(W1230-09-50) Preparation and Characterization of an Ultraflexible Liposomal Gel for Transdermal Delivery of a Novel Pan-RAS Inhibitor for Melanoma

Purpose: Ultraflexible liposomal gels (UFLs) offer a promising approach to delivering lipophilic compounds topically [1]. This study focuses on the preparation and characterization of UFLs designed to improve the delivery of a novel pan-RAS inhibitor, ADT-007, to treat early-stage melanoma. ADT-007 has been reported to potently and selectively inhibit the growth of cancer cells with mutant or activated RAS by binding RAS in a nucleotide-free state, blocking GTP loading, and disrupting RAF and PI3K binding, thereby suppressing MAPK and AKT signaling [2]. ADT-007 has previously been shown to be efficacious against human melanoma cells [3].

Methods: Formulations were prepared using soy phosphatidyl choline (SPC) and sodium cholate, which allows for enhanced flexibility of the liposome membrane [4]. The thin film hydration method was employed, where SPC and sodium cholate, along with lipophilic drug (i.e., sulindac derivative) were dissolved in a mixture of chloroform and methanol to form a thin lipid film upon solvent evaporation. This film was then hydrated with phosphate buffer saline (PBS). The hydrated liposomal suspensions were passed through polycarbonate membranes with 200 nm and 100 nm pore sizes to achieve the desired liposomal size and ensure uniformity. Alternatively, traditional liposomes (TLs) with the compound were prepared without sodium cholate, to study the difference between liposomes with and without sodium cholate. Dynamic light scattering (DLS) was used to determine the size distribution of the liposomes, while the surface charge of the liposomes was measured using a zeta potential analyzer. The amount of lipophilic compound encapsulated within the liposomes was quantified using UV-visible spectrophotometry at the wavelength of 434 nm. In vitro drug release studies were conducted using a dialysis method to evaluate the release profile of the compound from the liposomes over a 5 h period at 37 °C in PBS with 10% ethanol, which was used to solubilize the sulindac derivative. For the preparation of the gel, Carbopol 940 was dispersed in water and neutralized with triethanolamine. The UFL or TL liposomes were then dispersed in the gel the following day. The permeability of the lipophilic compound from the gels through Strat-M membranes was assessed at 37 °C using an in vitro Franz diffusion cell setup. Strat-M is commonly used to simulate skin in drug permeability studies [5]. The receptor medium contained PBS with 10% ethanol.

Results: DLS measurements showed that the UFLs containing the sulindac derivative had a size of 133.1 ± 2.1 nm, a polydispersity index (PDI) of 0.13 ± 0.01, and zeta potential of -15.0 ± 2.1 mV. The TL version of this formulation had a size of 252.7 ± 3.8 nm, a PDI of 0.27 ± 0.01, and a zeta potential of -2.2 ± 0.6 mV. UFLs had an encapsulation efficiency of 83.6 ± 1.2%, and TLs had an encapsulation efficiency of 78.1 ± 0.9%. In vitro release studies in PBS with 10% ethanol at 37 °C showed a 37.2% release of cargo from UFLs after 60 minutes. The UFLs released 74.1% of its cargo after 5 h. The TLs released 28.5% after 60 minutes and 62.1% after 5 h. Studies performed with the final gel formulation and Strat-M membranes at 37 °C showed enhanced permeability of ADT-007 when delivered in UFLs. UFLs allowed for sustained permeability over a 2 h period, and reached 96.0%. TLs, in contrast, allowed for a more gradual permeability and achieved 88.3%. This suggests that UFLs allow for a quicker and more enhanced permeation, compared to TLs. Previous studies conducted using lidocaine as the lipophilic cargo demonstrated similar results.

Conclusion: UFLs present a potentially superior alternative to TL in topical drug delivery. The UFLs evaluated here and in the literature [4] show that UFLs enhance permeability of lipophilic drugs through skin-like membranes, which have been shown to be comparable to human skin [3]. This enhanced permeability is due to the greater flexibility of the liposome membrane, allowed for by the addition of sodium cholate. Furthermore, both blank UFLs and TLs were previously shown to be biocompatible [4], further supporting UFLs as a versatile and effective drug delivery system. Thus, UFLs offer a promising alternative to TL for various topical therapeutic applications, and may enhance patient outcomes.

References: [1] Sun M, Osipitan OO, Sulicz EK, Di Pasqua AJ. Preparation and optimization of an ultraflexible liposomal gel for lidocaine transdermal delivery. Materials. 2022; 15(14):4895. https://doi.org/10.3390/ma15144895
[2] Foote JB, Mattox TE, Keeton AB, et al. A Novel Pan-RAS Inhibitor with a unique mechanism of action blocks tumor growth in mouse models of GI Cancer. bioRxiv (Cold Spring Harbor Laboratory). Published online May 19, 2023. doi:https://doi.org/10.1101/2023.05.17.541233
[3] Saville, K. M., Lee, K., Mattox, T. E. et al. (2017) Abstract 5166: Sensitivity of melanoma cells to a novel class of Ras inhibitors. Cancer Res. 77, 5166.
[4] Kim A, Lee EH, Choi SH, Kim CK. In vitro and in vivo transfection efficiency of a novel ultradeformable cationic liposome. Biomaterials. 2004;25(2):305-313. doi:10.1016/s0142-9612(03)00534-9
[5] Kaur L, Singh K, Paul S, Singh S, Singh S, Jain SK. A Mechanistic study to determine the structural similarities between artificial membrane Strat-M™ and biological membranes and its application to carry out skin permeation study of amphotericin B nanoformulations. AAPS PharmSciTech. 2018;19(4):1606-1624. doi:10.1208/s12249-018-0959-6

Figure 1. Structure of ADT-007, a novel pan-RAS inhibitor.

Figure 2. Release of ADT-007 from ultraflexible (UFL) and traditional (TL) liposomes in PBS with 10% ethanol, 37 °C, over a period of 5 h. Each point represents n = 3; all STDs < 1.


Figure 3. Permeability of ADT-007delivered in ultraflexible (UFL) or traditional (TL) liposomes through a Strat-M skin-like membrane, 37 °C, over a period of 5 h. Each point represents n = 3; all STDs < 1.