Abstract P2-03-07: Backwards translation: Exploring beta-adrenoreceptors (ßAR) in triple negative breast cancer (TNBC), a novel and druggable pathway

Introduction: several retrospective studies suggest that ßAR blocking drugs (BB) are associated with improved survival in patients with a wide range of cancers. Recently, we retrospectively showed an association between BB intake and improved progression free survival in patients with HER2 negative advanced breast cancer (BC), particularly striking in triple-negative disease (TNBC) (Reference). Based on this finding we decided to conduct an in silico study in which we have interrogated ßARs in a publicly available BC sample database and the Translational Oncology Research Lab (TORL) translational platform with a genomic, transcriptomic and proteomic approach. Methodology: genomic and transcriptomic data sets for ßAR 1, 2 and 3 were retrieved from cBioPortal considering all BC samples available with this information in The Cancer Genome Atlas (TCGA). Transcriptomic and proteomic data sets from 48 BC cell lines obtained from TORL were queried for ßARs as well and used with validation and exploratory intent. Mutations, amplifications and deletions were queried in DNA; gene expression profiles were interrogated using RNAseq data together with protein expression by RPPA. Average expression, log ratio and fold change in mRNA and Reverse Phase Protein Array (RPPA) quantitative assessments for corresponding proteins were noted. BC cell lines with top 10 mRNA and protein levels of ßAR 1, 2 and 3 were identified. Results: CBioPortal DNA data shows ß AR1 amplified in 1-10% and deleted in 0,4%; ß-AR2 amplified in 1-3% and deleted in 0,1%; ß-AR3 amplified in 15-20% and deleted in 2% of the BC samples. CBioPortal mRNA data shows ß-AR1 is upregulated in 2.7% (mostly Progesterone Receptor negative BC); ßAR2 is upregulated in 4% (mostly TNBC); ßAR3 is upregulated in 4% (mostly HER2 negative BC) in BC samples. TORL cell line panel shows that ßARs are heterogeneously expressed between the BC cell lines (fold change range: ßAR 1 2.015-3.636; ßAR2 2.545-8.248; ßAR3 1.809-2.444). Within the 10 BC cell lines with highest ßAR1 and ßAR2 expression, 7(COLO-824, HCC1937, BT-549, BT-20, HCC1599, HCC1143, HCC1806) and 6 (184A1, MDA-MB-231, 184B5, HCC1806, MCF-10A and MDA-MB-468) of them respectively correspond to the basal BC subtype. RPPA identifies caveolin 1, PAI 1, EGFR and Bax as the proteins with the higher co-expression with ßAR1 and ßAR2. Conclusions: DNA alterations are infrequent in ßARs in BC samples. Transcriptional mRNA data from BC samples shows ßARs mostly expressed in non-luminal BC subtypes, being ßAR 2 the one with highest expression. In silico data results from BC cell line panel show ßAR 1 and ßAR 2 are highly expressed in basal BC subtype. The above data suggest that ßAR, and ßAR 2 in particular could be a relevant target to explore in in vivo BC models.

Table 1:mRNA and RPPA in BC cell linesCell lineAverage mRNALog RatioFold ChangeCaveolin 1PAI1EGFR184A1313173.048.244.183.411.72SUM-190223292.811.03-1.37-0.570.09MDA-MB-231151002.997.993.853.251.57184B5130121.973.933.902.361.82HCC1806124112.375.193.750.491.67MCF-10A119122.194.583.892.670.08ZR-75-3093001.893.72-1.51-0.61-0.25JIMT-163541.593.013.082.010.81MDA-MB-41562391.242.370.96-0.39-0.13MDA-MB-46862801.342.541.06-0.251.72

Citation Format: Spera G, Von Euw E, Fresco R, Slamon DJ. Backwards translation: Exploring beta-adrenoreceptors (ßAR) in triple negative breast cancer (TNBC), a novel and druggable pathway [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-03-07.

Abstract P3-04-15: The PI3K-inhibitor, copanlisib, has selective activity in luminal breast cancer cell lines and shows robust combined activity with hormonal blockade and CDK-4/6 inhibition in ER+ breast cancer cell line xenografts

Background: Genetic and epigenetic alterations in the PI3K/mTOR and cyclin D:CDK-4/6:Rb signaling axes occur frequently in breast cancer and have been attributed to resistance to both ER- and HER2-directed therapeutics. Pharmacologically targeting CDK-4/6 in combination with hormonal blockade provides clinical benefit in patients with advanced ER+ breast cancer. In this study, we evaluated the activity of the pan-class I PI3K inhibitor, copanlisib (BAY-80-6946), with potent alpha and delta activity as a single agent or in combination with CDK-4/6 inhibition and hormonal blockade in a panel of breast cancer cell lines.

Methods: The growth inhibitory activity of copanlisib was evaluated against a large panel of 48 breast cancer cell lines molecularly characterized by genomic, transcriptomic and proteomic profiling. IC50 values were determined from direct cell counts using a Z1-particle counter. The activity of copanlisib in combination with hormone blockade and CDK-4/6 inhibition, by palbociclib, was assessed in two cell line xenograft models of ER+ breast cancer; MCF7(PIK3CA-E545K) and ZR751(PIK3CA WT). For xenograft studies, tumor bearing mice were treated once weekly (BID) by intravenous injection with clinically achievable doses of copanlisib (10 mg/kg) as single agent or in combination with tamoxifen or fulvestrant with or without 75 mg/kg daily palbociclib for 21 days.

Results: A broad range of IC50 values (0.491-895 nM), with a high degree of separation between sensitive and resistant histologically defined subgroups were determined for copanlisib, indicating the potential for a wide therapeutic window. Luminal subtype, the presence of activating mutations in PIK3CA, high levels of ER, HER2, HER3 and EGFR protein enriched for sensitivity to copanlisib. Activating mutations of KRAS and BRAF were associated with resistance to copanlisib. Single agent copanlisib induced significant tumor growth inhibition (TGI) relative to vehicle control in each of the xenograft models. Modest increases in anti-tumor activity were achieved when copanlisib was combined with hormonal blockade by either tamoxifen or fulvestrant. However, robust tumor regressions were observed with the triple combinations of copanlisib-palbociclib-tamoxifen and copanlisib-palbociclib-fulvestrant. Furthermore, these triple combinations achieved a statistically significant improvement in anti-tumor activity over the standard of care combination of palbociclib plus fulvestrant. Each of the single agent and treatment combinations tested were well tolerated in animals.

Discussion: These preclinical data illustrate the potent and selective activity of the pan class I PI3K inhibitor copanlisib in luminal breast cancers and support the clinical investigation of copanlisib in combination with CDK-4/6 inhibition and hormonal blockade in ER+ breast cancer.

Citation Format: O'Brien NA, Conklin D, Luo T, Ayala R, Issakhanian S, Kalous O, Von Euw E, Politz O, Wilhelm S, Childs BH, Hurvitz SA, Slamon DJ. The PI3K-inhibitor, copanlisib, has selective activity in luminal breast cancer cell lines and shows robust combined activity with hormonal blockade and CDK-4/6 inhibition in ER+ breast cancer cell line xenografts [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 P3-04-15.

Abstract P4-08-01: PI3K/mTOR inhibition overcomes in vitro and in vivo trastuzumab resistance independent of feedback activation of pAKT

Background: Aberrant activity of the PI3K/mTOR pathway has been implicated in resistance to trastuzumab and anti-hormonal therapy for HER2-amplified and ER-positive breast cancer, respectively. Previous studies in our laboratory and others have shown that increased PI3K/mTOR signaling, either through PTEN loss or activating PIK3CA mutations, can confer resistance to trastuzumab therapy. In this study, we assessed the potential of targeting the PI3K/mTOR pathway in overcoming both de novo and acquired trastuzumab resistance.

Materials and Methods: The in vitro activity of the pan-PI3K inhibitor BKM120, the mTORC1 inhibitor RAD001 and the dual PI3K/mTORC1/2 inhibitor BEZ235 were evaluated in a panel of 49 human breast cancer and immortalized cell lines. The in vivo activity of these molecules was assessed in six cell line xenografts models representing, ER+/HER2− (KPL-1, ZR75-1), ER+/HER2+ (UACC812, MDA361), ER−/HER2+ (SUM190), PIK3CA mutant (SUM190, MDA361), PTEN-null (ZR75-1) and trastuzumab resistant (BT-TR) breast cancer. Finally, the effect of PI3K/mTOR inhibition on feedback activation of PI3K signaling and compensatory pathways was measured by Western blot, immunohistochemistry (IHC) and reverse phase protein analysis (RPPA) of control and treated cell lysates/tumors.

Results: Using a sensitivity cut-off of an IC50 of < 1 µmol/L, 16 of the 18 HER2-amplified breast cancer cell lines and 8 of 10 cell lines with activating mutations in PIK3CA were sensitive to the pan-PI3K inhibitor BKM120. BEZ235 showed the most potent efficacy across the panel with IC50s < 100 nmol/L for each of the 49 cell lines tested. The HER2-amplified/PIK3CA mutant cell lines were also unexpectedly sensitive to the mTORC1 inhibitor RAD001, this was despite the silencing of mTORC1 signaling being followed by a feedback increase in phospho-AKT signaling. Furthermore, each of these molecules showed remarkable in vivo activity across the panel of xenografts models. BKM120, RAD001 and BEZ235 induced both tumor stabilization and regression independent of PTEN, PI3K, ER and HER2 status. Pharmacodynamic analysis of tumor tissue revealed that BEZ235 and RAD001 both inhibited mTORC1 signaling as indicated by a reduction in the levels of phosphorylated ribosomal protein S6 (pS6). However, in contrast to BKM120 and BEZ235, RAD001 did not induce a reduction in the levels of pAKT (S473 or TH308) yet showed comparable in vivo efficacy to each of these molecules. Finally, combined targeting of HER2 and PI3K/mTOR in vitro increased the anti-proliferative activity of the molecules and led to an increased induction of apoptosis. The efficacy of these molecules (alone or in combination with trastuzumab) was assessed in a model of in vivo trastuzumab resistance generated through long-term treatment of the trastuzumab sensitive BT474 cells (BT-TR). All PI3Ki induced complete inhibition of tumor proliferation in monotherapy, while the combination of trastuzumab and each of these molecules induced tumor regression in the trastuzumab resistant tumors.

Discussion: These pre-clinical data indicate that targeting the PI3K/mTOR pathway either alone or in combination with trastuzumab is effective strategy for overcoming trastuzumab resistance.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-08-01.