Aplidin as a potential adjunct to radiation therapy: in vitro studies.
OBJECTIVE
Aplidin (plitidespin) is a novel cyclic depsipeptide, currently in Phase II clinical trials for solid and hematologic malignancies. We examined the effects of oxygen on the cytotoxicity of Aplidin and the interactions between Aplidin and radiation. These factors will be important if Aplidin is used clinically in combination with radiotherapy.


METHODS
Exponentially-growing EMT6 mouse mammary tumour cells in monolayer cultures were treated with Aplidin and 250 kV X-rays.


RESULTS
The cytotoxicity of Aplidin was not altered either by incubation in moderate hypoxia before and during a 24 h drug treatment or by incubation in severe hypoxia before and during a 2 h drug treatment. Treatment with Aplidin plus radiation produced cytotoxicities compatible with additive or supraadditive cytotoxicities. Cells treated with 1 microM Aplidin for 24 h then killed by 100 Gy of radiation were toxic to untreated cells co-cultured with them.


CONCLUSIONS
The cytotoxicity of Aplidin is independent of the oxygenation during treatment. Aplidin, or an active metabolite of Aplidin, is retained in the cells and later released as the radiation-sterilised cells die, producing a Bystander effect that kills neighbouring cells. This Bystander effect could affect the outcome of therapeutic regimens combining Aplidin and radiation.
Rockwell
Sara
S
Department of Therapeutic Radiology,Yale Comprehensive Cancer Center, Yale University School of Medicine, New, Haven, Connecticut 06520-8040, USA. sara.rockwell@yale.edu
Liu
Yanfeng
Y
D000818:Animals; D024201:Bystander Effect; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D047630:Depsipeptides / Q000494:pharmacology*; D051379:Mice; D009369:Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D010456:Peptides, Cyclic; D011836:Radiation Tolerance
D047630:Depsipeptides; D010456:Peptides, Cyclic; C098980:plitidepsin