In vitro evaluation of the inhibition and induction potential of olaparib, a potent poly(ADP-ribose) polymerase inhibitor, on cytochrome P450.

1. In vitro studies were conducted to evaluate potential inhibitory and inductive effects of the poly(ADP-ribose) polymerase (PARP) inhibitor, olaparib, on cytochrome P450 (CYP) enzymes. Inhibitory effects were determined in human liver microsomes (HLM); inductive effects were evaluated in cultured human hepatocytes. 2. Olaparib did not inhibit CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2D6 or CYP2E1 and caused slight inhibition of CYP2C9, CYP2C19 and CYP3A4/5 in HLM up to a concentration of 100 µM. However, olaparib (17-500 µM) inhibited CYP3A4/5 with an IC50 of 119 µM. In time-dependent CYP inhibition assays, olaparib (10 µM) had no effect against CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP2E1 and a minor effect against CYP3A4/5. In a further study, olaparib (2-200 µM) functioned as a time-dependent inhibitor of CYP3A4/5 (KI, 72.2 µM and Kinact, 0.0675 min-1). Assessment of the CYP induction potential of olaparib (0.061-44 µM) showed minor concentration-related increases in CYP1A2 and more marked increases in CYP2B6 and CYP3A4 mRNA, compared with positive control activity; however, no significant change in CYP3A4/5 enzyme activity was observed. 3. Clinically significant drug-drug interactions due to olaparib inhibition or induction of hepatic or intestinal CYP3A4/5 cannot be excluded. It is recommended that olaparib is given with caution with narrow therapeutic range or sensitive CYP3A substrates, and that prescribers are aware that olaparib may reduce exposure to substrates of CYP2B6.

In vivo studies of the PARP inhibitor, AZD-2281, in combination with fractionated radiotherapy: An exploration of the therapeutic ratio.

BACKGROUND AND PURPOSE: Pre-clinical data have shown that PARP inhibitors (PARPi) may increase the efficacy of radiotherapy in prostate cancer. However, it is uncertain as to whether PARPi lead to clonogenic kill when combined with radiotherapy (RT). MATERIAL AND METHODS: We tested the PARP inhibitor AZD-2281 as a radiosensitizing agent under oxic and hypoxic conditions for clonogenic survival in vitro and in vivo using the human prostate cancer cell line, 22Rv1. In addition, the effects of PARPi+RT on normal tissue were investigated using a crypt clonogenic assay. RESULTS: AZD-2281 inhibited cellular PARP activity under both oxic and hypoxic conditions. The addition of AZD-2281 radiosensitized 22Rv1 cells under oxia, acute hypoxia and chronic hypoxia in vitro. The combination of AZD-2281 with fractionated radiotherapy resulted in a significant growth delay and clonogenic kill in vivo. No increased gut toxicity was observed using this combined PARPi+radiotherapy regimen. CONCLUSIONS: This is the first preclinical study to demonstrate direct clonogenic kill in vivo by the addition of AZD-2281 to radiotherapy. As we did not observe gut toxicity, the use of PARPi in the context of prostate cancer radiotherapy warrants further investigation in clinical trials.

Autoinduction of MKC-963 [(R)-1-(1-cyclohexylethylamino)-4-phenylphthalazine] metabolism in healthy volunteers and its retrospective evaluation using primary human hepatocytes and cDNA-expressed enzymes.

MKC-963, (R)-1-(1-cyclohexylethylamino)-4-phenylphthalazine, a potent inhibitor of platelet aggregation, was synthesized and used in clinical trials in the 1990s. In the process of clinical study, it was found that urinary excretion ratios for 6beta-hydroxycortisol and free cortisol increased significantly in parallel with decreases in the plasma concentrations of MKC-963 after repeated oral administration of the compound to healthy volunteers. These findings suggested that MKC-963 caused autoinduction (defined as the ability of a drug to induce enzymes that enhance its own metabolism, resulting in dispositional tolerance) in humans, and clinical studies using the compound were stopped. This experience prompted us to reevaluate the effects of this compound on CYP3A4 using primary human hepatocytes and cDNA-expressed human cytochrome P450 (P450) enzymes to determine whether the autoinduction of MKC-963 metabolism in humans could have been predicted if these in vitro systems had been used for the evaluation of MKC-963 in the preclinical study. The results of in vitro study showed that MKC-963 increased CYP3A4 mRNA expression level and activity of testosterone 6beta-hydroxylation to extents similar to those observed with rifampicin in primary human hepatocytes. In addition, approximately 90% of the MKC-963 metabolism in human liver microsomes was estimated to be attributable to CYP3A4. These in vitro findings are in good agreement with the results of clinical study, suggesting that studies using human hepatocytes and cDNA-expressed human P450s are useful for assessing the autoinductive nature of compounds under development before starting clinical studies.

Biomarkers for assessment of pharmacologic activity for a vascular endothelial growth factor (VEGF) receptor inhibitor, PTK787/ZK 222584 (PTK/ZK): translation of biological activity in a mouse melanoma metastasis model to phase I studies in patients with advanced colorectal cancer with liver metastases.

PTK/ZK is a novel, oral angiogenesis inhibitor that specifically targets all 3 vascular endothelial growth factor (VEGF) receptor tyrosine kinases and is currently in phase III clinical trials. In early clinical trials, PTK/ZK demonstrated a dose-dependent reduction in tumor vascular parameters as measured by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and an acute increase in plasma VEGF levels. The reduction in tumor vascularity was significantly correlated with improved clinical outcome in patients with advanced colorectal cancer and liver metastases. To assess the predictive value of a mouse model of tumor metastases, comparisons were performed for the biological activity of PTK/ZK in the mouse model and in patients with liver metastases in the clinical phase I trials. An orthotopic, syngeneic mouse model was used: C57BL/6 mice injected in the ear with murine B16/BL6 melanoma cells which metastases to the cervical lymph-nodes. The primary tumor and spontaneous metastases express VEGF and VEGF receptors and respond to treatment with VEGFR tyrosine kinase inhibitors. PTK/ZK was administered orally, with assessments by DCE-MRI of the metastases and plasma VEGF taken predose and at 3 days posttreatment and efficacy determined at 7 days posttreatment. Dose-ranging studies in naive mice provided preclinical pharmacokinetic data, while two dose-escalation phase I studies provided clinical pharmacokinetic data. An exposure-response relationship was observed both for mouse metastases (measured as % tumor weight treated/control) and for human liver metastases (measured as % regression). In the B16/BL6 model, the active dose of 50 mg/kg PTK/ZK yielded 62.4 (+/- 16.0) h microM plasma exposure, which is comparable to the plasma area under the concentration time curve (AUC) achieved by the 1000 mg dose of PTK/ZK used in clinical trials. At this exposure level in clinical trials, DCE-MRI showed a reduction in the area under the enhancement curve (IAUC) to 47% of baseline. At a similar exposure in the PTK/ZK-treated mice, a reduction in IAUC to 75% of baseline was observed. Furthermore, at doses of 50 mg/kg PTK/ZK and above, an increase in plasma VEGF level 10 h after drug administration was observed in mice which was consistent with findings from the clinical trials. In conclusion, the preclinical pharmacodynamics of PTK/ZK correlate well with clinical activity in phase I trials over comparable exposures to the drug. Thus, data from this preclinical model proved to be consistent with and thus predictive of the biologic effects of PTK/ZK in phase I/II clinical trials.

Pharmacokinetic interactions between Japanese traditional medicine (kampo) and modern medicine (III). Effect of Sho-seiryu-to on the pharmacokinetics of azelastine hydrochloride in rats.

Sho-seiryu-to (SST) is widely used herbal formula in Japanese traditional medicine (kampo) to treat allergic diseases. Since Japanese physicians frequently prescribe this formula combined with azelastine hydrochloride, one of anti-histamine and anti-allergic medicines, we evaluated the pharmacokinetic interactions between SST and azelastine hydrochloride in rats to obtain the drug information for the prevention from disadvantage or adverse effects by their combined therapy. Oral administration of SST did not influence the plasma concentration profile of azelastine after its intravaneous injection, suggesting that SST would not change the activities of metabolic enzymes such as cytochrome P450s. However, maximum concentration (C(max)) of azelastine after oral administration of azelastine hydrochloride was significantly reduced and mean residence time (MRT) was significantly lengthened when SST was orally administered at 20 times amount of human daily dosage. There was not significant difference in the area under the plasma concentration-time curve (AUC), suggesting that SST might delay the absorption of azelastine without affecting the extent of bioavailability. Since this delay was independent of ephedrine that is a main constituent of SST and that a suppressor for gastric transit, SST might form unsoluble complex with azelastine to reduce its absorption. At the double of human daily dose, SST did not made the absorption of azelastine delay. The possibility that SST reduce the absorption of azelastine hydrochloride could not be denied completely, however, it is suggested that SST would not cause pharmacokinetic interaction with azelastine hydrochloride clinically.