Characterization of a Novel Selective Cytochrome P450 3A5 Substrate

描述(申请人提供)：人们普遍认为，当其中一种药物干扰涉及药物代谢的关键酶，主要是细胞色素P450家族的酶的活性时，服用多种药物的患者容易受到药代动力学药物-药物相互作用的影响。在过去的十年里，FDA通常要求公司进行临床试验，以确定这种药物-药物相互作用的结果。一些药物，如酮康唑，已被证明抑制单个P450酶的活性；而其他药物，如利福平或奥美拉唑，则诱导肝脏中更高水平的P450表达。这些相互作用可能需要调整剂量，以避免药物浓度升高和潜在的毒性增加，或药物水平不足而无法发挥作用。现有的体外工具可以合理地预测可能导致大多数常见的基于新陈代谢的药物-药物相互作用的化合物。然而，目前还没有工具来区分主要的细胞色素P3A酶，细胞色素P3A4和细胞色素P3A5。这两种酶比任何其他P450酶参与更多药物的新陈代谢。CYP3A4/5活性的改变可能会产生严重的后果，通过这一途径代谢的药物通常会受到警告：不能与西柚汁、酮康唑、圣约翰沃特和许多其他CYP3A抑制剂或诱导剂一起服用。CYP3A5可能是导致处方药代谢个体间和种族间差异的最重要的遗传因素。至少有一个激活的CYP3A5*1等位基因的个体表达大量功能性的CYP3A5，而CYP3A5*3*3导致剪接变体导致最低水平的CYP3A5表达。大约60%的非裔美国人和30%的高加索人至少有一个*1等位基因，并表达大致相同水平的细胞色素P3A5和细胞色素P3A4。在与生物相关的样品中，不能清楚地区分CYP3A4和CYP3A5的活性。目前，几乎所有已批准的化合物的CYP3A抑制数据都是通过CYP3A测定人肝微粒子的睾酮羟化或咪达唑仑羟化来产生的。虽然这两种底物都是由CYP3A4和CYP3A5代谢的，但由此产生的抑制常数主要反映了CYP3A4，因为多个肝微体供体池中含有的CYP3A4大约是CYP3A5的五到六倍。我们已经确定了第一个高选择性的CYP3A5底物，并建议建立一种选择性的CYP3A5检测方法，该方法能够定量测定肝微粒体中的CYP3A5的活性和抑制。 公共卫生相关性：细胞色素P450 3A家族的酶代谢大约50%的药物。遗憾的是，人类两种主要的细胞色素P3A酶--细胞色素P3A4和细胞色素P3A5的活性无法区分。我们建议使用我们实验室发现的一种新的高选择性底物来建立第一个选择性的CYP3A5检测方法。

DESCRIPTION (provided by applicant): It is widely accepted that patients on multiple medications are susceptible to pharmacokinetic drug-drug interactions when one of the drugs interferes with the activity of key enzymes involved in drug metabolism, chiefly enzymes in the cytochrome P450 family. In the past decade the FDA has commonly required companies to conduct clinical trials to determine the result of such drug-drug interactions. Some drugs such as ketoconazole have been shown to inhibit the activity of individual P450 enzymes; while other drugs such as rifampicin or omeprazole induce expression of higher P450 levels in the liver. These interactions can require dose adjustments to avoid having elevated drug concentrations and potentially increasing toxicities or having insufficient drug levels to be efficacious. Existing in vitro tools can reasonably predict compounds that are likely to cause most of the common metabolism-based drug-drug interactions. However, tools are not currently available to distinguish between the major CYP3A enzymes, CYP3A4 and CYP3A5. These two enzymes are implicated in the metabolism of more pharmaceuticals than any other P450s. Alteration of CYP3A4/5 activity can have serious consequences and drugs that are metabolized through this pathway often come with warnings: not to take with grapefruit juice, ketoconazole, St. Johns Wart, and numerous other CYP3A inhibitors or inducers. CYP3A5 may be the most important genetic contributor to interindividual and interracial differences in the metabolism of prescription drugs. Individuals with at least one gene for the active CYP3A5*1 allele express large amounts of functional CYP3A5, whereas CYP3A5*3*3 causes a splice variant that results in minimal CYP3A5 expression. Approximately 60% of African Americans and 30% of Caucasians have at least one *1 allele and express roughly equivalent levels of CYP3A5 and CYP3A4. CYP3A4 and CYP3A5 activity cannot be clearly differentiated in biologically relevant samples. Currently, the data for CYP3A inhibition of almost every approved compound is generated using a CYP3A assay measuring testosterone hydroxylation or midazolam hydroxylation by pooled human liver microsomes. While both of these substrates are metabolized by CYP3A4 and CYP3A5, the resulting inhibition constants primarily reflect CYP3A4 because multiple donor pools of hepatic microsomes contain approximately five to six times more CYP3A4 than CYP3A5. We have identified the first highly selective substrate of CYP3A5 and propose to build a selective CYP3A5 assay capable of quantifying CYP3A5 activity and inhibition in hepatic microsomal incubations. PUBLIC HEALTH RELEVANCE: The cytochrome P450 3A family of enzymes metabolize approximately 50% of pharmaceutical drugs. Unfortunately the activities of the two major human CYP3A enzymes, CYP3A4 and CYP3A5, cannot be differentiated. We propose to develop the first selective CYP3A5 assay using a novel highly selective substrate discovered in our laboratory.