Development of a resistance-like phenotype to sorafenib by human hepatocellular carcinoma cells is reversible and can be delayed by metronomic UFT chemotherapy.

Acquired resistance to antiangiogenic drugs, such as sorafenib, is a major clinical problem. We studied development of a resistance to sorafenib in new preclinical models of human hepatocellular carcinoma (HCC) along with a strategy to delay such resistance--combination with metronomic chemotherapy. Three different xenograft models were studied using human Hep3B HCC cells, which are highly responsive to sorafenib, namely, orthotopic and subcutaneous transplant in severe combined immunodeficient mice, and an orthotopic transplant in nude mice. The complementary DNA for the β-subunit of human choriogonadotropin was transfected into HCC cells, and urine levels of the protein were monitored as a surrogate of tumor burden. Extended daily treatments, sometimes interrupted by a break period of 3 to 7 days to allow recovery from toxicity at sorafenib doses of 30 to 60 mg/kg, were maintained until and after evidence of tumor relapse. Initially responsive tumors seemed to develop a resistance-like phenotype after long-term daily treatment (e.g., >42 days) at doses of 30 to 60 mg/kg. Transplantation of cell lines established from progressing tumors into new hosts showed that the resistant phenotype was not propagated. Furthermore, a regimen of daily metronomic uracil + tegafur (UFT, an oral 5-fluorouracil prodrug) chemotherapy with a less toxic regimen of sorafenib (15 mg/kg per day) significantly delayed the onset of resistance (>91 days). In conclusion, development of a resistance-like phenotype to sorafenib is reversible, and metronomic UFT plus sorafenib may be a promising and well-tolerated treatment for increasing efficacy by delaying emergence of such resistance.