Comprehensive assessment of cellular drug delivery and efficacy via noninvasive functional and time-resolved molecular optical imaging

Abstract

During drug development, preclinical in vivo validation of a viable drug candidate is a necessary unavoidable step before successful Food and Drug Administration’s (FDA) approval process for clinical trial. Conventional preclinical in vivo studies are performed using immunocompromised mouse models – including cell-line-based and patient-derived xenograft (PDX) models. Further, the validation of a drug’s delivery efficacy is performed ex vivo – that is, via animal sacrifice, tissue extraction and subsequent biomolecular assays. This method is time/financially consuming, does not permit longitudinal study, requires many animal subjects, and does not accurately reflect in vivo physiology. For any viable preclinical imaging platform, especially ones associated with the assessment of drug delivery and efficacy, it is crucial to be able to image the whole body of small animal models. Hence, any proposed imaging approach should be able to image a large field of view with high sensitivity. In addition, biological investigations are greatly enhanced by the ability to image multiple biomarkers simultaneously. This can be done by multiplexing the fluorescence probes spectrally and via lifetime sensing. However, increasing the dimensionality of the acquired data leads to significantly increased complexity in the imaging apparatus, data quantification and experimental protocols. Förster Resonance Energy Transfer (FRET) imaging can sense protein-protein interaction events at the distance of 2-10nm, which is the range in which binding of antibodies/protein ligands to their respective receptors often occur. Indeed, we have demonstrated the capability of Macroscopic Fluorescence Lifetime Imaging (MFLI)-FRET for noninvasive, whole-body quantitative monitoring of receptor-ligand binding (e.g. Transferrin-Transferrin Receptor, [Tf-TfR]) both in tumor xenografts and for monitoring pharmacokinetic activity in mice. The capability to monitor drug efficacy noninvasively over an entire live intact animal model would offer many significant improvements to the current paradigm: true longitudinal studies, decrease of the number of animal models needed (minimizing intra-animal variances), intact physiological context and, if imaging can be performed fast enough, pharmacokinetic monitoring post-injection. Most importantly, a technique capable of whole-body imaging as described above should result in higher success rates upon reaching human trials, given the significantly richer information that can be collected and used to decide whether to proceed with a candidate. The objective of the project presented herein is to further develop a cost-effective, noninvasive, and user-friendly whole-body optical imaging workflow capable of meeting these needs. Hence, the results of this project will act as a giant leap forward with regards to propelling optical molecular imaging into conventional preclinical research and development.