Induction of intratumoral tumor necrosis factor by a synthetic lipid A analog, ONO-4007, with less tolerance in repeated administration and its implication in potent antitumor effects with low toxicity

To evaluate the anti-tumor characteristics of ONO-4007, a synthetic analog of lipid A, the authors examined its acute toxicity and anti-tumor activity in a mouse MM46 mammary tumor system in comparison with LA-15-PP, an E. coli-type synthetic lipid A and LPS. Systemic and local (tumor site) induction of tumor necrosis factor (TNF) by a single i.v. shot of ONO-4007 and LA-15-PP correlated with manifestation of their toxicity, showing that ONO-4007 is 100-fold less effective than LA-15-PP. However, a protocol of repeated administration (3 shots twice a week) exhibited about 10 times more therapeutic potency of ONO-4007 for cancer therapy than expected in the above experiments. In a dose inducing submaximal systemic and intratumoral TNF production, repeated injections (twice a week) of ONO-4007 (10 mg/kg), LA-15-PP (0.1 mg/kg) and LPS (0.1 mg/kg) commonly generated a tolerant state in the systemic response (serum and liver) to subsequent stimulation. The intratumoral response was retained with this repeated administration of ONO-4007, but was not with LA-15-PP or LPS. TIM (tumor-infiltrating macrophages) isolated from mice pre-injected with ONO-4007 and LA-15-PP were found to lose their response to both substances, but the response was rapidly recovered until 72 h after injection and virtually no difference was observed in their response to either drug. The in vitro treatment of naive TIM with ONO-4007 or LA-15-PP for 2 h depressed the response to both substances and the depression continued for 72 h even in culture with fresh medium. The relatively high efficacy of ONO-4007 in cancer therapy likely depends on the retraction of the tolerant state, especially at the tumor site where the response to ONO-4007 is recovered much more efficiently than that to lipid A. While constant recruitment of macrophages to tumor tissue might be involved in the difference of tolerance recovery between this region and others, selective response to ONO-4007 may not be explained simply by the sensitivity of recruited TIM. Pharmacokinetical experiments revealed that repeated injections of LA-15-PP enhanced its clearance from blood circulation, while the clearance of ONO-4007 was stable after repeated injections. Thus, pharmacokinetical properties of ONO-4007 may also possibly be implicated in this event.