RG-7841

Monomethyl auristatin E (MMAE) is a promising treatment option for patients diagnosed with prostate cancer (PCa); however, toxicities prevent MMAE from being administered as free drug. No MMAE-based treatment is currently marketed for PCa. Herein, we describe a small-molecule-drug conjugate, CTT2274, for the selective delivery of MMAE. CTT2274 is composed of a prostate-specific membrane antigen (PSMA)-binding scaffold, a biphenyl motif, a pH-sensitive phosphoramidate linker, and MMAE payload. We demonstrate that CTT2274 shows selective binding to PSMA, which is overexpressed on PCa cells, and induces tumor cell death in vitro. In a patient-derived xenograft tumor model of PCa in mice, we show that weekly intravenous dosing of CTT2274 at 3.6 mg/kg for six weeks is superior to treatment with free MMAE at equivalent doses. Mice treated with CTT2274 experienced prolonged tumor suppression and significantly greater overall survival than mice treated with PBS. Additionally, the safety of CTT2274 compared to an equivalent dose of MMAE was assessed in healthy, non-tumor-bearing mice. Our results demonstrate that CTT2274 therapy is as efficacious as MMAE, results in superior overall survival, and has a more favorable safety profile. Together, these data indicate that CTT2274 is a candidate for clinical translation for the treatment of PCa.

Dendrimers are branched macromolecular structures that are useful nanocarriers for small-molecule drugs, such as cancer therapeutics. Their small size permits penetration into solid tumors, coupled with functionalization with a low-fouling PEG coating that minimizes transient cellular interactions and enhances plasma circulation time. While PEGylated dendrimers show significant promise as anticancer therapeutics, there is potential to increase tumor cell specificity and drive uptake of drugs into cells by conjugating cell-targeting ligands onto the dendrimers. To achieve this, we used an expanded genetic code and bio-orthogonal click chemistry to functionalize monomethyl auristatin E (MMAE)-loaded PEGylated dendrimers with a single tumor cell-targeting nanobody per dendrimer. The uniform addition of a single nanobody ligand facilitated greater intracellular uptake of the drug payload into HER2-positive target cells, while preserving the desirable circulatory characteristics of dendrimers. While the nanobody-dendrimer conjugates show similar levels of tumor infiltration over 24 h compared to unmodified dendrimers, the targeted dendrimers had significantly greater inhibition of tumor growth and long-term retention in the tumors. Our results highlight that biodistribution studies alone are poor predictors of therapeutic performance. The controlled conjugation strategy presented here preserves the size advantage and tissue penetration of dendrimers while maximizing targeted cellular uptake and potency in difficult-to-access solid tumor tissue.