Abstract 271: Influence of autophagy modulation on synergistic interactions of lapatinib and mTOR targeted agents in HER2-amplified lapatinib resistant breast cancer models in vitro and in vivo

Background: Resistance against HER2 targeted agents ultimately limits the therapeutic success in patients with HER2-positive breast cancer. It was shown that PIK3CA mutations contribute to lapatinib resistance and achieving control of a downstream PI3K/mTOR signaling is necessary for optimal effectiveness of HER2 blockade. We and others have shown that catalytic mTORC1/2 inhibitors reverse lapatinib resistance and inhibit growth of HER2-overexpressing breast cancer models in vitro and in vivo. However, activity of these targeted agents is hindered by the compensatory and adaptive mechanisms that arise to assure cell survival. One of the pro-survival responses is cytoprotective autophagy induced by lapatinib and mTORC1/2 inhibitors. Thus, we examined whether impairing autophagy could augment activity of lapatinib/mTORC1/2 inhibitors combinations in lapatinib-resistant breast cancer models. Methods: The combination of lapatinib with catalytic mTORC1/2 inhibitors KU-0063794 (KU) or AZD2014 (AZD) was evaluated in vitro and in vivo in lapatinib resistant PIK3CA mutated HER2-overexpressing/amplified MDA-MB-361, JIMT-1 and MDA-MB-453 breast cancer models in the presence of siRNA-based (Atg7, Beclin-1) and pharmacological (hydroxychloroquine (HCQ)) inhibitors of autophagy. Results: In vitro lapatinib/mTORC1/2 combinations elevated autophagy to a greater extent that either compound alone. Genetic or pharmacological inhibition of treatment-induced autophagy further decreased cell viability, suggesting that autophagy was playing a cytoprotective role in this context. In vivo, lapatinib and AZD combinations achieved effective tumor growth inhibition of 98%, 111% and 152% in MDA-MB-361, JIMT-1 and MDA-MB-453 models respectively, however addition of HCQ did not significantly enhance this therapeutic response (p>0.05). Conclusion: Negligible effects of HCQ in vivo in tumors treated with lapatinib/AZD combinations may be attributed to ineffective inhibition of autophagy-mediated survival signals that, if significantly blocked, could increase efficacy of the treatment. Utilizing carrier nanotechnology to optimize delivery of HCQ to the tumor site and molecular analysis of HCQ-engendered off target effects on survival and proliferation pathways in tumor tissue are being pursued.

Citation Format: Wieslawa H. Dragowska, Sherry A. Weppler, William Wei Chu, Norman S. Chow, Jenna S. Rawji, Ashleen S. Prasad, Karen A. Gelmon, Sharon M. Gorski, Marcel B. Bally. Influence of autophagy modulation on synergistic interactions of lapatinib and mTOR targeted agents in HER2-amplified lapatinib resistant breast cancer models in vitro and in vivo. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 271.

Abstract 1334: Lipid-based nanoparticulate hydroxychloroquine (HCQ) formulations for use in combination with autophagy inducing drugs for treatment of breast cancer

Many targeted and broad spectrum anticancer drugs used to treat breast cancer trigger survival responses exemplified by the induction of cytoprotective macroautophagy (autophagy). Previously, we and others have shown that the anti-malarial agent hydroxychloroquine (HCQ) can improve the effects of anticancer drugs by inhibiting autophagy when used in high concentrations (1-20 μM). These levels are difficult to attain in vivo, thus, we developed novel liposomal formulations of HCQ (L-HCQ) designed to maintain therapeutic concentrations in plasma and tumor sites over extended periods of time.

Liposomes (1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and cholesterol (CHOL) (55:45 molar ratio)) were prepared by extrusion to exhibit a mean particle size of 100 ± 20 nm. Copper HCQ complexation or ammnonium sulphate methods were used for loading HCQ into liposomes achieving >99% encapsulation efficiency (HCQ to lipid ratio: 0.22 ± 0.02 (mol:mol)). In vitro stability studies indicated that more than 80% of the liposomal associated HCQ was retained in the formulation for at least 24 h at 37 °C. In vivo pharmacokinetic studies, demonstrated that free HCQ was eliminated from the plasma compartment within 30 minutes following i.v. injection while the L-HCQ formulations maintained significantly higher plasma HCQ levels (>100 μM) over 24 h regardless of the loading method. Tolerability studies in non-tumor bearing CD1 mice showed no signs of toxicity following single and multiple doses (3 x week, i.v., 75 mg/kg). Inhibition of autophagy in vivo was examined in liver, heart and pancreas tissues of C57B1/6 mice 6 h after dosing with L-HCQ or free HCQ in combination with the autophagy inducing drug rapamycin. The results show that L-HCQ inhibited rapamycin-induced autophagy more effectively than free HCQ, as evident by a significant increase in LC3-II levels in all the examined tissue. Finally, the efficacy of L-HCQ alone (3 x week, i.v., 60 mg/kg) or in combination with the autophagy promoting drug gefitinib, an EGFR tyrosine kinase inhibitor (5 x week, oral gavage, 100 mg/kg), was tested in the JIMT-1 breast cancer xenograft model (s.c.) established in Rag2M mice. After four weeks of treatment, there were no significant differences in tumor volume between untreated and L-HCQ or gefitinib alone treated animals (p>0.05). In contrast, the gefitinib and L-HCQ combination engendered a significant inhibition of tumor growth compared to untreated controls (p<0.05). Moreover, molecular analysis confirmed inhibition of gefitinib-induced autophagy in vivo by L-HCQ, as judged by increased LC3-II and p62 protein levels in tumor tissue.

In summary, this study established that L-HCQ was able to inhibit autophagy and improved sensitivity in an in vivo model of breast cancer treated with gefitinib.

Citation Format: Jagbir Singh, Wieslawa H. Dragowska, Malathi Anantha, Ashleen S. Prasad, Jenna S. Rawji, Norman S. Chow, Marcel B. Bally. Lipid-based nanoparticulate hydroxychloroquine (HCQ) formulations for use in combination with autophagy inducing drugs for treatment of breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1334.

Induction of autophagy is an early response to gefitinib and a potential therapeutic target in breast cancer

Gefitinib (Iressa(®), ZD1839) is a small molecule inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase. We report on an early cellular response to gefitinib that involves induction of functional autophagic flux in phenotypically diverse breast cancer cells that were sensitive (BT474 and SKBR3) or insensitive (MCF7-GFPLC3 and JIMT-1) to gefitinib. Our data show that elevation of autophagy in gefitinib-treated breast cancer cells correlated with downregulation of AKT and ERK1/2 signaling early in the course of treatment. Inhibition of autophagosome formation by BECLIN-1 or ATG7 siRNA in combination with gefitinib reduced the abundance of autophagic organelles and sensitized SKBR3 but not MCF7-GFPLC3 cells to cell death. However, inhibition of the late stage of gefitinib-induced autophagy with hydroxychloroquine (HCQ) or bafilomycin A1 significantly increased (p<0.05) cell death in gefitinib-sensitive SKBR3 and BT474 cells, as well as in gefitinib-insensitive JIMT-1 and MCF7-GFPLC3 cells, relative to the effects observed with the respective single agents. Treatment with the combination of gefitinib and HCQ was more effective (p<0.05) in delaying tumor growth than either monotherapy (p>0.05), when compared to vehicle-treated controls. Our results also show that elevated autophagosome content following short-term treatment with gefitinib is a reversible response that ceases upon removal of the drug. In aggregate, these data demonstrate that elevated autophagic flux is an early response to gefitinib and that targeting EGFR and autophagy should be considered when developing new therapeutic strategies for EGFR expressing breast cancers.