TAS-102 is a novel oral nucleoside antitumor agent containing trifluridine (FTD) and tipiracil hydrochloride (TPI). The compound improves overall survival of colorectal cancer (CRC) patients who are insensitive to standard chemotherapies. FTD possesses direct antitumor activity since it inhibits thymidylate synthase (TS) and is itself incorporated into DNA. However, the precise mechanisms underlying the incorporation into DNA and the inhibition of TS remain unclear. We found that FTD-dependent inhibition of TS was similar to that elicited by fluorodeoxyuridine (FdUrd), another clinically used nucleoside analog. However, washout experiments revealed that FTD-dependent inhibition of TS declined rapidly, whereas FdUrd activity persisted. The incorporation of FTD into DNA was significantly higher than that of other antitumor nucleosides. Additionally, orally administered FTD had increased antitumor activity and was incorporated into DNA more effectively than continuously infused FTD. When TAS-102 was administered, FTD gradually accumulated in tumor cell DNA, in a TPI-independent manner, and significantly delayed tumor growth and prolonged survival, compared to treatment with 5-FU derivatives. TAS-102 reduced the Ki-67-positive cell fraction, and swollen nuclei were observed in treated tumor tissue. The amount of FTD incorporation in DNA and the antitumor activity of TAS-102 in xenograft models were positively and significantly correlated. These results suggest that TAS-102 exerts its antitumor activity predominantly due to its DNA incorporation, rather than as a result of TS inhibition. The persistence of FTD in the DNA of tumor cells treated with TAS-102 may underlie its ability to prolong survival in cancer patients.

TAS-102 is a novel oral nucleoside antitumor agent that consists of trifluridine (FTD) and tipiracil hydrochloride (TPI) at a molecular ratio of 1:0.5, and was approved in Japan in March 2014 for the treatment of patients with unresectable advanced or recurrent colorectal cancer that is refractory to standard therapies. In the present study, we used colorectal cancer xenografts to assess whether the efficacy of TAS-102 could be improved by combining it with bevacizumab, cetuximab or panitumumab. TAS-102 was orally administered twice a day from day 1 to 14, and bevacizumab, cetuximab and panitumumab were administered intraperitoneally twice a week for 2 weeks. Growth inhibitory activity was evaluated based on the relative tumor volume (RTV) after 2 weeks of drug administration and time taken for the relative tumor volume to increase five-fold (RTV5). Tumor growth inhibition and RTV5 with TAS-102 and bevacizumab combination treatment were significantly better than those with TAS-102 or bevacizumab alone in the SW48 and HCT116 tumor models, and the concentration of phosphorylated FTD in tumors determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was higher in the TAS-102 and bevacizumab combination group than in the TAS-102 monotherapy group. The combination of TAS-102 and cetuximab or panitumumab was also significantly more effective than either monotherapy in the SW48 tumor model. There was no significant difference in the body weight between the mice treated with TAS-102 monotherapy and any of the combination therapies on day 29. Our preclinical findings indicate that the combination therapy of TAS-102, bevacizumab and cetuximab or panitumumab is a promising treatment option for colorectal cancer.

Mitochondrial heat shock protein 70 (mthsp70) functions as a mitochondrial import motor and is essential in mitochondrial biogenesis and energy generation in eukaryotic cells. HSP-6 (hsp70F) is a nematode orthologue of mthsp70. Knockdown of HSP-6 by RNA interference in young adult nematodes caused a reduction in the levels of ATP-2, HSP-60 and CLK-1, leading to abnormal mitochondrial morphology and lower ATP levels. As a result, RNA interference-treated worms had lower motility, defects in oogenesis, earlier accumulation of autofluorescent material, and a shorter life span. These are the major phenotypes observed during the aging of worms, suggesting that the reduction of HSP-6 causes early aging or progeria-like phenotypes. The amount of HSP-6 became dramatically reduced at the expected mean life span in not only wild-type but also in long and short life span mutant worms (wild-type, daf-2, and daf-16). Mitochondrial HSP-60 and ATP-2 were also reduced following the reduction of HSP-6 during aging. These results suggest that the reduction of HSP-6 causes defects in mitochondrial function at the final stage of aging, leading to mortality.Mitochondria are major organelles that carry out cellular oxidation and produce most of the cellular ATP by oxidative phosphorylation. Mitochondria also play essential roles in controlling cell viability and proliferation (1, 2). A large number of studies have shown the essential roles of mitochondria in development and differentiation (3, 4). Furthermore, mitochondria are thought to be deeply involved in the aging process, based on the free radical theory of aging, because mitochondria are a major source of reactive oxygen species (ROS) 3 (5, 6). Accumulating evidence supports this idea. For example, abnormal mitochondria accumulate during aging (7), and enforced breakdown of mtDNA or their repair mechanism causes premature aging in mice (8,9). In Caenorhabditis elegans, mutations in mev-1 (a subunit of the enzyme succinate dehydrogenase cytochrome b, a component of complex II of the mitochondrial electron transport chain) and gas-1 (a subunit of mitochondrial NADH-ubiquinone oxidoreductase, a component of complex I of the mitochondrial electron transport chain) increase ROS production and sensitivity to stress, resulting in a shorter life span (10 -13).A mammalian mitochondrial heat shock protein 70 (mthsp70, also known as mortalin or Grp75) has been shown to function as a mitochondrial protein import motor and is involved in mitochondrial biogenesis (14, 15). It has also been shown to be involved in the production of ROS (16), cell proliferation (17), and the regulation of life span (18) in mammalian cells. Increased expression of HSP-6 (hsp70F), the predicted C. elegans orthologue of mthsp70, by the introduction of an extra hsp-6 gene copies extended the life span of C. elegans (19). In contrast, deletion mutations of SSC1, the yeast orthologue of mthsp70, were lethal (20 -22), and knockdown of mthsp70 caused growth arrest in human cancer cells (17,23). Recently, it has been ...

Trifluridine (FTD) and 2′-deoxy-5-fluorouridine (FdUrd), a derivative of 5-fluorouracil (5-FU), are antitumor agents that inhibit thymidylate synthase activity and their nucleotides are incorporated into DNA. However, it is evident that several differences occur in the underlying antitumor mechanisms associated with these nucleoside analogues. Recently, TAS-102 (composed of FTD and tipiracil hydrochloride, TPI) was shown to prolong the survival of patients with colorectal cancer who received a median of 2 prior therapies, including 5-FU. TAS-102 was recently approved for clinical use in Japan. These data suggest that the antitumor activities of TAS-102 and 5-FU proceed via different mechanisms. Thus, we analyzed their properties in terms of thymidine salvage pathway utilization, involving membrane transporters, a nucleoside kinase, a nucleotide-dephosphorylating enzyme, and DNA polymerase α. FTD incorporated into DNA with higher efficiency than FdUrd did. Both FTD and FdUrd were transported into cells by ENT1 and ENT2 and were phosphorylated by thymidine kinase 1, which showed a higher catalytic activity for FTD than for FdUrd. deoxyUTPase (DUT) did not recognize dTTP and FTD-triphosphate (F3dTTP), whereas deoxyuridine-triphosphate (dUTP) and FdUrd-triphosphate (FdUTP) were efficiently degraded by DUT. DNA polymerase α incorporated both F3dTTP and FdUTP into DNA at sites aligned with adenine on the opposite strand. FTD-treated cells showed differing nuclear morphologies compared to FdUrd-treated cells. These findings indicate that FTD and FdUrd are incorporated into DNA with different efficiencies due to differences in the substrate specificities of TK1 and DUT, causing abundant FTD incorporation into DNA.

Long interspersed elements (LINEs) and short interspersed elements (SINEs) are retrotransposons. These elements can mobilize by the "copy-and-paste" mechanism, in which their own RNA is reverse-transcribed into complementary DNA (cDNA). LINEs and SINEs not only are components of eukaryotic genomes but also drivers of genomic evolution. Thus, studies of the amplification mechanism of LINEs and SINEs are important for understanding eukaryotic genome evolution. Here we report the characterization of one LINE family (UnaL2) and two SINE families (UnaSINE1 and UnaSINE2) from the eel (Anguilla japonica) genome. UnaL2 is approximately 3.6 kilobases (kb) and encodes only one open reading frame (ORF). UnaL2 belongs to the stringent type--thought to be a major group of LINEs--and can mobilize in HeLa cells. We also show that UnaL2 and the two UnaSINEs have similar 3' tails, and that both UnaSINE1 and UnaSINE2 can be mobilized by UnaL2 in HeLa cells. These elements are thus useful for delineating the amplification mechanism of stringent type LINEs as well as that of SINEs.