Re‐engineering the Immune Response to Metastatic Cancer: Antibody‐Recruiting Small Molecules Targeting the Urokinase Receptor

Abstract

Developing selective strategies to treat metastatic cancers remains a significant challenge. Herein, we report the first antibody-recruiting small molecule (ARM) that is capable of recognizing the urokinase-type plasminogen activator receptor (uPAR), a uniquely overexpressed cancer cellsurface marker, and facilitating the immune-mediated destruction of cancer cells. A co-crystal Correspondence to: David A. Spiegel. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201510866. HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript structure of the ARM-U2/uPAR complex was obtained, representing the first crystal structure of uPAR complexed with a non-peptide ligand. Finally, we demonstrated that ARM-U2 substantially suppresses tumor growth in vivo with no evidence of weight loss, unlike the standard-of-care agent doxorubicin. This work underscores the promise of antibody-recruiting molecules as immunotherapeutics for treating cancer. Keywordsantitumor agents; cell recognition; drug design; immunology; medicinal chemistryTumor metastasis involves the invasion of cancer cells into surrounding tissues, a process often accelerated by cell-surface proteases. One such protease, the urokinase-type plasminogen activator (uPA), breaks down extracellular matrix proteins and activates migration-inducing signal cascades upon binding to the urokinase-type plasminogen activator receptor (uPAR). [1] Both uPA and uPAR expression are substantially upregulated in invasive cancer cells com-pared to healthy cells or benign tumors. [2] In clinical settings, uPAR levels have been shown to correlate with metastatic potential and poor clinical outcomes. [1a] As such, uPAR has gained recognition as a promising target for treating metastatic cancers from diverse tissues of origin, including breast, colon, stomach, and bladder. [3,4] Antibody-recruiting molecules (ARMs) are bifunctional molecules capable of delivering endogenous antibodies to disease-causing entities, leading to their destruction and/or clearance by the immune system. Our group and others have previously developed ARMs that target various cancers and infectious agents. These novel immunotherapies have the potential both to complement protein-based agents while overcoming their challenges, such as poor oral bioavailability, high molecular weights, and immunogenicity. [5] Our group previously reported an ARM capable of targeting uPAR-expressing cancer cells for immune-mediated cell death. [5] Although effective in vitro, the reported con-struct (termed ARM-U1) contained the uPA protein at its target binding terminus (TBT), imparting many of the limitations of biologics. We therefore hypothesized that the therapeutic potential of this agent could be significantly improved upon by replacing the uPA protein with a highaffinity uPAR-binding small molecule (Figure 1 A).Herein, we report the design, synthesis, and in vitro and in vivo evaluation of a secondgeneration, low-molecular...

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