Abstract P2-08-02: Novel tumor suppressor regulating the PI3K/AKT pathway in breast cancer

Breast cancer affects approximately 1 in 8 women over the course of their lifetime. Of the many genes and pathways deregulated by this heterogeneous disease, alterations of members in the PI3K/AKT pathway are present in approximately 20% of all cases, making it one of the more frequently mutated pathways in breast cancer. The PI3K/AKT pathway is well known to be involved in essential cellular processes necessary for cancer development and progression, including altered proliferation, metabolism, and cell survival. Previous studies have made it well known that the activation of AKT is regulated through its phosphorylation, but recent studies have also shown that AKT can also be regulated via ubiquitination, leading to AKT hyperactivation. However, the mechanism and players involved in this process are not well understood. Better understanding of these pathways could inform on better potential therapeutics to target this disease.

Recent work in our lab has identified GPS2, a member of the NCoR/SMRT complex, as a regulator of the insulin-signaling pathway through the inhibition of AKT ubiquitination by Ubc13. As many human cancers frequently have an increase in activated AKT, here we explore the potential of GPS2 as a tumor suppressor in the context of breast cancer and hope to elucidate the mechanism by which AKT ubiquitination regulates its activation.

Citation Format: Chan S, Cardamone MD, Perissi V. Novel tumor suppressor regulating the PI3K/AKT pathway in breast cancer [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 P2-08-02.

Phase II study of buparlisib (BKM120) and trastuzumab in patients with HER2+ locally advanced or metastatic breast cancer resistant to trastuzumab-based therapy

PURPOSE

A Phase Ib study in patients with trastuzumab-resistant, human epidermal growth factor receptor-2- (HER2)-positive advanced breast cancer defined the recommended Phase II dose of buparlisib as 100 mg/day in combination with 2 mg/kg weekly trastuzumab, and reported preliminary signs of clinical activity. Here we present results from the Phase II portion.

METHODS

Patients with trastuzumab-resistant, HER2-positive advanced breast cancer received buparlisib plus trastuzumab. Study endpoints included safety/tolerability and antitumour activity. The study was extended to include a Phase Ib dose-escalation phase, in which patients with progressive brain metastases also received capecitabine.

RESULTS

In the Phase II portion, of 50 patients treated with buparlisib and trastuzumab, the most common (≥ 30%) all-grade adverse events (AEs) were diarrhoea (54%), nausea (48%), decreased appetite, increased alanine aminotransferase (36% each), increased aspartate aminotransferase (34%), fatigue, rash (32% each), cough and hyperglycemia (30% each). One (2%) patient achieved complete response and four (8%) patients had confirmed partial responses [PR; including two patients with phosphatidylinositol 3-kinase (PI3 K) pathway-activated tumours]. Overall response rate (ORR) was 10%: the primary endpoint (ORR ≥ 25%) was therefore not met. In the Phase Ib portion, all patients with measurable brain lesions at baseline showed tumour shrinkage to some degree; due to low enrollment, maximum tolerated dose of buparlisib in combination with trastuzumab and capecitabine was not determined.

CONCLUSION

Buparlisib plus trastuzumab, as a chemotherapy-free regimen, demonstrated an acceptable safety profile but limited efficacy in patients with heavily pretreated, trastuzumab-resistant HER2-positive breast cancer, and in patients with progressive brain metastases also receiving capecitabine.

Abstract P2-08-01: Results from a randomized placebo-controlled phase 2 trial evaluating exemestane ± enzalutamide in patients with hormone receptor–positive breast cancer

This abstract was withdrawn by the authors.

Abstract P3-07-18: Exercise and triple negative breast cancer: Unravelling the anti-neoplastic molecular factors through novel culture method

Background

Despite advances to ameliorate breast cancer survival, triple negative breast cancers (TNBCs) attribute to highly disproportionate mortalities due to its aggressiveness and poor therapeutic response (Bao et al., Cancer Medicine 2014). Despite the lack of target-specific drugs, chemotherapy is the mainstay treatment, warranting more efficacious measures against TNBCs. Studies have shown that physical activity intervention reduced breast cancer risk between 20-80% (Monnikohf et. al., Epidemiology 2007) as well as breast cancer related mortality by 34% (Ibrahim et al., Med Onc 2010). However, it is clear that such intervention uptake in the population may not be feasible given the longstanding public health drive to increase physical activity. Therefore it is imperative to identify the molecular factors that might be involved in cancer prevention and therapy with the long term goal of developing a supplement. Due to the recent epidemiological findings on exercise and breast cancer, we wanted to develop a system to comprehensively identify beneficial myokines using a cell culture system.

Methods

For this study we differentiated C2C12 myoblasts into myotubules. Myotubules were contracted in Krebs Ringer Buffer solution with the C-Pace EP Pacer for 8 hours. Buffer was collected and concentrated using Amicon Ultra-0.5 centrifugal filter tubes to produced an exercise/conditioned medium. To explore the effects of exercise on breast cancer cell lines MCF-7 (ER+) and MDA-MB468 (TNBC line) were treated with conditioned medium for 48 hrs. To explore the effects of exercise and chemotherapeutic efficacy MDA-MB468 cells were treated with doxorubicin, conditioned medium or both for 48 hrs. Protein was isolated and processed for immunoblot analysis. Cell cycle markers p21, pRb, cyclin D1, PCNA as well as apoptotic marker cPARP were assessed to reveal the effects treatment.

Results

Treatment of conditioned medium in MCF-7 revealed marked changes in both p21 (92% increase, p=0.05) and pRb protein expression (62% decrease, p<0.05) as well as a modest reduction in PCNA (24% decrease , p<0.02). Conditioned medium treatment in MDA-MB468 cells showed a reduction in cyclin D1 and PCNA expression (40%, p<0.01 and 30%, p<0.02) as well as an induction of cPARP expression (32%, p=0.09). Doxorubicin treatment increased p21 and cPARP protein expression (2.2-fold increase, p<0.01 and 80% increase, p<0.05 respectively). Treatment of conditioned medium and doxorubicin displayed a synergistic effect with a 3.65-fold increase in p21 (p<0.01) and 130% increase in cPARP (p=0.01).

Conclusions

We have developed a novel system that may enable, for the first time, mechanistic studies to elucidate the role of skeletal muscle/exercise in breast cancer prevention and chemotherapy. Our data indicates a secreted factor(s) from skeletal muscles that plays a role in anti-proliferative and pro-apoptotic effects, which are the hallmark of exercise's anti-neoplastic properties. Studies are ongoing to further understand, characterize and isolate this factor(s) for therapeutic purposes. Given the limited chemotherapeutic options and heterogeneity in TNBC, our exercise culture system sheds a promising light on novel drug development and chemo-sensitization.

Citation Format: Dela Cruz MA, Roy P, Chowdhury S, Chan S, Roy HK. Exercise and triple negative breast cancer: Unravelling the anti-neoplastic molecular factors through novel culture method [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 P3-07-18.

Abstract P4-22-08: A single-arm phase 2 study to assess clinical activity, efficacy and safety of enzalutamide with trastuzumab in HER2+ AR+ metastatic or locally advanced breast cancer

Background:Androgen receptor (AR) expression has been observed in up to 77% of human epidermal growth factor receptor 2–positive (HER2+) breast cancer (BC).References:1 Enzalutamide (ENZA) is a potent AR inhibitor approved for patients (pts) with metastatic castration-resistant prostate cancer. In vitro, ENZA enhances antitumor activity of trastuzumab in HER2+ AR+ cell lines and inhibits proliferation in trastuzumab-resistant HER2+ cell lines.2

Methods:Pts with metastatic or locally advanced BC that was HER2+ AR+ by local or central laboratory assessment were enrolled in a single-arm, Simon 2-stage phase 2 study (NCT02091960). Key eligibility criteria included availability of a tissue sample, presence of measurable or evaluable disease per RECIST v1.1, progression on prior trastuzumab and ≥1 prior line of anti-HER2 therapy as the most recent regimen. Brain metastases and history of seizure were exclusionary. Evaluable pts were those with centrally confirmed nuclear AR expression≥10% by immunohistochemistry who received ≥1 dose of ENZA and had ≥1 postbaseline tumor assessment. Pts received ENZA 160 mg daily and trastuzumab 6 mg/kg every 21 days until disease progression. The primary objective was clinical benefit rate at 24 weeks (CBR24), defined as complete or partial response (CR or PR) or stable disease (SD) for ≥24 weeks in evaluable pts. Additional endpoints included safety and progression-free survival (PFS). CBR24 in ≥3 of 21 evaluable pts was required to continue to stage 2 and enrollment of up to 66 evaluable pts total. This design yields a 1-sided type 1 error of 5% and 90% power when the true response is 25%.

Results:Here we present results from stage 1 (data cutoff: Mar 23, 2016), with 22 evaluable pts enrolled (pts 21 and 22 enrolled simultaneously); 18 had received ≥4 prior lines of therapy. Median duration of ENZA exposure was 144 days (range, 22-495), mean number of complete trastuzumab infusions was 6.5. CBR24 was 27.3% (95% confidence interval [CI], 10.7-50.2); 2 confirmed PR and 4 SD ≥24 weeks. Median PFS was 108 days (95% CI, 56-144). All pts experienced ≥1 adverse event (AE) any grade; 5 pts experienced AEs grade ≥3. ENZA-related AEs were reported in 16 pts (72.7%), the most common (in ≥10% of pts) were fatigue (22.7%), nausea (18.2%), diarrhea (13.6%) and arthralgia (13.6%). Serious AEs were reported in 6 pts (27.3%; 2 each of infection and back pain, 1 each of abdominal pain, nausea, vomiting, pyrexia, urinary retention and pulmonary edema). Two pts discontinued due to drug-related AEs: 1 related to both drugs, 1 related to trastuzumab. One on-study death from pulmonary edema was reported, which was not considered related to either drug.

Conclusion:Stage 1 met its primary objective. No new safety signals were identified, and the safety profile in this study was similar to that in men with prostate cancer and women with other BC subtypes treated with ENZA. These results are encouraging for a heavily pretreated population with advanced HER2+ AR+ BC. Enrollment in stage 2 continues with the combination of ENZA and trastuzumab.

1. Micello D et al. Virchows Arch. 2010;457:467-476.

2. Richer J. Presented at AACR Advances in Breast Cancer, San Diego, CA, 2013.

Citation Format: Krop I, Cortes J, Miller K, Huizing MT, Provencher L, Gianni L, Chan S, Trudeau M, Steinberg J, Sugg J, Liosatos M, Paton VE, Peterson A, Wardley A. A single-arm phase 2 study to assess clinical activity, efficacy and safety of enzalutamide with trastuzumab in HER2+ AR+ metastatic or locally advanced breast cancer [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 P4-22-08.