Beyond the Very Important Pharmacogenes (VIPs): Uncovering Shadow Pharmacogenes in the Human Drug Response Network

Understanding the molecular determinants of interindividual
drug
response variability remains a major challenge in pharmacogenomics.
Very Important Pharmacogenes (VIPs), as defined by PharmGKB, represent
genes with well-established roles in drug metabolism and efficacy.
However, their activity occurs within complex molecular networks that
extend beyond direct pharmacogenetic associations. We constructed
a VIP-centered subnetwork and applied network topology analyses, including
shortest path, signal propagation, and degree centrality, to identify
key nodes mediating VIP interactions. Functional enrichment, transcription
factor (TF) association, and drug–gene interaction analyses
were subsequently performed to characterize the biological and pharmacological
context of these networks. Our results revealed a dense VIP interactome
enriched in metabolic, endocrine, and signaling pathways. Notably,
we identified a subset of highly connected non-VIP genes that frequently
bridge canonical VIPs, termed shadow VIPs. These genes, often encoding
transcriptional regulators, such as NR1I2, NR1H4, and ESR2, and more frequent in the
shortest paths connecting VIPs, such as POR, APP, and GIPC1, exhibited
strong associations with approved drugs, particularly hormone-related
and antineoplastic agents. This suggests that shadow VIPs may act
as indirect regulators of pharmacogenomic phenotypes by influencing
the expression or activity of canonical VIPs. Additionally, the analysis
revealed that shadow VIPs, on average, exhibit lower RVIS values than
VIPs, indicating a higher intolerance to functional mutations. This
suggests that shadow VIPs are under stronger selective selection,
underscoring their essential biological roles. Together, these findings
expand the current pharmacogenomic framework, demonstrating that drug
response mechanisms emerge from a wider network of regulatory and
functional interactions. Introducing the concept of shadow VIPs highlights
new molecular candidates for pharmacogenetic exploration and emphasizes
the value of network-based approaches in advancing precision medicine.