Therapeutic Considerations in Treating HER2-Positive Metastatic Breast Cancer

Depicting Biomarkers for HER2-Inhibitor Resistance: Implication for Therapy in HER2-Positive Breast Cancer

HER2 (human epidermal growth factor receptor 2) is highly expressed in a variety of cancers, including breast, lung, gastric, and pancreatic cancers. Its amplification is linked to poor clinical outcomes. At the genetic level, HER2 is encoded by the ERBB2 gene (v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 2), which is frequently mutated or amplified in cancers, thus spurring extensive research into HER2 modulation and inhibition as viable anti-cancer strategies. An impressive body of FDA-approved drugs, including anti-HER2 monoclonal antibodies (mAbs), antibody-drug conjugates (ADCs), and HER2-tyrosine kinase inhibitors (TKIs), have demonstrated success in enhancing overall survival (OS) and disease progression-free survival (PFS). Yet, drug resistance remains a persistent challenge and raises the risks of metastatic potential and tumor relapse. Research into alternative therapeutic options for HER2+ breast cancer therefore proves critical for adapting to this ever-evolving landscape. This review highlights current HER2-targeted therapies, discusses predictive biomarkers for drug resistance, and introduces promising emergent therapies-especially combination therapies-that are aimed at overcoming drug resistance in the context of HER2+ breast cancer.

Exploring the role of PI3K/AKT/mTOR inhibitors in hormone-related cancers: A focus on breast and prostate cancer

Breast cancer (BC) and prostate cancer (PC) are at the top of the list when it comes to the most common types of cancers worldwide. The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway is important, in that it strongly influences the development and progression of these tumors. Previous studies have emphasized the key role of inhibitors of the PIK3/AKT/mTOR signaling pathway in the treatment of BC and PC, and it remains to be a crucial method of treatment. In this review, the inhibitors of these signaling pathways are compared, as well as their effectiveness in therapy and potential as therapeutic agents. The use of these inhibitors as polytherapy is evaluated, especially with the use of hormonal therapy, which has shown promising results.

Curcumin: Modulator of Key Molecular Signaling Pathways in Hormone-Independent Breast Cancer

Simple Summary

Breast cancer remains the most commonly diagnosed cancer and the leading cause of cancer death among females worldwide. It is a highly heterogeneous disease, classified according to hormone and growth factor receptor expression. Patients with triple negative breast cancer (TNBC) (estrogen receptor-negative/progesterone receptor-negative/human epidermal growth factor receptor (HER2)-negative) and hormone-independent HER2 overexpressing subtypes still represent highly aggressive behavior, metastasis, poor prognosis, and drug resistance. Thus, new alternative anticancer agents based on the use of natural products have been receiving enormous attention. In this regard, curcumin is a promising lead in cancer drug discovery due its ability to modulate a diverse range of molecular targets and signaling pathways. The current review has emphasized the underlying mechanism of curcumin anticancer action mediated through the modulation of PI3K/Akt/mTOR, JAK/STAT, MAPK, NF-ĸB, p53, Wnt/β-catenin, apoptosis, and cell cycle pathways in hormone-independent breast cancer, providing frameworks for future studies and insights to improve its efficiency in clinical practice.

Abstract

Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death among women worldwide. Despite the overall successes in breast cancer therapy, hormone-independent HER2 negative breast cancer, also known as triple negative breast cancer (TNBC), lacking estrogens and progesterone receptors and with an excessive expression of human epidermal growth factor receptor 2 (HER2), along with the hormone-independent HER2 positive subtype, still remain major challenges in breast cancer treatment. Due to their poor prognoses, aggressive phenotype, and highly metastasis features, new alternative therapies have become an urgent clinical need. One of the most noteworthy phytochemicals, curcumin, has attracted enormous attention as a promising drug candidate in breast cancer prevention and treatment due to its multi-targeting effect. Curcumin interrupts major stages of tumorigenesis including cell proliferation, survival, angiogenesis, and metastasis in hormone-independent breast cancer through the modulation of multiple signaling pathways. The current review has highlighted the anticancer activity of curcumin in hormone-independent breast cancer via focusing on its impact on key signaling pathways including the PI3K/Akt/mTOR pathway, JAK/STAT pathway, MAPK pathway, NF-ĸB pathway, p53 pathway, and Wnt/β-catenin, as well as apoptotic and cell cycle pathways. Besides, its therapeutic implications in clinical trials are here presented.

Randomized Phase II Trial of Capecitabine and Lapatinib with or without IMC-A12 (Cituxumumab) in Patients with HER2-Positive Advanced Breast Cancer Previously Treated with Trastuzumab and Chemotherapy: NCCTG N0733 (Alliance)

PURPOSE

To compare efficacy and safety of capecitabine and lapatinib with or without IMC-A12 (cituxumumab) in patients with HER2-positive metastatic breast cancer (MBC) previously treated with trastuzumab.

PATIENTS AND METHODS

Following an initial safety run-in cohort, patients were randomized 1:2 to Arm A (capecitabine and lapatinib) or to Arm B (capecitabine, lapatinib, and cituxumumab). Given the frequency of non-hematologic grade ≥ 3 adverse events in those receiving the three-drug combination in the safety cohort, lapatinib and capecitabine doses were reduced in Arm B only. The primary objective was to determine if the addition of cituxumumab to capecitabine and lapatinib improved progression-free survival (PFS) compared with capecitabine and lapatinib. Secondary objectives included a comparison between arms of other clinical endpoints, safety, change in overall quality of life (QOL) and self-assessed fatigue, rash, diarrhea, and hand-foot syndrome.

RESULTS

From July 2008 to March 2012, 68 patients (out of 142 planned) were enrolled and 63 were evaluable, including 8 for the safety run-in and 55 for the randomized cohort. Study enrollment was stopped early due to slow accrual. The addition of cituxumumab to capecitabine and lapatinib did not improve PFS (HR 0.93, 95% CI: 0.52-1.64). Furthermore, no difference in objective response rate or overall survival (OS) was observed. No difference between arms was observed in grade ≥ 3 adverse events, overall QOL change from baseline after 4 cycles of treatment.

CONCLUSION

The addition of cituxumumab to lapatinib and capecitabine did not improve PFS or OS compared with lapatinib and capecitabine in patients with HER2-positive MBC.

CLINICAL TRIAL REGISTRY

ClinicalTrials.gov Identifier: NCT00684983.

The emerging role of CDK4/6i in HER2-positive breast cancer

Prior to the advent of the monoclonal antibody trastuzumab, human epidermal growth-factor receptor 2 (HER2)-positive (HER2+) breast cancer (BC) was associated with an aggressive clinical course and poor survival outcomes. In the era of effective HER2-directed therapies, median survival rates for patients with metastatic HER2+ BC now approach 5 years. Despite these improvements, the majority of affected patients unfortunately die from disease. Therapies to overcome treatment resistance are being actively pursued. One strategy has been to target the cyclin-dependent kinases 4/6 (CDK4/6), as they are downstream of HER2 and many of the cellular pathways driving resistance to HER2-targeted therapies, and play a key role in proliferation by controlling transition through the G1 restriction point to the S phase of the cell cycle. In this article, we review the published literature with regard to the rationale for CDK4/6-directed therapies in HER2+ BC and discuss ongoing clinical research and new challenges in the field.

Ibrutinib as a potential therapeutic option for HER2 overexpressing breast cancer - the role of STAT3 and p21

Treatment response rates to current anticancer therapies for HER2 overexpressing breast cancer are limited and are associated with severe adverse drug reactions. Tyrosine kinases perform crucial roles in cellular processes by mediating cell signalling cascades. Ibrutinib is a recently approved Tyrosine Kinase Inhibitor (TKI) that has been shown be an effective therapeutic option for HER2 overexpressing breast cancer. The molecular mechanisms, pathways, or genes that are modulated by ibrutinib and the mechanism of action of ibrutinib in HER2 overexpressing breast cancer remain obscure. In this study, we have performed a kinome array analysis of ibrutinib treatment in two HER2 overexpressing breast cancer cell lines. Our analysis shows that ibrutinib induces changes in nuclear morphology and causes apoptosis via caspase-dependent extrinsic apoptosis pathway with the activation of caspases-8, caspase-3, and cleavage of PARP1. We further show that phosphorylated STAT3^Y705 is upregulated and phosphorylated p21^T145 is downregulated upon ibrutinib treatment. We propose that STAT3 upregulation is a passive response as a result of induction of DNA damage and downregulation of phosphorylated p21 is promoting cell cycle arrest and apoptosis in the two HER2 overexpressing cell lines. These results suggest that inhibitors of STAT3 phosphorylation may be potential options for combination therapy to help increase the efficacy of ibrutinib against HER2-overexpressing tumors.

A Viral Nanoparticle Cancer Vaccine Delays Tumor Progression and Prolongs Survival in a HER2+ Tumor Mouse Model

Human epidermal growth factor receptor 2 (HER2) overexpression is associated with aggressive tumors with increased incidence of metastasis and recurrence. Therapeutic antibodies such as Trastuzumab inhibit tumor growth through blockade of HER2 receptors. However, the short lifespan of such therapeutic antibodies necessitates repeat administrations with ensuing cardiac toxicity and development of resistance, while offering no protection against relapse. Cancer vaccines targeting HER2 can overcome these shortcomings of passive immunotherapy by instigating an endogenous and sustained immune response and memory against the cancer antigen. The efficacy of a viral nanoparticle (VNP)-based cancer vaccine is demonstrated here in activating a potent anti-HER2 immune response that delays progression of primary tumors as well as metastases and prolongs survival in mice. The results illustrate that the VNP-based vaccine instigates HER2-specific antibodies as well as effector and memory T cells, which contributes to the effectiveness of the vaccine. Given the highly aggressive course of HER2+ cancers, inhibition of disease progression by such cancer vaccines could provide a critical window for interventions with other adjuvant therapies. Moreover, the immune memory generated by this viral nanoparticle-based cancer vaccine could mitigate relapse of the disease.

Updates in the Evaluation and Management of Breast Cancer

Breast cancer is the most commonly diagnosed cancer worldwide. More than 200,000 new cases of invasive breast cancer are diagnosed annually in the United States; approximately 40,000 patients die of the disease. The etiology of most breast cancer cases is unknown, although multiple factors predisposing to the disease have been identified. Apart from increasing age and female sex, these other factors account for only a minority of breast cancer diagnoses. This article provides an overview of the management of noninvasive and invasive breast cancer, which is often complex and varies according to patient factors, disease stage, and breast cancer subtype. Although much progress has been made, continued research endeavors are ongoing; enrollment of eligible patients in prospective clinical trials is an essential way to improve patient outcomes.

Tumor regression is mediated via the induction of HER263-71- specific CD8+ CTL activity in a 4T1.2/HER2 tumor model: no involvement of CD80 in tumor control

In the CT26/HER2 and 4T1.2/HER2 tumor models, CT26/HER2 cells form tumors that continue to grow, whereas 4T1.2/HER2 cells form tumors that eventually regress. Here, we investigated the differences in the behaviors of these two cell lines. When immune cells from 4T1.2/HER2 tumor-bearing animals were stimulated with HER2 class I peptides, they displayed a 2-fold increase in IFN-γ levels, in response to the peptides, HER263-71 and HER2342-350. In contrast, extremely high levels of antigen-non-specific IFN-γ production were observed with immune cells and sera from CT26/HER2 tumor-bearing mice. However, IFN-γ had no effect on tumor progression in the CT26/HER2 model, as determined by an IFN-γ knockout assay. 4T1.2/HER2 tumor-bearing mice displayed CTL activity in response to HER263-71 but not to HER2342-350, whereas no such induction was observed in CT26/HER2 tumor-bearing mice. When 4T1.2/HER2 cell-challenged mice were depleted of CD8+ T cells, they lost their tumor-regressing activity, suggesting an antitumor role of HER263-71-specific CD8+ CTLs in the control of this tumor type. CT26/HER2 cells also expressed CD80. However, CD80-transfected 4T1.2/HER2 and CD80-non-expressing CT26/HER2 cells failed to alter their tumorigenicity, suggesting no role of CD80 in tumor control. Despite increased levels of myeloid-derived suppressor cells in the tumor, they were not associated with tumor progression in the CT26/HER2 model, as determined by a cell depletion assay. Overall, these data show that, contrary to CT26/HER2 tumors, 4T1.2/HER2 tumors regress via the induction of HER263-71-specific CD8+ CTLs and that CD80 is not associated with the regression of these tumors.

Restoring Lost Anti-HER-2 Th1 Immunity in Breast Cancer: A Crucial Role for Th1 Cytokines in Therapy and Prevention

The ErbB/B2 (HER-2/neu) oncogene family plays a critical role in the development and metastatic spread of several tumor types including breast, ovarian and gastric cancer. In breast cancer, HER-2/neu is expressed in early disease development in a large percentage of DCIS lesions and its expression is associated with an increased risk of invasion and recurrence. Targeting HER-2 with antibodies such as trastuzumab or pertuzumab has improved survival, but patients with more extensive disease may develop resistance to therapy. Interestingly, response to HER-2 targeted therapies correlates with presence of immune response genes in the breast. Th1 cell production of the cytokines interferon gamma (IFNγ) and TNFα can enhance MHC class I expression, PD-L1 expression, augment apoptosis and tumor senescence, and enhances growth inhibition of many anti-breast cancer agents, including anti-estrogens and HER-2 targeted therapies. Recently, we have identified that a loss of anti-HER-2 CD4 Th1 in peripheral blood occurs during breast tumorigenesis and is dramatically diminished, even in Stage I breast cancers. The loss of anti-HER-2 Th1 response is specific and not readily reversed by standard therapies. In fact, this loss of anti-HER-2 Th1 response in peripheral blood correlates with lack of complete response to neoadjuvant therapy and diminished disease-free survival. This defect can be restored with HER-2 vaccinations in both DCIS and IBC. Correcting the anti-HER-2 Th1 response may have significant impact in improving response to HER-2 targeted therapies. Development of immune monitoring systems for anti-HER-2 Th1 to identify patients at risk for recurrence could be critical to improving outcomes, since the anti-HER-2 Th1 response can be restored by vaccination. Correction of the cellular immune response against HER-2 may prevent recurrence in high-risk patients with DCIS and IBC at risk of developing new or recurrent breast cancer.

Efflux transporters at the blood-brain barrier limit delivery and efficacy of cyclin-dependent kinase 4/6 inhibitor palbociclib (PD-0332991) in an orthotopic brain tumor model

6-Acetyl-8-cyclopentyl-5-methyl-2-([5-(piperazin-1-yl)pyridin-2-yl]amino)pyrido(2,3-d)pyrimidin-7(8H)-one [palbociclib (PD-0332991)] is a cyclin-dependent kinase 4/6 inhibitor approved for the treatment of metastatic breast cancer and is currently undergoing clinical trials for many solid tumors. Glioblastoma (GBM) is the most common primary brain tumor in adults and has limited treatment options. The cyclin-dependent kinase 4/6 pathway is commonly dysregulated in GBM and is a promising target in treating this devastating disease. The blood-brain barrier (BBB) limits the delivery of drugs to invasive regions of GBM, where the efflux transporters P-glycoprotein and breast cancer resistance protein can prevent treatments from reaching the tumor. The purpose of this study was to examine the mechanisms limiting the effectiveness of palbociclib therapy in an orthotopic xenograft model. The in vitro intracellular accumulation results demonstrated that palbociclib is a substrate for both P-glycoprotein and breast cancer resistance protein. In vivo studies in transgenic mice confirmed that efflux transport is responsible for the limited brain distribution of palbociclib. There was an ∼115-fold increase in brain exposure at steady state in the transporter deficient mice when compared with wild-type mice, and the efflux inhibitor elacridar significantly increased palbociclib brain distribution. Efficacy studies demonstrated that palbociclib is an effective therapy when GBM22 tumor cells are implanted in the flank, but ineffective in an orthotopic (intracranial) model. Moreover, doses designed to mimic brain exposure were ineffective in treating flank tumors. These results demonstrate that efflux transport in the BBB is involved in limiting the brain distribution of palbociclib and this has critical implications in determining effective dosing regimens of palbociclib therapy in the treatment of brain tumors.

Antibody response to HER2 extracellular domain and subdomains in mouse following DNA immunization

Human epidermal growth factor receptor 2 (HER2) is overexpressed in 15-20 % of breast cancer patients and is an appropriate target for immunotherapy in these patients. Monoclonal antibodies (mAbs) specific to HER2 are currently applied to treat breast cancer patients with HER2 overexpression. Active immunization with HER2 DNA or protein has been considered as a suitable alternative. The aim of this study is to evaluate anti-HER2 antibody response in serum of mice immunized with DNA constructs containing full extracellular domain (fECD) or subdomains of human HER2. Four extracellular subdomains and also fECD of HER2 were cloned into pCMV6-Neo vector. Different groups of Balb/C mice were immunized with HER2 DNA constructs and boosted with HER2 recombinant protein. The anti-HER2 antibody was subsequently determined by ELISA, flow cytometry, and immunohistochemistry. Anti-HER2 antibody was detected only in serum of mice immunized with fECD DNA. None of HER2 extracellular subdomains induced appreciable levels of anti-HER2 antibody. However, boosting with fECD or extracellular subdomain III (DIII) recombinant protein resulted in enhanced anti-HER2 fECD as well as anti-HER2 subdomain antibody responses. In this regard, almost all (99 %) of HER2-overexpressing BT474 cells could be detected by serum antibody from mice immunized with HER2 subdomain DNA and boosted with recombinant HER2 protein by flow cytometry. Similarly, serum of mice immunized with DIII DNA construct and boosted with recombinant DIII protein could also recognize these cells, but to a lesser extent (50 %). Our findings suggest that combination of HER2 DNA and protein immunization could effectively induce anti-HER2 antibody response in Balb/C mice.

Improving drug delivery to primary and metastatic brain tumors: strategies to overcome the blood-brain barrier

Brain tumor diagnosis has an extremely poor prognosis, due in part to the blood-brain barrier (BBB) that prevents both early diagnosis and effective drug delivery. The infiltrative nature of primary brain tumors and the presence of micro-metastases lead to tumor cells that reside behind an intact BBB. Recent genomic technologies have identified many genetic mutations present in glioma and other central nervous system (CNS) tumors, and this information has been instrumental in guiding the development of molecularly targeted therapies. However, the majority of these agents are unable to penetrate an intact BBB, leading to one mechanism by which the invasive brain tumor cells effectively escape treatment. The diagnosis and treatment of a brain tumor remains a serious challenge and new therapeutic agents that either penetrate the BBB or disrupt mechanisms that limit brain penetration, such as endothelial efflux transporters or tight junctions, are required in order to improve patient outcomes in this devastating disease.