Metabolism of the vitamin D₃ derivative (24R)‐hydroxycalcidiol by human promyelocytic leukemia cells (HL‐60): Isolation and identification of (5Z) and (5E)‐(24R)‐19‐nor‐10‐oxo‐24‐hydroxycalcidiol

Human promyelocytic leukemia cells (HL‐60 cells) incubated with (24R)‐hydroxy[26,27‐methyl‐³H]calcidiol (0.2 μCi) or non‐radioactive (24R)‐hydroxycalcidiol (370 μg) produced significant quantities of two new vitamin D₃ (calciol) metabolites. The metabolites were isolated from HL‐60 cell culture media by methanol/chloroform extraction and a series of chromatographic procedures. The two new metabolites were identified as (5Z)‐ and (5E)‐(24R)‐19‐nor‐10‐oxo‐24‐hydroxycalcidiol by HPLC analysis, ultraviolet absorption spectrophotometry, mass spectrometry and Fourier‐transfrom infrared spectrophotometry. According to the isolation and purification procedures, the total amounts of 3.04 μg (5Z)‐(24R)‐19‐nor‐10‐oxo‐24‐hydroxycalcidiol (λ_max= 310 nm, ɛ= 17070 M⁻¹ cm⁻¹) and 8.89 μg (5E)‐(24R)‐19‐nor‐10‐oxo‐24‐hydroxycalcidiol (λ_max= 312 nm, e= 24500 M⁻¹ cm⁻¹) were calculated, assuming an M₁ of 418. The activity of 19‐nor‐10‐oxo‐(24R)‐hydroxycalcidiol to promote HL‐60 cell differentiation was higher than the activity of the precursor (24R)‐hydroxycalcidiol suggesting a possible biological action of this metabolite in HL‐60 cells.