Enhancement of radiation response of prostatic carcinoma by lonidamine

Potential application of Ionidamine (LND) to enhance radiation toxicity in prostate cancer was investigated using human prostate cancer cell lines and a rat tumor model (Dunning MAT LyLu). LND alone was cytotoxic with 50% inhibition concentration (IC₅₀) between 0.5 and 0.8 mM. Preincubation with LND increased clonogenic toxicity of radiation. The sensitizer enhancement ratio was 1.8 to 2.2, depending on the cell line tested and it was consistent with inhibition of repair from potentially lethal damage. LND had limited effect in vivo on the Dunning model, consistent with its in vitro effect on the same cell line. LND did not alter the primaiy growth of the tumor. Fractionated irradiation caused a 40% decrease in tumor growth. LND injection (50 mg/kg) before fractionation did not cause any further decrease in tumor growth. Radiation dose fractionation and the combination treatment significantly reduced tumor metastasis in lungs.