Identification of Cell Surface Proteins as Potential Immunotherapy Targets in 12 Pediatric Cancers

Abstract

Technological advances now allow us to rapidly produce CARs and other antibody-derived therapeutics targeting cell surface receptors. To maximize the potential of these new technologies, relevant extracellular targets must be identified. The Pediatric Oncology Branch of the NCI curates a freely accessible database of gene expression data for both pediatric cancers and normal tissues, through which we have defined discrete sets of over-expressed transcripts in 12 pediatric cancer subtypes as compared to normal tissues. We coupled gene expression profiles to current annotation databases (i.e., Affymetrix, Gene Ontology, Entrez Gene), in order to categorize transcripts by their sub-cellular location. In this manner we generated a list of potential immune targets expressed on the cell surface, ranked by their difference from normal tissue. Global differences from normal between each of the pediatric tumor types studied varied, indicating that some malignancies expressed transcript sets that were more highly diverged from normal tissues than others. The validity of our approach is seen by our findings for pre-B cell ALL, where targets currently in clinical trials were top-ranked hits (CD19, CD22). For some cancers, reagents already in development could potentially be applied to a new disease class, as exemplified by CD30 expression on sarcomas. Moreover, several potential new targets shared among several pediatric solid tumors are herein identified, such as MCAM (MUC18), metadherin (MTDH), and glypican-2 (GPC2). These targets have been identified at the mRNA level and are yet to be validated at the protein level. The safety of targeting these antigens has yet to be demonstrated and therefore the identified transcripts should be considered preliminary candidates for new CAR and therapeutic antibody targets. Prospective candidate targets will be evaluated by proteomic analysis including Westerns and immunohistochemistry of normal and tumor tissues.

CIC-DUX sarcomas demonstrate frequent MYC amplification and ETS-family transcription factor expression

“…Expression of MTDH has been recently noted as a poor prognostic factor in Ewing sarcoma and other sarcomas, 35,36 and proposed as a targetable cell surface marker. 37 In contrast, we found that expression of p21 was significantly greater in CIC-DUX sarcomas. Though only a subset of nuclei in these tumors was positive for p21, this observation identifies another difference in cell signaling between CIC-DUX and Ewing sarcomas despite their shared expression of, and implicitly, shared dependency on, oncogenic ETS transcription factor signaling.…”

Therapeutically targeting glypican-2 via single-domain antibody-based chimeric antigen receptors and immunotoxins in neuroblastoma

“…A microarray study showed that GPC2 mRNA was overexpressed in a panel of pediatric cancers, including neuroblastoma (5). To examine the expression of GPC2 protein in neuroblastoma, we used anti-GPC2 antibodies as research tools to examine established human cell lines and clinical tissue samples.…”

“…Interestingly, glypican-2 (GPC2) was recently found as one of several mRNA transcripts that were highly expressed in multiple pediatric cancers, including neuroblastoma (5). Whereas these candidate markers have shown promise at the mRNA level, they have yet to be validated at the protein level.…”

Targeted immunotherapy for pediatric solid tumors

“…28 RMS tumors that were highly expressing FGFR4 were associated with advanced stage and poor survival. 29 Ponatinib (AP23534), a tyrosine kinase inhibitor of FGFR4, was found to be a potent inhibitor of growth in RMS cell lines and in a RMS mouse model and therefore deserves further exploration as a target in RMS. 30 Insulin-like growth factor-1 receptors Insulin-like growth factor-1 receptor (IGF-1R) has been found to be important in the growth of solid tumors, specifically sarcomas.…”