Search

Cocaine use continues to be a major public health problem in the United States. Although many of the initial signs and symptoms of cocaine intoxication result from increased stimulation of the sympathetic nervous system, this condition can present as a spectrum of acuity from hypertension and tachycardia to multiorgan system failure. Classic features of acute intoxication include tachycardia, arterial vasoconstriction, enhanced thrombus formation, mydriasis, psychomotor agitation, and altered level of consciousness. At the extreme end of this toxidrome is a rare condition known as cocaine-induced agitated delirium. This syndrome is characterized by severe cardiopulmonary dysfunction, hyperthermia, and acute neurologic changes frequently leading to death. We report a case of cocaine-induced agitated delirium in a man who presented to our institution in a paradoxical form of circulatory shock. Rapid evaluation, recognition, and proper management enabled our patient not only to survive but also to leave the hospital without neurologic sequelae., (© The Author(s) 2013.)

Imatinib (Gleevec) is currently the frontline therapy for chronic myeloid leukemia (CML), a disease characterized by the presence of a constitutively activated chimeric tyrosine kinase protein Bcr-AbI. However, drug resistance often occurs at later stages of the disease, principally because of the occurrence of mutations in the kinase domain. Second generation Bcr-AbI inhibitors, such as dasatinib and nilotinib are capable of inhibiting many imatinib-resistant forms of the kinase but not the form in which threonine is mutated to isoleucine at the gatekeeper position (T315I). In this study, we present the crystal structure of the kinase domain of the c-AbI T315I mutant, as well as the wild-type form, in complex with a pyrrolopyridine inhibitor, PPY-A. The side chain of Ile315 is accommodated in the AbI T315I mutant structure without large conformational changes proximal to the site of mutation. In contrast to other inhibitors, such as imatinib and dasatinib, PPY-A does not occupy the hydrophobic pocket behind the gatekeeper residue. This binding mode, coupled with augmented contacts with the glycine-rich loop, appears to be critical for its ability to override the T315I mutation. The data presented here may provide structural guidance for the design of clinically useful inhibitors of Bcr-AbI T315I.

The tyrosine kinase pp60src (Src) is the prototypical member of a family of proteins that participate in a broad array of cellular signal transduction processes, including cell growth, differentiation, survival, adhesion, and migration. Abnormal Src family kinase (SFK) signaling has been linked to several disease states, including osteoporosis and cancer metastases. Src has thus emerged as a molecular target for the discovery of small-molecule inhibitors that regulate Src kinase activity by binding to the ATP pocket within the catalytic domain. Here, we present crystal structures of the kinase domain of Src in complex with two purine-based inhibitors: AP23451, a small-molecule inhibitor designed to inhibit Src-dependent bone resorption, and AP23464, a small-molecule inhibitor designed to inhibit the Src-dependent metastatic spread of cancer. In each case, a trisubstituted purine template core was elaborated using structure-based drug design to yield a potent Src kinase inhibitor. These structures represent early examples of high affinity purine-based Src family kinase-inhibitor complexes, and they provide a detailed view of the specific protein-ligand interactions that lead to potent inhibition of Src. In particular, the 3-hydroxyphenethyl N9 substituent of AP23464 forms unique interactions with the protein that are critical to the picomolar affinity of this compound for Src. The comparison of these new structures with two relevant kinase-inhibitor complexes provides a structural basis for the observed kinase inhibitory selectivity. Further comparisons reveal a concerted induced-fit movement between the N- and C-terminal lobes of the kinase that correlates with the affinity of the ligand. Binding of the most potent inhibitor, AP23464, results in the largest induced-fit movement, which can be directly linked to interactions of the hydrophenethyl N9 substituent with a region at the interface between the two lobes. A less pronounced induced-fit movement is also observed in the Src-AP23451 complex. These new structures illustrate how the combination of structural, computational, and medicinal chemistry can be used to rationalize the process of developing high affinity, selective tyrosine kinase inhibitors as potential therapeutic agents.

Major advances have been made in the past 10 years in our understanding of the molecular basis of bone cell formation and bone remodeling. For example, the discovery of osteoprotegerin, the decoy receptor and inhibitor of receptor activator of NF-kappaB ligand (RANKL), and the RANKL/receptor activator of NF-kappaB (RANK) signaling pathway that is essential for osteoclastogenesis, has helped clarify the mechanisms regulating osteoclast formation, activation, and survival. PTH, like most other osteoclast stimulating factors, promotes RANKL production by osteoblast/stromal cells when they are exposed to it continuously, but when given intermittently it stimulates bone formation and reduces fracture risk in postmenopausal women. This anabolic effect is associated with increased expression of insulin-like and fibroblast growth factors and decreased osteoblast apoptosis. Src tyrosine kinase is essential for osteoclast activation and also negatively regulates osteoblast activity. Thus, it is a well-validated therapeutic target for the prevention of postmenopausal and other forms of bone loss. Preliminary in vitro and in vivo studies of specifically designed, bone targeted, non-peptide Src inhibitors have shown that these compounds inhibit bone resorption and stimulate new bone formation. The design of drugs using structure/function approaches such as this should lead to the development of novel therapeutics that could be used to counteract the negative effects of chronic renal failure on the skeleton.

Targeted disruption of the pp60(src) (Src) gene has implicated this tyrosine kinase in osteoclast-mediated bone resorption and as a therapeutic target for the treatment of osteoporosis and other bone-related diseases. Herein we describe the discovery of a nonpeptide inhibitor (AP22408) of Src that demonstrates in vivo antiresorptive activity. Based on a cocrystal structure of the noncatalytic Src homology 2 (SH2) domain of Src complexed with citrate [in the phosphotyrosine (pTyr) binding pocket], we designed 3',4'-diphosphonophenylalanine (Dpp) as a pTyr mimic. In addition to its design to bind Src SH2, the Dpp moiety exhibits bone-targeting properties that confer osteoclast selectivity, hence minimizing possible undesired effects on other cells that have Src-dependent activities. The chemical structure AP22408 also illustrates a bicyclic template to replace the post-pTyr sequence of cognate Src SH2 phosphopeptides such as Ac-pTyr-Glu-Glu-Ile (1). An x-ray structure of AP22408 complexed with Lck (S164C) SH2 confirmed molecular interactions of both the Dpp and bicyclic template of AP22408 as predicted from molecular modeling. Relative to the cognate phosphopeptide, AP22408 exhibits significantly increased Src SH2 binding affinity (IC(50) = 0.30 microM for AP22408 and 5.5 microM for 1). Furthermore, AP22408 inhibits rabbit osteoclast-mediated resorption of dentine in a cellular assay, exhibits bone-targeting properties based on a hydroxyapatite adsorption assay, and demonstrates in vivo antiresorptive activity in a parathyroid hormone-induced rat model.