Caveolae-Mediated Endocytosis as a Novel Mechanism of Resistance to Trastuzumab Emtansine (T-DM1)

Development of a human immuno-oncology therapeutic agent targeting HER2: targeted delivery of granzyme B

Background

Immunotherapeutic approaches designed to augment T and B cell mediated killing of tumor cells has met with clinical success in recent years suggesting tremendous potential for treatment in a broad spectrum of tumor types. After complex recognition of target cells by T and B cells, delivery of the serine protease granzyme B (GrB) to tumor cells comprises the cytotoxic insult resulting in a well-characterized, multimodal apoptotic cascade.

Methods

We designed a recombinant fusion construct, GrB-Fc-4D5, composed of a humanized anti-HER2 scFv fused to active GrB for recognition of tumor cells and internal delivery of GrB, simulating T and B cell therapy. We assessed the construct’s antigen-binding specificity and GrB enzymatic activity, as well as in vitro cytotoxicity and internalization into target and control cells. We also assessed pharmacokinetic and toxicology parameters in vivo.

Results

GrB-Fc-4D5 was highly cytotoxic to Her2 positive cells such as SKBR3, MCF7 and MDA-MB-231 with IC₅₀ values of 56, 99 and 27 nM, respectively, and against a panel of HER2+ cell lines regardless of endogenous expression levels of the PI-9 inhibitor. Contemporaneous studies with Kadcyla demonstrated similar levels of in vitro activity against virtually all cells tested. GrB-Fc-4D5 internalized rapidly into target SKOV3 cells within 1 h of exposure rapidly delivering GrB to the cytoplasmic compartment. In keeping with its relatively high molecular weight (160 kDa), the construct demonstrated a terminal-phase serum half-life in mice of 39.2 h. Toxicity studies conducted on BALB/c mice demonstrated no statistically significant changes in SGPT, SGOT or serum LDH. Histopathologic analysis of tissues from treated mice demonstrated no drug-related changes in any tissues examined.

Conclusion

GrB-Fc-4D5 shows excellent, specific cytotoxicity and demonstrates no significant toxicity in normal, antigen-negative murine models. This construct constitutes a novel approach against HER2-expressing tumors and is an excellent candidate for further development.

miRNA profile obtained by next‑generation sequencing in metastatic breast cancer patients is able to predict the response to systemic treatments

Metastatic breast cancer (MBC) is a challenge for oncologists, and public efforts should focus on identifying additional molecular markers and therapeutic management to improve clinical outcomes. Among all diagnosed cases of breast cancer (BC; approximately 10%) involve metastatic disease; notably, approximately 40% of patients with early-stage BC develop metastasis within 5 years. The management of MBC consists of systemic therapy. Despite different treatment options, the 5-year survival rate is <20%, which may be due to a lack of response with de novo or acquired resistance. MicroRNAs (miRNAs or miRs) are promising biomarkers as they are readily detectable and have a broad spectrum and potential clinical applications. The aim of this study was to identify a miRNA profile for distinguishing patients with MBC who respond to systemic treatment. Patients with MBC were treated according to the National Comprehensive Cancer Network guidelines. We performed miRNA-Seq on 9 primary tumors using the Thermo Fisher Scientific Ion S5 system. To obtain global miRNA profiles, we carried out differentially expressed gene elimination strategy (DEGES) analysis between the responsive and non-responsive patients. The results identified a profile of 12 miRNAs associated with the response to systemic treatment. The data were validated in an independent cohort (TCGA database). Based on the results, the upregulation of miR-342-3p and miR-187-3p was associated with the response to systemic treatment, and with an increased progression-free survival (PFS) and overall survival (OS); by contrast, the downregulation of miR-301a-3p was associated with a higher PFS and OS. On the whole, the findings of this study indicate that these miRNAs may serve as biomarkers for the response to systemic treatment or the prognosis of patients with MBC. However, these data should be validated experimentally in other robust cohorts and using different specimens before implementing these miRNAs as biomarkers in clinical practice to benefit this group of patients.

Temporal Modulation of HER2 Membrane Availability Increases Pertuzumab Uptake and Pretargeted Molecular Imaging of Gastric Tumors

Human epidermal growth factor receptor 2 (HER2) is used as a tumor biomarker and therapeutic target. Pertuzumab is an anti-HER2 antibody, and its binding to tumor cells requires HER2 to be present at the cell membrane. However, the cellular distribution of HER2 protein in gastric tumors is dynamic, and HER2 internalization decreases antibody binding to tumor cells. These features preclude the use of pretargeted strategies for molecular imaging and therapy. We explored the pharmacological modulation of HER2 endocytosis as a strategy to improve pertuzumab uptake in HER2-positive gastric tumors and allow the use of a pretargeted imaging approach. Methods: We conducted in vitro and in vivo studies with NCI-N87 gastric cancer cells to determine how HER2 endocytosis affects pertuzumab binding to tumor cells. Lovastatin, a clinically approved cholesterol-lowering drug, was used to modulate caveolae-mediated HER2 endocytosis. Results: Administration of lovastatin to NCI-N87 cancer cells resulted in significant accumulation of non-activated HER2 dimers at the cell surface. Pretreatment of NCI-N87 cells with lovastatin increased in vitro specific accumulation of membrane-bound ⁸⁹Zr-labeled pertuzumab. Lovastatin-enhanced pertuzumab tumor uptake was also observed in NCI-N87 gastric cancer xenografts, allowing tumor detection as early as 4 h and high-contrast images at 48 h after tracer administration via PET. Temporal enhancement of HER2 membrane availability by lovastatin allowed imaging of cell surface HER2 with transcyclooctene-conjugated antibodies and ¹⁸F-labeled tetrazine. Conclusion: Temporal pharmacological modulation of membrane HER2 may be clinically relevant and exploitable for pretargeted molecular imaging and therapy in gastric tumors.

SORLA regulates endosomal trafficking and oncogenic fitness of HER2

The human epidermal growth factor receptor 2 (HER2) is an oncogene targeted by several kinase inhibitors and therapeutic antibodies. While the endosomal trafficking of many other receptor tyrosine kinases is known to regulate their oncogenic signalling, the prevailing view on HER2 is that this receptor is predominantly retained on the cell surface. Here, we find that sortilin-related receptor 1 (SORLA; SORL1) co-precipitates with HER2 in cancer cells and regulates HER2 subcellular distribution by promoting recycling of the endosomal receptor back to the plasma membrane. SORLA protein levels in cancer cell lines and bladder cancers correlates with HER2 levels. Depletion of SORLA triggers HER2 targeting to late endosomal/lysosomal compartments and impairs HER2-driven signalling and in vivo tumour growth. SORLA silencing also disrupts normal lysosome function and sensitizes anti-HER2 therapy sensitive and resistant cancer cells to lysosome-targeting cationic amphiphilic drugs. These findings reveal potentially important SORLA-dependent endosomal trafficking-linked vulnerabilities in HER2-driven cancers.

The EGF receptor HER2 is an oncogene protein thought to reside at the plasma membrane, but its endosomal trafficking is currently unclear. Here, the authors report that HER2 is endocytosed and that sortillin-related receptor 1 (SORLA) promotes endosomal HER2 recycling and HER2 oncogenic signalling.

Hexahistidine-metal assemblies: A promising drug delivery system

It is of considerable interest to construct an ideal drug delivery system (i.e., high drug payload, minimal cytotoxicity, rapid endocytosis, and lysosomal escape) under mild conditions for disease treatment, tissue engineering, bioimaging, etc. Inspired by the coordinative interactions between histidine and metal ions, we present the facile synthesis of hexahistidine (His₆)-metal assembly (HmA) particles under mild conditions for the first time. The HmA particles presented a high loading capacity, a wide variety of loadable drugs, minimal cytotoxicity, quick internalization, the ability to bypass the lysosomes, and rapid intracellular drug release. In addition, HmA encapsulation largely improved the antitumor ability of camptothecin (CPT) relative to free CPT. By capitalizing on these promising features in drug delivery, HmA will have great potential in various biomedical fields. STATEMENT OF SIGNIFICANCE: It is of considerable interest to construct an ideal drug delivery system (i.e., high drug payload, minimal cytotoxicity, rapid endocytosis, and lysosomal escape) under mild conditions. Inspired by the coordinative interactions between histidine and metal ions, we present for the first time the facile synthesis of Hexahistidine (His₆)-metal assembly (HmA) particles under mild conditions. The HmA particles exhibited a high loading capacity, a wide variety of loadable drugs, minimal cytotoxicity, quick internalization, the ability to bypass the lysosomes, and rapid intracellular drug release. By capitalizing on these promising features in drug delivery, HmA will have great potential in various biomedical fields.

Acquired Resistance to Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) combine the tumor selectivity of antibodies with the potency of cytotoxic small molecules thereby constituting antibody-mediated chemotherapy. As this inherently limits the adverse effects of the chemotherapeutic, such approaches are heavily pursued by pharma and biotech companies and have resulted in four FDA (Food and Drug Administration)-approved ADCs. However, as with other cancer therapies, durable responses are limited by the fact that under cell stress exerted by these drugs, tumors can acquire mechanisms of escape. Resistance can develop against the antibody component of ADCs by down-regulation/mutation of the targeted cell surface antigen or against payload toxicity by up-regulation of drug efflux transporters. Unique resistance mechanisms specific for the mode of action of ADCs have also emerged, like altered internalization or cell surface recycling of the targeted tumor antigen, changes in the intracellular routing or processing of ADCs, and impaired release of the toxic payload into the cytosol. These evasive changes are tailored to the specific nature and interplay of the three ADC constituents: the antibody, the linker, and the payload. Hence, they do not necessarily endow broad resistance to ADC therapy. This review summarizes preclinical and clinical findings that shed light on the mechanisms of acquired resistance to ADC therapies.

Caveolin-1: a multifaceted driver of breast cancer progression and its application in clinical treatment

Human breast cancer is one of the most frequent cancer diseases and causes of death among female population worldwide. It appears at a high incidence and has a high malignancy, mortality, recurrence rate and poor prognosis. Caveolin-1 (Cav1) is the main component of caveolae and participates in various biological events. More and more experimental studies have shown that Cav1 plays a critical role in the progression of breast cancer including cell proliferation, apoptosis, autophagy, invasion, migration and breast cancer metastasis. Besides, Cav1 has been found to be involved in chemotherapeutics and radiotherapy resistance, which are still the principal problems encountered in clinical breast cancer treatment. In addition, stromal Cav1 may be a potential indicator for breast cancer patients' prognosis. In the current review, we cover the state-of-the-art study, development and progress on Cav1 and breast cancer, altogether describing the role of Cav1 in breast cancer progression and application in clinical treatment, in the hope of providing a basis for further research and promoting CAV1 gene as a potential target to diagnose and treat aggressive breast cancers.

Natural Product Bis-Intercalator Depsipeptides as a New Class of Payloads for Antibody-Drug Conjugates

A potent class of DNA-damaging agents, natural product bis-intercalator depsipeptides (NPBIDs), was evaluated as ultrapotent payloads for use in antibody-drug conjugates (ADCs). Detailed investigation of potency (both in cells and via biophysical characterization of DNA binding), chemical tractability, and in vitro and in vivo stability of the compounds in this class eliminated a number of potential candidates, greatly reducing the complexity and resources required for conjugate preparation and evaluation. This effort yielded a potent, stable, and efficacious ADC, PF-06888667, consisting of the bis-intercalator, SW-163D, conjugated via an N-acetyl-lysine-valine-citrulline- p-aminobenzyl alcohol- N, N-dimethylethylenediamine (AcLysValCit-PABC-DMAE) linker to an engineered variant of the anti-Her2 mAb, trastuzumab, catalyzed by transglutaminase.

Caveolin-1 mediates cellular distribution of HER2 and affects trastuzumab binding and therapeutic efficacy

Human epidermal growth factor receptor 2 (HER2) gene amplification and/or protein overexpression in tumors is a prerequisite for initiation of trastuzumab therapy. Although HER2 is a cell membrane receptor, differential rates of endocytosis and recycling engender a dynamic surface pool of HER2. Since trastuzumab must bind to the extracellular domain of HER2, a depressed HER2 surface pool hinders binding. Using in vivo biological models and cultures of fresh human tumors, we find that the caveolin-1 (CAV1) protein is involved in HER2 cell membrane dynamics within the context of receptor endocytosis. The translational significance of this finding is highlighted by our observation that temporal CAV1 depletion with lovastatin increases HER2 half-life and availability at the cell membrane resulting in improved trastuzumab binding and therapy against HER2-positive tumors. These data show the important role that CAV1 plays in the effectiveness of trastuzumab to target HER2-positive tumors.

Trastuzumab binding to tumor cells depends on the availability of HER2 at the cell membrane. Here the authors show that caveolin-1 (CAV1) regulates HER2 density at the cell membranes and that CAV1 gene knockdown or protein depletion via the cholesterol modulator lovastatin, increases trastuzumab binding and anti-tumor activity.

T-DM1-resistant cells gain high invasive activity via EGFR and integrin cooperated pathways

Ado-trastuzumab emtansine (Kadcyla®; T-DM1) is an antibody-drug conjugate developed to treat trastuzumab-resistant disease. Despite initial favorable outcomes, most patients eventually cease to respond due to developing acquired resistance to T-DM1. Currently, there is no targeted therapy to treat T-DM1-resistant disease. To explore novel therapeutic targets to improve therapeutic efficacy of T-DM1, we generated T-DM1-resistant cells using trastuzumab-resistant JIMT1 cells. We found that the loss of human epidermal growth factor receptor 2 confers T-DM1 resistance, which in turn activates a compensatory mechanism that increases epidermal growth factor receptor (EGFR) expression. Upregulation of EGFR increases the protein levels of α5β1 and αVβ3 integrins, resulting in enhanced motility and invasion of T-DM1-resistant cells. This study delineates previously unappreciated relationships between α5β1 and αVβ3 and suggests that specific integrins should be carefully selected as therapeutic targets to treat T-DM1-resistant disease. Specifically, silencing β1 integrin expression by siRNA in T-DM1-resistant cells destabilizes α5, but increases expression of αV, a critical integrin mediating the invasion and metastases in many different cancers. As a consequence, T-DM1-resistant cells gain metastatic potential and become more invasive. This finding is underscored by the fact that β1 integrin blockage induced by an inhibitory antibody, MAB 13, significantly increases invasion of T-DM1-resistant cells. However, the increased cell invasion induced by β1 integrin blockage can be significantly reduced by either EGFR inhibitor or specific siRNA against αV integrin. The discovery of functional cooperation between EGFR and αV integrin in regulating cell growth and invasion provides an opportunity to develop novel therapeutic strategy by dual-targeting EGFR and specific integrin to overcome T-DM1 resistance.

Resistance to Antibody-Drug Conjugates

Antibody-drug conjugates (ADC) are multicomponent molecules constituted by an antibody covalently linked to a potent cytotoxic agent. ADCs combine high target specificity provided by the antibody together with strong antitumoral properties provided by the attached cytotoxic agent. At present, four ADCs have been approved and over 60 are being explored in clinical trials. Despite their effectiveness, resistance to these drugs unfortunately occurs. Efforts to understand the bases underlying such resistance are being carried out with the final purpose of counteracting them. In this review, we report described mechanisms of resistance to ADCs used in the clinic along with other potential ones that may contribute to resistance acquisition. We also discuss strategies to overcome resistance to ADCs. Cancer Res; 78(9); 2159-65. ©2018 AACR.

Caveolin-1, cancer and therapy resistance

Resistance of solid tumors to chemo- and radiotherapy remains a major obstacle in anti-cancer treatment. Herein, the membrane protein caveolin-1 (CAV1) came into focus as it is highly expressed in many tumors and high CAV1 levels were correlated with tumor progression, invasion and metastasis, and thus a worse clinical outcome. Increasing evidence further indicates that the heterogeneous tumor microenvironment, also known as the tumor stroma, contributes to therapy resistance resulting in poor clinical outcome. Again, CAV1 seems to play an important role in modulating tumor host interactions by promoting tumor growth, metastasis, therapy resistance and cell survival. However, the mechanisms driving stroma-mediated tumor growth and radiation resistance remain to be clarified. Understanding these interactions and thus, targeting CAV1 may offer a novel strategy for preventing cancer therapy resistance and improving clinical outcomes. In this review, we will summarize the resistance-promoting effects of CAV1 in tumors, and emphasize its role in the tumor-stroma communication as well as the resulting malignant phenotype of epithelial tumors.

Metformin-induced caveolin-1 expression promotes T-DM1 drug efficacy in breast cancer cells

Trastuzumab emtansine (T-DM1) is an antibody drug conjugate (ADC) that was recently approved for the treatment of HER-2-positive metastatic breast cancer. The drug sensitivity of ADCs depends mainly on the internalization efficiency of the drug. Caveolin-1 was shown to promote T-DM1 internalization and enhance drug sensitivity. Whether caveolin-1 can be overexpressed to improve T-DM1 efficacy is interesting and has the potential for clinical application. In this study, diabetes drug metformin was investigated in terms of induction of caveolin-1 expression for increased efficacy of subsequent T-DM1 application. BT-474 cells were pretreated with metformin, followed by combined therapy with metformin and T-DM1. The T-DM1 internalization and drug efficacy were determined, and the protein expressions for signal transduction were also monitored. Caveolin-1 shRNA was applied to suppress endogenous caveolin-1 expression, and the ability of metformin to promote T-DM1 efficacy was investigated. Result showed that in BT-474 cells pretreated with metformin, cellular caveolin-1 overexpression was induced, which then promoted drug efficacy by enhancing T-DM1 internalization. As cellular caveolin-1 was suppressed by shRNA, the effect of metformin-enhanced T-DM1 cytotoxicity was decreased. This study demonstrated that metformin can be applied prior to T-DM1 treatment to improve the clinical efficacy of T-DM1 by enhancing caveolin-1-mediated endocytosis.

Trastuzumab emtansine: determining its role in management of HER2+ breast cancer

Trastuzumab emtansine is an antibody-drug conjugate comprised of the anti-HER2 monoclonal antibody trastuzumab linked to DM1 (emtansine), a potent cytotoxic maytansinoid derivative, by a stable linker. This structure results in improved tumor-directed cytotoxicity in HER2+ breast cancer with reduced systemic toxicities, particularly the cardiac toxicities associated with single agent trastuzumab. Phase III trials have demonstrated improved progression-free and overall survival in heavily pretreated patients with advanced HER2+ breast cancer, with an acceptable toxicity profile. However, its role in first-line treatment is less clear. Ongoing studies continue to evaluate its role in neoadjuvant and adjuvant management of HER2+ breast cancer.