(T1230-12-83) In Vivo Studies of Letrozole Non-aqueous Nano Emulgel Transdermal Delivery Systems

Purpose: The current study aimed to examine the in vivo behavior of a new transdermal drug delivery system (TDDS) of letrozole (LZ) loaded non-aqueous nanoemulgel (LZNGEL) used in cancer therapy.

Methods: The general preparation method of LZNGEL is as follows: The emulsifying agent Sepineo 600 (SP) was mixed with glyceryl monooleate (GMO) in a 1:1 ratio in a heating water bath at 70° C until a clear mixture was obtained (MIX 01). LZ was dissolved in transcutol (TC) in a heating water bath at 70° C until a clear solution was obtained (MIX 02). MIX 02 was added gradually to MIX 01 to form a mixture (MIX 03). Propylene glycol (PG) was progressively added to MIX 03 to form the final gel. In formulations containing penetration enhancers (ex. Captex (CX)), the amount required was added to MIX 02, which was then mixed into MIX 01 to form MIX 03. The following represents the percentage in w/w of the prepared and in vivo tested LZNGEL presented in this abstract: 1.5 LZ, 32 GMO/SP, 35 TC, 5.5 CX, and 26 PG. The LZNGEL (1.5% LZ w/w) prepared was a clear, viscous gel with a particle size of less than 500 nm. Complete physicochemical characterizations and in vitro testing of the prepared gels were reported earlier. In vivo studies were carried out using rats (200 – 250 g) in a parallel study design; each group was assigned 12 rats. The bioavailability of LZNGEL / TDDS was compared to the oral solution of LZ in alcohol. Twelve doses (1mg/ml solution for the 200 g weighing rats and 1.25 / 1.25 ml solution for 250 g weighing rats per day) were given orally early in the morning for 12 days. The LZNGEL / TDDS was given as 800 mg (containing 12 mg of LZ) gel incorporated into an Aluminum cavity having a surface area of approximately 3.5 cm² and fixed by surgical adhesive tape on a shaved dorsal skin of the rat. The TDDS was removed after 14 days of application. Blood samples were taken daily for 14 days on timing, as shown in Figure 1. HPLC system used for the blood analysis was equipped with an isocratic pump LC-10AD, autosampler SIL-20A, fluorescence detector RF-20A, and controller SCL-10A, managed by CLASS VP 6.14 software. The column used was HiQ sil C₁₈HS 150mm x 4.6mm, 5µm particles and mobile phase composed of Acetonitrile: Buffer KH₂PO₄ 10mM 40:60 respectively, and delivered at a flow rate of 1.2ml/min. The fluorescence detector used was monitored at EX230nm and EM 295nm, and the injection volume was 25µl. Sample preparation was carried out by mixing 80 µl plasma with 40 µl (Internal standard) in an Eppendorf tube. 1 ml of ethyl acetate was added, and the sample was shaken vigorously for 1 minute. The sample was then centrifuged at 12000 rpm for 5 minutes, and the ethyl acetate layer was aspirated into a glass tube 12X75 mm and then evaporated to dryness and reconstituted with 250 µl of the mobile phase. A 25 µl was then injected into the HPLC. The method was validated following ICH guidelines. The LOQ was determined as 1ng/ml of LZ spiked plasma sample, and the LOQ was estimated to be 0.33 ng/ml.

Results: The pharmacokinetic parameters (PK) of LZ for oral solution and LZNGEL / TDDS were evaluated by determining the C_max (µg/ml), AUC_0-t (µg/ml.hr), AUC _0-¥ (µg/ml.hr), and T_max (hr). The PK parameters were presented as mean (CV%) for the three parameters, while the last one was presented as median (min-max). The oral solution showed C_max as 0.60 (17.4%), AUC_0-t as 1.13 (32.0%), AUC_0-¥ as 1.17 (39.3%), and T_max as 174 (54.0 - 246.0). The LZNGEL / TDDS showed C_max as 0.54 (46.1%), AUC_0-t as 0.65 (32.5%), AUC _0-¥ as 0.66 (31.6%), and T_max as 27.0 (24.0 - 216). For a 3.5 cm² application, the relative bioavailability of LZNGEL/TDDS was about 60%. This enables a high bioavailability to be achieved by expanding the LZNGEL/TDDS surface area. Consequently, two-week administration could be accomplished by optimizing the LZNGEL / TDDS surface area. Figure 1 illustrates the biphasic absorption profile that best describes the abnormal behavior of LZNGEL/TDDS. The nanoemulgel's diffusion may have contributed to the initial phase of the absorption, which lasted seven days. Following this stage, the LZ began to crystallize from the emulgel and create suspension emulgel. After one week, permeation from this suspension emulgel finally began, exhibiting a new absorption phase.

Conclusion: It was shown that the relative bioavailability of letrozole-loaded non-aqueous nanoemulgel (LZNGEL) / TDDS for 3.5 cm² application was around 60% of the letrozole oral solution. In the LZNGEL/TDDS absorption profile, there were two phases: one for the nanoemulgel and one that appeared after one week of application and was caused by the formation of suspension emulgel as a result of LZ crystallization.

Acknowledgements: This project was made possible by Project NPRP 4-496-3-157 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.

Plot of LZ plasma concentration (ng/ml) versus time (hr)