Increased In Vivo Exposure of N-(4-Hydroxyphenyl) Retinamide (4-HPR) to Achieve Plasma Concentrations Effective against Dengue Virus

N-(4-hydroxyphenyl) retinamide (4-HPR, or fenretinide) has promising in vitro and in vivo antiviral activity against a range of flaviviruses and an established safety record, but there are challenges to its clinical use. This study evaluated the in vivo exposure profile of a 4-HPR dosage regime previously shown to be effective in a mouse model of severe dengue virus (DENV) infection, comparing it to an existing formulation for human clinical use for other indications and developed/characterised self-emulsifying lipid-based formulations of 4-HPR to enhance 4-HPR in vivo exposure. Pharmacokinetic (PK) analysis comprising single-dose oral and IV plasma concentration-time profiles was performed in mice; equilibrium solubility testing of 4-HPR in a range of lipids, surfactants and cosolvents was used to inform formulation approaches, with lead formulation candidates digested in vitro to analyse solubilisation/precipitation prior to in vivo testing. PK analysis suggested that effective plasma concentrations could be achieved with the clinical formulation, while novel lipid-based formulations achieved > 3-fold improvement. Additionally, 4-HPR exposure was found to be limited by both solubility and first-pass intestinal elimination but could be improved through inhibition of cytochrome P450 (CYP) metabolism. Simulated exposure profiles suggest that a b.i.d dosage regime is likely to maintain 4-HPR above the minimum effective plasma concentration for anti-DENV activity using the clinical formulation, with new formulations/CYP inhibition viable options to increase exposure in the future.

Dihydroceramide Δ4-Desaturase 1 Is Not Involved in SARS-CoV-2 Infection

Dihydroceramide Δ4-desaturase 1 (DEGS1) enzymatic activity is inhibited with N-(4-hydroxyphenyl)-retinamide (4-HPR). We reported previously that 4-HPR suppresses severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry through a DEGS1-independent mechanism. However, it remains unclear whether DEGS1 is involved in other SARS-CoV-2 infection processes, such as virus replication and release. Here we established DEGS1 knockout (KO) in VeroE6^TMPRSS2 cells. No significant difference was observed in virus production in the culture supernatant between wild-type (WT) cells and DEGS1-KO cells, although the levels of dihydroceramide (DHCer), a DEGS1 substrate, were significantly higher in DEGS1-KO cells than WT cells. Furthermore, the virus-induced cytopathic effect was also observed in DEGS1-KO cells. Importantly, the EC₅₀ value of 4-HPR in DEGS1-KO cells was almost identical to the value reported previously in WT cells. Our results indicated the lack of involvement of DEGS1 in SARS-CoV-2 infection.

[Effects of N-(4-hydroxyphenyl) retinamide lipid microbubble combined with ultrasound on human keloid fibroblasts]

Objective: To explore the effects of N-(4-hydroxyphenyl) retinamide (4HPR), 4HPR liposome (4HPR-L), and 4HPR lipid microbubble (4HPR-LM) combined with ultrasound on proliferation, apoptosis, and cell cycle of human keloid fibroblasts (Fbs). Methods: (1) 4HPR-L and 4HPR-LM were prepared by hydration ultrasonic method. The appearance morphology, particle size distribution, Zeta potential, loading drug concentration, encapsulation efficiency, and drug loading rate of 4HPR-L were investigated by high performance liquid chromatography, dynamic light scattering, and transmission electron microscope. (2) Human keloid Fbs were cultured and divided into 13 groups by random number table (the same grouping method below), with 6 wells in each group. Cells in control group were given no treatment, while cells in 12 ultrasound groups including 0.5 W 30 s group, 0.5 W 60 s group, 0.5 W 120 s group, 0.7 W 30 s group, 0.7 W 60 s group, 0.7 W 120 s group, 1.0 W 30 s group, 1.0 W 60 s group, 1.0 W 120 s group, 1.5 W 30 s group, 1.5 W 60 s group, and 1.5 W 120 s group were treated by ultrasound with corresponding parameters. The cells viability was measured by a microplate reader after 24 hours of routine culture. Another batch of human keloid Fbs were divided into 5 groups, with 6 wells in each group. Cells in control group were given no treatment, while cells in 1, 10, 20, and 50 μg/mL blank lipid microbubble groups were treated with blank lipid microbubbles in corresponding mass concentration. The cells viability was measured as before after 24 hours of routine culture. Another batch of human keloid Fbs were divided into 6 groups, with 12 wells in each group. Cells in control group were given no treatment, while cells in 1, 10, 20, 50, and 100 μg/mL 4HPR-L groups were added with 4HPR-L carrying corresponding mass concentration of 4HPR. The cells viability in 6 wells of each group was detected after 24 and 48 hours of routine culture, respectively. Another batch of human keloid Fbs were divided into 4 groups, with 6 wells in each group. Cells in control group were given no treatment, while cells in 4HPR, 4HPR-L, and 4HPR-LM+ ultrasound groups were treated with 4HPR, 4HPR-L, and 4HPR-LM (all the mass concentration of 4HPR was 20 μg/mL), respectively, and cells in 4HPR-LM+ ultrasound group were given 0.5 W 60 s ultrasound treatment immediately after drug administration. The cells viability was measured as before after 24 hours of routine culture. (3) Another batch of human keloid Fbs were divided into control group, 4HPR group, 4HPR-L group and 4HPR-LM+ ultrasound group, with 3 wells in each group, and the cells in each group were treated as before. Apoptosis of the cells was detected by flow cytometer after 24 hours of routine culture. (4) Another batch of human keloid Fbs were grouped and treated as in (3), and then the cell cycle distribution was detected by flow cytometer after 24 hours of routine culture. Data were processed with one-way analysis of variance and t test. Results: (1) 4HPR-L particles had a spherical or spheroidal structure and were uniform in size, with particle size of (100.1±1.3) nm and Zeta potential of (-34.3±2.3) mV. The mass concentration of 4HPR in 4HPR-L solution was about 1 400 μg/mL, with the encapsulation efficiency of (95.8±1.2)% and drug loading rate of (8.3±0.4)%. (2) The viability of cells in the 12 ultrasound groups was higher than 93.0%, and the viability of cells in 1, 10, 20, and 50 μg/mL blank lipid microbubble groups was higher than 95.0%. The viability of cells in 1 μg/mL 4HPR-L group at administration hour 24 was similar to that at 48 (t=0.393, P>0.05). The viability of cells in 10, 20, 50, and 100 μg/mL 4HPR-L groups at administration hour 24 was significantly higher than that at administration hour 48 (t=44.593, 22.961, 32.224, 35.337, P<0.01). The viability of cells in 4HPR group, 4HPR-L group, and 4HPR-LM+ ultrasound group was (47.3±0.7)%, (42.3±1.7)%, and (38.6±0.8)%, respectively. The viability of cells in 4HPR group was significantly higher than that in 4HPR-L group and 4HPR-LM+ ultrasound group (t=4.551, 15.895, P<0.05 or P<0.01). The viability of cells in 4HPR-L group was significantly higher than that in 4HPR-LM+ ultrasound group (t=-3.360, P<0.05). (3) The percentages of total apoptotic cells in 4HPR group, 4HPR-L group, and 4HPR-LM+ ultrasound group were (32.8±2.4)%, (42.5±2.4)%, and (58.5±6.3)%, respectively, which were significantly higher than the percentage of control group [(14.9±1.6)%, t=8.748, 13.637, 9.500, P<0.01]. The percentages of total apoptotic cells in 4HPR-L group and 4HPR-LM+ ultrasound group were significantly higher than the percentage in 4HPR group (t=4.049, 5.393, P<0.05 or P<0.01), and the percentage of total apoptotic cells in 4HPR-LM+ ultrasound group was significantly higher than that in 4HPR-L group (t=3.371, P<0.01). (4) The percentage of G2/M phase cells in 4HPR group was higher than that in control group, but there was no statistically significant difference (t=2.107, P>0.05). The percentage of G2/M phase cells in 4HPR-L group was significantly higher than that in 4HPR group or control group (t=18.169, 30.026, P<0.01). The percentage of G2/M phase cells in 4HPR-LM+ ultrasound group was significantly higher than that in 4HPR-L group, 4HPR group, and control group (t=4.932, 25.854, 66.231, P<0.01). Conclusions: 4HPR can inhibit proliferation, induce apoptosis, and arrest G2/M phase of human keloid Fbs, and the effects of 4HPR-LM combined with ultrasound are better than those of 4HPR-L and free 4HPR.

Antiviral activity of N-(4-hydroxyphenyl) retinamide (4-HPR) against Zika virus

The rapid spread of Zika virus (ZIKV) in recent years has highlighted the severe diseases associated with ZIKV infection, such as Guillain-Barré syndrome in adults and microcephaly in newborns; yet no vaccines or antivirals currently exist to prevent or treat ZIKV infection. We and others have previously identified N-(4-hydroxyphenyl) retinamide (fenretinide or 4-HPR) as an antiviral compound that inhibits dengue virus 2 (DV2) and other flaviviruses by limiting the steady-state accumulation of viral RNA. Here we show that 4-HPR potently inhibits ZIKV in mammalian cell culture and significantly reduces both serum viremia and brain viral burden in a murine model of ZIKV infection. Consistent with previous observations with dengue virus, this antiviral activity is associated with a significant reduction in the steady-state abundance of viral genomic RNA. We show this reduction is due to a major decrease in the rate of viral RNA synthesis, though not via direct inhibition of the activity of the viral replicase. These results establish 4-HPR's mode of action against DV and ZIKV and, taken with previous clinical trials that established 4-HPR's safety and tolerability, illustrate the potential utility of 4-HPR as an agent for treatment of ZIKV infection.