New era in drug interaction evaluation: US Food and Drug Administration update on CYP enzymes, transporters, and the guidance process.

Predicting clinically significant drug interactions during drug development is a challenge for the pharmaceutical industry and regulatory agencies. Since the publication of the US Food and Drug Administration's (FDA's) first in vitro and in vivo drug interaction guidance documents in 1997 and 1999, researchers and clinicians have gained a better understanding of drug interactions. This knowledge has enabled the FDA and the industry to progress and begin to overcome these challenges. The FDA has continued its efforts to evaluate methodologies to study drug interactions and communicate recommendations regarding the conduct of drug interaction studies, particularly for CYP-based and transporter-based drug interactions, to the pharmaceutical industry. A drug interaction Web site was established to document the FDA's current understanding of drug interactions (http://www.fda.gov/cder/drug/drugInteractions/default.htm). This report provides an overview of the evolution of the drug interaction guidances, includes a synopsis of the steps taken by the FDA to revise the original drug interaction guidance documents, and summarizes and highlights updated sections in the current guidance document, Drug Interaction Studies-Study Design, Data Analysis, and Implications for Dosing and Labeling.

Application of semisimultaneous midazolam administration for hepatic and intestinal cytochrome P450 3A phenotyping.

OBJECTIVES: Determination of hepatic and intestinal cytochrome P450 (CYP) 3A activity is important, because CYP3A substrates show substantial variability in plasma concentrations as a result of variations in both hepatic and intestinal metabolism. The goals of this study were (1) to determine whether the hepatic and intestinal extraction ratios (ER(H) and ER(G), respectively) of the CYP3A probe drug midazolam are different when determined after semisimultaneous administration, as compared with administration on separate occasions (traditional method), and (2) to evaluate the hepatic and intestinal metabolism of midazolam in the presence and absence of ketoconazole by the semisimultaneous method. METHODS: Midazolam pharmacokinetics was assessed in 12 healthy volunteers after administration of midazolam, 5 mg orally, followed at 6 hours by 2 mg given by intravenous infusion. Concentration-time data were fitted to a combined oral-intravenous infusion model by nonlinear regression (semisimultaneous method). Data from the semisimultaneous method were compared with those obtained after individual midazolam doses, 1 week apart (traditional approach). The effect of ketoconazole on midazolam pharmacokinetics after semisimultaneous administration was also determined in 4 healthy volunteers. RESULTS: There were no significant differences in bioavailability (0.343 +/- 0.100 versus 0.343 +/- 0.094), ER(H) (0.269 +/- 0.064 versus 0.267 +/- 0.077), and ER(G) (0.534 +/- 0.135 versus 0.531 +/- 0.124) between the traditional and semisimultaneous methods. As expected, ketoconazole markedly increased the mean bioavailability to 0.838 (2.4-fold), the mean ER(H) was decreased 3.7-fold, and the mean ER(G) was decreased 5.7-fold. CONCLUSIONS: Midazolam pharmacokinetic parameters that are specific to liver and intestinal metabolism were not different between the traditional and semisimultaneous methods. The semisimultaneous method also yielded expected marked changes in the parameters as a result of ketoconazole inhibition. Thus the semisimultaneous midazolam method appears to be a suitable approach to determine hepatic and intestinal CYP3A activity at baseline and with enzyme inhibition.

Lactam-based HDAC inhibitors for anticancer chemotherapy: restoration of RUNX3 by posttranslational modification and epigenetic control.

Expression and stability of the tumor suppressor runt-related transcription factor 3 (RUNX3) are regulated by histone deacetylase (HDAC). HDAC inhibition alters epigenetic and posttranslational stability of RUNX3, leading to tumor suppression. However, HDAC inhibitors can nonselectively alter global gene expression through chromatin remodeling. Thus, lactam-based HDAC inhibitors were screened to identify potent protein stabilizers that maintain RUNX3 stability by acetylation. RUNX activity and HDAC inhibition were determined for 111 lactam-based analogues through a cell-based RUNX activation and HDAC inhibition assay. 3-[1-(4-Bromobenzyl)-2-oxo-2,5-dihydro-1H-pyrrol-3-yl]-N-hydroxypropanamide (11-8) significantly increased RUNX3 acetylation and stability with relatively low RUNX3 mRNA expression and HDAC inhibitory activity. This compound showed significant antitumor effects, which were stronger than SAHA, in an MKN28 xenograft model. Thus, we propose a novel strategy, in which HDAC inhibitors serve as antitumor chemotherapeutic agents that selectively target epigenetic regulation and protein stability of RUNX3.

New synthetic aliphatic sulfonamido-quaternary ammonium salts as anticancer chemotherapeutic agents.

RhoB is expressed during tumor cell proliferation, survival, invasion, and metastasis. In malignant progression, the expression levels of RhoB are commonly attenuated. RhoB is known to be linked to the regulation of the PI3K/Akt survival pathways. Based on aliphatic amido-quaternary ammonium salts that induce apoptosis via up-regulation of RhoB, we synthesized novel aliphatic sulfonamido-quaternary ammonium salts. These new synthetic compounds were evaluated for their biological activities using an in vitro RhoB promoter assay in HeLa cells, and in a growth inhibition assay using human cancer cell lines including PC-3, NUGC-3, MDA-MB-231, ACHN, HCT-15, and NCI-H23. Compound 5b (ethyl-dimethyl-{3-[methyl-(tetradecane-1-sulfonyl)-amino]-propyl}-ammonium; iodide) was the most promising anticancer agent in the series, based upon the potency of growth inhibition and RhoB promotion. These new aliphatic sulfonamido-quaternary ammonium salts could be a valuable series for development of new anticancer chemotherapeutic agents.

CYP-mediated therapeutic protein-drug interactions: clinical findings, proposed mechanisms and regulatory implications.

Therapeutic proteins (TPs) may affect the disposition of drugs that are metabolized by cytochrome P450 (CYP) enzymes, as is evident from a review of data in recently published literature and approved Biologic License Applications. Many TPs belonging to the cytokine class appear to differentially affect CYP activities. Cytokine modulators may affect CYP enzyme activities by altering cytokine effects on CYP enzymes. The alteration in CYP enzyme activities seems to result from changes in transcription factor activity for CYP enzyme expression or changes in CYP enzyme stability, which have been observed during altered immunological states such as infection and inflammation. Human growth hormone also appears to differentially affect CYP activities through unknown mechanisms. Because TP-drug interaction research is an evolving area, limited information is available during drug development on TP-drug interactions mediated by CYP inhibition or induction. The authors of this review suggest that effort be made to understand TP-drug interactions for the safe and effective use of TPs in combination with small-molecule drugs.