Ritonavir reverses resistance to docetaxel and cabazitaxel in prostate cancer cells with acquired resistance to docetaxel.

Aim: Docetaxel is a microtubule-stabilizing drug used for the treatment of several cancers, including prostate cancer. Resistance to docetaxel can either occur through intrinsic resistance or develop under therapeutic pressure, i.e., acquired resistance. A possible explanation for the occurrence of acquired resistance to docetaxel is increased drug efflux via P-glycoprotein (P-gp) drug transporters. Methods: We have generated docetaxel-resistant cell lines DU-145DOC10 and 22Rv1DOC8 by exposing parental cell lines DU-145DOC and 22Rv1 to increasing levels of docetaxel. Gene expression levels between DU-145DOC10 and 22Rv1DOC8 were compared with those of their respective originator cell lines. Both parental and resistant cell lines were treated with the taxane drugs docetaxel and cabazitaxel in combination with the P-gp/CYP3A4 inhibitor ritonavir and the P-gp inhibitor elacridar. Results: In the docetaxel-resistant cell lines DU-145DOC10 and 22Rv1DOC8, the ABCB1 (P-gp) gene was highly up-regulated. Expression of the P-gp protein was also significantly increased in the docetaxel-resistant cell lines in a Western blotting assay. The addition of ritonavir to docetaxel resulted in a return of the sensitivity to docetaxel in the DU-145DOC10 and 22Rv1DOC8 to a level similar to the sensitivity in the originator cells. We found that these docetaxel-resistant cell lines could also be re-sensitized to cabazitaxel in a similar manner. In a Caco-2 P-gp transporter assay, functional inhibition of P-gp-mediated transport of docetaxel with ritonavir was demonstrated. Conclusion: Our results demonstrate that ritonavir restores sensitivity to both docetaxel and cabazitaxel in docetaxel-resistant cell lines, most likely by inhibiting P-gp-mediated drug efflux.

Investigating ABCB1-Mediated Drug-Drug Interactions: Considerations for In vitro and In vivo Assay Design.

BACKGROUND: ABCB1 is a key ABC efflux transporter modulating the pharmacokinetics of a large percentage of drugs. ABCB1 is also a site of transporter mediated drug-drug interactions (tDDI). It is the transporter most frequently tested for tDDIs both in vitro and in the clinic. OBJECTIVE: Understanding the limitations of various in vitro and in vivo models, therefore, is crucial. In this review we cover regulatory aspects of ABCB1 mediated drug transport as well as inhibition and the available models and methods. We also discuss protein structure and mechanistic aspects of transport as ABCB1 displays complex kinetics that involves multiple binding sites, potentiation of transport and probe-dependent IC50 values. RESULTS: Permeability of drugs both passive and mediated by transporters is also a covariate that modulates apparent kinetic values. Levels of expression as well as lipid composition of the expression system used in in vitro studies have also been acknowledged as determinates of transporter activity. ABCB1-mediated clinical tDDIs are often complex as multiple transporters as well as metabolic enzymes may play a role. This complexity often masks the role of ABCB1 in tDDIs. CONCLUSION: It is expected that utilization of in vitro data will further increase with the refinement of simulations. It is also anticipated that transporter humanized preclinical models have a significant impact and utility.

Screen3D: a novel fully flexible high-throughput shape-similarity search method.

3D shape- or volume-based virtual screening is a broadly used approach in drug discovery. In recent years a large number of publications have appeared in which these tools were compared not only to competitive methods but to docking studies as well. Studies often showed that the effectiveness of docking could be highly variable due to a large number of possible confounding factors, while ligand-based, shape-based approaches were more consistent. Here, we describe a novel, fully flexible shape-based virtual screening algorithm that does not require previous 3D conformation or conformer generation. Due to its solid consistency it can easily be used on desktop computers by non-expert scientists. The algorithm is demonstrated in a study for the investigation of ß-secretase inhibitors and benchmarked on the Directory of Useful Decoys data set.

The preclinical properties of a novel group II metabotropic glutamate receptor agonist LY379268.

Activation of group II metabotropic glutamate (mGlu2/3) receptors reduces excessive glutamate release that is often associated with neurodegenerative and psychiatric disorders. This finding encouraged the search for potent and selective agonists as potential therapeutic agents. The search led to the discovery of LY379268 {(-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylic acid}, which is a highly potent and systemically available mGlu2/3 receptor agonist. LY379268 was effective in several animal models of stroke, epilepsy, drug abuse, schizophrenia, and pain. Suppression of motor activity is the major side effect of LY379268. Upon repeated administration tolerance develops to this side effect, while the therapeutic effects of LY379268 remain. To date, no clinical data with LY379268 are available. This review article summarizes the preclinical pharmacology of LY379268.

Effects of the mGluR2/3 agonist LY379268 on ketamine-evoked behaviours and neurochemical changes in the dentate gyrus of the rat.

One of the functions of group II metabotropic glutamate receptors (mGluR2/3) is to modulate glutamate release. Thus, targeting mGluR2/3s might be a novel treatment for several psychiatric disorders associated with inappropriate glutamatergic neurotransmission, such as schizophrenia. In an effort to evaluate the antipsychotic properties of LY379268, a potent and selective mGluR2/3 agonist, we examined its effect on ketamine-evoked hyperlocomotion and sensorimotor gating deficit (PPI) in rats, an animal model of schizophrenia. We also measured the ex vivo tissue level of glutamate (Glu), dopamine (DA) and serotonin (5-HT) as well as the DA metabolites DOPAC and the major 5-HT metabolite HIAA to determine the neurochemical effects of ketamine (12 mg/kg) and LY379268 (1 mg/kg) in the dentate gyrus (DG). While LY379268 (1-3 mg/kg) reduced ketamine-evoked hyperlocomotion (12 mg/kg), it could not restore ketamine-evoked PPI deficits (4-12 mg/kg). In the DG we found that ketamine decreased Glu and DA levels, as well as HIAA/5-HT turnover, and that LY379268 could prevent ketamine effects on Glu level but not on monoamine transmission. These results may indicate that the inability of LY379268 to reverse PPI deficits is attributable to its lack of effect on ketamine-induced changes in monoamine transmission, but that LY379268 can prevent ketamine-evoked changes in glutamate, which is sufficient to block hyperlocomotion. In addition to the partial effectiveness of LY379268 in the ketamine model of schizophrenia, we observed a dual effect of LY379268 on anxious states, whereby a low dose of this compound (1 mg/kg) produced anxiolytic effects, while a higher dose (3 mg/kg) appeared to be anxiogenic. Additional work is needed to address a possible role of LY379268 in schizophrenia and anxiety treatment.

Subchronic administration of LY354740 does not modify ketamine-evoked behavior and neuronal activity in rats.

Acute treatment with LY354740 {1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate monohydrate}, a potent and selective agonist for group II metabotropic glutamate receptors (mGlu2/3), has previously been shown to block some schizophrenia-like effects of N-methyl-D-aspartate (NMDA) receptor antagonists, suggesting a novel therapeutic strategy for schizophrenia. The present study examined the effects of subchronic pretreatment with LY354740 (0.3, 3 and 10 mg/kg i.p.) on ketamine-evoked (12 mg/kg s.c.) prepulse inhibition deficits, hyperlocomotion and c-fos expression. At all doses, LY354740 failed to reverse both behavioral and neuronal effects of the ketamine. These results therefore do not support the putative antipsychotic role of LY354740.

Dose-response characteristics of ketamine effect on locomotion, cognitive function and central neuronal activity.

The present dose-response study sought to determine the effects of subanesthetic dosages (4-16 mg/kg) of ketamine on locomotion, sensorimotor gating (PPI), working memory, as well as c-fos expression in various limbic regions implicated in the pathogenesis of schizophrenia. In addition, we examined whether ketamine-induced locomotion was influenced by the dark/light cycle. We found that ketamine increased locomotor activity in a dose dependent manner, but found no influence of the dark-light cycle. Additionally, ketamine dose-dependently interrupted PPI, resulting in prepulse facilitation at doses of 8 and 12 mg/kg. The dose of 12 mg/kg also induced impairments in working memory assessed by the discrete-trial delayed-alternation task. C-fos expression indicated that the dose-dependent behavioral effects of ketamine might be related to changes in the activity of limbic regions, notably hippocampus and amygdala.