In silico and in vitro screening for inhibition of cytochrome P450 CYP3A4 by comedications commonly used by patients with cancer.

Cytochrome P450 3A4 (CYP3A4) is the major enzyme responsible for phase I drug metabolism of many anticancer agents. It is also a major route for metabolism of many drugs used by patients to treat the symptoms caused by cancer and its treatment as well as their other illnesses, for example, cardiovascular disease. To assess the ability to inhibit CYP3A4 of drugs most commonly used by our patients during cancer therapy, we have made in silico predictions based on the crystal structures of CYP3A4. From this set of 33 common comedicated drugs, 10 were predicted to be inhibitors of CYP3A4, with the antidiarrheal drug loperamide predicted to be the most potent. There was significant correlation (r(2) = 0.75-0.66) between predicted affinity and our measured IC(50) values, and loperamide was confirmed as a potent inhibitor (IC(50) of 0.050 +/- 0.006 microM). Active site docking studies predicted an orientation of loperamide consistent with formation of the major (N-demethylated) metabolite, where it interacts with the phenylalanine cluster and Arg-212 and Glu-374; experimental evidence for the latter interaction comes from the approximately 12-fold increase in K(M) for loperamide observed for the Glu-374-Gln mutant. The commonly prescribed drugs loperamide, amitriptyline, diltiazem, domperidone, lansoprazole, omeprazole, and simvastatin were identified by our in silico and in vitro screens as relatively potent inhibitors of CYP3A4 that have the potential to interact with cytotoxic agents to cause adverse effects, highlighting the likelihood of drug-drug interactions affecting chemotherapy treatment.

Calcium has a permissive role in interleukin-1beta-induced c-jun N-terminal kinase activation in insulin-secreting cells.

The c-jun N-terminal kinase (JNK) signaling pathway mediates IL-1beta-induced apoptosis in insulin-secreting cells, a mechanism relevant to the destruction of pancreatic beta-cells in type 1 and 2 diabetes. However, the mechanisms that contribute to IL-1beta activation of JNK in beta-cells are largely unknown. In this study, we investigated whether Ca(2+) plays a role for IL-1beta-induced JNK activation. In insulin-secreting rat INS-1 cells cultured in the presence of 11 mm glucose, combined pharmacological blockade of L- and T-type Ca(2+) channels suppressed IL-1beta-induced in vitro phosphorylation of the JNK substrate c-jun and reduced IL-1beta-stimulated activation of JNK1/2 as assessed by immunoblotting. Inhibition of IL-1beta-induced in vitro kinase activity toward c-jun after collective L- and T-type Ca(2+) channel blockade was confirmed in primary rat and ob/ob mouse islets and in mouse betaTC3 cells. Ca(2+) influx, specifically via L-type but not T-type channels, contributed to IL-1beta activation of JNK. Activation of p38 and ERK in response to IL-1beta was also dependent on L-type Ca(2+) influx. Membrane depolarization by KCl, exposure to high glucose, treatment with Ca(2+) ionophore A23187, or exposure to thapsigargin, an inhibitor of sarco(endo)plasmic reticulum Ca(2+) ATPase, all caused an amplification of IL-1beta-induced JNK activation in INS-1 cells. Finally, a chelator of intracellular free Ca(2+) [bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid-acetoxymethyl], an inhibitor of calmodulin (W7), and inhibitors of Ca(2+)/calmodulin-dependent kinase (KN62 and KN93) partially reduced IL-1beta-stimulated c-jun phosphorylation in INS-1 or betaTC3 cells. Our data suggest that Ca(2+) plays a permissive role in IL-1beta activation of the JNK signaling pathway in insulin-secreting cells.

Rainbow tags: a visual tag system for recombinant protein expression and purification.

Visualization systems for tracking proteins are standard experimental tools in most areas of biological research apart from protein purification. Here, we have sought to plug this gap by producing red and yellow visual tags using the heme-binding domain of mosquito cytochrome b5 and the flavin mononucleotide (FMN)-binding domain of human P450 reductase. Tests with colorless glutathione-S-transferase (GST) show them to be simple and effective tools for visually identifying correctly folded protein and tracking protein molecules through protein expression and purification. Furthermore, the characteristic absorbance signatures of the colored tags can be used to quantify protein concentrations directly, which allows purification to be linked to colorimetric detection. This technology, which we call Rainbow Tagging, facilitates expression and downstream processing of recombinant proteins, paving the way for the development of automated high-throughput protein expression systems.

On-line monitoring of apoptosis in insulin-secreting cells.

Apoptosis was monitored in intact insulin-producing cells both with microfluorometry and with two-photon laser scanning microscopy (TPLSM), using a fluorescent protein based on fluorescence resonance energy transfer (FRET). TPLSM offers three-dimensional spatial information that can be obtained relatively deep in tissues. This provides a potential for future in vivo studies of apoptosis. The cells expressed a fluorescent protein (C-DEVD-Y) consisting of two fluorophores, enhanced cyan fluorescent protein (ECFP) and enhanced yellow fluorescent protein (EYFP), linked by the amino acid sequence DEVD selectively cleaved by caspase-3-like proteases. FRET between ECFP and EYFP in C-DEVD-Y could therefore be monitored on-line as a sensor of caspase-3 activation. The relevance of using caspase-3 activation to indicate beta-cell apoptosis was demonstrated by inhibiting caspase-3-like proteases with Z-DEVD-fmk and thereby showing that caspase-3 activation was needed for high-glucose-and cytokine-induced apoptosis in the beta-cell and for staurosporine-induced apoptosis in RINm5F cells. In intact RINm5F cells expressing C-DEVD-Y and in MIN6 cells expressing the variant C-DEVD-Y2, FRET was lost at 155 +/- 23 min (n = 9) and 257 +/- 59 min (n = 4; mean +/- SE) after activation of apoptosis with staurosporine (6 micromol/l), showing that this method worked in insulin-producing cells.