A sensitive LC-MS-MS assay for the determination of lapatinib in human plasma in subjects with end-stage renal disease receiving hemodialysis.

Most bioanalytical methods reported in literature for the quantitation of lapatinib in human plasma are either for lapatinib alone or lapatinib administered along with other tyrosine kinase inhibitors (TKIs) for therapeutic drug monitoring (TDM) in cancer patients. Recently there was a need for the quantitation of lapatinib in patients with end-stage renal disease (ESRD) receiving hemodialysis (HD). This special patient population normally receives many concomitant medications which have the potential to interfere with the quantitation of lapatinib. Here we describe an LC-MS-MS bioanalytical assay for the quantitation of lapatinib in human plasma containing potential concomitant medications which are commonly given to patients with ESRD receiving HD. The lapatinib calibration curve range was 2.50-1000 ng/mL. Lapatinib was fortified with its isotopically labeled internal standard in a 50 µL plasma aliquot and extracted with protein precipitation. The chromatographic separation was achieved on a Zorbax SB-C18 (5 µm, 2.1 × 50 mm) column with isocratic elution. Assay precision, accuracy, linearity, selectivity, sensitivity and analyte stability covering sample storage and analysis were established. No interferences were observed for the quantitation of lapatinib in the presence of concomitant medications. The validated LC-MS-MS method has been successfully applied to a clinical study for the determination of lapatinib concentrations in human plasma for patients with ESRD receiving HD.

Phosphodiesterase 9A regulates central cGMP and modulates responses to cholinergic and monoaminergic perturbation in vivo.

Cyclic nucleotides are critical regulators of synaptic plasticity and participate in requisite signaling cascades implicated across multiple neurotransmitter systems. Phosphodiesterase 9A (PDE9A) is a high-affinity, cGMP-specific enzyme widely expressed in the rodent central nervous system. In the current study, we observed neuronal staining with antibodies raised against PDE9A protein in human cortex, cerebellum, and subiculum. We have also developed several potent, selective, and brain-penetrant PDE9A inhibitors and used them to probe the function of PDE9A in vivo. Administration of these compounds to animals led to dose-dependent accumulation of cGMP in brain tissue and cerebrospinal fluid, producing a range of biological effects that implied functional significance for PDE9A-regulated cGMP in dopaminergic, cholinergic, and serotonergic neurotransmission and were consistent with the widespread distribution of PDE9A. In vivo effects of PDE9A inhibition included reversal of the respective disruptions of working memory by ketamine, episodic and spatial memory by scopolamine, and auditory gating by amphetamine, as well as potentiation of risperidone-induced improvements in sensorimotor gating and reversal of the stereotypic scratching response to the hallucinogenic 5-hydroxytryptamine 2A agonist mescaline. The results suggested a role for PDE9A in the regulation of monoaminergic circuitry associated with sensory processing and memory. Thus, PDE9A activity regulates neuronal cGMP signaling downstream of multiple neurotransmitter systems, and inhibition of PDE9A may provide therapeutic benefits in psychiatric and neurodegenerative diseases promoted by the dysfunction of these diverse neurotransmitter systems.

Discovery of novel benzothiazolesulfonamides as potent inhibitors of HIV-1 protease.

The human immunodeficiency virus (HIV) has been shown to be the causative agent for AIDS. The HIV virus encodes for a unique aspartyl protease that is essential for the production of enzymes and proteins in the final stages of maturation. Protease inhibitors have been useful in combating the disease. The inhibitors incorporate a variety of isosteres including the hydroxyethylurea at the protease cleavage site. We have shown that the replacement of t-butylurea moiety by benzothiazolesulfonamide provided inhibitors with improved potency and antiviral activities. Some of the compounds have shown good oral bioavailability and half-life in rats. The synthesis of benzothiazole derivatives led us to explore other heterocycles. During the course of our studies, we also developed an efficient synthesis of benzothiazole-6-sulfonic acid via a two-step procedure starting from sulfanilamide.