CXCR4 inhibition by T22 potentiates cyclophosphamide in reducing established lung metastases of CXCR4-luc-B16 melanoma in vivo. CXCR4-luc-B16 cells (4 × 105 per mouse) were injected via tail vein of C57BL/6 mice (n = 5 per treatment group). Mice were euthanized on day 14 to measure luciferase activity in lungs. A, on day 5, the indicated doses of cyclophosphamide were administered i.p. to mice. B, in addition to cyclophosphamide treatment at 100 mg/kg on day 5, some of the mice were also treated with T22 40 μg (or the nonactive control peptide ALA, 40 μg) i.p. daily on day 4 to 7. Representative of three or more independent experiments. Luciferase activity is shown in relative light units.