Increased radiosensitivity and radiothermosensitivity of human pancreatic MIAPaCa-2 and U251 glioblastoma cell lines treated with the novel Hsp90 inhibitorNVP-HSP990

Abstract

Background and purposeHeat shock Protein 90 (Hsp90) is a molecular chaperone that folds, stabilizes, and functionally regulates many cellular proteins involved in oncogenic signaling and in the regulation of radiosensitivity. It is upregulated in response to stress such a heat. Hyperthermia is a potent radiosensitizer, but induction of Hsp90 may potentially limit its efficacy. Our aim was to investigate whether the new Hsp90 inhibitor NVP-HSP990 increases radiosensitivity, thermosensitivity and radiothermosensitivity of human tumor cell lines.Material and methodsU251 glioblastoma and MIA PaCa-2 pancreatic carcinoma cells were used. To determine clonogenic survival, colony forming assays were performed. Cell viability and proliferation were assesed by Trypan blue staining. Cell cycle and apoptosis analyses were performed by flow cytometry. DAPI staining was used to detect mitotic catastrophe.ResultsNVP-HSP990 increased the thermosensitivity, radiosensitivity and radio-thermosensitivity of both cell lines in clonogenic assays. 72 hours after irradiation with 4 Gy, a significant reduction in cell number associated with considerable G2/M acumulation and mitotic catastrophe as well as cell death by apoptosis/necrosis was observed.ConclusionsTreatment with NVP-HSP990 strongly sensitized U251 and MIA PaCa-2 cells to hyperthermia and ionizing radiation or combination thereof through augmentation of G2/M arrest, mitotic catastrophe and associated apoptosis.

Efficacy of Onalespib, a Long-Acting Second-Generation HSP90 Inhibitor, as a Single Agent and in Combination with Temozolomide against Malignant Gliomas

“…They bind to the N-terminal ATPase-pocket, affecting the chaperone activity and leading to the depletion of HSP90 substrates by subsequent proteosomal degradation (11–13). Recent studies in several solid tumor models have shown sensitization to currently used chemotherapeutic agents when combined with new generation HSP90 inhibitors (20, 21). Onalespib, a potent second-generation HSP90 inhibitor differs from other HSP90 inhibitors in its longer duration of target inhibition (22) and its favorable toxicity profile in phase I studies in patients with refractory solid tumors (17).…”

Hsp90 Inhibitor Ganetespib Sensitizes Non–Small Cell Lung Cancer to Radiation but Has Variable Effects with Chemoradiation

“…Radiosensitization effect in vivo by Hsp90 inhibitors has also been demonstrated (14, 21, 23). These data strongly suggest that targeting Hsp90 with its inhibitors represents a promising strategy for enhancing the sensitivity of cancer cells to radiation (19–24). Ganetespib is an investigational small molecule inhibitor of Hsp90 with favorable pharmacologic properties that distinguishes it from other first- and second-generation Hsp90 inhibitors in terms of potency, safety, and tolerability (27, 42).…”

“…As Hsp90 inhibitors are known to affect the cell cycle checkpoint (19, 21–24, 35, 36), as does irradiation, which causes a G1/S arrest in P53 WT cells (37), we next determined the interaction of radiation with ganetespib on the cell cycle effects in both H460 and A549 cells (Figure 3A–D). G2/M arrest was induced by ganestepib, radiation, and the combination, at 4 hours postirradiation.…”

“…Studies have shown that one of the causes of sensitization could be inhibition of DNA double strand break (DSB) repair (17–21, 36). Checkpoint arrest mainly at G2/M phase has also been suggested as a cause of radiosensitization with Hsp90 inhibitors (19–24, 36). Radiosensitization effect in vivo by Hsp90 inhibitors has also been demonstrated (14, 21, 23).…”

Hypoxia-inducible factor–1 and associated upstream and downstream proteins in the pathophysiology and management of glioblastoma

“…131,204 Several groups have studied Hsp90 involvement in GBM and have proposed that its inhibition is a possible therapeutic measure for direct reduction of glioma tumor growth. 58,154,252,255 Furthermore, current research has focused on the ability of Hsp90 knockdown or inhibition to attenuate the effects of radiation 155,228 and drug therapy 13 through increased cell sensitization, potentially offering a combinatorial and aggressive approach to GBM treatment by using Hsp90 targeting. The RACK1 protein has been shown to be a potent molecular enhancer of tumorigenesis in several types of cancers, making it a potentially viable target for suppressing tumor growth, tumor cell proliferation, and tumor-associated angiogenesis.…”