Raf-1
protein serine threonine kinase plays an important role in cell survival and proliferation. Antisense inhibition of Raf-1 expression has been shown to enhance the cytotoxic effects of radiation and anticancer drugs. Here we have evaluated the toxicity, pharmacokinetics, and antitumor efficacy of a novel formulation of
liposome-entrapped raf
antisense oligodeoxyribonucleotide (
LErafAON). The
LErafAON preparation showed high
liposome entrapment efficiency of rafAON (>85%) and stability at room temperature. In CD2F1 mice, administration of
LErafAON produced no morbidity/mortality (5-35 mg/kg/dose, i.v., x12). Dose-related elevations in liver
enzymes (
alanine aminotransferase and
aspartate aminotransferase) and histopathological changes in liver were noted in
LErafAON and blank
liposome groups. No morbidity/mortality and changes in clinical chemistry or histopathology were observed in New Zealand white rabbits (3.75 mg/kg/dose, i.v., x8; 6.5 mg/kg/dose, i.v., x6) or in cynomolgous monkeys (3.75 or 6.25 mg/kg/dose, i.v., x9). Transient decrease in total
hemolytic complement activity (approximately 62-74%) and increases in C3a (approximately 3-fold) and Bb levels (approximately 5-12-fold) were observed in
LErafAON and blank
liposome groups of monkeys. A 30 mg/kg i.v. dose of
LErafAON in human prostate
tumor (PC-3)-bearing BALB/c athymic mice gave a terminal plasma half-life of 27 h, and intact rafAON could be detected in plasma and in normal and
tumor tissues for up to at least 48 h. In monkeys, the terminal plasma half-life of 30.36 +/- 23.87 h was observed at an i.v. dose of 6.25 mg/kg.
LErafAON (25 mg/kg/dose, i.v., x10) or ionizing radiation (3.8 Gy/day, x5) treatment of PC-3
tumor-bearing athymic mice led to
tumor growth arrest, whereas a combination of
LErafAON and ionizing radiation treatments resulted in
tumor regression.
LErafAON treatment caused inhibition of Raf-1
protein expression in normal and
tumor tissues in these mice (>50%, versus controls). These data have formed a basis of the clinical Phase I studies of
LErafAON for
cancer treatment.