The effects of pentoxifylline (PTX), a drug commonly used for vascular disorders in humans, on the <tex-math>$p{\rm O}_{2}$</tex-math> in SCK tumors of A/J mice and FSa-II tumors of C3Heb/FeJ mice as well as on the radioresponse of SCK tumors were investigated. When the host mice were injected intraperitoneally (ip) with 5 mg/kg PTX, the tumor <tex-math>$p{\rm O}_{2}$</tex-math> increased slowly, peaked 20-50 min postinjection, and returned to its original level in 70-90 min. The magnitude of the increase in tumor <tex-math>$p{\rm O}_{2}$</tex-math> varied markedly depending on the site and tumors. The magnitude of the changes in tumor <tex-math>$p{\rm O}_{2}$</tex-math> after an ip injection of 25 or 50 mg/kg PTX was similar to that caused by 5 mg/kg PTX, but the <tex-math>$p{\rm O}_{2}$</tex-math> tended to remain elevated longer with the higher dose of PTX. When the A/J mice bearing SCK tumors in the legs were injected ip with 50 mg/kg PTX and the tumors were X-irradiated 20 min later, the radiation-induced growth delay of the tumors was greater than that caused by X irradiation alone. The present study demonstrated that PTX is potentially useful for increasing the <tex-math>$p{\rm O}_{2}$</tex-math> and the radioresponse of human tumors.

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