Antineoplaston AS2-1 is a mixture of
sodium salts of
phenylacetic acid (PAA) and
phenylacetylglutamine (PAG) in the ratio 4:1. The uptake of both compounds has been examined in human
hepatoma cell line, Hep G-2. The accumulation of PAA was characterized by temperature sensitivity, saturability and energy dependency. Organic
anions (
probenecid, p-aminonohippuric
acid and
stilbene) inhibited PAA uptake suggesting the involvement of organic
anion system in PAA transport. PAG cellular uptake exhibited dependency on metabolic energy, since the accumulation was sensitive to lowered temperature as well as to replacement of
sodium ions by
choline in the incubation medium. In contrast, the process showed tolerance to
lithium ions as a substitute to
sodium ions. This finding, together with the strong inhibition of PAG accumulation by
histidine and
glutamine, indicates that system N, known to be specific for hepatic tissue and the
glutamine-preferring
amino acid transport system, mediates PAG uptake. We conclude that PAG, through competition with
glutamine for the same membrane carrier, may reduce
glutamine transport leading to intracellular
glutamine depletion. The physiological consequence of this biochemical event could be critical to
cancer cells and therefore might contribute to the mechanism of
antineoplaston AS2-1 action.