Controlled Release of Avastin® from the Tethadur™ Biodegradable Matrix C.A. Kelly, D.K. Nadarassan, H. O’Brien, C. Storey, K. Webb, Q. Shabir, A. Loni and L.T. Canham pSiMedica Ltd, Malvern Hills Science Park, Malvern, Worcestershire, WR14 3SZ, UK Email: ckelly@psivida.com Introduction Bevacizumab (Avastin®) is used to treat back of the eye diseases such as age-related macular degeneration (AMD) Currently administered intravitreally every 1-2 months1 – T1/2 4.9 days2 Tethadur™ is a silicon-based, biocompatible, tuneable mesoporous matrix Tethadur™ degrades over time into benign silicic acid, which occurs naturally within the body3 Therapeutics can be loaded into Tethadur™ through electrostatic attraction – silicon matrix has a negative charge above pH 4; Avastin® has a positive charge below its pI of 8.3 Sustained release can be obtained from the Tethadur™ matrix Activity of the released Avastin® was greater than 80 % for the first 30 time points Tethadur™ matrix erodes into silicic acid at a linear rate (Figure 1) – projected complete erosion after 127 days Dissolution rate of Avastin® from Tethadur™ was initially 2.4 % / time point (Table 1) Rate slows to 0.8 % / time point after 35 times points which is comparable to the rate of Tethadur™ erosion Model Avastin® dissolution Tethadur™erosion Whole curve T1 - 12 T34 -50 T2 – 50 Higuchi (R2) - diffusion 0.995 0.988 Hixson-Crowell (R2) - erosion 0.996 0.989 Korsmeyer-Peppas (diffusion exponent) 0.752 0.810 1.010 Rate (%/time point) 2.398 0.803 0.788 Aims To load Avastin® into Tethadur™ and analyse the release and activity by VEGF-binding To monitor the degradation of Tethadur™ into silicic acid To use dissolution models to study Avastin® release from the Tethadur™ matrix Methods Avastin® (100 µL of 25 mg/mL) was added to Tethadur™ (5 mg) and left at room temperature overnight (n=2) Vitreous-like media (900 µL) was added and the samples centrifuged at 14000 rpm for 5 minutes. Supernatant was removed and analysed by SE-HPLC to calculate the Avastin® loading Fresh vitreous-like media (1 mL) was added and the release at 37 °C monitored daily via 50 % media replacement. Protein release was measured by SE-HPLC VEGF-binding activity of released Avastin® was monitored by ELISA Tethadur™ (10 mg) erosion in vitreous-like media (2 mL) at 37 °C was monitored daily via a 50 % media replacement. Silicon content in samples was analysed by inductively coupled plasma optical emission spectroscopy (ICP-OES) Changes in physical properties of Tethadur™ during erosion were monitored using sacrificial samples (200 mg Tethadur™ in 40 mL vitreous-like media with a daily 50% media replacement) by TGA, BET and particle sizing Higuchi, Hixson-Crowell and Korsmeyer-Peppas models were used to analyse the methods of Avastin® release Table 1: Modelling analysis of the release of Avastin® from Tethadur™ Linear regression analysis of the Higuchi and Hixson-Crowell models show release by both diffusion from and erosion of the matrix Korsmeyer-Peppas model shows initial release was via both diffusion and erosion followed by erosion only after 35 time points Matrix erosion results in a 6.7 % decrease in the D50 particle size Figure 2: Effect of matrix erosion on Tethadur™ particle size (D50) Results Avastin® was successfully loaded (24.2 ± 0.3 %w/w) into the Tethadur™ matrix Controlled release of Avastin® from Tethadur™ was maintained for over 50 time points (Figure 1) with only a 12 % burst – approximate release 23 µg/day Pore volume and surface area decrease during matrix erosion by 22.9 and 6.9 %, respectively Pore size increases by 4.5 % Figure 3: Effect of matrix erosion on the physical properties of Tethadur™ Conclusion Avastin® was loaded onto Tethadur™ with a high payload – 24 %w/w Low burst and controlled release for over 50 time points Activity of released Avastin® high (>80 %) for over 30 time points Erosion of the matrix into benign silicic acid results in a decrease in particle size, surface area and pore volume coupled with an increase in pore diameter Figure 1: Dissolution of Avastin® from Tethadur™ and erosion of the matrix References Tuffail, A.; et al. BMJ 2010 340:2459 2. Moisseiev, E.; et al. Graefes Arch Clin Exp Ophthalmol. 2014 252(2):331-7 3. Nieto, A.; Hou, H; Sailor, M.J.; Freeman, W.R.; Cheng, L. Exp Eye Res 2013 116:161-8