Objective: We have developed an efficient nanobipolymer drug delivery system Polycefin based on natural-derived biodegradable, non-toxic and non-immunogenic polymalic acid (PMLA) platform. We have shown that Polycefin was able to block brain tumor growth and angiogenesis. Our goal is to engineer the new Polycefin variant for systemic (I.V.) treatment of HER2-positive breast tumors in order to enhance the efficacy of trastuzumab/Herceptin®.

Materials and Methods: For in vitro and in vivo treatment, we used (1) Herceptin, (2) Antisense oligonucleotides (AON) to HER2/neu, (3) three versions of Polycefin carrying either (3a) Herceptin alone, (3b) anti-mouse (M) and anti-human (H) transferrin receptor antibodies and AON (P-AON-TfRM+H), (3c) combination of Herceptin, anti-mouse TfR, and AON (P-AON-Herceptin-TfRM), and (4) PBS as a control. Anti-mouse TfR antibody mediated polymer transcytosis through tumor vascular endothelial cells, and Herceptin (and anti-human TfR) ensured polymer binding and internalization by tumor cells. HER2 overexpressing (BT-474, SKBR-3) and HER2 low-expressing (MDA-MB-231, MDA-MB-435) breast cancer cells were used to evaluate cell viability in vitro after treatments. Western blot analysis of cell lysates upon various treatments was used to detect HER2, phosphorylated Akt, and cleaved PARP expression. For in vivo study, BT-474 cells were inoculated S.C. into nude mice. Drugs were injected I.V. and tumor size was measured. For Polycefin distribution, drugs labeled with Alexa Fluor 680 were I.V. injected and tumors and major organs were harvested in 24 hours. Drug accumulation was analyzed by Xenogen IVIS 200 imager and subsequent confocal microscopy.

Results: Polycefin variant P-AON-Herceptin-TfRM (3c) inhibited tumor cell growth in vitro significantly more than Herceptin (P<0.01 for HER2 overexpressing cells and P<0.02 for HER2 low-expressing cells). It also displayed a stronger inhibition of HER2 expression and Akt phosphorylation leading to apoptosis (cleaved PARP increase by Western blot analysis) than Herceptin alone or any other Polycefin variant (3a or 3b). In vivo imaging revealed that drug accumulation was markedly enhanced in tumors treated with P-AON-Herceptin-TfRM (3c) compared to other treatments. The same Polycefin version P-AON-Herceptin-TfRM (3c) produced the strongest reduction of tumor size compared to PBS or Herceptin (P<0.001).

Summary: The leading version of nanobioconjugate with covalently attached combination of TfRM, Herceptin (anti-HER2 antibody) and anti-HER2 AON showed significant anti-tumor effect on HER2-positive breast cancer by enhancing tumor targeting, inhibition of HER2 synthesis and signaling, as well as suppression of tumor growth as compared with Herceptin treatment alone. The new version of nanoconjugate Polycefin could be promising next generation therapy for HER2-positive breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3854.