Response to radioimmunotherapy correlates with tumor pO(2) measured by EPRoximetry in human tumor xenografts

The efficacy of radiation treatment depends upon local oxygen concentration . We postulated that the variability in responsiveness of tumor xenografts to a fixed dose of radioimmunotherapy might be related to the tumor pO(2) a t the time that radioimmunotherapy was administered. We evaluated the growt h of xenografts of CALU-3 tumors, a non-small cell lung carcinoma, in respo nse to an 8.9-MBq dose of I-131-RS-7-anti-EGP-1 and correlated tumor growth rate with initial tumor pO(2) measured by EPR oximetry. The greatest growt h delay in response to radioimmunotherapy had the highest initial pO(2). an d the fastest-growing tumors had the lowest initial pO(2). We then determin ed the dynamic effect of radioimmunotherapy on tumor pO(2) by serial measur ements of pO(2) for 35 days after radioimmunotherapy. This information coul d be important for ascertaining the likelihood that a tumor will respond to additional doses as part of a multiple dose scheme. Serial tumor pO(2) mea surements may help identify a window of opportunity when the surviving tumo r regions will be responsive to a second round of radioimmunotherapy or a s econd therapeutic modality such as chemotherapy or an antivascular agent. A fter radioimmunotherapy, there was an increase in tumor pO(2) followed by a decrease below initial levels in most mice. Thus defined times may exist w hen a tumor is more or less radiosensitive after radioimmunotherapy. (C) 20 01 by Radiation Research Society.