While the work in my laboratory has focused on anumber of topics, I am the PI of one of
the three projects on Xavier’s RCMI grant. Thisproject involves the design and testing of
PROTAC molecules to treat non-small cell lungcancer via the degradation of oncogenic forms of
anaplastic lymphoma kinase.
Anaplastic lymphoma kinase(ALK) is a receptor tyrosine kinase that was first
identified in a chromosomaltranslocation associated with anaplastic large cell lymphoma,
a subtype of T-cellnon-Hodgkin’s lymphoma. This chromosomal translocation generates
a truncated form of the ALKprotein containing the tyrosine kinase domain fused to a
dimerization motif,generating a cytoplasmic, constitutively active form of ALK that serves
as a potent oncogenicdriver. Since this initial discovery, similar ALK fusion proteins have
also been found in diffuselarge B-cell lymphoma, inflammatory myofibroblastic tumor,
breast cancer, colorectalcancer, esophageal squamous cell cancer, renal cell cancer, and
non-small-cell lung cancer(NSCLC). ALK inhibitors have been developed for the
treatment of patients withadvanced ALK -rearranged (i.e., ALK-positive) NSCLC, but
mean time to relapse is 11months, due to mutations in the inhibitor binding site of ALK.
Second- and third-generationinhibitors have been approved, but each suffer from
suppressor mutations overtime. Rather than continue to develop mutation-resistant
inhibitors, we are insteadtargeting ALK for degradation via PROTACs.
Proteolysis-targetingchimeras (PROTACs) are small, bifunctional molecules that
contain a warhead domainspecific to the targeted protein of interest coupled by a short
linker to an E3 ubiquitinligase binding domain. These small molecules promote
ubiquitination andsubsequent proteosomal degradation of the target protein. Since their
initial description in 2001,development of PROTACs targeting over 60 separate proteins
have been published. Usingthis technique to degrade pathological proteins has the
added benefit that PROTACscan often be used at concentrations significantly lower than
standard inhibitors, asthere is no need for PROTACs to be present at stoichiometric
concentrations. Once aPROTAC induces ubiquitination of the target protein, the protein
is degraded and the PROTACis free to bind another protein and repeat the cycle. Finally,
because PROTACs do not haveto bind the active site of their target, this proteolytic
alternative tostoichiometric inhibition has greater flexibility in the design of the warhead
targeting motif.
We have designed andsynthesized small molecule PROTACs to efficiently induce
degradation of ALK fusionproteins and have investigated their therapeutic potential in
ALK-positive NSCLC models in vitro and in vivo. Ourpreliminary data strongly suggest
that targeting ALKdegradation is a novel and potentially effective therapeutic approach
for the treatment of NSCLCrelapsed from ALK inhibitors. Importantly, our PROTACs
induce the degradation ofboth “wild type” dimerized ALK, as well as ALK with suppressor
mutations that conferresistance to FDA-approved inhibitors. We are now in the process
of optimizing our PROTACsfor greater potency (they are already effective at single
nanomolar concentrations)and selectivity. Our ongoing work is directed at bringing these
PROTACs intotranslational work to determine therapeutic usefulness.
