Evidence for an immune component in the enhancement of tumor growth delay with x-ray/fluosolda/oxygen breathing combination therapy

When Fluosol-DA (FDA) (0.3 ml) and 95% oxygen breathing (O/sub 2/) was maintained in 1 hr prior to and during x-ray therapy, dose modifying, factors (DMF's) up to 2.5 were observed in the Lewis lung tumor. If O/sub 2/ and radiation (20 Gy) were delivered 24 hrs after FDA, an even greater DMF (3.1) was observed. When animals wre pretreated with carageenan (a specific macrophage inhibitor) DMF's in Lewis lung tumor-bearing animals after treatment with FDA/O/sub 2//x-irradiation ranged from 1.6-1.8. When O/sub 2/ and radiation (20 Gy) were delivered 24 hrs after FDA, no enhancement in DMF was observed in carageenan pretreated animals. These results indicate that FDA may act as a macrophage activating substance as well as an oxygen carrier. Peritoneal exudate (PE) cells induced by a bolus of starch i.p. were isolated from normal mice treated with FDA with or without O/sub 2/. Cytostasis toward EMT6 cells in vitro was measured. Ratios of effector to target cells ranged from 20:1 to 0.5:1. With FDA/O/sub 2/ the percent cytostasis was 75-55%, with FDA/air it was 60-45?% and with O/sub 2/ or air alone it was 25-2%. Thus, FDA activated PE cells. These data provide evidence for a possible secondary mechanism of FDA action