cell line. Duodenal extracts display a peak of biological activity that is not present in colon and that does not comigrate with guanylin or proguanylin. The activity co-purifies with a novel peptide (TIATDECELCINVACTGC) that has high homology with uroguanylin, a peptide initially purified from human and opossum urine. A rat uroguanylin cDNA clone was found to encode a propeptide whose C-terminus corresponds to our purified peptide. Northern blots with probes generated from this clone reveal that prouroguanylin mRNA is strongly expressed in proximal small intestine, but virtually absent from colon, corroborating our biochemical measurements. Taken together, these studies demonstrate an intestinal origin for uroguanylin, and show that within the intestine its distribution is complementary to that of guanylin.

Binding of [3H](+)-BW373U86 to delta-opioid receptors in rat brain membranes

A tritiated form of the non-peptide delta-opioid receptor agonist (+)-BW373U86 ((+)-4-((alpha-R)-alpha-((2S,5R)-4-allyl-2, 5-dimethyl-l-piperazinyl)-3-hydroxybenzyl)-N,N-diethylbenzamide) was synthesized and its binding characteristics studied. [3H](+)-BW373U86 bound with subnanomolar affinity to rat brain membranes and was displaced most effectively by ligands selective for delta-opioid receptors. Naltrindole, naltriben, and 7-benzylidenenaltrexone exhibited apparent inhibition constants of 0.06, 1.54, and 4.49 nM, respectively, while mu- or kappa-selective ligands showed little affinity for this site. [3H](+)-BW373U86 binding was sensitive to the presence of guanine nucleotides; GDP caused a 3-fold decrease and 5'-guanylyl-imidodiphosphate (Gpp[NH]p) caused a 25% increase in binding affinity.

Characterization of delta opioid receptors in lung cancer using a novel nonpeptidic ligand

Cancer cells are often characterized by the presence of membrane receptors not normally associated with nontransformed cells from the same tissue type. Recent studies have demonstrated increased expression of high-affinity binding sites for opioid receptor-selective ligands in lung cancer cell lines relative to normal lung tissue. We investigated the binding of a nonpeptidic delta opioid receptor ligand in small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) cells with the aim of developing the ligand as a novel lung cancer imaging agent. The ligand, [3H] (+)-4-[alpha-R)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3- hydroxybenzyl)-N,N-diethylbenzamide ([3H](+)BW373U86), bound with high-affinity [Kd (dissociation constant) = 0.066 +/- 0.012 nM] to membranes prepared from six different SCLC cell lines but not to those from seven NSCLC cell lines, including one mesothelioma. The number of biding sites varied from 10 to 300 fmol/mg membrane protein. Competition binding studies demonstrated displacement of [3H](+)BW373U86 binding by the delta-selective antagonists naltriben and 7-benzylidenenaltrexone but not with the mu- and kappa- selective antagonists D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 and trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]ben zeneacetamide methanesulfonate. Mean apparent Kis for naltriben and 7-benzylidenenaltrexone in membranes from two SCLC cell lines were 0.17 and 3.9 nM, respectively, but were >10 microM for the mu and kappa ligands. The nonselective antagonist naloxone displaced [3H](+)BW373U86 binding with an apparent Ki of approximately 29 nM. On the basis of these data, we believe the lung cancer receptor to be similar, if not identical, to the human brain delta opioid receptor. The lack of high-affinity [3H](+)BW373U86 binding in normal mouse lung membranes suggests a potential role for this ligand as a novel therapeutic or imaging agent.

Microinjection of Rap2B protein or RNA induces rearrangement of pigment granules in Xenopus oocytes

Rap2B, a member of the ras superfamily of low-molecular-mass GTP-binding proteins, induced a characteristic rearrangement of the pigment granules in Xenopus oocytes following its microinjection, resulting in numerous unpigmented spots on the animal hemisphere. This phenomenon, termed 'mottling', was also induced by microinjection of in vitro-transcribed Rap2B RNA or of purified recombinant Rap2A. Following the microinjection of Rap2B, more than 90% of the oocytes showed signs of mottling within 10 h. The time course of mottling paralleled the association of the recombinant Rap2B with an oocyte membrane fraction. Like other members of the ras superfamily, Rap2B possesses a C-terminal CAAX motif that serves as a signal for post-translational processing. Mutation of the cysteine residue in the CAAX motif to serine prevents the association of Rap2B with oocyte membranes, and also prevents mottling. This result suggests that post-translational processing of Rap2B is required for the observed effect. Mottling was blocked by boiling Rap2B prior to its microinjection or by co-injection of the cytoskeletal reagent phalloidin.

The antibiotic azatyrosine suppresses progesterone or [Val12]p21 Ha-ras/insulin-like growth factor I-induced germinal vesicle breakdown and tyrosine phosphorylation of Xenopus mitogen-activated protein kinase in oocytes

The antibiotic azatyrosine [DL-3-(5-hydroxy-2-pyridyl)alanine] suppressed meiotic maturation in oocytes induced by progesterone or the combination of [Val12]p21Ha-ras microinjection and insulin-like growth factor I. The suppression was dose-dependent in the range of 20-250 microM azatyrosine. In addition, azatyrosine blocked the tyrosine phosphorylation of Xp42, a member of the mitogen-activated protein kinase family, after progesterone or [Val12]p21Ha-ras/insulin-like growth factor I stimulation. Activation of maturation-promoting factor, as shown by a decrease in the tyrosine phosphorylation of the Xenopus homolog of p34cdc2, was also suppressed by azatyrosine. Azatyrosine had no effect in vivo or in vitro on the growth factor-induced autophosphorylation of the oocyte insulin-like growth factor I receptor. Azatyrosine has been shown by others [Shindo-Okada, N., Makabe, O., Nagahara, H. & Nishimura, S. (1989) Mol. Carcinog. 2, 159-167] to inhibit the growth of ras-transformed cells without affecting that of nontransformed cells. In oocytes, the antibiotic exerts an inhibitory action on both a ras-dependent and a ras-independent pathway. Lack of an effect of azatyrosine on germinal vesicle breakdown induced by the microinjection of an extract from mature oocytes, however, suggests that azatryosine is acting upstream of maturation-promoting factor activation.

Inhibition of ras-induced germinal vesicle breakdown in Xenopus oocytes by rap-1B

A cDNA clone (Krev-1) has recently been identified that possesses the ability to reverse the transformed phenotype when introduced into a K-ras-transformed NIH/3T3 cell line. The Krev-1 protein, also known as rap-1A, was found to share 50% homology with the ras proteins. The rap-1A protein has also been shown to block the interaction of ras with its GTPase activating protein in vitro, leading to speculation regarding its role in vivo. A closely related protein, rap-1B, has also been identified in platelets, human erythroleukemia cells, neutrophils, and aortic smooth muscle cells. Unlike rap-1A, rap-1B has been shown to be phosphorylated in platelets. Given the high degree of similarity between the amino acid sequences of rap-1A and rap-1B, we sought to investigate the effect of microinjected rap-1B on H-ras(Val12)-induced germinal vesicle breakdown in Xenopus laevis oocytes. In this assay system, equimolar concentrations of rap-1B were found to block germinal vesicle breakdown triggered by the oncogenic ras protein. However, in the presence of IGF-1, this inhibition was not observed. Moreover, rap-1B is readily phosphorylated in the oocytes.

Expression of the mammalian system A neutral amino acid transporter in Xenopus oocytes

In this report, we demonstrate the expression of the mammalian System A neutral amino acid transporter in Xenopus laevis oocytes following microinjection of mRNA from rat liver, Chinese hamster ovary (CHO) cells, and human placenta. Stage 6 oocytes were injected with poly(A+) mRNA from one of these three sources and incubated for 24 h prior to assaying Na(+)-dependent 2-aminoisobutyric acid transport to monitor the increase in System A activity. The endogenous 2-aminoisobutyric acid uptake rates in oocytes were sufficiently slow so as to provide a low background value that was subtracted to obtain transport rates for the mammalian carrier alone. The degree of expression of the mammalian System A activity in Xenopus oocytes corresponded to the known transport rates in the tissue from which the mRNA was prepared. For example, hepatic mRNA from glucagon-treated rats produced greater System A activity than mRNA from control animals, and the mRNA from the CHO transport mutant cell line alar4-H3.9, which overproduces System A, resulted in higher transport rates than mRNA from the parental cell line (CHO-K1). Fractionation of total mRNA poly(A+) by nondenaturing agarose gel electrophoresis revealed transport activity associated with a 2.0-2.5-kilobase mRNA fraction common to each of the three tissues tested.

Characterization of neutral and cationic amino acid transport in Xenopus oocytes

Amino acid transport was characterized in stage 6 Xenopus laevis oocytes. Most amino acids were taken up by the oocytes by way of both Na+-dependent and saturable Na+-independent processes. Na+-dependent transport of 2-aminoisobutyric acid (AIB) was insensitive to cis- or trans-inhibition by the System A-defining substrate 2-(methylamino)-isobutyric acid (MeAIB), although threonine, leucine, and histidine were found to be effective inhibitors, eliminating greater than 80% of Na+-dependent AIB uptake. Lack of inhibition by arginine eliminates possible mediation by System Bo,+ and suggests uptake by System ASC. The Na+-dependent transport of characteristic System ASC substrates such as alanine, serine, cysteine, and threonine was also insensitive to excess MeAIB. Evidence to support the presence of System Bo,+ was obtained through inhibition analysis of Na+-dependent arginine transport as well arginine inhibition of Na+-dependent threonine uptake. The Na+-independent transport of leucine was subject to trans-stimulation and was inhibited by the presence of excess phenylalanine, histidine, and, to a lesser extent, 2-amino-(2,2,1)-bicycloheptane-2-carboxylic acid (BCH). These observations are consistent with mediation by System L. The characteristics of Na+-independent uptake of threonine are not consistent with assignment to System L, and appear to be reflective of Systems asc and bo,+. In its charged state, histidine appears to be transported by a carrier similar in its specificity to System y+, but is taken up by System L when present as a zwitterion.