RB loss determines selective resistance and novel vulnerabilities in ER-positive breast cancer models

The management of metastatic estrogen receptor (ER) positive HER2 negative breast cancer (ER+) has improved; however, therapeutic resistance and disease progression emerges in majority of cases. Using unbiased approaches, as expected PI3K and MTOR inhibitors emerge as potent inhibitors to delay proliferation of ER+ models harboring PIK3CA mutations. However, the cytostatic efficacy of these drugs is hindered due to marginal impact on the expression of cyclin D1. Different combination approaches involving the inhibition of ER pathway or cell cycle result in durable growth arrest via RB activation and subsequent inhibition of CDK2 activity. However, cell cycle alterations due to RB loss or ectopic CDK4/cyclin D1 activation yields resistance to these cytostatic combination treatments. To define means to counter resistance to targeted therapies imparted with RB loss; complementary drug screens were performed with RB-deleted isogenic cell lines. In this setting, RB loss renders ER+ breast cancer models more vulnerable to drugs that target DNA replication and mitosis. Pairwise combinations using these classes of drugs defines greater selectivity for RB deficiency. The combination of AURK and WEE1 inhibitors, yields synergistic cell death selectively in RB-deleted ER+ breast cancer cells via apoptosis and yields profound disease control in vivo. Through unbiased efforts the XIAP/CIAP inhibitor birinapant was identified as a novel RB-selective agent. Birinapant further enhances the cytotoxic effect of chemotherapies and targeted therapies used in the treatment of ER+ breast cancer models selectively in the RB-deficient setting. Using organoid culture and xenograft models, we demonstrate the highly selective use of birinapant based combinations for the treatment of RB-deficient tumors. Together, these data illustrate the critical role of RB-pathway in response to many agents used to treat ER+ breast cancer, whilst informing new therapeutic approaches that could be deployed against resistant disease.

Alpelisib for the treatment of PIK3CA-mutated, hormone receptor-positive, HER2-negative metastatic breast cancer

Introduction: Two-thirds of advanced breast cancers are hormone receptor (HR)-positive and human epidermal growth factor receptor 2 (HER2)-negative (HR+/HER2-). Gene mutations in PIK3CA, encoding the PI3K catalytic subunit alpha of phosphatidyl-inositol 3-kinase (PI3K), are a frequent event in this population and are implicated in hormone therapy resistance. Alpelisib is a PI3K-alpha inhibitor and is the first PI3K inhibitor approved, in association with fulvestrant, by the FDA and EMA, based on improved progression-free survival (PFS) versus fulvestrant alone in a randomized phase III trial in HR+/HER2-, PIK3CA-mutated tumors following progression on/after HT.Areas covered: The scientific rationale, preclinical development, pharmacokinetics, and clinical efficacy/safety of alpelisib-fulvestrant are summarized. The role of alpelisib in the clinical setting is discussed, referencing current therapeutic options and clinical challenges associated with alpelisib's safety profile.Expert opinion: Alpelisib is an option for patients with HR+/HER2-, PIK3CA-mutated tumors whose disease progressed during/after aromatase inhibitor treatment. The PFS benefit appears clinically significant over fulvestrant alone, with a 7.9 months, non-significant, improvement in overall survival. Its safety profile requires strict patient selection, mainly based on baseline glycemic status, and close monitoring.

Targeting activated PI3K/mTOR signaling overcomes acquired resistance to CDK4/6-based therapies in preclinical models of hormone receptor-positive breast cancer

Background

Combined targeting of CDK4/6 and ER is now the standard of care for patients with advanced ER+/HER2− breast cancer. However, acquired resistance to these therapies frequently leads to disease progression. As such, it is critical to identify the mechanisms by which resistance to CDK4/6-based therapies is acquired and also identify therapeutic strategies to overcome resistance.

Methods

In this study, we developed and characterized multiple in vitro and in vivo models of acquired resistance to CDK4/6-based therapies. Resistant models were screened by reverse phase protein array (RPPA) for cell signaling changes that are activated in resistance.

Results

We show that either a direct loss of Rb or loss of dependence on Rb signaling confers cross-resistance to inhibitors of CDK4/6, while PI3K/mTOR signaling remains activated. Treatment with the p110α-selective PI3K inhibitor, alpelisib (BYL719), completely blocked the progression of acquired CDK4/6 inhibitor-resistant xenografts in the absence of continued CDK4/6 inhibitor treatment in models of both PIK3CA mutant and wild-type ER+/HER2− breast cancer. Triple combination therapy against PI3K:CDK4/6:ER prevented and/or delayed the onset of resistance in treatment-naive ER+/HER2− breast cancer models.

Conclusions

These data support the clinical investigation of p110α-selective inhibitors of PI3K, such as alpelisib, in patients with ER+/HER2− breast cancer who have progressed on CDK4/6:ER-based therapies. Our data also support the investigation of PI3K:CDK4/6:ER triple combination therapy to prevent the onset of resistance to the combination of endocrine therapy plus CDK4/6 inhibition.

CapG promotes resistance to paclitaxel in breast cancer through transactivation of PIK3R1/P50

Background: Chemotherapy resistance is a major problem in breast cancer treatment and a leading cause of mortality in breast cancer patients. Biomarkers for chemotherapy resistance is under investigation.

Methods: Paclitaxel resistant cells were established and subjected to RNA sequencing. Analysis combined with two additional RNA-seq datasets was conducted. CapG expression in patients with adjuvant chemotherapy was studied in breast cancer resection specimens using IHC and related to pathological response and disease-free survival. Paclitaxel resistance was assessed by half-maximal inhibitory concentrations (IC50) and a mouse xenograft model.

Results: Increased expression of actin-binding protein CapG strongly correlated with the resistance to paclitaxel chemotherapy and decreased probability to achieve pathological complete response in breast cancer patients. Overexpressing CapG significantly enhanced paclitaxel resistance in breast cancer cells and xenograft tumors. High CapG level also significantly correlated with shorter relapse-free survival as well as hyper-activation of PI3K/Akt signaling in breast cancer patients. Mechanistically, CapG enhanced PIK3R1 expression which led to increased PI3K/Akt activation. Unexpectedly, CapG was found to bind to the variant-specific promoter of PIK3R1/P50 and directly enhance its transcription. We also identified p300/CBP as a transcriptional coregulator of CapG, which is recruited to PIK3R1 promoter through interaction with CapG, thereby increasing PIK3R1/P50 transcription by enhancing histone H3K27 acetylation. Consistently, inhibiting p300/CBP substantially decreased CapG-dependent upregulation of PIK3R1/P50 and subsequent PI3K/Akt activation, resulting in increased sensitivity to paclitaxel treatment in breast cancer cells.

Conclusion: High CapG levels may predict poor paclitaxel response in breast cancer patients. Targeting CapG-mediated hyperactivation of PI3K/Akt pathway may mitigate resistance to chemotherapy in breast cancer.

PIK3CA mutations early persistence in cell-free tumor DNA as a negative prognostic factor in metastatic breast cancer patients treated with hormonal therapy

PURPOSE

The identification of biomarkers of hormonal therapy (HT) failure would allow tailored monitoring in metastatic breast cancer (mBC) patients. PIK3CA gene mutation is one of the most frequent events in mBC and is associated with HT resistance. We evaluated the early prognostic value of cell-free DNA (cfDNA) PIK3CA detection in first-line HT-treated mBC patients.

METHODS

Between June 2012 and January 2014, 39 patients were prospectively included in a dedicated clinical trial (NCT01612871). Blood sampling was performed before (M0) and 4 weeks (M1), 3 months (M3) and 6 months (M6) after HT initiation, and at tumor progression. Patients were followed until progression or until the end of the study (2 years). Mutation detection was performed using droplet-based digital PCR (ddPCR). Progression-free survival (PFS) was used as primary endpoint.

RESULTS

Median age at inclusion was 63 years (range 40-86). Most patients (34/39) received an aromatase inhibitor and presented a non-measurable disease (71.8%). PIK3CA mutations were reported in 10 (27.8%) and 5 (14.3%) cases at M0 and M1, respectively. The persistence of a detectable circulating mutation at M1 was highly correlated with a worse progression-free survival (PFS), rate at 1 year: 40% versus 76.7%; p = 0.0053).

CONCLUSIONS

Four-week persistence of cfDNA PIK3CA mutation appears highly correlated with PFS.

TRIAL REGISTRATION

NCT01612871, registered on June 6th, 2012; https://clinicaltrials.gov/ct2/show/NCT01612871 .

Treatment of advanced HR+/HER2- breast cancer with new targeted agents in combination with endocrine therapy: a review of efficacy and tolerability based on available randomized trials on everolimus, ribociclib, palbociclib and abemaciclib

INTRODUCTION

Recently, new targeted agents have been developed, which can prolong the effect of endocrine treatment (ET) by targeting resistance pathways in HR+/HER2- advanced breast cancer. This review examines available studies of everolimus, an mTOR inhibitor, and the CDK 4/6 inhibitors ribociclib, palbociclib and abemaciclib in terms of efficacy, tolerability and safety.

MATERIAL AND METHODS

A systematic literature search was performed in Pubmed. Evaluation of the quality of the identified studies was based on selected elements from the GRADE guidelines.

RESULTS

The literature search yielded eight randomized trials that all presented a significant increase in the progression free survival (PFS)/time to progression (TTP) for the targeted agents plus ET vs ET only. The improvement was evident as first-line therapy with an increase in PFS of 10-11 months when adding a CDK4/6 inhibitor to ET, as well as in patients previously treated for metastatic disease, with an increase of 5-6 months. The common adverse events (AEs) of the CDK 4/6 inhibitors were due to myelosuppression. In addition, abemaciclib was associated with liver toxicity and diarrhea, and ribociclib with liver toxicity and QTcF prolongation. The most common grade 3/4 AE of everolimus was stomatitis. The majority (five) of the trials had no serious limitations, and thus the quality of evidence was high.

DISCUSSION

The new targeted agents are all associated with an improvement of the PFS with an acceptable tolerability, and they should be offered to women with advanced HR+/HER2- breast cancer both as first-line therapy as well as among patients previously treated in metastatic regimens. However, further data regarding the impact on overall survival are required to evaluate the full benefit for patients. Price and differences in AEs could become substantial arguments for the choice of therapy for the individual patient.

Nelfinavir targets multiple drug resistance mechanisms to increase the efficacy of doxorubicin in MCF-7/Dox breast cancer cells

Development of multidrug resistance (MDR) remains a significant problem in cancer chemotherapy and underscores the importance of using chemosensitizers. Well known MDR mechanisms include: (i) upregulation of drug-efflux; (ii) increased signaling via AKT; and (iii) decreased apoptosis. Therefore, chemosensitizers should target multiple resistance mechanisms. We investigated the efficacy of nelfinavir (NFV), a clinically approved anti-HIV drug, in increasing doxorubicin (DOX) toxicity in a MDR breast cancer cell line, MCF-7/Dox. As compared to parental MCF-7 cells, the MCF-7/Dox were 15-20 fold more resistant to DOX-induced cytotoxicity at 48 h post-exposure (DOX IC50 = 1.8 μM vs. 32.4 μM). Coexposures to NFV could significantly (p < 0.05) decrease DOX-IC50 in MCF-7/Dox cells. Multiple exposures to physiologic concentrations of NFV (2.25 μM or 6.75 μM) decreased DOX-IC50 by 21-fold and 50-fold, respectively. Interestingly, although single exposure to NFV transiently induced P-glycoprotein (P-gp) levels, multiple treatments with NFV inhibited both P-gp expression and efflux function, which increased intracellular DOX concentrations. Single exposure to NFV augmented the markers of cell-survival (AKT) and autophagy (LC3-II), whereas multiple exposures enabled suppression of both total AKT (t-AKT) and insulin like growth factor-1 (IGF-1)-induced phosphorylated AKT (p-AKT) levels. Multiple exposures to NFV also resulted in increased unfolded protein response (UPR) transducers, e.g. Grp78, p-PERK, p-eIF2α, and ATF-4; and endoplasmic reticulum (ER) stress induced death sensors, e.g. CHOP & TRIB-3. Multiple exposures to NFV also abrogated the mitogenic effects of IGF-1. In mice carrying MCF-7/Dox tumor xenografts, intraperitoneal (i.p.) injection of NFV (20 mg/kg/day) and DOX (2 mg/kg/twice/wk) decreased tumor growth more significantly (p < 0.01) than either agent alone. Immunohistochemical (IHC) analysis revealed decreased p-AKT and Ki-67 levels. Thus, NFV overcomes MDR in breast cancer cells and should be tested as an adjunct to chemotherapy.

Aromatase Inhibitor-Mediated Downregulation of INrf2 (Keap1) Leads to Increased Nrf2 and Resistance in Breast Cancer

Aromatase inhibitors are effective drugs that reduce or eliminate hormone-sensitive breast cancer. However, despite their efficacy, resistance to these drugs can occur in some patients. The INrf2 (Keap1):Nrf2 complex serves as a sensor of drug/radiation-induced oxidative/electrophilic stress. INrf2 constitutively suppresses Nrf2 by functioning as an adapter protein for the Cul3/Rbx1-mediated ubiquitination/degradation of Nrf2. Upon stress, Nrf2 dissociates from INrf2, is stabilized, translocates to the nucleus, and coordinately induces a battery of cytoprotective gene expression. Current studies investigated the role of Nrf2 in aromatase inhibitor resistance. RT-PCR and immunoblot assays showed that aromatase inhibitor-resistant breast cancer LTLTCa and AnaR cells express lower INrf2 and higher Nrf2 protein levels, as compared with drug-sensitive MCF-7Ca and AC1 cells, respectively. The increase in Nrf2 was due to lower ubiquitination/degradation of Nrf2 in aromatase inhibitor-resistant cells. Higher Nrf2-mediated levels of biotransformation enzymes, drug transporters, and antiapoptotic proteins contributed to reduced efficacy of drugs and aversion to apoptosis that led to drug resistance. shRNA inhibition of Nrf2 in LTLTCa (LTLTCa-Nrf2KD) cells reduced resistance and sensitized cells to aromatase inhibitor exemestane. Interestingly, LTLTCa-Nrf2KD cells also showed reduced levels of aldehyde dehydrogenase, a marker of tumor-initiating cells and significantly decreased mammosphere formation, as compared with LTLTCa-Vector control cells. The results together suggest that persistent aromatase inhibitor treatment downregulated INrf2 leading to higher expression of Nrf2 and Nrf2-regulated cytoprotective proteins that resulted in increased aromatase inhibitor drug resistance. These findings provide a rationale for the development of Nrf2 inhibitors to overcome resistance and increase efficacy of aromatase inhibitors.

Management of patients with hormone receptor-positive breast cancer with visceral disease: challenges and treatment options

Endocrine therapy is an important treatment option for women with hormone receptor-positive (HR+) advanced breast cancer (ABC), yet many tumors are either intrinsically resistant or develop resistance to these therapies. Treatment of patients with ABC presenting with visceral metastases, which is associated with a poor prognosis, is also problematic. There is an unmet need for effective treatments for this patient population. Although chemotherapy is commonly perceived to be more effective than endocrine therapy in managing visceral metastases, patients who are not in visceral crisis might benefit from endocrine therapy, avoiding chemotherapy-associated toxicities that might affect quality of life. To improve outcomes, several targeted therapies are being investigated in combination with endocrine therapy for patients with endocrine-resistant, HR+ ABC. Although available data have considered patients with HR+ ABC as a whole, there are promising data from a prespecified analysis of a Phase III study of everolimus (Afinitor(®)), a mammalian target of rapamycin (mTOR) inhibitor, in combination with exemestane (Aromasin(®)) in patients with visceral disease progressing after nonsteroidal aromatase inhibitor therapy. In this review, challenges and treatment options for management of HR+ ABC with visceral disease, including consideration of therapeutic approaches undergoing clinical investigation, will be assessed.

One-pot synthesis of cinnamylideneacetophenones and their in vitro cytotoxicity in breast cancer cells

A series of cinnamylideneacetophenones were synthesized via a modified Claisen-Schmidt condensation reaction and evaluated for cytotoxicity against breast cancer cells using the Alamar Blue™ assay. Derivatives 17 and 18 bearing a 2-nitro group on the B ring, exhibited sub-micromolar cytotoxicity in MCF-7 cells (IC50=71 and 1.9 nM), respectively. Derivative 17 also displayed sub-micromolar (IC50=780 nM) cytotoxicity in MDA-MB-468 cells. Additionally, 17 and 18 displayed significantly less cytotoxicity than the chemotherapeutic doxorubicin in non-tumorigenic MCF-10A cells. This study provides evidence supporting the continued development of nitro-substituted cinnamylideneacetophenones as small molecules to treat breast cancer.

Copper as a key regulator of cell signalling pathways

Copper is an essential element in many biological processes. The critical functions associated with copper have resulted from evolutionary harnessing of its potent redox activity. This same property also places copper in a unique role as a key modulator of cell signal transduction pathways. These pathways are the complex sequence of molecular interactions that drive all cellular mechanisms and are often associated with the interplay of key enzymes including kinases and phosphatases but also including intracellular changes in pools of smaller molecules. A growing body of evidence is beginning to delineate the how, when and where of copper-mediated control over cell signal transduction. This has been driven by research demonstrating critical changes to copper homeostasis in many disorders including cancer and neurodegeneration and therapeutic potential through control of disease-associated cell signalling changes by modulation of copper-protein interactions. This timely review brings together for the first time the diverse actions of copper as a key regulator of cell signalling pathways and discusses the potential strategies for controlling disease-associated signalling processes using copper modulators. It is hoped that this review will provide a valuable insight into copper as a key signal regulator and stimulate further research to promote our understanding of copper in disease and therapy.

Estrogen controls the survival of BRCA1-deficient cells via a PI3K-NRF2-regulated pathway

Mutations in the tumor suppressor BRCA1 predispose women to breast and ovarian cancers. The mechanism underlying the tissue-specific nature of BRCA1's tumor suppression is obscure. We previously showed that the antioxidant pathway regulated by the transcription factor NRF2 is defective in BRCA1-deficient cells. Reactivation of NRF2 through silencing of its negative regulator KEAP1 permitted the survival of BRCA1-null cells. Here we show that estrogen (E2) increases the expression of NRF2-dependent antioxidant genes in various E2-responsive cell types. Like NRF2 accumulation triggered by oxidative stress, E2-induced NRF2 accumulation depends on phosphatidylinositol 3-kinase-AKT activation. Pretreatment of mammary epithelial cells (MECs) with the phosphatidylinositol 3-kinase inhibitor BKM120 abolishes the capacity of E2 to increase NRF2 protein and transcriptional activity. In vivo the survival defect of BRCA1-deficient MECs is rescued by the rise in E2 levels associated with pregnancy. Furthermore, exogenous E2 administration stimulates the growth of BRCA1-deficient mammary tumors in the fat pads of male mice. Our work elucidates the basis of the tissue specificity of BRCA1-related tumor predisposition, and explains why oophorectomy significantly reduces breast cancer risk and recurrence in women carrying BRCA1 mutations.

Risk factors and survival outcome in cerebral metastatic breast cancer

The development of brain metastases (BM) of primary breast cancer patients leads to limited survival. HER2-positive and triple-negative status are risk factors for the development of BM. Estrogen receptor (ER)/progesterone receptor (PR)/HER2 are important prognostic markers and are essential for effective treatment decisions. We retrospectively analyzed the impact of known risk factors and the outcome after the development of BM. Eighty consecutive patients, treated between January 1, 2001, and June 30, 2012, on the basis of primary non-metastatic operable breast cancer and who developed BM, were enrolled. Clinical parameters (TNM; ER, PR, HER2) and their impact on the occurrence of BM and additionally their prognostic influence after the occurrence of BM were investigated. A small tumor size, ductal histology, grade 3, hormone receptor-negative, triple-negative and HER2+ tumors were associated with BM. Median time from breast cancer diagnosis to BM was 35 months (range 26.2-43.8). Grade 3 versus 2 has significantly negative prognostic impact with earlier development of BM (median 23 vs. 41 months; p=0.033). HER2-positive patients had significantly longer survival after the occurrence of BM than HER2-negative patients (p=0.009). The risk of BM varies significantly by subtype. In high-risk patients, the occurrence of BM must be considered, and possibly, general screening in these patients is warranted. The survival advantage of HER2-positive breast cancer patients compared with HER2-negative patients after the occurrence of BM is possibly explainable by systemic control of disease. Standard of care for patients with BM is whole-brain radiotherapy, with/without surgery, or stereotactic radiosurgery. Perhaps novel therapies may additionally improve survival in these patients.