Objective: To assess the efficacy of 3-bromopyruvate (3-BrPA), a strong alkylating agent that inhibits hexokinase and mitochondrial oxidative phosphorylation, resulting in decreased cellular ATP production, on rabbit VX2 tumor cells.
Methods: Adult New Zealand White rabbits were used for the study. The rabbit VX2 tumor was originally grown on the hind leg of a carrier rabbit for two weeks and then excised, minced in Hank's solution and 0.1-0.2 ml of tumor cells were directly implanted into the left lobe of six rabbit livers and allowed to grow for 14 days. After appropriate anesthesia, 25 ml of 0.5 mM 3-BrPA was injected in bolus form, over 2 minutes, into the left hepatic artery through a transcatheter approach, under fluoroscopic guidance. Additionally, embolization of the left hepatic artery was then performed in a similar manner, using a mixture of Ethiodol and polyvinyl alcohol. Animals treated identically but not receiving 3-BrPA served as controls. Four days later, the liver was harvested and normal tissue and tumors were fixed in 10% formalin, sliced at 5-mM intervals, embedded in paraffin, and then sliced into 4-um sections and stained with H & E. Tumor viability was assessed by visual inspection.
Results: Compared with controls which had nearly 100% viable cells, the tumors treated with 3-BrPA contained essentially no viable cells, in other words nearly 100% necrosis. A small number of viable cells were noted in a few localized areas near arteries feeding the tumors, and at the tumor periphery, where sinusoidal blood flow was available. No damage to the normal tissue surrounding the tumor was noted. These results were reproduced in several experiments. Statistical evaluation revealed that tumors untreated with 3-BrPA contained 74 ุ 5% viable cells, and those treated with a single injection of 3-BrPA decreased the number of viable cells to 16 ุ 5%. The only apparent damage was seen occasionally in the peribiliary arteriolar complexes at much higher concentrations of 3-BrPA (5mM).
Furthermore, the effect of embolization of the VX2 tumor on adjacent liver tissue was assessed in a separate group of similar rabbits. It was found that embolization alone of the left hepatic artery caused significant injury to surrounding tissue manifested by extensive amounts of nonviable tissue when examined histologically. Interestingly, tissue from nine other organ systems was evaluated histologically 4 days after intra-arterial injection of 3-BrPA and no injury was seen. However, secondary tumors were found in the lungs of all rabbits implanted with VX2 tumors, in both the treated and control groups. Systemic delivery of 25 ml, 0.5 mM 3-BrPA was then performed. Animal toxicity was then assessed. Interestingly, the control rabbits that had been harboring liver implanted VX2 tumors for 14 days and now were given 3-BrPA systemically through an ear vein, demonstrated no obvious tissue damage in nine different organ systems examined. Moreover, there was no killing effect on the liver tumors. However, the lung tumors, the largest of which were several millimeters in diameter, were markedly decreased in size or completely obliterated.
Conclusions: 3-BrPA, when given through intra-arterial injection into VX2 tumor cells, appears to be effective in killing the great majority of tumor cells without any collateral tissue damage. Additionally, when given systemically, this potent inhibitor of cellular ATP production significantly decreases the size of metastatic tumors to the lung, again without evidence of native tissue damage.