Strong antitumor synergy between DNA crosslinking and HSP90 inhibition causes massive premitotic DNA fragmentation in ovarian cancer cells

Abstract

All current regimens for treating ovarian cancer center around carboplatin as standard first line. The HSP90 inhibitor ganetespib is currently being assessed in advanced clinical oncology trials. Thus, we tested the combined effects of ganetespib and carboplatin on a panel of 15 human ovarian cancer lines. Strikingly, the two drugs strongly synergized in cytotoxicity in tumor cells lacking wild-type p53. Mechanistically, ganetespib and carboplatin in combination, but not individually, induced persistent DNA damage causing massive global chromosome fragmentation. Live-cell microscopy revealed chromosome fragmentation occurring to a dramatic degree when cells condensed their chromatin in preparation for mitosis, followed by cell death in mitosis or upon aberrant exit from mitosis. HSP90 inhibition caused the rapid decay of key components of the Fanconi anemia pathway required for repair of carboplatin-induced interstrand crosslinks (ICLs), as well as of cell cycle checkpoint mediators. Overexpressing FancA rescued the DNA damage induced by the drug combination, indicating that FancA is indeed a key client of Hsp90 that enables cancer cell survival in the presence of ICLs. Conversely, depletion of nuclease DNA2 prevented chromosomal fragmentation, pointing to an imbalance of defective repair in the face of uncontrolled nuclease activity as mechanistic basis for the observed premitotic DNA fragmentation. Importantly, the drug combination induced robust antitumor activity in xenograft models, again accompanied with depletion of FancA. In sum, our findings indicate that ganetespib strongly potentiates the antitumor efficacy of carboplatin by causing combined inhibition of DNA repair and cell cycle control mechanisms, thus triggering global chromosome disruption, aberrant mitosis and cell death. 6 This provides a strong rationale for HSP90 inhibitors in cancer therapy 7 and raises the possibility that HSP90 inhibitors can be used in combination with DNAdamaging chemotherapeutics. 8 Ovarian cancer is among the most common gynecological tumor types and carries the worst prognosis. HSP90 is highly expressed in advanced ovarian carcinoma 9 and thus constitutes a potential therapeutic drug target. 10 In support, HSP90 inhibitors were found effective against ovarian cancer in preclinical models, 11-14 alone or in combination with conventional chemotherapy. 15,16 Carboplatin is the key component of all current first-line therapies for ovarian carcinoma. However, while initially often responding with regression, most tumors relapse and develop resistance within less than a year. 17,18 Like other platinum compounds, carboplatin acts by forming crosslinks within DNA. 17 Platinum compounds form intrastrand DNA lesions but also interstrand crosslinks (ICLs) by covalently linking opposite DNA strands. Such ICLs represent major obstacles to the DNA replication fork 19 and are therefore considered the principal toxic lesion of carboplatin's mode of action. The ICLs can only be removed by a sophisticated DNA repair systemthe Fanconi ...

The HSP90 inhibitor Onalespib exerts synergistic anti-cancer effects when combined with radiotherapy: an in vitro and in vivo approach

“…Onalespib for example, has been found to sensitize malignant glioma cells to temozolomide. The HSP90 antagonist ganetespib, has recently been investigated for sensitizing effects in ovarian cancer and pancreatic cancer cells to chemotherapy 25 and radiochemotherapy 26 , respectively. The HSP90 antagonist NVP-AUY922 potentiated anti-cancer effects of a BCL-2 inhibitor in small cell lung cancer 27 and demonstrated synergy in combination with trastuzumab in breast cancer 28 .…”

Boosting the effects of hyperthermia-based anticancer treatments by HSP90 inhibition

“…In nearly all experiments, we observed that Ganetespib considerably potentiates cell killing by hyperthermia, in line with a recent study that reported enhancement of the effects of hyperthermia by 17-DMAG [ 47 , 48 ]. It is worth noting that prolonged administration of Ganetespib alone can also sensitize cancer cells to radiation and some chemotherapeutic drugs [ 49 – 51 ]. Second, the increased inhibition of HR (and, potentially, other DNA repair mechanisms) by hyperthermia and Ganetespib sensitizes cells to multiple DSB-inducing agents, indirectly increasing their cytotoxicity.…”

The identification of six risk genes for ovarian cancer platinum response based on global network algorithm and verification analysis

“…In the research of Kramer et al, it was shown that by jointly inhibiting DNA repair and cell cycle control mechanisms, HSP90 inhibitor ganetespib blocked the degradation of FANCA and the imbalance of nuclease DNA2. On this basis, ganetespib enhanced the anti‐tumour efficacy of carboplatin, thereby triggering overall chromosomal destruction, abnormal mitosis and cell death in ovarian cancer cells 46 . It has been reported that heterozygous carriers of FA gene mutations will not cause FA phenotype, but may increase the risk of cancer.…”