Palifosfamide (Isophosphamide mustard) lysine (ZIO-201) is a stable form of palifosfamide. Palifosfamide lysine has broad activity in sarcoma lines in vitro. The IC50 ranges from 2.25 to 6.75 μM for most cell lines except OS222 (IC50=31.5 μM).

OS222:31.5 μM

Differential gene expression of ALDH3A1 but not ALDH1A1 is noted in the OS31 xenograft. Stabilized palifosfamide administered to mice suppresses MX-1 tumor growth by greater than 80% with 17% complete antitumor responses. Oral bioavailability in rats is 48-73% of parenteral administration, and antitumor activity in mice is equivalent by both routes. Treatment with palifosfamide-tris combined with docetaxelor doxorubicin at optimal regimens results in complete tumor regression in 62-75% of mice.

Palifosfamide is dissolved in phosphate buffered saline (PBS). Cells are plated in 96-well microtiter plates with approximately 500 cells per well in 100 μL of media. After 24 h of incubation at 37°C, cells are treated with increasing concentrations of palifosfamide lysine in separate plates either as a single-day treatment or three consecutive days of treatment, with fresh drug being added each day. The plates are incubated for 72 h at 37°C with 5% CO2. After 72 h, 250 μg of MTT is added to each well and incubated at 37°C for 6 h. MTT is converted to formazine crystals by mitochondria of viable cells, which are then dissolved in 100 μL of dimethyl sulfoxide. Optical density is measured at 595 nm.

Mouse: CB17 female SCID mice are used in the study. Once the tumors reached 50–150 mm3, mice are randomized into control and treatment groups (5-8 mice/group) for each tumor line. Cyclophosphamide is administered at the dose of 150 mg/kg intraperitoneally once a week for 6 weeks. Palifosfamide lysine is administered intravenously at the maximum tolerated dose of 100 mg/kg for three consecutive days as a one-time treatment and serial tumor volumes are determined over the next 6 weeks. Mice are sacrificed at the end of the experiment.