High-dose vitamin C can act as a prodrug to kill aggressive tumors, but only if specific membrane proteins let the toxic byproducts inside. This review reveals exactly which transporters determine whether cancer cells survive or die.

Cancer remains a global crisis with nearly ten million deaths recorded in two thousand twenty alone, and cases are expected to rise sharply by two thousand forty. Aggressive solid tumors like pancreatic cancer and glioblastoma display high treatment resistance, creating an urgent need for novel therapeutic approaches.

Preclinical data suggests that administering pharmacological ascorbate responds well in some aggressively growing tumor entities. Membrane transport proteins are critical because they control the transfer of active substances like ascorbate and hydrogen peroxide into malignant cells to induce antiproliferative effects.

Vitamin C acts as a prodrug by preferentially forming the ascorbate free radical and hydrogen peroxide in the extracellular space rather than in the blood. This mechanism requires a threshold concentration of the ascorbate free radical of at least one hundred nanomolar to function effectively.

While low levels of hydrogen peroxide promote cell survival, supraphysiological concentrations induced by high-dose ascorbate lead to intracellular accumulation and cell death. These high concentrations cause destruction of biomolecules, disrupt redox signaling, and result in cell growth arrest.

Cancer cells often have a decreased ability to metabolize hydrogen peroxide due to inefficient enzymes, making them susceptible to pharmacologic ascorbate. An increase in the intracellular labile iron pool significantly contributes to the cancer cell-selective toxicity of pharmacological ascorbate.

Ferroptosis is defined as an iron-dependent and lipid peroxidation-driven regulated cell death pathway triggered by these mechanisms. In malignant cells, labile iron participates in the pro-oxidative reaction of ascorbate to form reactive oxygen species.

Table 1 summarizes the major proteins responsible for transporting hydrogen peroxide and vitamin C across cell membranes, specifically listing aquaporins and sodium-dependent vitamin C transporters. The authors detail where these proteins are expressed in normal versus tumor tissues and highlight specific genetic polymorphisms that influence clinical outcomes, such as chemotherapy response or disease risk.

By connecting these molecular transport mechanisms to patient survival metrics like disease-free survival, this table underscores how genetic variations in transporter function may impact cancer progression and treatment efficacy. Aquaporins are channel proteins that facilitate the diffusion of hydrogen peroxide and are sometimes called peroxiporins.

The expression of these peroxiporins is suggested to be an important determinant modulating cancer cell susceptibility to therapeutic hydrogen peroxide formation. Human sodium-dependent vitamin C transporter one is encoded by the solute carrier family twenty-three member one gene.

Both SVCT one and two actively transport ascorbic acid against gradients by coupling its entry with sodium influx into the cell. When ascorbate oxidizes into dehydroascorbic acid, it accumulates through facilitated diffusion via glucose transporters known as GLUTs. Human colorectal cancer cells harboring KRAS or BRAF mutations were selectively killed in vitro when exposed to high levels of vitamin C due to increased uptake of DHA via GLUT one.

Transferrin receptor one is overexpressed on many different types of cancer cells, often at levels many times higher than in normal cells. Significant overexpression of this receptor correlates with tumor stage, progression, and short patient survival. Divalent metal transporter one accepts a broad range of transition metal ions and transports ferrous iron with high affinity.

Overexpression of this transporter promoted the progression of ovarian tumors in cell sphere models. Ferroportin one is the only cellular efflux channel for iron, and its activity is downregulated in cancer cells to increase the iron pool. Conversely, stimulating ferroportin leads to reduced growth and proliferation of cancer cells due to cellular iron deprivation.

This figure illustrates the complex transport systems for ascorbate, iron, and hydrogen peroxide across the plasma membrane of tumor cells. It details how cancer cells import these molecules via specific channels like SVCTs and TfRs to fuel intracellular redox interactions. The diagram highlights a critical pathway where dehydroascorbate reacts with iron to form an adduct that generates reactive oxygen species, ultimately driving lipid peroxidation and ferroptosis.

Figure 2 contrasts the iron and ascorbate metabolism between healthy physiological tissue and malignant cancer cells. Crucially, the figure highlights how tumor cells frequently overexpress glucose transporters, leading to increased uptake of dehydroascorbic acid and enhanced formation of reactive radicals like the ascorbate free radical.

This visual comparison underscores the distinct metabolic vulnerabilities in cancer cells that can be targeted by high-dose ascorbate therapy. For effective treatment, vitamin C importers, iron importers, and aquaporins can be considered as relevant shuttle systems.

Data indicates that ascorbate reduces intracellular unbound iron, which in return generates a greater amount of reactive oxygen species. There is an urgent need for a nuanced understanding of the interplay between ascorbate, hydrogen peroxide transporters, and iron shuttle systems.

Identifying tumors sensitive to ascorbate therapy is necessary to further substantiate the success of this application. The success of pharmacological ascorbate therapy depends on the expression of specific gatekeeper proteins that control the entry of vitamin C and iron, ultimately triggering lethal oxidative stress in tumor cells.