Abstract P2-07-04: A novel diagnostic androgen receptor gene signature links clinical outcomes and preclinical response to enzalutamide, paclitaxel or the combination in triple-negative breast cancer

Background: The androgen receptor (AR) is expressed in ≈70% of all breast cancers (BCs) and may be necessary for proliferation and survival advantage in AR+ tumors. A novel gene signature associated with AR-signaling biology (PREDICT AR) was developed by sequencing triple-negative BC (TNBC) tumors collected in a phase 2 study evaluating enzalutamide (ENZA) monotherapy1; clinical outcomes were superior in patients (pts) with PREDICT AR+ vs PREDICT AR- tumors.1,2 ENZA blocks nuclear localization and suppresses its activity.3 Paclitaxel (PTX) stabilizes microtubules and may also block AR nuclear localization. Thus we hypothesize that response to PTX-based therapy may be additive in PREDICT AR+ vs PREDICT AR- disease. This study sought to identify independent clinical datasets with PREDICT AR+ gene signature to assess outcomes following PTX-based therapy. Preclinically, we investigated the antitumor activity of ENZA, PTX, or ENZA+PTX in AR-driven TNBC models.

Methods: We probed publicly available TNBC clinical databases from Gene Expression Omnibus datasets to assess PREDICT AR status and clinical outcomes. Similarly, we assessed 21 TNBC lines for PREDICT AR status. BT549, MDA-MB-436, and MDA-MB-453 were treated with ENZA, PTX, or ENZA+PTX to determine activity. Cell signaling and pathway activation were assessed by western blot. ENZA and PTX activity was assessed in PREDICT AR+ xenograft models. Tumor RNA sequencing and immunohistochemistry were used to identify gene signatures, potentially predictive biomarkers, and potential synergistic effects of ENZA+PTX.

Results: The prevalence of PREDICT AR+ tumors in one cohort of 182 pts with primary TNBC4 was 51%. Distant relapse-free survival following PTX-based adjuvant/neoadjuvant therapy was not statistically different between pts with PREDICT AR+ vs PREDICT AR- TNBC (p=0.605). Pathologic complete response rates were 12.5% for PREDICT AR+ vs 21.0% for PREDICT AR- TNBC. Additional sets of pts with primary TNBC are being evaluated. Preclinically, we observed a dose-dependent inhibition of cell viability with either ENZA or PTX in AR+ TNBC cell lines and additive effects from ENZA+PTX. In PREDICT AR+ xenograft models, ENZA or PTX treatment resulted in a dose-dependent antitumor response. Combination studies are underway. Tumor RNA sequencing are being evaluated for gene signature of synergistic antitumor response to ENZA+PTX.

Conclusion: Analyzing publicly available clinical datasets, we found that PREDICT AR+ status was not associated with differential outcomes following PTX-based therapy in primary TNBC, suggesting there is potential to provide additive benefits in PTX-based therapy with ENZA. In preclinical studies, we observed additive effects when combining ENZA+PTX in PREDICT AR+ TNBC lines compared with single agent treatments. Taken together, these data suggest ENZA combined with PTX might provide additive benefits in a clinical setting for pts with PREDICT AR+ TNBC.

References

1. Traina TA et al. J Clin Oncol 2015:33(suppl):abstr 1003.

2. Parker J et al. J Clin Oncol 2015;33(suppl):abstr 1083.

3. Tran C et al. Science 2009;324:787-90.

4. Hatzis C et al. JAMA 2011;305:1873-81.

Citation Format: Phan VT, Protter AA, Peterson AC, Parker JS, Yoon K, Tudor IC, Paton V, Noonberg S, Uppal H. A novel diagnostic androgen receptor gene signature links clinical outcomes and preclinical response to enzalutamide, paclitaxel or the combination in triple-negative breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-07-04.

Construction of adenovirus for high level expression of small RNAs in mammalian cells. Application to a Bcl-2 ribozyme

A series of plasmid vectors have been generated to allow the rapid construction of adenoviral vectors designed to express small RNA sequences. A truncated human U6 gene containing convenient restriction sites has been shown to be expressed at high levels following electroporation into a series of human cell lines. This gene was ligated into a promoterless adenoviral plasmid, and we have generated high titer virus by homologous recombination with adenoviral Addl327 DNA in 293 cells. Recombinant adenovirus containing a hammerhead ribozyme sequence targeted toward the Bcl-2 mRNA has been used to transduce a panel of human tumor cell lines. We have demonstrated high level expression of the recombinant U6 gene containing the ribozyme and reduction of Bcl-2 protein in transduced cells. These plasmids are suitable for the development of adenoviral vectors designed to express both ribozymes and antisense RNA in human cells.

Biological availability and nuclease resistance extend the in vitro activity of a phosphorothioate-3'hydroxypropylamine oligonucleotide

Augmented biological activity in vitro has been demonstrated in oligonucleotides (oligos) modified to provide nuclease resistance, to enhance cellular uptake or to increase target affinity. How chemical modification affects the duration of effect of an oligo with potent activity has not been investigated directly. We postulated that modification with internucleotide phosphorothioates and 3' alkylamine provided additional nuclease protection which could significantly extend the biological activity of a 26 mer, (T2). We showed this analog, sT2a, could maximally inhibit interferon gamma-induced HLA-DR mRNA synthesis and surface expression in both HeLa and retinal pigmented epithelial cells and could continue to be effective, in the absence of oligo, 15 days following initial oligo treatment; an effect not observed with its 3'amine counterpart, T2a. In vitro stability studies confirmed that sT2a conferred the greatest stability to nucleases and that cellular accumulation of 32P-sT2a in both cell types was also greater than other T2 oligos. Using confocal microscopy, we revealed that the intracellular distribution of sT2a favored greater nuclear accumulation and release of oligo from cytoplasmic vesicles; a pattern not observed with T2a. These results suggest that phosphorothioate-3'amine modification could increase the duration of effect of T2 oligo by altering nuclease resistance as well as intracellular accumulation and distribution; factors known to affect biological availability.