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Abstract Altered metabolism helps sustain cancer cell proliferation and survival. Most cancers, including prostate cancers, express the M2 splice isoform of pyruvate kinase (PKM2), which can support anabolic metabolism to support cell proliferation. However, Pkm2 expression is dispensable for the formation and growth of many cancers in vivo. Expression of pyruvate kinase isoform M1 (Pkm1) is restricted to relatively few tissues and has been reported to promote growth of select tumors, but the role of PKM1 in cancer has been less studied than PKM2. To test how differential expression of pyruvate kinase isoforms affects cancer initiation and progression, we generated mice harboring a conditional allele of Pkm1 and crossed these mice, or those with a Pkm2 conditional allele, with a Pten loss-driven prostate cancer model. Pkm1 loss led to increased PKM2 expression and accelerated prostate cancer development, whereas Pkm2 deletion led to increased PKM1 expression and suppressed tumor progression. Metabolic profiling revealed altered nucleotide levels in tumors with high PKM1 expression, and failure of these tumors to progress was associated with DNA replication stress and senescence. Consistent with these data, a small molecule pyruvate kinase activator that mimics a high activity PKM1-like state suppressed progression of established prostate tumors. Analysis of human specimens showed PKM2 expression is retained in most human prostate cancers. Overall, this study uncovers a role for pyruvate kinase isoforms in prostate cancer initiation and progression, and argues that pharmacologic pyruvate kinase activation may be beneficial for treating prostate cancer. Significance: Differential expression of PKM1 and PKM2 impacts prostate tumorigenesis and suggests a potential therapeutic vulnerability in prostate cancer.

The pyruvate kinase M2 isoform (PKM2) is expressed in cancer and plays a role in regulating anabolic metabolism. To determine whether PKM2 is required for tumor formation or growth, we generated mice with a conditional allele that abolishes PKM2 expression without disrupting PKM1 expression. PKM2 deletion accelerated mammary tumor formation in a Brca1-loss-driven model of breast cancer. PKM2 null tumors displayed heterogeneous PKM1 expression, with PKM1 found in nonproliferating tumor cells and no detectable pyruvate kinase expression in proliferating cells. This suggests that PKM2 is not necessary for tumor cell proliferation and implies that the inactive state of PKM2 is associated with the proliferating cell population within tumors, whereas nonproliferating tumor cells require active pyruvate kinase. Consistent with these findings, variable PKM2 expression and heterozygous PKM2 mutations are found in human tumors. These data suggest that regulation of PKM2 activity supports the different metabolic requirements of proliferating and nonproliferating tumor cells., National Institutes of Health (U.S.) (Grant R01CA168653), National Institutes of Health (U.S.) (Grant 5P01CA117969), National Institutes of Health (U.S.) (Grant P30CA147882), National Institutes of Health (U.S.) (Grant 5P30CA14051), National Institutes of Health (U.S.) (Grant 5K08CA136983), National Institutes of Health (U.S.) (Grant DK059635), National Institutes of Health (U.S.) (Grant R01DK092606), National Institutes of Health (U.S.) (Grant R00CA131472), National Institutes of Health (U.S.) (Grant R01GM056203), American Diabetes Association (Grant 7-12-BS-09), Smith Family Foundation, Burroughs Wellcome Fund, Damon Runyon Cancer Research Foundation, Stern Family

Metabolic regulation influences cell proliferation. The influence of pyruvate kinase isoforms on tumor cells has been extensively studied, but whether PKM2 is required for normal cell proliferation is unknown. We examine how PKM2 deletion affects proliferation and metabolism in nontransformed, nonimmortalized PKM2-expressing primary cells. We find that deletion of PKM2 in primary cells results in PKM1 expression and proliferation arrest. PKM1 expression, rather than PKM2 loss, is responsible for this effect, and proliferation arrest cannot be explained by cell differentiation, senescence, death, changes in gene expression, or prevention of cell growth. Instead, PKM1 expression impairs nucleotide production and the ability to synthesize DNA and progress through the cell cycle. Nucleotide biosynthesis is limiting, as proliferation arrest is characterized by severe thymidine depletion, and supplying exogenous thymine rescues both nucleotide levels and cell proliferation. Thus, PKM1 expression promotes a metabolic state that is unable to support DNA synthesis., United States. Dept. of Defense. Congressionally Directed Medical Research Programs (Postdoctoral Award W81XWH-12-1-0466), Smith Family Foundation, Burroughs Wellcome Fund, Damon Runyon Cancer Research Foundation, Stern Family, American Association for Cancer Research, National Cancer Institute (U.S.) (NIH 5P30CA1405141), National Cancer Institute (U.S.) (R01CA168653)

Metformin inhibits cancer cell proliferation, and epidemiology studies suggest an association with increased survival in patients with cancer taking metformin; however, the mechanism by which metformin improves cancer outcomes remains controversial. To explore how metformin might directly affect cancer cells, we analyzed how metformin altered the metabolism of prostate cancer cells and tumors. We found that metformin decreased glucose oxidation and increased dependency on reductive glutamine metabolism in both cancer cell lines and in a mouse model of prostate cancer. Inhibition of glutamine anaplerosis in the presence of metformin further attenuated proliferation, whereas increasing glutamine metabolism rescued the proliferative defect induced by metformin. These data suggest that interfering with glutamine may synergize with metformin to improve outcomes in patients with prostate cancer., German Science Foundation (Grant FE1185), National Institutes of Health (U.S.), Glenn Foundation for Medical Research, National Institutes of Health (U.S.) (Grant 5-P50-090381-09), National Institutes of Health (U.S.) (Grant 5-P30-CA14051-39), Burroughs Wellcome Fund, Smith Family Foundation, Damon Runyon Cancer Research Foundation, National Institutes of Health (U.S.) (Grant 1R01DK075850-01), National Institutes of Health (U.S.) (Grant 1R01CA160458-01A1)

American Cancer Society (Grant PF-08215-01-TBE)

Control of intracellular reactive oxygen species (ROS) concentrations is critical for cancer cell survival. We show that, in human lung cancer cells, acute increases in intracellular concentrations of ROS caused inhibition of the glycolytic enzyme pyruvate kinase M2 (PKM2) through oxidation of Cys[superscript 358]. This inhibition of PKM2 is required to divert glucose flux into the pentose phosphate pathway and thereby generate sufficient reducing potential for detoxification of ROS. Lung cancer cells in which endogenous PKM2 was replaced with the Cys[superscript 358] to Ser[superscript 358] oxidation-resistant mutant exhibited increased sensitivity to oxidative stress and impaired tumor formation in a xenograft model. Besides promoting metabolic changes required for proliferation, the regulatory properties of PKM2 may confer an additional advantage to cancer cells by allowing them to withstand oxidative stress., National Institutes of Health (U.S.) (R03MH085679), National Institutes of Health (U.S.) (1P30CA147882), Burroughs Wellcome Fund, Damon Runyon Cancer Research Foundation, Smith Family Foundation, Starr Cancer Consortium