Motoyuki Kataoka

Pronounced antitumor effect of LAK-like cells induced in the peritoneal cavity of mice after intraperitoneal injection of OK-432, a killed Streptococcal preparation

SummaryMore than 80% of BALB/c mice bearing BAMC-1 ascites tumor were completely cured after five consecutive (once every 2 days) i. p. injections of a 0.1 mg dose of OK-432, beginning on day 2 after tumor implantation. The antitumor effect of OK-432 was abolished in athymic nu/nu mice and in anti-thymocyte globulin-treated euthymic BALB/c mice, so although OK-432 treatment did increase the length of survival, all animals eventually died as a result of tumor growth. When peritoneal exudate cells (PEC), obtained on day 12 from OK-432-treated BAMC-1-bearing euthymic mice were evaluated for in vivo tumor neutralization activity, all mice receiving an i. p. injection of the admixture of the nonadherent PEC (1×107 cells) with BAMC-1 cells (1×105) survived for more than 60 days. When the same nonadherent PEC (1×107 cells) were i. p. transferred adoptively 1 day after the inoculation of 1×105 BAMC-1 tumor cells, again all mice survived.When these in vivo active PEC were tested for cytotoxicity in vitro against fresh BAMC-1 tumor cells, natural killer (NK) sensitive syngeneic RL ♂ 1, NK-sensitive allogeneic YAC-1 cells, NK-resistant syngeneic Meth-A cells, allogeneic tumor cells (EL4, B16, and P815) and xenogenic human cells, the PEC were found to be capable of lysing BAMC-1 tumor cells together with almost all of the other tumor cells, including NK-resistant cells. Nonadherent PEC contained at least two subpopulations of killer cells. One, directed to syngeneic BAMC-1 cells, was both Thy1.2 and asialo GM1 positive, and another, directed to allogeneic YAC-1 cells, was asialo GM1 positive but Thy1.2 negative. A cold target inhibition assay also suggested the presence of more than two subpopulations.These results indicate that T cells play a determined role in the immunotherapeutic effect of OK-432 on BALB/c mice bearing BAMC-1 tumor, although the participation of activated macrophages could not be excluded. The cells responsible for killing BAMC-1 and other tumor cells appearing in the PEC on day 12 were characterized as containing at least two kinds of lymphokine-activated killer cells.

Effect of erythropoietin on human tumor growth in xenograft models

Recombinant human erythropoietin (rhEPO) has been used in the EU and the United States for the treatment of anemia in cancer patients after myelosuppressive chemotherapy or radiotherapy. However, several conflicting results have been reported concerning the detrimental effect of rhEPO on survival benefit in cancer patients. In experimental studies, contradictory results were also reported in in vitro tumor cell proliferation studies and in vivo tumor growth studies using tumor cells expressing EPO-receptor (EPO-R). Therefore, we tried to clarify the effect of epoetin β, a product of rhEPO, on tumor growth in xenograft models using five EPO-R-positive human cancer cell lines, namely the MCF7 breast, 786-O renal, SCH gastric, A549 lung and SK-OV-3 ovarian cancer cell lines. Epoetin β was administered once a week for 3 weeks at doses of 1,000, 3,000 and 10,000 IU/kg in accordance with the clinical administration schedule and dosages. As a result, no enhancement of tumor growth from the administration of epoetin β was observed in any of the xenograft models throughout the experiment duration. The effect of epoetin β on the antitumor activity of bevacizumab, an anti-angiogenic agent, was additionally examined using A549 and MCF7 xenograft models, since rhEPO reportedly stimulates tumor neovascularization. Epoetin β showed no significant effect on the antitumor activity of bevacizumab in either xenograft model. These findings suggest that epoetin β is not involved in in vivo tumor growth promotion.

Analysis of antitumor effects of OK-432 against syngeneic mouse fibrosarcoma: Combination effect of OK-432 and recombinant lymphokines

OK-432, a streptococcal preparation with potent biological response modifying activities, had the ability to cure mice bearing BAMC-1 (fibrosarcoma) ascites when it was injected intraperitoneally five times, 2, 4, 6, 8, and 10 days after the tumor inoculation. Previously, it was shown that the OK-432 injection on day 2 was indispensable since only a minimal antitumor effect was obtained when an inflammation-inducing agent such as thioglycolate instead of OK-432 was injected on day 2, followed by four OK-432 injections on days 4, 6, 8 and 10. In the present study, the injection of OK-432 on day 2 and a subsequent injection of either IL-2 or IFN-gamma on day 4 or 6 showed a significant antitumor effect, achieving a complete cure in approximately 50% of mice treated, although none of the mice could be cured by a single injection of either OK-432, IL-2, or IFN-gamma on day 2. Interestingly, however, the mice treated with an injection of a lymphokine (IL-2 or IFN-gamma) on day 2 followed by OK-432 on day 4 were not cured either. Peritoneal cells on day 12 in mice treated with OK-432 and either of the lymphokines contained pantropic killer cells, which were Thy-1+ and asialo GM1+ (AsGM1+). Moreover, the antitumor effect of the combined treatment was abolished when mice were pre-treated with anti-AsGM1. No significant antitumor effect was observed in athymic nu/nu mice. Together with our previous findings, these results indicate that lymphokines induced by OK-432 administration may account for some of its therapeutic effects and that these lymphokines may also facilitate the subsequent induction of specific killer cells. These results warrant further investigation on possible effective therapeutic protocols with the combined use of OK-432 and lymphokines.

Search for immunobiological parameters predictive of clinical effects of OK-432 in patients with malignant ascites

Although OK-432, a potent BRM, has been known to induce the remarkable improvement of clinical conditions in cancer patients through its strong effects on their immune capabilities, no specific immune parameters have been identified to best predict the clinical outcome after the OK-432 treatment. In an attempt to identify early parameters indicative of the clinical effects, we have administered 0.1 mg of OK-432 intraperitoneally to a total of 12 patients with malignant ascites and examined peritoneal fluid and peripheral blood obtained on 4 days before, 1, 3, and 7 days after the OK-432 injection using various immunobiological assays. Four weeks later, clinical improvements were evaluated by the disappearance of malignant cells from and/or substantial decrease in ascites. Four patients (responders) showed the improvements while 8 patients (nonresponders) showed no clinical evidence for improvement. In a few parameters among the many examined, significantly different patterns of changes were noted between responders and nonresponders. Thus, in nonresponder patients MØ and T cell population returned to an initial low level after early increases (on days 1 and/or 3), while they remained increased day 1 through 7 in responders. In responder patients, the cytotoxicity of peritoneal mononuclear cells against K562 and Daudi cells were augmented on day 7, but not in nonresponder patients. Thein vitro stimulation of the mononuclear cells with OK-432 enhanced the cytotoxic activity and induced the interferon (IFN) production in the responders but not in nonresponders. These parameters will be useful for the early prediction of the expected clinical effects of OK-432.