Synergistic activity of the Hsp90 inhibitor ganetespib with taxanes in non-small cell lung cancer models

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.

New targets in non-small cell lung cancer

Lung cancer remains the most common cause of cancer-related death in the United States. At presentation, the majority of patients have regional or systemic metastases and therefore require systemic therapy. For years, chemotherapy was the only systemic therapy option. A major paradigm shift has occurred in recent years with the identification of driver genetic alterations in some non-small cell lung cancers (NSCLCs). It is part of current standard of care to assess epidermal growth factor receptor (EGFR) mutations and anaplastic lymphoma kinase (ALK) translocations in tumors of patients with advanced NSCLC. Drugs targeting these mutations provide significant clinical benefit and are the preferred therapeutic option in these patients. Ongoing clinical trials are assessing the clinical benefit from targeting other driver genetic alterations. Further therapeutic targets have been identified through greater understanding of the variety of molecular processes that facilitate tumor formation and progression. Some of these new therapeutic targets are heat shock proteins and targets that can allow enhanced anti-tumor immune response. It is expected that these advances will allow personalized management of NSCLC patients and move us away from approaching all NSCLC patients with the same therapeutic tools.

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.

ALK inhibitors in the treatment of advanced NSCLC

Pharmacologic agents that target protein products of oncogenes in tumors are playing an increasing clinical role in the treatment of cancer. Currently, the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) represent the standard of care for patients with locally advanced or metastatic non-small cell lung cancer (NSCLC) harboring activating EGFR mutations. Subsequently other genetic abnormalities with "driver" characteristics - implying transforming and tumor maintenance capabilities have been extensively reported in several small distinct subsets of NSCLC. Among these rare genetic changes, anaplastic lymphoma kinase (ALK) gene rearrangements, most often consisting in a chromosome 2 inversion leading to a fusion with the echinoderm microtubule-associated protein like 4 (EML4) gene, results in the abnormal expression and activation of this tyrosine kinase in the cytoplasm of cancer cells. This rearrangement occurs in 2-5% of NSCLC, predominantly in young (50 years or younger), never- or former-smokers with adenocarcinoma. This aberration most commonly occurs a independently of EGFR and KRAS gene mutations. A fluorescent in situ hybridization assay was approved by the US Food and Drug Administration (FDA) as the standard method for the detection of ALK gene rearrangement in clinical practice and is considered the gold standard. Crizotinib, a first-in-class dual ALK and c-MET inhibitor, has been shown to be particularly effective against ALK positive NSCLC, showing dramatic and prolonged responses with low toxicity, predominantly restricted to the gastro-intestinal and visual systems, and generally self-limiting or easily managed. However, resistance to crizotinib inevitably emerges. The molecular mechanisms of resistance are currently under investigation, as are therapeutic approaches including crizotinib-based combination therapy and novel agents such as Hsp90 inhibitors. This review aims to present the current knowledge on this fusion gene, the clinic-pathological profile of ALK rearranged NSCLC, and to review the existing literature on ALK inhibitors, focusing on their role in the treatment of NSCLC.

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.

Molecular-targeted agents combination therapy for cancer: developments and potentials

Although chemotherapy has advanced into the era of targeted drugs, the antitumor efficacies of current therapies are limited, most likely because of the high degree of cancer clonal heterogeneity, intratumor genetic heterogeneity and cell signal complexity. As shutdown of a single target does not necessarily eradicate the cancer, the use of combinations of molecular-targeted agents (MATs) has been proposed, and some pioneering research has been conducted to examine the efficacy of this strategy. In this article, the clinical and preclinical studies that are underway in an attempt to improve the anticancer efficacy of chemotherapies through combination strategies are summarized. Studies of combining cytotoxic agents with MATs, coinhibiting two or more targets in a single pathway or coinhibiting parallel or compensatory pathways as well as specific combinations will be introduced, and the antitumor potentials of each combination strategy will be evaluated.

Targeted inhibition of Hsp90 by ganetespib is effective across a broad spectrum of breast cancer subtypes

Heat shock protein 90 (Hsp90) is a molecular chaperone essential for the stability and function of multiple cellular client proteins, a number of which have been implicated in the pathogenesis of breast cancer. Here we undertook a comprehensive evaluation of the activity of ganetespib, a selective Hsp90 inhibitor, in this malignancy. With low nanomolar potency, ganetespib reduced cell viability in a panel of hormone receptor-positive, HER2-overexpressing, triple-negative and inflammatory breast cancer cell lines in vitro. Ganetespib treatment induced a rapid and sustained destabilization of multiple client proteins and oncogenic signaling pathways and even brief exposure was sufficient to induce and maintain suppression of HER2 levels in cells driven by this receptor. Indeed, HER2-overexpressing BT-474 cells were comparatively more sensitive to ganetespib than the dual HER2/EGFR tyrosine kinase inhibitor lapatinib in three-dimensional culture. Ganetespib exposure caused pleiotropic effects in the inflammatory breast cancer line SUM149, including receptor tyrosine kinases, MAPK, AKT and mTOR signaling, transcription factors and proteins involved in cell cycle, stress and apoptotic regulation, as well as providing combinatorial benefit with lapatinib in these cells. This multimodal activity translated to potent antitumor efficacy in vivo, suppressing tumor growth in MCF-7 and MDA-MB-231 xenografts and inducing tumor regression in the BT-474 model. Thus, ganetespib potently inhibits Hsp90 leading to the degradation of multiple clinically-validated oncogenic client proteins in breast cancer cells, encompassing the broad spectrum of molecularly-defined subtypes. This preclinical activity profile suggests that ganetespib may offer considerable promise as a new therapeutic candidate for patients with advanced breast cancers.

Gefitinib versus erlotinib as salvage treatment for lung adenocarcinoma patients who benefited from the initial gefitinib: A retrospective study

BACKGROUND

  The optimal strategy was not established for patients who initially responded to gefitinib although re-administration of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) has been proven to be an option. Gefitinib and erlotinib were compared as salvage treatment after gefitinib failure.

METHODS

  Thirty-eight lung adenocarcinoma patients were analyzed retrospectively as they received the second EGFR-TKIs treatment with either gefitinib or erlotinib. All of them had obtained disease control from initial gefitinib. Sixteen patients received gefitinib (G-G group) and 22 patients received erlotinib (G-E group).

RESULTS

  Of all patients, progress free survival (PFS) and overall survival (OS) were three and 12 months, respectively, and the disease controlled rate (DCR) of the second EGFR-TKIs treatment was 52.6%. One patient (6.3%) had partial remission (PR) and 10 (62.5%) had stable disease (SD), in the G-G group, whereas, three (13.6%) had PR and six (27.2%) had SD, in the G-E group. There was no statistical significance observed, although the DCR in the G-G group was higher than that in G-E group (68.8% vs. 40.8%, P= 0.09). Adverse events of both gefitinib and erlotinib were mild and administered. The median PFS and OS in G-G and G-E groups were similar (PFS four vs. three months; OS 22 vs. 12 months). In multivariate analysis, patients with SD in initial gefitinib treatment had significantly longer OS (P= 0.04).

CONCLUSIONS

  Gefitinib as well as erlotinib could be an option for patients who benefited from prior gefitinib treatment. Patients with SD in initial gefitinib obtained a significantly longer OS than those with PR.

A first in human, safety, pharmacokinetics, and clinical activity phase I study of once weekly administration of the Hsp90 inhibitor ganetespib (STA-9090) in patients with solid malignancies

Background

This phase I study investigated the maximum tolerated dose (MTD), safety, pharmacokinetics and antitumor activity of ganetespib in patients with solid malignancies.

Methods

Patients were enrolled in cohorts of escalating ganetespib doses, given as 1 hour IV infusion, once weekly for 3 weeks, followed by a 1-week rest until disease progression or unacceptable toxicity. Endpoints included safety, pharmacokinetic and pharmacodynamic parameters and preliminary clinical activity.

Results

Fifty-three patients were treated at doses escalating from 7 to 259 mg/m². The most common adverse events were Grade 1 and 2 diarrhea, fatigue, nausea or vomiting. Dose-limiting toxicities (DLT) observed were: one Grade 3 amylase elevation (150 mg/m²), one Grade 3 diarrhea and one Grade 3 and one Grade 4 asthenia (259 mg/m²). The MTD was 216 mg/m² and the recommended phase 2 dose was established at 200 mg/m² given IV at Days 1, 8, and 15 every 4 weeks. There was a linear relationship between dose and exposure. Plasma HSP70 protein levels remained elevated for over a week post treatment. Disease control rate (objective response and stable disease at ≥ 16 weeks) was 24.4%.

Conclusions

Ganetespib is well tolerated as a weekly infusion for 3 of every 4 weeks cycle. The recommended phase II dose is 200 mg/m², and is associated with an acceptable tolerability profile.

Trial registration

NCT00687934

Hsp90, an unlikely ally in the war on cancer

On the surface heat shock protein 90 (Hsp90) is an unlikely drug target for the treatment of any disease, let alone cancer. Hsp90 is highly conserved and ubiquitously expressed in all cells. There are two major isoforms α and β encoded by distinct genes and together they may constitute 1%-3% of the cellular protein. Deletion of the protein is embryonic lethal and there are no recognized polymorphisms suggesting an association or causal relationship with any human disease. With respect to cancer, the proteins absence from two recent high profile articles, 'Hallmarks of cancer: the next generation' [Hanahan & Weinberg (2011) Cell 144, 646-674] and 'Comprehensive molecular portraits of human breast tumours' [Koboldt et al. (2012) Nature] underlines the perception that it is an unlikely bona fide target to treat this disease. Yet, to date, there are 17 distinct Hsp90 inhibitors in clinical trials for multiple indications in cancer. The protein has been championed for over 20 years by the National Cancer Institute (Bethesda, MD, USA) as a cancer target since the discovery of the antitumor activity of the natural product geldanamycin. This review aims to look at the conundrum of why Hsp90 can even be considered a druggable target for the treatment of cancer. We propose that in contrast to the majority of chemotherapeutics our growing armamentarium of investigational Hsp90 drugs represents an elegant choice that offers real hope in the long-term treatment of certain cancers.

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.