Folate-receptor mediated targeting of diagnostics and therapeutics to activated macrophages in inflammation

A subset of activated macrophages expressing a high affinity folate receptor (FR) has been identified as important mediators of inflammatory processes in many inflammatory diseases. The folate receptor has been exploited to specifically target diagnostics and therapeutics to the surface of these FR+ macrophages in diseases like rheumatoid arthritis, osteoarthritis, and lupus erythematosus. Here we explore further applications for folate targeting in inflammatory diseases. In Part I, we have developed a macrophage-based system for evaluating thepotency of folate-conjugated drugs in vitro. For this purpose, FR expression was inducedin the macrophage cell line RAW264.7 by continued culture in folate-deficient medium.The cell line was then used to evaluate the anti-inflammatory properties of a newlysynthesized folate-drug conjugate, folate-didemnin B. Folate-didemnin B showed increased cytotoxic and anti-inflammatory activities by inhibiting the synthesis of proteins and TNF-α with nanomolar IC 50 only when internalized through the FR pathway. Thus, it seems to be a promising anti-inflammatory drug candidate. In Part II, we examine the targeting of FR+ macrophages in inflammatory diseases. We use the folate-radionuclide EC20-99mTc, and the folate-NIR dye folate-DyLightTM680, as diagnostics in the apoE-/- murine model of atherosclerosis. Both folate-conjugates accumulate in atherosclerotic lesions by specific targeting of the FR+ macrophage and were used for in vivo imaging of atherosclerosis. We also analyzed the efficacy of folate-DNP and folate-TNP, both folate-hapten conjugates, for their use in immunotherapy of adjuvant-induced arthritis in rats. Treatment of arthritic rats with both folate-haptens promoted a decrease in the severity of the symptoms of arthritis, presumably by elimination of FR+ macrophages present in inflammation sites. Finally, targeting of EC20-99mTc was also examined for imaging inflammation in lung transplant rejection. Specific accumulation of the radionuclide was observed in the transplanted lung of rats that were undergoing a rejection process. All of the data presented shows the versatility of folate-targeting of macrophages for the diagnosis and therapy of macrophage-mediated inflammatory processes