Investigational agents for epithelial ovarian cancer

Ovarian cancer is the leading cause of gynecologic cancer deaths and accounts for 4% of women's cancer diagnoses and 5% of all cancer mortalities. Despite the ability of current chemotherapy and cytoreductive surgery to put patients in remission, most patients with advanced cancer will eventually relapse. Many advances in the treatment of ovarian cancer have been reported in the past several years and a historical background is provided. Attention will then turn to analogs of current chemotherapeutic agents, new cytotoxic drugs, targeted molecular therapy, intraperitoneal therapy and immunotherapy. This review will give a perspective on current drugs, potential agents and upcoming clinical trials.

Targeting the function of the HER2 oncogene in human cancer therapeutics

The year 2007 marks exactly two decades since human epidermal growth factor receptor-2 (HER2) was functionally implicated in the pathogenesis of human breast cancer (Slamon et al., 1987). This finding established the HER2 oncogene hypothesis for the development of some human cancers. An abundance of experimental evidence compiled over the past two decades now solidly supports the HER2 oncogene hypothesis. A direct consequence of this hypothesis was the promise that inhibitors of oncogenic HER2 would be highly effective treatments for HER2-driven cancers. This treatment hypothesis has led to the development and widespread use of anti-HER2 antibodies (trastuzumab) in clinical management resulting in significantly improved clinical antitumor efficacies that have transformed the clinical practice of oncology. In the shadows of this irrefutable clinical success, scientific studies have not yet been able to mechanistically validate that trastuzumab inhibits oncogenic HER2 function and it remains possible that the current clinical advances are a consequence of the oncogene hypothesis, but not a translation of it. These looming scientific uncertainties suggest that the full promise of the treatment hypothesis may not yet have been realized. The coming decade will see a second generation of HER2-targeting agents brought into clinical testing and a renewed attempt to treat HER2-driven cancers through the inactivation of HER2. Here, I review the development of treatments that target HER2 in the context of the HER2 oncogene hypothesis, and where we stand with regards to the clinical translation of the HER2 oncogene hypothesis.

Targeting the Raf-MEK-ERK mitogen-activated protein kinase cascade for the treatment of cancer

Mitogen-activated protein kinase (MAPK) cascades are key signaling pathways involved in the regulation of normal cell proliferation, survival and differentiation. Aberrant regulation of MAPK cascades contribute to cancer and other human diseases. In particular, the extracellular signal-regulated kinase (ERK) MAPK pathway has been the subject of intense research scrutiny leading to the development of pharmacologic inhibitors for the treatment of cancer. ERK is a downstream component of an evolutionarily conserved signaling module that is activated by the Raf serine/threonine kinases. Raf activates the MAPK/ERK kinase (MEK)1/2 dual-specificity protein kinases, which then activate ERK1/2. The mutational activation of Raf in human cancers supports the important role of this pathway in human oncogenesis. Additionally, the Raf-MEK-ERK pathway is a key downstream effector of the Ras small GTPase, the most frequently mutated oncogene in human cancers. Finally, Ras is a key downstream effector of the epidermal growth factor receptor (EGFR), which is mutationally activated and/or overexpressed in a wide variety of human cancers. ERK activation also promotes upregulated expression of EGFR ligands, promoting an autocrine growth loop critical for tumor growth. Thus, the EGFR-Ras-Raf-MEK-ERK signaling network has been the subject of intense research and pharmaceutical scrutiny to identify novel target-based approaches for cancer treatment. In this review, we summarize the current status of the different approaches and targets that are under evaluation and development for the therapeutic intervention of this key signaling pathway in human disease.

Open-label phase II study evaluating the efficacy and safety of two doses of pertuzumab in castrate chemotherapy-naive patients with hormone-refractory prostate cancer

PURPOSE

To determine the prostate-specific antigen (PSA) 50% decline rate within 24 weeks of starting treatment with single-agent pertuzumab in castrate patients with hormone-refractory prostate cancer (HRPC).

PATIENTS AND METHODS

Two independent Simon's two-stage designs were used to evaluate two doses of pertuzumab administered intravenously once every 3 weeks. An interim analysis of the first 23 assessable patients in the first cohort treated at 420 mg (loading dose of 840 mg) allowed termination of additional enrollment if three patients had a 50% decline in PSA after all patients had completed at least three cycles of therapy or withdrew due to insufficient therapeutic response, death, or study-related toxicity before completing three cycles. A second cohort of patients treated at 1,050 mg could be enrolled with the same design, and if more than three patients had a 50% decline in PSA, 27 more patients would be treated at 1,050 mg.

RESULTS

Sixty-eight castrate, chemotherapy-naive men with HRPC were enrolled. A total of 35 patients were treated at 420 mg; no PSA declines 50% were observed at the interim analysis and recruitment was stopped. A total of 33 patients were then treated at 1,050 mg, and no PSA declines 50% were observed at the interim analysis. Pertuzumab was well tolerated.

CONCLUSION

Pertuzumab has no clinically significant single-agent activity in castrate patients with HRPC at either of the tested dose levels. This may reflect the continued presence of significant levels of intraprostatic androgen driving androgen receptor signaling.

Current stumbling blocks in oncology drug development

The prognosis of patients with metastatic cancer remains poor and treatment strategies including newer generations of chemotherapeutics have not significantly improved survival in most solid tumors. New approaches are required to further improve patient outcome and survival. Recently, a major leap in the understanding of the molecular mechanisms involved in signal transduction pathways that contribute to tumor growth have been identified as therapeutic targets. Particularly molecules involved in cellular proliferation (e.g., tyrosine kinases) and angiogenesis have been considered as targets for new treatment approaches. Novel therapeutics that specifically target kinase transduction pathways have shown promise as single agents and in combination with standard chemotherapy. In addition, results of recent studies with antiangiogenic monoclonal antibodies validate the use of this class of targeted therapeutics as an important new treatment modality in cancer. This review will focus on the drug development stumbling blocks of targeted treatment modalities in cancer.

Epidermal growth factor receptor inhibitors in development for the treatment of non-small cell lung cancer

The epidermal growth factor receptor (EGFR) inhibitors erlotinib, gefitinib, and cetuximab have undergone extensive clinical testing and have established clinical activity in non-small cell lung cancer and other types of solid tumors. A number of newer inhibitors are currently in clinical development with different spectra of activity or mechanisms of receptor inhibition. These include monoclonal antibodies, such as panitumumab and matuzumab; dual inhibitors of EGFR and vascular endothelial growth factor receptor, such as ZD6474 and AEE788; inhibitors of multiple EGFR family members, such as lapatinib; and irreversible inhibitors, such as canertinib and HKI272. Preclinical studies suggest that several of these agents may have activity in tumors refractory to erlotinib or gefitinib. Among these agents, ZD6474 has undergone the most extensive clinical testing. The antitumor activity of ZD6474 in these two randomized phase II clinical trials in patients with non-small cell lung cancer was felt to be sufficiently promising to warrant phase III clinical testing. Several of the other EGFR inhibitors are also undergoing advanced clinical testing, either alone or in combination with other agents. EGFR has now been validated as a clinically relevant target, and several different types of agents inhibiting this receptor are currently in development. Future research will be needed to elucidate the role of these agents in patients with EGFR inhibitor-naive and EGFR inhibitor-refractory disease, to define the molecular characteristics that predict response, and to determine whether these drugs should be used in combination with other targeted agents or chemotherapy.

Her-2 targeted therapy: beyond breast cancer and trastuzumab

Her-2 is a validated therapeutic target in breast cancer. The two critical questions that remain regarding Her-2 targeting concern 1) the relevance of Her-2 inhibition in other malignancies and 2) the ability of novel agents to achieve greater Her-2 inhibition than trastuzumab. The contribution of cell signaling effects and immunologic mechanisms to the effect of trastuzumab in vivo remains poorly understood. Thus, the preclinical data that support the greater efficacy of novel Her-2 antibodies or small molecule tyrosine kinase inhibitors remain to be validated in clinical trials. In this review, we discuss the evidence from recent trastuzumab clinical trials as a point of departure for consideration of novel Her-2 targeted therapies. Preliminary results from early clinical trials suggest that Her-2 tyrosine kinase inhibitors may extend the population for which this strategy offers therapeutic effect.