laniquidar and tariquidar

Modulation of P glycoprotein (Pgp) in clinical oncology has had limited success. Contributing factors have included the limitation in our understanding of the tumours in which Pgp overexpression is mechanistically important in clinical drug resistance; the failure to prove that concentrations of modulators achieved in patients were sufficient to inhibit Pgp; and the inability to conclusively prove that Pgp modulation was occurring in tumours in patients. New approaches are needed to determine the clinical settings in which Pgp overexpression plays a major role in resistance. (Clinical trials with third generation modulators are ongoing, including trials with the compounds LY335979, R101933 and XR9576. Using the Pgp substrate Tc-99m Sestamibi as an imaging agent, increased uptake has been seen in normal liver and kidney after administration of PSC 833, VX710 and XR9576. These studies confirm that the concentrations of modulator achieved in patients are able to increase uptake of a Pgp substrate. Furthermore, CD56+ cells obtained from patients treated with PSC 833 demonstrate enhanced rhodamine retention in an ex vivo assay after administration of the antagonist. Finally, a subset of patients treated with Pgp antagonists show enhanced Sestamibi retention in imaged tumours. These results suggest that Pgp modulators can increase drug accumulation in Pgp-expressing tumours and normal tissues in patients. Using third generation Pgp antagonists and properly designed clinical trials, it should be possible to determine the contribution of modulators to the reversal of clinical drug resistance.

Topics: Animals; Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily B, Member 1; Benzazepines; Clinical Trials as Topic; Cyclosporins; Dibenzocycloheptenes; Drug Interactions; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Enzyme Inhibitors; Fluorescent Dyes; Gene Expression Regulation, Neoplastic; Genes, MDR; Humans; Mice; Mice, Knockout; Neoplasm Proteins; Neoplasms; Piperidines; Pyridines; Quinolines; Radionuclide Imaging; Radiopharmaceuticals; Rhodamines; Technetium Tc 99m Sestamibi; Tissue Distribution; Tumor Cells, Cultured

To analyse the impact of both epilepsy and pharmacological modulation of P-glycoprotein on brain uptake and kinetics of positron emission tomography (PET) radiotracers [(11)C]quinidine and [(11)C]laniquidar.. Metabolism and brain kinetics of both [(11)C]quinidine and [(11)C]laniquidar were assessed in naive rats, electrode-implanted control rats, and rats with spontaneous recurrent seizures. The latter group was further classified according to their response to the antiepileptic drug phenobarbital into "responders" and "non-responders". Additional experiments were performed following pre-treatment with the P-glycoprotein modulator tariquidar.. [(11)C]quinidine was metabolized rapidly, whereas [(11)C]laniquidar was more stable. Brain concentrations of both radiotracers remained at relatively low levels at baseline conditions. Tariquidar pre-treatment resulted in significant increases of [(11)C]quinidine and [(11)C]laniquidar brain concentrations. In the epileptic subgroup "non-responders", brain uptake of [(11)C]quinidine in selected brain regions reached higher levels than in electrode-implanted control rats. However, the relative response to tariquidar did not differ between groups with full blockade of P-glycoprotein by 15 mg/kg of tariquidar. For [(11)C]laniquidar differences between epileptic and control animals were only evident at baseline conditions but not after tariquidar pretreatment.. We confirmed that both [(11)C]quinidine and [(11)C]laniquidar are P-glycoprotein substrates. At full P-gp blockade, tariquidar pre-treatment only demonstrated slight differences for [(11)C]quinidine between drug-resistant and drug-sensitive animals.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; Benzazepines; Carbon Radioisotopes; Chronic Disease; Disease Models, Animal; Epilepsy; Female; Gene Expression Regulation; Kinetics; Male; Phenobarbital; Positron-Emission Tomography; Quinidine; Quinolines; Radiochemistry; Rats; Rats, Sprague-Dawley; Recurrence; Treatment Outcome