Cell cycle parameters of Chinese hamster ovary cells during exponential, polyamine-limited growth

The Pharmacological or Genetic Blockade of Endogenous De Novo Fatty Acid Synthesis Does Not Increase the Uptake of Exogenous Lipids in Ovarian Cancer Cells

Ovarian cancer(OC) is a serious threat to women worldwide. Peritoneal dissemination, ascites and omental metastasis are typical features for disease progression, which occurs in a micro-environment that is rich in high-energy lipids. OC cells require high amounts of lipids for survival and growth. Not only do they import lipids from the host, they also produce lipids de novo. Inhibitors of fatty acid(FA) synthase(FASN) – the rate-limiting enzyme of endogenous FA synthesis that is overexpressed in OC – induce growth-arrest and apoptosis, rendering them promising candidates for cancer drug development. However, cancer researchers have long hypothesized that the lipid deficiency caused by FASN inhibition can be circumvented by increasing the uptake of exogenous lipids from the host, which would confer resistance to FASN inhibitors. In contrast to a very recent report in colorectal cancer, we demonstrate in OC cells (A2780, OVCAR3, SKOV3) that neither FASN inhibitors (G28UCM, Fasnall) nor FASN-specific siRNAs can stimulate a relief pathway leading to enhanced uptake of extrinsic FAs or low density lipoproteins (LDLs). Instead, we observed that the growth-arrest due to FASN inhibition or FASN knock-down was associated with significant dose- and time-dependent reduction in the uptake of fluorescently labeled FAs and LDLs. Western blotting showed that the expression of the FA receptor CD36, the LDL receptor(LDLR) and the lipid transport proteins fatty acid binding proteins 1–9 (FABP1–9) was not affected by the treatment. Next, we compared experimental blockade of endogenous lipid production with physiologic depletion of exogenous lipids. Lipid-free media, similar to FASN inhibitors, caused growth-arrest. Although lipid-depleted cells have diminished amounts of CD36, LDLR and FABPs, they can still activate a restorative pathway that causes enhanced import of fluorophore-labeled FAs and LDLs. Overall, our data show that OC cells are strictly lipid-depend and exquisitely sensitive to FASN inhibitors, providing a strong rationale for developing anti-FASN strategies for clinical use against OC.

Investigating the Effects of Stove Emissions on Ocular and Cancer Cells

More than a third of the world’s population relies on solid fuels for cooking and heating, with major health consequences. Although solid fuel combustion emissions are known to increase the prevalence of illnesses such as chronic obstructive pulmonary disease and lung cancer, however, their effect on the eyes is underexplored. This study assesses the acute toxicity of solid fuel combustion emissions on healthy ocular cells and a cancer cell line. Three healthy ocular cell lines (corneal, lens, and retinal epithelial cells) and a cancer cell line (Chinese hamster ovary cells) were exposed to liquid and gas phase emissions from applewood and coal combustion. Following the exposure, real-time cell attachment behavior was monitored for at least 120 hours with electrical cell impedance spectroscopy. The viability of the cells, amount of apoptotic cells, and generation of reactive oxygen species (ROS) were quantified with MTT, ApoTox-Glo, and ROS-Glo H₂O₂ assays, respectively. The results showed that coal emissions compromised the viability of ocular cells more than applewood emissions. Interestingly, the cancer cells, although their viability was not compromised, generated 1.7 to 2.7 times more ROS than healthy cells. This acute exposure study provides compelling proof that biomass combustion emissions compromise the viability of ocular cells and increase ROS generation. The increased ROS generation was fatal for ocular cells, but it promoted the growth of cancer cells.

Hitting two oncogenic machineries in cancer cells: cooperative effects of the multi-kinase inhibitor ponatinib and the BET bromodomain blockers JQ1 or dBET1 on human carcinoma cells

In recent years, numerous new targeted drugs, including multi-kinase inhibitors and epigenetic modulators have been developed for cancer treatment. Ponatinib blocks a variety of tyrosine kinases including ABL and fibroblast growth factor receptor (FGFR), and the BET bromodomain (BRD) antagonists JQ1 and dBET1 impede MYC oncogene expression. Both drugs have demonstrated substantial anti-cancer efficacy against several hematological malignancies. Solid tumors, on the other hand, although frequently driven by FGFR and/or MYC, are often unresponsive to these drugs. This is due, at least in part, to compensatory feedback-loops in the kinome and transcription network of these tumors, which are activated in response to drug exposure. Therefore, we hypothesized that the combination of the multi-kinase inhibitor ponatinib with transcription modulators such as JQ1 or dBET1 might overcome this therapeutic recalcitrance. Using ³H-thymidine uptake, cell cycle analysis, and caspase-3 or Annexin V labeling, we demonstrate that single drugs induce moderate dose-dependent growth-inhibition and/or apoptosis in colon (HCT116, HT29), breast (MCF-7, SKBR3) and ovarian (A2780, SKOV3) cancer cells. Ponatinib elicited primarily apoptosis, while JQ1 and dBET1 caused G0/G1 cell cycle arrest and very mild cell death. Phospho-FGFR and MYC, major targets of ponatinib and BET inhibitors, were downregulated after treatment with single drugs. Remarkably, ponatinib was found to sensitize cells to BET antagonists by enhancing apoptotic cell death, and this effect was associated with downregulation of MYC. In summary, our data shows that ponatinib sensitizes colon, breast, and ovarian cancer cells to BET bromodomain inhibitors. Further studies are warranted to determine the clinical value of this phenomenon.

Cell cycle phase perturbations and apoptosis in tumour cells induced by aplidine

Aplidine, dehydrodidemnin B, is a marine depsipeptide isolated from the Mediterranean tunicate Aplidium albicans currently in phase II clinical trial. In human Molt-4 leukaemia cells Aplidine was found to be cytotoxic at nanomolar concentrations and to induce both a G(1) arrest and a G(2) blockade. The drug-induced cell cycle perturbations and subsequent cell death do not appear to be related to macromolecular synthesis (protein, RNA, DNA) since the effects occur at concentrations (e.g. 10 nM) in which macromolecule synthesis was not markedly affected. Ten nM Aplidine for 1 h inhibited ornithine decarboxylase activity, with a subsequently strong decrease in putrescine levels. This finding has questionable relevance since addition of putrescine did not significantly reduce the cell cycle perturbations or the cytotoxicity of Aplidine. The cell cycle perturbations caused by Aplidine were also not due to an effect on the cyclin-dependent kinases. Although the mechanism of action of Aplidine is still unclear, the cell cycle phase perturbations and the rapid induction of apoptosis in Molt-4 cells appear to be due to a mechanism different from that of known anticancer drugs.

Cellular accumulation of 18F-labelled boronophenylalanine depending on DNA synthesis and melanin incorporation: a double-tracer microautoradiographic study of B16 melanomas in vivo

The cellular distribution of 4-borono-2-[18F]fluoro-L-phenylalanine ([18F]FBPA, an analog of p-boronophenylaline), a potential agent for boron neutron capture therapy (BNCT), and [6-3H]thymidine ([3H]Thd, a DNA precursor) in murine two B16 melanoma sublines and FM3A mammary carcinoma was studied in vivo using double-tracer microautoradiography. Tumour volume, tumour age, cell density in the tissues and the proportion of S phase cells in the cell cycle were the same in the three tumour models. Volume doubling time, which represents tumour growth rate, was fastest in B16F10, followed by B16F1 (P < 0.05), the slowest being in FM3A (P < 0.001). The rate of DNA synthesis in S phase cells corresponded to the volume doubling time. The greatest amount of [18F]FBPA was observed in S phase melanocytes and the lowest amount was found in non-S phase non-melanocytes. The [18F]FBPA accumulation was primarily related to the activity of DNA synthesis and, secondarily, to the degree of pigmentation in melanocytes. The therapeutic efficacy of BNCT with p-boronophenylalanine may be greater in melanoma that exhibits greater DNA synthesis activity and higher melanin content.

Mutant strain of Chinese hamster ovary cells with no detectable ornithine decarboxylase activity

We previously described an arginase-deficient, polyamine-dependent Chinese hamster ovary cell line which grows in serum-free medium. From this strain we isolated a new mutant strain that has no detectable catalytic ornithine decarboxylase activity. The mutant cells contain, however, immunoreactive ornithine decarboxylase-like protein roughly in the same quantity as the parent strain. The mutant and the parent cell line strains also contain similar amounts of ornithine decarboxylase-mRNA hybridizable to a specific cDNA. If polyamines are omitted from the medium, proliferation of the mutant cells is considerably retarded and ceases in 6 to 10 days. Addition of ornithine or alpha-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, has no effect on these cells. Putrescine and spermidine decreased in the mutant cells to undetectable levels during polyamine starvation, whereas spermine was reduced to 1/5th of that found in the control cultures. Polyamines appear to be indispensable for the mutant strain, but this was obvious only after the amount of polyamines, found as impurities in bovine serum albumin used in the medium, was reduced by dialysis to 10(-12) M. Because sera contain polyamines, the ability of the mutant strain to grow in serum-free medium is a great advantage in elucidation of the mechanisms of polyamine function.

Mutant strain of Chinese hamster ovary cells with no detectable ornithine decarboxylase activity

We previously described an arginase-deficient, polyamine-dependent Chinese hamster ovary cell line which grows in serum-free medium. From this strain we isolated a new mutant strain that has no detectable catalytic ornithine decarboxylase activity. The mutant cells contain, however, immunoreactive ornithine decarboxylase-like protein roughly in the same quantity as the parent strain. The mutant and the parent cell line strains also contain similar amounts of ornithine decarboxylase-mRNA hybridizable to a specific cDNA. If polyamines are omitted from the medium, proliferation of the mutant cells is considerably retarded and ceases in 6 to 10 days. Addition of ornithine or alpha-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, has no effect on these cells. Putrescine and spermidine decreased in the mutant cells to undetectable levels during polyamine starvation, whereas spermine was reduced to 1/5th of that found in the control cultures. Polyamines appear to be indispensable for the mutant strain, but this was obvious only after the amount of polyamines, found as impurities in bovine serum albumin used in the medium, was reduced by dialysis to 10(-12) M. Because sera contain polyamines, the ability of the mutant strain to grow in serum-free medium is a great advantage in elucidation of the mechanisms of polyamine function.

Polyamine starvation prolongs the S and G2 phases of polyamine-dependent (arginase-deficient) CHO cells

This study analyzes the effects of polyamine starvation on cell cycle traverse of an arginase-deficient CHO cell variant (CHO-A7). These cells grow well in serum-free medium, provided that it contains ornithine or polyamines or both. In the absence of ornithine or polyamines or both, the CHO-A7 cells develop severe polyamine deficiency and, as a consequence, grow more slowly. When grown to a stationary phase in the presence of ornithine or putrescine or both, the CHO-A7 cells became arrested in G0/early G1. However, when starved for ornithine and polyamines, they accumulated in the S and G2 phases. Ornithine and polyamine starvation of CHO-A7 cells causes an increase in ornithine decarboxylase activity. When this increase was prevented by treatment with DL-alpha-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ornithine decarboxylase, growth was further suppressed, and a greater fraction of cells were found in the S and G2 phases of the cell cycle.

Polyamine starvation prolongs the S and G2 phases of polyamine-dependent (arginase-deficient) CHO cells

This study analyzes the effects of polyamine starvation on cell cycle traverse of an arginase-deficient CHO cell variant (CHO-A7). These cells grow well in serum-free medium, provided that it contains ornithine or polyamines or both. In the absence of ornithine or polyamines or both, the CHO-A7 cells develop severe polyamine deficiency and, as a consequence, grow more slowly. When grown to a stationary phase in the presence of ornithine or putrescine or both, the CHO-A7 cells became arrested in G0/early G1. However, when starved for ornithine and polyamines, they accumulated in the S and G2 phases. Ornithine and polyamine starvation of CHO-A7 cells causes an increase in ornithine decarboxylase activity. When this increase was prevented by treatment with DL-alpha-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ornithine decarboxylase, growth was further suppressed, and a greater fraction of cells were found in the S and G2 phases of the cell cycle.

Growth inhibitory and stimulatory effects of retinoic acid on murine 3T3 cells

All-trans-beta-retinoic acid (RA) has both comitogenic and antiproliferative effects on murine Swiss 3T3 cells. Treatment of quiescent 3T3 cells for less than 24 hr with micromolar concentrations of RA potentiates subsequent mitogenic response of those cells to phorbol 12-myristate 13-acetate. Longer exposures of 3T3 cells to RA result in inhibition of DNA replication as measured by [3H]thymidine incorporation and decreased growth rates and saturation densities for cells grown in either 2% or 10% serum. Both the comitogenic and antiproliferative activities of RA for 3T3 cells are RA-dose dependent. RA-induced decreases in the 3T3 cell saturation density are reversible only after resuspension of cells by trypsinization and replating. Treatment of 3T3 cells for 48 hr with RA inhibits the rate of [3H]thymidine incorporation by 35--50%, while autoradiographic data show that labeling indices are similar to control values. Equal percentages of control and 48-hr RA-treated quiescent 3T3 cells respond to subsequent stimulation with 10% serum as determined by autoradiographic and flow cytometric analyses. However, the progression of RA-treated cells through the S phase of the cell cycle is slowed. These data suggest that inhibition of 3T3 cell proliferation by RA is established after a minimum 24-hr treatment and that this inhibition is the result of a decreased rate of DNA replication in S-phase cells.