Abstract:
A collection of 9050 natural products, their derivatives, and mimetics, was virtually screened against the human
Atg3-Atg8 (Atg - autophagy) binding scaffold. By blocking this interaction, the lipidation of Atg8 does not occur
and the formation of autophagosomes is inhibited. Forty-three (43) potential ligands were tested using enhanced
Green Fluorescent Protein (eGFP) tagged LC3, the human ortholog of Atg8, in MCF7 breast cancer cells. Three
hits showed single digit μM IC50 values with AT110, an isoflavone derivative, being the best at 1.2 ± 0.6 μM.
Molecular modelling against Atg8 in conjunction with structural activity relationship (SAR) strongly supports the
binding to this target. Testing in a panel of cancer cell lines showed little cytotoxic effect as compared to
chloroquine. However, same concentration of AT110 was shown to be toxic to young zebrafish embryos. This can
be explained in terms of the autophagy process being very active in the zebrafish embryos rendering them
susceptible to AT110 whereas in the cancer cells tested the autophagy is not usually active. Nevertheless, AT110
blocks autophagy flux in the zebrafish confirming that the ligand is modulating autophagy. A small molecule
non-cytotoxic autophagy inhibitor would open the door for adjunct therapies to bolster many established anticancer
drugs, reducing their efficacious concentration thus limiting undesirable site effects. In addition, since
many cancer types rely on the autophagy mechanism to survive a therapeutic regime, recurrence can potentially
be reduced. The discovery of AT110 is an important step in establishing such an adjunct therapy.
