Oncol Res
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The partially modified retro- and retro-inverso peptides of the Arg-Gly Asp (RGD) sequence of fibronectin, in which the direction of the Arg residue is reversed and/or the chirality of the amino acid residue is inverted, i.e., mainly R(rev)-COCH2CO-D and DR(rev)-COCH2CO-D, have been synthesized to examine their antimetastatic effects in murine lung or liver metastasis models, as well as their inhibitory effect on tumor cell invasion in vitro. R(rev)-COCH2CO-D inhibited lung metastasis produced by i.v. coinjection with B16-BL6 melanoma more potently than did other pseudo-peptides or the original RGDS peptide. Rrev-COCH2CO-D also showed antimetastatic effects against several different types of tumor cells such as B16-BL6 melanoma, Colon26 M3.1 carcinoma, and L5178Y-ML25 lymphoma cells, in a dose-dependent manner, and multiple administrations had a therapeutic effect on spontaneous lung metastasis. ⋯ The RGDS peptide decomposed when incubated with fresh plasma in vitro, whereas R(rev)-COCH2CO-D was not affected by this treatment. Thus, the reversion of the Arg-Gly linkage in the RGD sequence resulted in protease resistance leading to the retardation of the clearance of the peptide in vivo, and consequently augmented its antimetastatic and antiinvasive properties. Designed peptide analogues may provide various advantages and be useful for preventing cancer metastasis.
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Mouse leukemia L1210 cells were generated for resistance to 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone (MAIQ), a potent inhibitor of ribonucleotide reductase that is directed in the nonheme iron subunit (NHI) of the enzyme. The resistant cells, MQ-580, showed an 8-fold increase in IC50 toward MAIQ, a 4-fold increase in IC50 toward hydroxyurea, and also showed resistance to other ribonucleotide reductase inhibitors. In addition, the MQ-580 cell line was resistant to nonribonucleotide reductase inhibitors such as etoposide, daunomycin and vinblastine, but not to cisplatin. ⋯ The supernatant fraction from the MQ-580 cells after-SDS-PAGE showed the appearance of a strong Coomassie blue-staining band at 50 kDA that was not apparent in either the wild-type or hydroxyurea-resistant cells. This new resistant cell line offers an opportunity to explore differences in resistance mechanisms of drugs (e.g. MAIQ and hydroxyurea) that are directed at the same subunit of ribonucleotide reductase.
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The effect of hyperthermia and lonidamine, alone and in combination, on the clonogenic activity of a human glioma cell line was investigated. The time-temperature relationship of asynchronous, exponentially growing cells was defined in the range of 40-45 degrees C. All survival curves were exponential and an Arrhenius plot for heat killing was linear over the temperature range tested, with an activation energy of 192 Kcal/mol. ⋯ This "drug-induced heat resistance" was not associated with the induction of heat shock proteins, but rather with modification of cell cycle. On the contrary, showing a purely additive effect, the sequence hyperthermia-->lonidamine allowed achievement of the pre-established cell killing (70%), with exposure times (1-2 hr) and with a temperature (42 degrees C) generally accepted as clinically achievable. Therefore, also considering its low systemic toxicity, lonidamine may be useful in reducing the side effects of hyperthermia.
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2',2'-Difluorodeoxycytidine (Gemcitabine, dFdCyd) is a cytotoxic agent which is active toward a variety of tumor cells. It has been shown that there are multiple intracellular sites of action which include ribonucleotide reductase and DNA polymerase. In these studies, the effects of dFdCyd on wild-type mouse leukemia L1210 cells and variant L1210 cell lines which had alterations at the ribonucleotide reductase site or at the deoxyribonucleoside kinase site were studied. ⋯ Ribonucleotide reductase activity in cell-free extracts prepared from L1210 cells treated with dFdCyd (20 nM) overnight was reduced by 50%. These results show that cell lines which have increased levels of ribonucleotide reductase activity (HU and ED2) or loss of feedback inhibition by dATP (ED2 and Y8) are still sensitive to dFdCyd. The findings indicate that ribonucleotide reductase is not the primary site of inhibition by dFdCyd.(ABSTRACT TRUNCATED AT 250 WORDS)