Abstract 3074: Targeting sanctuary sites of cancer: Novel approaches to treatment of lung localized tumors
Authors: Zielinski Rafal , Grela Krzysztol , Zuniga Roberto Cardena , Kang Yaan , Skora Stanislaw , Felix Edward , Tuchalska-Czuron Julia , Fokt Izabela , Priebe Waldemar 
Published: September 2020

The lung is one of the most common sites of cancer metastasis. We hypothesize that the lack of effective chemotherapeutics for lung localized tumors might in part be due to the lungs acting as a sanctuary site for cancer cells. To identify more effective anticancer therapies, we focused on the discovery and development of drugs reaching tumor sanctuaries either by design and synthesis of novel drugs, use of a compatible delivery system or a combination of both. To test our hypothesis and develop a novel approach to eliminate cancer sanctuary sites we focused on anthracycline antibiotics, specifically on the therapeutic limitations of doxorubicin (DOX). We have developed Annamycin (ANN), a novel, non-cardiotoxic DOX analog formulated in multilamellar liposomes (L-ANN) with high activity against multidrug resistant (MDR) cancer cells and an organ distribution dramatically different from that of DOX. L-ANN is currently in multicenter Phase I clinicals studies.

Objective: The objective of our study was to confirm high uptake and retention of free ANN in lungs, demonstrate the same for L-ANN, and to assess the efficacy of L-ANN in lung metastatic cancer models.

Methods: Pharmacokinetics and biodistribution of ANN were tested using LC/MS/MS in naïve CD-1 mice after intravenous administration of the drug. In vitro activity of ANN was analyzed in different human and murine cancer cells. Cellular uptake and subcellular distribution of ANN was assessed using fluorescent microscopy and FACS. Efficacy of L-ANN was tested in CT26 colon and 4T1 triple negative breast cancer lung metastatic mouse models.

Results: Biodistribution experiments showed high levels of ANN in lung tissue either for free or L-ANN that exceeded that in plasma by 7 to 10 fold. ANN levels in lungs were also more than 6-fold greater than that of DOX. In addition, on a cellular level, immunofluorescence and FACS analysis demonstrated significantly higher uptake of ANN than that of DOX, as well as potent induction of double-strand DNA breaks. ANN showed consistently high cytotoxicity across all tested cell lines including MDR cells with IC50s in the low nanomolar range. Based on bioluminescent imaging in models of lung localized cancers, L-ANN displayed high antitumor activity ranging from inhibition of tumor progression to complete tumor eradication. Importantly, the delay in tumor growth and, in some cases, tumor regression led to significant improvement of survival in all tested models.

Conclusion: The high cytotoxic potency of ANN against MDR cancer cells is related, in part, to its ability to overcome ABC transporter-mediated efflux and, in contrast to DOX, achieve high intracellular uptake. A greatly increased concentration of ANN in the lung, as compared to DOX, leads to high drug efficacy in vivo in lung-localized tumor models. In summary, our studies (1) support the hypothesis of lungs being a sanctuary site for cancer cells and (2) demonstrate that effective targeting of cancers metastatic to the lung is possible by chemical modification of clinically used but currently ineffective drugs, especially in combination with appropriate drug delivery. In more general terms, these studies indicate that the proposed approach can also lead to the identification and elimination of cancer sanctuary sites other than the lungs and creation of more effective anticancer therapies.

Citation Format: Rafal Zielinski, Krzysztol Grela, Roberto Cardena Zuniga, Yaan Kang, Stanislaw Skora, Edward Felix, Julia Tuchalska-Czuron, Izabela Fokt, Waldemar Priebe. Targeting sanctuary sites of cancer: Novel approaches to treatment of lung localized tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3074.