Targeting tumor angiogenic vasculature using polymer-RGD conjugates

Sites of neovascular angiogenesis are important chemotherapy targets. In this study, the synthesis, characterization, in-vivo imaging and biodistribution of a technetium-99m labeled, water-soluble, N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer carrying doubly cyclized Arg-Gly-Asp motifs (HPMA copolymer-RGD4C conjugate) are reported. In vitro endothelial cell adhesion assays indicated that HPMA copolymer-RGD4C conjugates inhibited αVβ3-mediated endothelial cell adhesion while HPMA copolymer Arg-Gly-Glu control conjugates (HPMA copolymer-RGE4C conjugate) and hydrolyzed HPMA copolymer precursor (HPMA copolymer) showed no activity. The scintigraphic images of prostate tumor bearing SCID mice obtained 24 h post-i.v. injection indicated greater tumor localization of HPMA copolymer-RGD4C conjugate than the control, HPMA copolymer-RGE4C conjugate. The 24-h necropsy radioactivity data showed that HPMA copolymer-RGD4C conjugate had significantly higher (p<0.001) tumor localization compared to HPMA copolymer-RGE4C conjugate and HPMA copolymer. Also, HPMA copolymer-RGD4C conjugates had sustained tumor retention over 72 h and reasonably efficient clearance from the background organs. These results suggest that specific tumor angiogenesis targeting is possible with HPMA copolymer-RGD4C conjugates. This construct provides a foundation that should support targeted delivery of radionuclides and drugs to solid tumors for diagnostic and therapeutic applications.