Immunological studies on mouse mammary tumors. IV. Extraction and solubilization of transplantation antigen of mouse mammary tumor

Preparation and in vitro cytotoxicity of a methotrexate-anti-MM46 monoclonal antibody conjugate via an oligopeptide spacer

A method was developed by which conjugates of methotrexate (MTX) with antibody were prepared via an oligopeptide spacer which, after internalization of the conjugates into the target cells, would be cleaved by lysosomal enzymes to liberate MTX or its derivative(s) for entry of the drug into the cytoplasm through the lysosomal membrane. The conjugate of MTX with a monoclonal antibody (MAb) (aMM46) to mouse mammary carcinoma MM46 cells prepared by this method via Leu-Ala-Leu-Ala showed potent, antibody-directed cytotoxicity through lysosomal degradation of the conjugate, most likely at the tetrapeptide spacer. This was supported by the following observations: (a) the cytotoxicity of the aMM46 conjugate was more potent than that of the corresponding normal gamma-globulin conjugate, the antibody alone not being cytotoxic; (b) the conjugate retained its potent cytotoxicity to MM46 cells even after removal, by hydroxylamine treatment, of a less stably bound MTX derivative which might have been released extracellularly and have caused non-specific cytotoxicity by entering the cells via the membrane active transport system for MTX; (c) the cytotoxicity was not inhibited by thiamine pyrophosphate, an inhibitor of the MTX transport system; (d) the cytotoxicity was inhibited significantly with ammonium chloride, which inactivates lysosomal enzymes by raising the pH; and (e) the cleavability of the Leu-Ala-Leu-Ala spacer by the lysosomal enzymes was verified by using bio-undegradable poly(D-lysine) and biodegradable poly(L-lysine) as the lysosomotropic macromolecular carriers: unlike the poly(L-lysine) counterpart, the direct MTX-poly(D-lysine) conjugate showed very weak cytotoxicity while the tetrapeptide-mediated conjugate of MTX with poly(D-lysine) exhibited potent cytotoxicity.

Extraction of immunogenic murine mammary tumor antigens with 1-butanol

Solubilized tumor associated antigens (TAA) were prepared by a single phase 1-butanol extraction of a transplantable murine mammary adenocarcinoma (H2712), other syngeneic non-mammary tumors, normal mammary tissue, and embryonic tissues. The crude butanol extract (CBE) of H2712 was found to have tumor-specific activity both in vitro in the leukocyte adherence inhibition (LAI) assay and in vivo in an immunoprophylaxis assay. The failure to detect any of the major mammary tumor virus (MTV) envelope glycoproteins or internal core protein in CBE-H2712 and the failure of tumor-bearing mice to give a LAI response to CBE prepared from embryonic tissues suggests that the CBE antigens which are responsible for LAI activity are not viral or oncofetal antigens. Enzymatic treatment of the CBE-H2712 indicated that a sialated glycoprotein formed the antigenic determinants recognized in CBE by the LAI assay. Gel filtration of LAI-reactive CBE-H2712 on a Sephadex G-75 column isolated both the in vitro and in vivo tumor-specific activity in a fraction pool. Polyacrylamide gel electrophoresis revealed the presence of a 67 kD subunit as the major species in the active fraction.

Two new C3H mouse ascites tumor cell lines capable of proliferation in vivo and in suspension culture: morphological, karyological, kinetic and immunological properties

The establishment of mouse tumor cell lines capable of proliferating in vivo and in suspension culture was undertaken. The MM-46 tumor line, initiated from primary mammary carcinoma arising in a C3H/He mouse, was maintained for over 100 generations in the peritoneal cavities of syngenic mice. At the 50th generation of the tumor suspension, cultures were initiated. The established cell lines, designated TMT-1 and TMT-2, were characterized in vitro and in vivo. The morphological finding indicated that THT-1 and TMT-2 cells from mice closely resembled the MM-46 tumor cells. The oncogenic potential of the cultured cells was comparable to that of the original ascites tumor. The population doubling time of TMT-1 and TMT-2 cell lines was about 12 hr in mice, whereas the population doubling time of both cell lines lengthened to 20 hr in suspension culture. The increase in doubling time in culture was due to the prolongation of the G1 period. The cell lines, TMT-1 and TMT-2, whether fropm culture or mice, possessed colony forming ability in in soft agar medium. The colony forming ability of the cells decreased gradually through in vivo passages but it recovered upon recultivation of the cells from mouse to culture. Chromosome analysis and cytotoxicity test by anti-MM antiserum indicated that TMT-1 and TMT-2 cell lines closely resembled and had been derived from MM-46 tumor line. Therefore, it is possible to assay cell survival in vitro after in vivo experiments on these cells.

Structure of tumor antigen on hybrid cells between mouse mammary ascites tumor and mouse fibroblast L cells

Somatic cell hybrids between mouse fibroblast L cells and MM2 mouse mammary ascites tumor grown in BALB/c mice were isolated and the structures of tumor-associated surface antigen of the hybrid cells, and parental MM2 and mouse L cells were investigated by the methods of radioiodination of membrane proteins, immunoprecipitation with a specific antiserum against tumor-associated surface antigens of MM2 tumor (anti-MM2 serum), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two molecules of 105,000 and 76,000 daltons were detected on the MM2 cell surface, but no MM2 tumor antigen was detected on the mouse L cells. On the hybrids between these two kinds of cells, in addition to the two MM2 tumor antigens, molecules of 48,000-51,000 and 12,000 daltons were observed. On Sendai-virus-infected mouse L cells only a molecule of 68,000 daltons was detected by the anti-MM2 serum, and furthermore this molecule was also detected by normal mouse serum, indicating that antibodies against Sendai virus were contaminating in both the anti-MM2 and normal mouse sera used, and thus the molecules detected on the hybrid cells were distinguishable from possible viral components of Sendai virus on the hybrid cells. The results indicate that somatic cell hybrids between mouse L cells and MM2 tumor grown in BALB/c mice expressed on their cell surface the molecules that were not exposed on either parent cell. The experiments comparing newly detected molecules with the H-2 antigen suggested that they were similar to H-2 in their electrophoretic pattern.

Dissociation of anti-tumor immune responses in rats immunized with solubilized tumor-associated antigens from a methylcholanthrene-induced fibrosarcoma

Soluble tumor antigens were prepared from chemically-induced rat fibrosarcoma KMT-17 cells by various methods [Na-deoxycholate (DOC), 3 M-KCI extraction, and crude membrane preparations by mechanical disruption]. Soluble tumor antigens prepared by DOC extraction (DOC-STA) could be detected by a radioisotopic footpad assay (FPA) and they showed the strongest antigenic activity in KMT-17 immune rats. Anti-tumor immune responses in rats previously immunized with DOC-STA were measured by FPA, Winn assay, and transplantation resistance. Significant responses detected by the FPA and Winn assay were demonstrated in rats immunized with DOC-STA. However, rats previously immunized with DOC-STA showed a significant enhancement of tumor growth when challenged with KMT-17 cells. This enhancement was specific for the tumor line used. Normal rats which received adoptive transfer of thymus and spleen cells from rats immunized with DOC-STA produced specific enhancement of tumor growth as compared with non-treated rats. Administration of cyclophosphamide before immunization with DOC-STA abrogated the enhanced tumor growth in the host. These results suggest that immunization with soluble tumor antigens specifically enhanced tumor grwoth by the induction of immunosuppressor cells. Dissociation between the anti-tumor immunity detected by the FPA and Winn assay and the enhanced tumor growth detected by transplantation resistance in rats immunized with DOC-STA is discussed.