Wednesday, December 19, 2012

Hard-to-treat Myc-driven cancers may be susceptible to drug already used in clinic

In continuation of my update on Everolimus

Treatment with everolimus led to tumor regression and  gnificantly improved survival compared  with placebo in mice with established lymphomas. However,  all  of  these  mice  eventually  relapsed as a result   of the growth of lymphoma  cells  resistant to the effec ts  of everolimus.
"These data confirmed our hypothesis that mTORC1 inhibition could suppress Myc-driven tumor initiation and growth," said McArthur. "The surprise was found in how mTORC1 inhibition led to tumor regression. We had expected that it would trigger cancer cells to die by a cellular process known as apoptosis, but we found that this was not the case."
Detailed analysis of the tumors indicated that everolimus caused tumor regression by inducing cellular senescence.

According to McArthur, normal cells protect themselves when cancer-driving genes are switched on is by entering a state called senescence. When cancers develop, they have found ways to overcome this safeguard. "Our data indicate that one way in which cancers bypass senescence, in particular senescence induced by Myc, is through a signaling pathway involving mTORC1," he said.

Resistance to everolimus treatment in mice with established lymphomas was associated with loss of the function of p53, a protein known to help suppress tumor formation and growth.
"The loss of effectiveness of everolimus therapy against lymphoma cells deficient in p53 function has important clinical implications," said McArthur. "Everolimus could be a useful new string to the bow for clinicians treating patients with Myc-driven cancers, in particular B cell lymphomas, but that it would be helpful only to those patients with functional p53."

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