Abstract LB-061: HER2-targeted PEGylated liposomal doxorubicin (MM-302) efficiently targets the HER2 intermediate cell population in vitro and in vivo

Abstract

Introduction: MM-302 is an antibody-liposomal drug conjugate designed specifically to target doxorubicin to HER2-overexpressing tumor cells. MM-302 is currently being evaluated in a Phase II trial in HER2 positive metastatic breast cancer (NCT02213744). HER2-positive breast cancer accounts for about 15-20% of breast cancer cases and is defined as IHC 3+ or 2+ and HER2 FISH amplified. A substantial percentage (∼30%) of breast cancer patients show positive HER2 IHC (1+/2+) without HER2 gene amplification (“HER2 intermediate”). This population is not eligible for treatment with currently approved HER2-targeted therapies. The purpose of this study is to investigate the in vitro and in vivo delivery/activity of MM-302 in the HER2 intermediate population. Methods: In vitro binding and viability studies were performed with MM-302, PEGylated liposomal doxorubicin (PLD) and T-DM1 with a panel of cell lines representing a range of HER2 expression. HER2-mediated cellular delivery of MM-302 was investigated in vivo in different HER2 expressing tumor models using a novel PEG immunofluorescent assay herein described. Frozen tumor tissues were stained for PEG, HER2 and cytokeratin, side-by-side with two cell standard arrays: A PEG array, obtained by cell incubation with increasing concentrations of MM-302, and a HER2 array, built with a panel of cell lines at different HER2 expression (from ∼50,000 to over 1,000,000 HER2). Image analysis and subsequent regression of the PEG and HER2 fluorescent intensities from the respective standards allowed for the quantification of the number of liposomes in individual tumor cells at distinct HER2 receptor numbers. Tumor cell apoptosis following MM-302 cellular delivery was measured by immunofluorescence followed by image analysis. Results: MM-302 efficiently bound to, and induced, tumor cell death across a panel of cell lines, with no significant distinction between cell lines expressing 300-400,000 HER2 or above 1,000,000 HER2 (IHC 3+). Conversely, T-DM1, used as control, significantly bound to and induced cell death only to cells above 1,000,000 HER2 (IHC 3+). In vivo evaluation of HER2-mediated cellular delivery via PEG immunofluorescent staining showed that MM-302 can be equally efficiently internalized in tumor cells above 1,000,000 HER2 (IHC 3+) and in the HER2 intermediate expression range. Preliminary analysis on post-treatment patient biopsies collected during a MM-302 Phase I study (NCT01304797) support clinical translation of these preclinical observations. Conclusions: Treatment with MM-302 results in efficient HER2 binding and liposome cellular delivery across a panel of HER2 models that extend beyond the traditional HER2 positive definition. This study suggests that MM-302 may be a promising candidate for the treatment of patients with intermediate HER2 expression who represent a significant unmet medical need. Citation Format: Elena Geretti, Christopher Espelin, Bambang Adiwijaya, Nancy Dumont, Silvia Coma, Zachary Koncki, Minh Pham, Gabriela Garcia, Troy Bloom, Victoria Rimkunas, Joe Reynolds, Karen Campbell, Victor Moyo, Istvan Molnar, Patricia LoRusso, Ian Krop, Kathy Miller, Cynthia Ma, Pamela Munster, Thomas Wickham. HER2-targeted PEGylated liposomal doxorubicin (MM-302) efficiently targets the HER2 intermediate cell population 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 LB-061.

Anti‐HER2 Immunoliposomes: Antitumor Efficacy Attributable to Targeted Delivery of Anthraquinone‐Fused Enediyne

“…Furthermore, a single administration of HER2‐TNM A‐ILs (0.02 mg kg −1 ) elicited a pronounced antitumor effect when compared with MM‐302 ILs, administered once every 7 days at 3 mg kg −1 for three doses. [ 12a ] The enhanced potency of the encapsulated enediyne TNM A compared with that of doxorubicin in MM‐302 may be a key contributing factor. Additionally, whether HER2‐TNM A‐ILs exhibit bystander effects, as reported for uncialamycin‐ADCs, in small‐cell lung cancer mouse models needs to be explored in the future.…”

“…For instance, MM‐302 ILs have been engineered to encapsulate ≈20000 molecules of doxorubicin within their cores in conjunction with 45 single‐chain anti‐HER2 antibodies. [ 12a ] TNM A is a potent antitumor antibiotic exhibiting efficacy within the picomolar to single‐digit nanomolar range. [ 19a ] Unlike widely used antitumor agents such as doxorubicin, with IC 50 values ranging from 60 to 390 n m against a broad spectrum of cancer cell lines, we postulated that TNM A‐encapsulated ILs may not necessitate large loading doses to achieve enhanced antitumor effects.…”

“…With the advancement of liposome‐based technology and the adaptable use of commercial monoclonal antibodies such as trastuzumab in the form of ILs, a promising avenue has emerged for translating these novel enediynes for cancer therapy. Despite the early development of ILs in the last century, [ 11,12,15 ] to the best of our knowledge, no ILs have been approved for treating human cancers. Only a relatively small percentage of the ILs likely reach the tumor sites via the EPR effect (Figure 4).…”

“…[ 11 ] Furthermore, the payloads in ILs currently undergoing clinical trials primarily comprise well‐established chemotherapeutic drugs such as doxorubicin, docetaxel, and oxaliplatin, with half‐maximal inhibitory concentrations (IC 50 ) largely falling within the nanomolar to micromolar range. [ 12a,14 ] In light of the successful development of approved ADCs, the inclusion of highly potent toxins, such as calicheamicin and camptothecin derivatives, may be instrumental in enhancing IL efficacy. [ 16 ] Notably, a recent setback in a phase II trial assessing anti‐epidermal growth factor receptor 1‐ILs loaded with doxorubicin as a first‐line therapy for advanced triple‐negative breast cancer further underscores the formidable challenges facing IL‐based antitumor therapy.…”

“…[ 11 ] For instance, PEGylated ILs carrying the anti‐HER2 antibody trastuzumab, such as MM‐302, have shown promise in the treatment of HER2‐overexpressing breast cancer by encapsulating the antitumor agent doxorubicin. [ 12 ] It is well‐established that PEGylation can extend the circulation time of ILs in the bloodstream, while trastuzumab enhances the therapeutic index of doxorubicin by enabling a more selective delivery. [ 13 ] Other ILs employ distinct antibodies (e.g., C225‐ILs‐DOX, MCC‐465, and 2B3‐101) to achieve targeted doxorubicin delivery, while ILs containing microtubule inhibitors, such as docetaxel, or DNA alkylation agents, such as oxaliplatin (e.g., MM‐310 or MBP‐426), are also in various stages of development.…”