Macromolecular Diamidobenzimidazole Conjugates Can Activate Stimulator of Interferon Genes

A promising class of stimulator of interferon genes (STING)
agonists
is the non-nucleotide, small molecule, dimeric amidobenzimidazoles
(diABZI), which have recently been incorporated into polymer- and
antibody-drug conjugates to improve pharmacokinetics and modulate
biodistribution for disease-specific applications. These approaches
have leveraged diABZI variants functionalized at the 7-position of
the benzimidazole for conjugation and tunable drug release from carriers.
However, since this position does not interact with STING and is exposed
from the binding pocket when bound in an “open lid”
configuration, we sought to evaluate the activity of macromolecular
diABZI conjugates that lack stimuli-responsive release and are instead
conjugated to polymers via a stable amide linker. By synthesizing
stable mPEG-diABZI conjugates and N,N-dimethylacrylamide (DMA) homopolymers from a diABZI-functionalized
reversible addition–fragmentation chain-transfer (RAFT) agent,
we found that these conjugates could activate STING in vitro with similar kinetics to highly potent diABZI analogues. Our data
indicate that although diABZI-DMA conjugates enter cells via endocytosis,
they can still colocalize with the ER, suggesting that intracellular
trafficking processes can promote the delivery of endocytosed macromolecular
diABZI compounds to STING. Furthermore, we demonstrated the in vivo activity of these macromolecular diABZI platforms,
which inhibited tumor growth to a similar extent as small molecule
variants. In conclusion, we have described new chemical strategies
for the synthesis of stable macromolecular diABZI conjugates with
unexpected immunostimulatory activityfindings that have potential
implications for the design of polymer-diABZI conjugates and further
motivate investigation of endosomal and intracellular trafficking
as an alternative route for STING activation.