Farnesyl transferase inhibitors are a new class of biologically active anticancer drugs. The exact mechanism of action of this class of agents is, however, currently unknown. The drugs inhibit farnesylation of a wide range of target proteins, including Ras. It is thought that these agents block Ras activation through inhibition of the enzyme farnesyl transferase, ultimately resulting in cell growth arrest. In preclinical models, the farnesyl transferase inhibitors showed great potency against tumor cells; yet in clinical studies, their activity was far less than anticipated. Reasons for this disappointing clinical outcome might be found in the drug-development process. In this paper, we outline an algorithm that is potentially useful for the development of biologically active anticancer drugs. The development of farnesyl transferase inhibitors, from discovery to clinical trials, is reviewed on the basis of this algorithm. We found that two important steps of this algorithm were underestimated. First, understanding of the molecular biology of the defective pathway has mainly been focused on H-Ras activation, whereas activation of K-Ras or other farnesylated proteins is probably more important in tumorigenesis. Inhibition of farnesylation is possibly not sufficient, because geranylgeranylation might activate K-Ras and suppress the effect of farnesyl transferase inhibitors. Furthermore, a well-defined proof of concept in preclinical and clinical studies has not been achieved. Integrating the proposed algorithm in future studies of newly developed biologically active anti-cancer drugs might increase the rate of success of these compounds in patients.

Development of Farnesyl Transferase Inhibitors: A Review

Purpose To determine the efficacy and safety of single-agent sorafenib in patients with recurrent and/or metastatic squamous cell carcinoma of the head and neck (SCCHN) and nasopharyngeal carcinoma (NPC). Patients and Methods In this single-arm phase II trial, oral continuous sorafenib was administered in 28-day cycles. Patients had ≤ one line of chemotherapy for recurrent and/or metastatic disease, Eastern Cooperative Oncology Group performance status of ≤ 2, and adequate organ function. At the end of stage 1, efficacy criteria for further accrual were not met, but the study was amended to enroll an additional five patients for paired tumor biopsies. Results Twenty-seven and 26 patients were eligible for toxicity and efficacy evaluations, respectively. One patient (3.7%; 95% CI, 0.1% to 19.0%) achieved a partial response. Disease stabilization was maintained in 10 patients (37.0%; 95% CI, 22.4% to 61.2%). The median time to progression was 1.8 months (95% CI, 1.6 to 3.4 months), and median overall surviv...

Phase II Trial of Sorafenib in Patients With Recurrent or Metastatic Squamous Cell Carcinoma of the Head and Neck or Nasopharyngeal Carcinoma

Investigation and utilization of molecularly targeted agents has induced a number of drug adverse effects that are not typically associated with conventional chemotherapy. QT interval prolongation, a cardiac toxicity that increases the risk of fatal arrhythmia, is associated with several novel oncology therapies. Classes of molecularly targeted agents with described QT effects include histone deacetylase inhibitors, multitargeted tyrosine kinase inhibitors, vascular disruption agents, farnesyl protein transferase inhibitors, Src/Abl kinase inhibitors, and protein kinase C inhibitors. Concurrently, guidelines for monitoring the QT-prolonging effects of drugs under development have become increasingly rigorous. Although these guidelines apply to anticancer agents, they were not specifically designed for the oncology patient population. This article will review the pathophysiology of QT prolongation, methods of preclinical QT assessment, and current guidelines for QT evaluation in early phase trials. Additionally, molecularly targeted agents with QT effects will be summarized, and mechanisms of addressing this toxicity in the context of oncology drug development will be explored.

Molecularly Targeted Oncology Therapeutics and Prolongation of the QT Interval

PURPOSE To assess the efficacy and toxicity of sunitinib monotherapy in palliative squamous cell carcinoma of the head and neck (SCCHN). PATIENTS AND METHODS Thirty-eight patients with SCCHN having evidence of progressive disease (PD) were treated with sunitinib 37.5 mg/d given continuously until PD or unacceptable toxicity. The primary end point was the rate of disease control, defined as stable disease (SD) or partial response (PR) at 6 to 8 weeks after treatment initiation (two-stage design, Simon). Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was performed in a subset of patients before and 6 to 8 weeks after treatment. The volume transfer constant of the contrast agent (K(trans)) was used to measure changes in the microcirculation blood flow and endothelial permeability of the tumor. Results A PR was observed in one patient, SD in 18, and PD in 19 (Response Evaluation Criteria in Solid Tumors [RECIST]), resulting in a disease control rate of 50%. Among the 18 patients with SD, there were five unconfirmed PRs and six additional minor responses. A significant decrease in K(trans) was seen in three of the four patients who received DCE-MRI monitoring. Grade 5 head and neck bleeds occurred in four patients. Local complications, including the appearance or worsening of tumor skin ulceration or tumor fistula, were recorded in 15 patients. CONCLUSION Sunitinib demonstrated modest activity in palliative SSCHN. The severity of some of the complications highlights the importance of improved patient selection for future studies with sunitinib in head and neck cancer. Sunitinib should not be used outside clinical trials in SSCHN.

Phase II Study of Sunitinib in Recurrent or Metastatic Squamous Cell Carcinoma of the Head and Neck: GORTEC 2006-01

Farnesyl transferase inhibitors (FTIs) are anticancer agents that were designed to block the post-translational attachment of the prenyl moiety to C-terminal cysteine residue of Ras and thus inactivate it. Because Ras plays an important role in tumour progression and the ras mutation is one of the most frequent aberrations in cancer, FTIs have been expected to exert excellent therapeutic activities. Phase I and II clinical trials confirmed relevant antitumour activity and low toxicity; however, no improvement in overall survival has been reported in Phase III trials. The exact mechanism of action of this class of agents is currently unknown. Increasing lines of evidence indicate that the cytotoxic actions of FTIs are not due to the inhibition of Ras proteins exclusively, but to the modulation of other targets, including RhoB, the centromere-binding proteins and other proteins that have not yet been identified. This review describes the pharmacological and clinical data as well as mechanisms of action of FTIs, especially lonafarnib (SCH-66336), a non-peptidomimetic inhibitor that has shown anticancer activity.

Lonafarnib in cancer therapy

5565 Background: Treatment options for advanced disease are limited and for those patients failing chemotherapy, there are few viable options. Lonafarnib is a novel tricyclic peptidomimetic compound that is a potent and specific inhibitor of farnesyl protein transferase. We have previously reported clinical activity of lonafarnib in untreated HNSCC (4 of 22 patients showed response despite drug exposure for only 7–14 days). We proposed to assess the activity of lonafarnib in advanced HNSCC patients. Methods: An open-label phase II single-center study was conducted to determine the objective response rate of lonafarnib administered at 200 mg bid, enrolling patients who were incurable and who failed at least one platinum-containing regimen, but received no more than three prior regimens. Results: Fifteen patients, aged 32 to 66 (median age 57) were enrolled. All patients had baseline ECOG PS 0 or 1. Median treatment duration was 61 days (range 0–224 days). Median time to progression was 62 days. No objectiv...

A phase II study of lonafarnib (SCH66336) in patients with chemo-refractory advanced head and neck squamous cell carcinoma (HNSCC)

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A phase II study of lonafarnib (SCH66336) in patients with chemo-refractory advanced head and neck squamous cell carcinoma (HNSCC)