Therapeutic Destruction of Insulin Receptor Substrates for Cancer Treatment

“Insulin receptor substrates 1 and 2 (IRS1/2) mediate mitogenic and antiapoptotic signaling from insulin-like growth factor 1 receptor (IGF-IR), insulin receptor (IR), and other oncoproteins. IRS1 plays a central role in cancer cell proliferation, its expression is increased in many human malignancies, and its upregulation mediates resistance to anticancer drugs. IRS2 is associated with cancer cell motility and metastasis. Currently, there are no anticancer agents that target IRS1/2. We present new IGF-IR/IRS-targeted agents (NT compounds) that promote inhibitory Ser-phosphorylation and degradation of IRS1 and IRS2. Elimination of IRS1/2 results in long-term inhibition of IRS1/2-mediated signaling. The therapeutic significance of this inhibition in cancer cells was shown while unraveling a novel mechanism of resistance to B-RAFV600E/K inhibitors. We found that IRS1 is upregulated in PLX4032-resistant melanoma cells and in cell lines derived from patients whose tumors developed PLX4032 resistance. In both settings, NT compounds led to the elimination of IRS proteins and evoked cell death. Treatment with NT compounds in vivo significantly inhibited the growth of PLX4032-resistant tumors and displayed potent antitumor effects in ovarian and prostate cancers. Our findings offer preclinical proof-of-concept for IRS1/2 inhibitors as cancer therapeutics including PLX4032-resistant melanoma. By the elimination of IRS proteins, such agents should prevent acquisition of resistance to mutated-B-RAF inhibitors and possibly restore drug sensitivity in resistant tumors.”

New Combination Treatment May Target Melanomas with BRAF Mutations Safely

While melanomas with BRAF mutations can be targeted with a combination of BRAF inhibitors and MEK inhibitors, the treatment can have side effects such as fever, light sensitivity, and rashes. But early results of a phase I clinical trial suggest that BRAF-mutant melanomas could be treated safely and effectively with a new combination: LGX818, a BRAF inhibitor developed by Novartis and MEK162, a MEK inhibitor developed by Array BioPharma. Moreover, using these drugs together may decrease common side effects of targeted BRAF treatments, including skin toxicities and muscle and joint pain. A phase III trial of this new combination treatment is expected to begin later in 2013.

A costly revolution for a subgroup of patients with metastatic melanoma

Dabrafenib, an inhibitor of mutated BRAF, has clinical activity with a manageable safety profile in phase I and II studies in patients with BRAF (V600)–mutated metastatic melanoma. The study aims to assess the efficacy of dabrafenib in a phase III trial of patients with BRAF (V600)–mutated metastatic melanoma. Dabrafenib significantly improved PFS compared with dacarbazine.” – from

Host immunity contributes to the anti-melanoma activity of BRAF inhibitors.

“The BRAF mutant, BRAFV600E, is expressed in nearly half of melanomas, and oral BRAF inhibitors induce substantial tumor regression in patients with BRAFV600E metastatic melanoma. The inhibitors are believed to work primarily by inhibiting BRAFV600E-induced oncogenic MAPK signaling; however, some patients treated with BRAF inhibitors exhibit increased tumor immune infiltration, suggesting that a combination of BRAF inhibitors and immunotherapy may be beneficial. We used two relatively resistant variants of BrafV600E-driven mouse melanoma (SM1 and SM1WT1) and melanoma-prone mice to determine the role of host immunity in type I BRAF inhibitor PLX4720 antitumor activity.”

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.

Ipilimumab Could Treat Small Melanomas in the Brain

A study in The Lancet shows that the drug ipilimumab could treat melanomas that have spread to the brain, particularly in people who do yet not have neurological symptoms. Of 51 such patients treated with ipilimumab, 12 had tumors in the brain that shrank or did not get worse and 14 had tumors outside the brain that shrank or did not get worse. Ipilimumab (Yervoy) is an immune system booster that the FDA has approved for treating advanced melanomas.

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Drug Targets Two Common Melanoma Mutations

An experimental drug could help control some melanomas that have BRAF or NRAS mutations, according to a report at an American Society of Clinical Oncology meeting. Tumors shrank or did not get worse in 8 out of 35 patients with the most common BRAF mutation (V600E), and in 6 out of 28 patients with NRAS mutations. This is the first targeted treatment for melanomas that have NRAS mutations. BRAF and NRAS mutations can activate a protein called MEK that is involved in cell division. The experimental drug, which is called MEK162, is a MEK inhibitor. The side effects of MEK162, which included diarrhea, rashes and swelling, were manageable.

Dabrafenib May Shrink Melanomas in the Brain

An early stage clinical trial suggests that dabrafenib, a BRAF inhibitor, could treat melanomas that have spread to the brain. The study, reported in The Lancet, included 10 people with brain metastases of melanomas that had BRAF mutations. Tumors shrank in 9 patients and were not evident in 4 patients. This is a surprise because the drug had not been expected to cross the blood-brain barrier effectively. Indeed, melanoma patients with brain metastases have been routinely excluded from previous trials of vemurafenib (Zelboraf) and other BRAF inhibitors.

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Vemurafenib Benefits People Previously Treated for Melanoma

A New England Journal of Medicine study found that vemurafenib, which was approved by the FDA in 2011, controlled melanomas in about half of people who had been previously treated for this disease. The trial included 132 repeat patients; tumors shrank in 47% of the patients and were not evident in 6% during the course of the trial. Vemurafenib is a BRAF inhibitor and about half of melanoma patients have BRAF mutations. While 26% of patients developed another kind of skin cancer called squamous cell carcinoma, these lesions were successfully removed surgically.

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