Preparation of radiolabeled erlotinib analogues and analysis of the effect of linkers.

Erlotinib is a first generation epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) which was granted Food and Drug administration (FDA) approval for treatment of patients with locally advanced or metastatic NSCLC. The present study aimed at development of radiolabeled erlotinib variants as tyrosine kinase inhibitors. Three DOTA-erlotinib conjugates were prepared for radiolabeling with 177Lu. The terminal alkyne group of erlotinib was modified by performing Cu-catalyzed click chemistry and three different linkers were introduced which were then conjugated to the chelator, DOTA. The DOTA-erlotinib conjugates were characterized by 1H NMR and ESI-MS. 177Lu-DOTA-erlotinib complexes were characterized using natLu-DOTA-erlotinib conjugates. The 177Lu-complexes exhibited high in vitro stability in human serum up to 48 h. They were highly hydrophilic in nature as observed from their log Po/w values (177Lu-DOTA-propyl-Er: -2.5 ± 0.1; 177Lu-DOTA-PEG3-Er: -3.0 ± 0.1; 177Lu-DOTA-PEG6-Er: -3.3 ± 0.1). The MTT assay in A431 human epidermoid carcinoma cell lines indicates that the chemical modification at the terminal alkyne group of the erlotinib molecule does not have significant effect on its TKI property. Biodistribution studies in normal Swiss mice demonstrated fast clearance and excretion of 177Lu-labeled erlotinib complexes. These studies indicate that erlotinib variants with hydrophobic pharmacokinetic modifiers/chelators may enhance the retention of 177Lu-labeled complexes in blood thereby increasing the probability to reach EGFR-expressing tumor.

Dosimetry and radiobiological studies of automated alpha-particle irradiator.

Understanding the effect of alpha radiation on biological systems is an important component of radiation risk assessment and associated health consequences. However, due to the short path length of alpha radiation in the atmosphere, in vitro radiobiological experiments cannot be performed with accuracy in terms of dose and specified exposure time. The present paper describes the design and dosimetry of an automated alpha-particle irradiator named 'BARC BioAlpha', which is suitable for in vitro radiobiological studies. Compared to alpha irradiators developed in other laboratories, BARC BioAlpha has integrated computer-controlled movement of the alpha-particle source, collimator, and electronic shutter. The diaphragm blades of the electronic shutter can control the area (diameter) of irradiation without any additional shielding, which is suitable for radiobiological bystander studies. To avoid irradiation with incorrect parameters, a software interlock is provided to prevent shutter opening, unless the user-specified speed of the source and collimator are achieved. The dosimetry of the alpha irradiator using CR-39 and silicon surface barrier detectors showed that ~4 MeV energy of the alpha particle reached the cells on the irradiation dish. The alpha irradiation was also demonstrated by the evaluation of DNA double-strand breaks in human cells. In conclusion, 'BARC BioAlpha' provides a user-friendly alpha irradiation system for radiobiological experiments with a novel automation mechanism for better accuracy of dose and exposure time.

Oxidative stress-mediated apoptotic death in human peripheral blood lymphocytes treated with plasma from gamma-irradiated blood.

The present study is aimed to investigate the effect of plasma from irradiated human blood on the induction of apoptotic death in human peripheral blood lymphocytes. Our results showed that plasma obtained from γ-irradiated human blood showed a significant decrease in viability and an increase in apoptotic death in unirradiated lymphocytes, which is correlated with increase in intracellular reactive oxygen species level. Moreover, a decrease in the activity of superoxide dismutase in lymphocytes further seems to be associated with oxidative stress-mediated apoptotic death. The diffusible factors from irradiated blood were found to be generated from the cellular components of blood. Based on our results, we suggest induction of oxidative stress-mediated apoptotic death in unirradiated lymphocytes by diffusible factors from irradiated blood.