Heme Binding Biguanides Target Cytochrome P450-Dependent Cancer Cell Mitochondria

Abstract

Summary The mechanisms by which cancer cell-intrinsic CYP monooxygenases promote tumor progression are largely unknown. CYP3A4 was unexpectedly associated with breast cancer mitochondria and synthesized arachidonic acid (AA)-derived epoxyeicosatrienoic acids (EETs), which promoted the electron transport chain/respiration and inhibited AMPKα. CYP3A4 knockdown activated AMPKα, promoted autophagy, and prevented mammary tumor formation. The diabetes drug metformin inhibited CYP3A4-mediated EET biosynthesis and depleted cancer cell-intrinsic EETs. Metformin bound to the active site heme of CYP3A4 in a co-crystal structure, establishing CYP3A4 as a biguanide target. Structure-based design led to discovery of N1-hexyl-N5-benzyl-biguanide (HBB), which bound to the CYP3A4 heme with higher affinity than metformin. HBB potently and specifically inhibited CYP3A4 AA epoxygenase activity. HBB also inhibited growth of established ER+ mammary tumors and suppressed intratumoral mTOR. CYP3A4 AA epoxygenase inhibition by biguanides thus demonstrates convergence between eicosanoid activity in mitochondria and biguanide action in cancer, opening a new avenue for cancer drug discovery.

Cellular and Molecular Mechanisms of Metformin Action

“…It is likely that metformin has many additional effects and may in fact alter the activity of several complexes of the electron transport chain, which in turn indirectly leads to inhibition of GPD2. Metformin and other guanides have consistently been shown to bind metal ions, such as copper and iron, possibly by acting as a Schiff base, which is consistent with reports that metformin interacts with heme or cytochrome c directly ( 166-168 ). Indeed, downstream inhibition of the electron transport chain is shown to backlog the entire electron transport chain, providing a potential link between metformin interaction with downstream complexes and indirect inhibition of GPD2 ( 169 , 170 ).…”

Metabolism pathways of arachidonic acids: mechanisms and potential therapeutic targets

“… 396 CYP3A4 knockdown or inhibition by biguanides activated AMPKα, promoted autophagy, and prevented mammary tumor formation. 397 These results indicate that AA metabolizing CYP epoxygenases and EETs also are associated with mitochondrial function and oxidative stress of cancer cells, which may be another potential mechanism of their anti-apoptosic actions.…”

Integrated Bioinformatic Analysis Identifies Networks and Promising Biomarkers for Hepatitis B Virus-Related Hepatocellular Carcinoma

“…Heme binding protein-released heme exhibits highly prooxidative and proinflammatory effects [ 54 ] and thereby may accelerate the development and progression of HCC. The medication such as biguanides targeting heme binding has recently been reported to display an antineoplastic effect [ 55 ]. It should be noted that KEGG enrichment analysis in the present study reveals various amino acid-associated metabolism pathways linked with HBV-related HCC including “biosynthesis of amino acids,” “arginine biosynthesis,” “tryptophan metabolism,” “tyrosine metabolism,” “glycine, serine, and threonine metabolism,” and “alanine, aspartate, and glutamate metabolism.” Results from metabolomics unveil that serum levels of serine, glutamate, phenylalanine, ornithine, and tyrosine are remarkably elevated in both patients suffering from HBV infection and HCC, compared with healthy subjects [ 56 ].…”