Gangliosides and organ-specific metastatic colonization

Direct validation of NGcGM3 ganglioside as a new target for cancer immunotherapy

OBJECTIVE

The target concept means not only an aberrant expression of a particular molecule in tumour tissues but also evidence of a clear therapeutic advantage, as a consequence of immune-intervention, in an antigen-positive relevant tumour model. Since we reported the presence of NGcGM3 ganglioside in human breast tumours years ago and though Phase I clinical trials of a ganglioside containing vaccine have been conducted, a definitive direct validation of this peculiar molecule as target for cancer immunotherapy has remained unperformed.

METHODS

Two animal models were used: leghorn chickens and C57BL/6 mice. The murine 3LL-D122 cell line, the derived subcutaneous tumours and metastatic lung lesions were processed for gangliosides identification. Active immunotherapy experiments in the 3LL-D122 spontaneous lung metastasis model were performed with NGcGM3/VSSP vaccine prepared by conjugation of NGcGM3 with the outer membrane proteins of Neisseria meningitides.

RESULTS

The 3LL-D122 Lewis lung carcinoma results were consistent with an increased expression of NGcGM3 from primary tumours to metastatic lesions, as observed in human breast cancer samples. Both vaccines, prepared with synthetic or natural-source-derived ganglioside, showed similar anti-tumour and immunogenicity profiles. Finally, a clear involvement of NK1.1(+) cells and CD8(+) T cells in the anti-metastatic effect elicited by the vaccine was manifested.

CONCLUSIONS

While 'proof of concept' Phase II and III clinical trials with the NGcGM3/VSSP vaccine in cancer patients are currently ongoing these results reasonably sustain the validation of this peculiar ganglioside as a novel target for cancer immunotherapy.

Biology of colorectal liver metastases

The elucidation of the interaction of the tumor and its microenvironment has increased surgeons' understanding of the biologic mechanisms mediating metastases formation. The ability to develop effective biologic therapies will depend on understanding the complex interactions among endothelial cells and tumor cells and on the cytokine cross-talk among all cells within a particular tumor at a particular site. Biologic therapies must be targeted to both the site and the tumor. By the time metastases form, most steps in the metastatic cascade have been completed. Therapy to down-regulate or interrupt the last stages of metastases, proliferation, and angiogenesis and mechanisms to disrupt cell survival signals appear to be the most promising areas of investigation.

Ganglioside composition and histology of a spontaneous metastatic brain tumour in the VM mouse

Glycosphingolipid abnormalities have long been implicated in tumour malignancy and metastasis. Gangliosides are a family of sialic acid-containing glycosphingolipids that modulate cell-cell and cell-matrix interactions. Histology and ganglioside composition were examined in a natural brain tumour of the VM mouse strain. The tumour is distinguished from other metastatic tumour models because it arose spontaneously and metastasizes to several organs including brain and spinal cord after subcutaneous inoculation of tumour tissue in the flank. By electron microscopy, the tumour consisted of cells (15 to 20 microm in diameter) that had slightly indented nuclei and scant cytoplasm. The presence of smooth membranes with an absence of junctional complexes was a characteristic ultrastructural feature. No positive immunostaining was found for glial or neuronal markers. The total ganglioside sialic acid content of the subcutaneously grown tumour was low (12.6 +/- 0.9 microg per 100 mg dry wt, n = 6 separate tumours) and about 70% of this was in the form of N-glycolylneuraminic acid. In contrast, the ganglioside content of the cultured VM tumour cells was high (248.4 +/- 4.4 microg, n = 3) and consisted almost exclusively of N-acetylneuraminic acid. The ganglioside pattern of the tumour grown subcutaneously was complex, while GM3, GM2, GM1, and GD1a were the major gangliosides in the cultured tumour cells. This tumour will be a useful natural model for evaluating the role of gangliosides and other glycolipids in tumour cell invasion and metastasis.

Biology of liver metastases

A primary goal of cancer research is an increased understanding of the molecular mechanisms mediating the process of cancer metastasis. Analyses of colon cancer cells (the seeds) and the microenvironment (the soil) have increased our understanding of the biologic mechanisms mediating metastasis formation. Insight into the molecular mechanisms regulating the pathobiology of colon cancer metastasis, as well as a better understanding of the interaction between the metastatic cell and the host environment (including the vasculature), should provide a foundation for new therapeutic approaches. To the clinician, it is readily apparent that by the time metastases form, most steps in the metastatic cascade have completed. Therefore, therapy to down-regulate or interrupt the last stages of metastasis, proliferation and angiogenesis as well as mechanisms to disrupt cell survival signals seems the most promising areas of investigation.

Molecular determinants of colon cancer metastasis

Colon cancer metastasis is a tightly regulated process that requires a cancer cell to express genes that allow progression through various distinct steps. Aberrations in gene expression by cancer cells leads to transformation, growth, angiogenesis, invasion, dissemination and survival in the circulation, attachment in the organ of metastasis, and again invasion, growth, and angiogenesis. In addition to the genotype/phenotype of the tumor cell, for a tumor cell to become a clinically relevant metastasis, it must be able to respond appropriately to the environment. This includes being able to utilize growth factors and blood vessels from the organ of metastasis for the benefit of the tumor mass. Understanding the molecular and biologic mechanisms of colon cancer metastasis will allow the development of rationale therapeutic strategies that are more likely to impact the natural history of this disease than current therapies.

Influence of lipid diets on the number of metastases and ganglioside content of H59 variant tumors

We investigated the influence of the fatty acid composition of the diet on the number of hepatic metastases and the ganglioside profile of the primary tumor and metastases. C57BL/6 female mice were fed different diets containing either no fats (TEK) or 8% of fish oil (POL), linseed oil (LIN), safflower oil (SAF) or beef tallow (BT) and were injected subcutaneously in the dorsum with H59 cells, a variant of the Lewis lung carcinoma (3LLc) that metastasizes preferentially to the liver. The omega3 polyunsaturated fatty acid (PUFA)-rich diets (LIN and POL) elicited more metastases than the omega6 PUFA-rich (SAF), fat-free (TEK), or saturated fats (BT) diets. However, dietary fat did not influence the ganglioside composition of either the primary tumors or the metastases, at least in the glucidic part. However, comparison of diets with low (TEK, SAF, and BT) and high (LIN and POL) number of metastases showed that the levels of G3 (which could be a second band of GM2) were greater in metastases of the latter group. This study showed that the H59 hepatic metastases contained more GM2 than the s.c. tumors, irrespective of diet or the number of metastases produced. The small differences in the ganglioside profiles observed in this study could have resulted from the limitations of the HPTLC method. A detailed analysis of the lipid chains, as well as glycolipids other than gangliosides, could give more information on changes resulting from different lipid diets.

Gangliosides in human uveal melanoma metastatic process

The inability of current therapy to prevent metastases arising from uveal melanoma often results in patient mortality. With the goal of developing a treatment for metastasis, gangliosides were studied as potential tumor-associated antigens. Our report describes the production of a metastatic liver variant (MH) from a human uveal melanoma cell line (SP6.5). Cells were injected into nude mouse spleens and liver metastases collected 2 months later. After 21 days of in vitro subculture, the cells were re-injected into normal nude mice spleen; 10 cycles (MH10) were performed. Gangliosides were extracted, purified, chromatographed on HPTLC plates and sprayed with a resorcinol-HCl reagent, the sialic acid spots being quantified by densitometry. Gangliosides were analyzed in each metastatic liver variant and compared with the SP6.5 s.c. tumor. The results showed a significant increase in GM3 and a significant decrease in GD3 and GD2 in the last metastatic variants obtained (MH5, MH8, MH9 and MH1O) compared with the primary s.c. tumor, SP6.5. Such evolution in the ganglioside pattern was maintained throughout the progression of the different liver variants. Our results indicate that precursor ganglioside GM3 and gangliosides GD3 and GD2 could be associated with neoplastic evolution of malignancy of human uveal melanoma in nude mice.

Determinants of differential liver-colonizing potential of variants of the MCA-38 murine colon cancer cell line

We investigated factors that might contribute to the differing liver tumor colonizing potentials of MCA-38 colonic cancer cell line variants injected into the ileocolic veins of C57Bl/6J mice. Non-colonizing (MCA-38 CD) cells were sensitive to lysis by hepatic natural killer (NK) cells in vitro (51Cr-release assay) and cells with high liver-colonizing potential (MCA-38 LD) were resistant. Following abrogation of NK activity by treatment with anti-asialoGM1, liver-colonizing ability to LD cells but not CD cells was enhanced. MCA-38 CD cells were, however, capable of initial liver colonization after ileocolic vein injection. Differing patterns of membrane sialylation may have contributed to the contrasting hepatic tumorigenicities of LD and CD cells; beta-galactoside alpha 2,6-sialyltransferase mRNA levels and activity were approximately four-fold higher in LD than CD cells and qualitative and quantitative differences existed between their ganglioside profiles. In the MCA-38 model outlined, tumor cell susceptibility or resistance to NK lysis was a relatively unimportant determinant of liver-colonizing potential.

Possible involvement of tumour cell membrane gangliosides in platelet-tumour cell interactions

The possible correlation(s) between platelet proaggregating activity, and sialic acid content and ganglioside expression of six human colorectal tumour cell lines (CBS, GEO, HT-29, WiDr, MIP and DLD-1) was evaluated. The three cell lines (HT-29, WiDr and DLD-1) capable of inducing remarkable in vitro platelet aggregation, had significantly higher amounts of lipid-bound sialic acid than those cell lines characterised by a lower platelet proaggregating activity (GEO, CBS and MIP). High performance thin-layer chromatography demonstrated the presence of one band comigrating with GM3 in all cell lines, while GD1a and GT1b comigrating gangliosides were present only in HT-29, WiDr and DLD-1 cells. Finally, an increased platelet pro-aggregating activity of GEO and CBS cell lines was observed after the incorporation of exogenous gangliosides. The present data support the hypothesis that lipid-bound sialic acid may be involved in platelet-tumour cell interactions.