Optimization of a potent and cell active CK2 chemical probe for Alzheimer's disease therapy

Project Summary/Abstract
Alzheimer’s disease (AD), the most common cause of progressive dementia in adults over the age of 65, is a
devastating disorder without effective treatment options. Available drugs treat late-stage symptoms rather than
addressing disease-causing pathways. There is an urgent need for new protein targets that potentially act via
previously unexplored mechanisms to halt AD progression. Human protein kinases represent a highly tractable
class of targets that have largely been examined with respect to oncology, but which hold great promise in areas
such as neurodegeneration. Protein kinase casein kinase 2 (CK2) is highly expressed in the mammalian brain
and has many validated substrates that are critical in neural cell homeostasis and signaling processes across
synapses. These roles have indicated that CK2 is a key regulator of neuronal function and that it may represent
a novel target to treat neurodegenerative diseases like AD. Through extensive evaluation of our first library of
pyrazolopyrimidines, we identified SGC-CK2-1 as a potent, selective, and cell-active CK2 chemical probe.
Remarkably, despite years of research pointing to CK2 as a key driver in cancer, SGC-CK2-1 did not elicit a
significant antiproliferative phenotype when tested in nearly 180 cancer cell lines. SGC-CK2-1 also does not
demonstrate toxicity in human stem cell-derived neurons/microglia at doses required for CK2 inhibition. Guided
by crystal structures and published data, we have developed a medicinal chemistry plan to address the metabolic
liabilities of SGC-CK2-1 and develop it into a probe that is suitable for in vivo use. Part of this strategy involves
also adding functionalities into our CK2 inhibitors that improve their blood–brain penetrance. Calculations and
predictive software models will aid medicinal chemistry efforts and help prioritize compounds to be made. Many
of these simulations will be corroborated with experimental data, including kinetic solubility, lipophilicity,
microsomal stability, and CNS pharmacokinetic data, which will increase our confidence in their utility. Optimized
CK2 inhibitors will be profiled in stem cell-based assays that model key pathogenic signaling pathways in AD
related to neuroinflammation, a process we have shown to be at least partially regulated by CK2. Our lead CK2
chemical probe candidates will be dosed in a 3xTg mouse model of AD to validate CK2 target engagement in
vivo. All publications that have attempted to characterize CK2 function using a CK2 inhibitor have used a sub-
optimal compound, most often CX-4945 or TBB, that suffers from potent inhibition of off-target kinases and other
liabilities, including broad antiproliferative activity, that preclude its use in AD. Despite these issues, CX-4945
has been dosed systemically in humans for oncology indications, which confirms that clinical inhibition of CK2 is
tolerated. Development of a potent and selective in vivo probe targeting CK2 that lacks broad antiproliferative
activity will enable confirmation of its putative role in AD for the first time.

Grant Number: 5R56AG084730-02
NIH Institute/Center: NIH
Principal Investigator: Alison Axtman