Abstract P2-16-23: The ENCHANT-1 trial (NCT01677455): An open label multicenter phase 2 proof of concept study evaluating first line ganetespib monotherapy in women with metastatic HER2 positive or triple negative breast cancer (TNBC)

Background: Hsp90 is a molecular chaperone protein required for the stabilization and activation of many proteins, referred to as Hsp90 ‘clients’, such as HER2, HIF1-a, EGFR, ER, PI3K, AKT, P53 and VEGFR. The drug candidate, ganetespib is a novel triazolone inhibitor of Hsp90, with over 700 patients treated to date. Ganetespib has shown activity in preclinical models of HER2+, ER+/PR+ and TNBC. Early clinical trials documented ganetespib single agent activity in heavily pretreated HER2+ and TNBC patients. Ganetespib has been well tolerated in clinical trials with a favorable safety profile. This efficacy-screening study is designed to provide further evidence of ganetespib activity and identify potentially predictive biomarkers in metastatic breast cancer (BC).

Methods: The ENCHANT-1 Trial is an international, first-line 2-cohort Phase 2 study in BC patients: Cohort A, HER2 amplified (n = 35), and Cohort B, TNBC (n = 35). Patients who present with previously untreated metastatic disease are eligible for treatment with ganetespib at 150 mg/m2 twice weekly on 3 out of 4 wks, for a total of up to 12 wks. Primary endpoint: ORR assessed using RECIST1.1 criteria. Key secondary endpoints include metabolic response as assessed by PET/CT at wk 3 utilizing modified EORTC criteria. Disease progression (PD) at wk 3 by PET imaging indicates discontinuation of study therapy, and is performed to quickly offer patients with metabolic PD a standard of care treatment.

The study is designed as Simon 2-stage requiring at least one OR in 15 patients for the respective cohort to expand to 35 patients. A Steering Committee is established to oversee the overall study and review the interim results.

Results: The study was initiated in 23 centers globally. At the time of submission, a total of 17 patients had been enrolled; TNBC (n = 15) and HER2 (n = 2). Here we report the interim analysis in the TNBC cohort. The median age was 54 years (range 30 -77) with ECOG PS 0 (n = 7/15). Most patients (n = 9) presented with de novo metastatic disease. 5 patients were not evaluable for PET assessment (3 had not yet reached wk 3 and 2 withdrawn before wk 3 for clinical progression), and 9 patients were not evaluable for objective response at wk 6 (3 withdrawn before or at wk 3 for clinical progression and 6 had not yet reached wk 6 evaluation). In the 10 patients with evaluable PET imaging, 9 patients achieved metabolic (m) response (2 mPR, 4 mSD with dominant tumor shrinkage and 3 SD) and one patient with mPD. In the 6 patients evaluable for OR at wk 6, one patient achieved PR, 2 SD and 3 PD. Treatment with ganetespib was well tolerated; the most common AEs were mild or moderate diarrhea (8/15, 53%), fatigue (5/15, 33%), decreased appetite (4/15, 27%), insomnia (4/15, 27%), and nausea (4/15, 27%).

Conclusion: Ganetespib single agent was generally well tolerated and showed anti-tumor activity TNBC patients as early as 3 weeks following treatment. PET seems to be a good tool to screen antitumor activity of new agents in early settings rather that in heavily pretreated patients. The TNBC cohort has met the protocol criteria for proceeding to stage 2.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-16-23.

Abstract P4-16-05: Hsp90 inhibition potentiates chemotherapy effectiveness in triple negative breast cancer: Role of glucocorticoid receptor signaling

Background: Few promising molecular targets exist for chemoresistant triple negative breast cancer (TNBC). Our laboratory has previously demonstrated that a subset of TNBCs express high glucocorticoid receptor (GR) levels. In breast epithelial cells, GR transcriptional activity directly upregulates the expression of several anti-apoptotic target genes including serum/glucocorticoid regulated kinase 1 (SGK1). High GR and/or SGK1 expression are both associated with decreased chemotherapy-induced cell death in TNBC models. A meta-analysis of patients with early-stage TNBC found that high primary tumor GR (NR3C1) expression significantly associates with earlier relapse compared to GR-non expressing TNBC. Inhibiting GR/SGK1 activity is therefore a testable strategy for improving TNBC responsiveness to chemotherapy.

Both GR and SGK1 require Hsp90 for their activity; therefore, Hsp90 inhibition is predicted to disrupt both GR and SGK1 cell survival signaling in TNBC. Employing a second-generation Hsp90 inhibitor, ganetespib (Synta Pharmaceuticals), we determined the effectiveness of Hsp90 inhibition on GR/SGK1 activity and chemotherapy sensitivity using in vitro and in vivo TNBC models.

Hypothesis: Hsp90 inhibition will decrease GR and SGK1 activity in TNBC in association with improved chemotherapy effectiveness.

Results: Using TNBC cell lines treated with ganetespib at clinically relevant concentrations, we found that total GR and the relative proportion of phosphorylated Ser211 GR were significantly reduced beginning 2 hours following treatment. Reduced glucocorticoid-induced (SGK1) mRNA expression was also seen when cells were pre-treated with ganetespib. We next used fluorescent microscopy and live cell imaging to measure TNBC cell death over a 96 hour time course following chemotherapy +/- ganetespib therapy. Addition of ganetespib to paclitaxel treatment of MDA-MB-231 cells led to significant in vitro cytotoxic synergy; as hypothesized, this synergy was diminished in GR-depleted MDA-MB-231 cells. Cytotoxic synergy following ganetespib and chemotherapy treatment was also seen in vivo in MDA-MB-231 xenografts. Interestingly, tumor GR expression following Hsp90 inhibitor and paclitaxel treatment was significantly reduced compared to tumors from mice treated with paclitaxel alone. Using GR-depleted or control MDA-MB-231 xenografts, studies are currently underway to further characterize the role of GR/SGK1 activity as a target of Hsp90 inhibition to reverse TNBC chemoresistance.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-16-05.

Abstract OT3-2-05: Randomized phase II study of fulvestrant with or without ganetespib in patients (pts) with hormone receptor (HR)-positive metastatic breast cancer

Background: In pts with HR-positive metastatic breast cancer, endocrine resistance is a major clinical problem. Ganetespib is a small molecule inhibitor of heat shock protein 90 (HSP90), a molecular chaperone protein that regulates post-translational folding of numerous client proteins including estrogen and progesterone receptor. In preclinical HR-positive breast cancer models, ganetespib impairs endocrine resistance and reduces heterogeneity in the disease control achievable by hormonal therapies.

Trial Design and Eligibility: This is a randomized phase II study designed to evaluate the efficacy of ganetespib in combination with fulvestrant compared to fulvestrant alone. Pts with endocrine-resistant, HR-positive metastatic breast cancer and up to 1 prior line of metastatic chemotherapy are eligible. Endocrine resistance is defined as relapse while on or within 1 year of completion of adjuvant endocrine therapy (ET) or progression through at least one line of ET for advanced disease. Patients are treated with fulvestrant 500 mg IM on Cycle 1 Day 1 (C1D1) and C1D15, C2D1, and D1 of each subsequent 28-day cycle. Ganetespib is administered at a starting dose of 200 mg/m2 IV on Days 1, 8, and 15 of each cycle. Pts undergo optional research biopsies at baseline and time of progression. Pts with accessible disease undergo a required research biopsy on C2D9. Circulating tumor cells (CTCs) and peripheral blood mononuclear cells (PBMCs) are collected at baseline, C2D8, C2D9, and time of progression. Pts who progress on fulvestrant may cross over to the combination.

Aims: The primary endpoint is progression-free survival. Secondary endpoints include safety and tolerability, objective response rate by RECIST 1.1, clinical benefit rate, and overall survival. Correlative aims include comparison of biomarkers on the C2D9 biopsy in pts treated with fulvestrant alone versus the combination of fulvestrant plus ganetespib, analysis of CTCs and pharmacodynamic markers in PMBCs.

Statistical Methods: Pts will be randomized 1:2 to receive fulvestrant alone or the combination of fulvestrant plus ganetespib. The total accrual goal is 71 pts. The expected accrual rate is 3.5-4.5 pts per month over a period of ∼20 months; it is anticipated at ∼15% of pts may be censored for PFS, with similar probability on both arms. There will be 80% power to detect a prolongation of true median PFS from 4.0 months to 8.0 months, using a one-sided 0.05 log-rank test.

Acrrual: To date, 15 of 71 planned pts have been enrolled.

Funding: The trial is supported by a grant from the Susan G. Komen foundation and funding from Synta Pharmaceuticals.

Contact information: nlin@partners.org.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr OT3-2-05.