Tumor progression in metastasis: an experimental approach using lectin resistant tumor variants

Abstract

A novel model of tumor progression in metastatic cancer is described which grew out of attempts to derive stable non-metastatic variants from a highly metastatic mouse tumor called MDAY-D2. The variants were obtained by selection of so-called lectin-resistant (LecR) membrane mutants using toxic concentrations of wheat germ agglutinin (WGA) as the selective agent, after mutagenesis. Cloned WGAR variants almost all appeared to be highly tumorigenic and metastatic, but displayed altered growth properties which were highly suggestive of major cellular phenotypic alterations occurring prior to metastasis. This were confirmed with the discovery that spontaneous visceral metastases always consisted of WGA-sensitive (WGAS) 'revertant' tumor cells. Such revertants also arose at the site of the subcutaneous inoculation and, with time, comprised an increasing proportion of the tumor cells at that location. The WGAS/high metastatic phenotype was stable in vitro or in vivo, implying the WGAR leads to WGAS shift had an underlying genetic basis. Thus, it appeared that the WGAR tumor cells could not metastasize, because of either an intrinsic cellular defect or a host imposed barrier, but that this block could be circumvented through a genetic change in the WGAR tumor cells which was accompanied by reversion of the WGAR phenotype. Non-tumorigenic (tum-) WGAR variants were also obtained, but in these cases the mutagenesis treatment itself appeared responsible for development of the tum- phenotype. The reduced tumorigenicity had an underlying immunological basis, a finding which could be exploited to immunotherapeutically treat established visceral metastases of poorly immunogenic tumors. Throughout these studies, emphasis was placed on the considerable potential of using tumor cell populations having various stable drug-resistant genetic markers to monitor aspects of tumorigenesis, tumor progression, and metastasis.

Wheatgerm agglutinin-mediated toxicity in pancreatic cancer cells

“…WGA has been shown to react with cell membrane glycoproteins in a wide variety of neoplastic tissues (Willmott and Simpson, 1983;Walker, 1984;Kellokumpu et al, 1986;Dansey et al, 1988;Langkilde et al, 1989a;Bresalier et al, 1990;Welch et al, 1990;Mody et al, 1995). When WGA was used to generate lectin-resistant clones of cultured cancer cells, most resulting clones showed a remarkable loss of metastatic capabilities (Stanley et al, 1980;Kerbel et al, 1982;Ishikawa et al, 1988;Ishikawa and Kerbel, 1989;Kim et al, 1993). The abnormal truncation of asparagine-linked cell surface carbohydrate with loss of sialylated poly-N-acetyllactosamine complexes and the resulting increase in adherence to laminin, fibronectin and type-4 collagen appears to account for this loss of metastatic potential in WGA-resistant clones (Finne et al, 1980(Finne et al, , 1982Dennis, 1985Dennis, , 1986a.…”

Origin and biology of cancer metastasis

“…The cells are then tested in the appropriate host to determine their metastatic potential. This method has been used to examine whether properties as diverse as resistance to T lymphocytes (16,19,28,42,58,93), adhesive characteristics (a), invasive capacity (34,66,69,73), resistance to various lectins (42,43,79), and resistance to natural killer cells (33) are important in metastasis.One obvious criticism of these studies is that the surviving tumor cells may have arisen as a result of adaptive rather than selective processes. The first experimental proof for metastatic heterogeneity in neoplasms was provided by Fidler and Kripke in 1977 in work with the murine B16 melanoma (18).…”

Spontaneous fusion in vivo between normal host and tumor cells: possible contribution to tumor progression and metastasis studied with a lectin-resistant mutant tumor.

“…Cancer Inst., in press). We used the approach of altering membrane properties thought to be involved in many aspects of the metastatic process by selecting lectin-resistant (Lecr) mutants (10,35,36), particularly those which are wheat germ agglutinin resistant (WGAF), an approach pioneered by Tao and Burger (64). By way of example, the N-linked complex oligosaccharide structures on the surface of WGAT mutants are often undersialylated (18,62).…”

“…As far as our own studies are concerned, we discovered that some of our stable WGA' mutants, when injected subcutaneously (s.c.) into DBA/2 mice, resulted in the eventual recovery of WGA-sensitive (WGAS) tumor cell "revertants" in spontaneous visceral metastases (10), as well as in the "primary" s.c. growing tumor (36 (9). However, the occurrence of spontaneous host cell-tumor cell fusions in vivo leading to highly metastatic hybrid cell variants in a completely syngeneic animal model has not yet been reported.…”