Ileo-colonic targeted drug delivery

Pancreatic cancer currently has a 5-year survival rate of less than 10% and there are more than 200 000 deaths worldwide from the disease (Klapman and Malfar, 2008; Parking et al,2005; Farley et al 2010), whilst colorectal cancer has similar survival rates (Venook, 2005). Recently researchers at Kingston University have developed two possible treatments for such cancers; anti-epidermal growth factor monoclonal antibodies and tyrosine kinase inhibitors (Cunningham et al 2006; Cunningham et al 2008; Ioannou et al 2011).

Antibodies are proteins and as such suffer from stability issues associated with changes in physical form and aggregation (Cleland et al., 2001; Jiskoot et al., 2000). Removal of water can improve the stability of a protein (Dráber et al., 1995). However, it is interactions with water that tend to stabilise a protein structure. Furthermore, drying a protein can change the physical structure or cause chemical degredation. Lyophilisation (freeze drying) is a low temperature drying technique which can be used to create solid formulations of proteins. However, crystallisation of the water can lead to stress of the protein, again leading to aggregation and other changes in physical form, as can changes in physical form during storage post-drying (Cleland et al., 2001). Lyoprotectants such as trehalose (Dráber et al., 1995; Liao et al., 2001), sucrose (Liao et al., 2001) and inulin (Henrichs et al., 2001) have all been show to protect native protein structure. Some combinations of lyoprotectants have also been shown to have a synergistic effect (Liao et al., 2001). There are number of mechanisms by which the protein is stabilised, all largely linked to retaining the lyoprotectant carrier in the amorphous form (Lewis et al., 2010). However when using lyoprotectants (particularly small molecules such as trehalose), crystallisation may be observed during drying that may not then be present after the drying has completed (Sundaramudsrthi and Suryanarayanan, 2010).

The stability of the amorphous form has also been investigated with small molecules as a method to improve dissolution (Janssens and Van den Mooter, 2009). Typically polymers such as polyvinylpyrolidone (PVP), polyvinylalcohol or hydroxypropylmethylcellulose have been used to stabilise the amorphous form (Serajuddin, 1999; Leuner and Dressman, 2000). These tend to inhibit crystallisation through specific interactions (Matsumoto and Zografi, 1999) or through a non-specific increase in the glass transition temperature (Tg) of the molecular mixture (Van den Mooter et al, 2001) or a combination of both (Miyazaki et al, 2004).

Polyethylene glycol has historically and successfully been used to create stealth delivery systems to treat cancer (Allen and Cullis, 2004; Duncan et al. 2005). PVP has shown promise in a similar manner; its high hydration tends to limit the interaction with the immune system (Statch et al 2008). Poly(N-(2-hydroxypropyl)methacrylamide) also displays limited immunogenicity and has been used to target tumour cells but largely when conjugated to a small molecule anti-cancer active (Duncan 2006).

It is proposed to investigate the stability of freeze-dried antibodies in ternary mixtures with lyoprotectants and high Tg polymers. Drying will be confirmed by thermal gravimetric analysis and near infrared. The physical (amorphous) stability will be assessed using differential scanning calorimetry, infrared spectroscopy (IRS; both mid and near) and x-ray powder diffraction. Spectroscopic techniques (IR and Raman) will be used to investigate the presence of interactions between the polymers and antibodies. Biological assays will be used to confirm that the antibodies remain in their native, active form and to examine whether any self-association between the polymers and antibody enhances cell penetration or minimises immune response.

Having already undertaken some proof of concept pilot studies, in this project we are looking to build upon our earlier results by formulating a number of small molecule APIs as solid dispersions with a range of polymers. In this way a library of solid dispersions will be produced and tested for solubility at different pHs and for physio-chemical stability. In the later stages of the project we will look towards a proof of concept for ileocolonic drug targeting using peptides and proteins.