Specific cytotoxic effect of neocarzinostatin conjugated to monoclonal antibody A7 on human pancreatic carcinoma

Application of 99mTc labeled chimeric Fab fragments of monoclonal antibody A7 for immunoscintigraphy of pancreatic carcinoma

BACKGROUND

One of the reasons for the poor prognosis of pancreatic carcinoma is the difficulty of obtaining an early diagnosis of pancreatic carcinoma. One possibility is the application of radioimmunoscintigraphy using radiolabeled monoclonal antibodies (Mabs).

METHODS

We labeled chimeric (human/mouse) Fab fragments of Mab A7 (chA7Fab) with (99m)Tc and examined the distribution of (99m)Tc-labeled chA7Fab in nude mice bearing human pancreatic carcinoma.

RESULTS

The tumor accumulation of (99m)Tc-labeled chA7Fab was larger than that of (99m)Tc-labeled A7 from 2 to 6 hr after injection. (99m)Tc-labeled chA7Fab disappeared from blood more rapidly than (99m)Tc-labeled A7. For all resected normal tissues except kidney, the accumulation of (99m)Tc-labeled chA7Fab was low and similar to that of (99m)Tc-labeled A7.

CONCLUSIONS

Because the half-life of (99m)Tc is short (6 hr), chA7Fab, which accumulates rapidly in tumors, may be a better carrier of (99m)Tc than intact Mab A7.

Changes in expression of the antigen recognized by monoclonal antibody A7 in human pancreatic carcinoma cells following exposure to anticancer agents

Techniques which can increase the expression level of tumor-associated antigens may improve immunotargeting therapy. We studied the reactivity of MAb A7 toward an antigen expressed on the surface of the human pancreatic cancer cell line HPC-YS after treatment with various antitumoral agents. When we applied 1 microg/ml mitomycin C (MMC) or 0.1 microg/ml neocarzinostatin (NCS) for 1 h, A7 recognizing antigen expression was enhanced until 24 h after the treatments. At a dose that completely suppressed cell growth, increased antigen expression was maintained for 96 h. Therefore, this study suggests that the combined application of an anticancer drug and MAb A7 may be useful for immunotargeting chemotherapy.

Distribution of neocarzinostatin conjugated to biotinylated chimeric monoclonal antibody Fab fragments after administration of avidin

We have developed chimeric Fab fragments of MAb A7 (chA7Fab) and have reported on their potential usefulness as a carrier of neocarzinostatin (NCS). However, a large amount of chA7Fab accumulates in the kidneys which might cause renal failure. This was one of the major side-effects of the chA7Fab-NCS immunoconjugate administered to humans. To decrease the kidney accumulation of chA7Fab, chA7Fab was biotinylated and administered with a subsequent injection of avidin to nude mice with pancreatic cancer. The accumulation of biotinylated chA7Fab in the blood and the kidneys decreased significantly after the injection of avidin. In a separate experiment with biotinylated chA7Fab-NCS, the blood and kidney accumulation decreased significantly after the injection of avidin. These findings suggest that the injection of biotinylated chA7Fab complexed with NCS followed by avidin may be safer and may permit the administration of larger doses of NCS without the subsequent development of renal failure.

Effects of neocarzinostatin-chimeric Fab conjugates on the growth of human pancreatic carcinoma xenografts

Neocarzinostatin (NCS) was bound covalently to human/mouse chimeric Fab fragments of MAb A7 (chA7Fab) directed against human pancreatic carcinoma. The anti-tumour effect of chA7Fab-NCS was tested in a nude mouse model on pancreatic carcinoma and compared with A7-NCS or NCS alone. The anti-tumour effect of chA7Fab-NCS increased in a dose-dependent manner and was significantly greater than either A7-NCS or NCS. Tumour growth was completely suppressed after the administration of chA7Fab-NCS. An enzyme-linked immunosorbent assay with rabbit anti-mouse immunoglobulin was performed to examine the antigenicity of chA7Fab. ChA7Fab had less reactivity with rabbit anti-mouse immunoglobulin than either whole antibody A7 or murine Fab fragments of A7. Thus, chA7Fab-NCS can inhibit human pancreatic cancer growth in an animal and may be useful for targeting chemotherapy to pancreatic cancer in humans.

Applicability of monoclonal antibody Fab fragments as a carrier of neocarzinostatin in targeting chemotherapy

Two types of fragments of MAb A7 were produced to improve the efficacy and safety in targeting chemotherapy with neocarzinostatin. In this study, 125I-labeled F(ab')2 and Fab fragments of MAb A7 and 125I-labeled MAb A7 were injected intravenously into mice with pancreatic carcinoma xenografts, and the accumulation of each antibody in the tumors was compared. A greater amount of the 125I-labeled Fab fragments of MAb A7 localized in the tumor 2 h following the injection than was observed with the other probes. Relatively less 125I-labeled MAb A7 localized in the tumor 2 h following the injection than was observed with the other two probes. Moreover, reaction of rabbit antimouse IgC with the Fc portion, which is the most immunopotent region of the Fab and F(ab')2 fragments of MAb A7 and MAb A7, was determined by ELISA; the weakest reaction was observed with the Fab fragments of MAb A7. These results suggest that the Fab fragments of MAb A7 may be more suitable carriers of an anticancer drug that is inactivated rapidly in the blood, such as NCS, in targeting chemotherapy than either intact MAb A7 or the F(ab')2 fragments of MAb A7.

The effect of intravenous and intra-tumoural chemotherapy using a monoclonal antibody-drug conjugate in a xenograft model of pancreatic cancer

In order to investigate the efficacy of the intra-tumoural administration of an anticancer drug-monoclonal antibody conjugate in athymic nude mice bearing xenografts of a human pancreatic carcinoma, we examined the clearance of the murine monoclonal antibody A7 from the xenografts after intravenous or intra-tumoural administration and measured the antitumour effect of neocarzinostatin conjugated to MAb A7 following intravenous or intra-tumoural injection. Compared with 125I-labelled normal mouse IgG, a larger amount of 125I-labelled A7 remained in the tumour after both intravenous and intra-tumoural injection, and a significantly larger amount of 125I-labelled A7 remained in the tumour after intra-tumoural injection than that after intravenous injection. Moreover, a larger amount of 125I-labelled A7-NCS localized in the tumour after intra-tumoural injection than that after intravenous injection. Neocarzinostatin conjugated to MAb A7 showed greater activity against human pancreatic cancer than neocarzinostatin alone after both intravenous and intra-tumoural administration. Tumour growth was suppressed completely by the intra-tumoural administration of A7-NCS at a dose that did not suppress tumour growth via the intravenous route. These observations suggest that the intra-tumoural injection of neocarzinostatin conjugated to MAb A7 offers promise in treating pancreatic carcinoma.

Antitumor effect of neocarzinostatin conjugated to human/mouse chimeric Fab fragments of the monoclonal antibody A7 on human pancreatic carcinoma

The anticancer agent neocarzinostatin (NCS) was bound covalently to human/mouse chimeric Fab fragments of the monoclonal antibody A7 to form the conjugate chA7Fab-NCS. The antitumor effect of chA7Fab-NCS was tested by measuring the inhibition of 3H-thymidine incorporation into human pancreatic carcinoma cells. The chA7Fab-NCS was approximately 2.3 times as effective as free NCS against human pancreatic carcinoma cells which reacted with the monoclonal antibody A7. The antitumor activity of chA7Fab-NCS was inhibited by excess chA7Fab. ChA7Fab-NCS had an antitumor effect equivalent to free NCS on human pancreatic carcinoma cells which did not react with the monoclonal antibody A7. ChA7Fab-NCS appears to be a potentially useful conjugate for immunotargeting chemotherapy against pancreatic carcinoma.

In vitro reactivity and in vivo biodistribution of the monoclonal antibody A7 using human gastric carcinoma cell lines

The monoclonal antibody (MAb) A7 has been used to treat patients with colorectal or pancreatic carcinoma with encouraging results. We therefore determined if MAb A7 would also react with gastric carcinoma cell lines. MAb A7 reacted with seven of eight gastric carcinoma cell lines tested. The intensity of the reaction, measured by flow cytometry, was equal to that of WiDr (colon) and HPC-YS (pancreas) cell lines. In nude mice bearing xenografts of the MAb A7-reactive gastric cancer line MKN45, the percentage injected dose of MAb A7 per g of tumour tissue on day 7 was 9.79; this value was 77% of that on day 1. The in vivo tumour-to-blood ratio of MAb A7 was 2.77 on day 7. Therefore, MAb A7 has long-term retention at binding sites as well as a high probability, high intensity and high specificity of reactivity against gastric cancer, which make it an ideal drug carrier for immunotargeted chemotherapy and immunodiagnosis.

Biodistribution of neocarzinostatin conjugated to chimeric Fab fragments of the monoclonal antibody A7 in nude mice bearing human pancreatic cancer xenografts

In this study, we conjugated chimeric Fab fragments of the monoclonal antibody (MAb) A7, which reacts with pancreatic cancers, to the antitumor drug neocarzinostatin (chA7Fab-NCS) and intravenously injected 125I-labeled chA7Fab-NCS into nude mice bearing a human pancreatic cancer xenograft. We compared the tumor localization of 125I-labeled chA7Fab-NCS with that of conventional 125I-labeled A7-NCS, which was produced by conjugation of MAb A7 and NCS. 125I-Labeled chA7Fab-NCS accumulated in the tumor earlier than 125I-labeled A7-NCS, and significantly larger amounts of 125I-labeled chA7Fab-NCS had accumulated in the tumor 1 hour after injection. The results suggest that chA7Fab may be a suitable carrier for NCS in immunotargeting therapy against pancreatic cancer.

Enhanced tumor localization of radiolabeled Fab fragments of monoclonal antibody A7 in nude mice bearing human pancreatic carcinoma xenografts

Much recent research has been directed toward the use of monoclonal antibodies (MAb) for the immunodetection of solid tumors. In pancreatic cancer, the results of conventional immunoscintigraphy using intact MAb remain disappointing. Clear immunoscintigraphy with radiolabeled MAb requires a high tumor tissue/blood ratio of radioactivity and a low normal tissue/blood ratio of radioactivity. In this study, 125I-labeled Fab fragments produced by papain digestion of MAb A7 were injected intravenously into nude mice bearing a human pancreatic cancer (HPC-YS) xenograft previously shown to react specifically with MAb A7. The radioactivity of tumors and normal organs was subsequently measured. The tumor tissue/blood ratio of 125I-labeled Fab fragments of MAb A7 was 1.00 +/- 0.24 and 9.68 +/- 2.54 at 2 and 24 h after injection, respectively. The tumor tissue/blood ratio of radioactivity was significantly higher than those of normal organs at 24 h after injection. Moreover, the tumor tissue/blood ratio of 125I-labeled Fab fragments of MAb A7 was greater than that of intact MAb A7, although the 125I-labeled Fab accumulation level was much less than that of 125I-labeled intact MAb A7 in the tumor. When mice bearing tumors which did not react with MAb A7 were studied, 125I-labeled Fab fragments did not specifically localize to the tumors. These results suggest that Fab fragments of MAb A7 may be suitable carriers of radionuclides for the immunodetection of human pancreatic cancer.

Intratumoral administration of neocarzinostatin conjugated to monoclonal antibody A7 in a model of pancreatic cancer

We investigated the following in athymic nude mice with xenografts of a human pancreatic carcinoma: 1) clearance of the murine monoclonal antibody A7 from the carcinoma; and 2) the antitumor effect of neocarzinostatin conjugated to MAb A7 (A7-NCS) on the carcinoma following intratumoral injection. Compared with 125I-labeled normal mouse IgG, a significantly larger amount of 125I-labeled A7 remained in the tumor after intratumoral injection. Neocarzinostatin conjugated to MAb A7 showed a greater antitumor activity against human pancreatic cancer than neocarzinostatin alone after intratumoral administration. The conjugate completely suppressed tumor growth macroscopically during the experiment. Tumor tissue in mice became necrotic 32 days after injection with A7-NCS. These observations suggest that the intratumoral injection of A7-NCS offers promise in treating pancreatic carcinoma.

Increased tumor localization by monoclonal antibody A7 after F(ab')2 fragmentation in athymic nude mice bearing human pancreatic carcinomas

Much recent research has been directed toward the use of monoclonal antibodies (MoAbs) for the immunodetection of solid tumors. In pancreatic cancer, conventional immunoscintigraphy using intact MoAbs remains disappointing. In this study, 125I-labeled F(ab')2 fragments produced by pepsin digestion of MoAb A7 were injected intravenously into nude mice bearing human pancreatic cancer, HPC-YS, xenografts that have previously been shown to react specifically with MoAb A7. The tumor tissue/blood ratio of 125I-labeled F(ab')2 fragments of MoAb A7 increased with time and was much higher than those for normal tissues. Moreover, the tumor tissue/blood ratio of 125I-labeled F(ab')2 fragments was greater than that of intact MoAb A7, although the F(ab')2 accumulation was less than that of intact MoAb A7 in the tumor. These results suggest that F(ab')2 fragments of MoAb A7 may be suitable carriers of radionuclides for immunodetection of human pancreatic cancer.

Biodistribution of monoclonal antibody A7 and its F(ab')2 fragment in athymic nude mice bearing human pancreatic carcinoma

Xenografts of a human pancreatic carcinoma cell line, HPC-YS, which reacted with the monoclonal antibody (MAb) A7, were used to investigate the in vivo localization of radioiodinated MAb A7 after intraperitoneal injection. MAb A7 localized to the tumor 4 days and 8 days after injection with a tissue/blood ratio of 1.45 +/- 0.18 and 2.04 +/- 0.20, respectively. The accumulation of MAb A7 in the tumor was 5%/g and 3.3%/g of the injected dose on day 4 and on day 8, respectively. In contrast, the F(ab')2 fragment of MAb A7 localized to the tumor 4 days after intravenous injection with a tissue/blood ratio of 14.2. The accumulation of the F(ab')2 fragment in the tumor was 1.2%/g of the injected dose. These results suggested that MAb A7 might be a suitable carrier of anticancer drugs for immunotargeting chemotherapy and that the F(ab')2 fragment might be potentially useful for the immunodetection of human pancreatic carcinomas.

Efficacy and specificity of a monoclonal antibody-drug conjugate in chemotherapy by intratumoral injection

The murine monoclonal antibody (Mab) A7 conjugated to neocarzinostatin (A7-NCS) was injected intratumorally (IT) into tumor bearing nude mice. Its pharmacokinetics and tumoricidal effects were compared in the high, moderate and low antigen expressing xenograft for SW1116, WiDr and KB tumor-bearing nude mice, respectively. When injected IT into nude mice, [125I]A7-NCS was retained in the tumors according to the degree of antigen expression; it was also disseminated into the blood inverse proportion to the antigen expression. Addition of an excess amount of Mab A7 reduced [125I]-A7-NCS accumulation in SW1116 xenograft and elevated the [125I]A7-NCS concentration in the circulation. Complete tumor reduction was found in all 5 mice with SW1116 tumor, and 2 of 5 mice with WiDr tumor. However, only incomplete tumor suppression was observed in mice with the KB tumor. The significant tumor reduction in SW1116 bearing nude mice was attenuated when excess of Mab A7 was simultaneously administered with A7-NCS. These findings indicate that A7-NCS was localized in the target tumors and exerted its tumoricidal effects depending on the degree of antigen-antibody interaction when administered IT. Thus, A7-NCS can be used successfully in vivo for local therapy, auguring new and promising applications for local cancer therapy.