Preclinical Efficacy of Ado-trastuzumab Emtansine in the Brain Microenvironment

Trastuzumab distribution in an in-vivo and in-vitro model of brain metastases of breast cancer

Background

Drug and antibody delivery to brain metastases has been highly debated in the literature. The blood-tumor barrier (BTB) is more permeable than the blood-brain barrier (BBB), and has shown to have highly functioning efflux transporters and barrier properties, which limits delivery of targeted therapies.

Methods

We characterized the permeability of ¹²⁵I-trastuzumab in an in-vivo, and fluorescent trastuzumab-Rhodamine123 (t-Rho123) in a novel microfluidic in-vitro, BBB and BTB brain metastases of breast cancer model. In-vivo: Human MDA-MB-231-HER2+ metastatic breast cancer cells were grown and maintained under static conditions. Cells were harvested at 80% confluency and prepped for intra-cardiac injection into 20 homozygous female Nu/Nu mice. In-vitro: In a microfluidic device (SynVivo), human umbilical vein endothelial cells were grown and maintained under shear stress conditions in the outer compartment and co-cultured with CTX-TNA2 rat brain astrocytes (BBB) or Met-1 metastatic HER2+ murine breast cancer cells (BTB), which were maintained in the central compartment under static conditions.

Results

Tissue distribution of ¹²⁵I-trastuzumab revealed only ~3% of injected dose reached normal brain, with ~5% of injected dose reaching brain tumors. No clear correlation was observed between size of metastases and the amount of ¹²⁵I-trastuzumab localized in-vivo. This heterogeneity was paralleled in-vitro, where the distribution of t-Rho123 from the outer chamber to the central chamber of the microfluidic device was qualitatively and quantitatively analyzed over time. The rate of t-Rho123 linear uptake in the BBB (0.27 ± 0.33 × 10⁴) and BTB (1.29 ± 0.93 × 10⁴) showed to be significantly greater than 0 (p < 0.05). The BTB devices showed significant heterogenetic tendencies, as seen in in-vivo.

Conclusions

This study is one of the first studies to measure antibody movement across the blood-brain and blood-tumor barriers, and demonstrates that, though in small and most likely not efficacious quantities, trastuzumab does cross the blood-brain and blood-tumor barriers.

Developmental therapeutics for patients with breast cancer and central nervous system metastasis: current landscape and future perspectives

Breast cancer is the second-leading cause of metastatic disease in the central nervous system (CNS). Recent advances in the biological understanding of breast cancer have facilitated an unprecedented increase of survival in a subset of patients presenting with metastatic breast cancer. Patients with HER2 positive (HER2+) or triple negative breast cancer are at highest risk of developing CNS metastasis, and typically experience a poor prognosis despite treatment with local and systemic therapies. Among the obstacles ahead in the realm of developmental therapeutics for breast cancer CNS metastasis is the improvement of our knowledge on its biological nuances and on the interaction of the blood–brain barrier with new compounds. This article reviews recent discoveries related to the underlying biology of breast cancer brain metastases, clinical progress to date and suggests rational approaches for investigational therapies.

Closing the gap: astrocytes and brain metastasis

Astrocytes are emerging as essential regulators of brain metastasis progression. In a current issue of Nature, Chen et al. identify a novel mechanism of astrocyte-carcinoma interaction and exploit vulnerabilities therein to slow brain metastatic growth in pre-clinical models.

Central nervous system relapse in patients with untreated HER2-positive esophageal or gastroesophageal junction adenocarcinoma

Although HER2-positive breast cancers demonstrate a propensity for central nervous system (CNS) metastasis, it is unknown whether other HER2-positive tumors, including adenocarcinomas of the esophagus/gastroesophageal junction (EAC), share this characteristic. Insight into this association may inform the development of HER2-targeted therapies that penetrate the blood-brain barrier. We examined HER2 overexpression and gene amplification in 708 patients with EAC who underwent curative-intent surgery during a time period (1980-1997) when no patient received HER2-targeted therapy. We identified patients whose site of first cancer recurrence was CNS and those who had a CNS relapse at any time. After a median follow-up of 61.2 months, 3.4% (24/708) of patients developed CNS relapse (all involved the brain). Patients with HER2-positive (vs -negative) primary tumors showed a higher 5-year cumulative incidence of CNS relapse as first recurrence (5.8% vs. 1.2%; p = 0.0058) and at any time (8.3% vs. 2.4%; p = 0.0062). In a multivariable model that included covariates previously associated with HER2 or with CNS relapse in breast cancer, HER2 positivity was the only variable that was statistically significantly associated with shorter time to CNS relapse as first recurrence (p = 0.0026) or at any time (hazard ratio 4.3 [95% confidence interval 1.8 to 10.3]; p = 0.001). These are the first data in a non-breast cancer to demonstrate an association between HER2 positivity and higher CNS relapse risk after surgery, and suggest that HER2-positive EACs have a predilection for CNS metastases.

ACTIVITY OF TRASTUZUMAB-EMTANSINE (TDM1) IN HER2-POSITIVE BREAST CANCER BRAIN METASTASES: A CASE SERIES

The incidence of breast cancer brain metastasis (BCBM) is increasing due in part to improved management of systemic disease and prolonged survival. Despite this growing population of patients, there exists little consensus for the treatment of HER2-positive BCBM. Lapatinib, the only brain permeable targeted agent for HER2-positive cancer, has demonstrated limited intracranial response rates and little improvement in progression free survival (PFS) for HER-2 positive patients. Size constraints are believed to prevent larger monoclonal antibodies, such as pertuzumab and trastuzumab, from crossing the blood brain barrier (BBB). However, emerging evidence reveals that the BBB is perturbed in the setting of metastases, allowing for improved penetrance of these larger targeted agents. The disrupted BBB may allow for passage of ado-trastuzumab emtansine (TDM1), though little clinical information about its activity in BCBM patients is currently known.