Remodeling of Cancer-Specific Metabolism under Hypoxia with Lactate Calcium Salt in Human Colorectal Cancer Cells

Decreased pyruvate dehydrogenase activity in Tafazzin-deficient cells is caused by dysregulation of pyruvate dehydrogenase phosphatase 1 (PDP1)

Cardiolipin (CL), the signature lipid of the mitochondrial inner membrane, is critical for maintaining optimal mitochondrial function and bioenergetics. Disruption of CL metabolism, caused by mutations in the CL remodeling enzyme TAFAZZIN, results in the life-threatening disorder Barth syndrome (BTHS). While the clinical manifestations of BTHS, such as dilated cardiomyopathy and skeletal myopathy, point to defects in mitochondrial bioenergetics, the disorder is also characterized by broad metabolic dysregulation, including abnormal levels of metabolites associated with the tricarboxylic acid (TCA) cycle. Recent studies have identified the inhibition of pyruvate dehydrogenase (PDH), the gatekeeper enzyme for TCA cycle carbon influx, as a key deficiency in various BTHS model systems. However, the molecular mechanisms linking aberrant CL remodeling, particularly the primary, direct consequence of reduced tetralinoleoyl-CL (TLCL) levels, to PDH activity deficiency are not yet understood. In the current study, we found that remodeled TLCL promotes PDH function by directly binding to and enhancing the activity of PDH phosphatase 1 (PDP1). This is supported by our findings that TLCL uniquely activates PDH in a dose-dependent manner, TLCL binds to PDP1 in vitro, TLCL-mediated PDH activation is attenuated in the presence of phosphatase inhibitor, and PDP1 activity is decreased in Tafazzin-knockout (TAZ-KO) C2C12 myoblasts. Additionally, we observed decreased mitochondrial calcium levels in TAZ-KO cells and treating TAZ-KO cells with calcium lactate (CaLac) increases mitochondrial calcium and restores PDH activity and mitochondrial oxygen consumption rate. Based on our findings, we conclude that reduced mitochondrial calcium levels and decreased binding of PDP1 to TLCL contribute to decreased PDP1 activity in TAZ-KO cells.

Accumulation of poly (adenosine diphosphate-ribose) by sustained supply of calcium inducing mitochondrial stress in pancreatic cancer cells

BACKGROUND

The biochemical phenomenon defined as poly adenosine diphosphate (ADP)-ribosylation (PARylation) is essential for the progression of pancreatic cancer. However, the excessive accumulation of poly ADP-ribose (PAR) induces apoptosis-inducing factor (AIF) release from mitochondria and energy deprivation resulting in the caspase-independent death of cancer cells.

AIM

To investigate whether sustained calcium supply could induce an anticancer effect on pancreatic cancer by PAR accumulation.

METHODS

Two pancreatic cancer cell lines, AsPC-1 and CFPAC-1 were used for the study. Calcium influx and mitochondrial reactive oxygen species (ROS) were observed by fluorescence staining. Changes in enzyme levels, as well as PAR accumulation and energy metabolism, were measured using assay kits. AIF-dependent cell death was investigated followed by confirming in vivo anticancer effects by sustained calcium administration.

RESULTS

Mitochondrial ROS levels were elevated with increasing calcium influx into pancreatic cancer cells. Then, excess PAR accumulation, decreased PAR glycohydrolase and ADP-ribosyl hydrolase 3 levels, and energy deprivation were observed. In vitro and in vivo antitumor effects were confirmed to accompany elevated AIF levels.

CONCLUSION

This study visualized the potential anticancer effects of excessive PAR accumulation by sustained calcium supply on pancreatic cancer, however elucidating a clear mode of action remains a challenge, and it should be accompanied by further studies to assess its potential for clinical application.

The impact of hypoxia on immune state in cancer

Hypoxia is a known feature of solid tumors and a critical promoter of tumor hallmarks. Hypoxia influences tumor immunity in a way favoring immune evasion and resistance. Extreme hypoxia and aberrant hypoxia-inducible factor-1 (HIF-1) activity in tumor microenvironment (TME) is a drawback for effective immunotherapy. Infiltration and activity of CD8⁺ T cells is reduced in such condition, whereas regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) show high activities. Highly hypoxic TME also impairs maturation and activity of dendritic cell (DCs) and natural killer (NK) cells. In addition, the hypoxic TME positively is linked positively with metabolic changes in cells of immune system. These alterations are indicative of a need for hypoxia modulation as a complementary targeting strategy to go with immune checkpoint inhibitor (ICI) therapy.