4-oxo Isotretinoin is an active metabolite of the retinoid isotretinoin .¹It is formed from isotretinoin by several cytochrome P450 (CYP450) isoforms, including CYP3A, CYP2B6, and CYP2C19.²4-oxo Isotretinoin (10 ?M) increases protein expression of cytokeratin 7 (CK7) and CK19 in normal human epidermal keratinocytes.³It inhibits proliferation of retinoid-sensitive UM-SCC-22A and UM-SCC-35 head and neck squamous cell carcinoma (HNSCC) cells in a concentration-dependent manner.⁴4-oxo Isotretinoin has been found in influent and effluent wastewater.⁵It is teratogenic to mouse embryos when administered to pregnant dams at a dose of 100 mg/kg on day 11 of gestation.⁶

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