Abstract PD2-04: FOXA1 induces a pro-metastatic secretome through ER-dependent and independent transcriptional reprogramming in endocrine-resistant breast cancer

Background: Metastasis in ER-positive (+) breast cancer (BC) occurring years to decades after initial diagnosis presents a daunting challenge for clinical care and preclinical research due to limited known key players and experimental models. FOXA1 is a pioneer factor for ER-chromatin binding and function, and is highly expressed in ER+ BC metastases, yet the underlying mechanism is unclear. Tumor-secreted proteins play a crucial role in the reciprocal interplay between cancer cells and host microenvironmental factors at both primary and secondary sites. We hypothesized that high FOXA1 provokes an ER-dependent transcriptional program that includes a unique pro-tumorigenic secretome essential for promoting ER+ BC metastasis. Methods: A lentiviral doxycycline (Dox)-inducible FOXA1 overexpression vector and a dual luciferase/GFP (LG) tracking vector were integrated to construct a stable MCF7-LG/FOXA1 cell model. Ovariectomized nude mice bearing MCF7-LG/FOXA1 xenografts in the presence of exogenous estrogen (E2) were randomized to ± Dox, each with continued E2, E2 deprivation (ED), or tamoxifen (Tam). Survival surgery removing the therapy-naïve (E2 arm) and relapsed (ED/Tam arms) tumors was performed when tumors reached ∼1000 mm3. All mice then received ED/Tam 'adjuvant' therapy, with longitudinal luminescence imaging to monitor local/distant recurrences. Mice were or will be euthanized at the ethical end-point. Integrative bioinformatics was performed using RNA-seq and FOXA1/ER ChIP-seq data from our preclinical models to identify secretome targets for functional intervention. Times to tumor regression (TTR) and progression (TTP) were defined by when the tumor reached half or twice the volume at randomization. Results: Median (m) TTR was achieved in ED (31/34 days, -/+Dox, P = 0.184) but not in Tam groups — Tam delayed tumor growth but failed to prevent progression in all mice with mTTP of 94/93 days (-/+Dox, P = 0.517). Despite no difference in mTTP at Tam-/+Dox, a quarter of +Dox tumors (3/12) had volume doubled by day 11. No metastases were observed by imaging in any of the mice before surgery ('neoadjuvant' setting). Local relapse and lymph-node/lung metastases were detected after surgery ('adjuvant' setting). At day 90 in the adjuvant Tam group with previously relapsed tumors, +Dox mice succumbed to metastasis more often than -Dox mice (7/8 vs. 3/10, P = 0.023). Compared to the adjuvant Tam+Dox mice with previous therapy-naïve tumors, the Tam+Dox with previously relapsed tumors showed higher distant metastasis rate (7/8 vs. 5/14, P = 0.026). Analysis of the ED setting is pending due to late recurrence. Data integration and functional study revealed a set of cytokines, growth factors, and extracellular matrix components (including IL-8, CTGF, and LOX), regulated by FOXA1 often in conjunction with ER, that are highly involved in FOXA1-induced metastasis. Global secretome profiling by mass spectrometry and target validation are ongoing. Conclusions: FOXA1 overexpression increases metastatic potential in ER+ BC. We established a pertinent metastatic xenograft mouse model to characterize a pro-metastatic secretome with diagnostic and therapeutic potential for treating metastatic ER+ BC.

Citation Format: Fu X, Pereira R, Zhao D, Jung SY, Jeselsohn R, Creighton CJ, Shea M, Nardone A, Angelis CD, Tsimelzon A, Wang T, Gutierrez C, Huang S, Edwards DP, Rimawi MF, Hilsenbeck SG, Brown M, Chen K, Osborne CK, Schiff R. FOXA1 induces a pro-metastatic secretome through ER-dependent and independent transcriptional reprogramming in endocrine-resistant breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr PD2-04.

Reactive structural dynamics of synaptic mitochondria in ischemic delayed neuronal death

The effect of transient global ischemia on the ultrastructural features of synaptic mitochondria at the distal dendrites of CA1 hippocampal neurons was investigated in 3-month-old rats. Sham surgery was performed on age-matched controls. The number of mitochondria/microm3 of neurophils (Nv: numeric density), the mitochondrial average size (average volume: V), and longer diameter (Fmax) as well as the overall fraction of neurophils occupied by mitochondria (volume density: Vv) were measured by computer-assisted morphometry. In ischemic rats, a 10% nonsignificant decrease of Nv was found, V increased nonsignificantly by 11%, and Fmax increased nonsignificantly by 5% versus controls. As a final outcome of these balanced changes, Vv remained unchanged between the two experimental groups investigated. In ischemic animals, the percentage distribution of V showed that the population of CA1 synaptic mitochondria was composed by an increased fraction of oversized organelles, while the Fmax distribution revealed that this enlargement was due to an increased percentage of elongated organelles. Thus, the observed increase in size should not be considered as a swelling phenomenon; on the contrary, it may represent a physiological and well-documented step in mitochondrial biogenesis. The above parameters are currently supposed to provide information on the adaptive structural reorganization of mitochondrial morphology under different environmental stimulations. Conceivably, these findings document a positive reactive response to ischemia of the mitochondrial structural dynamics at CA1 synaptic terminals and suggest consideration of these organelles as reliable targets in the development of neuroprotective therapeutic interventions to treat vascular brain diseases, for example, stroke.

Improved Tumor Targeting by Combined Use of Two Antitenascin Antibodies

PURPOSE

In the pretargeted antibody-guided radioimmunotherapy (PAGRIT) system, the combined use of two different antibodies directed against the same tumor antigen could represent a valid approach for improving tumor targeting and therapeutic efficacy. We developed a novel monoclonal antitenascin antibody, ST2485, and studied its biochemical and functional properties by in vitro and in vivo assays. We then investigated the first of the three-step therapy combining ST2485 with another antitenascin antibody, ST2146, previously described, to increase accumulation of biotinylated antibodies at the tumor site.

EXPERIMENTAL DESIGN

Studies of immunoreactivity, affinity, immunohistochemistry, and biodistribution in xenograft model were carried out on ST2485. Analysis of the ST2485 and ST2146 combination was preliminary carried out by ELISA and BiaCore tests and then by in vivo distribution studies after administration of the radiolabeled biotinylated antibodies, followed by a chase with avidin as clearing agent.

RESULTS

ST2485 was found to be a suitable antibody for therapeutic applications. Indeed, for its behavior in all tests, it was comparable with ST2146 and better than BC2, an antibody already used for clinical trials. The additivity of ST2146 and ST2485 in tenascin C binding, shown by in vitro tests, was confirmed by biodistribution studies in a xenograft model where tumor localization of the antibodies was near the sum of each antibody alone, with a tumor-to-blood ratio higher than 24.

CONCLUSION

The results reported in this study suggest that a monoclonal antitenascin antibody mixture can improve tumor targeting. This strategy could represent progress for therapeutic approaches such as PAGRIT.