Hematological Changes as Prognostic Indicators of Survival: Similarities Between Gottingen Minipigs, Humans, and Other Large Animal Models

The animal efficacy rule addressing development of drugs for selected disease categories has pointed out the need to develop alternative large animal models. Based on this rule, the pathophysiology of the disease in the animal model must be well characterized and must reflect that in humans. So far, manifestations of the acute radiation syndrome (ARS) have been extensively studied only in two large animal models, the non-human primate (NHP) and the canine. We are evaluating the suitability of the minipig as an additional large animal model for development of radiation countermeasures. We have previously shown that the Gottingen minipig manifests hematopoietic ARS phases and symptoms similar to those observed in canines, NHPs, and humans.We establish here the LD50/30 dose (radiation dose at which 50% of the animals succumb within 30 days), and show that at this dose the time of nadir and the duration of cytopenia resemble those observed for NHP and canines, and mimic closely the kinetics of blood cell depletion and recovery in human patients with reversible hematopoietic damage (H3 category, METREPOL approach). No signs of GI damage in terms of diarrhea or shortening of villi were observed at doses up to 1.9 Gy. Platelet counts at days 10 and 14, number of days to reach critical platelet values, duration of thrombocytopenia, neutrophil stress response at 3 hours and count at 14 days, and CRP-to-platelet ratio were correlated with survival. The ratios between neutrophils, lymphocytes and platelets were significantly correlated with exposure to irradiation at different time intervals.As a non-rodent animal model, the minipig offers a useful alternative to NHP and canines, with attractive features including ARS resembling human ARS, cost, and regulatory acceptability. Use of the minipig may allow accelerated development of radiation countermeasures

The development of technology for effective respiratory-gated irradiation using an image-guided small animal irradiator

The development of image-guided small animal irradiators represents a significant improvement over standard irradiators enabling preclinical treatments to mimic radiotherapy in humans. The ability to deliver tightly collimated targeted beams, in conjunction with gantry or animal couch rotation, has the potential to maximise tumour dose while sparing normal tissues. However the current commercial platforms do not incorporate respiratory gating as required for accurate and precise targeting in organs subject to breath-related motions, which may be up to the order of 5 mm in mice. Therefore a new treatment head assembly for the Xstrahl Small Animal Radiation Research Platform (SARRP) has been designed. This includes a fast x-ray shutter subsystem, a motorised beam hardening filter assembly, an integrated transmission ionisation chamber to monitor beam delivery, a kinematically positioned removable beam collimator and a targeting laser exiting the centre of the beam collimator. The x-ray shutter not only minimises timing errors but also allows beam gating during imaging and treatment, with irradiation only taking place during the breathing cycle when tissue movement is minimal. The breathing-related movement is monitored by measuring, using a synchronous detector/lock-in amplifier that processes diffuse reflectance light from a modulated light source. Following thresholding of the resulting signal, delays are added around the inhalation/exhalation phases, enabling the ‘no movement’ period to be isolated and to open the x-ray shutter. Irradiation can either be performed for a predetermined time of x-ray exposure, or through integration of current from the transmission monitor ionisation chamber (corrected locally for air density variations). The ability to successfully deliver breathing gated x-ray irradiations has been demonstrated by comparing movies obtained using planar x-ray imaging with and without breathing gating, in addition to comparing dose profiles observed from a collimated beam on EBT3 radiochromic film mounted on the animals’ chest. Altogether, the development of breathing gated irradiation facilitates improved dose delivery during animal movement and constitutes an important new tool for preclinical radiotherapy studies. This arrangement is particularly well suited for treatments of orthotopic tumours or other targets within the chest and abdomen where breathing related movement is significant