in presence of PTX in early (2 weeks) as well as late (24 weeks) phase of radiation injury. the combination. We conducted 30-day survival study to determine the most efficacious dose and time of administration of PTX. We measured the percent survival over a wide range of radiation doses to calculate the DRF of the combination. We also tested radioprotective efficacy of PTX alone. We monitored peripheral blood counts to determine the effect of GT3 and PTX on the hematopoietic system. To decipher the mechanism of synergy between GT3 and PTX we used mevalonate to reverse the effect of HMGCR inhibition by GT3 and calmodulin to reverse phosphodiesterase inhibition and calcium and cAMP signaling [24 25 such GDC-0980 as PTX. Our results indicate that the increase in the radioprotective efficacy of GT3 by combining it with PTX was due to PDE inhibition an effect that was reversed by calmodulin administration. We also measured lipid hydroperoxide formation (malondialdehyde) in liver microsomes to determine the effect of PTX on the ability of GT3 to inhibit lipid peroxidation. Our results indicate that Mouse monoclonal to CRTC1 increase in the radioprotective effectiveness of GT3 by combining it with PTX was due to an increase in cAMP and calcium signaling an effect that was reversed by calmodulin administration. 2 Materials and Methods 2.1 Animals Male CD2F1 mice (6-8 weeks old) purchased from Harlan Laboratories (Indianapolis IN) were housed (eight per cage) in the Armed Forces Radiobiology Study Institute (AFRRI) in an air-conditioned facility accredited from the Association for Assessment and Accreditation of Laboratory Animal Care International. Mice were managed in air-conditioned rooms at a temp of 21 ± 2°C with a relative moisture of 50 ± 10% and 10-15?h cycles of fresh air. The mice were quarantined for 2 weeks on introduction from the vendor. Microbiology serology and histopathology examination of representative samples guaranteed absence of and common murine diseases. Mice were offered = 0.008) for both doses of PTX tested compared to the GT3 group alone. There was no significant difference GDC-0980 between 100 and 200?mg/kg of PTX. Consequently 200 of PTX was utilized for survival studies and 100?mg/kg of PTX was utilized for hematological studies. Number 1 GT3-PTX combination improved the radioprotective effectiveness of GT3 at 11.5?Gy. Postirradiation survival studies were carried out on mice (= 16) treated with GT3 or PTX or a combination of GT3 and PTX. (a) shows time optimization studies on GT3 … 3.2 Radioprotective Effectiveness of PTX Alone To determine whether increase in radioprotective effectiveness by combining PTX with GT3 was an effect we conducted 30-day time post-survival studies with PTX alone. PTX was given 15?min before 8.5?Gy TBI and postirradiation survival was monitored for 30 days. As demonstrated in Number 2 there was no significant increase in postirradiation survival with PTX only compared to the GDC-0980 vehicle. These studies show that PTX only was a poor radiation countermeasure. Therefore protecting effect of GT3-PTX combination was not merely an additive effect of GT3 and PTX. Number 2 Effect of PTX only GDC-0980 within the postirradiation survival in mice Percent survival in mice (= 16) treated with 200?mg/kg PTX or vehicle (saline) irradiated at 8.5?Gy TBI was followed for 30 days after irradiation. GDC-0980 PTX did not increase postirradiation … 3.3 Dedication of Dose Reduction Element (DRF) We reported earlier the DRF for 200?mg/kg GT3 was 1.29 [12]. In order to determine the radioprotective effectiveness of GT3 combined with 200?mg/kg of PTX DRF was calculated (Number 3) for vehicle GT3 and the GT3-PTX combination. There was no significant difference in the LD50/30 radiation doses between vehicle (8.5?Gy) and PTX (9.1?Gy). LD50/30 doses were determined to be 11.01 (95% CI) Gy for GT3 and 12.5 (95% GDC-0980 CI) Gy for the GT3-PTX combination. DRF of 1 1.5 (95% CI 1.45-1.54 Number 3) was acquired for the GT3-PTX combination which was significantly higher than the DRF reported for GT3. Number 3 Dedication of dose reduction element for the GT3-PTX combination. Mice (= 16) treated with one of.