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A phase I reaction is a biochemical process that introduces a functionally reactive polar group to a substance. This transformation predominantly occurs in the liver, facilitated by the cytochrome P450 system of hemoproteins situated in the lipophilic endoplasmic reticulum of cells. The metabolite generated through this process can have varying polarities. If it is sufficiently polar, it can be easily excreted in the urine due to its water compatibility. However, if the metabolite is nonpolar,...
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Pharmaceutical substances known as xenobiotics are predominantly lipophilic and nonionized. This enables them to permeate lipid bilayers, such as cell membranes, and interact with intracellular target receptors. Lipophilic drugs have an advantage in crossing biological barriers and reaching their intended sites of action. However, lipophilic drugs often have a restricted capacity for renal expulsion or elimination from the body. When these drugs enter the kidneys and undergo glomerular...
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Phase II biotransformations are detoxification mechanisms that conjugate xenobiotics with endogenous substances, neutralizing their toxicity.
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Phase II reactions are essential for the detoxification and elimination of drugs from the body. These reactions involve the conjugation of parent drugs or their phase I metabolites with endogenous molecules, resulting in more hydrophilic drug conjugates. The primary conjugation reactions in this phase are sulfation and glucuronidation. Both sulfation and glucuronidation typically produce biologically inactive metabolites. However, in some cases involving prodrugs, active metabolites may be...
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Phase I biotransformation reactions are integral to drug metabolism, predominantly involving oxidative, reductive, and hydrolytic transformations. Chief among these are oxidative reactions, which enhance the hydrophilicity of xenobiotics and introduce polar functional groups to facilitate their elimination from the body.
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Cytochrome P450 Mining for Bufadienolide Diversification.

Xiaolai Lei1, Xiaozheng Wang1, Weiliang Xiong1

  • 1State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory on Metabolic & Developmental Sciences, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.

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Researchers identified toad cytochrome P450 enzymes that produce novel bufadienolides with antitumor activity. These enzymes enable efficient, site-specific synthesis of valuable steroid compounds.

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Area of Science:

  • Biochemistry and Molecular Biology
  • Natural Product Synthesis
  • Pharmacology

Background:

  • Bufadienolides are steroids with significant cardiotonic and antitumor properties, used in traditional Chinese medicine.
  • Limited accessibility of bufadienolides due to costly extraction from toads and difficult chemical synthesis.
  • Need for efficient methods to produce diverse bufadienolides with specific modifications.

Purpose of the Study:

  • To identify enzymes involved in bufadienolide biosynthesis in toads.
  • To develop a method for producing novel and modified bufadienolides.
  • To evaluate the antitumor potential of newly synthesized bufadienolides.

Main Methods:

  • Transcriptome and genome analyses to identify candidate cytochrome P450 (CYP) enzymes.
  • Yeast-based screening platform for enzyme activity.
  • Production, structural identification, and biological evaluation of bufadienolides.

Main Results:

  • Eight toad CYP enzymes and one fungal CYP (Sth10) were identified as catalyzing bufadienolide hydroxylation.
  • Fifteen bufadienolides were produced, including six novel compounds.
  • 19-hydroxy-bufalin and 1β-hydroxy-bufalin, produced by CYP46A35, showed potent tumor cell proliferation inhibition.
  • CYP46A35 demonstrated enhanced catalytic efficiency and expanded substrate range to progesterone and testosterone.

Conclusions:

  • Elucidation of key enzymatic modifications in toad bufadienolide synthesis.
  • Development of an effective platform for site-specific synthesis of valuable bufadienolides.
  • Potential for producing novel steroid drugs with enhanced therapeutic activities.