Pentachlorophenol Promotes Bladder Cancer Cell Invasion by Disrupting Protein Stability

A persistent industrial pollutant may make bladder cancer cells more invasive at concentrations measured in human blood, according to a study that traces the effect to changes in the stability of three cancer-related proteins. The chemical, pentachlorophenol (PCP), was once widely used as a wood preservative, herbicide and biocide. Although many uses have been restricted, PCP remains environmentally persistent and continues to be detected in human blood, urine and tissues. The new findings suggest that exposure may influence not only whether bladder cancer develops, but also how aggressively existing cancer cells behave. The work, published in iScience, identifies epidermal growth factor receptor (EGFR), mitogen-activated protein kinase kinase 1 (MAP2K1) and the stress-response regulator NFE2L2 as key molecular players in the process.

Bladder cancer is among the most common malignancies of the urinary tract, accounting for approximately 630,000 new cases and 220,000 deaths worldwide each year. Tobacco smoke and occupational exposure to aromatic amines and polycyclic aromatic hydrocarbons are well-established risks, but researchers have increasingly turned their attention to contaminants in drinking water, air and industrial environments. PCP is an especially plausible suspect because its carbon–chlorine bonds make it resistant to degradation. The compound can persist in soils and sediments, particularly in oxygen-poor environments, and its affinity for organic matter and lipids allows it to accumulate in organisms and potentially move through food webs. Human exposure can occur through contaminated food and water, occupational inhalation or contact with treated materials.

The concentrations tested in the new study were designed to reflect this real-world exposure. In the general population, reported serum concentrations can be around 0.15 micromolar, while people living in homes treated with PCP have shown levels as high as 5 micromolar. A large Chinese cohort detected the chemical in more than 90 percent of serum samples, with concentrations reaching approximately 1.14 micromolar. The researchers therefore exposed two human bladder cancer cell lines, T24 and SW780, to 0.05, 0.5 or 5 micromolar PCP for 24 hours. They then measured three distinct cancer-cell behaviors: invasion through a tissue-like barrier, migration across a scratched surface and proliferation. This separation was important because a chemical can increase the number of cells or their general movement without specifically making them better able to penetrate surrounding tissue.

PCP produced a strikingly selective result. At 0.5 and 5 micromolar, it increased the ability of both bladder cancer cell lines to invade through a Matrigel-coated membrane, and the effect rose with dose. In contrast, the same treatments did not significantly change cell migration or proliferation. The lowest concentration, 0.05 micromolar, had no detectable effect on any of the tested behaviors. In the invasion assay, 0.5 micromolar PCP increased invasive cell counts by roughly 1.4-fold in T24 cells and 1.5-fold in SW780 cells. Those changes were comparable to effects previously reported for cigarette-smoke extract, a recognized bladder-cancer risk factor. A related chlorinated phenol, 2,4-dichlorophenol, failed to produce the same response at any tested dose, suggesting that the result was not simply a consequence of chlorophenol toxicity or nonspecific cellular stress.

To search for a molecular explanation, the researchers combined chemical-target databases with cancer-genomics data. Four computational resources predicted 262 unique genes that could potentially interact with PCP. Separately, databases and The Cancer Genome Atlas yielded 1,580 genes associated with bladder cancer, including genes altered in tumors and genes linked to patient survival. Intersecting the two datasets produced 58 possible PCP–bladder-cancer target genes. These genes were enriched in pathways involved in cancer, interleukin signaling, lipid metabolism, oxidative stress, hypoxia, cyclic AMP signaling and the mitogen-activated protein kinase, or MAPK, network. Such pathway enrichment does not prove that PCP acts through every identified gene, but it provided a map for narrowing the search to the most biologically influential candidates.

The team then evaluated 101 machine-learning combinations to determine which of the 58 overlapping genes best predicted survival in bladder-cancer patients. The strongest model used a Random Survival Forest combined with stepwise Cox regression and contained EGFR, MAP2K1 and NFE2L2. EGFR is a receptor tyrosine kinase that relays signals from outside the cell to pathways controlling growth, survival and tissue remodeling. MAP2K1, also known as MEK1, is a central component of the RAS–RAF–MEK–ERK signaling cascade, which can promote malignant behavior when persistently activated. NFE2L2, commonly called NRF2, is a transcription factor that coordinates antioxidant and cellular stress responses. In the patient datasets, high EGFR or MAP2K1 expression and low NFE2L2 expression generally predicted poorer overall survival.

The resulting three-gene PCP-related score was tested in the TCGA bladder-cancer cohort and four independent datasets. Patients with high scores had more advanced tumor grade, tumor stage and lymph-node involvement. Their risk of death remained higher after adjustment for conventional clinical factors: the hazard ratio was 1.95 in univariate analysis and 1.78 in multivariate analysis. Across the combined cohorts, the hazard ratio was 2.04 when the score was treated as a continuous variable and 1.82 when patients were divided into high- and low-score groups. Internal cross-validation and bootstrap testing produced concordance indices close to the original model performance, indicating limited overfitting. However, the score did not reach statistical significance in one small dataset containing only 27 patients, underscoring the need for larger prospective studies.

Computational chemistry offered a further clue. Molecular docking predicted that PCP could fit into binding pockets in EGFR, MAP2K1 and NFE2L2, with calculated binding energies of approximately −5.30, −6.59 and −6.27 kilocalories per mole, respectively. Simulations lasting 100 nanoseconds suggested that each protein–chemical complex remained structurally stable, based on measures including root-mean-square deviation, residue flexibility, radius of gyration and hydrogen-bond formation. These calculations are useful for generating mechanistic hypotheses, but they are not equivalent to experimentally demonstrating a physical interaction. The authors explicitly note that direct binding still needs to be confirmed with biochemical approaches such as purified-protein binding assays or structural studies.

The strongest evidence came from experiments examining protein turnover. In SW780 cells, exposure to 0.5 micromolar PCP extended the half-lives of EGFR and MAP2K1, allowing more of these signaling proteins to remain in the cell. At the same time, it shortened the half-life of NFE2L2, potentially weakening the cell’s antioxidant and stress-defense machinery. PCP did not significantly alter the stability of the corresponding messenger RNAs during a nine-hour observation period. This distinction points to post-translational regulation: rather than changing how much RNA is produced, PCP appears to influence how quickly the proteins are degraded or maintained after they are made. When researchers reduced EGFR or MAP2K1 using gene-silencing constructs, or increased NFE2L2 with an overexpression vector, PCP-induced invasion was partially suppressed in both cell lines. The partial nature of the rescue indicates that additional pathways are likely involved.

The findings do not establish that PCP exposure causes bladder cancer or that it will make a tumor more aggressive in every exposed person. The experiments used two established cell lines and an acute 24-hour exposure, conditions that cannot reproduce the genetic diversity of human tumors, long-term low-dose exposure or the interactions among cancer cells, immune cells and normal bladder tissue. The patient datasets also lacked information about individual PCP exposure, meaning that the three-gene signature is prognostic rather than a validated exposure-specific biomarker. Finally, the molecular machinery responsible for the altered protein stability remains unknown. Nevertheless, the study provides a mechanistic bridge between an environmental pollutant and a distinct malignant behavior: at concentrations compatible with those measured in some people, PCP enhanced bladder-cancer-cell invasion without increasing proliferation or general migration. Because drugs targeting EGFR and MAPK-pathway components already exist, the results may eventually help guide research into exposure-aware treatment strategies, while reinforcing the importance of controlling persistent environmental contaminants.