Taxol-oligoarginine conjugates overcome drug resistance in-vitro in human ovarian carcinoma.

OBJECTIVE: Multidrug resistance is the major cause of failure of many chemotherapeutic agents. While resistance can arise from several factors, it is often dominated by drug efflux mediated by P-glycoprotein (P-gp), a membrane-bound polysubstrate export pump expressed at high levels in resistant cells. While co-administration of pump inhibitors and a drug could suppress efflux, this two-drug strategy has not yet advanced to therapy. We recently demonstrated that the reversible attachment of a guanidinium-rich molecular transporter, polyarginine, to a drug provides a conjugate that overcomes efflux-based resistance in cells and animals. This study is to determine whether this strategy for overcoming resistance is effective against human disease. METHODS: Tumor samples from ovarian cancer patients, both malignant ascites cells and dissociated solid tumor cells, were exposed to Taxol-oligoarginine conjugates designed to release free drug only after cell entry. Cell viability was determined via propidium-iodide uptake by flow cytometry. To analyze bystander effect, toxicity of the drug conjugates was also tested on peripheral blood leucocytes. RESULTS: Human ovarian carcinoma specimens resistant to Taxol in vitro demonstrated increased sensitivity to killing by all Taxol-transporter conjugates tested. These studies also show that the drug conjugates were not significantly more toxic to normal human peripheral blood leukocytes than Taxol. CONCLUSIONS: These studies with human tumor indicate that oligoarginine conjugates of known drugs can be used to overcome the efflux-based resistance to the drug, providing a strategy that could improve the treatment outcomes of patients with efflux-based drug-resistance.