C. Hennequin

miR-210 as a marker of chronic hypoxia, but not a therapeutic target in prostate cancer

INTRODUCTION Radiotherapy in combination with medical castration is the standard treatment for high-risk prostate cancer. Some relapses may be explained by the presence of radioresistant clones arising from hypoxic microenvironment. Since microRNAs (miR) are increased upon hypoxia, the aim of this study was to see whether miR-210 is a potential marker for hypoxia and/or a therapeutic target in prostate cancer. METHODS Human LNCaP, DU145 or PC3 prostate cancer cells were exposed to normoxia or hypoxia for several hours. Gene expression of miR-210, miR-373 and several hypoxia markers were analyzed by Taqman and SYBR green qRT-PCR, respectively. Clonogenic survival after LNA miR-210 inhibitor (78 nM) and concomitant irradiation were evaluated. RESULTS During anoxia, CAIX and VEGF expressions were dramatically increased. miR-210 expression increased during anoxia exposure, while basal miR-373 expression was low and remained stable upon anoxia. LNA miR-210 inhibitor decreased anoxic miR-210 expression by 90% and clonogenic survival under anoxia (p=0.01). However, no enhanced effect was observed when miR-210 inhibitor was combined with irradiation. CONCLUSION miR-210 could be an interesting marker of chronic hypoxia irrespective of the androgen dependency and should, therefore, be tested as a prognostic marker in high risk prostate cancer patients.

Réparation cellulaire et radiosensibilité tumorale : focus sur le gène ATM

Numerous parameters influenced tumour radiosensitivity. The number of clonogenic cells, growth fraction, hypoxia and intrinsic radiosensitivity are among the most important determinants of radiocurability. Detection of DNA damage and repair pathways are important components of intrinsic radiosensitivity. ATM plays a major role in the cellular response to ionizing radiation: it induced DNA repair, cell cycle arrest, and apoptosis via induction of p53. Analysis of single nucleotide polymorphisms could help us to predict normal tissue sensitivity on an individual basis. Mutations of ATM is probably involved in some cases of severe radiation-induced late effects. Measure of residual double-strand breaks by immunochemistry of H2AX, but also ATM or MRE11, is another way to evaluate tumour radiosensitivity. Integration of genomics and functional approach are needed to better predict what the best candidates for a curative radiotherapy are.

Antagonistic interaction between bicalutamide™ (Casodex®) and radiation in androgen-positive prostate cancer LNCaP cells

Bicalutamide™ (Casodex®) reportedly improves high‐risk prostate cancer survival as an adjuvant treatment following radiotherapy. However, biological data for the interaction between bicalutamide and ionizing radiation in concomitant association are lacking.

A role for PKCζ in potentiation of the topoisomerase II activity and etoposide cytotoxicity by wortmannin

Enhanced cytotoxicity of etoposide by wortmannin, an inhibitor of enzymes holding a phosphatidylinositol 3-kinase domain, was investigated in eight cell lines proficient or deficient for DNA double-strand break repair. Wortmannin stimulated the decatenating activity of topoisomerase II, promoted etoposide-induced accumulation of DNA double-strand breaks, shifted the specificity for cell killing by etoposide from the S to G1 phase of the cell cycle, and potentiated the cytotoxicity of etoposide through two mechanisms. (a) Sensitization to high, micromolar amounts of etoposide required integrity of the nonhomologous end-joining repair pathway. (b) Wortmannin dramatically increased the susceptibility to low, submicromolar amounts of etoposide in a large fraction of the cell population irrespective of the status of ATM, Ku86, and DNA-PKCS. It is shown that this process correlates depression of phosphatidylinositol 3-kinase–dependent phosphorylation of the atypical, ζ isoform of protein kinase C (PKCζ). Stable expression of a dominant-negative, kinase-dead mutant of PKCζ in a tumor cell line reproduced the hypersensitivity pattern induced by wortmannin. The results are consistent with up-regulation of the topoisomerase II activity in relation to inactivation of PKCζ and indicate that PKCζ may be a useful target to improve the efficiency of topoisomerase II poisons at low concentration.

Association of radiotherapy and hormonotherapy in locally advanced prostate cancer

Combination of radiotherapy and androgen deprivation is now considered as the standard of care for patients with a localized prostate cancer but poor prognostic factors. Two groups of randomized trials have led to this recommendation. Some have compared radiotherapy alone versus hormonal treatment and radiotherapy: these trials demonstrated, now with a long follow-up, an improvement in 10-year survival for the combined treatment. Three recent trials compared androgen deprivation alone or combined with radiotherapy; a benefit in survival was also demonstrated in favour of the combination. Some questions remained concerning the optimal duration of hormonal treatment, in view of its potential side effects. Patients in the intermediate prognostic groups could receive a short-term androgen deprivation, but those with a high Gleason score must be treated with a long-term hormonal treatment. Modalities of radiotherapy, regarding volumes and dose must also be precised in the next years.

Cancer du rectum : radiothérapie longue ou courte, pour quelles tumeurs et quels patients ?

Afin de diminuer les recidives locales, deux types d’irradiation preoperatoires ont ete developpes dans le traitement des cancers du rectum localement avances : une radiotherapie courte delivrant 5 fractions de 5 Gy en une semaine et une radiotherapie longue delivrant 5 fractions de 1,8 a 2 par semaine pendant 5 semaines en association concomitante a une chimiotherapie a base de fluoropyrimidine. L’ensemble des etudes ayant compare ces deux schemas d’irradiation n’a pas montre de difference que ce soit en termes d’efficacite ou d’effets secondaires. L’avantage de la radiotherapie longue est la possibilite d’obtenir une diminution en taille et en volume de la tumeur. Ces effets peuvent etre utilises dans le cadre d’une strategie therapeutique de conservation sphincterienne pour des tumeurs du bas rectum ou pour obtenir des marges de resection chirurgicales saines en cas de tumeur proche du fascia recti.