Adrian C. Begg

Cell kinetic measurements in prostate cancer.

PURPOSEnTwo approaches have been suggested for escalating the total dose in radiotherapy treatment of prostate cancer. One is conformal radiotherapy; the other is hyperfractionation using many small fractions. Both imply some possible prolongation in overall treatment time. To judge whether prolonged treatment schedules would be detrimental, it is necessary to know the proliferation rates in human prostate tumors, specifically, the potential doubling time (Tpot). There is a lack of data on this parameter in the literature.nnnMETHODS AND MATERIALSnSeven patients with adenocarcinoma of the prostate were studied. A tracer dose of 100 mg/m2 of IUdR was infused intravenously 4-12 h before biopies were taken. Biopsies were fixed in 70% ethanol, stored at 4 degrees C, and later prepared and stained by standard methods for flow cytometry, using the red fluorescence signal for DNA and the green fluorescence signal (fluorescein isothiocyanate) for 5-iodo-2-deoxyuridine. The duration of DNA synthesis (Ts) was determined by the relative movement (RM) method, knowing the interval between tracer administration and biopsy. Tpot was calculated as the quotient of Ts by labeling index (LI).nnnRESULTSnIn two of the seven tumors the LI was too low (<0.6%) for a reliable estimate of RM to be made, so no determination of Tpot was possible for these tumors. The mean LI values in the other five tumors were 2.4%, 1.4%, 1.0%, 3.0%, and 0.9%. The durations of Ts were 13.2, 9.5, 10.0, 11.7, and 12.7 h, respectively. The resulting values of Tpot were 23, 28, 42, 16, and 61 days, respectively.nnnCONCLUSIONnThe low labeling indices in prostate tumors, also reported by others, made estimation of Ts by RM impossible in about a third of these tumors. However, five tumors yielded long estimates for Tpot, implying that prolongation from 6 to about 8 weeks should not be detrimental.

Editorial radiotherapy and oncology 2002: predictive assays for normal tissue damage.

In this issue of radiotherapy and oncology, two groups present their work on developing a predictive assay for the degree of radiation-induced normal tissue damage. Both groups have utilised in vitro tests using patients’ lymphocytes. The rational behind these studies is based on the fact that for curative radiotherapy, the tolerance of patients with the most severe normal tissue reactions determines the dose level for the patient group as a whole for a given tumour site and type. The ultimate aim is to develop a sufficiently robust predictive assay to enable individual dose adjustment, and thus improve the therapeutic ratio for the patient population as a whole [1,6,34–36,51]. Such studies can indeed provide information on the role of cell kill and/or DNA damage in determining morbidity, but are time consuming and unlikely to be used routinely in the clinic. The questions therefore arise as to the value of these studies for the future, and what the best way forward is.

Ionizing Radiation Sensitivity of DNA Polymerase Lambda-Deficient Cells

Abstract Vermeulen, C., Bertocci, B., Begg, A. C. and Vens, C. Ionizing Radiation Sensitivity of DNA Polymerase Lambda-Deficient Cells. Radiat. Res. 168, 683–688 (2007). Ionizing radiation induces a diverse spectrum of DNA lesions, including strand breaks and oxidized bases. In mammalian cells, ionizing radiation-induced lesions are targets of non-homologous end joining, homologous recombination, and base excision repair. In vitro assays show a potential involvement of DNA polymerase lambda in non-homologous end joining and base excision repair. In this study, we investigated whether DNA polymerase lambda played a significant role in determining ionizing radiation sensitivity. Despite increased sensitivity to hydrogen peroxide, lambda-deficient mouse embryonic fibroblasts displayed equal survival after exposure to ionizing radiation compared to their wild-type counterparts. In addition, we found increased sensitivity to the topoisomerase inhibitors camptothecin and etoposide in the absence of polymerase lambda. These results do not reveal a major role for DNA polymerase lambda in determining radiosensitivity in vivo.

Involvement of DNA Polymerase Beta in Repair of Ionizing Radiation Damage as Measured by In Vitro Plasmid Assays

Abstract Vens, C., Hofland, I. and Begg, A. C. Involvement of DNA Polymerase Beta in Repair of Ionizing Radiation Damage as Measured by In Vitro Plasmid Assays. Radiat. Res. 168, 281– 291 (2007). Characteristic of damage introduced in DNA by ionizing radiation is the induction of a wide range of lesions. Single-strand breaks (SSBs) and base damages outnumber double-strand breaks (DSBs). If unrepaired, these lesions can lead to DSBs and increased mutagenesis. XRCC1 and DNA polymerase beta (polβ) are thought to be critical elements in the repair of these SSBs and base damages. XRCC1-deficient cells display a radiosensitive phenotype, while proliferating polβ-deficient cells are not more radiosensitive. We have recently shown that cells deficient in polβ display increased radiosensitivity when confluent. In addition, cells expressing a dominant negative to polβ have been found to be radiosensitized. Here we show that repair of radiation-induced lesions is inhibited in extracts with altered polβ or XRCC1 status, as measured by an in vitro repair assay employing irradiated plasmid DNA. Extracts from XRCC1-deficient cells showed a dramatically reduced capacity to repair ionizing radiation-induced DNA damage. Extracts deficient in polβ or containing a dominant negative to polβ also showed reduced repair of radiation-induced SSBs. Irradiated repaired plasmid DNA showed increased incorporation of radioactive nucleotides, indicating use of an alternative long-patch repair pathway. These data show a deficiency in repair of ionizing radiation damage in extracts from cells deficient or altered in polβ activity, implying that increased radiosensitivity resulted from radiation damage repair deficiencies.

Effect of simultaneous administration of bleomycin on the acute skin reactions of mice after single and fractionated doses of radiation.

The effect of bleomycin on the acute mouse foot skin reactions, occurring after irradiation, was investigated. Bleomycin was delivered simultaneously with the irradiation treatment, either by intraperitoneal injection or by subcutaneous continuous infusion. Experiments were carried out to investigate (a) the modification by bleomycin of the response to single doses of radiation (b) the effect of total drug dose on this modification (c) the influence of the drug on repair of sublethal radiation damage and (d) the interference by the drug with compensatory repopulation after irradiation. In none of the experiments could any influence of the drug on these radiation induced reactions and recovery processes be demonstrated. These results are in direct contrast to what we have observed previously for similar types of experiments in another epithelial system, the mouse lip mucosa.