Practice question

Abzyme-directed enzyme prodrug therapy ADEPT-like strategy employs two-step approach achieving localized drug activation minimizing systemic exposure toxicity. First step abzyme engineered single-chain variable fragment fused tumor-targeting antibody anti-CEA or anti-HER2 or PEGylated enhancing permeability retention leaky tumor vasculature poor lymphatic drainage accumulates tumor interstitium reaching micromolar concentration while blood levels decline rapidly clearance liver kidney. Abzyme remains enzymatically active non-toxic alone because mammalian substrates lacking scissile bond recognized or catalytic efficiency insufficient endogenous esters avoiding off-target damage. Second step after 24-48h clearance interval reducing circulating abzyme inert prodrug administered IV designed ester carbonate carbamate amide derivative cytotoxic agent para-hydroxybenzyl nitrogen mustard alkylating DNA crosslinks doxorubicin intercalating topoisomerase II inhibitor auristatin microtubule inhibitor protected moiety cleavable only abzyme active site requiring specific arrangement transition state. Prodrug circulates without activity blocked pharmacophore but at tumor site abzyme hydrolyzes protecting group releasing active drug concentrations exceeding cytotoxic threshold locally 10 uM achieving high tumor to plasma ratio 100:1 sparing rapidly dividing marrow intestinal epithelium. pH substrate specificity engineered avoiding activation serum esterases paraoxonase. Preclinical xenograft models increased therapeutic index 10-100 fold compared conventional chemotherapy due spatial restriction.