Increased but error-prone nonhomologous end joining in immortalized lymphoblastoid cell extracts from adult cancer patients with late radionecrosis.

PURPOSE: To study nonhomologous end joining in extracts of two lymphoblastoid cell lines derived from patients with late radionecrosis after radiotherapy. Both cell lines were previously shown to exhibit impaired rejoining of DNA double-strand breaks in a pulse-field gel electrophoresis assay. METHODS AND MATERIALS: We used a cell-free system and quantitative real-time polymerase chain reaction, as well as sequencing analysis of end joining products. RESULTS: Paradoxically, extracts of the two cell lines display increased rates of in vitro end joining of noncohesive termini compared with normal cell extracts. This increase was seen in the absence of added deoxyribonucleoside triphosphates and was sensitive to inhibition by wortmannin. Sequencing of the joined products revealed that, despite increased rates of end joining, the process was error prone with a greater frequency of deletions compared with that observed in normal controls. CONCLUSION: These findings are consistent with the suggestion that a promiscuous, deletion-prone abnormality of nonhomologous end joining might underpin the predisposition of certain radiotherapy patients to late radionecrosis. We hypothesize that some individuals might harbor subclinical defects in nonhomologous end joining that clinically manifest on challenge with high-dose radiation. Because both quantitative and qualitative aspects of end joining have demonstrably been influenced, we recommend that the study of patient samples should involve a combination of quantitative methods (e.g., quantitative real-time polymerase chain reaction), sequencing analysis, and a comparison of multiple join types.

Complete tumor response following intratumoral 32P BioSilicon on human hepatocellular and pancreatic carcinoma xenografts in nude mice.

PURPOSE: 32P BioSilicon is a new, implantable, radiological medical device that comprises particles of highly pure silicon encapsulating 32phosphorus (32P) for the treatment of unresectable solid tumors. Prior to administration, the device particles are suspended in a formulant which provides an even suspension of the intended dose for implantation. The primary objective of this animal trial study was to investigate the effects of intratumoral injection of 32)P BioSilicon on human hepatocellular (HepG2) and pancreatic carcinoma (2119) xenografts implanted in nude mice (BALB/c). A secondary objective was the histopathologic examination of the tumor foci and surrounding tissue during the study. METHODS: Cultured human carcinoma cells (HepG2 and 2119) were injected s.c. into the gluteal region of nude mice. When the implanted tumors were approximately 1 cm in diameter, 32P BioSilicon (0.5, 1.0, and 2.0 MBq) or formulant was injected into the tumors. Implanted tumor size was measured once a week for 10 weeks. At study termination, the tumor and surrounding normal tissue were collected and fixed in 10% formalin and processed for histopathologic analysis. RESULTS: 32P BioSilicon produced a reduction in HepG2 tumor volume when compared with formulant control, and complete response was observed among tumors in the 1.0 and 2.0 MBq treatment groups after week 8. There was also significant reduction in 2119 tumor volume in all treated groups, with the complete response rate of 67% in the 2.0 MBq group. CONCLUSION: 32P BioSilicon suppressed the growth of both human hepatocellular and pancreatic carcinoma xenografts implanted in nude mice and complete responses were also observed in tumors at higher radiation doses.

Reduced DNA-dependent protein kinase activity in two cell lines derived from adult cancer patients with late radionecrosis.

Epstein-Barr virus-immortalized lymphoblastoid cell lines were derived from five patients with late radionecrosis. Two of these cell lines exhibited postradiation viability levels intermediate between normal cell lines and that from an individual with ataxia telangiectasia. Compared with controls, these two cell lines exhibited impaired ability to rejoin DNA double-strand breaks on pulsed-field gel electrophoresis and 6-10-fold reduced DNA-dependent protein kinase (DNA-PK) activity in vitro in cell-free extracts. Immunoblotting showed normal levels of Ku70, Ku80 and XRCC4 and the presence of DNA-PKcs in both cell lines. These findings suggest that DNA-PK might be an important factor affecting the predisposition of radiotherapy patients to late radionecrosis.