Page 230 - 2014 Printable Abstract Book
P. 230
(PS3-74) Radioprotection of the mouse oral mucosa by the combination of DNA binding antioxidants
2
1
1
2
and aminothiol radical scavengers. Jai Smith ; Andrea Smith ; Colin Skene ; Jonathan White ; Pavel
1
1
1
Lobachevsky ; and Roger F. Martin , Peter MacCallum Cancer Centre, East Melbourne, Vic, Australia
Despite improvements in the targeting of radiation for tumour radiotherapy some normal tissue
is unavoidably irradiated. For example, during head and neck radiotherapy the irradiated normal tissue
often includes the radiosensitive oral mucosa which can result in serious dose limiting side effects such as
oral mucositis. The search for a pharmacological radioprotector of normal tissue has a long history.
Amifostine, the prodrug of the aminothiol WR1065 that acts mainly as a radical scavenger, was the first
clinically approved radioprotector for this purpose. A family of radioprotectors with a different
mechanism of action comprises DNA minor groove binding bibenzimidazoles (analogues of Hoechst). It
has been suggested that methylproamine, a member of this family, acts as a reducing agent by donating
an electron to transient radiation induced oxidising species formed on the DNA. In combination, DNA
binding antioxidants and amifostine (or WR1065) have been shown to provide additive radioprotection.
We have previously reported radioprotection in vitro using the clonogeic survival endpoint for WR1065
(DMF=2.5), M2PB (another bibenzimidazole, DMF=2.8) and a combination (DMF=4.4). Similar results
have also been reported for WR1065 with methylproamine. In addition, in vivo radioprotection using the
Withers micro colony survival assay has been reported for M2PB (DMF=1.21), amifostine (DMF=1.13) and
in combination (DMF=1.49). We now report additive radioprotection by M2PB (70 mg/kg SC) and
amifostine (175 mg/kg IP) in the mouse oral mucosa ulceration endpoint. A 3mm by 3mm area on the
dorsal surface of the mouse tongue was irradiated with 25 keV X-rays (20 Gy) either with or without the
drug treatment. The appearance and severity of radiation induced ulcers was the endpoint for this assay.
Pre-treatment with amifostine or M2PB alone failed to result in a significant reduction in the formation of
ulcers. However, a significant reduction in the severity of the ulcers was observed. The mice treated with
the combination had a dramatic 50% reduction in ulcer formation and an 80% reduction in the formation
of severe ulcers compared radiation alone. This result demonstrates additive radioprotection by the
combination of DNA binding antioxidants and aminothiol radical scavengers in a clinically relevant
endpoint.
(PS3-75) Pharmacological inhibition and genetic ablation of the Egr1 transcription factor radioprotects
the mouse hippocampus and small intestine. Diana Y. Zhao; Keith M. Jacobs; Rowan M. Karvas; Jarrett L.
Joubert; Dinesh Thotala; and Dennis E. Hallahan, Washington University in St Louis, St Louis, MO
Radiotherapy can decrease quality of life for cancer survivors by causing cell death in normal
tissues, such as the hippocampus and the intestine, which can lead to neurocognitive disorders and
intestinal malabsorption. The Early Growth Response 1 (Egr1) transcription factor has emerged as a key
mediator of radiation-induced apoptosis, a major form of cell death seen in normal tissues. In response
to radiation, expression levels of Egr1 increase and it activates the transcription of pro-apoptosis genes.
Therefore, we hypothesized that inhibition of Egr1 could attenuate radiotoxicity in the hippocampus and
small intestine. First, we employed the Egr1 knockout mouse to study whether genetic abrogation of Egr1
could reduce apoptosis in the hippocampus and small intestine. Egr1 null mice had significantly less
apoptosis in these tissues following irradiation than their wild-type (WT) littermates. Next, we used
Mithramycin A (MMA), an antibiotic that prevents binding of Egr1 to target promoters to demonstrate
whether pharmacological inhibition of Egr1 could confer radioprotection. Mice pretreated with MMA
prior to irradiation showed significantly less apoptosis in the intestine than mice treated with vehicle.
228 | P a g e
2
1
1
2
and aminothiol radical scavengers. Jai Smith ; Andrea Smith ; Colin Skene ; Jonathan White ; Pavel
1
1
1
Lobachevsky ; and Roger F. Martin , Peter MacCallum Cancer Centre, East Melbourne, Vic, Australia
Despite improvements in the targeting of radiation for tumour radiotherapy some normal tissue
is unavoidably irradiated. For example, during head and neck radiotherapy the irradiated normal tissue
often includes the radiosensitive oral mucosa which can result in serious dose limiting side effects such as
oral mucositis. The search for a pharmacological radioprotector of normal tissue has a long history.
Amifostine, the prodrug of the aminothiol WR1065 that acts mainly as a radical scavenger, was the first
clinically approved radioprotector for this purpose. A family of radioprotectors with a different
mechanism of action comprises DNA minor groove binding bibenzimidazoles (analogues of Hoechst). It
has been suggested that methylproamine, a member of this family, acts as a reducing agent by donating
an electron to transient radiation induced oxidising species formed on the DNA. In combination, DNA
binding antioxidants and amifostine (or WR1065) have been shown to provide additive radioprotection.
We have previously reported radioprotection in vitro using the clonogeic survival endpoint for WR1065
(DMF=2.5), M2PB (another bibenzimidazole, DMF=2.8) and a combination (DMF=4.4). Similar results
have also been reported for WR1065 with methylproamine. In addition, in vivo radioprotection using the
Withers micro colony survival assay has been reported for M2PB (DMF=1.21), amifostine (DMF=1.13) and
in combination (DMF=1.49). We now report additive radioprotection by M2PB (70 mg/kg SC) and
amifostine (175 mg/kg IP) in the mouse oral mucosa ulceration endpoint. A 3mm by 3mm area on the
dorsal surface of the mouse tongue was irradiated with 25 keV X-rays (20 Gy) either with or without the
drug treatment. The appearance and severity of radiation induced ulcers was the endpoint for this assay.
Pre-treatment with amifostine or M2PB alone failed to result in a significant reduction in the formation of
ulcers. However, a significant reduction in the severity of the ulcers was observed. The mice treated with
the combination had a dramatic 50% reduction in ulcer formation and an 80% reduction in the formation
of severe ulcers compared radiation alone. This result demonstrates additive radioprotection by the
combination of DNA binding antioxidants and aminothiol radical scavengers in a clinically relevant
endpoint.
(PS3-75) Pharmacological inhibition and genetic ablation of the Egr1 transcription factor radioprotects
the mouse hippocampus and small intestine. Diana Y. Zhao; Keith M. Jacobs; Rowan M. Karvas; Jarrett L.
Joubert; Dinesh Thotala; and Dennis E. Hallahan, Washington University in St Louis, St Louis, MO
Radiotherapy can decrease quality of life for cancer survivors by causing cell death in normal
tissues, such as the hippocampus and the intestine, which can lead to neurocognitive disorders and
intestinal malabsorption. The Early Growth Response 1 (Egr1) transcription factor has emerged as a key
mediator of radiation-induced apoptosis, a major form of cell death seen in normal tissues. In response
to radiation, expression levels of Egr1 increase and it activates the transcription of pro-apoptosis genes.
Therefore, we hypothesized that inhibition of Egr1 could attenuate radiotoxicity in the hippocampus and
small intestine. First, we employed the Egr1 knockout mouse to study whether genetic abrogation of Egr1
could reduce apoptosis in the hippocampus and small intestine. Egr1 null mice had significantly less
apoptosis in these tissues following irradiation than their wild-type (WT) littermates. Next, we used
Mithramycin A (MMA), an antibiotic that prevents binding of Egr1 to target promoters to demonstrate
whether pharmacological inhibition of Egr1 could confer radioprotection. Mice pretreated with MMA
prior to irradiation showed significantly less apoptosis in the intestine than mice treated with vehicle.
228 | P a g e
