Abstract P4-07-03: Immunomodulation of triple negative breast cancer by caffeic acid phenethyl ester (CAPE)
Authors: Omene C , Patel M , Karagoz K , Gatza ML , Barcellos-Hoff MH 
Published: May 2019

Background: CAPE is the major active component of propolis, a widely available, safe, honeybee natural product with anti-inflammatory, antioxidant, and antitumor properties. We have previously shown diverse effects of CAPE in breast cancer. We postulated that CAPE may be useful in primary or secondary prevention for triple-negative breast cancers (TNBC) and evaluated this in a Trp53 null mammary chimera model in which the tumor spectrum is shifted to TNBC when the host is irradiated (Nguyen, 2011). Bioinformatics species comparisons show that TNBC from this model exhibits a spectrum of tumors that is molecularly similar to that seen in human TNBC (Nguyen, 2013).

Methods: The model consists of Trp53 null mammary epithelium transplanted to cleared mammary glands of wildtype mice. Mice irradiated with 1 Gy received transplants 3 days later and were placed on a CAPE or a control diet at 1month post transplantation that was maintained throughout the experiment. Tumor development was monitored by palpation for up to 18 months. Tumors were immunostained for estrogen receptor (ER) status and ER negative tumors were selected from all the groups for RNA sequencing. TNBC molecular subtypes were determined for control (n=5) and CAPE treated (n=9) samples using methods described by Lehman, 2011. Gene expression signatures consisting of 270 genes was analyzed for functional enrichment to identify patterns of signaling, as well as additional tumor characteristics, in each cohort of tumors.

Results: Host irradiation significantly accelerated tumor growth rate compared to the control sham irradiated mice. CAPE treatment blocked this effect, but did not affect the control tumor growth rate. Resected tumors in CAPE treated mice recurred at significantly longer intervals (40 days in control group versus 90 days with CAPE) and much less frequently than tumors from mice on a control diet. Mean expression analysis showed that CAPE induces a distinct gene expression pattern in ER negative tumors from irradiated mice. As previously described (Illa-Bochaca, 2014), ER negative tumors from sham irradiated mice on a control diet were enriched in immune response genes. These genes were suppressed in tumors arising in irradiated host, but this effect of host irradiation was abrogated in mice on the CAPE diet. While untreated tumors were classified into the Basal-like 2 (BL2) or Mesenchymal TNBC molecular subtypes, we observed an increase in subtype diversity after CAPE treatment with tumors being classified as Immunomodulatory and Luminal Androgen Receptor (LAR) in addition to BL2 and Mesenchymal subtypes. Consistent with these data, functional enrichment analyses of RNA sequencing data identified increased immune signaling as well as upregulation of a number of signaling pathways including TGFβ, HGF, and EGFR in treated samples.

Conclusion: These findings support the potential use of CAPE to modify the aggressive behavior of TNBC, which may be due to effects on the immune system in which CAPE acts to re-establish anti-tumor immunity. The finding that CAPE treatment shifts the tumor spectrum to Immunomodulatory subtypes suggests that it may be useful both for women at high risk for TNBC and to prevent or delay TNBC breast cancer recurrence, perhaps in combination with immunotherapy.

Citation Format: Omene C, Patel M, Karagoz K, Gatza ML, Barcellos-Hoff MH. Immunomodulation of triple negative breast cancer by caffeic acid phenethyl ester (CAPE) [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 P4-07-03.