Immunotherapeutic targeting of stage-specific embryonic antigen-4 (SSEA-4) has been shown to inhibit pancreatic cancer growth in animal models and cancer cell lines, indicating that this approach has promise for treating pancreatic ductal adenocarcinoma (PDAC) and possibly other SSEA-4-positive cancers, according to new a Taiwan/U.S. collaborative study.

"This is the first study to report that high expression of SSEA-4 or key enzymes associated with its biosynthesis significantly reduces overall survival rates in pancreatic cancer," said lead researcher Chi-Huey Wong, a professor of chemistry at The Scripps Research Institute in La Jolla, California.

"This suggests that SSEA-4 plays an important role in this disease and represents a potential promising target for therapeutic development," said Wong, who is also a distinguished professor in the Genomics Research Center at Academia Sinica in Taipei.

PDAC is the most common and aggressive type of pancreatic cancer. Early disease stages are usually asymptomatic and there is currently no effective treatment for PDAC, which has a 5-year survival of around 9%.

Development of new PDAC treatments has been restricted by problems including tumor heterogeneity, a complex tumor microenvironment, drug resistance, and lack of early detection.

Thus there is an urgent unmet medical need for identifying new targets for the development early diagnostics and effective treatments for PDAC.

While various cell surface markers have been investigated, most are also expressed in normal cells or frequently mutate to resist treatment, making an effective targeted therapy strategy difficult.

Altered glycolipids due to aberrant glycosylation have been identified as potential anticancer targets, especially many tumor-associated carbohydrate antigens (TACAs), which are often found on the surface of cancer cells and their stem cells.

Altered glycosylation is also a characteristic of tissue inflammation and neoplasia due to differential expression of glycosyltransferases.

Glycans are smaller molecules than proteins and are synthesized by glycan-associated enzymes. Therefore, when they grow abnormally in diseased cells, their structures could become unique, non-self and better markers than proteins.

SSEA-4

Among TACA glycol-conjugates, SSEA-4 is a cell-surface glycol-sphingolipid (GSL) used to define human embryonic stem cells, and human embryonal carcinoma cells or induced pluripotent stem cells.

In their new study, the authors showed that SSEA-4 was expressed in all pancreatic cancer cell lines examined, but undetectable in normal pancreatic cells, they reported in the December 8, 2021, online edition of Proceedings of the National Academy of Sciences.

"Using flow cytometry and anti-SSEA-4 antibody staining, we found that SSEA-4 was expressed in all 14 pancreatic cancer cell lines examined and that the SSEA-4 expression level was significantly higher than the other two globo-series glycolipids, SSEA-3 and Globo-H," said Wong.

Conversely, "a human pancreatic epithelial normal cell line had no expression of SSEA-4, highlighting the specificity of SSEA-4 for pancreatic cancer cells, in which it is more widely expressed," he told BioWorld Science.

The researchers further demonstrated that high expression of SSEA-4 or its key biosynthetic enzymes was associated with a significantly reduced overall survival.

"High expression of SSEA-4 or its biosynthesis enzymes, B3GALT5 and ST3GAL2, was associated with lower overall survival rate in pancreatic cancer patients," said Wong.

"Because expression of SSEA-4 and its synthetic enzymes may affect tumor growth, this will provide us with follow-up research in pancreatic cancer and other cancer models, including in mice and patients."

Moreover, "in animal and cell-based studies, we found that anti-SSEA-4 antibodies, either homogeneous or wild-type, were more effective against pancreatic cancers with higher expression of SSEA-4," Wong said.

Importantly, the researchers showed that a newly developed homogenous antibody against SSEA-4 with improved effector functions and a chimeric antigen receptor T (CAR-T) strategy designed to target SSEA4 were highly effective against pancreatic both cancer in vitro and in vivo.

"We demonstrated that the use of an homogeneous SSEA-4 antibody designed to optimize anticancer cytotoxicity and CAR-T cells with a single chain fraction variable (scFv) against SSEA-4 for effective treatment of pancreatic cancer, suggesting that targeting SSEA-4 has the potential to treat pancreatic cancer," said Wong.

This was supported by the discovery that a subpopulation of natural killer (NK) cells isolated by the homogeneous antibody showed enhanced cancer-cell killing activity compared to the undifferentiated NK cells.

The team was able to isolate a specific subpopulation of NK cells with better pancreatic cancer cell killing activity.

Collectively, these results indicate that targeting SSEA-4 using homologous antibodies or CAR-T strategies can effectively inhibit cancer growth, suggesting that SSEA-4 is a potential immunotherapy target for pancreatic and possibly other SSEA-4-positive cancers.

"SSEA-4 is expressed on at least 15 cancer types, including prostate, oral, stomach, liver and lung cancers, and glioblastomas, while we have shown that targeting SSEA-4 also showed efficacy in breast cancer and in non-small cell lung cancer," noted Wong.

However, before clinical use, "the SSEA-4 antibody and CAR-T constructs [described here] will require more extensive in vitro and in vivo testing to further verify their safety and efficacy," he said.

"For example, tissue cross-reactivity testing using various human biological specimens and multiple cytokines should be investigated, in order to validate the specificity of the antibody and the safety of SSEA-4 CAR-T cells, and both safety and efficacy should be confirmed in clinical trials."

In future, "we will continue to improve the efficacy of antibodies by optimizing the interaction of between the Fc-glycan and Fc receptors," said Wong.

"We are also interested in studying abnormal glycosylation, especially that of many tumor-associated carbohydrate antigens to understand their role in disease, which will hopefully lead to development of better of cancer treatments."