Abstract 34P
Background
Auger electron (AE) therapy is an emerging treatment in the radiation field; AEs have low energy and travel a short, linear trajectory when emitted, making them ideal for specific irradiation of cancer. However, for AEs to be effective killers of cancer, they must be bound to agents that target cancer cells. Hsp90 is an ATP-dependent molecular chaperone that aids in the folding and stabilization of proteins. Cancer cells express mutated proteins that have an enhanced dependence on chaperones such as Hsp90, and therefore, Hsp90 inhibitors are being developed for use as an anti-cancer drug. Interestingly, studies have shown that Hsp90 inhibitors are highly retained in tumors and have a greater binding affinity for tumor Hsp90 compared to Hsp90 found in normal cells, thus, Hsp90 inhibitors are an excellent candidate for radionuclide therapy.
Methods
Several novel Hsp90 inhibitors were synthesized and screened for Hsp90 affinity and cell permeability, using various protein-based assays and client signaling analysis in the triple-negative breast cancer cell line, MDA-MB-231. Fluorescence microscopy was also used to observe changes in Hsp90 localization upon inhibition.
Results
All ten compounds demonstrated the expected Hsp90 inhibitor properties, however, the bromine-derived compound, MH-25, was found to have the strongest affinity for Hsp90 and the greatest effect on Hsp90 client signaling. Our imaging data also confirmed the nuclear and perinuclear presence of Hsp90 in cells. The localization of Hsp90 to the nuclear region remained unchanged after treatment with Hsp90 inhibitors, suggesting our novel compounds will be satisfactory in delivering Auger-electrons directly to DNA.
Conclusions
MH-25 has been identified as a lead compound and will be radiolabelled with Br-77 for future DNA damage assays and mouse model experiments. This research provides an alternative application of Hsp90 inhibitors and a potential strategy to help reduce side effects for cancer patients undergoing radiation treatment. In addition, these novel inhibitors are expected to proceed to phase I of clinical trials.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Alberta Cancer Foundation.
Disclosure
All authors have declared no conflicts of interest.