Developing Isoxazoles as Novel Photo-cross-linkers and Its Application in Chemical Proteomics

Affinity-based proteome profiling (AfBP) has provided powerful tools to study drug and protein interactions in complex proteome. AfBP strategy relies on the usage of photocross-linkers to convert the noncovalent interactions between the drug and the proteintargets. A major problem associated with the existing photo-cross-linkers is that due to their bulky sizes, the biological activity of the designed probe often decreases. To tackle the problem, we seek to develop novel photo-cross-linkers based on pharmacophore,which is commonly found in drugs and bioactive molecules. This strategy does not require the introduction of an extra photo-cross-linker, thereby maintaining the biological activity of the probe to the maximum extent and facilitating target identification process. By examining the literature, we have identified isoxazoles that can be promising intrinsic photo-cross-linkers for AfBP design. Isoxazoles are commonly found in drugs and bioactive molecules. Numerous compounds with isoxazole rings have shown interestingbiological activity including anti-cancer and anti-microbial activity. Our preliminary study has shown that isoxazoles can potentially serve as excellent photo-cross-linkers for AfBP design. We will further synthesize a library of isoxazoles probes and analyzethe photo-cross-linking efficiency with various small molecules and proteins to gain a better understanding of how the photo-cross-linking efficiency of isoxazoles will change with different chemical structures. Subsequently we will design an AfBP probe based on Hsp90 inhibitor, AUY922, bearing an isoxazole unit. AUY922 has been found with potent anti-cancer activity. However, during clinical trials with the inhibitor, patients showed various side effects, such as night blindness. To investigate the side effects, we will install an alkyne moiety onto AUY922 and use chemical proteomics approach to decipher the biological target under native cellular environment. Through chemical proteomics study, the off-targets of AUY922 could be identified and help elucidate the side effect of this drug. Such information will aid in further optimizing the structural design of AUY922 analogues and accelerating the drug discovery process. We will also employ the same strategy to investigate the sulfamethoxazole/protein interactions in bacteria cells. Sulfamethoxazole is an antibiotic exhibiting a wide spectrum of antimicrobial activity. However, no systematic study has been conducted to investigate its interactions with bacteria proteomes. Through chemical proteomics analysis, we believe a comprehensive understanding of the sulfamethoxazole/protein interactions can be acquired. The identified protein hits can allow us to uncover new biological targets for antibiotic design. Through the study, we hope to generate useful tools for combating the antibiotic resistance problem prevalent today.