Toxicity of the Protein Kinase C Inhibitor Safingol Administered Alone and in Combination with Chemotherapeutic Agents

Safingol [(2S,3S)-2-amino-1,3-octadecanediol] potentiates thetoxicity of doxorubicin (DOX) and cisplatin (CIS) against tumorcells in vitro and in vivo. The present studies were conductedin rats and dogs to evaluate safingol toxicity when administerediv as a single agent and to evaluate safingol's ability to potentiatethe toxicity of established chemotherapeutic agents to normaltissues in vivo. In an escalating dose study, dogs were administeredsafingol iv at 5, 10, 20, 30, 40, and 75 mg/kg on Days 1 through6. Necropsies were performed on Day 7. Red urine was observedat 10 mg/kg and higher. Icterus was observed following 40 mg/kgwith additional signs of hypoactivity and anorexia occurringafter 75 mg/kg. Clinical and microscopic pathology revealedmarked hepatotoxicity, venous degeneration and necrosis at injectionsites, and evidence of intra-vascular hemolysis. Doses of 5,20, or 40 mg safingol/kg were utilized in single iv dose ratand dog studies. No evidence of adverse systemic toxicity wasseen up to 20 mg/kg in either species [for rats: C_max = 12,600(males) or 17,133 (females) ng/ml, AUC = 3853 (males) or 4365(females) ng x hr/ml; for dogs: C_max = 2533 ng/ml, AUC = 2851ng x hr/ml (no sex differences)]. Local effects of venous irritationor intravascular hemolysis were observed at all doses in ratsand at 20 and 40 mg/kg in dogs. A dose of 40 mg/kg [for rats:C_max = 31,233 (males) or 91,300 (females) ng/ml, AUC = 11,519(males) or 18,620 (females) ng x hr/ml; for dogs: C_max = 9033ng/ml, AUC = 11,094 ng x hr/ml (combined sex)] was associatedwith clinical pathologic and renal histomorphologic changesconsidered consequent to intravascular hemolysis in both species,lethality and testicular toxicity in rats, and clinical biochemicalchanges indicative of hepatobiliary injury in dogs. Studiesindicated that hemolysis occurred during infusion, was not causedby circulating levels of safingol, and was a function of doseconcentration and vein of delivery. Safingol at 10 or 20 mg/kgwas administered iv to rats 30–60 min prior to myelosuppressiveiv doses of DOX, CIS, or cyclophosphamide (CYP). Hematology,plus renal function and morphology for CIS-treated animals,was assessed 4 and 14 days later. Safingol did not potentiateDOX-, CIS-, or CYP-mediated leukopenia/thrombocytopenia. A minimalenhancement of CIS-mediated decrease in GFR and increase increatinine was observed at 20 mg safingol/kg. Dogs were administered20 mg safingol/kg iv followed 60 min later by 0.5 or 1.25 mgDOX/kg or 0.75 or 2.0 mg CIS/kg. A complete toxicologic assessment4 and 29 days postdose failed to show potentiation of DOX toxicityby safingol or vice versa. A renal lesion was inferred in dogsadministered 20 mg/kg safingol and 2 mg/kg CIS based on minimalto slight renal tubular regeneration observed 4 weeks post-treatment.There were no effects of safingol on the pharmacokinetic profilesof DOX or CIS or vice versa.