A strategically designed small molecule attacks alpha-ketoglutarate dehydrogenase in tumor cells through a redox process

Abstract

BackgroundTargeting cancer cell metabolism is recognized as a promising arena for development of cancer chemotherapeutics. Moreover, redox metabolism is also systematically altered in tumor cells. Indeed, there is growing reason to believe that tumor-specific alteration of redox control of metabolism will be central to understanding and attacking malignancy. We report here that lipoate analog CPI-613 attacks a gate-keeping, lipoate-using metabolic enzyme, alpha-ketoglutarate dehydrogenase (KGDH), by a redox mechanism selectively in tumors cells.ResultsCPI-613 inhibited KGDH function strongly and rapidly, selectively in tumor cells. Moreover, CPI-613 induced a correspondingly rapid, powerful redox signal in tumor cell mitochondria. This signal was associated with redox modification of KGDH (including extensive enzyme glutathionylation and redox blockage of enzyme lipoate sulfhydryls), correlating with KGDH inactivation. The source of this tumor-specific mitochondrial redox modulatory signal was not electron transport complexes (I or III), but was largely or entirely the E3 (dihydrolipoamide dehydrogenase) component of dehydrogenases, including KGDH. Finally, we demonstrated that KGDH activity was redox regulated (in tumor cells), as expected if a tumor-specific redox process (auto)regulates KGDH.ConclusionsOur data demonstrate that lipoate analog CPI-613 attacks redox control of KGDH activity in tumor cells, perhaps by modulation of an existing lipoate-sensitive allosteric process normally governing tumor cell KGDH activity. Together with its previously reported, mechanistically distinct (non-redox) effects on the other major, lipoate-using mitochondrial metabolic enzyme, pyruvate dehydrogenase, CPI-613’s KGDH effects indicate that this agent simultaneously attacks multiple central, essential components of tumor cell metabolic regulation.

A Phase I Study of the First-in-Class Antimitochondrial Metabolism Agent, CPI-613, in Patients with Advanced Hematologic Malignancies

“…As mentioned in the introduction, CPI-613 leads to increased phosphorylation of the E1 subunit of PDH and inhibits KDH in solid tumor cell lines(4, 5). To determine if CPI-613 directly inhibits mitochondrial metabolism in hematogic malignancies, we treated the human leukemia cell lines K562 and OCI-AML3 with CPI-613 and assessed mitochondrial respiration.…”

“…CPI-613 is a novel lipoate derivative that inhibits PDH and KDH(4, 5). It causes hyperphosphorylation of the E1α subunit of PDH, ATP depletion and cell death in malignant but not normal cells(4).…”

Targeting thiamine-dependent enzymes for metabolic therapies in oral squamous cell carcinoma?

“…In the presence of thiamine pyrophosphate (TPP), the E1 subunits of PDH, KGDH (OGDH), and BCKDH perform decarboxylation steps [11,[37][38][39]. Therefore, we preferentially used antibodies detecting the E1 subunits in our analyses for the description of potential therapeutic targets of antagonistic compounds like oxythiamine [40][41][42] or oxybenfothiamine.…”

“…Our results of significant upregulation of PDH, KGDH (OGDH), and BCKDH in precursor lesions suggest that a molecular 'survival of the fittest scenario involving TDEs (including the TCA) plays out in the carcinogenesis of OSCC, making this model the better fit. Therefore, TDEs (TKTL1, PDH, KGDH, BCKDH) may contribute to the concept of competing the PPP [7,41] and targeted antimitochondrial therapies leading consequently to apoptosis in tumor cells [5,19,38,44,[50][51][52]. 6 Immunohistochemical analysis of BCKDH in normal oral mucosal tissue, oral precursor lesions-hyperplasia, SIN, and invasive OSCC.…”

Glutamate Dehydrogenase 1 Signals through Antioxidant Glutathione Peroxidase 1 to Regulate Redox Homeostasis and Tumor Growth

“…Glutaminolysis also supports the production of molecules, such as glutathione and NADPH, which protect cells from oxidative stress (DeBerardinis and Cheng, 2010; Reitzer et al, 1979; Wise and Thompson, 2010). Mounting evidence suggests that many types of cancer cells have tumor-specific redox control alterations, with increased levels of reactive oxygen species (ROS) compared to normal cells (Kawanishi et al, 2006; Stuart et al, 2014; Szatrowski and Nathan, 1991; Toyokuni et al, 1995). A moderate increase in ROS can promote cell proliferation and differentiation (Boonstra and Post, 2004), whereas excessive amounts of ROS can cause oxidative damage to proteins, lipid and DNA (Perry et al, 2000).…”