Tumor-derived Parathyroid Hormone-Related Protein Is Associated with Suppression of Cytochrome P450 Expression:...

Cancer cachexia is frequently associated with altered pharmacokinetics and increased chemotherapy toxicity due to the downregulation of cytochrome P450 (CYP) enzymes. However, the molecular mechanisms driving this broad metabolic suppression remain poorly understood. This study investigated whether tumor-derived parathyroid hormone-related protein (PTHrP) is associated with, and may contribute to, suppression of multiple CYP families. In a rat cachexia model, protein expression of CYP3A, CYP1A, CYP2C, CYP2D, and CYP2E1 was significantly downregulated in both the liver and small intestine. Consistent with these changes, pharmacokinetic analyses using a CYP substrate cocktail demonstrated markedly increased AUC and reduced clearance for probe drugs. In vitro experiments showed that PTHrP treatment reduced these CYP isoforms in primary rat hepatocytes. In human data sets, analysis of The Cancer Genome Atlas (TCGA) hepatocellular carcinoma (HCC) data set revealed a significant negative correlation between PTHrP and CYP gene expression, together with enrichment of NF-κB-related transcriptional programs. Furthermore, multimodal analysis using single-cell RNA sequencing and spatial transcriptomics demonstrated that PTHrP-high tumor regions exhibit suppressed xenobiotic metabolism. Additionally, in breast cancer liver metastases, high tumor PTHrP expression correlated with reduced CYP expression in surrounding nontumor hepatocytes, consistent with a possible paracrine relationship. Collectively, these results support an association between tumor-derived PTHrP and suppression of drug-metabolizing programs. They further suggest that PTHrP may be one contributing factor, but not definitive proof of a principal suppressor, and should therefore be considered a candidate biomarker requiring further mechanistic and clinical validation.