Augmentation of tumor immunity in mice by intralesional injection of vitamin A.

We investigated the antitumor effect of vitamin A(VA) using the double grafted tumor technique to examine whether VA administered into a primary tumor (intralesionally or i.l.) accelerates antitumor immune reactions so that growth of the secondary tumor may be more effectively inhibited than by other systemic administration routes. In the double grafted tumor system, where BALB/c mice were inoculated with MethA fibrosarcoma cells into the right inguinal region (1 x 10[6] cells) on day 0 and later into the left (3 x 10[6] cells) on day 10, the injection of VA at a dose of 1000 IU/mouse i.l., s.c., i.p., and i.v. on days 3 through 7 inhibited the growth of the secondary tumor to the same extent, while VA at the i.l. dose of 100 IU/mouse into the primary tumor inhibited more effectively than by any other administration route. VA did not inhibit the secondary MethA growth in BALB/c (nu/nu) mice. The spleen cells taken from VA-treated tumor-bearing mice prevented the growth of MethA tumors in naive BALB/c mice when given as a mixture with the MethA inoculum (the Winn assay). The delayed-type hypersensitivity (DTH) response to methylated bovine serum albumin (MBSA) antigen was augmented when VA (1000 IU) was injected at the site of the antigen injection. These results suggest that the direct interaction of VA with the tumor cells may be necessary for the tumor immunity-potentiating effect of VA, and that T-lymphocyte-mediated tumor immunity is involved in the anti-tumor effect of VA. The antitumor mechanism of VA seems to involve retinoid receptors, because the benzoic acid derivative Am80, which has been reported to exert retinoidal activity by binding to specific retinoid receptors, also showed activity.

Augmentation of sinecomitant immunity in mice by gamma-(9H-purine-6-yl)thiomethyl L-glutamate (6-MPG), a water-soluble derivative of 6-mercaptopurine.

Effects of the administration of gamma-(9H-purine-6-yl)thiomethyl L-glutamate (6-MPG), a water-soluble derivative of 6-mercaptopurine, on concomitant and sinecomitant immunity against the implanted MethA tumor were studied in BALB/c mice. In the concomitant immunity experiments, mice were intradermally inoculated with 1x10(5) MethA cells at the right inguinal region on day 0. In sinecomitant immunity experiments, mice were similarly inoculated on day -21, and the grown tumor was excised on day -11. Both the tumor-bearing and tumor-ectomized animals were re-inoculated with 3x10(6) MethA cells intradermally at the left inguinal region on day 10. Administration of 6-MPG (100 mg/kg, i.p.) on days 3 through 7 significantly inhibited growth of the re-inoculated tumor in both series of experiments. Cyclophosphamide, adriamycin, mitomycin C and cis-diamminedichloroplatinum (II) had no significant effect on the growth of the re-inoculated tumor in the tumor-ectomized mice. Spleen cells harvested from the 6-MPG-treated tumor-ectomized mice showed a strong tumor-neutralizing activity (Winn assay).

Study on the mechanism of immunopotentiating antitumor effect of 6-MPG, a water-soluble derivative of 6-mercaptopurine.

We investigated possible mechanisms of the antitumor action of gamma-(9H-purine-6-yl) thiomethyl L-glutamate (6-MPG), a water-soluble derivative of 6-MP. In the double grafted tumor system, BALB/c mice were inoculated intradermally with 10(6) cells of MethA fibrosarcoma at the right inguinal region on day 0 (the primary tumor) and later with 3 x 10(6) cells at the left on day 10 (the secondary tumor). Intraperitoneal administration of 6-MPG at a dose of 100 mg/kg/day from day 3 through 7 completely prevented growth of the secondary tumor. 6-MPG showed no effect on growth of colon 26 adenocarcinoma cells inoculated in place of the secondary MethA cells (antigen specificity). 6-MPG did not inhibit the secondary MethA growth in the BALB/c (nu/nu) mouse. The inhibitory effect of 6-MPG on the secondary tumor growth was diminished by prior treatment of the primed animals with cyclosporin A and anti-Thy antibody. Spleen cells from the tumor-bearing mice treated with 6-MPG showed a tumor-neutralizing activity (Winn assay). Treatment of the spleen cells with anti-CD8 antibody plus complement diminished the tumor-neutralizing effect but that with anti-CD4 antibody plus complement did not, indicating that CD8-positive cells are responsible for potentiation of the tumor immunity. These results suggest that the antitumor effect of 6-MPG against the secondary tumor is elicited by augmenting tumor specific T-cell production.

Augmentation of tumor immunity by 6-MPG, a water-soluble derivative of 6-mercaptopurine, in mice.

Inhibitory effects on some immunological responses and MethA fibrosarcoma in the double grafted tumor system in mice were compared between 6-mercaptopurine (6-MP) and its novel water-soluble derivative, gamma-(9H-purine-6-yl)thiomethyl L-glutamate (6-MPG). The dose-dependent inhibitory effects by 6-MPG on the hemagglutinin response to SRBC, DTH reaction to MBSA, contact sensitivity to oxazolone, GVH response and growth of the primary tumor were 3-10 times weaker than those by 6-MP, probably reflecting the difference in their cytotoxicities antimetabolites. However, the two drugs were nearly equipotent in reproducing inhibition of the secondary tumor growth, which is a host-mediated immunological response to tumor antigen as shown by its dependency on the primary inoculation with 1 x 10(4) or more MethA cells and by the production of anti-tumor splenocytes in tumor-bearing animals (the Winn assay). Thus, 6-MPG may point to the direction of derivatization towards anti-tumor immunopotentiators with an improved therapeutic index.

Augmentation of tumor immunity by 6-mercaptopurine (6-MP) and its analogs in the double grafted tumor system in mice.

We investigated the antitumor effect of 6-mercaptopurine (6-MP) and its analogs using the double grafted tumor technique. BALB/c mice were inoculated intradermally with MethA fibrosarcoma cells at the right inguinal region on day 0 (the primary tumor) and at the left on day 10 (the secondary tumor). Intraperitoneal or intra-lesional administration of 6-MP, 6-mercaptopurine riboside (6-MP-r) and 6-mercaptopurine riboside triacetate (6-MPRTA) from day 3 to 7 dose-dependently inhibited growth of the secondary tumor. Without the primary inoculation, 6-MP showed no effect on growth of the tumor inoculated on day 10, indicating that the antitumor effect of 6-MP could not be attributable to its direct antimetabolic or tumoricidal action only, and that the primary tumor inoculation is necessary for these compounds to inhibits growth of the challenging tumor. 6-MP did not inhibit the secondary MethA growth in the BALB/c (nu/nu) mouse. Both CD4+ and CD8+ T cells increased in the spleen of mice treated with 6-MP. Meanwhile, delayed-type hypersensitivity (DTH) reaction to the methylated bovine serum albumin (MBSA) antigen at the footpad was not augmented but inhibited by 6-MP-r and 6-MPRTA in both normal and tumor-bearing mice. Thus, the immunomodulatory activity of 6-MP could be observed in two opposite directions, augmentation of tumor immunity and inhibition of DTH to MBSA. This indicates that the immune mechanism and/or the type of effector cells induced in these two cell-mediated immune systems are different from each other.

Water-soluble antitumor agents. I. Synthesis and biological activity of 6-S-aminoacyloxymethyl mercaptopurine derivatives.

In an attempt to improve the effectiveness and bioavailability of 6-mercaptopurine, various kinds of water-soluble analogues, such as 6-S-aminoacyloxymethyl mercaptopurine derivatives (3a--m) and 6-S,9-disubstituted derivates (7a,b and 9a,b), were synthesized. These compounds were evaluated for activity to augment antitumor immunity by using a double grated tumor system. Antitumor activities against solid tumors (sarcoma 180 and colon 26) were also evaluated. Many compounds exhibited potent activities in both test systems. In particular, the aminopropionate derivative (3a) and the L-glutamate derivative (3f) showed significant enhancement of antitumor immunity together with potent antitumor activities.

Difference among angiotensin-converting enzyme inhibitors in potentiating effects on bradykinin-induced microvascular leakage in guinea pig airways.

We investigated the effect of imidapril, a novel angiotensin-converting enzyme (ACE) inhibitor, on augmentation of airway microvascular leakage induced by bradykinin (BK) and substance P (SP) in guinea pigs and compared it with those of enalapril and captopril. The three ACE inhibitors significantly potentiated BK- and SP-induced airway microvascular leakage in a dose-dependent manner. In spite of the compatible or higher ACE inhibitory activity of imidapril, its potentiating activity in BK-induced leakage was lower than those of enalapril and captopril both by single administration (0.3-30 mg/kg, p.o.) and repeated administration for eight days (0.1-10 mg/kg/day, p.o.). The potentiating activities of the three ACE inhibitors were suppressed by pretreatment with a BK2-receptor antagonist, but not by neurokinin 1 and neurokinin 2 antagonists, suggesting that neurokinins may not be involved in BK-induced leakage under the conditions used. On the other hand, the potentiating effect of imidapril in SP-induced leakage was weaker than those of enalapril and captopril only after single high doses. The present study shows that the ACE inhibitors have different activity in potentiation of the airway microvascular leakage induced by BK, which may be ascribable to the difference in their inhibition of BK hydrolysis. This evidence may partly explain the smaller incidence of dry cough induced by imidapril compared with other ACE inhibitors when clinically used as antihypertensive drugs.