Synthesis and Immunomodulatory Activity of Fluorine‐Containing Bisphosphonates

Immune checkpoint blockade using anti‐PD‐1/PD‐L1 or anti‐CTLA‐4 monoclonal antibodies (mAbs) has revolutionized cancer treatment. However, many types of cancer do not respond and for those that do, only a minority of patients achieve durable remissions. Therefore, oncoimmunologists are working to develop adoptive cell therapies for non‐hematopoietic tumors by harnessing immune effector cells such as αβ T cells and γδ T cells. In contrast to conventional αβ T cells that recognize peptides in the context of MHC class I or II molecules, γδ T cells expressing Vγ2Vδ2 T cell receptors (also termed Vγ9Vδ2) are stimulated by isoprenoid metabolites (phosphoantigens) such as isopentenyl diphosphate in a butyrophilin‐3A1‐dependent manner. Vγ2Vδ2 T cells kill almost all types of tumor cells that have been treated with bisphosphonates. In this study, we synthesized a series of fluorine‐containing bisphosphonates based on current drugs and found that they stimulated Vγ2Vδ2 T cell killing of tumor cells. A fluorine‐containing prodrug analogue of zoledronate where phosphonate moieties were masked with pivaloyloxymethyl groups markedly enhanced Vγ2Vδ2 T‐cell‐mediated cytotoxicity, and also promoted the expansion of peripheral blood Vγ2Vδ2 T cells. These results demonstrate that a prodrug of a fluorine‐containing zoledronate analogue can sensitize tumor cells for killing as well as expand Vγ2Vδ2 T cells for adoptive cell therapy.