Extreme low dose of 5-fluorouracil reverses MDR in cancer by sensitizing cancer associated fibroblasts and down-regulating P-gp

We conducted a prospective, meaningful study of extreme low dose of 5-fluorouracil (5FU) as a metronomic agent targeting cancer associated fibroblasts (CAFs) to reverse Multidrug resistance (MDR) by sensitizing cancer associated fibroblasts and down-regulating P-glycoprotein (P-gp). The combination of 5FU and Taxol inhibited resistant KB-8-5 tumor growth by 79% and H460/Tax-R tumor growth by 55%. The inhibition was significant for both tumor types compared with Taxol treatment alone (p<0.001 and p = 0.0067, respectively). Nevertheless, the low-dose 5FU (2.2 mg/kg compared to the therapeutic dose of 50–150 mg/kg) showed negligible tumor inhibitory effect. The tumor growth inhibition study on resistant tumors demonstrated that the continuous administration of low dose 5FU with Taxol significantly inhibited the tumor growth. The treatment overcomes drug resistance in tumors by down-regulating multi-drug resistance transporter protein (P-gp), and more importantly, by eliminating CAFs recruited by resistant tumors. Compared with traditional metronomic chemotherapy, 5FU as metronomic agent targeting CAFs can avoid the disadvantages resulted from the concomitant administration of antiangiogenetic drug. The approach has good translational potential for clinical trials when treating stroma-rich drug resistant tumors.