Supp. Figure 1 MM-302 and trastuzumab co-localize in BT474-M3 xenograft tumors. Supp. Figure 2 In vivo deposition of MM-302 is specifically increased by trastuzumab or T-DM1. Supp. Figure 3 Pharmacokinetics (PK) of MM-302 remains the same with or without co-administration of trastuzumab. Supp. Figure 4 Combination of MM-302 and trastuzumab demonstrates synergistic anti-tumor activity in models of HER2-positive breast and gastric cancer.
ARTICLE ABSTRACTTrastuzumab is the standard of care for HER2-positive breast cancer patients, markedly improving disease-free and overall survival. Combined with chemotherapy, it enhances patient outcomes, but cardiotoxicity due to the trastuzumab treatment poses a serious adverse effect. MM-302 is a HER2-targeted PEGylated liposome that encapsulates doxorubicin to facilitate its delivery to HER2-overexpressing tumor cells while limiting exposure to nontarget tissues, including the heart. In this study, we evaluated the feasibility and preclinical activity of combining MM-302 with trastuzumab. MM-302 and trastuzumab target different domains of the HER2 receptor and thus could simultaneously bind HER2-overexpressing tumor cells in vitro and in vivo. Furthermore, trastuzumab did not disrupt the mechanism of action of MM-302 in delivering doxorubicin to the n0ucleus and inducing DNA damage. Reciprocally, MM-302 did not interfere with the ability of trastuzumab to block prosurvival p-Akt signaling. Interestingly, coadministration of the two agents acutely increased the deposition of MM-302 in human xenograft tumors and subsequently increased the expression of the DNA damage marker p-p53. Finally, the combination of MM-302 and trastuzumab induced synergistic antitumor activity in HER2-overexpressing xenograft models of breast and gastric cancer. Collectively, our findings highlight a novel combination therapy that efficiently targets HER2-overexpressing cells through multiple mechanisms and support the ongoing investigation of combined MM-302/trastuzumab therapy for HER2-positive metastatic breast cancer in a randomized phase II clinical trial. Cancer Res; 76(6); 1517–27. ©2016 AACR.