Organotin compound DBDCT induces CYP3A suppression through NF-κB-mediated repression of PXR activity

Area of Science:

• Pharmacology
• Molecular Biology
• Biochemistry

Background:

• Organotin compounds, like di-n-butyl-di-(4-chlorobenzohydroxamato)tin(iv) (DBDCT), are investigated for anticancer properties.
• DBDCT is known to inhibit cytochrome P450 3A (CYP3A), a key drug-metabolizing enzyme.
• The precise mechanisms of DBDCT's regulation of CYP3A, particularly involving nuclear receptors like pregnane X receptor (PXR) and constitutive androstane receptor (CAR), and transcription factors like NF-κB, are not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying DBDCT-mediated suppression of CYP3A.
• To investigate the roles of PXR, CAR, and NF-κB pathways in DBDCT's effects on CYP3A expression.

Main Methods:

• Dual luciferase reporter gene assays were used to assess transcriptional activity.
• Electrophoretic mobility shift assays (EMSA) were employed to study protein-DNA interactions.
• RNA interference (RNAi) and gene silencing techniques were utilized.
• Experiments were conducted in both NF-κB wild-type and knockout cells.

Main Results:

• DBDCT suppressed CYP3A expression, partly by inhibiting CAR.
• DBDCT increased both protein and mRNA levels of PXR.
• DBDCT induced CYP3A expression via PXR activation, but this was counteracted by NF-κB activation.
• NF-κB activation disrupted the PXR-RXRα complex binding to DNA, leading to CYP3A suppression.
• DBDCT-induced CYP3A reduction was observed only in NF-κB(+/+) cells, not in NF-κB(-/-) cells.
• NF-κB p65 activation directly contributed to CYP3A inhibition by interfering with PXR.

Conclusions:

• DBDCT activates NF-κB, which directly interacts with PXR's DNA-binding domain.
• This interaction disrupts the PXR-RXR dimer complex, inhibiting PXR-mediated CYP3A transcription.
• The study reveals a complex regulatory interplay where NF-κB activation by DBDCT overrides PXR-mediated induction of CYP3A, ultimately leading to CYP3A suppression.