Targeting intra- and extracellular K+ in cancer

With an estimated 9.6 million caused deaths in 2018, cancers represent a leading cause of death worldwide. Hence, it is of utmost importance to understand the molecular and cellular basis of the disease to encounter its onset and progression. Major cancer entities are associated with alterations in the expression and/or function of ion- and especially potassium ion (K+) channels. However, their impact on malignant cell behaviour and the (sub)cellular K+ homeostasis remains largely elusive, as intracellular [K+] measurements and correlations with cellular processes are challenging. We have demonstrated recently that the intracellular K+ concentration is a crucial regulator of cancer cell metabolism via modulating the activity of one of the first and essential enzymes of glycolysis, hexokinase-II. Based on these findings, we postulate, that a better understanding of the molecular mechanisms and protagonists that control the (sub)cellular K+ homeostasis of cancer cells and diverse procedures for manipulating cancer cell K+ gradients have the potential to guide us to novel strategies in the (personalized) diagnosis and therapy of cancerous diseases. By combining murine breast cancer models with our recently developed Genetically Encoded Potassium Ion Indicators to quantify and visualize intra- and extracellular K+ dynamics in primary cancer cells, we aim to obtain the breast cancer cell specific K + profiles. These studies will be corroborated by expression- and functionality analyses of cancer-associated calcium ion (Ca2+) activated K+ (KCa) channels, especially KCa1.1, a frequently cancer-associated K+ channel, using different quantitative and functional assays. Based on these profiles, we aim for a local manipulation of the intracellular [K+] in cancer cells using K+ channel modulators and genetic approaches to modify the cellular K+ profile. This profile will subsequently be correlated with cell metabolism and -malignancy parameters, using genetically encoded sensors and conventional assays. These results obtained in vitro will finally be translated into living animals and verified by the application of novel therapeutic approaches based on our findings. Based on our recent, striking finding of hexokinase-II representing a K+ modulated enzyme, identifying and exploring the importance of the intracellular K+ homeostasis as a key player regulating cancer cell metabolism has the potency to revolutionize our understanding of cellular energy generation pathways. Such identification may contribute to our understanding of yet unknown backgrounds of cancer development and progression. Eventually, novel anti-cancer strategies and therapies may develop and evolve from our findings.

This project shows that tiny potassium channels and sugar-processing enzymes inside cancer cells strongly influence how breast cancer grows, survives treatment, and changes its identity. Cancer cells need large amounts of energy to grow. They often rewire their metabolism so that they can produce energy very quickly, even in inefficient ways. Our project investigated two key components of this process in breast cancer: a potassium channel located inside mitochondria (the cell's "power plants") and a central enzyme involved in sugar breakdown. We first discovered that a specific potassium channel, called mitoBKCa, is present in the mitochondria of breast cancer cells and also in patient tumor samples. Potassium channels are best known for controlling electrical signals in nerves, but here we found that they also influence how mitochondria produce energy. When this channel is active, cancer cells shift their metabolism toward a fast, growth-promoting mode. This supports a well-known cancer feature where cells rely heavily on sugar breakdown even when oxygen is available. Blocking this channel changes how mitochondria function, reduces energy production efficiency, and slows down cancer cell growth. This suggests that mitoBKCa helps cancer cells adapt their energy supply to support tumor growth. In a second part of the project, we studied how cancer cells respond when a key sugar-processing enzyme called HK2 is blocked. HK2 is usually highly active in fast-growing cancer cells. We found that inhibiting HK2 does not always kill cancer cells. Instead, in many cases, it pushes them into a different state called "senescence." Senescent cells stop dividing but do not die. They also change their metabolism, switching from HK2 to a related enzyme called HK1. Importantly, we found that the balance between HK2 and HK1 is more important than the amount of either enzyme alone in determining whether a cell keeps growing or becomes senescent. We also showed that this metabolic shift can be seen in real patient tumor data at the single-cell level, confirming that it is not just an artificial laboratory effect. Overall, our results show that breast cancer cells are highly flexible and can switch their energy systems depending on internal signals and treatment pressure. Mitochondrial potassium channels and sugar-processing enzymes are closely linked to this flexibility. These findings are important because they suggest new ways to treat cancer. Targeting mitochondrial potassium channels could weaken the energy supply of tumors, while targeting HK2 could influence whether cancer cells keep dividing or enter a dormant-like state. In the future, combining these strategies, and considering how previous treatments have changed tumor cell states, may improve cancer therapy and help overcome resistance.