BSCI-17 TOPIRAMATE DECREASES RADIATION-INDUCED CYTOTOXIC EDEMA IN HER2+ BRAIN METASTASES VIA AQUAPORIN 4 INHIBITION

Brain metastasis (BM) occurs in 30-40 % of breast cancer patients with Her2+ tumors, and radiation is part of the standard treatment for BM. About 10% of BM patients treated with radiation develop brain edema. We have shown that combination of Ado-trastuzumab Emtansine (T-DM1)-the main targeted therapy for metastatic Her2+ Breast Cancer- and radiation increases the risk of developing radionecrosis by 13.5-fold (Stump et al., 2019). We also showed that T-DM1 enhances radiation-induced astrocytic toxicity and cytotoxic edema through upregulation of aquaporin-4 water-transporter (AQP4). Here, we determined whether blockage of AQP4 would prevent astrocytic swelling –cytotoxic edema- in vitro and in vivo models of Her2+ BM. Results: Electron microscopy of brain cortex from mice treated with 35 Gy (single dose), showed acute astrocytic end-feet swelling and a significant increase in AQP4 expression compared with non-irradiated mice. Consistent with prior findings in murine astrocytes, primary human astrocytes (huAST) also upregulated AQP4 levels 24 h post-radiation (8 Gy), and T-DM1 treatment exacerbated this effect. AQP4 upregulation was concomitant with 4.8 fold increase in the astrocytic area (indicative of cytotoxic edema). The FDA-approved anti-epileptic and migraine prevention drug, Topiramate (TPM), which works as an AQP4 inhibitor, blocked radiation-induced astrocytic swelling in huAST in vitro. Thus, we tested whether pre-treatment with TPM could prevent radiation-induced edema in a mouse model of HER2+BMs. Mice were injected intracardially JmT1BR3 brain metastatic cells and ten days later randomized based on the total head flux to (1) Radiation + vehicle, (2) Radiation + TPM (2 days prior to irradiation), (3) Non-Radiation + vehicle, and (4) Non-radiation + TPM. TPM decreased brain-water content (a marker of brain edema) in irradiated mice as compared with vehicle-treated mice, without alteration of metastatic burden 21 days post-injection. These results suggest TPM could be repurposed as a preventive agent of radiation-induced brain edema.

Abstract P2-20-03: Estrogen-depletion therapies prevent and delay progression of brain metastasis

Introduction: Triple negative breast cancers (TNBC, which lack estrogen receptor (ER), progesterone receptor and HER2), occur three times more frequently in premenopausal women and metastasize expeditiously to brain and lungs. Clinical and experimental evidence shows that estrogen, the main premenopausal ovarian hormone, promotes metastases of TNBC, through their action on the tumor microenvironment. We have shown that 17-β-Estradiol (E2) promotes experimental brain metastases (BM) of TNBC cells by inducing estrogen-receptor positive (ER+) astrocytes in the brain niche to secrete growth factors that promote cancer cell migration, invasion and growth. Given that 53% of pre-menopausal women with TNBC develops BM and 80% die within a year, it is now critical to define whether blocking estrogen signaling could have therapeutic value to prevent or delay progression of BM. Results: To assess whether E2-depletion could prevent brain metastatic colonization, brain trophic sublines of human TNBC (231BR), murine TNBC (4T1BR5), a non-selected TN cell line syngeneic to C57BL mice (E0771-GFP-luc) were intracardially (ic) injected two-days post-endocrine initiation, in ovariectomized (OVX) female mice treated with a) E2 (levels equivalent to those found in pre-menopausal women), b) placebo (OVX), or c) the aromatase-inhibitor (AI) letrozole (OVX + Letrozole) to block brain and peripheral E2-synthesis. BM were quantified histologically, via MRI or ex-vivo imaging of brains at euthanasia. E2-treated mice injected with E0771-GFP-luc cells showed an average of 6.6± 3.5 metastatic clusters per mice, compared to 3.6 ± 3.2 and 1.8 ± 1.8 in OVX mice alone or OVX + letrozole treated mice (a 3.6 fold increase, P=0.0013, E2 vs OVX + Let). Imaging of excised brains showed comparable results, with a mean total photon flux of 5.1 × 106 ± 5.3 × 106 in E2 vs 1.1 × 106 ± 1.5 × 106 in OVX + letrozole (P=0.0056). Similar preventive effects of E2-depletion were found in 4T1BR5 and 231BR-cell injected mice, using histological quantification and MRI as endpoints. To assess whether E2-depletion therapies could decrease brain metastatic progression in a therapeutic model mimicking the clinical setting, E0771-GFP-luc cells were injected in OVX-mice that had been supplemented with E2 and metastasis allowed to develop for 6 days. Mice were then randomized to a) E2, b) E2-withdrawal (E2WD) or c) E2WD+ letrozole, and then all mice were irradiated (whole brain irradiation, single-dose, 15 Gy) to mimic current standard of care for BMs. All mice were euthanized 10 days later, when E2-treated mice showed signs of CNS impairment. Mice that received E2WD+letrozole showed the lowest BM burden compared to mice that remained in E2-treatments, as assessed by histological quantification (0.7 ± 1.2 vs 6.5 ± 5.3 metastatic clusters, respectively, P=0.0132) and ex-vivo brain imaging (mean total-photon flux 3.4 × 105 ± 4.1 × 105 in E2WD + let vs 3.1 × 106 ± 1.4 × 106 in E2, P=0.037). Brain metastasis in TNBC often occur in women who also present with systemic metastatic disease, and E0771-GFP-luc cells can colonize multiple organs following ic injection. Thus, non-brain metastatic burden (systemic metastasis) was measured by in vivo imaging before euthanasia in this cohort. Unlike brain metastasis, E2WD or E2WD+letrozole showed no statistically significant effect on systemic metastatic burden (mean total flux 1.41 × 106 ± 0.9 × 106 in E2, vs 0.54 × 106 ± 2.6 × 106 in E2WD vs 0.79 × 106 ± 1.0 × 106 in E2WD+let, P=0.416), supporting the notion that brain-specific rather than systemic mechanisms drive progression of brain metastasis in response to E2. Conclusions: These studies have important clinical implications as they provide pre-clinical evidence that ovarian suppression in combination with AIs can prevent and delay progression of established brain metastasis in younger women with TNBC.

Citation Format: Diana M. Cittelly, Maria J. Contreras-Zarate, Ricaurte A. Marquez-Ortiz, Nicole Day, Bebhinn Nagle, Ryan Ormond, Virginia F. Borges, Peter Kabos. Estrogen-depletion therapies prevent and delay progression of brain metastasis [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-20-03.

Abstract P5-14-20: Mechanisms of radiation-induced brain edema alone and in combination with T-DM1 in Her2+ brain metastases

Introduction: Brain metastases (BM) occurs in ~40% of breast cancer patients with Her2+ tumors, which are typically treated with the Her-2 targeting drugs ado-trastuzumab emtansine (T-DM1) and trastuzumab. Radiotherapy (RTx), including stereotactic radiosurgery (SRS), is often utilized to treat BM. A subset of BM patients treated with SRS develops brain edema and radionecrosis (ERN), causing neurological deterioration, functional loss, and rarely death. We have reported an increased rate of ERN in patients treated with T-DM1 and SRS (39.1%), compared to those receiving SRS alone (4.5%). Thus, defining the mechanisms underlying ERN alone or in combination with T-DM1, is critical to reduce life-threatening side effects. While brain edema associated with BM and RTx is often attributed to blood-brain-barrier (BBB) disruption (vasogenic edema), recent studies now identify cytotoxic edema (osmotic cell expansion) as the initial andreversible step in a sequence of changes that leads to ionic edema, vasogenic edema, and ultimately brain swelling and necrosis. Here, we test the hypothesis that RTx alone and in combination with T-DM1 induces cytotoxic edema in astrocytes via upregulation of the water channel Aquaporin 4 (AQP4) and that blockage of cytotoxic edema will decrease ERN. Results: A cohort of BM from Her2+ patients treated with T-DM1/SRS showed enlarged reactive astrocytes expressing high levels of AQP4. To assess the role of astrocytic swelling in ERN, human astrocytes (THV) were treated with increasing doses of RTx and astrocytic cell size was measured 24 h later. A single 8 Gy RTx-dose increased cell size by 4.5 times compared to non-treated astrocytes (1248 ± 760.8 µm2 vs 5685 ± 4475 µm2, P<0.0001). Consistent with a role for AQP4 in mediating astrocytic swelling, western blot (WB) showed increased AQP4 levels in RTx treated cells. To assess whether Her2-targeting (or directed) therapies impacted AQP4 expression and astrocytic survival/swelling, astrocytes were treated with increasing doses of RTx alone (0, 2, 4, 8 Gy), with trastuzumab or T-DM1 (1 μg/mL). WBs showed that only T-DM1 further exacerbated RTx-induced AQP4 upregulation and increased PARP cleavage. The combination of 4 Gy-RTx and T-DM1 showed a synergistic effect in reducing astrocytic confluence (32.1%), compared with astrocytes treated with 4 Gy-RTx alone (32.8 ± 3 vs 64.9 ± 13.3% respectively, P=0.0001, at 5 days). Moreover, T-DM1/RTx increased astrocytic size (P = 0.004) to a greater extent than equivalent RTx dose in combination with trastuzumab (P = 0.005). Other chemotherapeutic agents (paclitaxel and cisplatin) did not affect AQP4 protein levels, astrocytic survival or astrocytic swelling. TGN-020, a novel AQP4 inhibitor, and topiramate (TPM), an FDA-approved anticonvulsant/antiepileptic able to inhibit AQP4 activity, were evaluated for their potential role in reducing astrocytic swelling. Pretreatment with 100 µM TPM reduced RTx-induced astrocytic swelling by 36 % (7153 ± 4522 µm2 vs 4627 ± 3999 µm2, P<0.0001). TPM pretreatment did not prevent 8 Gy-RTx-induced cell death (24.96 ± 5.7 % vs 23.47 ± 4.7 %) nor prevent DNA double stranded breaks measured by IF of p-γH2AX (89.17 ± 13.89 % vs 97.32 ± 2.94 %). Ongoing studies are assessing the effect of TPM on blocking astrocytic swelling and decreasing brain edema in vivo. Conclusions: These results suggest that astrocytic swelling (cytotoxic edema) is involved in the pathophysiology of ERN during BM treatment. In vitro, AQP4-inhibitors decreased astrocytic swelling without affecting astrocyte survival, suggesting that blockage of AQP4 could reduce brain edema without rescuing lethally-damaged astrocytes. Thus, a combination of drugs preventing vasogenic dysfunction (i.e bevacizumab) and AQP4-inhibitors (i.e TPM) could diminish ERN by targeting both, vasogenic and cytotoxic edema.

Citation Format: María J Contreras-Zárate, Steven Lai, Priscilla Stumpf, Christine Fisher, Ryan Ormond, Sana D Karam, Peter Kabos, Diana M Cittelly. Mechanisms of radiation-induced brain edema alone and in combination with T-DM1 in Her2+ brain metastases [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-14-20.

Abstract P6-05-04: Ligand dependent and independent roles of interleukin-13 receptor alpha 2 in breast cancer brain metastasis

Introduction: Interleukin-13 receptor alpha 2 (IL13Rα2) is a high affinity receptor for IL-13, best known as a decoy receptor that lacks intracellular kinase activity. Yet, IL13Rα2 has been shown to play an important role in the pathobiology of glioblastomas, colon, ovarian and pancreatic cancer, through the recruitment and activation of FAK, SRC and other intracellular signaling pathways. In breast cancer, the function of IL13Rα2 remains controversial. Increased IL13Rα2 expression is associated with poor prognosis for high grade tumors but not low-grade tumors, while was also reported to be associated with poor prognosis in luminal subtypes only. Increased levels of IL13Rα2 were reported in breast cancer cells with brain metastatic tropism, yet the function of IL13Rα2 during brain metastatic colonization remains unexplored. Since IL-13 is expressed by various cells within the brain niche, this study tests the hypothesis that ligand dependent and independent mechanisms modulate IL13Rα2 function during brain metastatic progression.

Methods and results: qPCR, Western blot and IHC analysis demonstrated that IL13Rα2 was expressed at various levels in HER2+ and TN brain-trophic breast cancer cell lines (231BR, JmT1BR3, 4T1BR5, F2-7), brain-metastasis patient-derived xenografts (BM-PDXs) and a cohort of 26 clinical breast cancer brain metastasis (BCBM) samples. To assess how IL13Rα2 influences pro-metastatic abilities independent of ligand, inducible-shRNAs and CRISPR/cas9 were used to downregulate IL13Rα2 expression in 231BR cells. Knockdown of IL13Rα2 reduced the ability of 231BR cells to migrate (41.7% ± 4.5 vs 71.5% ± 9.7; p=0.001) and invade (49.5% ± 6.5 vs 73.1% ± 2.9; p=0.001) compared to the empty vector (EV) control cells. Furthermore, inducible-IL13Rα2 downregulation decreased significantly the proliferation (-22.1% at 96 hours, p<0.0001) and migration (-10.6% at 24 hours, p<0.0001) as compared to EV controls. Consistently, inducible overexpression of IL13Rα2 in HER2+ BT474 cells (which lack endogenous IL13Rα2) increased proliferation by 22.8% (p<0.0005, at 5 days) compared to parental cells. Knockdown of IL13Rα2 in 231BR cells impaired their ability to colonize the brain in mice following intracardiac injection as compared to EV 231Br cells (median number of metastatic clusters: 11.8 ± 5.5 vs 30.5 ± 13.9, respectively, p=0.2671), suggesting that upregulation of IL13Rα2 facilitates early brain metastatic colonization. To assess whether levels of IL13Rα2 remain high at late stages of brain metastasis, a publicly available transcriptome profile of 21 matched primary tumor and brain metastases was analyzed. Surprisingly, high IL13RA2 mRNA expression in brain metastasis (but not in primary tumors) predicted better brain-metastasis free survival (n=21, p=0.0026). Since the brain has several sources of IL-13, we assessed whether ligand-dependent mechanisms alter IL13Rα2 function, leading to a loss of expression in more aggressive brain metastasis. Western blot and IF analyses showed IL-13 expressed in reactive astrocytes. IL-13 treatment of serum-deprived IL13Rα2+ 231BR and JmT1Br cells resulted in decreased proliferation, a moderate increase in invasion, and phosphorylation of FAK and SRC. Knockdown of IL13Rα2 blocked the ability of IL-13 to phosphoactive FAK and SRC, and prevented the antiproliferative effect of IL-13 on 231BR cells.

Conclusions: These results suggest that ligand-dependent and independent mechanisms modulate IL13Rα2 through brain metastatic colonization. Ligand-independent IL13Rα2 promotes proliferation and invasion of cancer cells, favoring early dissemination and brain colonization. Loss of IL13Rα2 at later stages of BM, may prevent IL-13-induced blockage of proliferation and promote aggressiveness of established BM.

Citation Format: Ricaurte Alejandro Marquez-Ortiz, Maria J Contreras-Zarate, Nicole L Day, Ryan Ormond, Virginia F Borges, Diana M Cittelly. Ligand dependent and independent roles of interleukin-13 receptor alpha 2 in breast cancer brain metastasis [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-05-04.