Differential activation of cell death and autophagy results in an increased cytotoxic potential for trifluorothymidine compared to 5-fluorouracil in colon cancer cells

Trifluorothymidine (TFT) is part of the oral drug formulation TAS-102. Both 5-fluorouracil (5-FU) and TFT can inhibit thymidylate synthase and be incorporated into DNA. TFT shows only moderate cross-resistance to 5-FU. Therefore, we examined whether mechanistic differences in cell death could underlie their different modes of action in colorectal cancer cell lines (WiDR, Lovo92 and Colo320). Drug cytotoxicity was determined by SRB- and clonogenic assays, cell death by flow cytometry (PI and annexin V), caspase cleavage by Western blotting and activity assays and in vivo activity in the hollow fiber assay. The IC50 values of TFT were 1-6 fold lower than for 5-FU, and clonogenic survival was less than 0.9% at 3 mu M TFT, while 2-20% of the cells still survived after 20 mu M 5-FU. In general, TFT was a more potent inducer of apoptosis than 5-FU, although the contribution of caspases varied between the used cell lines and necrosis-like cell death was detected. Accordingly, both drugs induced caspase (Z-VAD) independent cell death and lysosomal cathepsin B was involved. Activation of autophagy recovery mechanisms was only triggered by 5-FU, but not by TFT as determined by LC3B expression and cleavage. Inhibition of autophagy by 3-MA in 5-FU exposed cells reduced cell survival. Also, in vivo TFT (as TAS-102) caused more cell death than a 5-FU formulation. We conclude that TFT and 5-FU induce cell death via both caspase-dependent and independent mechanisms. The TFT was more potent than 5-FU, because it induces higher levels of cell death and does not elicit an autophagic survival response in the cancer cell lines. This provides a strong molecular basis for further application of TFT in cancer therapy

Roaring and repetition: How bowhead whales adjust their call density and source level (Lombard effect) in the presence of natural and seismic airgun survey noise

Over 500 000 automated and manual acoustic localizations, measured over seven years between 2008 and 2014,were used to examine how natural wind-driven noise and anthropogenic seismic airgun survey noise influence bowheadwhale call densities (calls/km2/min) and source levels during their fall migration in the Alaskan Beaufort Sea.Noise masking effects, which confound measurements of behavioral changes, were removed using a modified pointtransect theory. The authors found that mean call densities generally rose with increasing continuous wind-drivennoise levels. The occurrence of weak airgun pulse sounds also prompted an increase in call density equivalent to a10–15 dB change in natural noise level, but call density then dropped substantially with increasing cumulative soundexposure level (cSEL) from received airgun pulses. At low in-band noise levels the mean source level of theacoustically-active population changed to nearly perfectly compensate for noise increases, but as noise levelsincreased further the mean source level failed to keep pace, reducing the population’s communication space. Anincrease of >40 dB cSEL from seismic airgun activity led to an increase in source levels of just a few decibels.These resultsOver 500 000 automated and manual acoustic localizations, measured over seven years between 2008 and 2014,were used to examine how natural wind-driven noise and anthropogenic seismic airgun survey noise influence bowheadwhale call densities (calls/km2/min) and source levels during their fall migration in the Alaskan Beaufort Sea.Noise masking effects, which confound measurements of behavioral changes, were removed using a modified pointtransect theory. The authors found that mean call densities generally rose with increasing continuous wind-drivennoise levels. The occurrence of weak airgun pulse sounds also prompted an increase in call density equivalent to a10–15 dB change in natural noise level, but call density then dropped substantially with increasing cumulative soundexposure level (cSEL) from received airgun pulses. At low in-band noise levels the mean source level of theacoustically-active population changed to nearly perfectly compensate for noise increases, but as noise levelsincreased further the mean source level failed to keep pace, reducing the population’s communication space. Anincrease of >40 dB cSEL from seismic airgun activity led to an increase in source levels of just a few decibels.These results have implications for bowhead acoustic density estimation, and evaluations of the masking impacts ofdanthropogenic noisehave implications for bowhead acoustic density estimation, and evaluations of the masking impacts ofanthropogenic nois