The Mitogen-Activated Protein/Extracellular Signal-Regulated Kinase Kinase Inhibitor AZD6244 (ARRY-142886) Induces Growth Arrest in Melanoma Cells and Tumor Regression When Combined with Docetaxel

Abstract

Purpose: Disseminated melanoma is highly therapy resistant. The finding that 66% of melanomas harbor the activating BRAF V600E mutation has raised expectations for targeting the Ras/RAF/mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK pathway in melanoma. This study addresses the anti-melanoma activity of the MEK inhibitor AZD6244 (ARRY-142886). Experimental Design: We recently have shown that growing melanoma cells as threedimensional collagen-implanted spheroids enhances resistance to the MEK inhibitor U0126. Here, we investigated the anti-melanoma activity of AZD6244 in two-dimensional cell culture, the three-dimensional spheroid model, and an in vivo model. Results: In two-dimensional cell culture, AZD6244 was cytostatic and reduced the growth of melanoma cells in a concentration-dependent fashion through the induction of G 1 -phase cell cycle arrest. In our three-dimensional spheroid model, the effects of AZD6244 were largely cytostatic and reversible, with drug washout leading to spheroid regrowth. Finally, 1205Lu cells were grown as tumor xenografts in severe combined immunodeficient mice. After tumor establishment, mice were dosed twice daily with 0, 10, or 30 mg/kg AZD6244 p.o. AZD6244 treatment decreased phospho-ERK in the tumors and significantly suppressed tumor growth. The original tumors remained viable, suggesting that AZD6244 monotherapy was largely cytostatic, and not proapoptotic in this model. Further studies showed that co-administration of AZD6244 (30 mg/kg) with docetaxel (15 mg/kg) led to tumor regression, indicating the potential for MEK inhibitor/chemotherapy drug combinations. Conclusions: Inhibition of MEK is cytostatic as a monotherapy in melanoma, but cytotoxic when combined with docetaxel.

The influence of the BRAF V600E mutation in thyroid cancer cell lines on the anticancer effects of 5-aminoimidazole-4-carboxamide-ribonucleoside

“…Mutated BRAF activates the MEK-ERK kinase pathway, which is an essential regulator of cell growth, differentiation, cell cycle progression, and oncogenic transformation (Sebolt-Leopold & Herrera 2004). BRAF-targeting compounds and MEK inhibitors, designed to disrupt the RAF-MEK-ERK pathway have been developed and are currently being tested in clinical trials for treatment of various human cancers (Beeram et al 2005, Gray-Schopfer et al 2007, Haass et al 2008. Several studies have shown that BRAF mutant cancer cells may be susceptible to anti-cancer drugs, such as AZD6244 (used to treat melanoma) (Smalley & Flaherty 2009).…”

Integrating BRAF/MEK inhibitors into combination therapy for melanoma

“…The interpretation of these results is somewhat hindered by the poor pharmacological properties of this agent. Similar G1-phase growth arrest results have been observed with allosteric MEK inhibitors, such as U0126, PD0325901 and AZD6244, suggesting that inhibition of the MAPK pathway in melanoma is largely cytostatic Solit et al, 2006;Haass et al, 2008). Activating BRAF V600E mutations are also known to occur in subsets of thyroid and colon carcinomas (Davies et al, 2002), and similar to melanoma, the presence of the mutation also predicts for sensitivity to MEK inhibition (Solit et al, 2006;Leboeuf et al, 2008).…”

“…Analysis of patient samples pre-and posttreatment revealed that sorafenib incompletely inhibited ERK phosphorylation. This observation may be significant as preclinical studies show that complete pathway inhibition is needed to induce cell cycle arrest (Solit et al, 2006;Haass et al, 2008). In the single-agent phase II trials with sorafenib, the common toxicities were hypertension and hand-foot syndrome, consistent with the toxicities described with inhibitors of VEGF signalling.…”

“…Earlier studies from our laboratory, using cell lines derived from metastatic lesions, confirm this hypothesis and demonstrate that cells are resistant to both MEK and PI3K inhibitors when grown in 3D culture . It was further shown that targeting either the PI3K or MEK pathway alone led to cytostasis and was associated with a reversible G1-phase cell cycle arrest Haass et al, 2008). In other studies, there was a lack of good correlation between the inhibition of either the PI3K or MEK signalling pathway and the inhibition of cell growth, showing a functional redundancy between the various growth-promoting signalling pathways.…”

“…In vitro studies have shown that BRAF V600E is an oncogene in immortalised mouse melanocytes (Gray-Schopfer et al, 2007), and the selective downregulation of BRAF V600E using RNAi causes cell death and reversal of the melanoma phenotype (Hingorani et al, 2003). However, pharmacological inhibition of BRAF and MEK have not produced such dramatic effects in vivo (Sharma et al, 2005;Haass et al, 2008). This is partly due to inherent flaws in the agents tested to date, and also a likely indication of the greater vulnerability of melanoma cells in vitro where most of the cells are rapidly cycling under sub-confluent culture conditions in the continuous presence of serum.…”