Improved means to assess the clinical potential of drug candidates can critically influence development of new therapeutic entities, a central aim in medical life science. Drug discovery and development relies on construction and selection of small organic compounds or biological agents that bind targets of interest. This thesis includes new methodology to investigate target engagement - that is the tendency for these drugs and drug candidates to bind their intended target molecules versus any off-targets. This is a matter of great importance and current strong interest in the pharmaceutical industry as well as academically and an important aim for precision medicine. Paper I describes the target engagement-mediated amplification (TEMA) technique, an accurate, selective and physiological relevant techniques to monitor target binding by DNA-conjugated low molecular weight drug molecules. The DNA conjugated forms of the drugs are uniquely suited to accurately and sensitively reveal the binding characteristics of drugs directly in relevant tissues. Paper II describes the evaluation of cellular thermal shift assays (CETSA) by multiplex proximity extension assays (PEA), to sensitively measure binding of drugs to their proper targets and off-targets in minimal samples of cells and tissues, and for many targets and samples in parallel. The technique provides valuable advantages during drug development, and potentially also in clinical care. Paper III describes a high-throughput approach to use in situ proximity ligation assays to investigate protein interactions or modifications along with phenotypic responses to drugs or cytokines. The technique allows responses by large numbers of cells to be evaluated by automated microscopy and computer-based analysis. Our approach expands the scope for combined molecular and morphological profiling, offering an information-rich means to profile cellular responses to drugs and other agents at the single cell level.