Phase II study of tariquidar, a selective P-glycoprotein inhibitor, in patients with chemotherapy-resistant, advanced breast carcinoma

Cyclohexylpiperazine derivative PB28, a sigma2 agonist and sigma1 antagonist receptor, inhibits cell growth, modulates P-glycoprotein, and synergizes with anthracyclines in breast cancer

sigma Ligands have recently been shown to have cytotoxic activity, to induce ceramide-dependent/caspase-independent apoptosis, and to down-regulate P-glycoprotein (P-gp) mRNA levels in some mouse and human models. In this study, we verified whether a mixed sigma(2) agonist/sigma(1) antagonist, PB28, was able to have antitumor activity and to enhance anthracycline efficacy in two human breast cancer cell lines, MCF7 and MCF7 ADR, both characterized by significant sigma(2) receptor expression, by high and low sigma(1) receptor expression, and low and high P-gp expression, respectively. In both cell lines, PB28 showed high sigma(2) receptor affinity and low sigma(1) receptor affinity; furthermore, it inhibited cell growth with a clear effect at 48 hours (IC(50) in nanomolar range), a consistent time exposure-independent increase of G(0)-G(1)-phase fraction (of approximately 20% of both cell lines) and caspase-independent apoptosis (15% increased after 1-day drug exposure). PB28 also reduced P-gp expression in a concentration- and time-dependent manner ( approximately 60% in MCF7 and 90% in MCF7 ADR). We showed also a strong synergism between PB28 and doxorubicin by adopting either simultaneous or sequential schedules of the two drugs. We suggest that this synergism could depend on PB28-induced increase of intracellular accumulation of doxorubicin ( approximately 50% in MCF7 and 75% in MCF7 ADR by flow cytometry analysis). In conclusion, we suggest that the sigma(2) agonist PB28 could be an interesting antitumor agent either in monotherapy or in combination with conventional drugs.

Inhibition of the Multidrug Transporter P-Glycoprotein Improves Seizure Control in Phenytoin-treated Chronic Epileptic Rats

PURPOSE

Overexpression of multidrug transporters such as P-glycoprotein (P-gp) may play a significant role in pharmacoresistance, by preventing antiepileptic drugs (AEDs) from reaching their targets in the brain. Until now, many studies have described increased P-gp expression in epileptic tissue or have shown that several AEDs act as substrates for P-gp. However, definitive proof showing the functional involvement of P-gp in pharmacoresistance is still lacking. Here we tested whether P-gp contributes to pharmacoresistance to phenytoin (PHT) by using a specific P-gp inhibitor in a model of spontaneous seizures in rats.

METHODS

The effects of PHT on spontaneous seizure activity were investigated in the electrical post-status epilepticus rat model for temporal lobe epilepsy, before and after administration of tariquidar (TQD), a selective inhibitor of P-gp.

RESULTS

A 7-day treatment with therapeutic doses of PHT suppressed spontaneous seizure activity in rats, but only partially. However, an almost complete control of seizures by PHT (93 +/- 7%) was obtained in all rats when PHT was coadministered with TQD. This specific P-gp inhibitor was effective in improving the anticonvulsive action of PHT during the first 3-4 days of the treatment. Western blot analysis confirmed P-gp upregulation in epileptic brains (140-200% of control levels), along with approximately 20% reduced PHT brain levels. Inhibition of P-gp by TQD significantly increased PHT brain levels in chronic epileptic rats.

CONCLUSIONS

These findings show that TQD significantly improves the anticonvulsive action of PHT, thus establishing a proof-of-concept that the administration of AEDs in combination with P-gp inhibitors may be a promising therapeutic strategy in pharmacoresistant patients.

Simultaneous determination of paclitaxel and a new P-glycoprotein inhibitor HM-30181 in rat plasma by liquid chromatography with tandem mass spectrometry

An LC-MS/MS method for the simultaneous determination of a new P-glycoprotein inhibitor 4-oxo-4H-chromene-2-carboxylic acid [2-(2-(4-[2-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-ethyl]-phenyl)-2H-tetrazol-5-yl)-4,5-dimethoxy-phenyl]-amide (HM-30181) and a P-glycoprotein substrate paclitaxel in rat plasma was developed to simultaneously evaluate the pharmacokinetics of paclitaxel and HM-30181 in the rats. HM-30181, paclitaxel, HM-30059 (internal standard (I.S.) for HM-30181), and docetaxel (I.S. for paclitaxel) were extracted from rat plasma with methyl-tert-butyl ether and analyzed on an Atlantis C18 column (5 microm, 2.1 x 100 mm) with the mobile phase of ACN/10 mM ammonium formate (75:25 v/v). The analytes were detected using an ESI MS/MS in the multiple reaction monitoring (MRM) mode. The standard curves for HM-30181 and paclitaxel in plasma were linear (r > 0.999) over the concentration range of 2.0-500 ng/mL with a weighting of 1/concentration2. The method showed a satisfactory sensitivity (2 ng/mL using 50 microL plasma), precision (CV: < or = 6.6%), accuracy (relative error: -6.3 to 2.0%), and selectivity. This method was successfully applied to the pharmacokinetic study of HM-30181 and paclitaxel in rat plasma after oral-coadministration of paclitaxel and HM-30181 to male Sprague- Dawley rats.

Metabolism of a new P-glycoprotein inhibitor HM-30181 in rats using liquid chromatography/electrospray mass spectrometry

HM-30181, 4-oxo-4H-chromene-2-carboxylic acid, [2-(2-{4-[2-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-ethyl]-phenyl}-2H-tetrazol-5-yl)-4,5-dimethoxyphenyl]amide, is a new P-glycoprotein inhibitor. This study was performed to identify the in vitro and in vivo metabolic pathway of HM-30181 in rats. Rat liver microsomal incubation of HM-30181 in the presence of NADPH resulted in the formation of four metabolites, M1-M4. M1 and M2 were identified as 2-(2-{4-[2-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-ethyl]-phenyl}-2H-tetrazol-5-yl)-4,5-dimethoxyaniline and 4- or 5-O-desmethyl-HM-30181, respectively, on the basis of liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis with the synthesized authentic standards. M3 and M4 were suggested to be 6- or 7-O-desmethyl-HM-30181 and hydroxy-HM-30181, respectively. These in vitro metabolites were also detected in feces and urine samples after an intravenous administration of HM-30181 to male rats. The metabolic routes for HM-30181 were O-demethylation of the methoxy group to M2 and M3, hydrolysis of the amide group to M1, and hydroxylation to M4.

Reversal of doxorubicin resistance in breast cancer cells by photochemical internalization

Multiple drug resistance (MDR) is a problem that seriously reduces the efficacy of many chemotherapy agents. One mechanism for MDR is increased acidification of endocytic vesicles and increased cytosol pH, so weak base chemotherapeutic agents, including doxorubicin, are trapped in endocytic vesicles and exhibit a drug resistant phenotype. Treatments that selectively reverse this accumulation may therefore reverse the MDR phenotype. Photochemical internalization (PCI) is a novel technology developed for site-specific enhancement of the therapeutic efficacy of macromolecules by selective photochemical rupture of endocytic vesicles and consequent release of endocytosed macromolecules into the cytosol. This study evaluates PCI for release of doxorubicin from endocytic vesicles in MDR cells. Two breast cancer cell lines, MCF-7 and MCF-7/ADR (the latter resistant to doxorubicin), were selected. They were found equally sensitive to photochemical treatment with the photosensitiser TPPS(2) (a) (disulfonated meso-tetraphenylporphine) and light. On exposure to doxorubicin alone, the IC(50) (drug concentration for 50% reduction in colony formation) was 0.1 microM for MCF-7 and 1 microM for MCF-7/ADR. After PCI (photochemical treatment followed by doxorubicin), the IC(50) concentration was 0.1 microM for both cell lines. Comparable changes were seen with assay of cell viability using 3-(4,5-dimethyltiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). On fluorescence microscopy in MCF-7/ADR cells, doxorubicin localised in granules identified as lysosomes. After PCI, doxorubicin was released into the cytosol and entered cell nuclei, as was seen in MCF-7 cells without PCI. In conclusion, PCI reversed the MDR phenotype of doxorubicin resistant breast cancer cells by endo-lysosomal release of the drug. The technique is a promising new approach to tackling the problem of MDR.

Tesmilifene may enhance breast cancer chemotherapy by killing a clone of aggressive, multi-drug resistant cells through its action on the p-glycoprotein pump

Tesmilifene is a novel potentiator of chemotherapy which, when added to doxorubicin, achieved an unexpected and very large survival advantage over doxorubicin alone in a randomized trial in advanced breast cancer. This trial was unusual in that the early endpoints (response rate and median progression-free survival) were equivalent in the two arms, despite the ultimate survival difference. These aspects, coupled with the absence of a coherent molecular mechanism of action, and a pending confirmatory trial, have led oncologists to hold judgement on this drug. This paper reacts to this in three ways: firstly, a forensic subgroup analysis is presented with an explanation as to why it strongly supports the veracity of the survival difference; secondly a novel cellular explanation is provided for the decoupling of the early and late (survival) endpoints; finally, a molecular mechanism of action is proposed, for the first time, which reconciles the peculiarities of the trial with the laboratory data and background literature. This hypothesis explains how tesmilifene could meld two of the apparent strengths of the cancer cell (drug resistance pumps, and hypoxia-adapted energetics) into a potent weapon of self-destruction. Tesmilifene is proposed to allow chemotherapy (e.g. anthracycline or taxane) to additionally kill a small but critical population (clone) of aggressive, multi-drug resistant cells, the benefits of which cannot be appreciated until a period of time (about 6-8 months) has elapsed. These cells, present in women with more rapidly relapsing disease, very likely carry an energy-dependent extrusion pump which is paradoxically activated by tesmilifene plus the chemotherapy. The result is that, despite the chemotherapy's remaining extracellular, the cell dies from reactive oxygen species leaking from the electron chain transport in the abnormal mitochondria which characterize cancer. These mitochondria are activated in response to the ATP cost of this pump activation, in these predominantly glycolytic cells.