RRx-001 Radioprotection: Enhancement of Survival and Hematopoietic Recovery in Gamma-Irradiated Mice

Abstract

The present studies evaluate the in vivo prophylactic radioprotective effects of 1-bromoacetyl-3, 3-dinitroazetidine (RRx-001), a phase III anticancer agent that inhibits c-myc and downregulates CD-47, after total body irradiation (TBI), in lethally and sublethally irradiated CD2F1 male mice. A single dose of RRx-001 was administered by intraperitoneal (IP) injection 24 h prior to a lethal or sublethal radiation dose. When irradiated with 9.35 Gy, the dose lethal to 70% of untreated mice at 30 days (LD70/30), only 33% of mice receiving RRx-001 (10 mg/kg) 24 h prior to total body irradiation (TBI) died by day 30, compared to 67% in vehicle-treated mice. The same pretreatment dose of RRx-001 resulted in a significant dose reduction factor of 1.07. In sublethally TBI mice, bone marrow cellularity was increased at day 14 in the RRx-001-treated mice compared to irradiated vehicle-treated animals. In addition, significantly higher numbers of lymphocytes, platelets, percent hematocrit and percent reticulocytes were observed on days 7 and/or 14 in RRx-001-treated mice. These experiments provide proof of principle that systemic administration of RRx-001 prior to TBI significantly improves overall survival and bone marrow regeneration.

Feasibility of Reducing Animal Numbers in Radiation Countermeasure Experiments from Historic Levels when using Sample Size Calculations

“…The LD 50 for vehicle-treated animals was 9.22 (95% CI: 9.03-9.41); compared to our assumed 8.9 Gy. The DRF of RRx-001 was 1.07 (95% CI: 1.05-1.10) (32), which was lower than our DRF to detect; thus, actual power would have been decreased. The lethality slope on radiation dose was 41.6 (95% CI: 31.2-51.9), which was notably higher than our assumed slope of 25; this increase in precision would have increased actual power.…”

“…The planning of one DRF experiment was retrospective in that the experiment was not designed using the sample size calculation ( 16 ). The other DRF experiment was prospective in that we used the sample size calculation when planning it ( 32 ). We note that for the prospective DRF experiment, we increased the calculated number of animals for the express purpose of evaluating the feasibility of using the sample size calculation.…”

“…Jurgensen et al studied the use of RRx-001, a Phase 3 anticancer agent, as a radiation prophylactic ( 32 ). Part of the study included a DRF experiment.…”

“…We performed and reported the power analysis before conducting the experiment ( 32 ). From the protocol above, we had the planned radiation doses (parameter i ).…”

“…From the power curve, 7 mice/sub-group would provide 0.90 power; that is, 84 mice in total. Since a prospective feasibility study was part of the research objectives, we used 16 mice/subgroup – a standard number of mice per sub-group for that research group; thus, 192 mice in total ( 32 ).…”