New Drug Overcomes Resistance to BRAF Inhibitors in Mice and Cultured Human Cells

An experimental drug may strengthen treatments that target melanomas with mutations in the BRAF gene, reported researchers from the pharmaceutical company Merck at the American Association for Cancer Research’s 2013 meeting. Treatments that target BRAF often stop working because tumors activate a related protein called ERK, which is the target of Merck’s new drug. Called SCH772984, the drug inhibits ERK in cultured human tumor cells with BRAF, NRAS, or KRAS mutations; slows cell division in human tumor cells that resist treatments that target BRAF or MEK; and shrinks tumors in mice. The researchers have begun a phase I clinical trial of an ERK inhibitor in people with tumors.

Primary Melanoma of the CNS in Children Is Driven by Congenital Expression of Oncogenic NRAS in Melanocytes

“NRAS mutations are common in human melanoma. To produce a mouse model of NRAS-driven melanoma, we expressed oncogenic NRAS (NRASG12D) in mouse melanocytes. When NRASG12D was expressed in the melanocytes of developing embryos, it induced melanocyte proliferation and congenital melanocytic lesions reminiscent of human blue nevi but did not induce cutaneous melanoma…”

BRAF Mutations Less Likely in Melanomas in Ireland

BRAF mutations, which are found in about half of melanomas, are far less common amongst Irish people, suggests a study presented at the American Association for Cancer Research’s annual meeting. The researchers compared the melanomas of people in Ireland and Belgium and found that BRAF mutations occurred in only 21% of the former compared to the more typical 52% of the latter. This could be due to other genetic differences between the two countries. First, Irish patients had more NRAS mutations (21% vs 13%), which do not occur in melanomas with BRAF mutations. Second, 12% percent of the Irish patients had c-MET mutations, which are rare in melanomas, while none of the Belgian patients did. This work shows that treatments should be targeted to reflect genetic differences among populations.

Preclinical Study Indicates Potential for Novel Inhibitor to Overcome Drug Resistance Induced by RAF, MEK Inhibitors

WASHINGTON, D.C. — A new class of investigational medicines may help to treat patients with cancers driven by mutations in genes such as BRAF or KRAS/NRAS, including those patients who have become resistant to therapies that target BRAF directly,…

Inhibition of Wee1, AKT and CDK4 underlies the efficacy of the HSP90 inhibitor XL888 in an in vivo model of NRAS mutant melanoma

The HSP90 inhibitor XL888 is effective at reversing BRAF inhibitor resistance in melanoma, including that mediated through acquired NRAS mutations. The present study has investigated the mechanism of action of XL888 in NRAS mutant melanoma. Treatment of NRAS mutant melanoma cell lines with XL888 led to an inhibition of growth, G2/M phase cell cycle arrest and the inhibition of cell survival in 3D spheroid and colony formation assays…”

Selective RAF inhibitor impairs ERK1/2 phosphorylation and growth in mutant NRAS, vemurafenib-resistant melanoma cells

“The RAF inhibitor vemurafenib achieves remarkable clinical responses in mutant BRAF melanoma patients. However, vemurafenib is burdened by acquired drug resistance and by the side effects associated with its paradoxical activation of the ERK1/2 pathway in wild-type BRAF cells. This paradoxical effect has driven the development of a new class of RAF inhibitors. Here, we tested one of these selective, non-paradox-inducing RAF inhibitors termed paradox-breaker-04 (PB04) or PLX7904…”

First Treatment That Targets Melanomas with NRAS Mutations

A phase II study suggests that a MEK inhibitor drug benefits people who have melanomas with NRAS mutations, which currently have no targeted treatments. The drug, called MEK162, shrank tumors in 20% of NRAS-mutated melanoma patients (6 out of 30). MEK162 also shrank tumors in 20% of BRAF-mutated melanoma patients (8 out of 41), as well as tumors that had spread to the brain in two patients. This study is registered with ClinicalTrials.gove as number NCT01320085, and is now recruiting more patients with NRAS mutations.

MEK Inhibitor Active in NRAS-Mutated Melanoma

The MEK inhibitor MEK162 is the first agent to show some activity in patients with NRAS– and BRAF-mutated advanced melanoma, according to the conclusions of a phase II study, evaluating the drug’s safety and efficacy, published in Lancet Oncology. In addition, treatment with MEK162 resulted in the shrinkage of target brain metastases in two patients.

Research paper here:

Dabrafenib Bests Chemotherapy and May be Safer than Vemurafenib

A clinical trial found that dabrafenib, a BRAF inhibitor, was far more effective in treating melanomas that have BRAF mutations than the chemotherapy drug dacarbazine, according to a report at an American Society of Clinical Oncology meeting. Patients treated with this drug lived without getting worse for 70% longer than those treated with dacarbazine (5.1 vs. 2.7 months, respectively). Moreover, compared to those treated with vemurafenib in other studies, dabrafenib-treated patients had less risk of another kind of skin cancer called squamous cell carcinoma. This suggests that dabrafenib, which is experimental, could be safer than vemurafenib, which is FDA approved.