Further evaluation of quantum chemical methods for the prediction of non-specific binding of positron emission tomography tracers

The non-specific binding of candidate positron emission tomography (PET) radiotracers causes resulting PET images to have poor contrast and is a key determinant for the success or failure of imaging drugs. Non-specific binding is thought to arise when radiotracers bind to cell membranes and moieties other than their intended target. Our previous preliminary work has proposed the use of the drug-lipid interaction energy descriptor to predict the level of non-specific binding in vivo using a limited set of ten well known PET radiotracers with kinetic modelling data taken from the literature. This work validates and extends the use of the drug-lipid interaction energy descriptor using a new set of twenty-two candidate PET radiotracers with non-specific binding data recently collected at the same imaging centre with consistent methodology. As with the previous set of radiotracers, a significant correlation is found between the quantum chemical drug-lipid interaction energy and in vivo non-specific binding experimental values. In an effort to speed up the calculation process, several semi-empirical quantum chemical methods were assessed for their ability to reproduce the ab initio results. However no single semi-empirical method was found to consistently reproduce the level of correlation achieved with ab initio quantum chemical methods.