As these samples were taken prior to any treatment, it is possible that the other three poor-prognosis tumors represent a population of tumors that become resistant in response to treatment rather than possessing intrinsic therapeutic resistance.
To understand the challenges, it's necessary to look at how bacteria become resistant in the first place.
Bacteria become resistant in a process that Prof Piddock describes as a form of evolution, where the fittest bacteria survive - that is, the ones that can withstand antibiotics.
Sequence analysis of the siRNA target sites in this strain showed that no mutations had been generated, indicating that the virus may had become resistant in some other manner.
If the gene were that prevalent in the field, says entomologist Fred Gould of North Carolina State University, an entire pest population could become resistant in a year or two--an outcome that could hurt organic farmers, who rely on Bt sprays.
In short, exposing bacteria around us to antibiotics is what provides the "selection pressure" that drives them to become resistant in the first place.
This occurs when A. fumigatus became resistant in the environment due to the use of azole fungicides for crop protection and patients are believed to inhale azole-resistant A. fumigatus spores.
We performed the screen using melanoma cell lines (Lu1205 parental, sensitive [Lu1205S]), which became resistant in the presence of increasing concentrations (up to 5 μM) of the BRAFi PLX4032 (Lu1205 resistant [Lu1205R]; Figures 1A and S1A).
Several in vitro studies, in fact, demonstrated that cancer cells that are sensitive to 5FU when normally oxygenated may become resistant in hypoxic conditions (Teicher et al, 1981; Tannock, 1987; Grau and Overgaard, 1992).
This cell line constitutes a better physiological model for chemoresistance studies in comparison with other cell lines that become resistant in vitro by selective pressure after treatment with increasing concentrations of specific drugs.
