Copper Depletion Combats Metastatic Recurrence in High-Risk TNBC

Linda T. Vahdat, MD

Copper depletion with tetrathiomolybdate may decrease the risk of metastatic disease development in patients with triple-negative breast cancer (TNBC) at high risk of recurrence, according to Linda T. Vahdat, MD.

In an interview with OncLive®, Vahdat discussed known factors regarding the role of copper in the development of tumor metastases, prior findings with the copper chelator tetrathiomolybdate in patients with stage IV TNBC and no evidence of disease, and the design of an ongoing phase 1/2 trial (NCT06134375) evaluating tetrathiomolybdate plus capecitabine with or without pembrolizumab (Keytruda) in patients with high-risk disease.

Vahdat also provided additional insights on emerging antibody-drug conjugates and immunotherapy approaches in TNBC management and efforts dedicated to understanding the optimal use of adjuvant and neoadjuvant therapies in the disease.

Vahdat is the section chief of Medical Oncology, interim section chief of Hematology, and a professor of medicine at the Geisel School of Medicine at Dartmouth Health in Lebanon, New Hampshire.

OncLive: What was the rationale for investigating copper depletion in patients with TNBC?

Vahdat: We are excited about a strategy to prevent metastasis that we’ve been working on for at least 15 years. The concept behind it is that you target the tumor microenvironment and pull out the infrastructure the tumors need to spread so [the disease doesn’t] spread. We do this with a copper depletion approach because metals are important for tumor spread.

Metals don’t come with their own infrastructure; they hijack infrastructure. [If a] tumor is sitting [in its primary site], it doesn’t know how to get from point A to point B. What happens is that cells come from the bone marrow and leave a popcorn trail for tumor cells to follow to a distant metastatic site. Once the tumor gets to that distant metastatic site, that site doesn’t want it, so a reprogramming happens. A collagen landing pad is made so tumors can land there. However, when tumors land there, they don’t come with a suitcase full of infrastructure. They have to mobilize other bone marrow–derived progenitor cells to put down blood vessels so they can get the nutrients they need to grow and spread.

We found in the lab that copper is critical for each of these steps, from the fuel that’s made by the mitochondria to fuel [the tumor’s] effect on bone marrow–derived progenitor cells to influencing lysyl oxidase, which reprograms the collagen microenvironment, to decreasing VEGFR2-positive endothelial progenitor cells. Our approach was to start with a [phase 2] clinical trial [NCT00195091], in which we gave patients [with TNBC] at high risk for relapse an oral copper depletion compound. We collected lots of research specimens every month when they came to see us. When we observed that our results in TNBC were better than what we expected, we went back to the lab to work out mechanistically what was happening.

What is the potential role of copper as a therapeutic target in TNBC?

Copper is important for normal biologic processes, but it is also important for the processes that support metastasis. It is the required cofactor for activators of angiogenesis, such as FGF-β, VEGF, and NF-κB. Lysyl oxidase is a key component of [angiogenesis], as well as superoxide dismutase. Copper is important for RAS/MAPK signaling.

Copper is also important for the migration and invasion of endothelial cells, as well as other cells. Copper drives BRAF V600 signaling in multiple models, and it regulates expression of PD-L1 in breast cancer, as well as in neuroblastoma. Regarding the hallmarks of metastatic progression, copper is a key component in those steps: motility invasion, plasticity, modulation of the microenvironment, as well as colonization. We’ve published these data.

Copper gets into the cell through a receptor called CTR1. When we look at Molecular Taxonomy of Breast Cancer International Consortium and The Cancer Genome Atlas data, the higher the CTR1 expression in genes, the worse the overall survival [OS]. We see increasing CTR1 with increasing stage and increasing aggressiveness of tumors. CTR1 [levels] in HER2-positive and triple-negative breast cancers are high compared with [those in] luminal breast cancers.

TNBC has specific resistance mechanisms. Lysyl oxidase is upregulated in resistant TNBC. That creates a collagen moat around tumors, which prevents immune cell infiltration. This process leads to CD8-positive T-cell exhaustion. Resistant TNBC also shifts its metabolism, and resistant cells are enriched in oxidative phosphorylation. The leading edge of tumors, the stem cell component, has high copper levels, and is sensitive to copper depletion. These are well-known triple-negative resistance mechanisms, and copper depletion influences all these mechanisms.

How was this phase 2 study designed, and what has previously been seen with tetrathiomolybdate?

When we copper deplete patients, we give them a pill called tetrathiomolybdate, a copper chelator. Most of the original work [with this agent] was done by [researchers at] the University of Michigan. Because they saw that they could reduce tumor growth and proliferation [with tetrathiomolybdate], they initiated a series of phase 2 trials in patients with metastatic breast cancer. I would call [this research] a bust, because the best response they saw was stable disease, as opposed to a response, which, in our drug development world, is what’s exciting to people.

However, we thought that was not the right place to study tetrathiomolybdate, because [the University of Michigan group] had done a study in HER2 transgenic mice, which develop lung metastases when they are [approximately] 205 days old. They gave half the mice copper depletion in their water, and in the other half, they didn’t. As expected, [at approximately] 205 days, the mice who got no tetrathiomolybdate in their water developed lung metastases and died. However, the mice that were on tetrathiomolybdate did not die. Interestingly, they withdrew tetrathiomolybdate therapy, and 14 days later, the mice developed lung metastases, indicating that those metastases were there just ready to take hold, but for some reason, they couldn’t complete the deal [in the presence of tetrathiomolybdate].

This made me think of my patients with breast cancer who were at high risk of tumor recurrence. We initiated a phase 2 clinical trial when I was a faculty [member] at Cornell. We enrolled 75 patients who were at high risk of relapse. These patients had stage III and IV breast cancer with no evidence of disease. Their tumors had come back and somehow, they had gotten rid of them; we didn’t care how, but when we used every modality available, we couldn’t find them. However, we all know as clinicians [that these tumors] will recur. Patients had completed what was considered standard treatment and were looking for something extra.

We gave patients oral daily tetrathiomolybdate for 2 years in our initial trial, and our goal was to copper deplete them by [approximately] 30% using ceruloplasmin as a target. The primary end point of the trial was to assess the effect of tetrathiomolybdate on bone marrow–derived progenitor cells, which are important for the process of metastasis. Patients came to see us once every 4 weeks. At that time, we would talk to them, examine them, and check their blood to make sure they weren’t over–copper depleted. Then, we would take some research samples and put them in the freezer. We also imaged patients every 6 months to make sure they still had no evidence of disease.

What were the topline findings from this trial?

For patients with stage IV TNBC with no evidence of disease, the event-free survival [EFS] rate was 59.3%. We now have a medium follow-up of [approximately] 10.4 years. For patients in the adjuvant setting, the EFS rate was 88%. This made us think there was something special about copper [in relation to] metastasis in TNBC.

We also embedded a lot of science in this trial and found that when patients were copper depleted with tetrathiomolybdate, we reduced [levels of] bone marrow–derived progenitor cells, which we had associated with relapse in the past. Patients with lower levels of lysyl oxidase were more likely to have no evidence of disease. We also found, by looking at collagen biomarkers, that tetrathiomolybdate normalizes the collagen microenvironment.

We also went back to the lab and demonstrated that copper depletion didn’t affect primary tumor size but markedly reduced metastasis by decreasing disseminated tumor cells, which were unable to detach and invade. We also saw that we affected complex IV of the mitochondria, and we shifted metabolism from mitochondrial oxidative phosphorylation to glycolysis. [This is] a multipronged approach to preventing metastasis.

The most important finding was that tetrathiomolybdate was well tolerated. Patients get neutropenic when they’re over–copper depleted. [In these cases], our strategy is that we hold the tetrathiomolybdate and restart patients on a lower dose. That was the only [safety signal] we saw.

What are the next steps for investigating copper depletion in patients with TNBC?

This [research] has led us to [launch] a randomized phase 1/2 trial in the adjuvant setting. We are about to start, and we are excited. Eligible patients are those [with TNBC] who are at high risk for recurrence. They’ve received chemoimmunotherapy and have residual cancer burden [RCB]–II disease.

Patients will be randomly assigned to receive capecitabine plus or minus pembrolizumab vs tetrathiomolybdate [plus or minus pembrolizumab]. Why plus or minus pembrolizumab? I wanted to help patients who have the highest risk of their tumors coming back. Approximately 15% of patients cannot tolerate pembrolizumab. I did not want patients to come off the study if they couldn’t tolerate pembrolizumab, so we have a stratification in [the trial design] for pembrolizumab. We also have stratification for age greater than vs less than 40 years, as well as RCB status II vs III.

The primary end point of this trial is distant recurrence–free survival between the 2 arms. Our sample size is [approximately] 186 patients, and we’re [planning to administer] 3 years of active treatment with tetrathiomolybdate. Our secondary end points are OS; the effect of copper depletion on serial biomarkers, including VEGFR2 EPCs, LOXL2, and circulating tumor DNA; and patient-reported outcomes.

Pharmacokinetics are embedded in this study, as well as a lot of exploratory aims. [We are] trying to understand: Who are the right patients for this? We have a biomarker; we’ve been evaluating ATOX1. We’re investigating the effect of tetrathiomolybdate on immune function, metabolism, and biomarkers of collagen remodeling, and as well as [on a tumor’s] ability to be copper depleted by looking at single nucleotide polymorphisms in ceruloplasmin in the CTR gene.

We have 8 sites [whose investigators] are as excited as we are to get this study going: New York University with principle investigator [PI] Nancy Chan, MD; the University of Indiana [in Indianapolis] with PI Kathy Miller, MD; Houston Methodist [in Texas] with PI Jenny Chang, MD; Memorial Sloan Kettering Cancer Center [in New York, New York] with PI Mark Robson, MD; Massachusetts General Hospital [in Boston] with PI Neelima Vidula, MD; Vanderbilt University [in Nashville, Tennessee], with PI Ben Park, MD, PhD; and Emory University [in Atlanta, Georgia] with PI Kevin Kalinsky, MD, MS. We don’t have a pharmaceutical sponsor, so this has been funded with foundational grants. The Gateway Foundation [provided] an early grant, [as did the] Breast Cancer Research Foundation. [We have also received funding through] philanthropy [efforts], such as the Margaret Claire Pisani fund, as well as many anonymous donors. [Funding was also provided by] 2 National Cancer Institute [NCI] R01 grants. The NCI NExT program is also helping support our trial with compounding our drug. If you’re looking for the trial, you can email me at linda.t.vahdat@hitchcock.org, and I can direct you to a [participating] site.