Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates serum LDL cholesterol (LDL-C) by interacting with the LDL receptor (LDLR) and is an attractive therapeutic target for LDL-C lowering. We have generated a neutralizing anti-PCSK9 antibody, mAb1, that binds to an epitope on PCSK9 adjacent to the region required for LDLR interaction. In vitro, mAb1 inhibits PCSK9 binding to the LDLR and attenuates PCSK9-mediated reduction in LDLR protein levels, thereby increasing LDL uptake. A combination of mAb1 with a statin increases LDLR levels in HepG2 cells more than either treatment alone. In wild-type mice, mAb1 increases hepatic LDLR protein levels Ϸ2-fold and lowers total serum cholesterol by up to 36%: this effect is not observed in LDLR ؊/؊ mice. In cynomolgus monkeys, a single injection of mAb1 reduces serum LDL-C by 80%, and a significant decrease is maintained for 10 days. We conclude that anti-PCSK9 antibodies may be effective therapeutics for treating hypercholesterolemia.antibody ͉ LDL-C ͉ LDLR ͉ PCSK9 ͉ hypercholesterolemia P roprotein convertase subtilisin/kexin type 9 (PCSK9) has been implicated as an important regulator of LDL metabolism (1, 2). Human genetic studies provide strong validation for the role of PCSK9 in modulating LDL cholesterol (LDL-C) levels and the incidence of coronary heart disease (CHD) in man. Gain-of-function (GOF) mutations in the PCSK9 gene are associated with elevated serum LDL-C levels (Ͼ300 mg/dL) and premature CHD (3), whereas loss-of-function (LOF) mutations are associated with low serum LDL-C (Յ100 mg/dL) (4). Strikingly, subjects harboring the heterozygous LOF mutations exhibited an 88% reduction in the incidence of CHD over a 15-year period relative to noncarriers of the mutations (5). Moreover, despite a complete loss of PCSK9 and serum LDL-C of Ͻ20 mg/dL, the 2 subjects carrying compound heterozygote LOF mutations appear healthy (6, 7).PCSK9 belongs to the subtilisin family of serine proteases and consists of a prodomain, catalytic domain, and C-terminal V domain (8). Expressed highly in the liver, PCSK9 is secreted after autocatalytic cleavage of its zymogen form (1). The prodomain remains noncovalently associated with the catalytic domain and seems to inhibit further proteolytic enzyme activity (8, 9). Secreted PCSK9 modulates LDL-C levels by posttranslational downregulation of hepatic LDL receptor (LDLR) protein (1). The precise mechanism is unknown, but a direct interaction between repeat A of the LDLR EGF homology domain and the PCSK9 catalytic domain is required (10, 11). Proteolytic cleavage of the LDLR by PCSK9 does not occur (12, 13); rather, the PCSK9:LDLR complex is endocytosed and directed to the endosome/lysosome compartment for degradation (14, 15). Current understanding of the LDLR pathway asserts that apolipoprotein B (apoB) and E (apoE) containing lipoprotein particles endocytosed with the LDLR are transported to the acidic environment of the endosome, where they dissociate from the receptor and are subsequently catabolized in lysosomes, while t...

Fibroblast growth factor 21 (FGF21) is a distinctive member of the FGF family with potent beneficial effects on lipid, body weight, and glucose metabolism and has attracted considerable interest as a potential therapeutic for treating diabetes and obesity. As an alternative to native FGF21, we have developed a monoclonal antibody, mimAb1, that binds to βKlotho with high affinity and specifically activates signaling from the βKlotho/FGFR1c (FGF receptor 1c) receptor complex. In obese cynomolgus monkeys, injection of mimAb1 led to FGF21-like metabolic effects, including decreases in body weight, plasma insulin, triglycerides, and glucose during tolerance testing. Mice with adipose-selective FGFR1 knockout were refractory to FGF21-induced improvements in glucose metabolism and body weight. These results in obese monkeys (with mimAb1) and in FGFR1 knockout mice (with FGF21) demonstrated the essential role of FGFR1c in FGF21 function and suggest fat as a critical target tissue for the cytokine and antibody. Because mimAb1 depends on βKlotho to activate FGFR1c, it is not expected to induce side effects caused by activating FGFR1c alone. The unexpected finding of an antibody that can activate FGF21-like signaling through cell surface receptors provided preclinical validation for an innovative therapeutic approach to diabetes and obesity.

Rodent models of immune-mediated arthritis (RMIA) are the conventional approach to evaluating mechanisms of inflammatory joint disease and the comparative efficacy of antiarthritic agents. Rat adjuvant-induced (AIA), collagen-induced (CIA), and streptococcal cell wall-induced (SCW) arthritides are preferred models of the joint pathology that occurs in human rheumatoid arthritis (RA). Lesions of AIA are most severe and consistent; structural and immunological changes of CIA best resemble RA. Lesion extent and severity in RMIA depends on experimental methodology (inciting agent, adjuvant, etc.) and individual physiologic parameters (age, genetics, hormonal status, etc.). The effectiveness of antiarthritic molecules varies with the agent, therapeutic regimen, and choice of RMIA. All RMIA are driven by overactivity of proinflammatory pathways, but the dominant molecules differ among the models. Hence, as with the human clinical experience, the efficacy of various antiarthritic molecules differs among RMIA, especially when the agent is a specific cytokine inhibitor.