Abstract
Thorough preclinical target validation is essential for the success of drug discovery efforts. In this study, we combined chemical and genetic perturbants, including the development of a novel selective maternal embryonic leucine zipper kinase (MELK) inhibitor HTH-01-091, CRISPR/Cas9-mediated MELK knockout, a novel chemical-induced protein degradation strategy, RNA interference and CRISPR interference to validate MELK as a therapeutic target in basal-like breast cancers (BBC). In common culture conditions, we found that small molecule inhibition, genetic deletion, or acute depletion of MELK did not significantly affect cellular growth. This discrepancy to previous findings illuminated selectivity issues of the widely used MELK inhibitor OTSSP167, and potential off-target effects of MELK-targeting short hairpins. The different genetic and chemical tools developed here allow for the identification and validation of any causal roles MELK may play in cancer biology, which will be required to guide future MELK drug discovery efforts. Furthermore, our study provides a general framework for preclinical target validation.
Highlights
Maternal embryonic leucine zipper kinase (MELK) is a serine/threonine kinase in the adenosine monophosphate-activated protein kinase (AMPK)-related kinase family, and was first identified as a maternal gene in mouse eggs and preimplantation embryos (Heyer et al, 1997)
As there is still no tractable target identified in basal-like breast cancers (BBC), the finding encouraged a medicinal chemistry campaign to validate the therapeutic potential of MELK inhibition
The highly discrepant antiproliferative effects observed between the selective MELK inhibitor HTH-01-091 and the clinical candidate OTSSP167 led us to reexamine whether MELK is necessary for the survival of BBC
Summary
Maternal embryonic leucine zipper kinase (MELK) is a serine/threonine kinase in the adenosine monophosphate-activated protein kinase (AMPK)-related kinase family, and was first identified as a maternal gene in mouse eggs and preimplantation embryos (Heyer et al, 1997). Multiple studies have reported overexpression of MELK in various cancers, including breast (Lin et al, 2007), brain (Marie et al, 2008; Nakano et al, 2008), colorectal, lung and ovarian (Gray et al, 2005). Overexpression of MELK is observed in cancer stem cells (Ganguly et al, 2014; Hebbard et al, 2010; Liu et al, 2006), associated with undifferentiated phenotype (Rhodes et al, 2004), poor prognosis (Nakano et al, 2008; Pickard et al, 2009), and chemo and radioresistance (Choi and Ku, 2011; Kim et al, 2015; Speers et al, 2016).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
