Investigation into drug solubilisation potential of sulfonated calix[4] resorcinarenes

Increasing importance is being placed on the role of drug solubilisation in the drug development pipeline. In order for drugs to successfully pass through the pre-clinical studies required before clinical trials they often require addition of excipients or solubility modifying agents. This study highlights the use of sulfonated calix[4]resorcinarenes as drug solubilising agents. The rigid nature of these compounds form cone-like structures with hydrophobic interiors which are capable of accommodation of hydrophobic entities such as drugs. The calix[4]resorcinarenes in this work have varied length of alkyl chains attached to their lower rim. This work investigated the effect of chain length (C = 4 (SC(4)RC4), C = 7 (SC(4)RC7)) on the degree of solubilisation of two model hydrophobic drugs: propofol and griseofulvin. The data showed that the compounds were capable of solubilising both drugs up to 8 mgmL-1 (SC(4)RC7-propofol) and 3 mgmL-1 (SC(4)RC4-griseofulvin). The size measurements carried out using photon correlation spectroscopy indicated that the SC(4)RC4 was likely to form 1:1 interactions with drug molecules whilst the SC(4)RC7 formed supramolecular structures capable of increased drug loading in the case of propofol. In the case of griseofulvin it is postulated that similar structures were formed however these exceeded the limit of the filter used and may have been lost. Additionally, the supramolecular structures appeared more stable with a reduction in drug release. In vitro testing on BxPC-3 cells indicated that the calix[4]resorcinarenes were relatively non-toxic. These studies highlight the potential of these systems in drug delivery.