The Na+/K+-ATPase (NKA) consumes a substantial portion of cellular ATP to maintain essential electrochemical gradients across the plasma membrane. Beyond ion transport, the NKA also functions as a scaffolding receptor, creating complexity in interpreting how its perturbation affects cell physiology. The authors investigated how pharmacological blockade of the pump influences proliferation and metabolic phenotypes in a model of human chronic myelogenous leukemia, the K562 cell line.
Pharmacological NKA blockade was achieved using digoxin applied at submicromolar concentrations to K562 cells. The study focused on quantifying effects on cellular proliferation, metabolic reducing capacity, and viability, and on testing whether extracellular potassium supplementation could modulate digoxin responses.
Exposure to submicromolar concentrations of digoxin produced a concentration-dependent attenuation of K562 cell proliferation. The authors report an IC50 for growth inhibition of 151.0 nM, indicating that low-nanomolar to submicromolar digoxin levels were sufficient to reduce proliferation in this model.
Digoxin treatment caused a statistically significant depression of metabolic reducing capacity in K562 cells. Importantly, this metabolic depression occurred without impairing cell viability, consistent with a cytostatic effect in which cells reduce proliferative and metabolic activity but remain alive. The distinction between reduced metabolic capacity and loss of viability supports interpretation that NKA blockade primarily suppresses growth rather than inducing cell death under the tested conditions.
The authors used competitive supplementation with extracellular potassium salts to probe target specificity. Addition of potassium produced a surmountable rightward shift in digoxin sensitivity, consistent with competitive interaction at the pump. This pharmacologic rescue supports the conclusion that growth inhibition results from on-target NKA pump occupancy rather than non-specific off-target effects of digoxin.
Both the cytostatic growth attenuation and the metabolic depression induced by digoxin were fully reversible upon drug clearance. Cells recovered proliferative capacity and metabolic reducing activity after removal of the compound, demonstrating that the effects observed were not permanent under the experimental conditions and that NKA function restoration permits phenotypic recovery.
K562 cells harbor constitutive BCR-ABL tyrosine kinase activity and are deficient in canonical checkpoint responses: they possess non-functional TP53 and a homozygous deletion of CDKN2A (p16INK4a). Because these cells are largely refractory to canonical kinase-overdrive stress checkpoints, the authors infer that the growth attenuation observed with NKA blockade is driven primarily by ion dyshomeostasis and constraints on secondary active transport rather than by disruption of scaffold-mediated signaling pathways linked to the pump. In this context, impaired ion gradients and reduced ATP allocation to maintain them likely limit metabolic processes required for proliferation.
The authors present a model for using K562 cells to dissect the role of the Na+/K+-ATPase in cancer cell proliferation and to explore ion-mediated alterations in cancer cell physiology. Key implications are that targeted perturbation of ion transport can produce reversible, cytostatic suppression of growth without acute cytotoxicity, and that extracellular ionic conditions can modulate sensitivity to NKA inhibitors.
This article is a preprint and has not been certified by peer review. The report discloses funding from the NIH Common Fund (P20GM103442). Details beyond the abstract—such as specific experimental procedures, full quantitative data sets, time courses, and broader testing across other cell lines—were not reported in the provided source abstract and therefore are not summarized here.
In K562 human myelogenous leukemia cells, pharmacological blockade of the Na+/K+-ATPase with digoxin at submicromolar concentrations produces a reversible, concentration-dependent attenuation of proliferation and a depression of metabolic reducing capacity without impairing viability. Potassium supplementation surmountably shifts digoxin sensitivity, supporting an on-target pump mechanism. Given the genetic features of K562 cells, the authors conclude that ion dyshomeostasis and related transport constraints are the primary drivers of the observed cytostatic phenotype.