Phenylacetate is a naturally occurring plasma component that suppresses the growth of
tumor cells and induces differentiation in vitro. To evaluate the in vivo potential and preventive and therapeutic antitumor efficacy of
sodium phenylacetate against malignant
brain tumors, Fischer 344 rats (n = 50) bearing cerebral 9L
gliosarcomas received
phenylacetate by continuous s.c. release starting on the day of
tumor inoculation (n = 10) using s.c. osmotic minipumps (550 mg/kg/day for 28 days). Rats with established
brain tumors (n = 12) received continuous s.c.
phenylacetate supplemented with additional daily i.p. dose (300 mg/kg). Control rats (n = 25) were treated in a similar way with saline. Rats were sacrificed during treatment for electron microscopic studies of their
tumors, in vivo proliferation assays, and measurement of
phenylacetate levels in the serum and cerebrospinal fluid. Treatment with
phenylacetate extended survival when started on the day of
tumor inoculation (P < 0.01) or 7 days after inoculation (P < 0.03) without any associated adverse effects. In the latter group,
phenylacetate levels in pooled serum and cerebrospinal fluid samples after 7 days of treatment were in the therapeutic range as determined in vitro (2.45 mM in serum and 3.1 mM in cerebrospinal fluid). Electron microscopy of treated
tumors demonstrated marked
hypertrophy and organization of the rough endoplasmic reticulum, indicating cell differentiation, in contrast to the scant and randomly distributed endoplasmic reticulum in
tumors from untreated animals. In addition, in vitro studies demonstrated dose-dependent inhibition of the rate of
tumor proliferation and restoration of anchorage dependency, a marker of phenotypic reversion.
Phenylacetate, used at clinically achievable concentrations, prolongs survival of rats with malignant
brain tumors through induction of
tumor differentiation. Its role in the treatment of
brain tumors and other
cancers should be explored further.