Circumventing the Crabtree effect: forcing oxidative phosphorylation (OXPHOS) via galactose medium increases sensitivity of HepG2 cells to the purine derivative kinetin riboside

Marta Orlicka-Płocka,Dorota Gurda-Wozna,Agnieszka Fedoruk-Wyszomirska,Eliza Wyszko

doi:10.1007/s10495-020-01637-x

Marta Orlicka-Płocka, Dorota Gurda-Wozna + Show 2 more

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https://doi.org/10.1007/s10495-020-01637-x

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Abstract

Small-molecule compound-based therapies have provided new insights into cancer treatment against mitochondrial impairment. N6-furfuryladenosine (kinetin riboside, KR) is a purine derivative and an anticancer agent that selectively affects the molecular pathways crucial for cell growth and apoptosis by interfering with mitochondrial functions and thus might be a potential mitotoxicant. Metabolism of cancer cells is predominantly based on the Crabtree effect that relies on glucose-induced inhibition of cell respiration and thus on oxidative phosphorylation (OXPHOS), which supports the survival of cancer cells in metabolic stress conditions. The simplest way to circumvent this phenomenon is to replace glucose with galactose in the culture environment. Consequently, cells become more sensitive to mitochondrial perturbations caused by mitotoxicants. In the present study, we evaluated several cellular parameters and investigated the effect of KR on mitochondrial functions in HepG2 cells forced to rely mainly on OXPHOS. We showed that KR in the galactose environment is a more potent apoptosis-inducing agent. KR decreases the mitochondrial membrane potential, reduces glutathione level, depletes cellular ATP, and induces reactive oxygen species (ROS) production in the OXPHOS state, leading to the loss of cell viability. Taken together, these results demonstrate that KR directly acts on the mitochondria to limit their function and that the sensitivity of cells is dependent on their ability to cope with energetic stress.

Highlights

Metabolism of most cancer cells relies on anaerobic glycolysis
Mitochondria play a crucial role in the regulation of cellular energy metabolism, and they are responsible for many other important functions such as induction of apoptosis, calcium redox, and homeostasis
We used the xCELLigence system for monitoring HepG2 cell proliferation to compare the toxicity of Kinetin riboside (KR) in culture media supplemented with glucose or galactose

Summary

Introduction

Metabolism of most cancer cells relies on anaerobic glycolysis. Even in the presence of oxygen, mitochondrial respiration is suppressed, and this is a probable mechanism through which cells escape apoptosis [1]. Recent studies on drugs inducing mitochondrial dysfunction have demonstrated that these cells are able to switch their metabolic strategy alternatively, from fermentative to oxidative, and this phenomenon is termed as the Crabtree effect [8, 9] This effect frequently accompanies the Warburg effect; in contrast to an anaerobic glycolysis, the Crabtree effect is usually referred to as a reversible, short-termed adaptive mechanism of cancer cells, which is based on glucose-induced inhibition of respiration, and OXPHOS is observed in proliferating tumor cells but may occur in normal cells [10]. An increase in cellular ATP/ADP, a common intermediate for both glycolysis and OXPHOS, decreases the demand for respiratory flux to generate ATP [11]

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