Abstract 5690: Increased anti-tumor activity by novel systemic delivery and molecular targets of Tanshinone II A

Several chemoprevention clinical trials targeting high-risk individuals in the past have not been rewarding. One of the major problems for this apparent lack of success has been limited bioavailability of test agents given orally. On the other hand, chemotherapeutics administered intravenously in bolus doses result in undesirable large spikes in blood concentration. We have developed polymeric implants that can provide sustained release continuously (“24/7”). We embedded tanshinone IIA (Tan IIA), a diterpenoid naphthoquinone, found in the traditional Chinese medicine Danshen (Salvia miltiorrhiza), which is known for anti-tumor activity against several cancers. In this study we explored: i) a novel, implant system to deliver Tan IIA continuously in a xenograft model against cervical cancer; and ii) to elucidate molecular targets of Tan IIA in inhibiting growth of human cervical cancer cells. To determine anti-tumor activity, three groups of athymic nude mice were inoculated with human cervical cancer cells, CaSki cells. Two groups were treated with Tan IIA either intraperitoneally (0.7 mg/mouse, on alternate days) or by subcutaneous polycaprolactone implants (1 cm; 35 mg; 10% drug load); control animals received vehicle treatment. Eight weeks later, Tan IIA i.p. treatments resulted in 60% tumor growth inhibition; the growth inhibition was more pronounced with polymeric implants (75%). Notably, the effective dose of Tan IIA by the implant route was over 30-fold lower than the traditional i.p. route. CaSki cells were tested in vitro for cytotoxicity and to elucidate molecular mechanisms behind anti-proliferative activity of Tan IIA. Tan IIA demonstrated a dose- and time-dependent inhibitory effect on cell growth, with IC50 of 4.6 µM. Morphological changes of apoptosis induction was detected through EB/AO staining. Annexin V/PI double staining by flow cytometry revealed dose-dependent increase in early and late apoptotic cells with Tan IIA treatment. Cell-cycle studies suggested S-phase arrest of cells leading to apoptosis. Western-blot analysis demonstrated that Tan IIA modulated expressions of target molecules for apoptosis such as PARP cleavage, caspase-3 activation, Bcl-2 down regulation, Bax, p53 and p21(WAF1/CIP1) up regulation. We also found that Tan IIA treatment dose-dependently down regulated expression of HPV16-associated E6 and E7 oncoproteins that are linked with degradation of p53 and pRB, respectively. In summary, our data show that Tan IIA is highly potent for the prevention and treatment of cervical cancer. Our data also demonstrate for the first time that the novel polymeric implant device can enhance the efficacy by increasing the bioavailability, lowers the effective dose substantially, and challenges the existing paradigm of chemopreventive/chemotherapeutic approaches. (Supported from CA-118114, CA-125152 and Agnes Brown Duggan Endowment). 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 5690.