The sTAg (surface Tagged Antigen) platform is an innovative proteomics technology designed to identify antibody-accessible antigens as candidate targets for human antibody-based cancer therapeutics. sTAg systematically profiles the cell surface proteomes of primary tumors using in-solution labeling of intact cells from freshly-resected, patient-derived specimens. Tumor-specific surface proteins are identified and quantified by applying state-of-the-art instrumentation for solution-based liquid chromatography tandem mass spectrometry (LC-MS/MS). Using sTAg, Igenica identifies cancer antigens exhibiting high relative expression in tumors versus normal comparators that include both normal-adjacent and nondiseased-donor specimens. Using iTAb, Igenica generates the most appropriate monoclonal antibody and validates the target in vivo.

Primary tumor specimens as crucial biomaterial for development of effective therapeutics

A critical element of our strategy encompasses the use of freshly harvested, primary tumor and normal samples as source biomaterial for quantitative cell surface protein expression profiling. Interrogation of primary tumor samples reveals candidate surface protein expression profiles produced as a direct function of primary in vivo tumor biology, providing the most representative picture of tumor cell expression patterns as they occur in patients.

Biochemical enrichment of surface proteins from tumor and normal-associated-tissue specimens

Igenica has developed unique conditions for the optimized, low-bias labeling and enrichment of proteins that contain regions that are exposed to the extracellular space in the context of in-tact tumor cells in solution. Biological targeting of these surface-exposed proteins provides therapeutic avenues for tumor ablation via immune effector function and/or direct modulation of target protein activity. Igenica’s enrichment method produces a high-value, reduced-complexity pool of surface-associated candidate targets that can be rapidly and robustly profiled using high-resolution tandem mass spectrometry.

Surface protein interrogation using highly sensitive and accurate hybrid mass spectrometry

Captured tumor-specific surface proteins are identified and quantified via solution-based liquid chromatography tandem mass spectrometry (LC-MS/MS) using state-of-the-art instrumentation enabling a previously unattainable combination of accuracy, sensitivity and speed. Our method leveraging solution-based proteomics is especially suited to identifying and quantitating cell-surface-associated proteins whose characteristic hydrophobic nature often proves problematic for more traditionally employed gel-based and chromatographic strategies. As an additional advantage, Igenica’s technology has the ability to capture and sample all detectable peptides from the tagged surface proteins, increasing the strength of our quantitative protein abundance measurements and the statistical certainty of protein identifications.

Bioinformatic analysis of enriched target pool for target selection

Biostatistical analysis of the candidate pool to identify highest-value targets is performed considering both the magnitude of relative surface expression and the incidence of detection across multiple primary patient specimens. In parallel, bioinformatic tools are leveraged to explore critical aspects of each target including both defined and predicted structural features, shared homologies with related proteins, any characterized mechanisms of action, potential interplay with the immune system, and expression patterns in normal and diseased human tissues. These bioinformatic data are combined with our proteomic measurements of surface expression in primary tumor specimens to optimally prioritize targets for the iTAb antibody generation platform.