Study of the X-ray radiation interaction with a multislit collimator for the creation of microbeams in radiation therapy

Microbeam radiation therapy (MRT) is a developing radiotherapy, based on the use of beams only a few tens of micrometres wide, generated by synchrotron X-ray sources. The spatial fractionation of the homogeneous beam into an array of microbeams is possible using a multislit collimator (MSC), i.e. a machined metal block with regular apertures. Dosimetry in MRT is challenging and previous works still show differences between calculated and experimental dose profiles of 10-30%, which are not acceptable for a clinical implementation of treatment. The interaction of the X-rays with the MSC may contribute to the observed discrepancies; the present study therefore investigates the dose contribution due to radiation interaction with the MSC inner walls and radiation leakage of the MSC. Dose distributions inside a water-equivalent phantom were evaluated for different field sizes and three typical spectra used for MRT studies at the European Synchrotron Biomedical beamline ID17. Film dosimetry was utilized to determine the contribution of radiation interaction with the MSC inner walls; Monte Carlo simulations were implemented to calculate the radiation leakage contribution. Both factors turned out to be relevant for the dose deposition, especially for small fields. Photons interacting with the MSC walls may bring up to 16% more dose in the valley regions, between the microbeams. Depending on the chosen spectrum, the radiation leakage close to the phantom surface can contribute up to 50% of the valley dose for a 5 mm × 5 mm field. The current study underlines that a detailed characterization of the MSC must be performed systematically and accurate MRT dosimetry protocols must include the contribution of radiation leakage and radiation interaction with the MSC in order to avoid significant errors in the dose evaluation at the micrometric scale.

A commercial treatment planning system with a hybrid dose calculation algorithm for synchrotron radiotherapy trials

Synchrotron Radiotherapy (SyncRT) is a preclinical radiation treatment which delivers synchrotron x-rays to cancer targets. SyncRT allows for novel treatments such as Microbeam Radiotherapy, which has been shown to have exceptional healthy tissue sparing capabilities while maintaining good tumour control. Veterinary trials in SyncRT are anticipated to take place in the near future at the Australian Synchrotron's Imaging and Medical Beamline (IMBL). However, before veterinary trials can commence, a computerised treatment planning system (TPS) is required, which can quickly and accurately calculate the synchrotron x-ray dose through patient CT images. Furthermore, SyncRT TPS's must be familiar and intuitive to radiotherapy planners in order to alleviate necessary training and reduce user error. We have paired an accurate and fast Monte Carlo (MC) based SyncRT dose calculation algorithm with Eclipse^TM, the most widely implemented commercial TPS in the clinic. Using Eclipse^TM, we have performed preliminary SyncRT trials on dog cadavers at the IMBL, and verified calculated doses against dosimetric measurement to within 5% for heterogeneous tissue-equivalent phantoms. We have also performed a validation of the TPS against a full MC simulation for constructed heterogeneous phantoms in Eclipse^TM, and showed good agreement for a range of water-like tissues to within 5%-8%. Our custom Eclipse^TM TPS for SyncRT is ready to perform live veterinary trials at the IMBL.

Technical advances in x-ray microbeam radiation therapy

In the last 25 years microbeam radiation therapy (MRT) has emerged as a promising alternative to conventional radiation therapy at large, third generation synchrotrons. In MRT, a multi-slit collimator modulates a kilovoltage x-ray beam on a micrometer scale, creating peak dose areas with unconventionally high doses of several hundred Grays separated by low dose valley regions, where the dose remains well below the tissue tolerance level. Pre-clinical evidence demonstrates that such beam geometries lead to substantially reduced damage to normal tissue at equal tumour control rates and hence drastically increase the therapeutic window. Although the mechanisms behind MRT are still to be elucidated, previous studies indicate that immune response, tumour microenvironment, and the microvasculature may play a crucial role. Beyond tumour therapy, MRT has also been suggested as a microsurgical tool in neurological disorders and as a primer for drug delivery. The physical properties of MRT demand innovative medical physics and engineering solutions for safe treatment delivery. This article reviews technical developments in MRT and discusses existing solutions for dosimetric validation, reliable treatment planning and safety. Instrumentation at synchrotron facilities, including beam production, collimators and patient positioning systems, is also discussed. Specific solutions reviewed in this article include: dosimetry techniques that can cope with high spatial resolution, low photon energies and extremely high dose rates of up to 15 000 Gy s-1, dose calculation algorithms-apart from pure Monte Carlo Simulations-to overcome the challenge of small voxel sizes and a wide dynamic dose-range, and the use of dose-enhancing nanoparticles to combat the limited penetrability of a kilovoltage energy spectrum. Finally, concepts for alternative compact microbeam sources are presented, such as inverse Compton scattering set-ups and carbon nanotube x-ray tubes, that may facilitate the transfer of MRT into a hospital-based clinical environment. Intensive research in recent years has resulted in practical solutions to most of the technical challenges in MRT. Treatment planning, dosimetry and patient safety systems at synchrotrons have matured to a point that first veterinary and clinical studies in MRT are within reach. Should these studies confirm the promising results of pre-clinical studies, the authors are confident that MRT will become an effective new radiotherapy option for certain patients.

High resolution radiochromic film dosimetry: Comparison of a microdensitometer and an optical microscope

PURPOSE

Microbeam radiation therapy is a developing technique that promises superior tumour control and better normal tissue tolerance using spatially fractionated X-ray beams only tens of micrometres wide. Radiochromic film dosimetry at micrometric scale was performed using a microdensitometer, but this instrument presents limitations in accuracy and precision, therefore the use of a microscope is suggested as alternative. The detailed procedures developed to use the two devices are reported allowing a comparison.

METHODS

Films were irradiated with single microbeams and with arrays of 50 µm wide microbeams spaced by a 400 µm pitch, using a polychromatic beam with mean energy of 100 keV. The film dose measurements were performed using two independent instruments: a microdensitometer (MDM) and an optical microscope (OM).

RESULTS

The mean values of the absolute dose measured with the two instruments differ by less than 5% but the OM provides reproducibility with a standard deviation of 1.2% compared to up to 7% for the MDM. The resolution of the OM was determined to be ~ 1 to 2 µm in both planar directions able to resolve pencil beams irradiation, while the MDM reaches at the best 20 µm resolution along scanning direction. The uncertainties related to the data acquisition are 2.5-3% for the OM and 9-15% for the MDM.

CONCLUSION

The comparison between the two devices validates that the OM provides equivalent results to the MDM with better precision, reproducibility and resolution. In addition, the possibility to study dose distributions in two-dimensions over wider areas definitely sanctions the OM as substitute of the MDM.

Synchrotron Microbeam Radiation Therapy as a New Approach for the Treatment of Radioresistant Melanoma: Potential Underlying Mechanisms

PURPOSE

Synchrotron microbeam radiation therapy (MRT) is a method that spatially distributes the x-ray beam into several microbeams of very high dose (peak dose), regularly separated by low-dose intervals (valley dose). MRT selectively spares normal tissues, relative to conventional (uniform broad beam [BB]) radiation therapy.

METHODS AND MATERIALS

To evaluate the effect of MRT on radioresistant melanoma, B16-F10 murine melanomas were implanted into mice ears. Tumors were either treated with MRT (407.6 Gy peak; 6.2 Gy valley dose) or uniform BB irradiation (6.2 Gy).

RESULTS

MRT induced significantly longer tumor regrowth delay than did BB irradiation. A significant 24% reduction in blood vessel perfusion was observed 5 days after MRT, and the cell proliferation index was significantly lower in melanomas treated by MRT compared with BB. MRT provoked a greater induction of senescence in melanoma cells. Bio-Plex analyses revealed enhanced concentration of monocyte-attracting chemokines in the MRT group: MCP-1 at D5, MIP-1α, MIP-1β, IL12p40, and RANTES at D9. This was associated with leukocytic infiltration at D9 after MRT, attributed mainly to CD8 T cells, natural killer cells, and macrophages.

CONCLUSIONS

In light of its potential to disrupt blood vessels that promote infiltration of the tumor by immune cells and its induction of senescence, MRT could be a new therapeutic approach for radioresistant melanoma.

Introducing the concept of spiral microbeam radiation therapy (spiralMRT)

MOTIVATION

With interlaced microbeam radiation therapy (MRT) a first kilovoltage radiotherapy (RT) concept combining spatially fractionated entrance beams and homogeneous dose distribution at the target exists. However, this technique suffers from its high sensitivity to positioning errors of the target relative to the radiation source. With spiral microbeam radiation therapy (spiralMRT), this publication introduces a new irradiation geometry, offering similar spatial fractionation properties as interlaced MRT, while being less vulnerable to target positioning uncertainties.

METHODS

The dose distributions achievable with spiralMRT in a simplified human head geometry were calculated with Monte Carlo simulations based on Geant4 and the dependence of the result on the microbeam pitch, total field size, and photon energy were analysed. A comparison with interlaced MRT and conventional megavoltage tomotherapy was carried out.

RESULTS

SpiralMRT can deliver homogeneous dose distributions, while using spatially fractionated entrance beams. The valley dose of spiralMRT entrance beams is by up to 40% lower than the corresponding tomotherapy dose, thus indicating a better normal tissue sparing. The optimum photon energy is found to be around [Formula: see text].

CONCLUSIONS

SpiralMRT is a promising approach to delivering homogeneous dose distributions with spatially fractionated entrance beams, possibly decreasing normal tissue side effects in hypofractionated RT.

Effects of Synchrotron X-Ray Micro-beam Irradiation on Normal Mouse Ear Pinnae

PURPOSE

To analyze the effects of micro-beam irradiation (MBI) on the normal tissues of the mouse ear.

METHODS AND MATERIALS

Normal mouse ears are a unique model, which in addition to skin contain striated muscles, cartilage, blood and lymphatic vessels, and few hair follicles. This renders the mouse ear an excellent model for complex tissue studies. The ears of C57BL6 mice were exposed to MBI (50-μm-wide micro-beams, spaced 200 μm between centers) with peak entrance doses of 200, 400, or 800 Gy (at ultra-high dose rates). Tissue samples were examined histopathologically, with conventional light and electron microscopy, at 2, 7, 15, 30, and 240 days after irradiation (dpi). Sham-irradiated animals acted as controls.

RESULTS

Only an entrance dose of 800 Gy caused a significant increase in the thickness of both epidermal and dermal ear compartments seen from 15 to 30 dpi; the number of sebaceous glands was significantly reduced by 30 dpi. The numbers of apoptotic bodies and infiltrating leukocytes peaked between 15 and 30 dpi. Lymphatic vessels were prominently enlarged at 15 up to 240 dpi. Sarcomere lesions in striated muscle were observed after all doses, starting from 2 dpi; scar tissue within individual beam paths remained visible up to 240 dpi. Cartilage and blood vessel changes remained histologically inconspicuous.

CONCLUSIONS

Normal tissues such as skin, cartilage, and blood and lymphatic vessels are highly tolerant to MBI after entrance doses up to 400 Gy. The striated muscles appeared to be the most sensitive to MBI. Those findings should be taken into consideration in future micro-beam radiation therapy treatment schedules.

Hybrid dose calculation: a dose calculation algorithm for microbeam radiation therapy

Microbeam radiation therapy (MRT) is still a preclinical approach in radiation oncology that uses planar micrometre wide beamlets with extremely high peak doses, separated by a few hundred micrometre wide low dose regions. Abundant preclinical evidence demonstrates that MRT spares normal tissue more effectively than conventional radiation therapy, at equivalent tumour control. In order to launch first clinical trials, accurate and efficient dose calculation methods are an inevitable prerequisite. In this work a hybrid dose calculation approach is presented that is based on a combination of Monte Carlo and kernel based dose calculation. In various examples the performance of the algorithm is compared to purely Monte Carlo and purely kernel based dose calculations. The accuracy of the developed algorithm is comparable to conventional pure Monte Carlo calculations. In particular for inhomogeneous materials the hybrid dose calculation algorithm out-performs purely convolution based dose calculation approaches. It is demonstrated that the hybrid algorithm can efficiently calculate even complicated pencil beam and cross firing beam geometries. The required calculation times are substantially lower than for pure Monte Carlo calculations.

X-Tream quality assurance in synchrotron X-ray microbeam radiation therapy

Microbeam radiation therapy (MRT) is a novel irradiation technique for brain tumours treatment currently under development at the European Synchrotron Radiation Facility in Grenoble, France. The technique is based on the spatial fractionation of a highly brilliant synchrotron X-ray beam into an array of microbeams using a multi-slit collimator (MSC). After promising pre-clinical results, veterinary trials have recently commenced requiring the need for dedicated quality assurance (QA) procedures. The quality of MRT treatment demands reproducible and precise spatial fractionation of the incoming synchrotron beam. The intensity profile of the microbeams must also be quickly and quantitatively characterized prior to each treatment for comparison with that used for input to the dose-planning calculations. The Centre for Medical Radiation Physics (University of Wollongong, Australia) has developed an X-ray treatment monitoring system (X-Tream) which incorporates a high-spatial-resolution silicon strip detector (SSD) specifically designed for MRT. In-air measurements of the horizontal profile of the intrinsic microbeam X-ray field in order to determine the relative intensity of each microbeam are presented, and the alignment of the MSC is also assessed. The results show that the SSD is able to resolve individual microbeams which therefore provides invaluable QA of the horizontal field size and microbeam number and shape. They also demonstrate that the SSD used in the X-Tream system is very sensitive to any small misalignment of the MSC. In order to allow as rapid QA as possible, a fast alignment procedure of the SSD based on X-ray imaging with a low-intensity low-energy beam has been developed and is presented in this publication.

Conformal image-guided microbeam radiation therapy at the ESRF biomedical beamline ID17

PURPOSE

Upcoming veterinary trials in microbeam radiation therapy (MRT) demand for more advanced irradiation techniques than in preclinical research with small animals. The treatment of deep-seated tumors in cats and dogs with MRT requires sophisticated irradiation geometries from multiple ports, which impose further efforts to spare the normal tissue surrounding the target.

METHODS

This work presents the development and benchmarking of a precise patient alignment protocol for MRT at the biomedical beamline ID17 of the European Synchrotron Radiation Facility (ESRF). The positioning of the patient prior to irradiation is verified by taking x-ray projection images from different angles.

RESULTS

Using four external fiducial markers of 1.7  mm diameter and computed tomography-based treatment planning, a target alignment error of less than 2  mm can be achieved with an angular deviation of less than 2(∘). Minor improvements on the protocol and the use of smaller markers indicate that even a precision better than 1  mm is technically feasible. Detailed investigations concerning the imaging dose lead to the conclusion that doses for skull radiographs lie in the same range as dose reference levels for human head radiographs. A currently used online dose monitor for MRT has been proven to give reliable results for the imaging beam.

CONCLUSIONS

The ESRF biomedical beamline ID17 is technically ready to apply conformal image-guided MRT from multiple ports to large animals during future veterinary trials.

Medical physics aspects of the synchrotron radiation therapies: Microbeam radiation therapy (MRT) and synchrotron stereotactic radiotherapy (SSRT)

Stereotactic Synchrotron Radiotherapy (SSRT) and Microbeam Radiation Therapy (MRT) are both novel approaches to treat brain tumor and potentially other tumors using synchrotron radiation. Although the techniques differ by their principles, SSRT and MRT share certain common aspects with the possibility of combining their advantages in the future. For MRT, the technique uses highly collimated, quasi-parallel arrays of X-ray microbeams between 50 and 600 keV. Important features of highly brilliant Synchrotron sources are a very small beam divergence and an extremely high dose rate. The minimal beam divergence allows the insertion of so called Multi Slit Collimators (MSC) to produce spatially fractionated beams of typically ∼25-75 micron-wide microplanar beams separated by wider (100-400 microns center-to-center(ctc)) spaces with a very sharp penumbra. Peak entrance doses of several hundreds of Gy are extremely well tolerated by normal tissues and at the same time provide a higher therapeutic index for various tumor models in rodents. The hypothesis of a selective radio-vulnerability of the tumor vasculature versus normal blood vessels by MRT was recently more solidified. SSRT (Synchrotron Stereotactic Radiotherapy) is based on a local drug uptake of high-Z elements in tumors followed by stereotactic irradiation with 80 keV photons to enhance the dose deposition only within the tumor. With SSRT already in its clinical trial stage at the ESRF, most medical physics problems are already solved and the implemented solutions are briefly described, while the medical physics aspects in MRT will be discussed in more detail in this paper.

Energy spectra considerations for synchrotron radiotherapy trials on the ID17 bio-medical beamline at the European Synchrotron Radiation Facility

The aim of this study was to validate the kilovoltage X-ray energy spectrum on the ID17 beamline at the European Synchrotron Radiation Facility (ESRF). The purpose of such validation was to provide an accurate energy spectrum as the input to a computerized treatment planning system, which will be used in synchrotron microbeam radiotherapy trials at the ESRF. Calculated and measured energy spectra on ID17 have been reported previously but recent additions and safety modifications to the beamline for veterinary trials warranted a fresh investigation. The authors used an established methodology to compare X-ray attenuation measurements in copper sheets (referred to as half value layer measurements in the radiotherapy field) with the predictions of a theoretical model. A cylindrical ionization chamber in air was used to record the relative attenuation of the X-ray beam intensity by increasing thicknesses of high-purity copper sheets. The authors measured the half value layers in copper for two beamline configurations, which corresponded to differing spectral conditions. The authors obtained good agreement between the measured and predicted half value layers for the two beamline configurations. The measured first half value layer was 1.754 ± 0.035 mm Cu and 1.962 ± 0.039 mm Cu for the two spectral conditions, compared with theoretical predictions of 1.763 ± 0.039 mm Cu and 1.984 ± 0.044 mm Cu, respectively. The calculated mean energies for the two conditions were 105 keV and 110 keV and there was not a substantial difference in the calculated percentage depth dose curves in water between the different spectral conditions. The authors observed a difference between their calculated energy spectra and the spectra previously reported by other authors, particularly at energies greater than 100 keV. The validation of the beam spectrum by the copper half value layer measurements means the authors can provide an accurate spectrum as an input to a treatment planning system for the forthcoming veterinary trials of microbeam radiotherapy to spontaneous tumours in cats and dogs.

Pharmacological characterization of designer cathinones in vitro

BACKGROUND AND PURPOSE

Designer β-keto amphetamines (e.g. cathinones, 'bath salts' and 'research chemicals') have become popular recreational drugs, but their pharmacology is poorly characterized.

EXPERIMENTAL APPROACH

We determined the potencies of cathinones to inhibit DA, NA and 5-HT transport into transporter-transfected HEK 293 cells, DA and 5-HT efflux from monoamine-preloaded cells, and monoamine receptor binding affinity.

KEY RESULTS

Mephedrone, methylone, ethylone, butylone and naphyrone acted as non-selective monoamine uptake inhibitors, similar to cocaine. Mephedrone, methylone, ethylone and butylone also induced the release of 5-HT, similar to 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) and other entactogens. Cathinone, methcathinone and flephedrone, similar to amphetamine and methamphetamine, acted as preferential DA and NA uptake inhibitors and induced the release of DA. Pyrovalerone and 3,4-methylenedioxypyrovalerone (MDPV) were highly potent and selective DA and NA transporter inhibitors but unlike amphetamines did not evoke the release of monoamines. The non-β-keto amphetamines are trace amine-associated receptor 1 ligands, whereas the cathinones are not. All the cathinones showed high blood-brain barrier permeability in an in vitro model; mephedrone and MDPV exhibited particularly high permeability.

CONCLUSIONS AND IMPLICATIONS

Cathinones have considerable pharmacological differences that form the basis of their suggested classification into three groups. The predominant action of all cathinones on the DA transporter is probably associated with a considerable risk of addiction.

Carvedilol inhibits the cardiostimulant and thermogenic effects of MDMA in humans

BACKGROUND AND PURPOSE

The use of ± 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') is associated with cardiovascular complications and hyperthermia.

EXPERIMENTAL APPROACH

We assessed the effects of the α(1) - and β-adrenoceptor antagonist carvedilol on the cardiostimulant, thermogenic and subjective responses to MDMA in 16 healthy subjects. Carvedilol (50 mg) or placebo was administered 1 h before MDMA (125 mg) or placebo using a randomized, double-blind, placebo-controlled, four-period crossover design. KEY RESULTS Carvedilol reduced MDMA-induced elevations in blood pressure, heart rate and body temperature. Carvedilol did not affect the subjective effects of MDMA including MDMA-induced good drug effects, drug high, drug liking, stimulation or adverse effects. Carvedilol did not alter the plasma exposure to MDMA.

CONCLUSIONS AND IMPLICATIONS

α(1) - and β-Adrenoceptors contribute to the cardiostimulant and thermogenic effects of MDMA in humans but not to its psychotropic effects. Carvedilol could be useful in the treatment of cardiovascular and hyperthermic complications associated with ecstasy use.

Alterations of ubiquitin ligases in human cancer and their association with the natural history of the tumor

Protein ubiquitination is critical for many cellular processes, through its ability to regulate protein degradation and various signaling mechanisms. In the ubiquitin (Ub) system, substrate specificity is achieved through the E3 family of Ub ligases. Because alterations of the ubiquitination machinery have been reported in human cancers, the selective interference with Ub ligases might represent a powerful therapeutic tool. Here, we report the first wide survey of misregulation of Ub ligases in cancer. We analysed 82 Ub ligases in nine types of cancer by in situ hybridization on tissue microarrays. We found 27 instances in which an Ub ligase was altered in a given type of tumor, when compared with normal tissues: 21 cases of overexpression and 6 cases of underexpression. We further analysed selected Ub ligases in large cohorts of breast and non-small-cell lung carcinomas. In five, of six, of these extended analyses (HUWE1, CCNB1IP1, SIAH1 and SIAH2 in breast cancer and CCNB1IP1 in lung cancer), we found that the levels of Ub ligases correlated significantly with relevant prognostic factors, and with clinical outcome. Our findings show that the alteration of Ub ligases is a frequent event in cancer and identify candidate targets for molecular therapies.

Different effects of methotrexate on DNA mismatch repair proficient and deficient cells

Antifolates exert their antiproliferative activity through the inhibition of dihydrofolate reductase and, as a consequence, of thymidylate synthesis, thereby inducing nucleotide misincorporation and impairment of DNA synthesis. We investigated the processes involved in the repair of antifolate-induced damage and their relationship with cell death. Since misincorporated bases may be removed by DNA mismatch repair (MMR), the study was carried out on the MMR-proficient human cell lines HeLa and HCT116+chr3, and, in parallel, on the MMR-deficient cell lines HeLa cell-clone12, defective in the protein hPMS2, and HCT116, with an inactive hMLH1. After treatment with methotrexate (MTX), we observed that DNA repair synthesis occurs independently of the cellular MMR function. Clear signs of apoptosis such as nuclear shrinkage, chromatin condensation and degradation, DNA laddering, and poly (ADP-ribose) polymerase (PARP) proteolysis, were visible in both MMR(+) and MMR(-) cells. Remarkably, cell viability was lower and the apoptotic process was triggered more efficiently in the MMR-competent cells.

Apoptosis-prone phenotype of human colon carcinoma cells with a high level amplification of the c-myc gene

Although apoptosis can be induced by the enforced expression of exogenously introduced c-myc genes, it is not clear whether overexpression resulting from the amplification of the resident c-myc gene in tumor cells is sufficient to induce apoptosis. We have investigated the relationship between c-myc gene amplification and the propensity of tumor cells to undergo apoptosis, using the SW613-12A1 and SW613-B3 cell lines, which are representatives, respectively, of tumorigenic and non-tumorigenic clones isolated from the SW613-S human colon carcinoma cell line. Tumorigenic clones are characterized by a high level of amplification and expression of the c-myc gene, whereas cells of non-tumorigenic clones have a small number of copies and a lower level of expression of this gene. Analysis of c-myc mRNA level in cells cultured under low serum conditions indicated that the expression of the gene is tightly regulated by serum growth factors in non-tumorigenic B3 cells, whereas it is poorly regulated in tumorigenic 12A1 cells, the level of mRNAs remaining relatively high in serum-starved 12A1 cells. Under these conditions, 12A1 cells showed clear evidence of apoptosis, whereas B3 cells were completely refractory to the induction of apoptosis. Moreover, the study of cell lines derived from non-tumorigenic apoptosis-resistant clones following the introduction by transfection of exogenous c-myc gene copies showed that they have acquired an apoptosisprone phenotype. Altogether, our results strongly suggest that deregulated c-myc expression due to high-level amplification confers an apoptosis-prone phenotype to tumor cells. The possible consequences of these observations for cancer therapy are discussed.

Poly(ADP-ribose) synthesis: a useful parameter for identifying apoptotic cells

Cell death by apoptosis was analysed in HeLa cells either treated with the antitumoral drug bleomycin or depleted of growth factors by long-term culture without medium change. The interference of apoptosis with normal cell cycle progression was followed by flow cytometry in cells stained with propidium iodide and with antibody to S-phase-related PCNA protein. Bleomycin-treated cells showed a net accumulation in G2/M phase paralleled by the appearance of material with a subdiploid DNA content. Cells with a subdiploid DNA content were also present in growth factor-depleted cultures and were shown to derive from all the cell cycle phases. To identify apoptotic features in HeLa cell cultures, we applied a recently developed assay based on the simultaneous analysis in the single cell of three parameters, namely chromatin condensation, DNA degradation and poly(ADP-ribose) synthesis. Apoptotic cells were visualized by sequential reactions: Hoechst staining, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labelling assay and immunoreaction with anti-poly(ADP-ribose) monoclonal antibody. Positive reactions were obtained for cells at different stages of the apoptotic programme showing condensed nuclei, fragmented chromatin and apoptotic bodies.

Multiparametric staining to identify apoptotic human cells

To analyze relevant features of HeLa and HL60 cells driven into apoptosis by etoposide, we have developed a new "tricolor" assay, based on the simultaneous analysis in the single cell of chromatin condensation, DNA degradation, and cellular poly(ADP-ribose) synthesis. The latter reaction is catalyzed by poly(ADP-ribose)-polymerase (E.C. 2.4.2.30), an enzyme which is activated by the presence of DNA free ends. The protocol consists in the visualization of apoptotic cells by Hoechst staining, TUNEL assay, and immunoreaction with anti-poly(ADP-ribose) antibody. We thus provide the first evidence that endogenous poly(ADP-ribose) production is indeed stimulated in cells undergoing apoptosis after treatment with antitumoral drugs, and that the monitoring of this endogenous enzymatic reaction, combined with morphological and other biochemical parameters, should facilitate the detection of apoptotic cells.

Sequence of events leading to apoptosis in long term cultured HeLa cells

We have maintained HeLa cells in culture in the original medium for increasing times to induce growth arrest. Cell viability was evaluated by trypan blue dye exclusion assay. We observed that when cells are maintained in culture for several days, morphological hallmarks of apoptosis become evident. DNA synthesis rate, followed by (3)H-thymidine incorporation slowed down in long term cultured cells. This evidence was supported by the analysis of cell cycle progression determined by proliferating cell nuclear antigen (PCNA) immunostaining. Apoptotic cells have been characterized with respect to the sequential appearance of high molecular weight and internucleosomal DNA fragmentation. We have provided evidence that in this experimental model the first step in DNA degradation is represented by the formation of high molecular weight fragments, whereas nucleosomal DNA ladder is visible later on. The activation of the enzyme poly(ADP-ribose)polymerase, considered a marker of apoptotic death, has been observed. The results suggest that long term culture conditions activate the apoptotic programme.

Induction of apoptotic cell death by DNA topoisomerase II inhibitors

We have analyzed the interference of antitumoral drugs acting through the inhibition of DNA topoisomerase II on the human HeLa cell metabolism. Different compounds characterized by a diverse mechanism of action have been used, namely m-amsacrine, an intercalative drug, etoposide, which does not intercalate DNA, and suramin, which exerts its effect through an unknown mechanism. In HeLa cells treated with increasing doses of these drugs, we have examined cell viability and DNA synthesis capacity, and we have evaluated topoisomerase II activity. Cellular morphology and DNA integrity have been studied in order to characterize the mechanism of cell death. The results we have obtained clearly indicate that topoisomerase II poisons induce cell death by apoptosis. These observations suggest a role of the inhibition of topoisomerase II activity in the apoptotic program.

Analysis of phosphorylation level of DNA topoisomerase-ii-alpha and topoisomerase-ii-Beta in human hela-cells

We have studied the phosphorylation of DNA topoisomerases II in HeLa cells focusing on the beta isoform of the enzyme which is very difficult to analyze because of its instability. In proliferating cells, we observed that both the a and beta isozymes are labeled after cell incubation with (32)p. The phosphorylation of beta enzyme occurs to a low extent, thus reflecting the expression of topoisomerases II during cell cycle. In cells treated with etoposide, the activity of topoisomerase II is inhibited and the level of phosphorylation decreases, suggesting a possible cooperation between this modification and drug response.

Activation of poly(ADP-ribose)polymerase in apoptotic human cells

We have studied the effect of the chemotherapeutic drug VP-16 (etoposide) on the metabolism of HeLa cells by analysing different cellular parameters considered as markers of apoptosis. Typical features such as chromatin condensation and internucleosomal DNA cleavage are visible in HeLa cells exposed to VP-16. We investigated whether the appearance of small-sized DNA fragments could regulate the ADP-ribosylation process. To this purpose, we have analysed, by means of the activity gel technique; the structural and catalytical properties of poly(ADP-ribose)polymerase. In extracts from cells where etoposide-induced DNA fragmentation occurred, we have shown that the label of the autoribosylated form of the enzyme is greatly increased even if the amount of the protein remains constant. This phenomenon is completely abolished in cells preincubated with poly(ADP-ribose)polymerase inhibitor, 3-aminobenzamide. After VP-16 administration, we have observed that the level of NAD is not heavily decreased. It is widely agreed that zinc exerts an inhibitory effect on the endonuclease(s) responsible for the fragmentation of DNA during apoptosis. After incubation of cells with zinc/VP-16 we have found the occurrence of apoptotic parameters even in the absence of internucleosomal DNA cleavage. The inhibition of DNA fragmentation prevents the activation of poly(ADP-ribose)polymerase activity. These results indicate that the activation of the enzyme towards the automodification reaction is strictly dependent on the appearance of DNA internucleosomal fragments and could represent a way to control enzyme activity.

Dose-dependent zinc inhibition of DNA ladder in apoptotic HeLa cells regulates the activity of poly(ADP-ribose) polymerase and does not protect from death induced by VP-16

Zinc ions exert an inhibitory effect on Ca(2+)Mg(2+)-dependent endonuclease which is supposed to be responsible for the fragmentation of DNA during apoptosis. In the experimental system we used, that is HeLa cells treated with VP-16, the protection from internucleosomal DNA degradation is modulated by Zn concentration and appears to be dependent on the time after treatment. This effect does not prevent cell death or occurrence of apoptotic parameters, suggesting that DNA ladder appearance is not a crucial event in apoptosis. The activation of poly(ADP-ribose)polymerase following the administration of VP-16, is not observed in cells in which DNA fragmentation has been abolished by zinc, supporting the hypothesis that this event is regulated by the appearance of small-sized DNA fragments.

[Mitral valve replacement in young children: a long-term follow-up]

The Authors report follow-up data (mean 60, range 13-101 months) from 4 patients under two years of age (mean 11.5 months) operated on for prosthetic mitral valve implantation. Two patients were male and two female. Pre-operative diagnosis was partial atrioventricular septal defect with parachute mitral valve in one case and isolated mitral valve anomaly in the others (1 parachute, 2 hammock valves). One bioprosthesis (Liotta n. 23) and three mechanical prostheses (Björk-Shiley) were implanted. Complications occurred in two patients: one case of endocarditis on the bioprosthesis, leading to substitution with a Björk-Shiley valve; one case of acute thrombosis 8 months after implantation in the only pt receiving aspirin as prophylactic therapy. This complication was resolved by intravenous thrombolytic agents. All the patients are alive, in I NYHA functional class and receiving oral anti-coagulants. Instrumental follow-up with eco-Doppler demonstrated normal functioning prostheses in all the patients. A sub-aortic gradient was found in the patient with partial atrioventricular septal defect. Prosthesis-patient mismatch was identified in a patient operated on when she was 6 months old who was followed-up for 5 years.

[Kawasaki's disease. Presentation of 2 clinical cases]

The authors describe two cases of Kawasaki disease, one of whose is an "incomplete" form, and emphasize the importance to know this "new" disease in the differential diagnosis of febrile exanthemas of childhood. A complete diagnostic walk-up failed to find out a probably, while change of some immunological and flogistic parameters has permitted to suppose a probably immuno-mediated pathogenesis of Kawasaki disease. Both patients healed without any sequelae after therapy with low doses of salicylate for ten months, in confirmation of usefulness of this treatment in the prevention of heart complications of Kawasaki disease.

Supraventricular tachycardia in infants: use of the "diving reflex"

The effectiveness of the "diving reflex" in treating paroxysmal supraventricular tachycardia (PSVT) in 10 infants aged under 6 months is demonstrated. No rhythm disturbances were encountered during the maneuver, even in patients receiving digitalis. The recommended water temperature is 5 degrees C and the total time of facial immersion, between 6 and 7 seconds. The diving reflex might be considered the first therapeutic approach in infants under 6 months old with PSVT.