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The tumor inhibitory and radiomodifying effects of plumbagin (Pl), a naphthoquinone isolated from Plumbago rosea, on mouse Ehrlich ascites carcinoma was studied. Tumor response was assessed by increase in life span (% ILS) and animal survival at 120 days. The acute LD 50 of plumbagin in normal mice was 9.4 mg/kg body weight. Single doses from 2 to 6 mg/kg Pl, given intraperitoneally (i.p.), produced inhibition of exponentially growing tumors. However, increases in dose above 3 mg/kg did not increase 120 day survival significantly over that produced by 3 mg/kg. Multiple dose treatment, starting from 24 h after tumor cell inoculation, showed that a total dose of 9 mg/kg, administered in three fractions of 3 mg/kg, once daily, gave the maximum %ILS and tumor free survival. Combination of radiation (RT, 7.5 Gy to the abdomen) after the first Pl dose (1-3mg/kg/fraction) synergistically increased mouse survival at 120 days. The tumor inhibitory effect was less pronounced when treatment was started at more advanced tumor stages, but combination of low dose fractions (2.5 or 3 mg/kg/fraction) with RT enhanced the %ILS and animal survival. Higher dose fractions in combination with radiation were not tolerated by the mice. DNA appears to be the likely target of Pl cytotoxicity; the mechanism of interaction of Pl + RT in enhancing tumor response is not clear.

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