Blockade of the programmed cell death 1 (PD-1)/programmed cell death-ligand 1 (PD-L1) interaction has emerged as a powerful strategy in cancer immunotherapy. Recently, there have been enormous efforts to develop potent PD-1/PD-L1 inhibitors. In particular, Bristol-Myers Squibb (BMS) and Aurigene Discovery Technologies have individually disclosed several promising PD-1/PD-L1 inhibitors, whose detailed experimental data are not publicly disclosed. In this work, we report the rigorous and systematic in vitro characterization of a selected set of potent PD-1/PD-L1 macrocyclic peptide (BMSpep-57) and small-molecule inhibitors (BMS-103, BMS-142) from BMS and a peptidomimetic small-molecule inhibitor from Aurigene (Aurigene-1) using a series of biochemical and cell-based assays. Our results confirm that BMS-103 and BMS-142 are strongly active in biochemical assays; however, their acute cytotoxicity greatly compromised their immunological activity. On the other hand, Aurigene-1 did not show any activity in both biochemical and immunological assays. Furthermore, we also report the discovery of a small-molecule immune modulator, whose mode-of-action is not clear; however, it exhibits favorable drug-like properties and strong immunological activity. We hope that the results presented here will be useful in guiding the development of next-generation PD-1/PD-L1 small molecule inhibitors.

Natural peptides possess a unique target specificity for their endogenous receptor that allows them to be exploited as diagnostic and therapeutic agents. This has led to the discovery and derivatization of various natural peptides into molecular imaging agents.

A T140-derived peptide conjugated with a naphthalimide fluorophore/chelator was coordinated to rhenium or technetium-99m to image CXCR4 expression by fluorescence microscopy or SPECT imaging.

Zn concentrations in malignant prostate tissues are much lower than in benign or healthy, suggesting that Zn levels are a potential biomarker for prostate cancer (PCa). Five 2,2'-bipyridine ligands were synthesized containing amino substituents with varying electron-donating ability for investigation as fluorescent Zn indicators. The excited state characteristics of the ligands were explored by UV/Vis and fluorescence spectroscopy. 3,3'-Diamino-2,2'-bipyridine (1) was previously shown to be weakly fluorescent as a result of π→π* transitions. The other four ligands have properties consistent with an n→π* intraligand charge transfer excited state. Strongly donating amino and aminophenyl (2 and 4) substituents gave low quantum yields, while weaker donating benzimidazole substituents (6 and 7) gave high quantum yields. Absorption and fluorescence wavelengths underwent bathochromic shifts upon Zn binding in a majority of cases. Quantum yields drastically increased upon Zn binding for 1 and 2, but decreased for 4, 6, and 7. Compounds 6 and 7 were incubated with PC-3, DU 145 and BPH-1 cells to determine their Zn sensing abilities in a biological system. Weak fluorescence was observed in BPH-1 cells and subsequent incubation with Zn caused fluorescence intensity to increase. No fluorescence was observed in PCa cell lines. Further investigation of these ligands may allow for quantitative determination of Zn concentrations in ex vivo tissue samples.

4-Amino-1,8-naphthalimide ligands were coordinated to fac-Re/99mTc(CO)3 giving complexes of varying charge for applications in fluorescence microscopy and as components of SPECT imaging agents.