Palifosfamide, the
DNA-alkylating metabolite of
ifosfamide (IFOS), has been synthesized as a stabilized tris or
lysine salt and found to have preclinical and clinical antitumor activity. Stabilized
palifosfamide overcomes limitations of IFOS because of patient-to-patient variability in response resulting from variable
prodrug activation, resistance and toxicities of metabolic byproducts,
acrolein and
chloroacetaldehyde.
Palifosfamide represents an effective alternative to IFOS and other
DNA-alkylating
prodrugs. The antitumor activities of stabilized
palifosfamide were investigated in vivo. Dose response, route and schedule of administration, and interaction with
docetaxel or
doxorubicin were investigated in NCr-nu/nu mice bearing established orthotopic mammary MX-1
tumor xenografts. Oral activity was investigated in P388-1
leukemia in CD2F1 mice. Oral and intraperitoneal bioavailabilities were compared in Sprague-Dawley rats. Stabilized
palifosfamide administered by optimized regimens suppressed MX-1
tumor growth (P<0.05) by greater than 80% with 17% complete antitumor responses and up to three-fold increase in time to three
tumor doublings over controls. Median survival in the P388-1 (P<0.001) model was increased by 9 days over controls. Oral bioavailability in rats was 48-73% of parenteral administration, and antitumor activity in mice was equivalent by both routes. Treatment with
palifosfamide-tris combined with
docetaxel or
doxorubicin at optimal regimens resulted in complete
tumor regression in 62-75% of mice. These studies support investigation of stabilized
palifosfamide in human
cancers by parenteral or
oral administration as a single agent and in combination with other approved drugs. The potential for clinical translation of the cooperative interaction of
palifosfamide-tris with
doxorubicin by
intravenous administration is supported by results from a recent randomized Phase-II study in unresectable or metastatic
soft-tissue sarcoma.