1 × 106 K562 cells were incubated for 24 h and then irradiated (1 J/cm2) in HBSS with or without the test compounds. After 24 h from irradiation, cells were fixed with ice-cooled ethanol (70% v/v), treated overnight with RNAse A (0.1 mg/mL) in phosphate saline buffer and finally stained with propidium iodide (PI, 0.1 mg/mL). Samples were analyzed on a BD FACS Calibur flow cytometer collecting 10,000 events. Results of cell-cycle analysis were examined

using WinMDI 2.9 (Windows Multiple Document Interface for Flow Cytometry) [20]. K562 cells (300,000 cells/mL) were seeded in 24-well microplate CB-839 datasheet and incubated for 24 h prior irradiation. After medium removal, 1 mL of the drug solution was added to each well, incubated at 37 °C for 30 min

and then irradiated (1 J/cm2). After irradiation, the solution was replaced with complete medium and the plates were incubated for 24 h. Cells were collected by centrifugation and re-suspended in 1 μM JC-1 (5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazol-carbocyanine) solution PFT�� in HBSS or in 100 nM NAO (10-N-nonyl acridine orange) solution in RPMI medium. The cytofluorimetric analysis (BD FACS Calibur flow cytometer) was performed collecting green (FL1) and orange (FL2) fluorescence for JC-1 staining and only the green one (FL1) for NAO staining in at least 10,000 events for each sample [22] and [23]. Solutions of derivatives in methanol were irradiated in a quartz cuvette with different UV-A doses (0, 8, 16 and 32 J/cm2). After the irradiation, the solution was lyophilized, suspended in a known volume of methanol and stored at −20 °C. Concentrations of unknown photoproduct mixtures in this paper were expressed as if the initial psoralen was not photodegraded. RNA was isolated from K562 cells and measured by reverse transcription quantitative

real-time polymerase chain reaction (RT-qPCR) as described [24] using gene-specific double fluorescence labeled probes in an ABI Prism 7700 Sequence Detection System version 1.7.3 (Applied Biosystems). The following primer and probe sequences were used: α-globin forward primer, 5′-CAC GCG CAC AAG CTT CG-3′; α-globin reverse primer, 5′-AGG GTC ACC AGC AGG CAG T-3′; α-globin probe, 5′-FAM-TGG ACC CGG TCA ACT TCA AGC TCC T-TAMRA-3′; γ-globin forward until primer, 5′-TGG CAA GAA GGT GCT GAC TTC-3′; γ-globin reverse primer, 5′-TCA CTC AGC TGG GCA AAG G-3′; γ-globin probe, 5′-FAM-TGG GAG ATG CCA TAA AGC ACC TGG-TAMRA-3′. The kit for quantitative RT-PCR for ζ-globin mRNA and ε-globin mRNA were from Applied Biosystems (ζ-globin mRNA: Hs00923579_m1; ε-globin mRNA: Hs00362216_m1). The fluorescent reporter and the quencher were 6-carboxyfluorescein (FAM) and 6-carboxy-N,N,N′,N′-tetramethylrhodamine (TAMRA), respectively. For real-time PCR, the reference gene was 18S; this probe was fluorescent-labeled with VIC (Applied Biosystems) [24] and [25]. Unless indicated otherwise, results are presented as mean ± SEM.