De-risking drugs in multiplex assays before progressing to clinical trials

摘要

THE MAJORITY of small molecule therapeutics have been designed to potently act upon one specific protein target that is considered to be the root cause of a disease. Though largely accurate, the profile of any given drug across all proteins or even representatives of specific protein target classes is often lacking. The consequences of the unknown effects of drugs at the molecular protein level are then borne out in clinical trials, whereupon they fail in Phase I (safety) and Phase ll/lll (efficacy) studies where adverse events are reported. The comprehensive profiling of compounds using a wide range of in vitro multiplex spatial and temporal assays as part of the lead/candidate data package would be expected to de-risk them prior to their evaluation in the clinic.The human genome encodes -20,000 protein-coding genes, with about 10 percent of these being small molecule druggable.1 Dysregulation of a specific protein can lead to a specific disease and its normalisation is sought by targeting it with a suitable drug. In most cases, drugs lack absolute specificity and act upon the targets they were designed against as well as unrelated proteins. This can lead to unanticipated detrimental consequences in the clinic, namely poor safety profiles and lack of efficacy. As a case study to illustrate this, the BCR-ABL tyrosine kinase inhibitor Imatinib (250 nM IC50), approved as a therapy for chronic myeloid leukaemia, has been shown to be effective at relatively high doses (400-600 mg/day) yet is unfortunately associated with frequent adverse events (mainly mild or moderate in severity; serious adverse events included fluid retention, cytopenia and hepatotoxicity). The second- and third-generation and more potent BCR-ABL tyrosine kinase inhibitors, namely Dasatinib (3 nM IC50) and Bosutinib (1 nM IC50), have improved potency against the primary BCR-ABL tyrosine kinase target, but are also known to have additional liabilities in the nM potency range against other kinases including BTK, LYN and SRC. This-is unsurprising given that kinases often act in networks and pathways which can lead to drug resistance.2 Secondly, in the case of panobinostat, an approved histone deacetylase (HDAC) inhibitor, adverse clinical observations in the form of tyrosinaemia have been reported. A chemo-proteomics study revealed that panobinostat also targets phenylalanine hydroxylase leading to an increase in phenylalanine and decrease in tyrosine levels and thus the adverse clinical observation.