X-ray affinity and photoaffinity inhibitor of aldose reductase

A reversible affinity inhibitor of rat lens aldose reductase (RLAR), that can be transformed into an irreversible inhibitor by low doses of X-rays or by exposure to light, has been synthesized and characterized. The inhibitor consists of quercitrin, a reversible receptor binding moiety, that is connected through a hexanediamine spacer to an azido containing moiety which becomes chemically reactive when irradiated. This reagent, N-(2-nitro-4-azidophenyl)-hexamethylenediamine-N'-(3'-O-quercit rin), (NAP-HEX-Q), represents a new class of affinity agents which have potential applications as target-entrapped drugs. The KI's for quercitrin and NAP-HEX-Q, both non-competitive inhibitors, are 0.6 uM and 0.5 uM, respectively. Rates are calculated from the tangent of the angle of descent of the linear absorbance vs time plots, measured simply and rapidly with a protractor. Irreversible inhibition of RLAR by NAP-HEX-Q, as a function of the dose of irradiation with either X-rays or light, is consistent with apparent first order kinetics. NAP-HEX-Q is designed as a drug to prevent or reverse diabetic cataract formation by selective photoaffinity inhibition of RLAR with no significant effect on aldose reductase in other tissues. However, when not accessible to light, other potential target-entrapped drugs can be activated by low doses of X-rays at their targeted anatomic sites.