Novel approaches towards cancer-directed immune checkpoint inhibition

Blockade of the PD-1/PD-L1 interaction using immune checkpoint-inhibiting antibodies has yielded unprecedented clinical responses, albeit only in a small subgroup of cancer types. Moreover, treatment with these antibodies is frequently associated with serious auto-immune-related side effects due to 'on-target/off-tumor' binding to PD-L1 present on normal cells. Additionally, cancer cells are known to excrete large amounts of small extracellular vesicles called ‘tumor exosomes’ (TEX), which can expose large amounts of PD-L1. Notably, TEX-exposed immune checkpoint molecules are largely resistant to current clinically used checkpoint-inhibiting antibodies. Taken together, there is an unmet clinical need for novel checkpoint inhibitors that can selectively block PD-L1 and alternate immune checkpoints both on cancer cells and TEX. This thesis describes the construction and preclinical assessment of a novel series of bispecific antibodies (bsAbs) designed to selectively inhibit both cancer cell- and EV-exposed immune checkpoints (e.g. PD-L1, CD73, or CD47). Additionally, we describe the synthesis and subsequent preclinical assessment of a novel light-activatable small-molecule inhibitor (SMI) of the CD73 immune checkpoint.