title: P450 3A-Catalyzed O-Dealkylation of Lapatinib Induces Mitochondrial Stress and Activates Nrf2.
abstract: Lapatinib (LAP), an oral tyrosine kinase inhibitor for the treatment of metastatic breast cancer, has been associated with idiosyncractic hepatotoxicity. Recent investigations have implicated the importance of P450 3A4/5 enzymes in the formation of an electrophilic quinone imine (LAPQI) metabolite generated through further oxidation of O-dealkylated lapatinib (OD-LAP). In the current study, hepatic stress was observed via mitochondrial impairment. OD-LAP caused a time- and concentration-dependent decrease in oxygen consumption in HepG2 cells, whereas LAP did not alter the oxygen consumption rate. Interestingly, however, HepG2 cells transfected with human P450 3A4 did exhibit mitochondrial dysfunction via P450 3A4-mediated metabolism of LAP to OD-LAP. OD-LAP-induced mitochondrial toxicity was enhanced upon depletion of intracellular GSH levels, demonstrating that cellular GSH levels are important in the protection of mitochondrial function against LAPQI. Given the nature of LAPQI and the importance of GSH levels in LAP-induced mitochondrial stress, the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) was evaluated, as this transcription factor induces the expression of NAD(P)H quinone oxidoreductase 1, glutathione S-transferase, UDP-glucuronosyltransferases, and glutathione synthetase, all of which might be expected to decrease the toxicity of LAP. Using a FRET-based target gene assay in HepG2 cells, OD-LAP was indeed found to activate Nrf2. Follow-up assays showed increased mRNA levels of Nrf2 target genes after a 4 h treatment with OD-LAP but not with LAP. LAP activation of Nrf2 was observed only when HepG2 cells were transduced with P450 3A4. The significance of Nrf2 protection was established in vivo in Nrf2-KO mice. Increased transaminase levels were found after a single LAP dose in both Nrf2-KO and control mice, indicating elevated hepatic necrosis, although transaminase levels reverted to baseline levels in the control mice upon repeat dosing. They continued to rise in Nrf2-KO mice, however, indicating the likelihood that Nrf-2 plays a significant role in combatting the hepatotoxicity triggered by LAP.
authors.affiliation: Department of Molecular Therapeutics, The Scripps Research Institute, Scripps Florida , 130 Scripps Way, Jupiter, Florida 33458, United States.
authors.forename: Marsha Rebecca
authors.initials: MR
authors.lastname: Eno
authors.affiliation: Chemistry Department, Faculty of Science, Benha University , Benha 13518, Egypt.
authors.forename: Bahaa El-Dien M
authors.initials: Bel-D
authors.lastname: El-Gendy
authors.affiliation: Department of Molecular Therapeutics, The Scripps Research Institute, Scripps Florida , 130 Scripps Way, Jupiter, Florida 33458, United States.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Cameron
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000478:Alkylation; D000970:Antineoplastic Agents / Q000378:metabolism*; D002384:Catalysis; D045744:Cell Line, Tumor; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism*; D006801:Humans; D000077341:Lapatinib; D008930:Mitochondria, Liver / Q000378:metabolism*; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D011799:Quinazolines / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D011799:Quinazolines; D012333:RNA, Messenger; D000077341:Lapatinib; D000255:Adenosine Triphosphate; D051544:Cytochrome P-450 CYP3A