To accelerate the discovery of novel small molecule central nervous system (CNS) positron emission tomography (PET) ligands, we aimed to define a property space that would facilitate ligand design and prioritization, thereby providing a higher probability of success for novel PET ligand development. Toward this end, we built a database consisting of 62 PET ligands that have successfully reached the clinic and 15 radioligands that failed in late-stage development as negative controls. A systematic analysis of these ligands identified a set of preferred parameters for physicochemical properties, brain permeability, and nonspecific binding (NSB). These preferred parameters have subsequently been applied to several programs and have led to the successful development of novel PET ligands with reduced resources and timelines. This strategy is illustrated here by the discovery of the novel phosphodiesterase 2A (PDE2A) PET ligand 4-(3-[(18)F]fluoroazetidin-1-yl)-7-methyl-5-{1-methyl-5-[4-(trifluoromethyl)phenyl]-1H-pyrazol-4-yl}imidazo[5,1-f][1,2,4]triazine, [(18)F]PF-05270430 (5).

Background-Matrix metalloproteinase (MMP) activation contributes to tissue remodeling in several disease states, and increased MMP activity has been observed in left ventricular (LV) failure. The present study tested the hypothesis that MMP inhibition would influence LV remodeling and function in developing LV failure. Methods and Results-LV size and function were measured in 5 groups of rats: (1) obese male spontaneously hypertensive heart failure rats (SHHF) at 9 months (nϭ10), (2) SHHF at 13 months (nϭ12), (3) SHHF rats treated with an MMP inhibitor during months 9 to 13 (PD166793 5 mg ⅐ kg Ϫ1 ⅐ d Ϫ1 PO; nϭ14), (4) normotensive Wistar-Furth rats (WF) at 9 months (nϭ12), and (5) WF at 13 months (nϭ12). Plasma concentrations of the MMP inhibitor (116Ϯ11 mol/L) reduced in vitro LV myocardial MMP-2 activity by Ϸ100%. LV function and geometry were similar in WF rats at 9 and 13 months. LV peak ϩdP/dt was unchanged at 9 months in SHHF but by 13 months was reduced in the SHHF group compared with WF (3578Ϯ477 versus 5983Ϯ109 mm Hg/s, PՅ0.05). LV volume measured at an equivalent ex vivo pressure (10 mm Hg) was increased in SHHF at 9 months compared with WF (443Ϯ12 versus 563Ϯ33 mL, PՅ0.05) and increased further by 13 months (899Ϯ64 mL, PՅ0.05). LV myocardial MMP-2 activity was increased by Ϸ2-fold in SHHF at 9 and 13 months. With MMP inhibition, LV peak ϩdP/dt was similar to WF values and LV volume was reduced compared with untreated SHHF values (678Ϯ28 mL, PՅ0.05). Conclusions-MMP

. Louis MO 63110; {Departments of Artherosclerosis Therapeutics, }Biochemistry and }Chemistry Parke-Davis, Ann Arbor MI 48105 and #Department of Pharmacology, Columbia University, New York, NY 10032, U.S.A.1 15-Lipoxygenase (15-LO) has been implicated in the pathogenesis of atherosclerosis because of its localization in lesions and the many biological activities exhibited by its products. To provide further evidence for a role of 15-LO, the e ects of PD 146176 on the development of atherosclerosis in cholesterol-fed rabbits were assessed. This novel drug is a speci®c inhibitor of the enzyme in vitro and lacks signi®cant non speci®c antioxidant properties. 2 PD 146176 inhibited rabbit reticulocyte 15-LO through a mixed noncompetitive mode with a K i of 197 nM. The drug had minimal e ects on either copper or 2,2'-azobis(2-amidinopropane)hydrochloride (ABAP) induced oxidation of LDL except at concentrations 2 orders higher than the K i . 3 Control New Zealand rabbits were fed a high-fat diet containing 0.25% wt./wt. cholesterol; treated animals received inhibitor in this diet (175 mg kg 71 , b.i.d.). Plasma concentrations of inhibitor were similar to the estimated K i (197 nM). During the 12 week study, there were no signi®cant di erences in weight gain, haematocrit, plasma total cholesterol concentrations, or distribution of lipoprotein cholesterol. 4 The drug plasma concentrations achieved in vivo did not inhibit low-density lipoprotein (LDL) oxidation in vitro. Furthermore, LDL isolated from PD 146176-treated animals was as susceptible as that from controls to oxidation ex vivo by either copper or ABAP. 5 PD 146176 was very e ective in suppressing atherogenesis, especially in the aortic arch where lesion coverage diminished from 15+4 to 0% (P50.02); esteri®ed cholesterol content was reduced from 2.1+0.7 to 0 mg mg 71 (P50.02) in this region. Immunostainable lipid-laden macrophages present in aortic intima of control animals were totally absent in the drug-treated group. 6 Results of these studies are consistent with a role for 15-LO in atherogenesis.

Animal models are needed to better understand the pathogenic mechanisms of Zika virus (ZIKV) and to evaluate candidate medical countermeasures. Adult mice infected with ZIKV develop a transient viremia, but do not demonstrate signs of morbidity or mortality. Mice deficient in type I or a combination of type I and type II interferon (IFN) responses are highly susceptible to ZIKV infection; however, the absence of a competent immune system limits their usefulness for studying medical countermeasures. Here we employ a murine model for ZIKV using wild-type C57BL/6 mice treated with an antibody to disrupt type I IFN signaling to study ZIKV pathogenesis. We observed 40% mortality in antibody treated mice exposed to ZIKV subcutaneously whereas mice exposed by intraperitoneal inoculation were highly susceptible incurring 100% mortality. Mice infected by both exposure routes experienced weight loss, high viremia, and severe neuropathologic changes. The most significant histopathological findings occurred in the central nervous system where lesions represent an acute to subacute encephalitis/encephalomyelitis that is characterized by neuronal death, astrogliosis, microgliosis, scattered necrotic cellular debris, and inflammatory cell infiltrates. This model of ZIKV pathogenesis will be valuable for evaluating medical countermeasures and the pathogenic mechanisms of ZIKV because it allows immune responses to be elicited in immunologically competent mice with IFN I blockade only induced at the time of infection.