Suppression of lung cancer tumor growth in a nude mouse model by the Ras inhibitor salirasib (farnesylthiosalicylic acid)

Aberrant Ras pathway functions contribute to the malignant phenotype of lung cancers. Inhibitors of Ras might therefore be considered as potential drugs for lung cancer therapy. Here, we show that the Ras inhibitor farnesylthiosalicylic acid (salirasib) inhibits proliferation of human lung cancer cells harboring a mutated K-ras gene (A549, H23, or HTB54) or overexpressing a growth factor receptor (H1299 or HTB58) and enhances the cytotoxic effect of the chemotherapeutic drug gemcitabine. Salirasib inhibited active K-Ras in A549 cells, reversed their transformed morphology, and inhibited their anchorage-independent growth in vitro. Tumor growth in A549 and HTB58 cell nude mouse models was inhibited by i.p. administration of salirasib. P.o. formulated salirasib also inhibited A549 cell tumor growth. Our results suggest that p.o. salirasib may be considered as a potential treatment for lung cancer therapy.

Novel Combinations Based on Epidermal Growth Factor Receptor Inhibition: Fig. 1

In spite of recent advances in molecular biology leading to the introduction of clinically active novel agents, such as imatinib, erlotinib, and bevacizumab, therapy of the most common epithelial tumors, such as lung cancer, remains unsuccessful. The diversity of molecular abnormalities in these tumors is felt to partly contribute to their resistance to therapy. It is, therefore, widely accepted that one approach to improving the efficacy of cancer therapy is the development of rational, hypothesis-based combinations of anticancer agents that may exhibit synergistic cytotoxic interactions. A number of empirical combination studies with the epidermal growth factor receptor and classic cytotoxic agents were undertaken in clinical trials, with disappointing results. It is, therefore, felt that preclinical combinations of epidermal growth factor receptor inhibitors and other novel agents, based on sound knowledge of complementary signaling pathways whose concerted inhibition would be hypothesized to inhibit growth, is the reasonable approach in the future. A brief overview of some of these pathways (mammalian target of rapamycin, vascular endothelial growth factor receptor, and ras/mitogen-activated protein kinase signaling) is provided in this review.

A review of erlotinib and its clinical use

Erlotinib is an orally available, reversible tyrosine kinase inhibitor of the epidermal growth factor receptor. Encouraging activity as a single agent and in combination with other targeted agents has been demonstrated in Phase II trials in many tumour types. Erlotinib has an established role in the treatment of advanced, refractory non-small cell lung cancer-based on a pivotal trial demonstrating a survival advantage over best supportive care. In a Phase III trial, the addition of erlotinib to gemcitabine improved survival in advanced pancreatic cancer. The toxicity profile of erlotinib includes diarrhoea and rash, with no haematological side effects. Predictive factors for response include the presence of a rash, epidermal growth factor receptor expression and mutation status. This article reviews the current clinical status of erlotinib.

Tipifarnib: farnesyl transferase inhibition at a crossroads

Tipifarnib is an oral nonpeptidomimetic farnesyl transferase inhibitor developed to inhibit a variety of farnesylated targets potentially relevant to the therapy of various malignancies. The agent has, thus far, been tested in a wide array of both solid tumors and myeloid malignancies. Phase I trials have demonstrated that tipifarnib is best given in a twice-daily fashion in doses of 600-1200 mg/day to avoid significant neuropathy, fatigue and myelosuppression. Subsequent trials demonstrated that pauses in therapy (with staccato dosing schedules) seem to increase tolerability without a clear decrease in efficacy. Phase II and III trials of tipifarnib as monotherapy for breast, colorectal, lung (both non-small cell and small cell), brain, pancreatic and urothelial cancers have all been disappointing. Combination trials of tipifarnib with cytotoxic, hormonal or biological therapies are ongoing. Tipifarnib has displayed the most interesting activity in the myeloid malignancies of myelodysplastic syndrome, myelofibrosis with myeloid metaplasia and elderly/high-risk acute myeloid leukemia. Overall clinical response rates of approximately 20-30% have been reported in myelodysplastic syndrome and acute myeloid leukemia patients who have few alternative therapeutic options. US FDA approval for tipifarnib awaits results of subsequent Phase III trials of the agent in elderly acute leukemia.