ABSTRACT
Withaferin A (WA), a plant withanolide, has shown significant radiosensitizing effect in vitro and in vivo. Inhibition of DNA repair has been suggested as a mechanism of radiosensitization by WA. To test this, the effect of withaferin A on survival of DT40 chicken B-lymphocyte cell line and its repair deficient single gene mutants Rad54-/-, Ku70-/- and double mutant Ku70-/- /Rad54-/- after irradiation was studied. Exponentially growing cells were treated for 1 hr with 5 microM WA and then exposed to different doses of X-rays. Cell survival was studied by clonogenic assay. WA significantly reduced survival of DT40, Ku70-/- and Ku70-/- /Rad54-/-, but not Rad54-/- cells, suggesting that WA enhances radiosensitivity by interfering with homologous repair, the major pathway of DSB repair in these cells. Inhibition of DNA repair is further indicated in a significant decrease in surviving fraction of DT40 cells by post-irradiation incubation with WA. This could have relevance to cancer radiotherapy.
Subject(s)
Animals , B-Lymphocytes/radiation effects , Cell Death/radiation effects , Cell Line , Chickens , DNA Repair/drug effects , Ergosterol/analogs & derivatives , Nuclear Proteins/genetics , Radiation-Sensitizing Agents/pharmacology , X-Rays/adverse effectsABSTRACT
A radioterapia para o câncer da mama como para os de outros órgâos induz uma linfopenia significante. Em estudos anteriores de outros autores, há uma grande controvérsia sobre as proporçöes de diminuiçäo das populaçöes T e B. Quantificando os linfócitos T por rosetas E e os linfócitos B por imunofluorescência direta, observamos diminuiçäo semelhante das populaçöes. Pacientes com ou sem cirurgia prévia responderam do mesmo modo à radioterapia. Pacientes com linfopenia (<1500mm3) prévia à radioterapia sofrem reduçäo significativamente menor de ambas as populaçöes. Seis a oito semanas após a radioterapia já há recuperaçäo significante dos números de linfócitos T somente nas pacientes com mais de 60 anos.