Antibody drugs targeting HER2—a receptor tyrosine-protein kinase involved in a variety of oncogenic signaling pathways—have transformed the standard of care for patients with breast and gastric cancer. However, resistance mechanisms result in inevitable disease progression and thousands of patients bearing alterations in the human epidermal growth factor receptor 2 (ERBB2, encoding HER2) remain without effective therapies. As an example, not all HER2-targeted therapies effectively treat gastric cancer. Beyond Trastuzumab and Trastuzumab deruxtecan, clinical trials have failed to demonstrate the efficacy of other HER2-targeted therapies (Pertuzumab, T-DM1) in the first and later treatment lines for gastric cancer. In this study, we use antibody-positron emission tomography (immunoPET) to study the contribution of HER2 membrane dynamics in antibody-tumor binding and therapeutic efficacy (Scheme 1).
Scheme 1. HER2 proteins present in high quantities in gastric cancer cells are not always available at the cell surface for the effective binding of antibody drugs (outside the cell), which could explain why these therapies are not always effective. Antibody-PET imaging reveals new information about the mechanisms of HER2 membrane dynamics of cancer cells.
The motivation in studying receptor membrane dynamics relates to the fact that the efficacy of antibody drugs in killing the antibody-coated cancer cells depends on effective drug delivery and internalization in cancer cells. In our initial studies, we demonstrated that gastric cancer cells show dysregulated waves of recycling and internalization that contribute to HER2 heterogeneity and low antibody-drug delivery in tumors (Pereira P et al, Nat Commun 2018). In the present studies (Pereira P et al, Nat Commun 2022), we further validated that HER2 heterogeneity is associated with resistance in cancers and the major protein of caveolae-mediated endocytosis, caveolin-1 (CAV-1), contributes to this heterogeneity (Figure 1).
Figure 1. Gastric tumor samples with high protein levels of CAV-1 demonstrated low levels of membrane HER2. Additionally, T-DM1 accumulation is lower in CAV-1HIGH when compared with CAV-1LOW tumors.
Guided by preclinical data suggesting that CAV-1 reduces trastuzumab or T-DM1 binding to HER2-positive gastric tumors, we performed retrospective clinical analyses to validate CAV-1 as a complementary biomarker of HER2. Remarkably, Kaplan-Meier survival analyses demonstrated that HER2-positive gastric tumors expressing high CAV-1 (IHC 2+/3+) had worse overall survival than those expressing low CAV-1 (IHC 0/+1) after trastuzumab therapy. These promising preliminary results prompted us to pharmacologically deplete CAV-1 (which is present in cholesterol membrane domains) with, lovastatin, a cholesterol-depleting drug. We performed randomized imaging and therapeutic preclinical studies to show that temporal and controlled modulation of CAV-1 with statins enhances Trastuzumab and T-DM1 tumor binding and therapeutic efficacy (Figure 2). In addition to preclinical studies, we analyzed medical records to determine that concurrent statin use is associated with enhanced response to trastuzumab.
Figure 2. Statin-mediate CAV-1 depletion enhances anti-HER2 antibody binding to gastric tumors.
In summary, our studies show that CAV-1 may serve as a predictive biomarker when selecting tumors for HER2-targeted therapies and that statin-mediated temporal increase in HER2 receptors at the cell surface has the capability to enhance Trastuzumab and T-DM1 efficacy. The next steps will involve determining whether our findings can be extended to other antibody therapies and tumor types characterized by heterogeneous patterns of receptors at the cell membrane of tumor cells. Additionally, an extensive pharmacodynamic/pharmacokinetic study is required for a clinical investigation of statin use in combination with HER2-targeted therapies.
All our findings are published here: https://rdcu.be/cM9SW
Scheme 1 was made with Biorender.com