Increased expression and activity of the PD-L1/PD-1 pathway suppresses the activation of cytotoxic T cells, which is vital in anti-tumour defence, allowing tumours to rise, expand and progress. Current strategies using antibodies to target PD-1/PD-L1 have been very effective in cancer therapeutics and companion diagnostics. Aptamers are a new class of molecules that offer an alternative to antibodies. Herein, the systematic evolution of ligands by exponential enrichment (SELEX) using agarose slurry beads was conducted to isolate DNA aptamers specific to recombinant human PD-L1 (rhPD-L1). Isolated aptamers were sequenced and analysed using MEGA X and structural features were examined using mFold. Three aptamer candidates (P33, P32, and P12) were selected for evaluation of binding affinity (dissociation constant, Kd) using ELONA and specificity and competitive inhibition assessment using the potentiostat-electrochemical method. Among those three, P32 displayed the highest specificity (8 nM) against PD-L1. However, P32 competes for the same binding site with the control antibody, 28-8. This study warrants further assessment of P32 aptamer as a potential, cost-effective alternative tool for targeting PD-L1.
Aggressive tissue biopsy is commonly unavoidable in the management of most suspected tumor cases to conclusively verify the presence of cancerous cells through histological assessment. The extracted tissue is also immunostained for detection of antigens (tissue tumor markers) of potential prognostic or therapeutic importance to assist in treatment decision. Although liquid biopsies can be a powerful tool for monitoring treatment response, they are still excluded from standard cancer diagnostics, and their utility is still being debated in the scientific community. With a myriad of soluble tissue tumor markers now being discovered, liquid biopsies could completely change the current paradigms of cancer management. Recently, soluble programmed cell death ligand-1 (sPD-L1), which is found in the peripheral blood, i.e. serum and plasma, has shown potential as a pre-therapeutic predictive marker as well as a prognostic biomarker to monitor treatment efficacy. Thus, this review focuses on the emergence of sPD-L1 and promising technologies for its detection in order to support liquid biopsies for future cancer management.