Potentiation of chemotherapy cytotoxicity following iododeoxyuridine incorporation in Chinese hamster cells

A mammalian-like DNA damage response of fission yeast to nucleoside analogs

Nucleoside analogs are frequently used to label newly synthesized DNA. These analogs are toxic in many cells, with the exception of the budding yeast. We show that Schizosaccharomyces pombe behaves similarly to metazoans in response to analogs 5-bromo-2'-deoxyuridine (BrdU) and 5-ethynyl-2'-deoxyuridine (EdU). Incorporation causes DNA damage that activates the damage checkpoint kinase Chk1 and sensitizes cells to UV light and other DNA-damaging drugs. Replication checkpoint mutant cds1Δ shows increased DNA damage response after exposure. Finally, we demonstrate that the response to BrdU is influenced by the ribonucleotide reductase inhibitor, Spd1, suggesting that BrdU causes dNTP pool imbalance in fission yeast, as in metazoans. Consistent with this, we show that excess thymidine induces G1 arrest in wild-type fission yeast expressing thymidine kinase. Thus, fission yeast responds to nucleoside analogs similarly to mammalian cells, which has implications for their use in replication and damage research, as well as for dNTP metabolism.

Bleomycin genotoxicity and amifostine (WR-2721) cell protection in normal leukocytes vs. K562 tumoral cells

Recent advances in chemotherapy have focused on the benefit of high dose regimens, increasing the dose intensity of conventional chemotherapy. However, unacceptable cytotoxicity and genotoxicity on normal cells often impairs the proper management of patients. Phosphoaminothiol WR-1065, the active metabolite of amifostine, appears to protect normal cells and tissues against cytotoxic exposure to radiation or chemotherapeutic agents. Nevertheless, there is disagreement in findings on amifostine protection against bleomycin-induced severe side effects which have suggested that amifostine effectiveness against bleomycin-induced genotoxicity in normal leukocytes and tumour line cells K562 be studied. DNA damage was detected by single cell gel electrophoresis (or Comet) assay, a technique able to detect DNA strand breaks, alkali-labile sites and incomplete excision repair events in individual cells and which appears to be an ideal tool for assessing variability in response of different cell types in vitro. WR-2721 appears to selectively protect healthy leukocytes but not K562 tumoral cells. On the other hand, data on the inter- and intra-individual sensitivity to bleomycin and amifostine suggest that individual metabolic/genetic differences and other factors relating to lifestyle may be responsible for response variability. Application of the Comet assay in appropriate clinical settings to test the sensitivity of patients when undergoing chemotherapy appears possible.

Preoperative idoxuridine and radiation for large soft tissue sarcomas: clinical results with five-year follow-up

BACKGROUND

Local control remains an important issue in the management of large soft tissue sarcomas. Radiation is the main adjuvant to surgery for local therapy of sarcomas, but it requires relatively high doses, hitherto considered prohibitive in areas such as the retroperitoneum. We developed a preoperative treatment approach to large soft tissue sarcomas that would deliver a high total dose of radiation administered in conjunction with the halogenated pyrimidine radiosensitizer idoxuridine (IdUrd).

METHODS

Thirty-seven patients with large sarcomas of the head and neck, mediastinum, retroperitoneum, or extremity received three or five cycles of sequential IdUrd infusion (1000-1600 mg/m2/d x 5 d) alternating weekly with twice daily radiation (125-150 cGy per dose) and were then evaluated for resection. The delivered preoperative radiation dose was up to 6250 to 7500 cGy.

RESULTS

Five patients (14%) had a partial response to preoperative therapy, and 28 of 37 patients underwent successful resection. There were no intra- or postoperative deaths. Local control was achieved in 19 of 28 resected patients, but in only 1 of 6 patients who remained unresectable despite therapy. With a median follow-up of 5.8 years, 28% of patients are alive with no evidence of disease, 17% are alive with disease, and 53% have died of their disease.

CONCLUSIONS

Using the dose and schedule we employed, resection of large soft tissue sarcomas was possible after high-dose radiation delivered in conjunction with IdUrd. Although local control was acceptable, the high rate of distant failure represents a limitation of any local approach to the treatment of large soft tissue sarcomas and suggests the need for integration of this approach with an effective systemic therapy.

Cytostatic synergism between bromodeoxyuridine, bleomycin, cisplatin and chlorambucil demonstrated by a sensitive cell kinetic assay

Bromodeoxyuridine/Hoechst flow cytometry was used to analyse the interference of common cytostatic agents with cell activation and cell cycle progression of human B-cell lines. Bleomycin impaired both cell activation and G2 transit, the latter effect being oxygen dependent. The DNA alkylating agents cyclophosphamide, chlorambucil and mitomycin C caused G2 arrest, whereas cisplatin arrested cells in both the S and G2 phase of the cell cycle. Vinblastin interfered with mitosis, but in addition arrested cells in all phases of the cell cycle. The growth inhibitory action of bleomycin, cisplatin and chlorambucil was dependent upon the bromodeoxyuridine (BrdU) concentration in the culture medium. No interaction was found between BrdU and cyclophosphamide, mitomycin C and vinblastin. The cell cycle kinetic mechanism of the interaction between BrdU and bleomycin, cisplatin and chlorambucil was a potentiation of the G2 arrest. In conclusion, BrdU may be useful in clinical chemotherapy as a chemosensitizer for selected cytostatic agents.