Inhibiting PI3Kβ with AZD8186 Regulates Key Metabolic Pathways in PTEN-Null Tumors

Abstract

PTEN-null tumors become dependent on the PI3Kβ isoform and can be targeted by molecules such as the selective PI3Kβ inhibitor AZD8186. However, beyond the modulation of the canonical PI3K pathway, the consequences of inhibiting PI3Kβ are poorly defined. To determine the broader impact of AZD8186 in PTEN-null tumors, we performed a genome-wide RNA-seq analysis of PTEN-null triple-negative breast tumor xenografts treated with AZD8186. Mechanistic consequences of AZD8186 treatment were examined across a number of PTEN-null cell lines and tumor models. AZD8186 treatment resulted in modification of transcript and protein biomarkers associated with cell metabolism. We observed downregulation of cholesterol biosynthesis genes and upregulation of markers associated with metabolic stress. Downregulation of cholesterol biosynthesis proteins, such as HMGCS1, occurred in PTEN-null cell lines and tumor xenografts sensitive to AZD8186. Therapeutic inhibition of PI3Kβ also upregulated PDHK4 and increased PDH phosphorylation, indicative of reduced carbon flux into the TCA cycle. Consistent with this, metabolomic analysis revealed a number of changes in key carbon pathways, nucleotide, and amino acid biosynthesis. This study identifies novel mechanistic biomarkers of PI3Kβ inhibition in PTEN-null tumors supporting the concept that targeting PI3Kβ may exploit a metabolic dependency that contributes to therapeutic benefit in inducing cell stress. Considering these additional pathways will guide biomarker and combination strategies for this class of agents. .

Combined Inhibition of PI3Kβ and mTOR Inhibits Growth of PTEN-null Tumors

“…Recently, PI3K has been shown to control the glycolytic phenotype of tumor cells through the regulation of Aldolase (41). Inhibition of PI3K reduces nucleotide levels regulate nucleotide levels in cells (26,42). Finally PI3K and AKT inhibition can reduce lipid and cholesterol pathway activity (26,43,44), while mTORC2 signaling promoted development of liver cancer through regulation of lipid synthesis (45).…”

“…Inhibition of PI3K reduces nucleotide levels regulate nucleotide levels in cells (26,42). Finally PI3K and AKT inhibition can reduce lipid and cholesterol pathway activity (26,43,44), while mTORC2 signaling promoted development of liver cancer through regulation of lipid synthesis (45). Through coordinated targeting of FOXO, GSK3, and TSC2/mTORC1 function, there are significant impacts on pathway critical for tumor cell function (46).…”

“…Activation of both translation-dependent effects and anabolic metabolism as well as cell survival and proliferation pathways is important for all cells. In the PTEN-null cells, inhibition of PI3Kb reduces cholesterol biosynthesis enzymes, nucleotide levels, and induces cell stress (26). However, the balance of pathway dependency may vary between genotypes, and even between individual cells of a similar genotype.…”

“…Targeted gene expression was performed using the BioMark HDTM -Fluidigm Array platform (96.96 dynamic array) and TaqMan primers (human vs. mouse specific when possible) following manufacturer's instructions. Fifty nanograms of total RNA was reverse transcribed and preamplified (Thermo Fisher Scientific: #4374967, #4488593) for 14 cycles, with 96 selected primers selected from previous RNA-sequencing data (26). The 96.96 Fluidigm Dynamic Arrays were primed and loaded on an IFC Controller and qPCR experiments run on the Biomark System, using the standard 96 default protocol.…”

Targeting PI3Kβ alone and in combination with chemotherapy or immunotherapy in tumors with PTEN loss

“…AZD8186 is a selective and potent small-molecule inhibitor of PI3Kβ, with additional activity against PI3Kδ isoform [12][13][14]. Its antitumor activity has been demonstrated in PTEN-deficient prostate, squamous lung carcinoma and germinal-center diffuse large cell B-cell lymphoma preclinical models [12,15]. This raises the possibility that AZD8186 may have a role in TNBC with PTEN loss as well.…”