Abstract P2-15-03: Liposomal annamycin inhibition of lung localized breast cancer

Background and Rationale: Annamycin is an anthracycline antibiotic currently in clinical studies in AML patients. Our earlier studies showed that Annamycin is not cross-resistant with doxorubicin (DOX) and is a poor substrate for P-glycoprotein 1 (P-gp) [aka ATP-binding cassette sub-family B member 1 (ABCB1) or multidrug resistance protein 1 (MDR1)], a major mechanism of doxorubicin resistance in different types of cancer. Annamycin, in contrast to DOX, achieves relatively high levels of cellular accumulation, especially in multidrug resistant (MDR) cell lines, and induces significant DNA damage in MDR cancer cells. Clinically, Annamycin is administered in a liposomal formulation (L-Annamycin) the in vivo activity of which has been demonstrated in different tumor models. IND aimed preclinical studies revealed that in sharp contrast to DOX, Annamycin displays dramatically reduced to no cardiotoxicity. Subsequent pharmacokinetic and organ distribution studies revealed surprisingly high levels of Annamycin in lung tissue. Annamycin levels (AUC, 24 h) in lungs were over 10-fold greater than in plasma. In addition, when compared with DOX, lung levels of Annamycin were 6-fold higher than those achievable with DOX. Thus, studies aimed to assess efficacy of L-Annamycin in lung localized tumor models were initiated. Objective: The objective of this study was to assess the in vitro and in vivo activity of L-Annamycin in 4T1, a highly aggressive triple negative breast cancer (TNBC) lung colonization model. Methods: In vitro efficacy of Annamycin was investigated in a panel of TNBC cell lines including murine 4T1 and human MDA-MB 231, MDA-MB-468, BT20, and SUM149 cell lines. Uptake and subcellular distribution of Annamycin was assessed using fluorescent microscopy and FACS. Biodistribution of Annamycin was tested in naive CD-1 mice after intravenous administration of the drug. Efficacy of L-Annamycin was tested in a syngeneic TNBC lung model, specifically, in immune-competent Balb/c mice injected intravenously with 4T1 cells expressing firefly luciferase. Results: Annamycin shows consistently high cytotoxicity across all tested cell lines with IC50s in the low nanomolar range. Uptake analysis performed on 4T1 cells indicated significantly higher uptake of the drug as compared to DOX. Annamycin shows distinct subcellular distribution with high cytosolic deposition, while DOX was mostly confined to the nucleus. In vivo efficacy studies in mice treated with L-Annamycin showed significantly increased survival when compared to vehicle treated animals. Delayed tumor progression was assessed by bioluminescent imaging and correlated with increased survival. Conclusion: Our in vitro studies demonstrate the high potency of L-Annamycin in vitro and in vivo. Its unique intracellular uptake and distribution might in part be responsible for L-Annamycin’s activity profile and lack of cardiotoxicity. The observed high in vivo efficacy of L-Annamycin in an aggressive TNBC lung metastasis model coupled with consistently high accumulation of L-Annamycin in lung parenchyma, may prove to open new therapeutic options for patients with tumors metastatic to the lung. Citation Format: Rafal Zielinski, Krzysztol Grela, Stanislaw Skora, Izabela Fokt, Matthew Sander, Adam Didluch, Waldemar Priebe. Liposomal annamycin inhibition of lung localized breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-15-03.