(T1230-03-15) Colon Targeted Ibrutinib Amorphous Solid Dispersions for the Treatment of Colorectal Cancer

Purpose: Colorectal cancer has been reported to be the second leading cause of cancer-related deaths in the United States. A difficult cancer to treat, several targeted drug delivery systems have surfaced lately. However, the oral route of delivery is the choice of formulation for both patient and manufacturers because of two main reasons: ease of administration and tablets are extremely lucrative/inexpensive to manufacture. Majority of the first-line agents which high cytotoxicity and affinity to tumors in the colorectal region are either poorly water soluble or poorly permeable. Hence, enhancing the inherent solubility and delivering the entire payload of the drug to the target site for action has been a challenging task for researchers in the past few years. Apart from this, limited extrudable polymers are available for developing colon specific drug delivery systems. Ibrutinib (IBR), a Bruton’s tyrosine kinase inhibitor is novel drug molecule with potential application in cancer treatment, but it suffers from extremely poor solubility and off-target side effects. The objective of this study was to investigate anticancer activity of IBR in colon cancer cell lines and develop a controlled release amorphous solid dispersion by hot melt extrusion using a colon selective releasing polymer and P-gp inhibiting surfactant. This is a very first study demonstrating application of ibrutinib in colon cancer and colon targeted delivery system using hot melt extrusion.

Methods: In vitro cytotoxicity of IBR was analyzed in human colon cancer cell line - HT20 and HT116 using MTT assay. Effect of TPGS on anticancer activity of IBR was also evaluated. pH solubility profile for IBR was generated in gastrointestinal relevant medias (pH 1.2-7.5). For polymer/carrier selection, several pH-dependent and sustained release polymers were screened. Melt rheology was carried out to optimize the HME processing temperature. IBR-loaded filaments (10%w/w) were extruded using HME and mechanical characterization (three-point bend test) using TA.XTplus Texture Analyzer. To modulate the rate of release of IBR from the polymeric matrix, water soluble polymer/surfactant with P-gp inhibitory effects were added. Saturation solubility studies of IBR-loaded filaments was performed at different GI pH. In vitro cytotoxicity and solid-state characterization of the of the optimized batch was performed. In vitro dissolution studies were performed in two different pH 6.5 (intestinal pH) and pH 7.5 (colonic pH) phosphate buffer solution for 8 and 12 hrs, respectively. A colon selectivity index (ratio of drug release at intestinal pH vs colon pH). Sink and non-sink in vitro dissolution studies were performed for all these batches in pH 7.5.  A graphical representation of the study has been shown in Fig. 1.

Results: In vitro cytotoxicity assay suggested that IBR has a IC₅₀ of 14.4 µM and 18.2 µM in HT29 and HT116, respectively. It clearly justifies the need of local high concentration over systemic delivery. Preformulation studies suggested that IBR had a pH dependent solubility with negligible solubility at colonic pH. A sharp crystalline melting endotherm peak for neat IBR was observed at 152.2 °>C with a T_d at 347.26°C and distinct crystalline halos corresponding to IBR were also observed (Fig. 2(a)). From the preliminary studies, IBR with methyl acrylate-methyl methacrylate-methacrylic acid terpolymer (MAMM) was selected for colon specific release. Based on the melt viscosity and solid-state characterization results, a processing temperature of 150°C was optimized. As seen in Fig. 2(b), Clear glassy filaments were obtained with the extrusion of MAMM and TPGS whereas, hazy and partially amorphized filaments were obtained with poly-2-ethyl-tetra-oxazoline (P50) and poloxamer 407 (P407). Absence of a characteristic endothermic event in the filament suggested/confirmed the amorphization of IBR. Saturation solubility studies of the filaments suggested that there was a 55x fold increase in IBR solubility at colonic pH. Based on saturation solubility studies, ASD with TPGS were selected for further studies. Dissolution studies performed in non-sink conditions (pH 6.5) suggested that < 5% of drug was released followed by a sharp increase in release as the pH increased >7.0. Colon selectivity index of optimized batch was observed to be 19. From Fig. 3(a) and (b) it can be observed that 96.7 ± 5.3% and 86.6 ± 6.8% of drug was released at colonic pH (7.5) in sink (1%w/w Kolliphor HS 15) and non-sink conditions, respectively.

Conclusion: Novel non-invasive drug delivery systems delivering a significant drug payload at tumor site the need of the hour. This study successfully demonstrates the development of IBR-loaded amorphous solid dispersion with a pH-dependent polymer for the treatment of colorectal cancer.

Fig 1. Graphical Representation for development and application of FS-T-IBR tablets for colon cancer therapy.



Fig. 2. (a) Solid state characterization of IBR-ASD by Differential scanning calorimetry (DSC). A distinct sharp melting endothermic peak corresponding to IBR were observed to be absent from the formulation with MAMM and TPGS endotherms, suggesting that IBR is present in an amorphous/molecularly dispersed phase. (b) Filaments obtained after melt extrusion. It can be seen that clear glassy filaments were obtained with MAMM and TPGS, whereas opaque/hazy filaments were obtained with P50 and P407, thus confirming the solid state of IBR in the filaments.



Fig. 3. In vitro drug release studies in phosphate buffer solutions (pH 7.5) with non-sink (a) and sink conditions (b), respectively. It can be observed that in presence of TPGS, there was a sharp increase in the rate of release under non-sink conditions as compared to other batches. A similar trend can be seen in sink conditions also.