(T1430-02-10) Modified Dissolution-Permeation Assembly Mimicking In Vivo Condition: An Ideal Method to Test Dissolution Profile of Nanosuspension Formulation

Purpose: The successful absorption of orally administered drugs relies on two key factors: dissolution within the GI fluids and permeation across intestinal epithelium. Traditional USP dissolution apparatuses are designed to measure drug dissolution rates, but they do not directly predict how fast or slow drug will appear in the bloodstream. Additionally, the static nature of these tests does not replicate dynamic conditions of GI tract, where continuous movement and varying fluid volume affect drug dissolution and absorption. Maintaining sink condition using a surfactant solution is not a true representative of process of in vivo absorption and permeation. Most importantly, existing USP methods lack the ability to accurately predict dissolution-absorption relationship for nanoparticulate drug delivery systems, such as nanosuspensions. Nanosuspensions are promising advancements that can enhance the saturation solubility and bioavailability of poorly water-soluble drugs. However, the limitations of USP methods make it challenging to predict how these novel formulations will perform within the body. In light of these limitations, developing a physiological relevant in vitro customized dissolution study is crucial. This approach appears more physiologically relevant since any dissolved drug in vivo is continuously absorbed into the body ("sink"). The objective was to develop an integrated dissolution/permeability system to predict dissolution–permeation relationships to overall drug absorption for pure drug, nanosuspension (STR-NS) and freeze dried (STR-FZ) formulations of sotorasib.

Methods: Sotorasib nanosuspension with docusate sodium and Plasdon S630 as stabilizers was developed by nano-milling in our previous study. A novel modified dissolution assembly containing drug transfer elements withing dissolution jar was set up, mimicking the in vivo process (Fig. 1). This system allows for continuous drug permeation through a dialysis membrane (MWCO: 50 kD), and two peristaltic pumps continuously circulated the simulated plasma component (pH 7.4 phosphate buffer with 0.5% w/v SLS) in and out of the dialysis bag, mimicking blood circulation. The dialysis bag was immersed in a dissolution medium at pH 6.8 with 0.2 % w/v bile salt to represent the GI environment. The dissolution study was conducted at 50 rpm and 37 ± 0.5 °C. Prior to investigating sotorasib formulations, in-vitro model underwent initial optimization using immediate release crystal violet (1% w/v). This well-characterized model compound allowed for system validation and confirmation of its functionality in mimicking both dissolution and permeation processes. Samples were withdrawn from both dissolution medium (representing the simulated intestinal condition) and simulated blood fluid (representing the blood) at predetermined time points using a syringe. Samples were analyzed using HPLC method, and dissolution profile and simulated blood concentration vs. time were plotted. The apparent permeability coefficient (P_app) of STR was calculated using the following equation:
P_app = ( dQ/dt )* 1/ (A * C₀)
Where dQ/dt is the flux (mg/s), A is the area of dialysis bag (cm²) and C₀ is the initial concentration of STR in dissolution medium.

Results: A negative flow permeability chamber was incorporated withing dissolution jar enabling quick transfer of dissolved drug into circulating fluid. Immidtate release and absorption model (suitable for BCS class I molecules) was validated using crystal violet. The dissolution profile (Fig. 2) shows a significant improvement in dissolution rate for STR-NS and STR-FZ compared to pure drug. Both formulations achieved about 35-40% release within 4 h in intestinal medium (pH 6.8 with 0.2% w/v bile salt). In contrast, pure drug showed negligible release, highlighting the limited solubility of sotorasib in the GI environment. The permeation behavior (Fig. 3a) indicated a significant difference in mimicked plasma concentrations achieved by the different formulations. After 4 h of intestinal transit time, pure drug had a mimicked plasma concentration of 0.675 ± 0.02 µg/mL. In comparison, nanosuspension achieved a concentration of 14.978 ± 1.089 µg/mL and freeze-dried nanosuspension reached 13.931 ± 1.639 µg/mL. The apparent permeability coefficients (Papp) for different formulations are summarized in Fig. 3b. Addition of surfactant into dissolution media failed to discriminate into the dissolution rate of pure drug vs nanosuspension. This enhanced dissolution translates to a higher concentration of drug available for permeation across the intestinal barrier, as evidenced by increased blood plasma concentrations and Papp values for nano formulations.

Conclusion: The developed in vitro dissolution assembly successfully simulated drug dissolution and absorption processes in the GI tract, providing a valuable tool for evaluating the bioavailability of poorly soluble drugs. The substantial increase in plasma concentration and Papp values for the nanosuspension and freeze-dried formulations highlights their potential to enhance therapeutic efficacy. This approach offers a promising tool for the development and evaluation of novel oral drug delivery systems, particularly for poorly water-soluble drugs.

Fig 1: Schematic representation of the in-vitro dissolution and permeability model.

Fig. 2: Dissolution profiles of pure drug, nanosuspension, and freeze-dried formulation in pH 6.8 phosphate buffer with 0.2% w/v bile salt.

Fig. 3: (a) Simulated Blood Concentration-Time Profiles; and (b) Apparent Permeability Coefficients (Papp) of Pure Drug, Nanosuspension, and Freeze-Dried Formulation.