Abstract ND13: The discovery and characterization of CFT7455: A potent and selective degrader of IKZF1/3 for the treatment of relapsed/refractory multiple myeloma

Introduction: Ikaros family zinc finger protein 1 and 3 (IKZF1/3) are essential transcription factors (TF) for terminal differentiation of B and T cells. Depletion of IKZF1/3 inhibits the growth of multiple myeloma (MM) cells, confirming their dependency on IKZF1/3. IMiDs (lenalidomide, pomalidomide) are effective therapies for treatment of MM and promote degradation of IKZF1/3 via their interaction with CRL4-CRBN E3 ligase. However, most patients treated with lenalidomide or pomalidomide eventually develop progressive disease due to acquired resistance, underscoring the unmet medical need. CFT7455 is a novel IKZF1/3 degrader optimized for high binding affinity to cereblon (CRBN), rapid and deep IKZF1/3 degradation, and potent dose-dependent efficacy in vivo.

Results: A series of novel benzoimidazolone-based CRBN ligands with potent binding affinity were discovered and their binding modes were informed by CRBN co-crystal structures. Although the benzoimidazolone-based CRBN binders did not exhibit IKZF1/3 degradation activity, structural insights into their unique binding modes and knowledge of the IKZF1/3 degradation pharmacophore were combined to enable identification of a novel benzoisoindolone-based ligand that exhibited a 10-fold potency increase in biochemical CRBN binding and a 30-fold potency increase in H929 MM cell growth inhibition when compared to lenalidomide. Additional rounds of structure-based drug design, degradation and phenotypic profiling led to the discovery of CFT7455, a highly potent, selective and orally bioavailable degrader of IKZF1/3. CFT7455 demonstrated an 800 and 1600-fold improvement in CRBN binding compared to pomalidomide in biochemical and cellular NanoBRET assays, respectively. In H929 MM cells expressing HiBiT-tagged IKZF1, CFT7455 induced >75% degradation of IKZF1 within 1.5 hrs. The high binding affinity and degradation catalysis shown with CFT7455 enabled potent antiproliferative activity across a panel of MM cell lines, as well as H929 cells made resistant to IMiDs. In vivo, CFT7455 catalyzed deep and durable degradation of IKZF3, translating into potent antitumor activity in multiple myeloma xenograft models. CFT7455 also retained its activity in models resistant or insensitive to clinically approved IMiDs as single agent or in combination with standard of care agent dexamethasone.

Conclusion: Overall, CFT7455 is a next generation IKZF1/3 degrader, with improved potency and anticancer efficacy in preclinical models compared to existing IMiDs. These features make CFT7455 an exciting drug candidate, as a single agent or for use in combination. CFT7455 is currently being studied in a Ph1 clinical trial.

Citation Format: James A. Henderson, Scott J. Eron, Andrew Good, R Jason Kirby, Samantha Perino, Roman V. Agafonov, Prasoon Chaturvedi, Bradley Class, David Cocozziello, Ashley A. Hart, Christina S. Henderson, Marta Isasa, Brendon Ladd, Matt Schnaderbeck, Michelle Mahler, Adam S. Crystal, Roy M. Pollock, Christopher G. Nasveschuk, Andrew J. Phillips, Stewart L. Fisher, David A. Proia. The discovery and characterization of CFT7455: A potent and selective degrader of IKZF1/3 for the treatment of relapsed/refractory multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr ND13.

Evaluation of the Small-molecule BRD4 Degrader CFT-2718 in Small-cell Lung Cancer and Pancreatic Cancer Models

Targeted, catalytic degradation of oncoproteins using heterobifunctional small molecules is an attractive modality, particularly for hematologic malignancies, which are often initiated by aberrant transcription factors and are challenging to drug with inhibitors. BRD4, a member of the bromodomain and extraterminal family, is a core transcriptional and epigenetic regulator that recruits the P-TEFb complex, which includes Cdk9 and cyclin T, to RNA polymerase II (pol II). Together, BRD4 and CDK9 phosphorylate serine 2 (pSer2) of heptad repeats in the C-terminal domain of RPB1, the large subunit of pol II, promote transcriptional elongation. Small-molecule degraders of BRD4 have shown encouraging efficacy in preclinical models for several tumor types but less efficacy in other cancers including small-cell lung cancer (SCLC) and pancreatic cancer. Here, we evaluated CFT-2718, a new BRD4-targeting degrader with enhanced catalytic activity and in vivo properties. In vivo, CFT-2718 has significantly greater efficacy than the CDK9 inhibitor dinaciclib in reducing growth of the LX-36 SCLC patient-derived xenograft (PDX) model and performed comparably to dinaciclib in limiting growth of the PNX-001 pancreatic PDX model. In vitro, CFT-2718 reduced cell viability in four SCLC and two pancreatic cancer models. In SCLC models, this activity significantly exceeded that of dinaciclib; furthermore, CFT-2718 selectively increased the expression of cleaved PARP, an indicator of apoptosis. CFT-2718 caused rapid BRD4 degradation and reduced levels of total and pSer2 RPB1 protein. These and other findings suggest that BRD-mediated transcriptional suppression merits further exploration in the setting of SCLC.

A Method for Determining the Kinetics of Small-Molecule-Induced Ubiquitination

Recent advances in targeted protein degradation have enabled chemical hijacking of the ubiquitin-proteasome system to treat disease. The catalytic rate of cereblon (CRBN)-dependent bifunctional degradation activating compounds (BiDAC), which recruit CRBN to a chosen target protein, resulting in its ubiquitination and proteasomal degradation, is an important parameter to consider during the drug discovery process. In this work, an in vitro system was developed to measure the kinetics of BRD4 bromodomain 1 (BD1) ubiquitination by fitting an essential activator kinetic model to these data. The affinities between BiDACs, BD1, and CRBN in the binary complex, ternary complex, and full ubiquitination complex were characterized. Together, this work provides a new tool for understanding and optimizing the catalytic and thermodynamic properties of BiDACs.

Consecutive Day HSP90 Inhibitor Administration Improves Efficacy in Murine Models of KIT-Driven Malignancies and Canine Mast Cell Tumors

PURPOSE

STA-1474, prodrug of the heat shock protein 90 inhibitor (HSP90i) ganetespib, previously demonstrated activity in canine preclinical models of cancer; interestingly, prolonged infusions were associated with improved biologic activity. The purpose of this study was to identify the ideal treatment schedule for HSP90i in preclinical models of KIT-driven malignancies and in dogs with spontaneous mast cell tumors (MCT), where KIT is a known driver.

EXPERIMENTAL DESIGN

In vitro and murine xenograft experiments and clinical studies in dogs with MCTs were used to define the effects of HSP90i-dosing regimen on client protein downregulation and antitumor activity.

RESULTS

Continuous HSP90 inhibition led to durable destabilization of client proteins in vitro; however, transient exposure required >10× drug for comparable effects. In vivo, KIT was rapidly degraded following a single dose of HSP90i but returned to baseline levels within a day. HSP90 levels increased and stabilized 16 hours after HSP90i and were not elevated following a subsequent near-term exposure, providing a functional pool of chaperone to stabilize proteins and a means for greater therapeutic activity upon HSP90i reexposure. HSP90i administered on days 1 and 2 (D1/D2) demonstrated increased biologic activity compared with D1 treatment in KIT or EGFR-driven murine tumor models. In a trial of dogs with MCT, D1/D2 dosing of HSP90i was associated with sustained KIT downregulation, 50% objective response rate and 100% clinical benefit rate compared with D1 and D1/D4 schedules.

CONCLUSIONS

These data provide further evidence that prolonged HSP90i exposure improves biologic activity through sustained downregulation of client proteins.

STA-8666, a novel HSP90 inhibitor/SN-38 drug conjugate, causes complete tumor regression in preclinical mouse models of pediatric sarcoma

Long-term survival in patients with metastatic, relapsed, or recurrent Ewing sarcoma and rhabdomyosarcoma is dismal. Irinotecan, a topoisomerase 1 inhibitor, has activity in these sarcomas, but due to poor bioavailability of its active metabolite (SN-38) has had limited clinical efficacy. In this study we have evaluated the efficacy and toxicity of STA-8666, a novel drug conjugate which uses an HSP90 inhibitor to facilitate intracellular, tumor-targeted delivery of the topoisomerase 1 inhibitor SN-38, thus preferentially delivering and concentrating SN-38 within tumor tissue. We present in vivo evidence from mouse xenograft models that STA-8666 results in more persistent inhibition of topoisomerase 1 and prolonged DNA damage compared to irinotecan. This translates into superior antitumor efficacy and survival in multiple aggressive models of both diseases in mouse xenografts, as well as in an irinotecan-resistant model of pediatric osteosarcoma, demonstrated by dramatic tumor shrinkage, durable remission and prolonged complete regressions following short-term treatment, compared to conventional irinotecan. Gene expression analysis performed on xenograft tumors treated with either irinotecan or STA-8666 showed that STA-8666 affected expression of DNA damage and repair genes more robustly than irinotecan. These results suggest that STA-8666 may be a promising new agent for patients with pediatric-type sarcoma.

Ganetespib limits ciliation and cystogenesis in autosomal-dominant polycystic kidney disease (ADPKD)

Autosomal-dominant polycystic kidney disease (ADPKD) is associated with progressive formation of renal cysts, kidney enlargement, hypertension, and typically end-stage renal disease. In ADPKD, inherited mutations disrupt function of the polycystins (encoded by PKD1 and PKD2), thus causing loss of a cyst-repressive signal emanating from the renal cilium. Genetic studies have suggested ciliary maintenance is essential for ADPKD pathogenesis. Heat shock protein 90 (HSP90) clients include multiple proteins linked to ciliary maintenance. We determined that ganetespib, a clinical HSP90 inhibitor, inhibited proteasomal repression of NEK8 and the Aurora-A activator trichoplein, rapidly activating Aurora-A kinase and causing ciliary loss in vitro. Using conditional mouse models for ADPKD, we performed long-term (10 or 50 wk) dosing experiments that demonstrated HSP90 inhibition caused durable in vivo loss of cilia, controlled cystic growth, and ameliorated symptoms induced by loss of Pkd1 or Pkd2. Ganetespib efficacy was not increased by combination with 2-deoxy-d-glucose, a glycolysis inhibitor showing some promise for ADPKD. These studies identify a new biologic activity for HSP90 and support a cilia-based mechanism for cyst repression.-Nikonova, A. S., Deneka, A. Y., Kiseleva, A. A., Korobeynikov, V., Gaponova, A., Serebriiskii, I. G., Kopp, M. C., Hensley, H. H., Seeger-Nukpezah, T. N., Somlo, S., Proia, D. A., Golemis, E. A. Ganetespib limits ciliation and cystogenesis in autosomal-dominant polycystic kidney disease (ADPKD).

Radioresistant human lung adenocarcinoma cells that survived multiple fractions of ionizing radiation are sensitive to HSP90 inhibition

Despite the common usage of radiotherapy for the treatment of NSCLC, outcomes for these cancers when treated with ionizing radiation (IR) are still unsatisfactory. A better understanding of the mechanisms underlying resistance to IR is needed to design approaches to eliminate the radioresistant cells and prevent tumor recurrence and metastases. Using multiple fractions of IR we generated radioresistant cells from T2821 and T2851 human lung adenocarcinoma cells. The radioresistant phenotypes present in T2821/R and T2851/R cells include multiple changes in DNA repair genes and proteins expression, upregulation of EMT markers, alterations of cell cycle distribution, upregulation of PI3K/AKT signaling and elevated production of growth factors, cytokines, important for lung cancer progression, such as IL-6, PDGFB and SDF-1 (CXCL12). In addition to being radioresistant these cells were also found to be resistant to cisplatin.

HSP90 is a molecular chaperone involved in stabilization and function of multiple client proteins implicated in NSCLC cell survival and radioresistance. We examined the effect of ganetespib, a novel HSP90 inhibitor, on T2821/R and T2851/R cell survival, migration and radioresistance. Our data indicates that ganetespib has cytotoxic activity against parental T2821 and T2851 cells and radioresistant T2821/R and T2851/R lung tumor cells. Ganetespib does not affect proliferation of normal human lung fibroblasts. Combining IR with ganetespib completely abrogates clonogenic survival of radioresistant cells.

Our data show that HSP90 inhibition can potentiate the effect of radiotherapy and eliminate radioresistant and cisplatin -resistant residual cells, thus it may aid in reducing NSCLC tumor recurrence after fractionated radiotherapy.

Ganetespib, an HSP90 inhibitor, kills Epstein-Barr virus (EBV)-infected B and T cells and reduces the percentage of EBV-infected cells in the blood

HSP90 inhibitors have been shown to kill Epstein-Barr virus (EBV)-infected cells by reducing the level of EBV EBNA-1 and/or LMP1. We treated virus-infected cells with ganetespib, an HSP90 inhibitor currently being evaluated in multiple clinical trials for cancer and found that the drug killed EBV-positive B and T cells and reduced the level of both EBV EBNA-1 and LMP1. Treatment of cells with ganetespib also reduced the level of pAkt. Ganetespib delayed the onset of EBV-positive lymphomas and prolonged survival in SCID mice inoculated with one EBV-transformed B-cell line, but not another B-cell line. The former cell line showed lower levels of EBNA-1 after treatment with ganetespib in vitro. Treatment of a patient with T-cell chronic active EBV with ganetespib reduced the percentage of EBV-positive cells in the peripheral blood. These data indicate that HSP90 inhibitors may have a role in the therapy of certain EBV-associated diseases.

Anti-Müllerian Hormone Signaling Regulates Epithelial Plasticity and Chemoresistance in Lung Cancer

Anti-Müllerian hormone (AMH) and its type II receptor AMHR2, both previously thought to primarily function in gonadal tissue, were unexpectedly identified as potent regulators of transforming growth factor (TGF-β)/bone morphogenetic protein (BMP) signaling and epithelial-mesenchymal transition (EMT) in lung cancer. AMH is a TGF-β/BMP superfamily member, and AMHR2 heterodimerizes with type I receptors (ALK2, ALK3) also used by the type II receptor for BMP (BMPR2). AMH signaling regulates expression of BMPR2, ALK2, and ALK3, supports protein kinase B-nuclear factor κB (AKT-NF-κB) and SMAD survival signaling, and influences BMP-dependent signaling in non-small cell lung cancer (NSCLC). AMH and AMHR2 are selectively expressed in epithelial versus mesenchymal cells, and loss of AMH/AMHR2 induces EMT. Independent induction of EMT reduces expression of AMH and AMHR2. Importantly, EMT associated with depletion of AMH or AMHR2 results in chemoresistance but sensitizes cells to the heat shock protein 90 (HSP90) inhibitor ganetespib. Recognition of this AMH/AMHR2 axis helps to further elucidate TGF-β/BMP resistance-associated signaling and suggests new strategies for therapeutic targeting of EMT.

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

PURPOSE

HSP90 inhibition is well known to sensitize cancer cells to radiation. However, it is currently unknown whether additional radiosensitization could occur in the more clinically relevant setting of chemoradiation (CRT). We used the potent HSP90 inhibitor ganetespib to determine whether it can enhance CRT effects in NSCLC.

EXPERIMENTAL DESIGN

We first performed in vitro experiments in various NSCLC cell lines combining radiation with or without ganetespib. Some of these experiments included clonogenic survival assay, DNA damage repair, and cell-cycle analysis, and reverse-phase protein array. We then determined whether chemotherapy affected ganetespib radiosensitization by adding carboplatin-paclitaxel to some of the in vitro and in vivo xenograft experiments.

RESULTS

Ganetespib significantly reduced radiation clonogenic survival in a number of lung cancer cell lines, and attenuated DNA damage repair with irradiation. Radiation caused G₂-M arrest that was greatly accentuated by ganetespib. Ganetespib with radiation also dose-dependently upregulated p21 and downregulated pRb levels that were not apparent with either drug or radiation alone. However, when carboplatin-paclitaxel was added, ganetespib was only able to radiosensitize some cell lines but not others. This variable in vitro CRT effect was confirmed in vivo using xenograft models.

CONCLUSIONS

Ganetespib was able to potently sensitize a number of NSCLC cell lines to radiation but has variable effects when added to platinum-based doublet CRT. For optimal clinical translation, our data emphasize the importance of preclinical testing of drugs in the context of clinically relevant therapy combinations. Clin Cancer Res; 22(23); 5876-86. ©2016 AACR.

A Novel HSP90 Inhibitor-Drug Conjugate to SN38 Is Highly Effective in Small Cell Lung Cancer

PURPOSE

Small cell lung cancer (SCLC) is a highly aggressive disease representing 12% to 13% of total lung cancers, with median survival of <2 years. No targeted therapies have proven effective in SCLC. Although most patients respond initially to cytotoxic chemotherapies, resistance rapidly emerges, response to second-line agents is limited, and dose-limiting toxicities (DLT) are a major issue. This study performs preclinical evaluation of a new compound, STA-8666, in SCLC.

EXPERIMENTAL DESIGN

To avoid DLT for useful cytotoxic agents, the recently developed drug STA-8666 combines a chemical moiety targeting active HSP90 (concentrated in tumors) fused via cleavable linker to SN38, the active metabolite of irinotecan. We compare potency and mechanism of action of STA-8666 and irinotecan in vitro and in vivo RESULTS: In two SCLC xenograft and patient-derived xenograft models, STA-8666 was tolerated without side effects up to 150 mg/kg. At this dose, STA-8666 controlled or eliminated established tumors whether used in a first-line setting or in tumors that had progressed following treatment on standard first- and second-line agents for SCLC. At 50 mg/kg, STA-8666 strongly enhanced the action of carboplatin. Pharmacokinetic profiling confirmed durable STA-8666 exposure in tumors compared with irinotecan. STA-8666 induced a more rapid, robust, and stable induction of cell-cycle arrest, expression of signaling proteins associated with DNA damage and cell-cycle checkpoints, and apoptosis in vitro and in vivo, in comparison with irinotecan.

CONCLUSIONS

Together, these results strongly support clinical development of STA-8666 for use in the first- or second-line setting for SCLC. Clin Cancer Res; 22(20); 5120-9. ©2016 AACR.

Abstract B14: Hsp90-inhibitor drug conjugate STA-12-8666 demonstrates complete tumor regression in preclinical models of pediatric sarcoma

Long-term survival in patients with metastatic relapsed or recurrent Ewing sarcoma (ES) and rhabdomyosarcoma (RMS) is dismal. Encouraging responses to irinotecan, a topoisomerase 1 (Top1) inhibitor, have been seen in these patients; however, limitations in irinotecan bioavailability, including low conversion rate to the active metabolite (SN-38) and high excretion rate of the inactive form, hinder efficacy. HSP90 is widely expressed in cancer cells, and HSP90 inhibitors (HSP90i) have favorable pharmacokinetics for anticancer use, as they remain in tumors for longer periods of time and at higher steady-state levels compared to normal tissue. This property makes them ideal intracellular delivery vehicles for chemotherapeutic drugs, allowing for high tumor exposure and low systemic toxicity. STA-12-8666 (Synta Pharmaceuticals) is an HSP90i drug conjugate (HDC) consisting of a weak HSP90i attached to SN-38 through a cleavable chemical linker. The purpose of this study was to test this HDC in xenograft models of pediatric sarcoma and to investigate its mechanism of action.

To test therapeutic efficacy of this HDC, female SCID mice underwent orthotopic injection of ES or RMS cells from established cell lines or PDX tissue. When tumors reached a desired size, mice were randomized and then treated weekly with HDC, vehicle, ganetespib (a highly potent HSP90i), high dose irinotecan, protracted dose irinotecan, or irinotecan plus ganetespib. Tumors were measured twice per week, and mice were weighed weekly to determine drug tolerability. Tumors were harvested at midpoints and at study endpoint for biology studies. Activity of pharmacodynamic (PD) markers was investigated in tumor tissue.

In xenograft models of ES and RMS, treatment with HDC produced superior antitumor efficacy compared to the other arms. When initial treatment began in mice with palpable tumors (between 100 and 500 mm3 (ES) or 50 and 90 mm3 (RMS)), all tumors underwent complete regression after 2 doses of HDC, with total tumor eradication in all ES mice and several RMS mice. In the RMS group, 6/8 mice relapsed by 23 weeks, and all 6 of those responded to retreatment with HDC. When initial treatment was delayed until tumors reached between 800 mm3 and 1000 mm3, complete regressions were again achieved in ES after 2 doses and RMS after 4 doses. Compared with high dose weekly irinotecan, which also induced tumor regression, mice treated with HDC had longer and more persistent remissions. A dose response effect was seen in HDC with cures noted in mice with ES at the 100- and 150-mg/kg doses and longest remissions noted in RMS in the 150-mg/kg group. Tolerability of the HDC was excellent with no toxicity-related deaths or weight loss in any treated mice. Studies using PDX models are ongoing and will be reported.

Activity of γH2AX in tumor samples was explored as a PD marker of Top1 inhibitor activity. Mice bearing ES were treated with a single dose of vehicle, irinotecan, or HDC and one mouse per group was sacrificed at serial intervals between 6 hours and 10 days post-treatment. Expression of γH2AX in irinotecan mice began to wane between days 1 and 3, whereas in HDC mice, it was still detectable at day 7, suggesting that HDC results in more persistent inhibition of topoisomerase 1 compared to irinotecan. To look at the potential role of HSP90 inhibition in this HDC, HSP70 activity was investigated as a marker of HSP90 inhibition in samples from the dose finding experiment. In ES, no HSP70 was detected in samples from mice treated with irinotecan or HDC, suggesting the primary mechanism of action is via SN-38. In RMS, HSP70 was slightly induced in mice treated with higher doses of the HDC, perhaps contributing to the higher relapse rate in this model.

Preclinical data suggest that this HDC may be a promising anticancer agent for ES and RMS patients.

Citation Format: Christine M. Heske, Arnulfo Mendoza, Choh Yeung, David A. Proia, Len Neckers, Lee J. Helman. Hsp90-inhibitor drug conjugate STA-12-8666 demonstrates complete tumor regression in preclinical models of pediatric sarcoma. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Pediatric Cancer Research: From Mechanisms and Models to Treatment and Survivorship; 2015 Nov 9-12; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(5 Suppl):Abstract nr B14.

Hsp90 Inhibition Results in Glucocorticoid Receptor Degradation in Association with Increased Sensitivity to Paclitaxel in Triple-Negative Breast Cancer

Targetable molecular drivers for triple-negative breast cancer (TNBC) have been difficult to identify; therefore, standard treatment remains limited to conventional chemotherapy. Recently, new-generation small-molecule Hsp90 inhibitors (e.g., ganetespib and NVP-AUY922) have demonstrated improved safety and activity profiles over the first-generation ansamycin class. In breast cancer, clinical responses have been observed in a subset of TNBC patients following ganetespib monotherapy; however, the underlying biology of Hsp90 inhibitor treatment and tumor response is not well understood. Glucocorticoid receptor (GR) activity in TNBC is associated with chemotherapy resistance. Here, we find that treatment of TNBC cell lines with ganetespib resulted in GR degradation and decreased GR-mediated gene expression. Ganetespib-associated GR degradation also sensitized TNBC cells to paclitaxel-induced cell death both in vitro and in vivo. The beneficial effect of the Hsp90 inhibitor on paclitaxel-induced cytotoxicity was reduced when GR was depleted in TNBC cells but could be recovered with GR overexpression. These findings suggest that GR-regulated anti-apoptotic and pro-proliferative signaling networks in TNBC are disrupted by Hsp90 inhibitors, thereby sensitizing TNBC to paclitaxel-induced cell death. Thus, GR+ TNBC patients may be a subgroup of breast cancer patients who are most likely to benefit from adding an Hsp90 inhibitor to taxane therapy.

Abstract B25: Anti-Mullerian hormone (AMH) supports epithelial identity and survival signaling in lung cancer

The purpose of this study is to characterize resistance mechanisms of non-small cell lung cancer (NSCLC) to heat shock protein 90 (HSP90) inhibition. Unexpectedly, we identified anti-Mullerian hormone (AMH) and its type II receptor (AMHR2) as two resistance associated genes. AMH and AMHR2 are TGF-ß/BMP superfamily members that share common type I receptors with BMP, resulting in overlapping signaling outputs. AMH and AMHR2 have thus far predominantly been studied in the context of gonadal development, in regulation of the female reproductive cycle and in gynecological malignancies, and AMH is not known to be expressed outside of these tissues. Using a focused RNAi library designed to detect genes associated with resistance to the HSP90 inhibitor ganetespib, siRNAs against AMH and AMHR2 sensitized 4 out of 5 and 3 out of 5 NSCLC cell lines to ganetespib, respectively. We then for the first time confirmed expression of AMH and AMHR2 in this non-gonadal tumor environment. Furthermore, analysis of data from The Cancer Genome Atlas (TCGA) indicated that AMH and AMHR2 are significantly upregulated in a subpopulation of NSCLC.

Strikingly, depletion of AMH/AMHR2 induced EMT-like features, including downregulation of cadherins, a mesenchymal morphology, increased invasion, and expression of mesenchymal markers: features that are generally associated with resistance to chemotherapy. In contrast, inhibition of HSP90 selected for a more epithelial-like population of cells, as evident by increased E-cadherin or P-cadherin, and downregulation of mesenchymal markers such as VIM and ZEB1. To confirm that mesenchymal-like cells are indeed more responsive to HSP90 inhibition, we depleted E-cadherin or P-cadherin and again observed sensitization to ganetespib. We further found that AMH and AMHR2 did not confer sensitization to cisplatin. Interestingly, depletion of cadherins, and the associated induction of EMT-like properties, also resulted in downregulation of AMH and AMHR2, further supporting the link between AMH/AMHR2 expression and epithelial identity. In vivo studies confirmed that AMH depletion sensitizes NSCLC cells to ganetespib and showed that it also significantly reduces overall tumor volume.

Reduction of AMH or AMHR2 also decreased phosphorylation of direct effector SMAD proteins, and depressed activity of NFκB and AKT, both regulators of EMT and survival. These results for the first time indicate the presence of an AMH-AMHR2-NFκB-AKT signaling axis of therapeutic relevance in NSCLC. To further explore the therapeutic potential of this observation, we treated NSCLC with combinations of ganetespib and the proteasome inhibitor bortezomib- an inhibitor previously shown to disrupt NFκB signaling in some cancers - and observed significant synergy between the two drugs.

In conclusion, our work for the first time characterizes AMH and AMHR2 in NSCLC. We go on to show that AMH and AMHR2 regulated canonical-SMAD signaling as well as non-canonical AKT-NFκB signaling, in addition to regulating the epithelial identify of cancer cells. Importantly, our results also suggest that AMH and AMHR2 may serve as biomarkers to predict resistance to HSP90 inhibitors, and that it may be beneficial to prime lung tumors with HSP90 inhibitors, to reverse EMT and decrease survival signaling, prior to treatment with chemotherapy.

Note: This abstract was not presented at the conference.

Citation Format: Tim N. Beck, Vladislav Korobeynikov, Alexander Kudinov, Rachel Georgeopoulos, Emmanuelle Nicolas, Margret B. Einarson, Yan Zhou, Yanis Boumber, David A. Proia, Ilya G. Serebriiskii, Erica A. Golemis. Anti-Mullerian hormone (AMH) supports epithelial identity and survival signaling in lung cancer. [abstract]. In: Proceedings of the Fourth AACR International Conference on Frontiers in Basic Cancer Research; 2015 Oct 23-26; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2016;76(3 Suppl):Abstract nr B25.

Repeated PD-1/PD-L1 monoclonal antibody administration induces fatal xenogeneic hypersensitivity reactions in a murine model of breast cancer

Monoclonal antibodies (mAbs) targeting coinhibitory molecules such as PD-1, PD-L1 and CTLA-4 are increasingly used as targets of therapeutic intervention against cancer. While these targets have led to a critical paradigm shift in treatments for cancer, these approaches are also plagued with limitations owing to cancer immune evasion mechanisms and adverse toxicities associated with continuous treatment. It has been difficult to reproduce and develop interventions to these limitations preclinically due to poor reagent efficacy and reagent xenogenecity not seen in human trials. In this study, we investigated adverse effects of repeated administration of PD-1 and PD-L1 mAbs in the murine 4T1 mammary carcinoma model. We observed rapid and fatal hypersensitivity reactions in tumor bearing mice within 30-60 min after 4-5 administrations of PD-L1 or PD-1 mAb but not CTLA-4 antibody treatment. These events occurred only in mice bearing the highly inflammatory 4T1 tumor and did not occur in mice bearing non-inflammatory tumors. We observed that mortality was associated with systemic accumulation of IgG1 antibodies, antibodies specific to the PD-1 mAb, and accumulation of Gr-1^high neutrophils in lungs which have been implicated in the IgG mediated pathway of anaphylaxis. Anti-PD-1 associated toxicities were alleviated when PD-1 blockade was combined with the therapeutic HSP90 inhibitor, ganetespib, which impaired immune responses toward the xenogeneic PD-1 mAb. This study highlights a previously uncharacterized fatal hypersensitivity exacerbated by the PD-1/PD-L1 axis in the broadly used 4T1 tumor model as well as an interesting relationship between this particular class of checkpoint blockade and tumor-dependent immunomodulation.

Abstract 4409: STA-12-8666: a first-in-class HSP90 inhibitor drug conjugate (HDC) designed to selectively deliver chemotherapy to tumors

Chemotherapeutic drugs have been a mainstay of cancer therapy for decades; however, their effectiveness is often hampered by inefficient drug exposures and undesirable toxicity to normal tissues. Here we report on a novel drug delivery system, termed heat shock protein 90 (HSP90) inhibitor-drug conjugates (HDC), based on the property that small molecule inhibitors of HSP90 are preferentially retained in tumors cells in contrast to their rapid clearance from the circulation and normal tissues. By attaching chemotherapeutic drugs to HSP90 inhibitor backbones, HDC technology exploits this inherent retention property to efficiently deliver cytotoxic payloads directly into tumor tissues and provide extended drug exposure. STA-12-8666 is an HDC that comprises an HSP90 inhibitor fused to the topoisomerase inhibitor SN-38 (active metabolite of irinotecan). In vivo modeling showed that the HSP90 inhibitor moiety was required for tumor-selective retention of STA-12-8666. Prolonged exposure of STA-12-8666 provided extended release of active SN-38 within the tumor compartment, generating up to two weeks of biomarker engagement (γ-H2AX) in contrast to 3-4 days with irinotecan. The broad therapeutic window exhibited by STA-12-8666 conferred superior efficacy and durability over irinotecan treatment alone - resulting in complete or near complete responses (CR) across a broad spectrum of solid tumor models, including an irinotecan-insensitive bladder cancer model and an aggressive lung cancer model where biweekly treatment of STA-12-8666 was initiated at a starting tumor volume 5-times greater that of typical studies. CRs were also observed in a human pancreatic PDX model following 3 doses of STA-12-8666, which were maintained for more than a month. Of note, recurrent PDX tumors remained sensitive to subsequent therapeutic challenge with STA-12-8666 suggesting HDC delivery may circumvent common mechanisms of resistance to irinotecan. Preliminary findings from an ongoing Phase 1 dose escalation study in dogs with spontaneous tumors suggest a well-managed safety profile and encouraging tumor responses. Overall, STA-12-8666 is a promising investigational agent prototypical of a platform technology that can be applied to other cytotoxic payloads to improve therapeutic indices as well as generating new pharmaceutical entities for evaluation as novel anticancer drugs.

Citation Format: David A. Proia, Donald L. Smith, Junyi Zhang, Dan Zhou, John-Paul Jimenez, Jim Sang, Sarah Rippy, Cheryl London, Luisa S. Ogawa, Jun Jiang, Teresa Przewloka, Manuel Sequeira, Jaime Acquaviva, Suqin He, John Chu, Chaohua Zhang, Yuan Liu, Josephine Ye, Vladimir Khazak, Igor Astsaturov, Takayo Inoue, Noriaki Tatsuta, Richard C. Bates, Andrew Sonderfan, Dinesh Chimmanamada, Weiwen Ying. STA-12-8666: a first-in-class HSP90 inhibitor drug conjugate (HDC) designed to selectively deliver chemotherapy to tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4409. doi:10.1158/1538-7445.AM2015-4409

Abstract 1465: Development of patient-derived platform to assess activity of anticancer agents in pancreatic cancer

Pancreatic cancer (PDAC) affects 44,000 individuals yearly in the US. This cancer is almost universally lethal, with a very limited efficacy of approved chemotherapy (gemcitabine, nab-paclitaxel, platinum, 5FU). Clinical trials seeking to expand the portfolio of anti-cancer agents active in PDAC have been largely unsuccessful. PDAC is almost always characterized by activating mutations in the KRAS oncogene, which is difficult to directly inhibit, focusing therapeutic strategies on inhibiting downstream KRAS effectors in the RAF-MEK-ERK signaling cascade. However, disruption of these effectors has been complicated by the existence of extensive redundancies in signaling leading to rapid reversal of inhibition. Thus, there is a clear and urgent need for the development of new anti-PDAC agents as well as reliable models of PDAC that better recapitulate biological properties of pancreatic cancer.

Here, we report on the development of a new drug screening platform to evaluate the activity of existing and emerging chemotherapeutics against pancreatic cancer. Surgically resected pancreatic tumors were implanted in immunocompromised mice to develop direct patient-derived xenografts (PDX). Cell lines derived from the PDX models were subsequently screened for proliferation and viability following exposure to 867 clinical grade or FDA approved drugs. Top hits were then validated in mice bearing the PDX tumors as well as in a genetically modified KRAS/p53 mutant mouse model of pancreatic cancer (KPC).

Triptolide, a natural product compound from Chinese medicinal plant Tripterygium wilfordii, was found to be the most active agent in the screen. In vivo, triptolide produced complete tumor regressions for up to 6 weeks in c-Myc amplified PDX models. Molecular analysis revealed the specific ability of triptolide to quickly deplete c-Myc protein in Myc-amplified cancers by binding and inactivating ERCC3 protein. Finally, we used our PDX platform to evaluate the activity of a novel anticancer agent STA-12-8666 (Synta Pharmaceuticals), a small molecule drug conjugate consisting of a tumor selective delivery moiety (HSP90 inhibitor) attached via a cleavable linker to SN38, the active metabolite of the topoisomerase I inhibitor irinotecan. HSP90 inhibitors and irinotecan, members of the screening library, showed only modest activity when tested individually in the primary pancreatic cell lines and PDAC PDX models suggesting that the potent antitumor activity of STA-12-8666 is due in part to its tumor targeted delivery and prolonged SN38 exposure. Thus, STA-12-8666, that provides targeted delivery to the tumor with activated HSP90, was significantly more effective than irinotecan in all pancreatic PDX models tested, and providing complete, durable responses in a subset. In conclusion, our patient-derived platform provides a valuable tool for preclinical analysis of promising therapeutic agents for treatment of pancreatic cancer.

Citation Format: Vladimir Khazak, Natalia Skobeleva, Natalia Beglyarova, Eugenia Banina, Elena Lysenko, Igor Astsaturov, Sandra A. Jablonski, Louis M. Weiner, Ilya Serebriiskii, David A. Proia. Development of patient-derived platform to assess activity of anticancer agents in pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1465. doi:10.1158/1538-7445.AM2015-1465

Resistance to HSP90 inhibition involving loss of MCL1 addiction

Inhibition of the chaperone heat-shock protein 90 (HSP90) induces apoptosis, and it is a promising anti-cancer strategy. The mechanisms underpinning apoptosis activation following HSP90 inhibition and how they are modified during acquired drug resistance are unknown. We show for the first time that, to induce apoptosis, HSP90 inhibition requires the cooperation of multi BH3-only proteins (BID, BIK, PUMA) and the reciprocal suppression of the pro-survival BCL-2 family member MCL1, which occurs via inhibition of STAT5A. A subset of tumour cell lines exhibit dependence on MCL1 expression for survival and this dependence is also associated with tumour response to HSP90 inhibition. In the acquired resistance setting, MCL1 suppression in response to HSP90 inhibitors is maintained; however, a switch in MCL1 dependence occurs. This can be exploited by the BH3 peptidomimetic ABT737, through non-BCL-2-dependent synthetic lethality.

The HSP90 inhibitor ganetespib potentiates the antitumor activity of EGFR tyrosine kinase inhibition in mutant and wild-type non-small cell lung cancer

Small molecule inhibitors of epidermal growth factor receptor (EGFR) tyrosine kinase activity, such as erlotinib and gefitinib, revolutionized therapy for non-small cell lung cancer (NSCLC) patients whose tumors harbor activating EGFR mutations. However, mechanisms to overcome the invariable development of acquired resistance to such agents, as well as realizing their full clinical potential within the context of wild-type EGFR (WT-EGFR) disease, remain to be established. Here, the antitumor efficacy of targeted EGFR tyrosine kinase inhibitors (TKIs) and the HSP90 inhibitor ganetespib, alone and in combination, were evaluated in NSCLC. Ganetespib potentiated the efficacy of erlotinib in TKI-sensitive, mutant EGFR-driven NCI-HCC827 xenograft tumors, with combination treatment causing significant tumor regressions. In erlotinib-resistant NCI-H1975 xenografts, concurrent administration of ganetespib overcame erlotinib resistance to significantly improve tumor growth inhibition. Ganetespib co-treatment also significantly enhanced antitumor responses to afatinib in the same model. In WT-EGFR cell lines, ganetespib potently reduced cell viability. In NCI-H1666 cells, ganetespib-induced loss of client protein expression, perturbation of oncogenic signaling pathways, and induction of apoptosis translated to robust single-agent activity in vivo. Dual ganetespib/erlotinib therapy induced regressions in NCI-H322 xenograft tumors, indicating that the sensitizing properties of ganetespib for erlotinib were conserved within the WT-EGFR setting. Mechanistically, combined ganetespib/erlotinib exposure stabilized EGFR protein levels in an inactive state and completely abrogated extracellular-signal-regulated kinase (ERK) and AKT signaling activity. Thus, selective HSP90 blockade by ganetespib represents a potentially important complementary strategy to targeted TKI inhibition alone for inducing substantial antitumor responses and overcoming resistance, in both the mutant and WT-EGFR settings.

Improving survival by exploiting tumour dependence on stabilized mutant p53 for treatment

Missense mutations in p53 generate aberrant proteins with abrogated tumor suppressor functions that can also acquire oncogenic gain-of-functions (GOF) that promote malignant progression, invasion, metastasis and chemoresistance^1–5. Mutant p53 (mutp53) proteins undergo massive constitutive stabilization specifically in tumors, which is the key requisite for GOF^6–8. Although currently 11 million patients worldwide live with tumors expressing highly stabilized mutp53, it is unknown whether mutp53 is a therapeutic target in vivo.

Here we use a novel mutp53 mouse model expressing an inactivatible R248Q hotspot mutation (floxQ) to show that tumors depend on sustained mutp53 expression. Upon Tamoxifen-induced mutp53 ablation, allo-transplanted and autochthonous tumors curb their growth, thus extending animal survival by 37%, and advanced tumors undergo apoptosis and tumor regression or stagnation.

The HSP90/HDAC6 chaperone machinery, which is significantly upregulated in cancer compared to normal tissues, is a major determinant of mutp53 stabilization^9–12. We show that long-term HSP90 inhibition significantly extends the survival of mutp53 Q/−² and H/H (R172H allele³) mice by 59% and 48%, respectively, but not their respective p53−/− littermates. This mutp53-dependent drug effect occurs in H/H mice treated with 17DMAG+SAHA and in H/H and Q/− mice treated with the potent Hsp90 inhibitor ganetespib. Notably, drug activity correlates with induction of mutp53 degradation, tumor apoptosis and prevention of T-lymphomagenesis. These proof-of-principle data identify mutp53 as an actionable cancer-specific drug target.

The HSP90 Inhibitor Ganetespib Radiosensitizes Human Lung Adenocarcinoma Cells

The molecular chaperone HSP90 is involved in stabilization and function of multiple client proteins, many of which represent important oncogenic drivers in NSCLC. Utilization of HSP90 inhibitors as radiosensitizing agents is a promising approach. The antitumor activity of ganetespib, HSP90 inhibitor, was evaluated in human lung adenocarcinoma (AC) cells for its ability to potentiate the effects of IR treatment in both in vitro and in vivo. The cytotoxic effects of ganetespib included; G2/M cell cycle arrest, inhibition of DNA repair, apoptosis induction, and promotion of senescence. All of these antitumor effects were both concentration- and time-dependent. Both pretreatment and post-radiation treatment with ganetespib at low nanomolar concentrations induced radiosensitization in lung AC cells in vitro. Ganetespib may impart radiosensitization through multiple mechanisms: such as down regulation of the PI3K/Akt pathway; diminished DNA repair capacity and promotion of cellular senescence. In vivo, ganetespib reduced growth of T2821 tumor xenografts in mice and sensitized tumors to IR. Tumor irradiation led to dramatic upregulation of β-catenin expression in tumor tissues, an effect that was mitigated in T2821 xenografts when ganetespib was combined with IR treatments. These data highlight the promise of combining ganetespib with IR therapies in the treatment of AC lung tumors.

Targeting Heat-Shock Protein 90 (HSP90) as a Complementary Strategy to Immune Checkpoint Blockade for Cancer Therapy

The demonstration that immune checkpoint blockade can meaningfully improve outcomes for cancer patients has revolutionized the field of immuno-oncology. New biologic agents targeting specific checkpoints have shown remarkable durability in terms of patient response and, importantly, exhibit clinical activity across a range of human malignancies, including many that have traditionally proven refractory to other immunotherapies. In this rapidly evolving area, a key consideration relates to the identification of novel combinatorial strategies that exploit existing or investigational cancer therapies in order to optimize patient outcomes and the proportion of individuals able to derive benefit from this approach. In this regard, heat-shock protein 90 (HSP90) represents an important emerging target for cancer therapy because its inactivation results in the simultaneous blockade of multiple signaling pathways and can sensitize tumor cells to other anticancer agents. Within the context of immunology, HSP90 plays a dual regulatory role, with its functional inhibition resulting in both immunosuppressive and immunostimulatory effects. In this Cancer Immunology at the Crossroads overview, the anticancer activity profile of targeted HSP90 inhibitors is discussed along with their paradoxical roles in immunology. Overall, we explore the rationale for combining the modalities of HSP90 inhibition and immune checkpoint blockade in order to augment the antitumor immune response in cancer.

Inhibiting heat shock protein 90 (HSP90) limits the formation of liver cysts induced by conditional deletion of Pkd1 in mice

Polycystic liver disease (PLD) occurs in 75-90% of patients affected by autosomal dominant polycystic kidney disease (ADPKD), which affects 1∶400-1,000 adults and arises from inherited mutations in the PKD1 or PKD2 genes. PLD can lead to bile duct obstructions, infected or bleeding cysts, and hepatomegaly, which can diminish quality of life. At present, no effective, approved therapy exists for ADPKD or PLD. We recently showed that inhibition of the molecular chaperone heat shock protein 90 (HSP90) with a small molecule inhibitor, STA-2842, induced the degradation of multiple HSP90-dependent client proteins that contribute to ADPKD pathogenesis and slowed the progression of renal cystogenesis in mice with conditional deletion of Pkd1. Here, we analyzed the effects of STA-2842 on liver size and cystic burden in Pkd-/- mice with established PLD. Using magnetic resonance imaging over time, we demonstrate that ten weeks of STA-2842 treatment significantly reduced both liver mass and cystic index suggesting selective elimination of cystic tissue. Pre-treatment cystic epithelia contain abundant HSP90; the degree of reduction in cysts was accompanied by inhibition of proliferation-associated signaling proteins EGFR and others, and induced cleavage of caspase 8 and PARP1, and correlated with degree of HSP90 inhibition and with inactivation of ERK1/2. Our results suggest that HSP90 inhibition is worth further evaluation as a therapeutic approach for patients with PLD.

Abstract 5108: The Hsp90 inhibitor ganetespib is a potent chemosensitizer in preclinical colorectal cancer models

Background: More than half of all individuals diagnosed with colorectal cancer (CRC) will develop metastases and require chemotherapy. These treatments have significantly improved overall patient survival; however, drug resistance is a frequent cause of treatment failure often due to alteration in cell cycle regulators or DNA damage repair. The molecular chaperone HSP90 plays an important role in both processes by stabilizing proteins required for pathway activation and maintenance. Here, we sought to determine if HSP90 inhibition by the investigational drug ganetespib could enhance the activity of standard chemotherapeutics utilized in CRC in order to extend responses and bypass/delay drug resistance.

Results: Western blot analyses revealed that low nanomolar ganetespib treatment promoted the degradation of a number of proteins involved in proliferation (EGFR, PDGFR, PI3-K/AKT/p70 S6 kinase, cMET and MAPK), survival (MCL1), anigiogenesis (VEGFR), cell cycle check points and DNA repair (CDK1, CHK1, Survivin, WEE1) in a panel of CRC cell lines. This activity directly correlated with G0/G1 cell cycle arrest and loss of CRC cell viability (average IC50 in 19 CRC cell lines = 43 nM). In vitro combination of ganetespib with conventional chemotherapies (cisplatin, oxaliplatin, 5-FU) augmented the accumulation of DNA damage (phospho-H2AX) and mitotic catastrophe more effectively over monotherapy alone in HCT116, HT29 and LoVo CRC cells. Ganetespib also sensitized CRC cells to ionizing radiation by inducing aberrant mitosis and enhanced DNA damage/fragmentation, resulting in a significant increase in apoptosis. In vivo, ganetespib displayed comparable antitumor activity as capecitabine, cisplatin, and bevacizumab in human CRC tumor xenografts, with treatment/control values of ∼50 indicative of slowly progressive disease. Combining ganetespib with capecitabine resulted in significant tumor regression (T/C = -52, p&lt;0.01). Further, ganetespib improved the tumor suppressive capacity of cisplatin and bevacizumab.

Conclusions: The HSP90 inhibitor ganetespib promotes the destabilization of numerous proteins essential for tumor growth and survival as well as those involved in chemotherapeutic resistance. As a result, ganetespib sensitizes colon cancer tumor models to chemotherapy and targeted agents, including VEGF inhibitors. Ganetespib is currently being evaluated in combination with capecitabine and radiation in patients with locally-advanced rectal cancer as part of an open-label, investigator-sponsored Phase 1 clinical study.

Citation Format: Suqin He, Don Smith, Manuel Sequeira, John-Paul Jimenez, Chaohua Zhang, Jim Sang, Timothy Korbut, Jaime Acquaviva, Masazumi Nagai, Richard Bates, David A. Proia. The Hsp90 inhibitor ganetespib is a potent chemosensitizer in preclinical colorectal cancer models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5108. doi:10.1158/1538-7445.AM2014-5108

Abstract 3916: HSP90 mediates tumor-associated matrix metalloproteinase 2 and Cathepsin L protease activities in ovarian carcinoma

Ovarian cancer is the fifth leading cause of cancer-related deaths among women in the United States. At diagnosis, disease has commonly spread beyond the ovary. Ovarian cancer cells dislodge from primary tumor and spread locally throughout the abdominal cavity and lymphatics. Cancer cell shedding and colonization at other sites involves the degradation of extra cellular matrix (ECM) by tumor-associated proteases, such as matrix metalloproteinase (MMPs) and cathepsin proteases. Heat shock protein 90 (HSP90) is an ATP-dependent molecular chaperone that interacts with and stabilizes MMPs in some solid tumors. Whether HSP90 regulates cathepsin activity is currently unknown. To determine the role of HSP90 on tumor-associated MMP and cathepsin protease activities in ovarian carcinoma, HSP90 activity was inhibited using pharmacologic and RNA interference (RNAi) approaches. A small molecule inhibitor, ganetespib, and two HSP90 targeting siRNAs were used to determine the effects of HSP90 inhibition on ovarian carcinoma cell line invasion using transwell and spheroid invasion assays. The effects of ganetespib or HSP90 targeting siRNA treatment on MMP and cathepsin protease activities were assayed by gelatin zymography (MMPs), enzyme assay (cathepsins) and by dynamic imaging using protease cleavable imaging probes. The effects of ganetespib treatment on in vivo orthotopic tumor growth, dissemination and tumor associated protease activities were determined using human ovarian carcinoma xenograft models. In vitro, ganetespib treatment or expression of HSP90-targeted siRNAs inhibited transwell and spheroid invasion, and MMP-2 and cathepsin L protease activities. In vivo, ganetespib treatment resulted in decreased growth of primary tumors and disseminated tumor nodules and decreased tumor-associated MMP and cathepsin activities. Importantly, significant inhibition of MMP and cathepsin activities was detected prior to differences in tumor volume, demonstrating rapid functional response to the drug. These results show that HSP90 regulates ovarian carcinoma-associated proteolytic activities that are essential to tumor progression and dissemination. They also point to the potential utility of HSP90 inhibition as a therapeutic strategy for the treatment of ovarian cancer.

Citation Format: Shane W. O'Brien, Fang Xiao, Marsia A. Maglaty, Joshua S. Trinadad, Lainie P. Martin, David A. Proia, Denise C. Connolly. HSP90 mediates tumor-associated matrix metalloproteinase 2 and Cathepsin L protease activities in ovarian carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3916. doi:10.1158/1538-7445.AM2014-3916

Ganetespib, a novel Hsp90 inhibitor in patients with KRAS mutated and wild type, refractory metastatic colorectal cancer

BACKGROUND

Heat shock protein 90 (Hsp90) is a cellular chaperone that is required for the maturation and stability of a variety of proteins that play key roles in colon cancer initiation and progression. The primary objective of the current study was to define the safety and efficacy of ganetespib, a novel, selective small-molecule Hsp90 inhibitor, in patients with refractory metastatic colorectal cancer.

PATIENTS AND METHODS

The study was a single-arm, Simon 2-stage, phase II trial for patients with chemotherapy-refractory, metastatic colorectal cancer. Patients received ganetespib 200 mg/m(2) intravenously. Tumor tissue was collected before treatment and 48 hours after treatment for changes in expression of Hsp90 client proteins and other potential pharmacodynamics markers. V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS), v-Raf murine sarcoma viral oncogene homolog B, and phosphatidylinositol-4, 5-bisphosphate 3-kinase, catalytic subunit alpha (PIK3CA) mutational status was also determined.

RESULTS

Seventeen patients were treated (median age, 58; range, 44-79 years). No patients demonstrated objective regression of disease. Two patients had stable disease of 6.8 and 5.1 months duration. Serious adverse events that were potentially attributable to ganetespib included diarrhea (12%, n = 2), fatigue (17%, n = 3), and increased aspartate aminotransferase/alanine aminotransferase (12%, n = 2) and alkaline phosphatase (6%, n = 1) levels. Of the 17 evaluable patients, 9 (53%) including patients with stable disease as best response, had KRAS-mutant tumors.

CONCLUSION

In this first phase II investigation of an Hsp90 inhibitor in colorectal cancer, ganetespib as a single agent did not demonstrate activity in chemotherapy-refractory metastatic colorectal cancer. However, on the basis of the drug's promising preclinical combination data and the relatively mild toxicity profile, further clinical investigation of this agent in combination with standard cytotoxic agents is planned.

UDP glucuronosyltransferase 1A expression levels determine the response of colorectal cancer cells to the heat shock protein 90 inhibitor ganetespib

HSP90 inhibition represents a promising route to cancer therapy, taking advantage of cancer cell-inherent proteotoxic stress. The HSP90-inhibitor ganetespib showed benefit in advanced clinical trials. This raises the need to identify the molecular determinants of treatment response. We tested the efficacy of ganetespib on a series of colorectal cancer (CRC)-derived cell lines and correlated their sensitivities with comprehensive gene expression analysis. Notably, the drug concentration required for 50% growth inhibition (IC₅₀) varied up to 70-fold (from 36 to 2500 nM) between different cell lines. Correlating cell line-specific IC₅₀s with the corresponding gene expression patterns revealed a strong association between ganetespib resistance (IC₅₀>500 nM) and high expression of the UDP glucuronosyltransferase 1A (UGT1A) gene cluster. Moreover, CRC tumor samples showed a comparable distribution of UGT1A expression levels. The members of the UGT1A gene family are known as drug-conjugating liver enzymes involved in drug excretion, but their function in tumor cells is hardly understood. Chemically unrelated HSP90 inhibitors, for example, 17-N-allylamino-17-demethoxygeldanamycin (17-AAG), did not show correlation of drug sensitivities with UGT1A levels, whereas the ganetespib-related compound NVP-AUY922 did. When the most ganetespib-resistant cell line, HT29, was treated with ganetespib, the levels of HSP90 clients were unaffected. However, HT29 cells became sensitized to the drug, and HSP90 client proteins were destabilized by ganetespib upon siRNA-mediated UGT1A knockdown. Conversely, the most ganetespib-sensitive cell lines HCT116 and SW480 became more tolerant toward ganetespib upon UGT1A overexpression. Mechanistically, ganetespib was rapidly glucuronidated and excreted in resistant but not in sensitive CRC lines. We conclude that CRC cell-expressed UGT1A inactivates ganetespib and other resorcinolic Hsp90 inhibitors by glucuronidation, which renders the drugs unable to inhibit Hsp90 and thereby abrogates their biological activity. UGT1A levels in tumor tissues may be a suitable predictive biomarker to stratify CRC patients for ganetespib treatment.

FGFR3 translocations in bladder cancer: differential sensitivity to HSP90 inhibition based on drug metabolism

Activating mutations and/or overexpression of FGFR3 are common in bladder cancer, making FGFR3 an attractive therapeutic target in this disease. In addition, FGFR3 gene rearrangements have recently been described that define a unique subset of bladder tumors. Here, a selective HSP90 inhibitor, ganetespib, induced loss of FGFR3-TACC3 fusion protein expression and depletion of multiple oncogenic signaling proteins in RT112 bladder cells, resulting in potent cytotoxicity comparable with the pan-FGFR tyrosine kinase inhibitor BGJ398. However, in contrast to BGJ398, ganetespib exerted pleiotropic effects on additional mitogenic and survival pathways and could overcome the FGFR inhibitor-resistant phenotype of FGFR3 mutant-expressing 97-7 and MHG-U3 cells. Combinatorial benefit was observed when ganetespib was used with BGJ398 both in vitro and in vivo. Interestingly, two additional FGFR3 fusion-positive lines (RT4 and SW480) retained sensitivity to HSP90 inhibitor treatment by the ansamycins 17-AAG and 17-DMAG yet displayed intrinsic resistance to ganetespib or AUY922, both second-generation resorcinol-based compounds. Both cell lines, compared with RT112, expressed considerably higher levels of endogenous UGT1A enzyme; this phenotype resulted in a rapid glucuronidation-dependent metabolism and subsequent efflux of ganetespib from SW780 cells, thus providing a mechanism to account for the lack of bioactivity.

IMPLICATIONS

Pharmacologic blockade of the molecular chaperone HSP90 represents a promising approach for treating bladder tumors driven by oncogenic gene rearrangements of FGFR3. Furthermore, UDP-glucuronosyltransferase enzyme expression may serve as a predictive factor for clinical response to resorcinol-based HSP90 inhibitors.

The HSP90 inhibitor ganetespib has chemosensitizer and radiosensitizer activity in colorectal cancer

The integration of targeted agents to standard cytotoxic regimens has improved outcomes for patients with colorectal cancer (CRC) over recent years; however this malignancy remains the second leading cause of cancer mortality in industrialized countries. Small molecule inhibitors of heat shock protein 90 (HSP90) are one of the most actively pursued classes of compounds for the development of new cancer therapies. Here we evaluated the activity of ganetespib, a second-generation HSP90 inhibitor, in models of CRC. Ganetespib reduced cell viability in a panel of CRC cell lines in vitro with low nanomolar potency. Mechanistically, drug treatment exerted concomitant effects on multiple oncogenic signaling pathways, cell cycle regulation, and DNA damage repair capacity to promote apoptosis. Combinations of ganetespib and low-dose ionizing radiation enhanced the radiosensitivity of HCT 116 cells and resulted in superior cytotoxic activity over either treatment alone. In vivo, the single-agent activity of ganetespib was relatively modest, suppressing HCT 116 xenograft tumor growth by approximately half. However, ganetespib significantly potentiated the antitumor efficacy of the 5-Fluorouracil (5-FU) prodrug capecitabine in HCT 116 xenografts, causing tumor regressions in a model that is intrinsically resistant to fluoropyrimidine therapy. This demonstration of combinatorial benefit afforded by an HSP90 inhibitor to a standard CRC adjuvant regimen provides an attractive new framework for the potential application of ganetespib as an investigational agent in this disease.

Ganetespib and HSP90: translating preclinical hypotheses into clinical promise

As with many physiologic processes that become subverted during tumorigenesis, the chaperoning activity of heat shock protein 90 (HSP90) is often exploited by cancer cells to confer aberrant proliferative, survival, and/or metastatic potential. Functional inhibition of HSP90 results in the degradation of its client proteins, in turn providing a means to concomitantly disrupt multiple oncogenic signaling cascades through one molecular target. Pharmacologic blockade of HSP90 has, therefore, emerged as an innovative and multifaceted approach for the development of new antineoplastic agents. However, no HSP90 inhibitors are currently approved for cancer therapy and the full promise of this class of agents is yet to be realized. This review focuses on the preclinical activity profile of ganetespib, a potent small-molecule inhibitor of HSP90, the characterization of which has provided important frameworks for the optimal design and application of HSP90 inhibitor-based strategies in a variety of cancer types. Beyond client protein-driven tumors, ganetespib can also potentiate the effects of other molecularly targeted and standard-of-care therapeutics while simultaneously overcoming drug resistance in multiple tumor types, thereby positioning this compound as the leading HSP90 inhibitor currently under clinical development.

Preclinical activity of the heat shock protein 90 inhibitor ganetespib in clear cell renal cell carcinoma

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Background: Resistance invariably develops in all patients with metastatic ccRCC treated with mTOR inhibitors. Previously we demonstrated that dual inhibition of Hsp90 and the mTOR pathway in lung cancer models leads to synergistic reductions in tumor growth. Herein, we tested the efficacy of ganetespib as a single agent and in combination with mTOR inhibition using in vitro and in vivoccRCC models. Methods: For the in vitro work we utilized the following seven ccRCC cell lines: Caki-1, Caki-2, A-498, A-704, 769-P, 786-O, ACHN. For the in vivo work we used A498 xenografts. In vitro, we determined the single agent EC50 of everolimus and ganetespib at 72 hours by assessing percent viability of A498 cells compared to vehicle using the MTS assay. We then performed combinations of ganetespib and everolimus at EC20, EC30, and EC50 in A498 cells. Translating these studies in vivo, we compared the combinatorial activity of ganetespib and temsirolimus to monotherapy in mice bearing A498 tumor xenografts. Results: As a single agent, all ccRCC cell lines tested were sensitive to ganetespib at nanomolar concentration (EC50 15 – 75 nm) and to everolimus at micromolar concentrations (EC50 4 – 54 mm). In vitro, the combination of ganetespib and everolimus also decreased cell viability in an additive fashion. In vivo, ganetespib and temsirolimus demonstrated comparable single agent activity at sub-MTD doses (T/C = 63 and 60, respectively). Combining ganetespib with temsirolimus improved tumor growth suppression by ~30% (T/C = 43). Conclusions: Given the broad in vitro sensitivity of ccRCC cell lines to single agent ganetespib as well as the in vivo activity of the combination of ganetespib and temsirolimus, we believe ganetespib warrants further study in ccRCC. Updated results will be presented at the conference including the in vivo activity of the combination of ganetespib and antivascular endothelial growth factor agents.

Abstract PD5-3: Anti-metastatic activity, chemotherapeutic enhancement and therapeutic potential of targeting Hsp90 with ganetespib in triple negative breast cancer

Background: While the incidence of triple negative breast cancer (TNBC) is only 10-20%, these tumors show a disproportionate mortality for breast cancer patients. Due to a lack of effective molecular targets in this disease, therapeutic options are largely limited to systemic chemotherapeutic approaches which have shown disappointing efficacy in the metastatic setting. Here we undertook a comprehensive evaluation of the activity of the drug candidate, ganetespib, a potent inhibitor of heat shock protein 90 (Hsp90), in this malignancy.

Methods: The sensitivity of TNBC cells to ganetespib was determined in viability assays using a panel of tumor lines. The effects of ganetespib exposure on client proteins and their effector pathways were examined by Western blot and reverse phase protein array analysis. The anti-metastatic activity of ganetespib was evaluated using a 4T1 metastasis model. Combinatorial drug analyses were performed with chemotherapeutic agents. DNA damage and cell cycle disruption were assessed using the comet assay, Western blotting and fluorescence microscopy. The in vivo efficacy of the compound, both as a single agent and in combination, was established using MDA-MB-231 xenograft models. Computed tomography scans were obtained for a metastatic TNBC patient undergoing ganetespib treatment.

Results: Ganetespib reduced cell viability in TNBC cell lines with low nanomolar potency. Ganetespib treatment induced robust destabilization of multiple client proteins and oncogenic signaling pathways and suppressed lung metastasis in the experimental model. Ganetespib potentiated the cytotoxic activity of doxorubicin via enhanced DNA damage and mitotic arrest, conferring superior efficacy to the doxorubicin + cyclophosphamide (AC) regimen in MDA-MB-231 xenograft models. Ganetespib also promoted mitotic catastrophe and apoptosis in combination with taxanes in vitro, and these effects translated to significantly improved combinatorial activity in vivo. Marked tumor shrinkage of metastatic lung lesions was seen in the patient while on ganetespib monotherapy.

Conclusion: The preclinical activity profile and clinical evidence of tumor regression suggest that ganetespib offers considerable promise as a new therapeutic candidate to target TNBC. In particular, the capacity of ganetespib to potentiate the activity of standard of care chemotherapeutics provides a rationale for the exploration of this agent in novel combinatorial treatment strategies for this disease.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr PD5-3.

Abstract C130: The Hsp90 inhibitor ganetespib promotes the degradation of FGFR3 in bladder cancer models and induces regression in tumors harboring oncogenic FGFR3 fusions

Background: Fibroblast growth factor receptor 3 (FGFR3) is activated by point mutation, chromosomal rearrangement, and/or receptor overexpression in a high percentage of bladder cancers, making FGFR3 an attractive therapeutic target for bladder cancer. Heat shock protein 90 (Hsp90) is a molecular chaperone required for the stability of FGFR3 and hundreds of other kinases and oncoproteins (termed “client proteins”), many of which are known to support tumorigenesis. Ganetespib is a selective inhibitor of Hsp90 currently being evaluated in several clinical trials, including a pivotal Phase 3 study. Here, we investigated the preclinical activity of ganetespib in bladder cancer models expressing FGFR3, as monotherapy or in combination with an FGFR inhibitor.

Results: Ganetespib displayed strong anticancer activity across a panel of 20 bladder cancer cell lines with diverse genetic backgrounds (mean EC50 = 38 nM), including those overexpressing wt FGFR3 or FGFR3 fusions. Notably, ganetespib was 10 times more potent than the selective FGFR3 inhibitor BGJ398 in bladder cancer cells with activating mutations in FGFR3. At the molecular level, ganetespib induced the rapid destabilization of full-length FGFR3 and the FGFR3-TACC3 fusion protein within 4 hours suggesting that FGFR3 is a highly sensitive Hsp90 client. Consequently, MAPK and AKT/mTOR signaling were suppressed, resulting in apoptosis evident by decreased levels of P-BAD and an increase in BIM, cleaved Caspase-3, and PARP expression. In vivo, ganetespib treatment led to tumor regression in RT112 xenografts coordinate with the deactivation of FGFR3-TACC3, as well as numerous other client proteins and their downstream effectors, as determined by phosphoprotein array. Combining ganetespib with BGJ398 increased tumor regression 3-fold compared to monotherapy.

Conclusions: The Hsp90 inhibitor ganetespib elicits the rapid degradation of FGFR3 mutants and fusion proteins in bladder cancer cells resulting in tumor regression in animal models, which could be further enhanced by combination with an FGFR inhibitor. These results may provide a framework for the future treatment of FGFR3-dependent bladder cancer.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C130.

Citation Format: Jaime L. Acquaviva, Chaohua Zhang, Suqin He, John-Paul Jimenez, Masa Nagai, Jim Sang, Manuel Sequeira, Donald L. Smith, Margaret A. Knowles, David A. Proia. The Hsp90 inhibitor ganetespib promotes the degradation of FGFR3 in bladder cancer models and induces regression in tumors harboring oncogenic FGFR3 fusions. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C130.

Network analysis identifies an HSP90-central hub susceptible in ovarian cancer

PURPOSE

Epithelial ovarian cancer (EOC) is usually detected at an advanced stage and is frequently lethal. Although many patients respond to initial surgery and standard chemotherapy consisting of a platinum-based agent and a taxane, most experience recurrence and eventually treatment-resistant disease. Although there have been numerous efforts to apply protein-targeted agents in EOC, these studies have so far documented little efficacy. Our goal was to identify broadly susceptible signaling proteins or pathways in EOC.

EXPERIMENTAL DESIGN

As a new approach, we conducted data-mining meta-analyses integrating results from multiple siRNA screens to identify gene targets that showed significant inhibition of cell growth. On the basis of this meta-analysis, we established that many genes with such activity were clients of the protein chaperone HSP90. We therefore assessed ganetespib, a clinically promising second-generation small-molecule HSP90 inhibitor, for activity against EOC, both as a single agent and in combination with cytotoxic and targeted therapeutic agents.

RESULTS

Ganetespib significantly reduced cell growth, induced cell-cycle arrest and apoptosis in vitro, inhibited growth of orthotopic xenografts and spontaneous ovarian tumors in transgenic mice in vivo, and inhibited expression and activation of numerous proteins linked to EOC progression. Importantly, paclitaxel significantly potentiated ganetespib activity in cultured cells and tumors. Moreover, combined treatment of cells with ganetespib and siRNAs or small molecules inhibiting genes identified in the meta-analysis in several cases resulted in enhanced activity.

CONCLUSION

These results strongly support investigation of ganetespib, a single-targeted agent with effects on numerous proteins and pathways, in augmenting standard EOC therapies.

Antiangiogenic effects of ganetespib in colorectal cancer mediated through inhibition of HIF-1α and STAT-3

Hypoxia-inducible factors (HIFs) and STAT-3 play essential roles in angiogenesis. HIF-1α and STAT-3 are clients of the heat shock protein 90 (HSP90). We hypothesized that ganetespib, a potent HSP90 inhibitor, would disrupt angiogenesis in colorectal cancer (CRC) through inhibition of HIF-1α and STAT-3. CRC cell lines (HCT116 and HT29) were used in all the experiments. Egg CAM and HUVEC assays revealed decreased angiogenesis in ganetespib treated cell lines. Ganetespib inhibited matrigel plug vascularization and tumor growth of xenografts. Significant inhibition of PDGFA, FGF2, Ang-1, Ang-2, TGFβ1, VEGF, HIF-1α and STAT-3 expression was observed in both cell lines treated ganetespib. HIF-1α overexpression resulted in the increase VEGF and STAT-3 expression and this was inhibited by ganetespib. HIF-1α knockdown inhibited VEGF and STAT-3 expression. STAT-3 knockdown inhibited VEGF but not HIF-1α expression. HSP90, STAT-3 and VEGF expression was significantly higher in CRC compared to adjacent normal tissue. Significant downregulation of PDGFA, FGF2, Ang-1, Ang-2, TGFβ1, VEGF, STAT-3 and HIF-1α mRNA was observed in the post ganetespib treatment tumor samples from patients with rectal cancer. These results collectively suggest that inhibition of HSP90 is a promising antiangiogenic strategy in CRC. HSP90 angiogenic effects are mediated through HIF-1α and STAT-3.

Antimetastatic activity of ganetespib: Preclinical studies and assessment of progressions due to new lesions in the GALAXY-1 NSCLC trial

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Background: Heat shock protein 90 (Hsp90) maintains the stability and activity of numerous signaling proteins involved in metastasis including FAK (tumor cell adhesion), MET and MMP9 (cell motility), VEGFR and PDGFR (angiogenesis), and HIF-1α (metabolism, proliferation, motility, angiogenesis). In the GALAXY–1 trial in advanced non-small cell lung cancer (NSCLC) patients, docetaxel (D) plus ganetespib (G), an Hsp90 inhibitor, showed encouraging improvement in overall survival compared to D alone. We evaluated the antimetastatic activity of ganetespib in preclinical models, and compared radiological disease progression due to new lesion formation in the two arms of the GALAXY–1 trial. Methods: Effects of ganetespib were investigated on the: (1) migration of cancer cells under normoxic and hypoxic conditions via scratch assay, (2) expression of metastatic signaling factors using immunoblotting and reverse phase array, (3) architecture of NSCLC tumor xenografts including micro-vasculature, hypoxia, and apoptosis by immunostaining, and (4) metastasis to the lung in both tail vein and orthotopic breast cancer in vivo mouse models. In the GALAXY–1 trial, development of new metastatic lesions was evaluated using serial computed tomography scans. Results: In vitro, ganetespib blocked the migration of cancer cells and reduced the expression of key drivers of metastasis including P-AKT, FAK, HER2, IGF-1R, MET, HIF-1α, and VEGF. In vivo, ganetespib significantly reduced tumor angiogenesis and proliferation. In patients, in the population in the GALAXY–1 trial that exhibited the strongest survival improvement (diagnosis of advanced disease >6 months, N=175), radiologic progressions due to new lesion formation were 19 (50%) vs. 5 (17%), for D vs. D+G, respectively, at time of abstract submission. Updated results will be presented. Conclusions: Ganetespib inhibits multiple processes involved in tumor metastasis. Preliminary data from the GALAXY–1 study support reduced frequency of progression due to new metastatic lesion formation in advanced NSCLC patients treated with ganetespib.

Abstract 1038: Inhibition of mTOR enhances the activity of HSP90 inhibitors in part through cessation of heat shock protein synthesis

Background: Heat shock protein 90 (HSP90) is a molecular chaperone required for the stability of hundreds of client proteins, many of which promote tumor growth. While HSP90 inactivation abrogates multiple oncogenic pathways, it subsequently triggers a heat shock response that may limit its full cytotoxic potential. To overcome this limitation, we sought to identify a clinically feasible method to block heat shock protein synthesis induced by the HSP90 inhibitor ganetespib.

Results: An immunoassay was developed to screen a library of &gt;300 late stage or approved drugs for their ability to block the upregulation of HSP70 subsequent to HSP90 inhibition. A number of effective agents were identified, with the most prevalent and effective being those that target PI3K/mTOR signaling. Validating this result, mTOR inhibitors diminished ganetespib induced HSP70 and HSP90 protein levels in multiple cancer cell lines. To determine the mechanism of HSP regulation by mTOR inhibitors the expression of &gt;80 heat shock related genes was analyzed. Inhibitors of mTOR had no effect on HSP RNA levels but suppressed the upregulation of HSP genes induced by ganetespib. Heat shock factor 1 (HSF1) is the major transcriptional regulator of HSP's. Under conditions of stress or HSP90 inhibition, HSF1 is released from repressive cytoplasmic chaperone complexes and translocates into the nucleus to initiate heat shock gene transcription. Nuclear HSF1 levels increased within 1 h of ganetespib exposure but were dramatically reduced in the presence of an mTOR inhibitor. A major function of mTOR is regulating protein synthesis through activation of the cap-binding protein EIF4E, therefore we investigated whether inhibition of protein synthesis would affect HSF1 nuclear accumulation. Cycloheximide or an EIF4E inhibitor reduced ganetespib-mediated HSF1 entry into the nucleus suggesting that inhibition of mTOR can prevent HSP induction by blocking protein synthesis. Combinations of ganetespib with mTOR or dual mTOR/PI3K inhibitors resulted in a significant increase in anticancer activity compared to monotherapy in multiple in vitro and in vivo cancer models.

Conclusions: Inhibition of mTOR counteracts ganetespib induced upregulation of HSP's by blocking translocation of HSF1 into the nucleus, an effect potentially mediated by a decrease in mTOR driven protein synthesis. Attenuation of heat shock response may contribute to the synergy observed for ganetespib and PI3K/mTOR inhibitors in preclinical cancer models. Targeting mTOR signaling thus represents a promising, clinically feasible approach to maximize the therapeutic potential of ganetespib.

Citation Format: Suqin He, Jaime Acquaviva, Julie C. Friedland, Jim Sang, Donald L. Smith, Manuel Sequeira, Chaohua Zhang, David A. Proia. Inhibition of mTOR enhances the activity of HSP90 inhibitors in part through cessation of heat shock protein synthesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1038. doi:10.1158/1538-7445.AM2013-1038

Targeted inhibition of the molecular chaperone Hsp90 overcomes ALK inhibitor resistance in non-small cell lung cancer

EML4-ALK gene rearrangements define a unique subset of patients with non-small cell lung carcinoma (NSCLC), and the clinical success of the anaplastic lymphoma kinase (ALK) inhibitor crizotinib in this population has become a paradigm for molecularly targeted therapy. Here, we show that the Hsp90 inhibitor ganetespib induced loss of EML4-ALK expression and depletion of multiple oncogenic signaling proteins in ALK-driven NSCLC cells, leading to greater in vitro potency, superior antitumor efficacy, and prolonged animal survival compared with results obtained with crizotinib. In addition, combinatorial benefit was seen when ganetespib was used with other targeted ALK agents both in vitro and in vivo. Importantly, ganetespib overcame multiple forms of crizotinib resistance, including secondary ALK mutations, consistent with activity seen in a patient with crizotinib-resistant NSCLC. Cancer cells driven by ALK amplification and oncogenic rearrangements of ROS1 and RET kinase genes were also sensitive to ganetespib exposure. Taken together, these results highlight the therapeutic potential of ganetespib for ALK-driven NSCLC.

SIGNIFICANCE

In addition to direct kinase inhibition, pharmacologic blockade of the molecular chaperone Hsp90 is emerging as a promising approach for treating tumors driven by oncogenic rearrangements of ALK. The bioactivity profi le of ganetespib presented here underscores a new therapeutic opportunity to target ALK and overcome multiple mechanisms of resistance in patients with ALK-positive NSCLC.

Potent activity of the Hsp90 inhibitor ganetespib in prostate cancer cells irrespective of androgen receptor status or variant receptor expression

Androgen ablation therapy represents the first line of therapeutic intervention in men with advanced or recurrent prostate tumors. However, the incomplete efficacy and lack of durable response to this clinical strategy highlights an urgent need for alternative treatment options to improve patient outcomes. Targeting the molecular chaperone heat shock protein 90 (Hsp90) represents a potential avenue for therapeutic intervention as its inhibition results in the coordinate blockade of multiple oncogenic signaling pathways in cancer cells. Moreover, Hsp90 is essential for the stability and function of numerous client proteins, a number of which have been causally implicated in the pathogenesis of prostate cancer, including the androgen receptor (AR). Here, we examined the preclinical activity of ganetespib, a small molecule inhibitor of Hsp90, in a panel of prostate cancer cell lines. Ganetespib potently decreased viability in all lines, irrespective of their androgen sensitivity or receptor status, and more effectively than the ansamycin inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG). Interestingly, while ganetespib exposure decreased AR expression and activation, the constitutively active V7 truncated isoform of the receptor was unaffected by Hsp90 inhibition. Mechanistically, ganetespib exerted concomitant effects on mitogenic and survival pathways, as well as direct modulation of cell cycle regulators, to induce growth arrest and apoptosis. Further, ganetespib displayed robust antitumor efficacy in both AR-negative and positive xenografts, including those derived from the 22Rv1 prostate cancer cell line that co-expresses full-length and variant receptors. Together these data suggest that further investigation of ganetespib as a new therapeutic treatment for prostate cancer patients is warranted.

Targeting KRAS-mutant non-small cell lung cancer with the Hsp90 inhibitor ganetespib

Mutant KRAS is a feature of more than 25% of non-small cell lung cancers (NSCLC) and represents one of the most prevalent oncogenic drivers in this disease. NSCLC tumors with oncogenic KRAS respond poorly to current therapies, necessitating the pursuit of new treatment strategies. Targeted inhibition of the molecular chaperone Hsp90 results in the coordinated blockade of multiple oncogenic signaling pathways in tumor cells and has thus emerged as an attractive avenue for therapeutic intervention in human malignancies. Here, we examined the activity of ganetespib, a small-molecule inhibitor of Hsp90 currently in clinical trials for NSCLCs in a panel of lung cancer cell lines harboring a diverse spectrum of KRAS mutations. In vitro, ganetespib was potently cytotoxic in all lines, with concomitant destabilization of KRAS signaling effectors. Combinations of low-dose ganetespib with MEK or PI3K/mTOR inhibitors resulted in superior cytotoxic activity than single agents alone in a subset of mutant KRAS cells, and the antitumor efficacy of ganetespib was potentiated by cotreatment with the PI3K/mTOR inhibitor BEZ235 in A549 xenografts in vivo. At the molecular level, ganetespib suppressed activating feedback signaling loops that occurred in response to MEK and PI3K/mTOR inhibition, although this activity was not the sole determinant of combinatorial benefit. In addition, ganetespib sensitized mutant KRAS NSCLC cells to standard-of-care chemotherapeutics of the antimitotic, topoisomerase inhibitor, and alkylating agent classes. Taken together, these data underscore the promise of ganetespib as a single-agent or combination treatment in KRAS-driven lung tumors.