Effects of methotrexate-carcinoembryonic-antigen-antibody immunoconjugates on GW-39 human tumors in nude mice

Abstract

Methotrexate (MTX) was conjugated to an anti-carcinoembryonic antigen monoclonal antibody (NP2) by using amino-dextran as an intermediate carrier. The drug was chemically linked to amino-dextran (average Mr = 40,000), and the resulting MTX-dextran was then site-specifically attached to the carbohydrate moiety of the antibody. Athymic nude mice that carried human colonic GW-39 tumors (s.c.) were treated with the immunoconjugate. In this study, the specific conjugate caused a greater inhibition of the tumor growth than either free MTX or its conjugate with dextran and an irrelevant antibody. The intermediate MTX-dextran and the unlinked mixture of MTX-dextran with NP2 were both relatively ineffective in inhibiting tumor growth. The greatly reduced host toxicity permitted the use of the MTX-dextran-NP2 in a high-dose therapy of this tumor system.

A fluorouridine‐anti‐CEA immunoconjugate is therapeutically effective in a human colonic cancer xenograft model

“…No significant anti-tumor activities were observed when the animals were given the intermediate conjugate (FUR-dextran) , or the fresh mixture of this intermediate conjugate with free NP-2. These observations are similar to that of the methotrex-ate-CEA-antibody conjugate already described (Shih et al, 1990). By comparing the anti-tumor effects between different treatments, it is clearly indicated that FUR-dextran-NP-2 was more specifically delivered to the GW-39 tumor than the controls, and a higher tumoricidal effect was demonstrated.…”

“…This was indeed observed in our study using the methotrexatedextran-NP-2 conjugate(Shih et al, 1990). However, the extent of the increase in anti-tumor effects is not proportional to the dose given, thus indicating the existence of other limiting factors, such as antigen expression, antibody penetration and antigen saturation.…”

“…The anti-tumor effects of the specific conjugate would therefore be compared to the different controls at this dose level. Similar to MTX-dextran (Shih et al, 1990), the intermediate conjugate FUR-dextran at the dose of 35 mg/kg possessed lower host toxicity as well as diminished tumoricidal effect when compared with free drug. Mixing the intermediate conjugate with 10-fold in weight of unlinked NP-2 improved the anti-tumor effect of FUR-dextran slightly, but not significantly.…”

“…For maximum delivery of drug to the tumor, the immunoconjugate should be reasonably stable, should be capable of accretion by the tumor cells at the site of delivery, preferably in a stoichiometric manner with little or no uptake by non-tumor tissues. Previously, we described a site-specific linking method (Shih et al, 1988) in which rnethotrexate was linked to the carbohydrate of antibody via a bridging polymer (aminodextran, mw 40,000), resulting in an immunoconjugate with high substitution ratio, retentiion of immunoreactivity , preferred targeting properties as well as the retention of anti-tumor activity in tumor xenografts (Shih et al, 1990). Since malignant cells are likely to be heterogeneous in their sensitivity to drugs, or in their level of antigen expression, a promising regimen of immunochemotherapy may better comprise a cocktail of drug-conjugated antibodies.…”

In vivo antitumor activity of a panel of four monoclonal antibody-vinca alkaloid immunoconjugates which bind to three distinct epitopes of carcinoembryonic antigen

“…The normal physiologic role of CEA is still unclear, but recent studies have identified it as an adhesion-related protein and a member of the immunoglobulin supergene family (3). mAbs directed against numerous epitopes of CEA have been characterized (4-11) and many papers have described the diagnostic and therapeutic potential of radio-, toxin-, and chemoimmunoconjugates constructed using anti-CEA mAbs (22)(23)(24)(25)(26)(27)(28)(29)(30)(31). A number of recent publications have elucidated the potent in vivo antitumor activity of mAb-DAVLBHYD conjugates directed against various human solid tumor membrane antigens.…”