Enzymatic activation of pyruvate kinase increases cytosolic oxaloacetate to inhibit the Warburg effect.

Pharmacological activation of the glycolytic enzyme PKM2 or expression of the constitutively active PKM1 isoform in cancer cells results in decreased lactate production, a phenomenon known as the PKM2 paradox in the Warburg effect. Here we show that oxaloacetate (OAA) is a competitive inhibitor of human lactate dehydrogenase A (LDHA) and that elevated PKM2 activity increases de novo synthesis of OAA through glutaminolysis, thereby inhibiting LDHA in cancer cells. We also show that replacement of human LDHA with rabbit LDHA, which is relatively resistant to OAA inhibition, eliminated the paradoxical correlation between the elevated PKM2 activity and the decreased lactate concentration in cancer cells treated with a PKM2 activator. Furthermore, rabbit LDHA-expressing tumours, compared to human LDHA-expressing tumours in mice, displayed resistance to the PKM2 activator. These findings describe a mechanistic explanation for the PKM2 paradox by showing that OAA accumulates and inhibits LDHA following PKM2 activation.

Tyrosine Phosphorylation of Mitochondrial Creatine Kinase 1 Enhances a Druggable Tumor Energy Shuttle Pathway.

How mitochondrial metabolism is altered by oncogenic tyrosine kinases to promote tumor growth is incompletely understood. Here, we show that oncogenic HER2 tyrosine kinase signaling induces phosphorylation of mitochondrial creatine kinase 1 (MtCK1) on tyrosine 153 (Y153) in an ABL-dependent manner in breast cancer cells. Y153 phosphorylation, which is commonly upregulated in HER2+ breast cancers, stabilizes MtCK1 to increase the phosphocreatine energy shuttle and promote proliferation. Inhibition of the phosphocreatine energy shuttle by MtCK1 knockdown or with the creatine analog cyclocreatine decreases proliferation of trastuzumab-sensitive and -resistant HER2+ cell lines in culture and in xenografts. Finally, we show that cyclocreatine in combination with the HER2 kinase inhibitor lapatinib reduces the growth of a trastuzumab-resistant HER2+ patient-derived xenograft. These findings suggest that activation of the phosphocreatine energy shuttle by MtCK1 Y153 phosphorylation creates a druggable metabolic vulnerability in cancer.

Dual inhibition of Mcl-1 by the combination of carfilzomib and TG02 in multiple myeloma.

Carfilzomib (Kyprolis®), a second generation proteasome inhibitor, is FDA approved for single-agent use among relapsed/refractory multiple myeloma (MM). To enhance the therapeutic efficacy of carfilzomib, we sought to combine carfilzomib with other novel agents. TG02, a multi-kinase inhibitor, targets JAK2 and CDK9. The rationale for co-treatment with carfilzomib and TG02 is that both independently target Mcl-1 and most myeloma cells are dependent on this anti-apoptotic protein for survival. We observed at least additive effects using the combination treatment in MM cell lines and patient samples. To determine how the bone marrow environment affects the efficacy of the combination we conducted co-culture experiments with Hs-5 stromal cells. We also examined the mechanism of increased apoptosis by determining the affect on expression of the Bcl-2 family of proteins. We found that carfilzomib increases NOXA mRNA expression, as expected, and TG02 treatment caused a decrease in Mcl-1 protein but not mRNA levels. Consistent with this possibility, we find silencing CDK9 does not change carfilzomib sensitivity in the same manner as addition of TG02. Since changes in Mcl-1 protein occur in the presence of a proteasome inhibitor we hypothesize that regulation of Mcl-1 translation is the most likely mechanism. Taken together our data suggest that dual inhibition of Mcl-1 via decreased expression and the induction of its antagonist NOXA by the combination of carfilzomib and TG02 is active in myeloma and warrants further testing preclinically and in clinical trials. Moreover, regulation of Mcl-1 by TG02 is more complex than initially appreciated.