The present studies were undertaken to determine whether the multikinase inhibitors
sorafenib/
regorafenib cooperated with clinically relevant ,
phosphatidyl inositol 3
kinase (PI3K)-thymoma viral proto-oncogene (AKT) inhibitors to kill
tumor cells. In liver, colorectal, lung, breast, kidney, and
brain cancer cells, at clinically achievable doses,
sorafenib/
regorafenib and the PI3K inhibitor
acetic acid (1S,4E,10R,11R,13S,14R)-[4-diallylaminomethylene-6-hydroxy-1-methoxymethyl-10,13-dimethyl-3,7,17-trioxo-1,3,4,7,10,11,12,13,14,15,16,17-dodecahydro-2-oxa-cyclopenta[a]phenanthren-11-yl
ester (PX-866) cooperated in a greater than additive fashion to kill
tumor cells. Cells lacking
phosphatase and
tensin homolog were as sensitive to the
drug combination as cells expressing the
protein. Similar data were obtained using the AKT inhibitors
perifosine and 8-[4-(1-aminocyclobutyl)phenyl]-9-phenyl-1,2,4-triazolo[3,4-f] [1,6]naphthyridin-3(2H)-one hydrochloride (
MK2206).
PX-866 treatment abolished AKT/
glycogen synthase kinase 3 (GSK3) phosphorylation, and cell killing correlated with reduced activity of AKT and
mammalian target of rapamycin (mTOR). Expression of activated AKT and to a lesser extent activated mTOR reduced
drug combination lethality. Expression of
B-cell lymphoma-extra large or dominant negative
caspase 9, but not cellular FLICE (FADD-like IL-1b-converting enzyme)-inhibitory
protein short, protected cells from the
drug combination. Treatment of cells with
PX-866 increased
protein levels of p62,
lysosome-associated membrane protein 2 (LAMP2), and
microtubule-associated protein light chain (LC) 3 and LC3II that correlated with a large increase in LC3-green fluorescent
protein (GFP) vesicle numbers. Exposure of
PX-866 treated cells to
sorafenib reduced p62 and LAMP2 levels, decreased the ratio of LC3 to LC3II, and reduced LC3-GFP vesicle levels. Knockdown of
Beclin1 or autophagy-related 5 suppressed
drug toxicity by ∼40%. In vivo,
sorafenib and
PX-866 or
regorafenib and
MK2206 cooperated to suppress the growth of established HuH7 and HCT116
tumors, respectively. Collectively our data demonstrate that the combination of
sorafenib family
kinase inhibitors with inhibitors of the PI3K/AKT pathway kills
tumor cells in vitro and in vivo.