Abstract B37: Increased expression of poly (ADP-ribose) polymerase (PARP) and phospho-p65 in human HER2+ breast cancer

Abstract

Abstract Background: Despite the efficacy of targeted agents against the HER2 receptor, many patients with HER2+ breast cancer will develop resistance, thus necessitating novel treatment strategies. Poly (ADP-ribose) polymerase inhibitors (PARPi) are a well-tolerated class of drugs that target tumors with defective DNA repair pathways. Interestingly, we previously reported that HER2+ breast cancer cells are sensitive to PARPi alone both in vitro and in vivo independent of a basal or induced DNA repair defect (Nowsheen et al., Cancer Research 2012). Further, we found that attenuation of NF-κB signaling may account for this intriguing susceptibility. To further substantiate the potential utility of PARPi in HER2+ breast cancer, we investigated the expression and cellular location of PARP and phospho-p65, indicators of activity of the PARP and NF-κB pathways, respectively, in human HER2+ breast cancer specimens and compared to HER2- breast tumors. Methods: Breast cancer patients treated at UAB with available stored tissue blocks between the years 1999 and 2012 were identified. Formalin-fixed, paraffin-embedded tissue blocks were stained for PARP and phospho-p65 and evaluated independently by two blinded physicians, including a board-certified pathologist. An H-score was calculated by multiplying the percent of tumor cells with staining intensity of 0, 1, 2, and 3+ and subsequently adding these together for a final score of 0-300. Nuclear and cystosolic staining were scored separately for both proteins. The number of samples with 2 or 3+ staining of PARP or phospho-p65 in each group was also assessed. Results: Forty-one HER2+ and 32 HER2- cases were examined. PARP and phospho-p65 were found to be almost exclusively nuclear in both groups. The mean H-score for nuclear PARP was 122.3 in HER2+ cases compared to 61.6 in HER2- cases (p value <0.0001). Mean H-scores for nuclear phospho-p65 were 89.0 and 59.4 in HER2+ and HER2- groups, respectively (p value 0.0008). Further, a statistically significant positive correlation was observed between PARP and phospho-p65 levels. Interestingly, a significant difference was also observed between the percent of HER2+ and HER2- tumors with ≥2+ staining of PARP and phospho-p65. Seventy-three percent of HER2+ patients had ≥2+ PARP staining compared to 37% of the HER2- group (p value 0.0039). Likewise, 61% versus 16% of the HER2+ and HER2- patients, respectively, had ≥2+ phospho-p65 staining (p value 0.0001). Conclusions: Our study suggests that HER2+ breast cancers have elevated markers for PARP and NF-κB activity compared to HER2- cancers. A direct correlation between PARP and phospho-p65 levels was also found. Furthermore, staining of ≥2+ for either protein was significantly different between the two groups suggesting this as a potential biomarker for clinical application. When combined with our previously published preclinical findings, the current research supports the potential clinical utility of PARPi in patients with this aggressive form of breast cancer. Citation Format: Lisa Klepczyk, Shi Wei, Jason Brazelton, Kimberly Keene, Yufeng Li, James Bonner, Andres Forero, Albert LoBuglio, William Grizzle, Eddy Yang. Increased expression of poly (ADP-ribose) polymerase (PARP) and phospho-p65 in human HER2+ breast cancer. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Synthetic Lethal Approaches to Cancer Vulnerabilities; May 17-20, 2013; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(5 Suppl):Abstract nr B37.