Molecular aspects of cellular responses to radiotherapy

The effect of radiotherapy on rectal cancer: a histopathological appraisal and prognostic indicators

The management of rectal cancer is a major undertaking. There are currently multiple treatment modalities with variable degrees of complications. Radiotherapy (RT) is one of the more frequently used modalities either on its own or more frequently with chemotherapy mostly before the definitive surgery. The outcome of RT is unpredictable. RT has its serious side effects and there are no guarantees of its usefulness in all patients. This article outlines the effect of RT on the tumor, reviews the various staging systems of responses to RT and present recent evidence of which case is less responsive to such treatments to avoid unnecessary complications.

Radiation enteritis: from diagnosis to management

PURPOSE OF REVIEW

As cancer treatments improve more patients than ever are living for longer with the side effects of these treatments. Radiation enteritis is a heterogenous condition with significant morbidity. The present review aims to provide a broad overview of the condition with particular attention to the diagnosis and management of the condition.

RECENT FINDINGS

Radiation enteritis appears to be more prevalent than originally thought because of patient underreporting and a lack of clinician awareness. Patient-related and treatment-related risk factors have now been identified and should be modified where possible. Medical and surgical factors have been explored, but manipulation of the gut microbiota offers one of the most exciting recent developments in disease prevention. Diagnosis and treatment are best approached in a systematic fashion with particular attention to the exclusion of recurrent malignancy and other gastrointestinal conditions. Surgery and endoscopy both offer opportunities for management of the complications of radiation enteritis. Experimental therapies offer hope for future management of radiation enteritis but large-scale human trials are needed.

SUMMARY

Radiation enteritis is an important clinical problem, but awareness is lacking amongst patients and physicians. Clinical guidelines would allow standardised management which may improve the burden of the disease for patients.

Six fractions weekly as accelerated fraction radiotherapy: Is it applicable for nasopharyngeal cancer? A review

Standard therapy for nasopharyngeal cancer (NPC) is concurrent chemoradiation. Nevertheless, therapeutic outcomes are often unsatisfactory particularly for locally advanced stage. To enhance the therapeutic outcome, we may consider using altered fraction radiotherapy. Altered fraction radiotherapy is divided into two large groups for the therapy of NPC: hyperfraction radiotherapy and accelerated fraction radiotherapy. One of the accelerated fraction regimens suitable for NPC therapy is an accelerated regimen of six radiotherapy fractions weekly. This regimen is considered safe whether using conventional 2D planning technique or advance technique. Response to radiotherapy is better owing to the decrease in overall treatment time (OTT). Furthermore, acute or late side effects for this therapy are not very different to those of standard therapy. The conclusion is that we recommend the use of an accelerated regimen of six radiotherapy fractions weekly for locally advanced stage NPC with contraindication to concurrent chemoradiation, due to the high degree of clinical outcome as well as better tolerated side effect for NPC patients, particularly for those with locally advanced stage NPC.

Flavonoids sensitize tumor cells to radiation: molecular mechanisms and relevance to cancer radiotherapy

Purpose: Radiobiological research continues to focus on finding newer strategies for enhanced killing of tumor cells by ionizing radiation. In recent years, chemotherapeutic drugs have been found to possess the capabilities to sensitize tumor cells without affecting the normal cells. There have been increasing research efforts to identify novel and nontoxic compounds which cause minimal or no harm to normal cells but maximize tumor toxicity response to radiation exposure. Extensive researches on flavonoids that are compounds derived from plants have shown that these have promising abilities as radioprotectors and radiosensitizers.Conclusions: In this review, we examine the role of flavonoids as potential radiosensitizers, review the underlying molecular mechanisms and discuss their potential usefulness in improving cancer radiotherapy. It is emphasized that obtaining a deeper insight into the molecular mechanisms underlying the combined action of flavonoids and ionizing radiation may provide new directions for radiobiological research applicable to the much needed enhanced selective tumor cytotoxicity to treatment agents.

Antagonizing SET Augments the Effects of Radiation Therapy in Hepatocellular Carcinoma through Reactivation of PP2A-Mediated Akt Downregulation

Increasing evidence suggests that SET functions as an oncoprotein and promotes cancer survival and therapeutic resistance. However, whether SET affects radiation therapy (RT)-mediated anticancer effects has not yet been explored. We investigated the impact of SET on RT sensitivity in hepatocellular carcinoma (HCC). Using colony and hepatosphere formation assays, we found that RT-induced proliferative inhibition was critically associated with SET expression. We next tested a novel SET antagonist, N4-(3-ethynylphenyl)-6,7-dimethoxy-N2-(4-phenoxyphenyl) quinazoline-2,4-diamine (EMQA), in combination with RT. We showed that additive use of EMQA significantly enhanced the effects of RT against HCC in vitro and in vivo. Notably, compared with mice receiving either RT or EMQA alone, the growth of PLC5 xenografted tumor in mice receiving RT plus EMQA was significantly reduced without compromising treatment tolerability. Furthermore, we proved that antagonizing SET to restore protein phosphatase 2A-mediated phospho-Akt (p-AKT) downregulation was responsible for the synergism between EMQA and RT. Our data demonstrate a new oncogenic property of SET and provide preclinical evidence that combining a SET antagonist and RT may be effective for treatment of HCC. Further investigation is warranted to validate the clinical relevance of this approach.

Inhibition of FASN expression enhances radiosensitivity in human non-small cell lung cancer

Fatty acid synthase (FASN) is the key enzyme required for the de novo synthesis of long-chain fatty acids. FASN has been observed to be overexpressed in the majority of cancer tissues, and its expression is associated with a poor prognosis, potentially mediated by resistance to drug or radiation. The present study investigated whether the downregulation of FASN in non-small cell lung cancer (NSCLC) may increase radiosensitivity. A lentiviral vector containing short hairpin RNA targeted to FASN (pSIH-H1-Puro-shFASN) was successfully constructed and transfected into A549 cells to knockdown the gene by RNA interference. pSIH-H1-Puro-shFASN was used as the experimental group, while pSIH-H1-Puro-shGFP was used as a control group. The mRNA expression levels of FASN were determined using quantitative polymerase chain reaction. In addition, cell proliferation was measured using cell counting kit-8 assay, and colony formation assay was performed to determine the radiosensitizing effect of FASN knockdown. The cell cycle distribution and apoptotic rates were analyzed using flow cytometry, while western blot analysis was used to assess the expression of DNA-dependent protein kinase catalytic subunit protein, which is associated with DNA double-strand break (DSB) repair. The results of the present study revealed that NSCLC cells are more sensitive to radiation following the knockdown of FASN. Furthermore, the increased radiosensitivity may be associated with increased proliferation, promotion of apoptosis and cell cycle arrest in the G2/M phase. Furthermore, downregulated FASN expression reduced the levels of DNA DSB repair-associated proteins following treatment with radiation. These results indicate that silencing FASN may sensitize NSCLC cells to radiation treatment. Therefore, FASN may be a potential novel therapeutic target to improve the response of NSCLCs to radiation therapy.

Antioxidant Supplementation: A Linchpin in Radiation-Induced Enteritis

Radiation enteritis is one of the most feared complications of abdominal and pelvic regions. Thus, radiation to abdominal or pelvic malignancies unavoidably injures the intestine. Because of rapid cell turnover, the intestine is highly sensitive to radiation injury, which is the limiting factor in the permissible dosage of irradiation. Bowel injuries such as fistulas, strictures, and chronic malabsorption are potentially life-threatening complications and have an impact on patient quality of life. The incidence of radiation enteritis is increasing because of the current trend of combined chemotherapy and radiation. The consequences of radiation damage to the intestine may result in considerable morbidity and even mortality. The observed effects of ionizing radiation are mediated mainly by oxygen-free radicals that are generated by its action on water and are involved in several steps of signal transduction cascade, leading to apoptosis. The oxyradicals also induce DNA strand breaks and protein oxidation. An important line of defense against free radical damage is the presence of antioxidants. Therefore, administration of antioxidants may ameliorate the radiation-induced damage to the intestine.

Pelvic radiation therapy: Between delight and disaster

In the last few decades radiotherapy was established as one of the best and most widely used treatment modalities for certain tumours. Unfortunately that came with a price. As more people with cancer survive longer an ever increasing number of patients are living with the complications of radiotherapy and have become, in certain cases, difficult to manage. Pelvic radiation disease (PRD) can result from ionising radiation-induced damage to surrounding non-cancerous tissues resulting in disruption of normal physiological functions and symptoms such as diarrhoea, tenesmus, incontinence and rectal bleeding. The burden of PRD-related symptoms, which impact on a patient's quality of life, has been under appreciated and sub-optimally managed. This article serves to promote awareness of PRD and the vast potential there is to improve current service provision and research activities.

The need for laparoscopic ovarian transposition in young patients with cervical cancer undergoing radiotherapy

Maintaining the quality of life by preserving ovarian function in premenopausal patients with cervical cancer undergoing radiation is crucial. This can be accomplished with a simple and safe laparoscopic ovarian transposition procedure. This procedure aims to move the ovary out of the irradiation field, protecting it from direct radiation and irreversible damage and preserving its function. However, this procedure is often forgotten and seldom offered to patients. This review aims to lay stress on and reconsider the importance of laparoscopic ovarian transposition as a simple, safe, and extremely useful procedure. The biological effects of radiation are described briefly and several studies are evaluated, which reveal that this procedure has more benefits than risks.

Effects of radiation therapy on tissue and serum concentrations of tumour associated trypsin inhibitor and their prognostic significance in rectal cancer patients

BACKGROUND

We have previously demonstrated that elevated concentrations of tumour-associated trypsin inhibitor (TATI) in both tumour tissue (t-TATI) and in serum (s-TATI) are associated with a poor prognosis in colorectal cancer patients. It was also found that s-TATI concentrations were lower in patients with rectal cancer compared to patients with colon cancer. In this study, we investigated the effects of neoadjuvant radiotherapy (RT) on concentrations of t-TATI and s-TATI in patients with rectal cancer.

METHODS

TATI was analysed in serum, normal mucosa and tumour tissue collected at various time points in 53 rectal cancer patients enrolled in a case-control study where 12 patients received surgery alone, 20 patients 5 × 5 Gy (short-term) preoperative RT and 21 patients 25 × 2 Gy (long-term) preoperative RT. T-TATI was analysed by immunohistochemistry and s-TATI was determined by an immunofluorometric assay. Mann-Whitney U test and Wilcoxon Z (Z) test were used to assess t-TATI and s-TATI concentrations in relation to RT. Spearman's correlation (R) test was used to explore the associations between t-TATI, s-TATI and clinicopathological parameters. Overall survival (OS) according to high and low t-TATI and s-TATI concentrations was estimated by classification and regression tree analysis, Kaplan-Meier analysis and the log rank test.

RESULTS

RT did not affect concentrations of t-TATI or s-TATI. In patients receiving short-term but not long-term RT, s-TATI concentrations were significantly higher 4 weeks post surgery than in serum drawn prior to surgery (Z = -3.366, P < 0.001). T-TATI expression correlated with male gender (R = 0.406, P = 0.008). High t-TATI expression in surgical specimens was associated with a significantly shorter OS (P = 0.045). S-TATI concentrations in serum drawn at all time points were associated with an impaired OS (P = 0.035 before RT, P = 0.001 prior to surgery, P = 0.043 post surgery). At all time points, s-TATI correlated with higher age (P < 0.001-0.021) and with increased s-creatinine concentrations assessed prior to surgery (P = 0.041).

CONCLUSIONS

The results presented here further validate the utility of t-TATI and s-TATI as prognostic biomarkers in patients with rectal cancer, independent of neoadjuvant RT.

Low-dose local kidney irradiation inhibits progression of experimental crescentic nephritis by promoting apoptosis

BACKGROUND

Crescentic glomerulonephritis is a rapidly progressive form of nephritis and is usually resistant to therapeutic intervention. Apoptosis plays a role in the resolution of glomerulonephritis. We investigated the effects of local kidney irradiation on the progression of experimental crescentic glomerulonephritis.

METHODS

The following three experimental rat groups were generated: (1) Group I, sham-operated control (n = 12); (2) Group II, rats injected intravenously with rabbit anti-rat GBM antibody (nephrotoxic serum, NTS) (n = 23), and (3) Group III, a single low-dose irradiation of 0.5 Gy X-ray to both kidneys at days 6, 13, 20, and 27 after NTS injection (n = 55). Renal function and blood leukocyte count were examined in different groups of rats at various time points. Kidneys obtained at various time points were analyzed to determine the effects of radiation in experimental nephritis.

RESULTS

Radiation of the kidneys reduced the levels of blood urea nitrogen and serum creatinine compared with Group II nephritic rats of similar age (p < 0.05 or 0.001). No apparent changes in blood leukocyte counts were noted in various experimental groups. Glomerular hypercellularity, crescents, global sclerosis and tubulointerstitial damage developed gradually in Group II rats, but were decreased (p < 0.05 or 0.001) after radiation treatment. The extent of tubulointerstitial damage was also reduced, and radiation-associated histological improvements were accompanied by reduced infiltration of macrophages in the glomeruli and interstitium. The numbers of PCNA- and ED1-positive cells were reduced in the kidneys at 1 day post-irradiation, of rats irradiated at 6 and 13 days after NTS injection, compared with Group II at similar time intervals (p < 0.05). A larger numbers of TUNEL-positive cells were noted at 1 day post-irradiation in rats irradiated at 6 and 13 days after NTS injection, compared with Group II at similar time intervals (p < 0.05). Immunostaining for macrophages ED1 and TUNEL staining of serial sections of irradiated nephritic kidneys showed few ED1-positive macrophages stained for TUNEL. Overexpression of active caspases 3 and 7 was noted in irradiated kidneys, compared with the corresponding Group II rats at similar time intervals. Western blot analysis showed marked increase in active caspase 3 and active caspase 7 expression in irradiated kidneys compared with NTS injection only. A marked increase in the expression of p53 protein, which is closely related to radiation-induced apoptosis, was also observed in irradiated kidneys compared with NTS injection only.

CONCLUSION

Our study showed that renal radiation can alter acute glomerular inflammation by inducing apoptosis of intrinsic and infiltrating cells in the kidney in a rat model of crescentic glomerulonephritis. Low-dose kidney irradiation can inhibit the progression of experimental nephritis through inducing apoptosis.

Immunohistochemical expression of melan-A and tyrosinase in uveal melanoma

Background

Melan-A and tyrosinase are new immunohistochemical markers that can be used in the diagnosis of melanocytic lesions. The aim of this study was to investigate the correlation between radiotherapy or clinicohistopathological parameters and the expression of melan-A and tyrosinase in uveal melanoma.

Methods

Thirty-six enucleated cases of uveal melanoma were studied. The formalin-fixed, paraffin-embedded specimens were immunostained with monoclonal antibodies against melan-A and tyrosinase. The samples were classified as either positive or negative. The chi-square or the Student-t tests were used to test for the correlation of the expression rates of melan-A and tyrosinase with clinico-pathological parameters.

Results

Melan-A and tyrosinase were positive in 33 (91.7%) and 35 (97.2%) of the specimens, respectively. There was no significant association between the expression of melan-A or tyrosinase and radiotherapy or any clinico-pathological parameter. All specimens were positive for at least one of the immunohistochemical markers.

Conclusion

To the best of our knowledge this is the first study concluding that the expression of melanocytic markers such as melan-A and tyrosinase is not influenced by radiotherapy or any clinico-pathological parameter. Moreover, when tyrosinase and melan-A are used together, 100% of the formalin-fixed, paraffin-embedded uveal melanoma samples tested positive for one of those markers.

A generalised age- and phase-structured model of human tumour cell populations both unperturbed and exposed to a range of cancer therapies

We develop a general mathematical model for a population of cells differentiated by their position within the cell division cycle. A system of partial differential equations governs the kinetics of cell densities in certain phases of the cell division cycle dependent on time t (hours) and an age-like variable tau (hours) describing the time since arrival in a particular phase of the cell division cycle. Transition rate functions control the transfer of cells between phases. We first obtain a theoretical solution on the infinite domain -infinity < t < infinity. We then assume that age distributions at time t=0 are known and write our solution in terms of these age distributions on t=0. In practice, of course, these age distributions are unknown. All is not lost, however, because a cell line before treatment usually lies in a state of asynchronous balanced growth where the proportion of cells in each phase of the cell cycle remain constant. We assume that an unperturbed cell line has four distinct phases and that the rate of transition between phases is constant within a short period of observation ('short' relative to the whole history of the tumour growth) and we show that under certain conditions, this is equivalent to exponential growth or decline. We can then gain expressions for the age distributions. So, in short, our approach is to assume that we have an unperturbed cell line on t </= 0, and then, at t=0 the cell line is exposed to cancer therapy. This corresponds to a change in the transition rate functions and perhaps incorporation of additional phases of the cell cycle. We discuss a number of these cancer therapies and applications of the model.

Preclinical pharmacokinetics and metabolism of a novel prototype DNA-PK inhibitor NU7026

In this study we investigated the in vitro time dependence of radiosensitisation, pharmacokinetics and metabolism of NU7026, a novel inhibitor of the DNA repair enzyme DNA-dependent protein kinase (DNA-PK). At a dose of 10 muM, which is nontoxic to cells per se, a minimum NU7026 exposure of 4 h in combination with 3 Gy radiation is required for a significant radiosensitisation effect in CH1 human ovarian cancer cells. Following intravenous administration to mice at 5 mg kg(-1), NU7026 underwent rapid plasma clearance (0.108 l h(-1)) and this was largely attributed to extensive metabolism. Bioavailability following interperitoneal (i.p.) and p.o. administration at 20 mg kg(-1) was 20 and 15%, respectively. Investigation of NU7026 metabolism profiles in plasma and urine indicated that the compound undergoes multiple hydroxylations. A glucuronide conjugate of a bis-hydroxylated metabolite represented the major excretion product in urine. Identification of the major oxidation site as C-2 of the morpholine ring was confirmed by the fact that the plasma clearance of NU7107 (an analogue of NU7026 methylated at C-2 and C-6 of the morpholine ring) was four-fold slower than that of NU7026. The pharmacokinetic simulations performed predict that NU7026 will have to be administered four times per day at 100 mg kg(-1) i.p. in order to obtain the drug exposure required for radiosensitisation.

Investigation of metabolic changes in irradiated rat brain tissue by means of 1H NMR in vitro relaxation study

The effect of irradiation on concentrations and relaxation behaviour of brain metabolites was studied by means of high-resolution 1H NMR in vitro. The studies were performed on rat brains irradiated with the doses of 20 Gy applied in fractions of 2 Gy. Standard procedures were used to obtain HClO4 extracts of rat brains. The 1H NMR studies of the extracts solutions in D2O were performed using a Varian Inova-300 NMR spectrometer. The integral intensities of the metabolite signals were found to change during the irradiation cycle and after it. These changes are accompanied by the variations in the T1 relaxation times. N-acetylaspartate, glycerophosphocholine, phosphocholine, choline, creatine and phosphocreatine, myoinositol and taurine were analysed as potential markers of irradiation injury.

Altered expression of Rb and p53 in uveal melanomas following plaque radiotherapy

PURPOSE

To examine the expression of proteins in the Rb and p53 tumor suppressor pathways in uveal melanomas following plaque radiotherapy.

METHODS

Immunohistochemistry and cell culture studies. Immunohistochemistry for Rb, p16, cyclin D1, p53, HDM2, and Bcl-2 was performed on twelve eyes containing posterior uveal melanomas that were enucleated following plaque radiotherapy. Cell culture studies were performed in three cases.

RESULTS

The irradiated eyes were enucleated for radiation complications (five cases), local tumor recurrence (three cases), and other reasons (four cases). On histopathologic examination, all cases showed evidence of tumor cell loss. However, residual tumor cells were present in all cases, including those that were clinically regressed. Residual cells from three of the clinically regressed cases were cultured and demonstrated minimal cell division, marked cell death, and extensive chromosomal damage. Strong p53 staining was observed in six cases (50%) and was significantly associated with recent radiotherapy (P = .04). Abnormal cytoplasmic staining for Rb was observed in four cases (33%).

CONCLUSIONS

Plaque radiotherapy of uveal melanomas induces DNA damage, inhibits cell division, and promotes cell death. These changes may be due, at least in part, to induction of p53, which activates genes involved in both cell cycle arrest and apoptosis. Plaque radiotherapy can also cause alterations in the expression of Rb, but the significance of this finding will require further study.

TP53 and p21WAF1/CIP1 behave differently in euploid versus aneuploid bladder tumours treated with radiotherapy

The aim of this study was to examine any relation between DNA ploidy and previously detected TP53 (p53) or p21WAF1/CIP1 expression in 94 patients with muscle-invasive transitional cell carcinoma of the urinary bladder and to associate these factors with survival. DNA ploidy was determined by image cytometry. In a subgroup of patients, the mutational status of the TP53 gene was assessed by temporal temperature gradient electrophoresis (TTGE) or perpendicular denaturant gradient gel electrophoresis (DGGE) and subsequent sequencing. Significantly more aneuploid than euploid tumours showed TP53 accumulation (p = 0.003). Patients with aneuploid tumours lived longer than patients with euploid tumours (p = 0.003). In the euploid, but not in the aneuploid group, TP53 and p21WAF1/CIP1 were associated with cancer-specific survival (p = 0.002 and 0.02, respectively). Patients with > 50% TP53 expression had the longest survival time. Mutation analyses showed acceptable concordance with TP53 expression. We conclude that DNA aneuploidy may confer increased radiosensitivity in bladder cancer patients and that TP53 accumulation may confer increased radiosensitivity, but its effect is detectable only in euploid tumours.

Molecular pathways that modify tumor radiation response

Aberrant expression of signal transduction molecules in pathways controlling cell survival, proliferation, death, or differentiation are a common feature of all tumors. The identification of the molecules that are involved allows the development of novel tumor-specific strategies. Not surprisingly, targeting these pathways often also results in radiosensitization. The efficacy of such directed therapies may, however, be limited by the heterogeneity and the multiple mutations that are associated with the cancerous state. A more robust alternative may be to target global mechanisms of cellular control. The ubiquitin/proteasome degradation pathway is one candidate for such therapeutic intervention. This pathway is the main posttranscriptional mechanism that controls levels of many short-lived proteins involved in regulation of cell cycle progression, DNA transcription, DNA repair, and apoptosis. Many of these proteins are involved in various malignancies and/or radiation responses. In recent years, proteasome inhibitors have gained interest as a promising new group of antitumor drugs. PS-341, a reversible inhibitor of proteasome chymotryptic activity, is currently being tested in phase I clinical trials. In this study, we show that proteasome inhibition by PS-341 can alter cellular radiosensitivity in vitro and in vivo, in addition to having direct antitumor effects.

Treatment-related leukaemia--a clinical and scientific challenge

The development of a second tumour, including treatment-related leukaemia (TRL), is the most devastating complication of intensive cancer chemotherapy. This is especially relevant in the paediatric population as over 70% of children diagnosed with a malignancy will now live at least 5 years. Most TRLs are myeloid leukaemias and carry an overall poor prognosis when compared with their de novo counterparts. Despite the well known association with specific cytotoxic agents, improved understanding of the pathogenesis and risk factors of TRL is ultimately essential if we are to develop successful strategies for prevention and treatment. Here we review these aspects, together with the clinical and diverse biological features of this complication and the efficacy of current therapy.

Changes in oxygen tension during radiotherapy of head and neck tumours

Increased knowledge about changes that occur in tumour oxygenation during radiotherapy and the biological factors causing these changes can be useful in the development of optimal radiation treatments. The aims of this study were a) to study changes in the oxygen tension (pO2) of human head and neck tumours during radiotherapy in relationship to changes in cell density and vascular density, and b) to investigate whether the pO2, measured before or during therapy, can be used to predict the therapeutic outcome. Preliminary data from the first 11 patients included in the study are reported. The pO2 was measured before treatment (11 patients) and once a week during therapy (8 patients), using polarographic needle electrodes. Cell density and vascular density were determined from biopsies taken after each pO2 measurement in 5 patients. Significant fluctuations in pO2 occurred during therapy. Changes in hypoxic fraction; i.e., fraction of pO2 readings below 2.5 mm Hg, 5 mm Hg or 10 mm Hg, coincided with changes in cell density, but not with changes in vascular density, which suggests that the changes in hypoxic fraction were caused by changes in oxygen consumption rather than supply. Response evaluation after a median follow-up time of 19 months showed that progressive disease occurred among the patients with highly hypoxic tumour, regardless of whether hypoxic fraction before treatment or after two weeks of radiotherapy was considered.

Influence of p53 and bcl-2 on proliferative activity and treatment outcome in head and neck cancer patients

Knowledge about the influence of biomarkers on cell proliferative activity might explain differences in radiosensitivity between head and neck tumors and might improve patient selection for the most optimal treatment strategy. p53 and bcl-2 protein expression were determined immunohistochemically in 56 head and neck cancer patients, treated by surgery only in five cases and by radiotherapy, with or without surgery, in 51 cases. Relationships with various cell proliferation markers, determined by flow-cytometry (G1-phase fraction, S-phase fraction, BrdUrd-labeling index, duration of S-phase and potential doubling time) were investigated. Associations between these cell proliferation parameters, on the one hand, and both p53 and bcl-2, on the other, were not found. Furthermore, p53 and bcl-2 expression were both not related to clinicopathological parameters (T- and N-stage, site, grade) and did not affect loco-regional recurrence-free survival and/or disease-free survival. We could not find a prognostic value for both p53 and bcl-2 protein expression to differentiate radiosensitive from radioresistant head and neck tumors.

Expression levels of the DNA repair enzyme HAP1 do not correlate with the radiosensitivities of human or HAP1-transfected rat cell lines

Apurinic/apyrimidinic (AP) sites in DNA are potentially lethal and mutagenic. They can arise spontaneously or following DNA damage from reactive oxygen species or alkylating agents, and they constitute a significant product of DNA damage following cellular exposure to ionizing radiation. The major AP endonuclease responsible for initiating the repair of these and other DNA lesions in human cells is HAP1, which also possesses a redox function. We have determined the cellular levels of this enzyme in 11 human tumour and fibroblast cell lines in relation to clonogenic survival following ionizing radiation. Cellular HAP1 levels and surviving fraction at 2 Gy (SF2) varied five- and tenfold respectively. However, no correlation was found between these two parameters following exposure to gamma-irradiation at low (1.1 cGy per min) or high (108 cGy per min) dose rates. To examine this further, wild-type and mutant versions of HAP1 were overexpressed, using an inducible HAP1 cDNA expression vector system, in the rat C6 glioma cell line which has low endogenous AP endonuclease activity. Induction of wild-type HAP1 expression caused a > fivefold increase in the capacity of cellular extracts to cleave an oligonucleotide substrate containing a single abasic site, but increased expression did not confer increased resistance to gamma-irradiation at high- or low-dose rates, or to the methylating agent methyl methanesulphonate (MMS). Expression in C6 cell lines of mutant forms of HAP1 deleted for either the redox activator or DNA repair functions displayed no apparent titrational or dominant negative effects. These studies suggest that the levels of endogenous AP endonuclease activities in the various cell lines examined are not limiting for efficient repair in cells following exposure to ionizing radiation or MMS. This contrasts with the correlation we have found between HAP1 levels and radiosensitivity in cervix carcinomas (Herring et al (1998) Br J Cancer 78: 1128-1133), indicating that HAP1 levels in this case assume a critical survival role and hence that established cell lines might not be a suitable model for such studies.

Role of short TE 1H-MR spectroscopy in monitoring of post-operation irradiated patients

Post-surgical radiation therapy is a routine procedure in the treatment of primary malignant brain tumors. Along with modest therapeutic effects conventional fractionated radiotherapy, in spite of any modifications, produces damage to non-malignant brain tissues lying within the treatment volume, the extent of which depends on radiation dose. Serial 1H-MRS allows non-invasive investigation of tissue metabolic profiles. In the present study the ratios of resonance signals assigned to the major 1H-MRS-visible metabolites (N-acetylaspartate, choline, creatine, inositol, lactate and lipid methylene group) were evaluated before, during and after post-surgical fractionated radiotherapy in brain regions close to and more distant from the tumor bed, receiving different radiation exposures (60 and < 40 Gy, respectively). The study group consisted of ten patients (aged 28-51). A MRI/MRS system (Elscint 2T Prestige) operating at the field strength of 2 T and the proton resonance frequency of 81.3 MHz has been used and the 1H-MR spectra were acquired using single voxel double-spin-echo PRESS sequence with a short TE. The spectra were post-processed with automatic fitting in the frequency domain. It was found that although the metabolite profiles depend on the dose obtained, but other stress factors (like surgery) seem to contribute to the overall picture of the metabolic status of the brain as well. In studies of early irradiation injuries, an increase of choline related ratios may serve rather as cell proliferation indictors than as cell injury ones, whereas the mI/Cr ratio appears as one of the first indicators of local irradiation injury. In order to establish the prognostic marker for early radiation damage, however, it seems necessary to analyze all visible metabolites as well. None of the metabolites separately may serve as such an indicator due to the complexity of tissue metabolism. Interestingly, MRI reveals no changes during the therapy process, whereas the metabolite ratios are being affected in the course of time, thus supporting the presumption that the 1H-MRS is a valuable method of radiation therapy monitoring.

The involvement of p53 in dopamine-induced apoptosis of cerebellar granule neurons and leukemic cells overexpressing p53

1. The pathogenesis of the selective degeneration of the dopaminergic neurons in Parkinson's disease is still enigmatic. Recently we have shown that dopamine can induce apoptosis in postmitotic neuronal cells, as well as in other cellular systems, thus suggesting a role for this endogenous neurotransmitter and associated oxidative stress in the neuronal death process. 2. Dopamine has been shown to be capable of inducing DNA damage through its oxidative metabolites. p53 is a transcription factor that has a major role in determining cell fate in response to DNA damage. We therefore examined the possible correlation between dopamine-triggered apoptosis, DNA damage and levels of total phosphorylated p53 protein in cultured mouse cerebellar granule neurons. 3. Marked DNA damage and apoptotic nuclear condensation and fragmentation were detected within several hours of exposure to dopamine. An associated marked threefold increase in p53 phosphorylation was observed within this time window. Using a temperature-sensitive p53 activation system in leukemia LTR6 cells, were found that p53 inactivation dramatically attenuated dopamine toxicity. 4. We therefore conclude that DNA damage and p53 activation may have a role in mediating dopamine-induced apoptosis. Modulation of the p53 system may therefore have a protective role against the toxicity of this endogenous neurotransmitter and associated oxidative stress.

The role of the stress-activated protein kinase (SAPK/JNK) signaling pathway in radiation-induced apoptosis

Ionizing radiation, like a variety of other cellular stress factors, initiates apoptosis, or programmed cell death, in many cell systems. This mode of radiation-induced cell kill should be distinguished from clonogenic cell death due to unrepaired DNA damage. Ionizing radiation not only exerts its effect on the nuclear DNA, but also at the plasma membrane level where it may activate multiple signal transduction pathways. One of these pathways is the stress-activated protein kinase (SAPK) cascade which transduces death signals from the cell membrane to the nucleus. This review discusses recent evidence on the critical role of this signaling system in radiation- and stress-induced apoptosis. An improved understanding of the mechanisms involved in radiation-induced apoptosis may ultimately provide novel strategies of intervention in specific signal transduction pathways to favorably alter the therapeutic ratio in the treatment of human malignancies.

Radiosensitivity and oxidative signalling in ataxia telangiectasia: an update

Radiosensitivity is a major hallmark of the human genetic disorder ataxia telangiectasia. This hypersensitivity to ionizing radiation has been demonstrated in vivo after exposure of patients to therapeutic doses of radiation and in cells in culture. Clearly an understanding of the nature of the molecular defect in ataxia telangiectasia will be of considerable assistance in delineating additional pathways that determine cellular radiosensitivity/radioresistance. Furthermore, since patients with this syndrome are also predisposed to developing a number of leukaemias and lymphomas, the possible connection between radiosensitivity and cancer predisposition is of interest. Now that the gene (ATM) responsible for this genetic disease has been cloned and identified, progress is being made in determining the role of the ATM protein in mediating the effects of cellular exposure to ionizing radiation and other forms of redox stress. Proteins such as the product of the tumour suppressor gene p53 and the proto-oncogene c-Abl (a protein tyrosine kinase) have been shown to interact with ATM. Since several intermediate steps in both the p53 and c-Abl pathways, activated by ionizing radiation, are known it will be possible to map the position of ATM in these pathways and describe its mechanism of action. What are the clinical implications of understanding the molecular basis of the defect in ataxia telangiectasia (A-T)? As outlined above, since radiosensitivity is a universal characteristic of A-T, understanding the mechanism of action of ATM will provide additional information on radiation signalling in human cells. With this information it may be possible to sensitize tumour cells to radiation and thus increase the therapeutic benefit of radiotherapy. This might involve the use of small molecules that would interfere with the normal ATM-controlled pathways and thus sensitize cells to radiation or alternatively it might involve the efficient introduction of ATM anti-sense cDNA constructs into tumours to achieve the same end-point.

The clinical radiobiology of brachytherapy

The unique geometrical features of brachytherapy, together with the wide variety of temporal patterns of dose delivery, result in important interactions between physics and radiobiology. These interactions exert a major influence on the way in which brachytherapy treatments should be evaluated, both in absolute and comparative terms. This article reviews the main physical and radiobiological aspects of brachytherapy and considers examples of their influence on specific types of treatment. The issues relating to the optimization of high dose rate brachytherapy are presented, together with the implications of multiphasic repair kinetics for low dose-rate and pulsed high dose rate brachytherapy. The opportunities for application of radiobiological principles to improve various brachytherapy techniques, together with the integration of brachytherapy with teletherapy, are also outlined. Equations for the numerical evaluation of brachytherapy treatments are presented in the Appendices.

Of what use is molecular biology to the practicing radiation oncologist?

BACKGROUND AND PURPOSE

We are in a period of rapid advance in understanding the basic mechanisms behind the induction and progression of cancer. The relevance of this new knowledge to the daily clinical practice of radiation oncology may not necessarily be readily apparent. Familiarity with a few of the concepts of molecular biology and biochemistry are necessary to fully appreciate the clinical relevance of the new biology.

METHODS AND RESULTS

To illustrate how the new knowledge affects the practice of radiation oncology, examples of the use of molecular biology are presented for different clinical aspects of clinical oncology, i.e. screening and prevention, prognostic factors, predictive factors, treatment decision, novel therapy and follow-up. A number of the molecular biology techniques are illustrated.

CONCLUSIONS

The advances from molecular biology directly impact the role of radiation oncologists in the clinic. While major new therapies are still in development in the laboratory, these will likely have a very significant role in patient care and cancer prevention in the not-too-distant future. Given the central role of radiation oncologists in cancer management, a basic knowledge of molecular biology techniques and their application is essential so that we can be current with our colleagues and patients and as a specialty, participate actively in improving the outcome of patients with or at risk of developing cancer.