PARP Inhibitors as P-glyoprotein Substrates

Area of Science:

• Pharmacology and Toxicology
• Cancer Biology
• Drug Resistance Mechanisms

Background:

• Poly (ADP-ribose) polymerase (PARP) inhibitors are crucial in cancer therapy.
• P-glycoprotein (P-gp) overexpression is a common mechanism of multidrug resistance in cancer.
• Understanding PARP inhibitor interactions with P-gp is vital for optimizing treatment strategies.

Purpose of the Study:

• To investigate the cytotoxicity of PARP inhibitors (olaparib, veliparib, CEP-8983) in P-gp overexpressing drug-resistant cell models.
• To determine if olaparib, veliparib, and CEP-8983 are substrates of P-gp.
• To evaluate the potential of veliparib and CEP-8983 in combination chemotherapy for resistant cancers.

Main Methods:

• Cytotoxicity assays were performed on two P-gp overexpressing drug-resistant cell lines (IGROVCDDP and KB-8-5-11).
• The effect of P-gp inhibitors (elacridar, zosuquidar, valspodar) on olaparib resistance was assessed.
• Protein expression levels of P-gp were analyzed after treatment with PARP inhibitors.

Main Results:

• Both IGROVCDDP and KB-8-5-11 cells exhibited resistance to olaparib, which was reversed by P-gp inhibitors.
• Veliparib and CEP-8983 did not show cross-resistance in these P-gp overexpressing models.
• Olaparib was identified as a P-gp substrate, while veliparib and CEP-8983 did not appear to be P-gp substrates.

Conclusions:

• Olaparib's efficacy is limited by P-gp mediated efflux in resistant cell lines.
• Veliparib and CEP-8983 are not substrates of P-gp, suggesting potential utility in combination therapies.
• Veliparib and CEP-8983 may be effective in treating platinum and taxane-resistant ovarian cancers.