Combined effect of para-aminobenzoic acid (PABA) and ionizing radiation in a syngeneic murine model of breast carcinoma.

3189 Background: PABA or p-amino benzoic acid is a water-soluble natural compound and a component of Vitamin B-12, thought to play a role in nucleotide base synthesis. It is widely available as a dietary supplement and is a common component of sunscreens. Previously, we observed that PABA enhanced the effects of radiation in B16F10 and G361 melanoma and Lewis Lung carcinoma in vitro, as well as in 4T1 breast carcinoma and B16F10 melanoma in a chick CAM in vivo model (ACR-NCI-EORTC, Nov. 2003). To further explore the role of PABA pre-clinically, we studied its effects as a radiosensitizer in the 4T1 syngeneic murine model of mammary carcinoma (Fred Miller, The Michigan Cancer Center). Methods: 4T1 tumor cells (5 x 104) were injected subcutaneously into the flank of BALB/C mice. Three days later, 28 mice were randomly assigned to PABA, administered daily for the duration of the experiment (1 mg/day), or no PABA treatment. At 14 days post-implantation, a randomization to radiation treatment (RT) occurred in ...