Polymer conjugated retinoids for controlled transdermal delivery

Abstract

All-trans retinoic acid (ATRA), a derivative of vitamin A, is a common component in cosmetics and commercial acne creams as well as being a first-line chemotherapeutic agent. Today, formulations for the topical application of ATRA rely on creams and emulsions to incorporate the highly hydrophobic ATRA drug. These strategies, when applied to the skin, deliver ATRA as a single bolus, which is immediately taken up into the skin and contributes to many of the known adverse side effects of ATRA treatment, including skin irritation and hair loss. Herein we present a new concept in topical delivery of retinoids by covalently bonding the drug through a hydrolytically degradable ester linkage to a common hydrophilic polymer, polyvinyl alcohol (PVA), creating an amphiphilic nanomaterial that is water-soluble. This PVA bound ATRA can then act as a pro-drug and accumulate within the skin to allow for the sustained controlled delivery of active ATRA. This approach was demonstrated to release active ATRA out to 10days in vitro while significantly enhancing dermal accumulation of the ATRA in explant pig skin. In vivo we demonstrate that the pro-drug formulation reduces application site inflammation compared to free ATRA and retains the drug at the application site at measurable quantities for up to six days.

Keywords: All-trans retinoic acid; Poly (vinyl alcohol); Polymer conjugate; Transdermal drug delivery.

Figure 1. Chemical synthesis of PATRA (3)

Conjugation of ATRA (2) to PVA (1) was performed using DCC chemistry in DMF:DMSO mixture for 24h at room temperature under nitrogen.

Figure 2. Cartoon schematic of the adsorption of micellar PATRA into the dermis

Release of ATRA from the PATRA conjugate occurs in the hydrated dermis.

Figure 3. Nanofiber PATRA solubility and characterization

(a) Characterization of particle size and solution appearance for different concentrations of PATRA in water. (b) TEM images of nano-fiber PATRA formed in water. In water PATRA forms thin (3-5 nm) fibers (2) that agglomerate into nanoparticles (1). (c) Digital images of solubilization of PATRA dry powder (1) at 50mg/mL (2), 25mg/mL (3), and 5mg/mL (4) concentrations. (d) Solubility of ATRA and PATRA in different solutions. Data shown is mean ± S.D., n=3.

Figure 4. Controlled release of ATRA from PATRA and changes in particle size

(a) ATRA release followed daily at 20°C and at 37°C in hydroalcoholic solution out to two weeks. (b) Average particle size after degrading in water for specified periods of time. Data shown is mean ± S.D., n=3.

Figure 5. Comparison of impact of ATRA and PATRA on cell viability

(a) Relative cell density of cell cultures treated with ATRA, PATRA, or PVA. ATRA in-well concentration was set at 10μM and PATRA concentration was set at an equivalent ATRA concentration. The concentration of PVA was determined by the PVA concentration in PATRA treated wells. (b) Brightfield imaging after four days in culture of NIH-3T3 cells that are either untreated (1) or treated with (2) PVA, (3) PATRA, (4) ATRA. Scale bar = 50 μm. Data shown is mean ± S.D., n=5.

Figure 6. Uptake and transport of ATRA in explant pig skin

(a) Histological appearance of pig dermis. (b) Uptake of fluorescently labeled PATRA after 4 and 12 hours of exposure. Uptake is seen to significantly increase over this time and accumulate within the epidermis. (c) Fraction penetration of ATRA through pig dermis followed over 12 hours. (d) Quantification of fraction of ATRA accumulated within the pig dermis over 12 hours of exposure. Data shown is mean ± S.D., n=4.

Figure 7. Reaction to ATRA application to the dermis

(a) Digital imaging of mouse dermis 0, 3, and 5 days post-application. (b) Histological sections of treated mouse dermis. Changes in epidermal and stratum corneum thickness are clearly observed due to bolus administration of ATRA. These changes are not observed in other treatment groups. (c-d) Quantification of histological findings for the treatment groups after five days. Data shown are mean ± S.D., n = 4.

Figure 8. Retention of PATRA in the skin of mice

(a) IVIS imaging of fluorescently labeled PATRA over 7 days. Unconjugated dye is seen to disappear after only two days while PATRA conjugated dye stays for up to 5 days. Material was added at two locations on the midline of the backs of mice. (b) Quantification of total radiant efficiency for each application site for PATRA and dye treated mice. (c) Half-life and t₉₅ measured from first-order exponential fits of fluorescent data. Data shown is mean ± S.D., n=6.