Epidermal growth factor and insulin-like growth factor-1 protect MDA-231 cells from death induced by actinomycin D: the involvement of growth factors in drug resistance

Fibroblast growth factors: an epigenetic mechanism of broad spectrum resistance to anticancer drugs

Based on the observation that removal of tumors from metastatic organs reversed their chemoresistance, we hypothesized that chemoresistance is induced by extracellular factors in tumor-bearing organs. By comparing chemosensitivity and proteins in different tumors (primary vs. metastases) and different culture systems (tumor fragment histocultures vs. monolayer cultures derived from the same tumor), we found elevated levels of acidic (aFGF) and basic (bFGF) fibroblast growth factors in the conditioned medium (CM) of solid and metastatic tumors. These CM induced broad spectrum resistance to drugs with diverse structures and action mechanisms (paclitaxel, doxorubicin, 5-fluorouracil). Inhibition of bFGF by mAb and its removal by immunoprecipitation resulted in complete reversal of the CM-induced chemoresistance, whereas inhibition/removal of aFGF resulted in partial reversal. Using CM that had been depleted of aFGF and/or bFGF and subsequently reconstituted with respective human recombinant proteins, we found that bFGF but not aFGF induced chemoresistance whereas aFGF amplified the bFGF effect. aFGF and bFGF fully accounted for the CM effect, indicating these proteins as the underlying mechanism of the chemoresistance. The FGF-induced resistance was not due to reduced intracellular drug accumulation or altered cell proliferation. We further showed that an inhibitor of aFGF/bFGF (suramin) enhanced the in vitro and in vivo activity of chemotherapy, resulting in shrinkage and eradication of well established human lung metastases in mice without enhancing toxicity. These results indicate elevated levels of extracellular aFGF/bFGF as an epigenetic mechanism by which cancer cells elude cytotoxic insult by chemotherapy, and provide a basis for designing new treatment strategies.

Actinomycin D induces apoptosis and inhibits growth of pancreatic cancer cells

Pancreatic cancer cells are usually resistant to apoptosis induced by cytotoxic drugs, by activation of surface receptors such as Fas and TNF receptor or by serum or growth factor withdrawal. Actinomycin D (actD) is an inhibitor of RNA synthesis and acts as a potent inducer of apoptosis in several cell lines. In the present study, we investigated the effects of actD on PANC-1 pancreatic cancer cells. ActD caused apoptosis in PANC-1 cells in a dose-dependent manner, as determined by cell growth assays, DNA laddering and TUNEL assays. Induction of apoptosis correlated with activation of the JNK/SAPK pathway and increased expression of Bax but not Bad or p53. PANC-1 cells were completely resistant to Fas antibody and TNF-alpha. In contrast, TRAIL decreased the growth of PANC-1 cells by 22%. Low concentrations of actD (10 ng/ml) enhanced the cytotoxic effects of all 3 cytokines. EGF, FGF-2 and IGF-I did not protect PANC-1 cells from actD-mediated apoptosis. ActD (10 ng/ml) also inhibited the growth of CAPAN-1 and T3M4 pancreatic cancer cells but not MiaPaCa-2 cells. Our observations suggest that actD may act via JNK/SAPK and Bax to promote apoptosis in PANC-1 cells and that it may inhibit the growth of other pancreatic cancer cell lines.

Effects of actinomycin D on developing hamster molar tooth germs in vitro

The aim of this study was to evaluate the toxic effects of actinomycin D on the developing hamster tooth germ in organ culture. Hamster tooth germs during early secretory amelogenesis were exposed in vitro for 24 h to 10(-9) M-5 x 10(-5) M actinomycin D. Actinomycin D dose-dependently (> or = 10(-7) M) decreased the tooth germ dry weight but mineralization was affected only by doses > or = 10(-5) M. However, the uptakes of TCA-insoluble 32P and [3H]thymidine were significantly reduced dose-dependently from > or = 10(-8) M actinomycin D, indicating that the drug inhibits the synthesis of phosphate-containing macromolecules as well as DNA synthesis. Histologically, 10(-8) M actinomycin D was the lowest dose which was not toxic to any cell type in the developing tooth germ. At 10(-7) M actinomycin D, the most sensitive cells were the proliferating pre-odontoblasts followed by pre-ameloblasts; the mature secretory ameloblasts and odontoblasts appeared unaffected. Higher doses resulted in increased cytotoxicity to the secretory cells and, eventually, total degeneration of most cells. The data suggest that children treated for cancer during tooth development using anti-chemotherapy cocktails containing actinomycin D (serum levels > 10(-7) M) may develop defects later on in the mature dentition as a direct consequence of the toxicity of the drug to the tooth organ.

Final checkpoint in the drug-promoted and poliovirus-promoted apoptosis is under post-translational control by growth factors

The treatment of HeLa subline (HeLa-B) cells with cycloheximide or Actinomycin D resulted in a rapid (approximately 1.5 h and approximately 2.5 h, respectively) development of morphological and biochemical signs of apoptosis. The addition of fetal bovine serum to the cycloheximide-treated or Actinomycin D-treated cells suppressed the apoptotic reaction, as evidenced by the postponement of the DNA fragmentation for at least 9 and 5 h, respectively. A similar suppressive effect was observed upon the serum addition to cells undergoing abortive infection with poliovirus, which died of apoptosis in the absence of the serum. The serum appeared to exert its anti-apoptotic effect without any appreciable lag and even immediately blocked further progress of ongoing DNA fragmentation. The epidermal growth factor also suppressed, although less efficiently and more transiently, the apoptotic reaction promoted by the metabolic inhibitors. It is concluded that growth factors may affect, without modulating either transcription or translation, the balance of pro-apoptotic and anti-apoptotic activities at a final checkpoint, just preceding the irreversible effector step of apoptosis.

Induction of apoptosis in MDA-231 cells by protein synthesis inhibitors is suppressed by multiple agents

In the present study we investigated the ability of several diverse agents to inhibit MDA-231 cell death induced by two different protein synthesis inhibitors, cycloheximide (CHX) and ricin. Cell death was evaluated by several techniques: trypan blue staining, determination of the released lactic dehydrogenase, transmission electron microscopy, and DNA fragmentation. Results from DNA gel electrophoresis and electron microscopy suggest a mechanism of death by apoptosis which terminates in necrosis. Approximately 60% of cell death was induced either by a continuous exposure to 30 micrograms/ml CHX for 48 hr or by a 1-hr exposure to 250 pg/ml ricin followed by a subsequent incubation of 48 hr in the absence of the drug. Cell survival, in the protein synthesis-inhibited cells, was enhanced by the following diverse agents: the growth factors EGF (20 ng/ml) and IGF-1 (20 ng/ml), the protein kinase C activator 12-0-tetradecanoyl-phorbol-13-acetate (5 ng/ml), the protein kinase A activator 8-bromoadenosine 3':5'-cyclic monophosphate (650 micrograms/ml), the nuclease inhibitor aurintricarboxylic acid (100 micrograms/ml), and fetal bovine serum (5%). The survival agents that stimulated protein synthesis in the control untreated cells had no effect on the CHX-inhibited protein synthesis, which indicates that new protein synthesis is not required for cell survival. The same survival agents attenuated the continuous decrease in protein synthesis in the ricin-exposed cells; therefore, the involvement of new protein synthesis in the survival mechanism could not be excluded. The protein kinase C inhibitor staurosporine blocked, in a dose-dependent manner, the survival effect of 12-0-tetradecanoyl-phorbol-13-acetate and EGF, but not that of aurintricarboxyclic acid or fetal bovine serum, in the protein synthesis-inhibited cells. These results provide evidence for several distinctive pathways, the activation of which inhibits MDA-231 cell death induced by protein synthesis inhibitors. Some of these pathways involved activation of protein kinases, probably protein kinase C.

Epidermal growth factor, phorbol esters, and aurintricarboxylic acid are survival factors for MDA-231 cells exposed to adriamycin

The ability of epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), insulin, 12-O-tetradecanoylphorbol-13-acetate (TPA), and aurintricarboxylic acid (ATA) to protect the human breast cancer cell line MDA-231 from death induced by the anticancer drug adriamycin was investigated. Cell death was induced in the MDA-231 cells either by a short-time exposure to a high dose of adriamycin (2 micrograms.ml-1.1h-1) and further culturing in the absence of the drug, or by continuous exposure to a low dose of adriamycin (0.3 micrograms/ml). Cell death was evaluated after 48 h of incubation by several techniques (trypan blue dye exclusion, lactic dehydrogenase activity, cellular ATP content, transmission electron microscopy, and DNA fragmentation). EGF, TPA, and ATA, each at an optimal concentration of 20 ng/ml, 5 ng/ml, and 100 micrograms/ml respectively, substantially enhanced survival of cells exposed either to a high or low dose of adriamycin. Neither IGF-1 nor insulin, each at concentrations of 20 ng/ml, had an effect on cell survival. The three survival factors enhanced protein synthesis in the untreated cells and attenuated the continuous decrease in protein synthesis in the adriamycin-treated cells. Moreover, the three survival factors protected the MDA-231 cells from death in the absence of protein synthesis (cycloheximide 30 micrograms/ml). These results suggest that EGF, TPA, and ATA promote survival of adriamycin pretreated cells by at least two mechanisms: enhancement of protein synthesis and by a protein synthesis independent process, probably a posttranslational modification effect.