Abstract B42: Metabolic pathway changes induced by a PIK3 mutation and reverted by drugs
Authors: Lei Xiang-He , Noble Shawn , Bochner Barry R. 
Published: May 2016

In this study we applied two new technologies to elucidate the changes in cellular energy metabolism engendered by a cancer-associated gain-of-function mutation in the PIK3CA gene. We used Phenotype MicroArray Technology to measure and compare the metabolic rates of energy producing pathways in isogenic human breast cells. The isogenic cell lines, were created using new genetic technologies and provided by Horizon Discovery. They included the non-tumorigenic mammary epithelial cell line, MCF10A, which is wild-type for PI3Kα, and two isogenic clonally derived cell lines (CL1 and CL2) in which the endogenous PI3Kα is constitutively activated via the introduction by homologous recombination of a kinase domain mutation (H1047R) resulting in cells that are heterologous for this locus (H1047R/+). This mutation is very common in human breast cancers and also in other cancers.

The two cell lines with activated PI3Kα showed expected but small increases in energy production rates from glucose and glutamine, as well as from pyruvate. However a much more dramatic change was the observed decrease in catabolism of lactate and alanine. To verify that the loss of lactate and alanine catabolism resulted from PI3Kα activation, we examined whether drugs targeted against PI3Kα could reverse these metabolic changes. We used special Phenotype MicroArray plates to titrate the drugs and simultaneously follow the metabolism of lactate, alanine, glutamine, glycogen, hexanoate, oleate, and palmitate. The experimental Novartis drug, NVP BYL719, a specific PI3Kα inhibitor, was quite effective at simultaneously restoring the metabolism of lactate and alanine and reversing the metabolic phenotypes engendered by the PI3Kα mutation at concentrations above 32nM. These results substantiate a causal relationship between activation of PI3Kα and loss of lactate and alanine catabolism. Other experimental drugs that are less specific for the alpha isoform of PI3K were also tested and found to be less effective at reversing the metabolic phenotypes. Some of these drugs caused off-target effects on other metabolic pathways which were detected by Phenotype MicroArray analysis.

These results are interesting in many aspects. They uncover previously unrecognized effects of PI3Kα activation on lactate and alanine metabolism and demonstrate phenotypic reversal by properly targeted drugs. More broadly, they demonstrate the utility of using Phenotype MicroArrays to objectively analyze isogenic cell lines containing cancer-relevant mutations and determine which energy pathways are affected by oncogenic mutations. The phenotypic changes observed can then be used in simple colorimetric cell based assays to screen chemical libraries and find drug candidates that reverse the metabolic phenotypes. In the studies presented, the drugs tested were directly designed against specific oncogenic targets. However a broader screen using a cell based metabolic assay has the potential to uncover drug candidates which may work by indirect phenotypic suppression. Studying the mechanisms of indirect suppression can further expand our knowledge of the interworkings of relevant pathways. Clearly, the approach demonstrated by these studies can be used to give fundamental and important information on the metabolic effects engendered by any oncogene mutation, singly and in combination with other mutations and genetic alterations, and in model cell lines representing many types of human cancers.

Citation Format: Xiang-He Lei, Shawn Noble, Barry R. Bochner. Metabolic pathway changes induced by a PIK3 mutation and reverted by drugs. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr B42.