Standard of care and promising new agents for triple negative metastatic breast cancer

Triple negative breast cancer (TNBC) is a cluster of heterogeneous diseases, all of them sharing the lack of expression of estrogen and progesterone receptors and HER2 protein. They are characterized by different biological, molecular and clinical features, including a poor prognosis despite the increased sensitivity to the current cytotoxic therapies. Several studies have identified important molecular features which enable further subdivision of this type of tumor. We are drawing from genomics, transcription and translation analysis at different levels, to improve our knowledge of the molecular alterations along the pathways which are activated during carcinogenesis and tumor progression. How this information should be used for the rational selection of therapy is an ongoing challenge and the subject of numerous research studies in progress. Currently, the vascular endothelial growth factor (VEGF), poly (ADP-ribose) polymerase (PARP), HSP90 and Aurora inhibitors are most used as targeting agents in metastatic setting clinical trials. In this paper we will review the current knowledge about the genetic subtypes of TNBC and their different responses to conventional therapeutic strategies, as well as to some new promising molecular target agents, aimed to achieve more tailored therapies.

Advances in the clinical development of heat shock protein 90 (Hsp90) inhibitors in cancers

Hsp90 is an ATP dependent molecular chaperone protein which integrates multiple oncogenic pathways. As such, Hsp90 inhibition is a promising anti-cancer strategy. Several inhibitors that act on Hsp90 by binding to its N-terminal ATP pocket have entered clinical evaluation. Robust pre-clinical data suggested anti-tumor activity in multiple cancer types. Clinically, encouraging results have been demonstrated in melanoma, acute myeloid leukemia, castrate refractory prostate cancer, non-small cell lung carcinoma and multiple myeloma. In breast cancer, proof-of-concept was demonstrated by first generation Hsp90 inhibitors in combination with trastuzumab mainly in human epidermal growth factor receptor 2 (HER2)+metastatic breast cancer. There are a multitude of second generation Hsp90 inhibitors currently under investigation. To date, however, there is no FDA approved Hsp90 inhibitor nor standardized assay to ascertain Hsp90 inhibition. This review summarizes the current status of both first and second generation Hsp90 inhibitors based on their chemical classification and stage of clinical development. It also discusses the pharmacodynamic assays currently implemented in clinic as well as other novel strategies aimed at enhancing the effectiveness of Hsp90 inhibitors. Ultimately, these efforts will aid in maximizing the full potential of this class of agents. This article is part of a Special Issue entitled: Heat Shock Protein 90 (HSP90).

Hsp90 molecular chaperone inhibitors: are we there yet?

Heat shock protein (Hsp) 90 is an ATP-dependent molecular chaperone that is exploited by malignant cells to support activated oncoproteins, including many cancer-associated kinases and transcription factors, and it is essential for oncogenic transformation. Originally viewed with skepticism, Hsp90 inhibitors are now being actively pursued by the pharmaceutical industry, with 17 agents having entered clinical trials. Investigators established Hsp90's druggability using the natural products geldanamycin and radicicol, which mimic the unusual ATP structure adopted in the chaperone's N-terminal nucleotide-binding pocket and cause potent and selective blockade of ATP binding/hydrolysis, inhibit chaperone function, deplete oncogenic clients, and show antitumor activity. Preclinical data obtained with these natural products have heightened interest in Hsp90 as a drug target, and 17-allylamino-17-demethoxygeldanamycin (17-AAG, tanespimycin) has shown clinical activity (as defined by Response Evaluation Criteria in Solid Tumors) in HER2+ breast cancer. Many optimized synthetic, small-molecule Hsp90 inhibitors from diverse chemotypes are now in clinical trials. Here, we review the discovery and development of Hsp90 inhibitors and assess their potential. There has been significant learning from studies of the basic biology of Hsp90, as well as translational drug development involving this chaperone, enhanced by the use of Hsp90 inhibitors as chemical probes. Success will likely lie in treating cancers that are addicted to particular driver oncogene products (e.g., HER2, ALK, EGFR, and BRAF) that are sensitive Hsp90 clients, as well as malignancies (especially multiple myeloma) in which buffering of proteotoxic stress is critical for survival. We discuss approaches for enhancing the effectiveness of Hsp90 inhibitors and highlight new chaperone and stress-response pathway targets, including HSF1 and Hsp70.

HSP90 inhibition is effective in breast cancer: a phase II trial of tanespimycin (17-AAG) plus trastuzumab in patients with HER2-positive metastatic breast cancer progressing on trastuzumab

PURPOSE

HSP90 is a chaperone protein required for the stability of a variety of client proteins. 17-Demethoxygeldanamycin (17-AAG) is a natural product that binds to HSP90 and inhibits its activity, thereby inducing the degradation of these clients. In preclinical studies, HER2 is one of the most sensitive known client proteins of 17-AAG. On the basis of these data and activity in a phase I study, we conducted a phase II study of 17-AAG (tanespimycin) with trastuzumab in advanced trastuzumab-refractory HER2-positive breast cancer.

EXPERIMENTAL DESIGN

We enrolled patients with metastatic HER2(+) breast cancer whose disease had previously progressed on trastuzumab. All patients received weekly treatment with tanespimycin at 450 mg/m(2) intravenously and trastuzumab at a conventional dose. Therapy was continued until disease progression. The primary endpoint was response rate by Response Evaluation Criteria in Solid Tumors (RECIST) criteria.

RESULTS

Thirty-one patients were enrolled with a median age of 53 years and a median Karnofsky performance status (KPS) of 90%. The most common toxicities, largely grade 1, were diarrhea, fatigue, nausea, and headache. The overall response rate was 22%, the clinical benefit rate [complete response + partial response + stable disease] was 59%, the median progression-free survival was 6 months (95% CI: 4-9), and the median overall survival was 17 months (95% CI: 16-28).

CONCLUSIONS

This is the first phase II study to definitively show RECIST-defined responses for 17-AAG in solid tumors. Tanespimycin plus trastuzumab has significant anticancer activity in patients with HER2-positive, metastatic breast cancer previously progressing on trastuzumab. Further research exploring this therapeutic interaction and the activity of HSP90 inhibitors is clearly warranted.

A Phase II trial of 17-allylamino, 17-demethoxygeldanamycin (17-AAG, tanespimycin) in patients with metastatic melanoma

PURPOSE

A Phase II study to screen for anti-melanoma activity of the heat shock protein 90 (HSP90) inhibitor, 17-AAG (17-allylamino-17-demethoxygeldanamycin) was performed. The primary endpoint was the rate of disease stabilisation in patients with progressive, metastatic melanoma treated with 17-AAG. Secondary endpoints were to determine: the toxicity of 17-AAG, the duration of response(s), median survival and further study the pharmacokinetics and pharmacodynamics of 17-AAG.

PATIENTS AND METHODS

Patients with metastatic melanoma (progressive disease documented ≤6 months of entering study) were treated with weekly, intravenous 17-AAG. A Simon one sample two stage minimax design was used. A stable disease rate of ≥25% at 6 months was considered compatible with 17-AAG having activity.

RESULTS

Fourteen patients (8 male: 6 female) were entered, eleven received 17-AAG (performance status 0 or 1). Median age was 60 (range 29-81) years. The majority (93%) received prior chemotherapy and had stage M1c disease (71%). Toxicity was rarely ≥ Grade 2 in severity and commonly included fatigue, headache and gastrointestinal disturbances. One of eleven patients treated with 17-AAG had stable disease for 6 months and median survival for all patients was 173 days. The study was closed prematurely prior to completion of the first stage of recruitment and limited planned pharmacokinetic and pharmacodynamic analyses.

CONCLUSION

Some evidence of 17-AAG activity was observed although early study termination meant study endpoints were not reached. Stable disease rates can be incorporated into trials screening for anti-melanoma activity and further study of HSP90 inhibitors in melanoma should be considered.

Novel targets in esophageal and gastric cancer: beyond antiangiogenesis

Cancers of the stomach, gastroesophageal junction and esophagus are a major cause of cancer-related deaths worldwide. In Western countries, adenocarcinomas of the distal esophagus, gastroesophageal junction and proximal stomach have been increasing in frequency more rapidly than other malignancies. The majority of newly diagnosed patients present with advanced disease and the overall survival remains dismal at approximately 10% at 5 years. Better understanding of tumor biology has led to the development of promising novel therapeutic strategies. There is therefore increasing optimism that some of these approaches will improve the outcomes in these increasingly common cancers. Given the success of antiangiogenesis as a therapeutic strategy in various types of cancer, there are ongoing efforts to investigate the utility of other targeted therapies in the treatment of gastric and esophageal cancers. This review will focus on novel therapeutic targets other than angiogenesis and provide a rationale for the further clinical evaluation of these agents in patients with upper gastrointestinal tract cancers.

Phase I pharmacokinetic and pharmacodynamic study of 17-dimethylaminoethylamino-17-demethoxygeldanamycin, an inhibitor of heat-shock protein 90, in patients with advanced solid tumors

PURPOSE

To define the maximum tolerated dose, toxicities, pharmacokinetics, and pharmacodynamics of 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17DMAG).

METHODS

17DMAG was given intravenously over 1 hour daily for 5 days (schedule A) or daily for 3 days (schedule B) every 3 weeks. Plasma 17DMAG concentrations were measured by liquid chromatography/mass spectrometry. Heat-shock proteins (HSPs) and client proteins were evaluated at baseline and after treatment on day 1 in peripheral blood mononuclear cells (PBMCs) and in pre- and post-treatment (24 hours) biopsies done during cycle 1 at the recommended phase II dose (n = 7).

RESULTS

Fifty-six patients were entered: 26 on schedule A; 30 on schedule B. The recommended phase II doses for schedules A and B were 16 mg/m(2) and 25 mg/m(2), respectively. Grade 3/4 toxicities included liver function test elevation (14%), pneumonitis (9%), diarrhea (4%), nausea (4%), fatigue (4%) and thrombocytopenia (4%). There were no objective responses. Four patients had stable disease. 17DMAG half-life was 24 +/- 15 hours. 17DMAG area under the curve (range, 0.7 to 14.7 mg/mL x h) increased linearly with dose. The median HSP90, HSP70, and integrin-linked kinase levels were 87.5% (n = 14), 124% (n = 20), and 99.5% (n = 20) of baseline. Changes in HSPs and client proteins in tumor biopsies were not consistent between baseline and 24 hours nor did they change in the same direction as those in PBMCs collected at the time of biopsy.

CONCLUSION

The recommended phase II doses of 17DMAG (16 mg/m(2) x 5 days or 25 mg/m(2) x 3 days, every 3 weeks) are well tolerated and suitable for further evaluation.

Heat shock protein 90 as a drug target: some like it hot

Heat shock protein 90 (HSP90) is a ubiquitously expressed chaperone that is involved in the posttranslational folding and stability of proteins. Inhibition at the NH(2)-terminal ATP-binding site leads to the degradation of client proteins by the ubiquitin proteasome pathway. Inhibition of HSP90 leads to the degradation of known oncogenes, such as ERB-B2, BRAF, and BCR-ABL, leading to the combinatorial blockade of multiple signal transduction pathways, such as the RAS-RAF-mitogen-activated protein/extracellular signal-regulated kinase kinase-extracellular signal-regulated kinase and phosphatidylinositol 3-kinase pathways. Multiple structurally diverse HSP90 inhibitors are undergoing early clinical evaluation. The clinical focus of these drugs should be solid tumors, such as breast, prostate, and lung cancers, along with malignant melanoma, in addition to hematologic malignancies, such as chronic myeloid leukemia and multiple myeloma. HSP90 inhibitors can be used as single agents or in combination with other targeted treatments or conventional forms of treatment such as chemotherapy and radiotherapy. Clinical trials evaluating efficacy of these agents should include innovative designs to capture cytostasis evidenced by clinical nonprogression and enrichment of patient populations by molecular characterization. The results of clinical trials evaluating the efficacy of drugs targeting this exciting target are awaited.