Metastatic
epithelial ovarian cancer (EOC) cells can form multicellular spheroids while in
suspension and disperse directly throughout the peritoneum to seed secondary lesions. There is growing evidence that EOC spheroids are key mediators of
metastasis, and they use specific intracellular signalling pathways to control
cancer cell growth and metabolism for increased survival. Our laboratory discovered that AKT signalling is reduced during spheroid formation leading to cellular quiescence and autophagy, and these may be defining features of tumour cell dormancy. To further define the phenotype of EOC spheroids, we have initiated studies of the Liver
kinase B1 (LKB1)-5'-AMP-activated
protein kinase (AMPK) pathway as a master controller of the metabolic stress response. We demonstrate that activity of AMPK and its upstream
kinase LKB1 are increased in quiescent EOC spheroids as compared with proliferating adherent EOC cells. We also show elevated AMPK activity in spheroids isolated directly from patient
ascites. Functional studies reveal that treatment with the
AMP mimetic
AICAR or allosteric AMPK activator
A-769662 led to a
cytostatic response in proliferative adherent
ovarian cancer cells, but they fail to elicit an effect in spheroids. Targeted knockdown of STK11 by RNAi to reduce LKB1 expression led to reduced viability and increased sensitivity to
carboplatin treatment in spheroids only, a phenomenon which was AMPK-independent. Thus, our results demonstrate a direct impact of altered LKB1-AMPK signalling function in EOC. In addition, this is the first evidence in
cancer cells demonstrating a pro-survival function for LKB1, a
kinase traditionally thought to act as a tumour suppressor.