Susceptibility of Naegleria fowleri to delta 9-tetrahydrocannabinol.

Growth of the pathogenic amoeboflagellate Naegleria fowleri is inhibited by delta 9-tetrahydrocannabinol (delta 9-THC). delta 9-THC is amoebostatic at 5 to 50 micrograms/ml. delta 9-THC prevents enflagellation and encystment, but does not impair amoeboid movement. Calf serum at 10 and 20% (vol/vol) reduces the antiamoeba activity of delta 9-THC. Only 1-methoxy delta 8-tetrahydrocannabinol, of 17 cannabinoids tested, failed to inhibit growth of N. fowleri. Antinaeglerial activity was not markedly altered by opening the pyran ring, by converting the cyclohexyl ring to an aromatic ring, or by reversing the hydroxyl and pentyl groups on the benzene ring. delta 9-THC prevented the cytopathic effect of N. fowleri on African green monkey (Vero) cells and human epithelioma (HEp-2) cells in culture. delta 9-THC afforded modest protection to mice infected with N. fowleri.