(T1230-02-08) Quantitation of Soluble Tumor-Associated Antigens (sTAA) in Tumor Interstitial Fluid (TIF) Isolated from Frozen Solid Tumors

Purpose: Tumor-associated antigens (TAA) are membrane proteins with expression relatively restricted to tumor cells. Many TAA can be shed from the membrane or have secreted isoforms and become circulating soluble form (sTAA) in body fluid. For TAA-targeted therapeutics, sTAA are decoys of the MOA by competing with binding sites expressed on cell membranes (mTAA). Elevated or similar levels of sTAA in cancer patients compared to healthy populations have been reported in plasma, depending on the TAA and cancer disease indication. However, sTAA levels at the site of action in tumor interstitial fluid (TIF) are unknown for many targets. Here, we developed methods for collecting TIF from snap-frozen tumors and evaluating sTAA levels in TIF and plasma from cancer patients and healthy volunteers.

Methods: In brief, fresh and snap-frozen/thawed tumors were centrifuged at set conditions, resulting in a liquid collection known as TIF. Plasma from corresponding cancer patients and healthy volunteers were obtained for comparison. sTAA levels were measured in various matrices including TIF and plasma from cancer patients and healthy volunteers via a multiplex MSD assay using R-RLEX/U-PLEX capture and detection antibodies on custom MSD plates.

Results: Following the successful collection of TIF from freshly dissected mouse xenografts, we optimized the method for collecting TIF from xenograft tumors that were snap-frozen upon dissection. The level of sTAA between TIF isolated from fresh xenografts and frozen xenografts showed no significant difference. Using this protocol, TIF was isolated from frozen tumors from cancer patients to enable sTAA quantification. Preliminary results indicate higher levels of sTAA in TIF are measured compared to in plasma from cancer patients or healthy volunteers.

Conclusion: Preliminary results from multiple sTAA evaluations indicate significant differences in sTAA levels in TIF compared to plasma, which relying on sTTA levels in plasma may lead to inaccurate estimations of sTAA levels in tumor environments. Based on this promising outcome, we plan to expand our research to include more TAA covering different cancer disease indications. Our ultimate goal is to develop a mathematical model that will incorporate the concentration of sTAA in healthy plasma, cancer patient plasma, cancer TIF, and the molecular size of sTAA. This model has the potential to assist in the rapid and initial estimation of the concentration of specific sTAA in TIF. It can also help research teams understand the risks associated with targeting these TAA and design strategies to mitigate those risks. The experimentally collected sTAA concentrations in TIF are crucial parameters for the translation of pharmacokinetics and pharmacodynamics research.