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of extended daily oral BIO 300 dosing. We used a NSCLC xenograft model in which athymic CD1 nu/nu
mice were subcutaneously implanted with human A549 adenocarcinoma cells. In the first study, A549
cells were implanted dorsally such that the radiation field encompassed both tumor and lung. BIO 300
dosing (once daily by gavage, 200 or 400 mg/kg) was started one week before tumor cell implant and
continued for the duration of the study. A single dose of irradiation (12.5 Gy) was delivered when the
tumor size reached approximately 0.45 cc. In the second study, A549 cells were implanted subcutaneously
in the flank to facilitate animal handling and BIO 300 dosing was initiated after tumors were established.
As in the first study, mice were dosed daily for 31 consecutive days prior to irradiation therapy with the
exception of two groups that received BIO 300 daily starting only 7 days prior to
irradiation. This was done to evaluate BIO 300’s effect on different tumor sizes and to more closely mimic
clinical care. By histology, we found less (~20%) lung tissue injury in irradiated mice receiving BIO 300
(regardless of dose) compared with injury in irradiated mice receiving vehicle control. BIO
300 at either dose, combined with radiation, caused a significant tumor growth delay (30-140% increase
in days, p=0.008) compared to vehicle control and radiation. On microscopic analysis, we found no
significant adverse effect of BIO 300 (esophagus, terminal ileum, skin, GI tract, uterus, lung) supporting
the safety of extended daily oral BIO 300 dosing. In fact, mice receiving BIO 300 exhibited an initial
increase in body weight. Based on these in vivo findings, a clinical trial to assess the safety and efficacy of
this treatment approach in NSCLC patients is being planned. This project was funded in part by NIH/NCI
SBIR contract HHSN261201200078C.
(PS2-81) CDX-301: a novel countermeasure against mixed neutron/gamma radiation exposure. Lynnette
1
2
1
1
H. Cary, PhD ; Opeyemi T. Fadiyimu, BS ; Robert E. McMahon, MS ; Lawrence J. Thomas, PhD, DABT, ATS ;
1
1
and Mark H. Whitnall, PhD, Armed Forces Radiobiology Research Institute, Bethesda, MD and Celldex
2
Therapeutics, Inc., Needham, MA
The ability to confidently plan responses to a nuclear threat requires an arsenal of effective
countermeasures. The vast majority of studies on the Acute Radiation Syndrome (ARS) and
countermeasures have been performed using photon irradiation (gamma and x-rays). However, in the
event of a nuclear detonation, personnel will be exposed to lethal levels of neutrons mixed with gamma
rays (mixed fields, MF). Neutrons have different mechanisms of injury compared to photons, which may
affect countermeasure efficacy. The present work examined the effectiveness of CDX-301 as a mitigator
against MF exposure. CDX-301 is the soluble recombinant human form of flt3 ligand (FL). The receptor for
FL is known as Flt3 (CD135). It is expressed on multiple immune cell progenitors, including hematopoietic
stem cells (HSC), early progenitor cells, and immature thymocytes, resulting in the proliferation,
differentiation, development and mobilization of these cells in the bone marrow, peripheral blood, and
lymphoid organs. Radiation with 5.71 Gy MF (Dn/Dt=0.65) represents an approximate LD70 dose in CD2F1
mice. Treatment with a single dose of CDX-301 4 h after exposure increased survival 42.5% (80% survival
of CDX-treated mice vs 37.5% survival of saline treated mice). Survival was improved up to 88% when CDX-
301 was administered in two injections 4 and 48 h after radiation. A single injection administered 24 h
post-MF did not improve survival, while two injections (24, 48 h) improved survival 40%. This
administration schedule also improved survival of mice irradiated at 9.2 Gy with gamma, an approximate
LD70/30 dose. Blood, bone marrow, and spleen were collected from sublethally irradiated mice (3 Gy MF)
after euthanasia. Bone marrow recovery occurred more rapidly in mice treated with CDX-301 4 h or 4 h +
48 h after exposure. Circulating blood cell counts indicate an FL-mediated reduction in neutrophil nadir
181 | P a g e
mice were subcutaneously implanted with human A549 adenocarcinoma cells. In the first study, A549
cells were implanted dorsally such that the radiation field encompassed both tumor and lung. BIO 300
dosing (once daily by gavage, 200 or 400 mg/kg) was started one week before tumor cell implant and
continued for the duration of the study. A single dose of irradiation (12.5 Gy) was delivered when the
tumor size reached approximately 0.45 cc. In the second study, A549 cells were implanted subcutaneously
in the flank to facilitate animal handling and BIO 300 dosing was initiated after tumors were established.
As in the first study, mice were dosed daily for 31 consecutive days prior to irradiation therapy with the
exception of two groups that received BIO 300 daily starting only 7 days prior to
irradiation. This was done to evaluate BIO 300’s effect on different tumor sizes and to more closely mimic
clinical care. By histology, we found less (~20%) lung tissue injury in irradiated mice receiving BIO 300
(regardless of dose) compared with injury in irradiated mice receiving vehicle control. BIO
300 at either dose, combined with radiation, caused a significant tumor growth delay (30-140% increase
in days, p=0.008) compared to vehicle control and radiation. On microscopic analysis, we found no
significant adverse effect of BIO 300 (esophagus, terminal ileum, skin, GI tract, uterus, lung) supporting
the safety of extended daily oral BIO 300 dosing. In fact, mice receiving BIO 300 exhibited an initial
increase in body weight. Based on these in vivo findings, a clinical trial to assess the safety and efficacy of
this treatment approach in NSCLC patients is being planned. This project was funded in part by NIH/NCI
SBIR contract HHSN261201200078C.
(PS2-81) CDX-301: a novel countermeasure against mixed neutron/gamma radiation exposure. Lynnette
1
2
1
1
H. Cary, PhD ; Opeyemi T. Fadiyimu, BS ; Robert E. McMahon, MS ; Lawrence J. Thomas, PhD, DABT, ATS ;
1
1
and Mark H. Whitnall, PhD, Armed Forces Radiobiology Research Institute, Bethesda, MD and Celldex
2
Therapeutics, Inc., Needham, MA
The ability to confidently plan responses to a nuclear threat requires an arsenal of effective
countermeasures. The vast majority of studies on the Acute Radiation Syndrome (ARS) and
countermeasures have been performed using photon irradiation (gamma and x-rays). However, in the
event of a nuclear detonation, personnel will be exposed to lethal levels of neutrons mixed with gamma
rays (mixed fields, MF). Neutrons have different mechanisms of injury compared to photons, which may
affect countermeasure efficacy. The present work examined the effectiveness of CDX-301 as a mitigator
against MF exposure. CDX-301 is the soluble recombinant human form of flt3 ligand (FL). The receptor for
FL is known as Flt3 (CD135). It is expressed on multiple immune cell progenitors, including hematopoietic
stem cells (HSC), early progenitor cells, and immature thymocytes, resulting in the proliferation,
differentiation, development and mobilization of these cells in the bone marrow, peripheral blood, and
lymphoid organs. Radiation with 5.71 Gy MF (Dn/Dt=0.65) represents an approximate LD70 dose in CD2F1
mice. Treatment with a single dose of CDX-301 4 h after exposure increased survival 42.5% (80% survival
of CDX-treated mice vs 37.5% survival of saline treated mice). Survival was improved up to 88% when CDX-
301 was administered in two injections 4 and 48 h after radiation. A single injection administered 24 h
post-MF did not improve survival, while two injections (24, 48 h) improved survival 40%. This
administration schedule also improved survival of mice irradiated at 9.2 Gy with gamma, an approximate
LD70/30 dose. Blood, bone marrow, and spleen were collected from sublethally irradiated mice (3 Gy MF)
after euthanasia. Bone marrow recovery occurred more rapidly in mice treated with CDX-301 4 h or 4 h +
48 h after exposure. Circulating blood cell counts indicate an FL-mediated reduction in neutrophil nadir
181 | P a g e
