Novel Hsp90 Inhibitor NVP-AUY922 Radiosensitizes Prostate Cancer Cells

Abstract

Purpose/Objective(s): Recent studies have suggested a reciprocal negative feedback mechanism between the androgen receptor (AR) and PI3K-AKT-mTOR signaling pathways in prostate cancer. These recent data suggest that prostate cancer cells can use either PI3K-AKT-mTOR or AR survival pathways for tumor maintenance and point towards combined inhibition of these pathways as a means to improve cancer treatment. The effects of targeting both pathways concurrently on prostate cancer radioresponse are unknown. Critical components of both the PI3K-AKT-mTOR and AR pathways are client proteins of the molecular chaperone protein, Hsp90, which is overexpressed in many cancers. We sought to test the novel Hsp90 inhibitor, NVP-AUY922, for anti-cancer and radiosensitization properties in prostate cancer cells. Materials/Methods: The effect of the NVP-AUY922 alone and in combination with radiation on prostate cancer cells was examined in vitro. Prostate cancer cell immunoblotting assay was performed to assay for NVP-AUY922 effects on the PI3K-AKT-mTOR, MAPK and AR pathways, as well as additional client proteins ATR and CHK1. We examined NVP-AUY922 effects on prostate cancer cell death using annexinV FACS, clonogenic survival, and cell cycle arrest by FACS and DNA damage repair using 53BP1 and gamma-H2AX immunofluorescence. Hind-flank Myc-CaP and PC3 xenograft models were used to examine tumor growth delay following NVP-AUY922 treatment with or without radiation. Results: NVP-AUY922 was able to simultaneously downregulate the PI3K-AKT-mTOR and AR pathways in PC3 and Myc-CaP cells at nanomolar levels (10-50 nM). NVP-AUY922 was able to dramatically radiosensitize both PC3 and Myc-CaP cells at similar levels per clonogenic survival assays. NVP-AUY922 radiosensitization was correlated with delayed repair of DNA double-strand breaks (DSBs) in Myc-CaP cells as per DSB foci assays. Finally, preliminary xenograft experiments demonstrated the ability of NVP-AUY922 and radiation to further delay tumor growth in vivo as compared to either treatment alone (p < 0.05). Conclusions: NVP-AUY922 targets both the AR and PI3K-AKT-mTOR pathways resulting in inhibition of DSB repair and radiosensitization in vitro and in vivo. Our results provide a framework for clinical translation of NVP-AUY922 in combination with radiation therapy for prostate cancer.

The combination of Hsp90 inhibitor 17AAG and heavy‐ion irradiation provides effective tumor control in human lung cancer cells

“…As Hsp90 inhibitor is known to affect the cell cycle checkpoint , we also studied cell cycle effects after various combinations of treatment with 17AAG and radiation. Figure shows our cell cycle data.…”

“…In this report we have shown that the combination of Hsp90 inhibitor 17AAG and carbon ion irradiation provides good tumor control both in vitro and in vivo. As mentioned above, a number of reports have indicated radiosensitization effects by 17AAG or other Hsp90 inhibitors using gamma or X‐rays , but radiosensitization by combining Hsp90 inhibitor and heavy‐ion irradiation both in in vitro and in vivo has yet to be reported. Generally, it is thought that heavy‐ion irradiation alone may provide sufficient tumor control and other additional factors might not be necessary.…”

“…An interesting study recently reported that Hsp90 inhibitor 17AAG induces BRCA1 ubiquitination and proteasomal degradation, leading to repair inhibition of DSBs induced by ionizing radiation . Radiosensitization effect in vivo by Hsp90 inhibitors has also been demonstrated .…”

“…We and others have also shown that one of the causes of sensitization could be inhibition of DNA double strand break (DSB) repair . Checkpoint arrest mainly at G2/M phase has also been suggested as a cause of radiosensitization with Hsp90 inhibitors . An interesting study recently reported that Hsp90 inhibitor 17AAG induces BRCA1 ubiquitination and proteasomal degradation, leading to repair inhibition of DSBs induced by ionizing radiation .…”

“…Although there is no FDA‐approved Hsp90 inhibitor , 17 agents have entered clinical trials . The combination of Hsp90 inhibitor and radiation on tumor cells has been studied and enhancement of radiation effect with the inhibitors has been well documented . Hypoxic tumor cells were also radiosensitized by the combination strategy .…”