Conflicting effects of caffeine on apoptosis and clonogenic survival of human K1 thyroid carcinoma cell lines with different p53 status after exposure to cisplatin or UVc irradiation

Genotoxic effect of caffeine in Yarrowia lipolytica cells deficient in DNA repair mechanisms

Caffeine is a compound that can exert physiological-beneficial effects in the organism. Nevertheless, there are controversies about its protective-antioxidant and/or its negative genotoxic effect. To abound on the analysis of the possible genotoxic/antioxidant effect of caffeine, we used as research model the yeast Yarrowia lipolytica parental strain, and mutant strains (∆rad52 and ∆ku80), which are deficient in the DNA repair mechanisms. Caffeine (5 mM) showed a cytostatic effect on all strains, but after 72 h of incubation the parental and ∆ku80 strains were able to recover of this inhibitory effect on growth, whereas ∆rad52 was unable to recover. When cells were pre-incubated with caffeine and H₂O₂ or incubated with a mixture of both agents, a higher inhibitory effect on growth of mutant strains was observed and this effect was noticeably greater for the Δrad52 strain. The toxic effect of caffeine appears to be through a mechanism of DNA damage (genotoxic effect) that involves DSB generation since, in all tested conditions, the growth of Δrad52 strain (cells deficient in HR DNA repair mechanism) was more severely affected.

Overexpression of miR-101 promotes TRAIL-induced mitochondrial apoptosis in papillary thyroid carcinoma by targeting c-met and MCL-1

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) induces apoptosis in malignant cells, but not in normal cells. As papillary thyroid carcinoma cells broadly expressed TRAIL receptors (death receptor 4 and death receptor 5) on their surface, TRAIL is considered as a promising drug for treatment of papillary thyroid carcinoma. However, resistance to TRAIL still be a big obstacle to achieve a satisfactory effect for cancer therapy. Here, we found that overexpression of miR-101 was able to sensitize papillary thyroid carcinoma cells to TRAIL treatment in vitro and in vivo. Mechanically, we found that genes of c-met and MCL-1 were the targets of miR-101. Overexpression of miR-101 in TPC-1 significantly decreased the cellular protein levels of c-met and MCL-1, and thus inhibiting the PI3K/AKT pathway and reducing the resistance to TRAIL-induced mitochondrial apoptosis. Enforced expression of either c-met or MCL-1 could partially inhibit the miR-101 promoted apoptosis in TRAIL-treated TPC-1 cells. These results indicated that miR-101-c-met/MCL-1 axis determined the sensitivity of TRAIL to thyroid cancer in some extent. Combination with TRAIL and miR-101 may represent a novel approach to kill papillary thyroid carcinoma cells efficiently.

Redox modulation of the DNA damage response

Lesions to DNA trigger the DNA-damage response (DDR), a complex, multi-branched cell-intrinsic process targeted to DNA repair, or elimination of the damaged cells by apoptosis. DDR aims at reducing permanence of mutated cells, decreasing the risk of tumor development: the more stringent the response, the lower the likelihood that sub-lethally damaged, unrepaired cells survive and proliferate. Accordingly, leakage often occurs in tumor cells with compromised DDR, accumulating mutations and accelerating tumor progression. Oxidations mediate DNA damage upon different insults such as UV, X and γ radiation, pollutants, poisons, or endogenous disequilibria, producing different types of lesions that trigger DDR, which can be alleviated by antioxidants. But reactive oxygen species (ROS), and the enzymes involved in their production or scavenging, also participate in DDR signaling, modulating the activity of key enzymes, and regulating the stringency of DDR. Accordingly, antioxidant enzymes such as superoxide dismutase play intimate and complex roles in tumor development, exceeding the basal roles of preventing the initial DNA damage. Likewise, it is emerging that dietary antioxidants help controlling tumor onset and progression by preventing DNA damage and by acting on cell cycle checkpoints, opening a novel and promising frontier to anticancer therapy.

IGF1R-targeted therapy and its enhancement of doxorubicin chemosensitivity in human osteosarcoma cell lines

Type-I insulin-like growth factor receptor (IGF1R) and its signaling play an important role in osteosarcomagenesis, tumor progression, and chemoresistance. The purpose of this study was to investigate both the effect and mechanisms of IGF1R inhibition by tyrphostin AG1024 in the presence or absence of doxorubicin in a panel of six osteosarcoma cell lines and a self-established doxorubicin-resistant cell line. We are the first to indicate that targeting IGF1R together with doxorubicin achieved additive anti-osteosarcoma growth effect, accompanied with increased apoptosis, cytotoxicity, and dual cell cycle arrests. In conclusion, IGF1R inhibition can enhance doxorubicin chemotherapy in some osteosarcoma cell lines.

Protein kinase C inhibitor Gö6976 augments caffeine-induced reversal of chemoresistance to cis-diamminedichloroplatinum-II (CDDP) in a human ovarian cancer model

OBJECTIVES

Novel strategies for the treatment of chemoresistant ovarian cancer are needed. Caffeine and related compounds have been shown to over-ride G2/M arrest in ovarian cancer cells, increasing toxicity to chemotherapy. Newer compounds have been developed which may have the same effect as and exhibit synergism with caffeine, allowing the use of lower doses.

METHODS

We investigated the effects of caffeine and Gö6976 in the presence of CDDP in the SKOV3 and A2780 cell lines using proliferation, cell-cycle analysis, apoptosis, and AKT expression.

RESULTS

Proliferation of cancer cells was decreased in a dose-dependent manner with caffeine and CDDP, but doses of caffeine required for significant inhibition were higher than that achievable in patients. Gö6976, a global PKC inhibitor with G2/M over-ride capability similar to caffeine, when combined with caffeine and CDDP at doses below that required for cell-cycle over-ride produced the growth inhibitory effects of a ten-fold higher caffeine concentration in both cell lines. CDDP induced G2/M arrest was significantly abrogated by caffeine but not by Gö6976 alone and no additional effect was seen on G2/M over-ride by the addition of Gö6976 to caffeine. Addition of Gö6976 to caffeine and CDDP did increase apoptosis but without altering phospho-AKT.

CONCLUSIONS

Gö6976, when added to caffeine at doses below that required for cell-cycle over-ride, augments caffeine in overcoming CDDP resistance in this experimental system. G2/M over-ride is not the mechanism underlying the inhibition of proliferation. An AKT-independent apoptotic mechanism may be responsible.

Caffeine markedly sensitizes human mesothelioma cell lines to pemetrexed

Pemetrexed is a new generation antifolate approved for the treatment of mesothelioma and non-small cell lung cancer. Caffeine is known to augment radiation or chemotherapeutic drug-induced cell killing. The current study addresses the impact of caffeine on the activity of pemetrexed in mesothelioma cell lines. Caffeine enhanced pemetrexed activity in all four mesothelioma cell lines tested (H2052, H2373, H28 and MSTO-211H). Caffeine sensitized H2052 cells in a dose- and schedule-dependent manner, and was associated with a markedly decreased clonogenic survival. Caffeine sensitization occurred only in cells subjected to pulse, but not continuous, exposure to pemetrexed. Similar pemetrexed sensitization was also observed with the clinically better tolerated caffeine analog, theobromine. Pemetrexed sensitization by caffeine was associated with an increase in pemetrexed-induced phosphorylation of ataxia-telangiectasia-mutated (ATM) and Chk1. These data indicate that caffeine and its analog, theobromine, may be a useful approach to enhance pemetrexed-based chemotherapy.

The enigmatic effects of caffeine in cell cycle and cancer

Caffeine may very well be the most frequently ingested neuroactive drug in the world. Mechanistically, caffeine has been reported to affect cell cycle function, induce programmed cell death or apoptosis and perturb key cell cycle regulatory proteins. Although the effects of caffeine have been heavily investigated, much of the research data regarding caffeine's effects on cell cycle and proliferation seem ambiguous. One important factor may be that caffeine has been used experimentally in numerous cell types under a variety of conditions at concentrations ranging from micromolar to high millimolar. Physiologically, achieving experimental blood levels of caffeine would be extremely difficult without adverse side effects. Therefore, the relevance of experimental data obtained by using high concentrations of caffeine is not clear and may account for some of the discrepancies in the literature. This review attempts to reconcile data regarding the cellular effects of caffeine by examining reported effects on cell cycle, proliferation and apoptosis with careful attention to differences in experimental conditions and caffeine concentration utilized.

UV-induced apoptosis in XPG-deficient fibroblasts involves activation of CD95 and caspases but not p53

Mildly affected individuals from xeroderma pigmentosum complementation group G (XP-G) possess single amino acid substitutions in the XPG protein that adversely affects its 3' endonuclease function in nucleotide excision repair. More serious mutations in the XPG gene generate truncated or unstable XPG proteins and result in a particularly early and severe form of the combined XP/CS complex. Following UV irradiation, cells from such XP-G/CS patients enter apoptosis more readily than other DNA repair-deficient cells. Here, we explore the mechanisms by which UV triggers the apoptotic cell death program in XP-G and XP-G/CS primary fibroblasts. Activation of the CD95 signalling pathway occurs within minutes and it is the earliest detectable post-UV event in such cells. This is rapidly followed by activation of caspase-8 then caspase-3. Several hours later caspase-9 becomes activated and the mitochondrial membrane potential drops, but without any obvious prior release of cytochrome c. Although p53 accumulates in XPG-deficient cells after UV irradiation, use of RNA interference demonstrates that p53 is not required for their UV-induced apoptotic response. p53 ablation of wild-type fibroblasts reduces MDM2 mRNA levels, inhibits accumulation of the 90kDa/92kDa Mdm2 isoforms, and prevents the nuclear relocalisation of Mdm2 after UV treatment. The same post-UV effects occur in XPG-deficient cells that express normal p53 levels. These results emphasise the importance of the extrinsic apoptotic pathway and aberrant Mdm2 events for the severe UV-induced apoptosis of XPG-deficient primary fibroblasts. XP-G/CS cells constitutively overexpress the pro-apoptotic Bax protein and a long isoform of the E2F1 transcription factor that controls S phase entry, which may prime them to enter apoptosis very readily after UV irradiation.

Expression of common chromosomal fragile site genes, WWOX/FRA16D and FHIT/FRA3B is downregulated by exposure to environmental carcinogens, UV, and BPDE but not by IR

Common chromosomal fragile sites are unstable genomic loci susceptible to breakage, rearrangement, and are highly recombinogenic. Frequent alterations at these loci in tumor cells led to the hypothesis that they may contribute to cancer development. The two most common chromosomal fragile sites FRA16D and FRA3B which harbor WWOX and FHIT genes, respectively, are frequently altered in human cancers. Here we report that environmental carcinogens, ultraviolet (UV) light, and Benzo[a]pyrene diol epoxide (BPDE), significantly downregulate expression of both genes. On the other hand, we observe that ionizing radiation (IR) does not affect expression of these genes, suggesting that the effect of repression exerted by UV and BPDE is not just a consequence of DNA damage but may be a result of different signaling pathways triggered by specific DNA lesions. Such downregulation correlates with an induction of an S-phase delay in the cell cycle. Treatment of UV-irradiated cells with caffeine abrogates the S-phase delay while concomitantly overcoming the repression phenomenon. This suggests the involvement of unique cell cycle checkpoint mechanisms in the observed repression. Therefore, it is hypothesized that protracted downregulation of the putative tumor suppressor genes WWOX and FHIT by environmental carcinogens may constitute an additional mechanism of relevance in the initiation of tumorigenesis.