Abstract P2-03-01: Akt inhibition associated with change in immunophenotype of tumor microenvironment (TME) in breast cancer (BC)

Background: The PI3K/Akt/mTOR pathway is a known oncogenic pathway in BC. In addition, this pathway has demonstrated capacity to modulate host immune activity and may indirectly affect tumorigenesis. Clinicopathologic studies have demonstrated that lymphocyte density within the TME is predictive of chemosensitivity and improved prognosis in BC, while myeloid infiltration may play a deleterious role. To define the impact of Akt inhibition on the TME, we analyzed tumor tissue from patients (pts) with early-stage BC treated with single agent MK-2206, an Akt inhibitor, enrolled on a presurgical trial (NCT01319539).

Methods: Quantitative immunofluorescence (qmIF) was performed for CD3, CD8, CD4, FOXP3, CD68, Pancytokeratin on 4uM sections from biopsy and surgical specimens of MK-2206 (n=5) and control (n=5) pts. Images were analyzed using Vectra/inForm software (PerkinElmer), allowing for multiparameter phenotyping. Transcriptomic analysis was performed on surgical specimens to assess if differences exist in mRNA expression of tumor-associated and immune genes between pts treated with MK-2206 (n=5) and untreated matched controls (n=5) (nanoString). Statistical analysis was performed using t-Test, NetBID, and multiple comparison analysis by Benjamini-Hochberg. Gene set enrichment analysis (GSEA) was performed within R with gene sets from Molecular Signatures Database (Hallmark, Reactome, GO).

Results: On qmIF analysis, MK-2206 treated pts exhibited a significant increase in median cytotoxic T-cell (CD3+CD8+, CTL) density between pretreatment biopsy and surgical excision specimens, as compared to the control pts (87% vs.0.2%, p < 0.05). Mean macrophage density (CD68+) was numerically lower in surgical specimens of pts who received MK-2206 vs. control pts, although CD68+ infiltration was overall low (p=ns). mRNA expression supports in vivo activity of MK-2206 with lower expression levels of cell cycle, proliferation and anti-apoptotic genes (e.g. CTNNB1, CCND2, BAX) and greater expression of pro-apoptotic genes (e.g. BAD) associated with MK-2206 treatment (raw p-value <0.05). Additionally, greater mRNA copy number of IGF1R, a receptor tyrosine kinase (RTK) previously identified as upregulated in BC in the context of Akt inhibition, was found in post-MK-2206 surgical specimens as compared to control, non-MK-2206 specimens (raw p-value <0.05). MK-2206 was also associated with reduced expression of myeloid markers (e.g. CSF1R, CD163) (raw p-value <0.05). By GSEA, canonical gene sets related to interferon signaling were increased in post-MK-2206 specimens as compared to non-MK-2206 specimens, whereas monocyte chemotaxis genes were decreased in treated pts (adj p-value <0.05). RT-PCR is currently underway to compare biopsy and surgical specimens for a subset of RTK, immune and apoptosis related genes identified above.

Conclusion: mRNA and qmIF analysis suggest that Akt inhibition, may increase interferon signaling, CTL density, and decrease myeloid infiltration. Thus, Akt inhibition may promote a favorable TME. At present, there are both FDA approved and investigational agents that target the PI3K/mTOR pathway. Further investigation is warranted to understand the impact of Akt inhibition on the TME and potential therapeutic implications.

Citation Format: Marks DK, Gartrell RD, Pan Q, El Asmar M, Hart TD, Esancy CL, Lu Y, Yu J, Hibshoosh H, Connolly E, Kalinsky K, Saenger YM. Akt inhibition associated with change in immunophenotype of tumor microenvironment (TME) in breast cancer (BC) [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 P2-03-01.

Abstract P5-03-03: Cytotoxic t-lymphocyte density increased within the tumor immune microenvironment of patients with breast cancer following treatment with Akt inhibitor MK-2206

Background: The PAM (PI3K/Akt/mTOR) signaling pathway has been implicated in the oncogenesis of multiple solid malignancies, including breast cancer (BC). Tumor infiltrating lymphocytes (TILs) found within the tumor immune microenvironment (TME) are both prognostic of overall survival as well as predictive of response to neoadjuvant chemotherapy in BC. Our aim is to characterize the TME in a series of patients with operable stage I-III BC treated with MK-2206, an allosteric Akt inhibitor as part of a presurgical, window of opportunity, trial. In our presurgical trial (clinicaltrials.gov #: NCT01319539), patients received 2 doses of MK-2206 with first dose at day -9 and second at day -2 from surgery. Methods: Quantitative multiplex immunofluorescence (qmIF) was performed using immune biomarkers (DAPI, CD3, CD8, CD4, FOXP3, CD68, Pancytokeratin) on full section (4uM) tissue slides from core biopsy specimens and postsurgical specimens of 10 patients - 5 patient treated with MK-2206, and 5 prospectively collected untreated controls. Images were taken using Vectra, a novel pathology workstation and analyzed using inForm software to perform cell classification and phenotyping. Student T- test was used to compare biomarker changes before and after MK-2206. Results: Preliminary analysis demonstrates that patients treated with MK-2206 exhibited a significantly increased median cytotoxic T-cells (CD3CD8+) density, as compared to the matched control cohort (87% vs.0.2%, p < 0.05). We did not identify a change in macrophage (CD68) or T helper/T reg (CD4/CD4FOXP3+) density following MK-2206 treatment in this small cohort. Proximity comparison, using nearest neighbor analysis was used to assess for potential impact of therapy on interactions between CD3CD8+ cells and BC cells. The median distance from CD3+CD8+ cells to nearest neighboring tumor cell was determined in both the pre and post tissues specimens for both groups. In patients treated with MK-2206, a 12.5% reduction in median distance was observed between CD3+CD8+ cells and tumor cells following treatment, suggestive that the increased effector T cells are not relegated to the periphery. This observation was not seen in the pre and post samples of the control cohort. Conclusions: In our study, we found that presurgical Akt inhibition lead to a significant increase in the cytotoxic T-cell population which was in similar proximity, if not closer, to tumor cells as compared to matched controls. Limitations of this exploratory study include a small patient cohort size and use of a single pathology evaluation technique. We are currently expanding our characterization of the TME with a more comprehensive myeloid panel as well as performing additional tissue analysis to validate our findings. At present, there are currently FDA approved therapies, as well as agents in clinical development that exert antineoplastic activity through the PAM pathway. Investigations that endeavor to understand the impact of these therapies on the TME may lead to both an increased understanding of the bioactivity of these agents and potentially identify aspects of the immune response which can be exploited by future immunotherapy therapeutics.

Citation Format: Marks DK, Gartrell RD, Asmar ME, Hart TD, Lu Y, Esancy CL, Hibshoosh H, Connolly EP, Kalinsky KM, Saenger YM. Cytotoxic t-lymphocyte density increased within the tumor immune microenvironment of patients with breast cancer following treatment with Akt inhibitor MK-2206 [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-03-03.