[Antitumor effect of PSK (1). Interferon-inducing activity and intratumoral administration]

After oral administration of 20 mg/kg of PSK, a significant level of interferon (IFN) activity was detected in the sera of BCG (1 mg/mouse)-sensitized mice. A low titer of IFN was also detected in the sera of all of 4 cancer patients after 3 g/day oral administration of PSK for 7 consecutive days. Intratumoral administration of PSK (5 mg/mouse) strongly inhibited the growth of Meth-A solid tumors in male BALB/c mice and led to complete regression of tumors and resistance to reinoculated tumors in the host animals. Subsequently, the antimetastatic effect of PSK was examined in a "double grafted tumor system" in which mice first received simultaneous intradermal inoculations of Meth-A in the right (10(6) cells) and left (2 X 10(5) cells) flanks and were then injected with PSK in the right tumor on day 3. PSK significantly inhibited the growth of the left, non-treated tumor. When mice received an inoculation of Meth-A (2 X 10(5) cells) in the left flank and PSK was injected subcutaneously in the right flank on day 3 (single tumor system), the growth of the tumor was not inhibited. These findings suggest that intratumoral PSK immunotherapy in one region has an effect on tumor growth in another region.