Fibroblast growth factor 21 controls glycemia via regulation of hepatic glucose flux and insulin sensitivity

Fibroblast growth factor 21 (FGF21) is a novel metabolic regulator shown to improve glycemic control. However, the molecular and functional mechanisms underlying FGF21-mediated improvements in glycemic control are not completely understood. We examined FGF21 effects on insulin sensitivity and glucose fluxes upon chronic (daily injection for 8 d) and acute (6 h infusion) administration in ob/+ and ob/ob mice. Results show that chronic FGF21 ameliorated fasting hyperglycemia in ob/ob mice via increased glucose disposal and improved hepatic insulin sensitivity. Acute FGF21 suppressed hepatic glucose production, increased liver glycogen, lowered glucagon, and improved glucose clearance in ob/+ mice. These effects were blunted in ob/ob mice. Neither chronic nor acute FGF21 altered skeletal muscle or adipose tissue glucose uptake in either genotype. In conclusion, FGF21 has potent glycemic effects caused by hepatic changes in glucose flux and improved insulin sensitivity. Thus, these studies define mechanisms underlying anti-hyperglycemic actions of FGF21 and support its therapeutic potential.

Fibroblast growth factor-21 as a therapeutic agent for metabolic diseases

Fibroblast growth factor (FGF)-21 is a unique member of the FGF family, with several molecular characteristics that differ from classical FGFs and exhibiting a pharmacologic profile that includes a variety of metabolic responses in vitro and when tested in vivo in animal models. FGF21 represents a novel and attractive therapeutic agent for type 2 diabetes mellitus, because of its ability to modulate disease phenotype in preclinical settings without inducing any apparent adverse effects. Although FGF21 was discovered relatively recently, the understanding of its biology and therapeutic utility is rapidly evolving. A number of key metabolically linked molecules and pathways have been suggested to be involved in the mechanism of action of FGF21, depending on the specific target tissue/organ. Further research into these mechanisms should lead to important advances in the understanding of FGF21 biology and pave the way for novel therapeutic strategies. The specifics of FGF21 activities both in cell culture and in vivo, its potential as a target for diabetes, and insights into the molecular mechanisms of FGF21 metabolic actions will be discussed in this review.

The metabolic state of diabetic monkeys is regulated by fibroblast growth factor-21

Fibroblast growth factor (FGF)-21 has been recently characterized as a potent metabolic regulator. Systemic administration of FGF-21 reduced plasma glucose and triglycerides to near normal levels in genetically compromised diabetic rodents. Importantly, these effects were durable and did not come at the expense of weight gain, hypoglycemia, or mitogenicity. To explore the therapeutic properties of FGF-21 in a nongenetically modified primate species, and thus demonstrate the potential for efficacy in humans, we evaluated its bioactivity in diabetic nonhuman primates. When administered daily for 6 wk to diabetic rhesus monkeys, FGF-21 caused a dramatic decline in fasting plasma glucose, fructosamine, triglycerides, insulin, and glucagon. Of significant importance in regard to safety, hypoglycemia was not observed at any point during the study. FGF-21 administration also led to significant improvements in lipoprotein profiles, including lowering of low-density lipoprotein cholesterol and raising of high-density lipoprotein cholesterol, beneficial changes in the circulating levels of several cardiovascular risk markers/factors, and the induction of a small but significant weight loss. These data support the development of FGF-21 for the treatment of diabetes and other metabolic diseases.

Enhancing exposure of protein therapeutics

Therapeutic proteins have made a major impact on medicine, with significant expansion in the past two decades. The medicinal attributes of these agents, particularly their efficacy and often their safety profile, make protein therapeutics attractive, despite the general necessity of invasive (parenteral) delivery. This perceived hurdle has been a primary component in limiting expansion of this class of drug therapies. Strategies that reduce the frequency of administration directly provide greater convenience to the patient, and potentially greater efficacy, that can yield a significant treatment advantage.:

Engineering of recombinant antibody fragments to methamphetamine by anchored periplasmic expression

The detection of methamphetamine and other chemically related illicit drugs relies extensively on immunoassays. Here we report the cloning and affinity maturation of an anti-methamphetamine antibody which is being employed in the current commercial assays. An anti-methamphetamine scFv was cloned from hybridoma cells, expressed in bacteria and its affinity towards methamphetamine and N-ethylamphetamine (ethamphetamine) was determined by Surface Plasmon Resonance (SPR). The anti-methamphetamine scFv gene was subjected to random mutagenesis by error prone PCR and variants with improved affinity were isolated from the resulting library by a novel screening methodology termed Anchored Periplasmic Expression (APEx) [Harvey, B.R., Georgiou, G., Hayhurst, A., Jeong, K.J., Iverson, B.L., Rogers, G.K. (2004). Anchored periplasmic expression, a versatile technology for the isolation of high-affinity antibodies from Escherichia coli-expressed libraries. Proc. Natl. Acad. Sci. U. S. A. 101, 9193.]. The isolated clones exhibited improved affinity to these illicit drugs, yet maintained low cross-reactivity to over-the-counter drugs. In addition, all clones displayed improved expression characteristics in Escherichia coli. The affinity improved scFv antibodies are thus likely to be useful in methamphetamine class immunodiagnostics.

Diversity in Hapten Recognition: Structural Study of an Anti-cocaine Antibody M82G2

Antibodies against cocaine and other drugs of abuse are the basis for diagnostic tests for the presence of those drugs in human serum. The 1.7A resolution crystal structure of the anti-cocaine monoclonal antibody M82G2 in complex with cocaine is presented. This structure determination was undertaken to establish the stereochemical features in the antibody binding site that confer specificity for cocaine, and as part of an ongoing project to understand the rules that govern molecular recognition. The cocaine-binding site can be characterized topologically as a narrow groove on the protein surface. The antibody utilizes water-mediated hydrogen bonding, and cation-pi and stacking (pi-pi) interactions to provide specificity. Comparison with the previously published structure of the anti-cocaine antibody GNC92H2 shows that binding of a small ligand can be achieved in diverse ways, both in terms of a binding site structure/topology and protein-ligand interactions.

FGF-21 as a novel metabolic regulator

Diabetes mellitus is a major health concern, affecting more than 5% of the population. Here we describe a potential novel therapeutic agent for this disease, FGF-21, which was discovered to be a potent regulator of glucose uptake in mouse 3T3-L1 and primary human adipocytes. FGF-21-transgenic mice were viable and resistant to diet-induced obesity. Therapeutic administration of FGF-21 reduced plasma glucose and triglycerides to near normal levels in both ob/ob and db/db mice. These effects persisted for at least 24 hours following the cessation of FGF-21 administration. Importantly, FGF-21 did not induce mitogenicity, hypoglycemia, or weight gain at any dose tested in diabetic or healthy animals or when overexpressed in transgenic mice. Thus, we conclude that FGF-21, which we have identified as a novel metabolic factor, exhibits the therapeutic characteristics necessary for an effective treatment of diabetes.

Medicinally useful proteins – enhancing the probability of technical success in the clinic

Proteins that are normally present in organisms function to maintain the overall homeostatic balance of the living system. Although an understanding of the biology of these proteins is essential to determining their utility in the treatment of disease, the administration of wild-type forms of proteins in a therapeutic manner (often systemically and at concentrations much higher than those found in the healthy organism) can have the effect of inappropriate activation of cell types and compartments that can lead to an undesirable response. Modification of the sequence of the parent protein to yield selected biological properties can generate derivative versions (muteins) having an optimal therapeutic profile. In addition to consideration of the biological properties, protein therapeutics are typically not active when delivered orally. This can limit the frequency with which the therapeutic agent can be administered to the patient, exemplifying the need to understand the pharmacokinetic and pharmacodynamic relationships of the protein. The biophysical properties of the mutein (e.g., solubility and stability) must also be considered in this context. An additional consideration with therapeutic proteins, engineered or not, is the potential immune response resulting from sequence variation and/or exogenous presentation to the immune system. The composite application of these principles to therapeutic protein discovery and development drives the ultimate success of any given biopharmaceutical agent.

Anchoring a cationic ligand: the structure of the Fab fragment of the anti-morphine antibody 9B1 and its complex with morphine

The crystal structures of an anti-morphine antibody 9B1 (to 1.6A resolution) and its complex with morphine (to 2.0 A resolution) are reported. The morphine-binding site is described as a shallow depression on the protein surface, an unusual topology for a high-affinity ( Ka approximately 10(9) M(-1)) antibody against a small antigen. The polar part of the ligand is exposed to solvent, and the cationic nitrogen atom of the morphine molecule is anchored at the bottom of the binding site by a salt-bridge to a glutamate side-chain. Additional affinity is provided by a double cation-pi interaction with two tryptophan residues. Comparison of the morphine complex with the structure of the free Fab shows that a domain closure occurs upon binding of the ligand.

Generation of highly selective VPAC2 receptor agonists by high throughput mutagenesis of vasoactive intestinal peptide and pituitary adenylate cyclase-activating peptide

Pituitary adenylate cyclase-activating peptide (PACAP) has a specific receptor PAC1 and shares two receptors VPAC1 and VPAC2 with vasoactive intestinal peptide (VIP). VPAC2 activation enhances glucose-induced insulin release while VPAC1 activation elevates glucose output. To generate a large pool of VPAC2 selective agonists for the treatment of type 2 diabetes, structure-activity relationship studies were performed on PACAP, VIP, and a VPAC2 selective VIP analog. Chemical modifications on this analog that prevent recombinant expression were sequentially removed to show that a recombinant peptide would retain VPAC2 selectivity. An efficient recombinant expression system was then developed to produce and screen hundreds of mutant peptides. The 11 mutations found on the VIP analog were systematically replaced with VIP or PACAP sequences. Three of these mutations, V19A, L27K, and N28K, were sufficient to provide most of the VPAC2 selectivity. C-terminal extension with the KRY sequence from PACAP38 led to potent VPAC2 agonists with improved selectivity (100-1000-fold). Saturation mutagenesis at positions 19, 27, 29, and 30 of VIP and charge-scanning mutagenesis of PACAP27 generated additional VPAC2 selective agonists. We have generated the first set of recombinant VPAC2 selective agonists described, which exhibit activity profiles that suggest therapeutic utility in the treatment of diabetes.

Therapeutic enhancement of IL-2 through molecular design

A recombinant human IL-2 analog (rIL-2, Proleukin) is currently being evaluated for clinical benefit in HIV infected patients. It is approved for therapy of patients with metastatic melanoma and renal cell carcinoma. Treatment of cancer patients with rIL-2 results in durable responses but is associated with life-threatening toxicity, which limits its use to patients in relatively good health. Antitumor efficacy associated with rIL-2 therapy are hypothesized to be mediated by distinct types of cells that express structurally different forms of the IL-2 receptor. This hypothesis suggests that it might be possible to engineer an IL-2 variant addressing the risks associated with the therapeutic use of IL-2. In this article, we review the clinical experience with IL-2 and its analogs, the evidence that different IL-2 receptors may dissociate efficacy and toxicity, and describe the generation of a novel IL-2 variant with the potential for a superior therapeutic index.

Receptor-based design of cytokine therapeutics

Cytokines hold huge potential for the treatment of disease due to their often fundamental roles in development and homeostasis. However, it is this same primary biological function that can both cause disease through dysregulation as well as prevent their therapeutic use due to systemic consequences arising from this inherent pleiotropy. Molecularly, this can be explained through an understanding of the receptor system specific to each cytokine and the cells on which they are expressed. This knowledge has been exploited to yield muteins (mutated proteins) that exhibit selective, and sometimes novel, biological properties dependent upon receptor subunit usage. In some cases, these muteins have been evaluated in clinical trials and have been approved for clinical use; in most instances, however, these muteins are not suitable for therapeutic application due to intrinsic characteristics of the muteins themselves or the cellular and receptor system to which they are directed. Ultimately, molecular insight to the biological processes governing disease pathology underlies the successful application of mutein-based therapy. The clinical success enjoyed by a subset of these proteins signals the advent of a new mode of therapeutic protein development.

Interleukin-4 variant (BAY 36-1677) selectively induces apoptosis in acute lymphoblastic leukemia cells

Interleukin 4 (IL-4) suppresses the growth of acute lymphoblastic leukemia (ALL) cells, but its clinical usefulness is limited by proinflammatory activity due mainly to the interaction of cytokine with endothelial cells and fibroblasts. Stroma-supported cultures of leukemic lymphoblasts were used to test the antileukemic activity of an IL-4 variant, BAY 36-1677, in which the mutations Arg 121 to Glu and Thr 13 to Asp ensure high affinity for IL-4Ralpha/IL-2Rgamma receptors expressed by lymphoid cells, without activation of the IL-4Ralpha/IL-13Ralpha receptors mainly expressed by other cells. BAY 36-1677 (25 ng/mL) was cytotoxic in 14 of 16 cases of B-lineage ALL; the median reduction in cell recovery after 7 days of culture was 85% (range, 17%-95%) compared to results of parallel cultures not exposed to the cytokine. Twelve of the 14 sensitive cases had t(9;22) or 11q23 abnormalities; 3 were obtained at relapse. BAY 36-1677 induced apoptosis in leukemic lymphoblasts but did not substantially affect the growth of normal CD34+ cells, thus conferring a growth advantage to normal hematopoietic cells over leukemic lymphoblasts in vitro. BAY 36-1677 had antileukemic activity equal or superior to that produced by native IL-4, but it lacked any effects on the growth of endothelial cells and fibroblasts. The molecular manipulation of IL-4 to abrogate its proinflammatory activity has generated a novel and therapeutically promising cytokine for the treatment of high-risk ALL.

A T-cell-selective interleukin 2 mutein exhibits potent antitumor activity and is well tolerated in vivo

Human interleukin 2 (IL-2; Proleukin) is an approved therapeutic for advanced-stage metastatic cancer; however, its use is restricted because of severe systemic toxicity. Its function as a central mediator of T-cell activation may contribute to its efficacy for cancer therapy. However, activation of natural killer (NK) cells by therapeutically administered IL-2 may mediate toxicity. Here we have used targeted mutagenesis of human IL-2 to generate a mutein with approximately 3,000-fold in vitro selectivity for T cells over NK cells relative to wild-type IL-2. We compared the variant, termed BAY 50-4798, with human IL-2 (Proleukin) in a therapeutic dosing regimen in chimpanzees, and found that although the T-cell mobilization and activation properties of BAY 50-4798 were comparable to human IL-2, BAY 50-4798 was better tolerated in the chimpanzee. BAY 50-4798 was also shown to inhibit metastasis in a mouse tumor model. These results indicate that BAY 50-4798 may exhibit a greater therapeutic index than IL-2 in humans in the treatment of cancer and AIDS.

An immune cell-selective interleukin 4 agonist

Interleukin 4 (IL-4) is a pleiotropic cytokine. Of the cell types responsive to IL-4, T cells express one IL-4 receptor (IL-4R) type, IL-4Ralpha/IL-2Rgamma (class I IL-4R), whereas endothelial cells express another type, IL-4Ralpha/IL-13Ralpha (class II IL-4R). It was hypothesized that IL-4 variants could be generated that would be selective for cell types expressing the different IL-4Rs. A series of IL-4 muteins were generated that were substituted in the region of IL-4 implicated in interactions with IL-2Rgamma. These muteins were evaluated in T cell and endothelial cell assays. One of these muteins, containing the mutation Arg-121 to Glu (IL-4/R121E), exhibited complete biological selectivity for T cells, B cells, and monocytes, but showed no activity on endothelial cells. Receptor binding studies indicated that IL-4/R121E retained physical interaction with IL-2Rgamma but not IL-13Ralpha; consistent with this observation, IL-4/R121E was an antagonist of IL-4-induced activity on endothelial cells. IL-4/R121E exhibits a spectrum of activities in vitro that suggest utility in the treatment of certain autoimmune diseases.

Antibodies to murine CD40 stimulate normal B lymphocytes but inhibit proliferation of B lymphoma cells

A rat anti-mouse CD40 antiserum has been prepared by hyperimmunisation of Lewis rats with a highly purified preparation of the recombinant extracellular domain of murine CD40. This antiserum specifically binds CD40-expressing L cell transfectants, but not untransfected L cells, and induces vigorous proliferation of highly purified small dense B cells obtained from the spleens of unstimulated mice. Anti-CD40-induced B cell proliferation can be augmented by the addition of IL-4 and is inhibited by purified recombinant soluble mouse CD40. Interestingly the same anti-CD40 antiserum specifically inhibits the in vitro growth of A.20 murine B lymphoma cells. The specificity of this inhibition can be demonstrated by reversing the effect with purified recombinant soluble mouse CD40. These data implicate CD40 as a possible target for therapeutic intervention in the treatment of B lymphomas.

High affinity ligand binding is not essential for granulocyte-macrophage colony-stimulating factor receptor activation

The high affinity receptor of the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) is a heterodimer composed of two members of the cytokine receptor superfamily. GM-CSF binds to the alpha-subunit (GM-R alpha) with low affinity and to the receptor alpha beta complex (GM-R alpha beta) with high affinity. The GM-CSF.GM-R alpha beta complex is responsible for biological activity. Interactions of the N-terminal helix of mouse GM-CSF with mGM-R alpha beta were examined by introducing single alanine substitutions of hydrophilic residues in this region of mGM-CSF. The consequences of these substitutions were evaluated by receptor binding and biological assays. Although all mutant proteins exhibited near wild-type biological activity, most were defective in high affinity receptor binding. In particular, substitution of Glu-21 with alanine abrogated high affinity binding leaving low affinity binding unaffected. Despite near wild-type biological activity, no detectable binding interaction of this mutant with mGM-R beta in the context of mGM-R alpha beta was observed. Cross-linking studies showed an apparent interaction of this mutant protein with mGM-R alpha beta. The deficient receptor binding characteristics and near wild-type biological activity of this mutant protein demonstrate that mGM-CSF receptor activation can occur independently of high affinity binding, suggesting that conformational changes in the receptor induced by mGM-CSF binding generate an active ligand-receptor complex.

Requirement of hydrophilic amino-terminal residues for granulocyte-macrophage colony-stimulating factor bioactivity and receptor binding

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a glycoprotein required for the proliferation and differentiation of granulocyte and macrophage precursors. Previous investigations have identified regions in human and murine GM-CSF that are required for bioactivity. In the present study, alanine substitution mutagenesis was undertaken to define more precisely specific amino-terminal residues in murine GM-CSF that are involved in bioactivity and receptor binding. Five double alanine mutants were identified that showed at least 10-fold reductions in bioactivity (K14AK20A, K14AE21A, H15AK20A, H15AE21A, K20AE21A). Each of these mutants maintained a normal N-linked glycosylation pattern when expressed in COS-1 cells, suggesting that native polypeptide backbone conformation was preserved. The purified prokaryotic expression products of two mutants (K14AE21A and H15AE21A) had a 100-fold decrease in bioactivity and a decrease in receptor binding, indicating that the side chains of K14, H15, and E21 are required for optimal receptor binding and maximal bioactivity.

The amino-terminal helix of GM-CSF and IL-5 governs high affinity binding to their receptors

Transduction of the biological effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-5 (IL-5) requires the interaction of each cytokine with at least two cell surface receptor components, one of which is shared between these two cytokines. A strategy is presented that allowed us to identify receptor binding determinants in GM-CSF and IL-5. Mixed species (human and mouse) receptors were used to locate unique receptor binding domains on a series of human-mouse hybrid GM-CSF and IL-5 cytokines. Results show that the interaction of these two cytokines with the shared subunit of their high affinity receptor complexes is governed by a very small part of their peptide chains. The presence of a few key residues in the amino-terminal alpha-helix of each ligand is sufficient to confer specificity to the interaction. Comparison with other cytokines suggests that the amino-terminal helix of many of these proteins may contain the recognition element for the formation of high affinity binding sites with the alpha subunit of their multi-component receptors.

Identification of critical amino acid residues in human and mouse granulocyte-macrophage colony-stimulating factor and their involvement in species specificity

Segments critical to the activity of human granulocyte-macrophage colony-stimulating factor (GM-CSF) were identified by scanning deletion analysis and compared with the critical regions previously identified in the homologous mouse GM-CSF protein. Three of the four critical regions thus identified are in equivalent positions in their respective polypeptides, while a fourth critical region of each is uniquely located. To investigate whether unique critical regions are responsible for the observed species specificity of human and mouse GM-CSF, all critical regions were substituted into their opposite homologue. This identified one specific, but different, critical region in each homologue that could not be replaced. Further characterization of the nature of the species specificity of these two proteins was accomplished by the generation of a series of human/mouse GM-CSF hybrids. Each hybrid protein was assayed for specific activity on human- and mouse GM-CSF-dependent cell lines. Significant differences in the specific activity of these hybrids was observed, suggesting that different segments of each molecule interact with their respective receptors. Based on these two approaches, individual amino acids were identified that could provide, at least in part, the interactions between these protein ligands and their respective receptors. These residues are Thr-78 and Met-80 in human GM-CSF and Asp-92, Thr-98, and Asp-102 in mouse GM-CSF.

Identification of critical regions in mouse granulocyte-macrophage colony-stimulating factor by scanning-deletion analysis

Structure-function relationships for mouse granulocyte-macrophage colony-stimulating factor were examined by generating a series of small deletions scanning the entire length of the molecule. Deletions of three amino acids were introduced at intervals of five amino acids by site-directed mutagenesis of the mature mouse granulocyte-macrophage colony-stimulating factor gene. The mutant proteins were expressed in Escherichia coli and assayed for biological activity. This procedure identified four regions critical to activity. These critical regions were further delineated by additional three-amino acid deletion mutants. Larger deletions at each terminus were also made, as well as changes of specific amino acid residues. The four critical regions span amino acid residues 18-22, 34-41, 52-61, and 94-115. The disulfide bridge between Cys-51 and Cys-93 was also shown to be essential for activity, whereas that between Cys-85 and Cys-118 could be removed without loss of activity. The possible structural and/or functional roles of the critical regions are discussed.

Cloning and overexpression of the colicin E1 immunity gene

A DNA fragment containing only the putative immunity gene-coding sequence was cloned under the control of the trp and lambda PL promoters, generating pRKA11 and pIPL, respectively. Escherichia coli hosts containing either construction were immune to colicin E1. Cells harboring both pIPL and pNT204, which encodes a temperature-sensitive cI repressor, were sensitive to colicin E1 at 30 degrees C, but became immune after 0.5 h of incubation at 42 degrees C. In addition, pRKA11 directed the synthesis of a 14.5-kDA protein in maxicells, identical to that found with the wild-type immunity gene. This evidence identifies unequivocally the coding sequence of the immunity gene as that extending from bases 1214 to 1552 [OKA, A., et al., Mol. Gen. Genet. 172, 151-159 (1979)]. The entire immunity gene operon was also cloned under the control of the tac promoter, generating pTCU2, which, upon induction with isopropyl beta-D-thiogalactopyranoside, produced the imm gene product in amounts sufficient to be visualized by autoradiography.