Giorgio Valabrega

TGFalpha expression impairs Trastuzumab-induced HER2 downregulation.

The HER2 gene encodes a tyrosine kinase receptor overexpressed in 25–30% of human breast cancers. Clinical trials have shown the efficacy of the anti-HER2 monoclonal antibody Trastuzumab in metastatic breast cancer patients. Nevertheless, 70% of patients are unresponsive from start of treatment and nearly all become unresponsive during treatment. Possible mechanisms for these failures could depend on impairment of the machinery responsible for receptor downregulation. To test this hypothesis, we analysed the genomic sequences encoding regions known to be critical for HER2 downregulation, of both HER2 and of the ubiquitin ligase Cbl. We investigated 63 breast cancers, and found no mutations in these regions. We thus considered alternative mechanisms – such as TGFα production – possibly interfering with HER2 downregulation. In selected cases, by comparing breast cancer neoplastic tissue before and after Trastuzumab treatment, we found induction of TGFα expression. Moreover, by in vitro expression of exogenous TGFα in breast cancer cells, we observed a dramatic reduction in Trastuzumab-induced HER2 endocytosis, downregulation and cell growth inhibition. Our results suggest that unresponsiveness to Trastuzumab may not be due to intrinsic defects in the machinery responsible for HER2 downregulation, but can be associated with a TGFα-related mechanism of escape to HER2 downregulation.

Lapatinib: a dual inhibitor of EGFR and HER2 tyrosine kinase activity.

Lapatinib (GW 572016) is an oral inhibitor of the tyrosine kinase activity of epidermal growth factor receptor (EGFR) and human EGFR-2 (HER2), which are both frequently altered in human malignant tumors. Being a multitargeting agent, it has the theoretical ability to provide more efficient antitumor activity and delay the onset of tumor resistance. Based on promising preclinical results, lapatinib is being extensively studied in cancer patients. In Phase I clinical trials, the side effect profile of lapatinib results are favorable, with a few patients experiencing serious toxicity. Phase II studies showed that lapatinib has meaningful clinical activity in the setting of HER2-positive advanced breast cancer patients. Unfortunately, its activity in epidermal growth factor receptor-dominated cancers, such as colorectal cancer or squamous cell carcinoma of the head and neck, is modest. An extensive program is now ongoing in breast cancer patients to establish the correct role of lapatinib in this clinical setting. Studies in breast cancer, as well as in other solid tumors are also collecting a large amount of biological data. Correlative studies will hopefully clarify predictive factors of lapatinib efficacy that can be applied in clinical practice in order to select patients for treatment.

Active immunotherapy in HER2 overexpressing breast cancer: current status and future perspectives

BACKGROUND The use of anti-HER2 monoclonal antibodies (mAbs) has improved the clinical outcome of HER2-overexpressing breast cancers (BCs). Unfortunately, often these tumors tend to relapse and, when metastatic, the duration of clinical benefit is limited over time and almost invariably followed by tumor progression. Alternative approaches to this essentially passive immunotherapy are therefore needed in HER2-overexpressing BC patients. As HER2 is one of the most suitable targets for active immunotherapy in BC, manipulating the immune system is a highly attractive approach. MATERIAL AND METHODS A computer-based literature search was carried out using PubMed (keywords: breast neoplasm, HER2 vaccine, immunology); data reported at international meetings were included. RESULTS This review provides a focus on the following active vaccinal approaches under clinical investigation against HER2-overexpressing BC: (i) peptide and protein based; (ii) DNA based; (iii) whole tumor cell based; (iv) dendritic cell based. Moreover, the review discuss future challenges in the field, trying to define the best setting for the development of this innovative strategy, considering both immunological and clinical aspects of HER2 targeting. CONCLUSIONS Development of effective vaccines for BC remains a distinct challenge but is likely to become a substantial advance for patients with HER2-overexpressing BCs.BACKGROUND The use of anti-HER2 monoclonal antibodies (mAbs) has improved the clinical outcome of HER2-overexpressing breast cancers (BCs). Unfortunately, often these tumors tend to relapse and, when metastatic, the duration of clinical benefit is limited over time and almost invariably followed by tumor progression. Alternative approaches to this essentially passive immunotherapy are therefore needed in HER2-overexpressing BC patients. As HER2 is one of the most suitable targets for active immunotherapy in BC, manipulating the immune system is a highly attractive approach. MATERIAL AND METHODS A computer-based literature search was carried out using PubMed (keywords: breast neoplasm, HER2 vaccine, immunology); data reported at international meetings were included. RESULTS This review provides a focus on the following active vaccinal approaches under clinical investigation against HER2-overexpressing BC: (i) peptide and protein based; (ii) DNA based; (iii) whole tumor cell based; (iv) dendritic cell based. Moreover, the review discuss future challenges in the field, trying to define the best setting for the development of this innovative strategy, considering both immunological and clinical aspects of HER2 targeting. CONCLUSIONS Development of effective vaccines for BC remains a distinct challenge but is likely to become a substantial advance for patients with HER2-overexpressing BCs.

Trastuzumab-based combination therapy for breast cancer

Trastuzumab, a humanised monoclonal antibody directed against the extracellular domain of HER-2, has been shown to be active against HER-2-overexpressing metastatic breast cancer, either as single agent or when used in combination with chemotherapy. In preclinical models, trastuzumab has shown additive and even synergistic anti-tumour activity with the most active chemotherapeutic agents used in the treatment of breast cancer. In a large, randomised, Phase III trial, the combination of trastuzumab plus chemotherapy was shown to improve response rate and survival. The high incidence of cardiotoxicity seen with the combination of trastuzumab plus anthracycline drugs prompted carrying out of several clinical studies combining trastuzumab with other chemotherapeutic agents, including docetaxel, vinorelbine, platinum salts, gemcitabine and capecitabine. This article summarises the available data on trastuzumab-based combinations for breast cancer.

Overcoming endocrine resistance in metastatic breast cancer: Current evidence and future directions

About 75% of all breast cancers are estrogen receptor (ER)-positive. They generally have a more favorable clinical behavior, prognosis, and pattern of recurrence, and endocrine therapy forms the backbone of treatment. Anti-estrogens (such as tamoxifen and fulvestrant) and aromatase inhibitors (such as anastrozole, letrozole, and exemestane) can effectively control the disease and induce tumor responses in a large proportion of patients. However, the majority of patients progress during endocrine therapy (acquired resistance) and a proportion of patients may fail to respond to initial therapy (de novo resistance). Endocrine resistance is therefore of clinical concern and there is great interest in strategies that delay or circumvent it. A deeper knowledge of the molecular mechanisms that drive endocrine resistance has recently led to development of new strategies that have the promise to effectively overcome it. Many resistance mechanisms have been described, and the crosstalk between ER and growth factor receptor signaling pathways seems to represent one of the most relevant. Compounds that are able to inhibit key elements of these pathways and restore endocrine sensitivity have been studied and more are currently under development. The aim of this review is to summarize the molecular pathophysiology of endocrine resistance in breast cancer and its impact on current clinical management.

Multitarget drugs: the present and the future of cancer therapy

Target therapies for the treatment of human cancers have revolutionized the concept of oncological medicine. This type of therapeutic approach is directed to the inhibition of molecular targets that play a pivotal role in tumor progression – such as tyrosine kinase receptors (TKIs) controlling cell proliferation and survival – mainly by means of compounds able to block their activity. In the beginning, the aim of target therapies was specifically to hit a single molecule expressed in neoplastic cells. Now the prevailing idea is that inhibiting both cancer cells and cells of the stroma supporting the tumor would gain better results in fighting the disease. Therefore, the single-target therapy is fading in favor of a multitarget approach and the new generation of TKIs is selected on the basis of their ability simultaneously to target different molecules. This review summarizes the molecular basis of multitarget therapies and the most relevant results obtained in different cancer types.

Hormone-receptor expression and activity of trastuzumab with chemotherapy in HER2-positive advanced breast cancer patients

The relationship between quantitative immunohistochemical hormone receptor expression and response to the combination of trastuzumab with chemotherapy in HER2‐positive advanced breast cancer is currently unknown.

Metastatic breast cancer subtypes and central nervous system metastases

BACKGROUND Breast cancer (BC) subtypes have different survival and response to therapy. We studied predictors of central nervous system metastases (CNS-M) and outcome after CNS-M diagnosis according to tumor subtype. PATIENTS AND METHODS 488 patients with diagnosis of metastatic BC were retrospectively evaluated. According to the combination of hormone receptors (HR) and HER2 status, tumors were grouped in: Luminal (Lum), Luminal/HER2+, pure HER2-positive (pHER2+) and triple negative (TN). Time to CNS progression, CNS-M free interval and Overall Survival (OS) after CNS-M occurrence were compared by the log-rank test. Cox-proportional hazard models were used to study predictor factors associated with CNS progression, including tumor subtype and all potentially clinical relevant variables. RESULTS 115 patients (pts) developed CNS-M with a median time to CNS progression of 31 months. The rate of CNS-M by subtype was: Lum 14%, Lum/HER2+ 35%, pHER2+ 49%, TN 22% (p < 0.001). Compared with Lum tumors, Lum/HER2+ (HR 2.514, p < 0.001), pHER2+ (HR 6.799, p < 0.0001) and TN (HR = 3.179, p < 0.001) subtypes were at higher risk of CNS-M. Median OS in months after CNS-M was: Lum 7.4, Lum/HER2+ 19.2, pHER2+ 7, TN 4.9 (p < 0.002). Belonging to the Lum/HER2+ subtype (HR 0.48, p < 0.037) and having isolated CNS (HR 0.37, p < 0.004) predicted significantly reduced risk of death. CONCLUSIONS After CNS-M, the Lum/HER2+ subtype appears associated with the longest OS. Prospective clinical trials would be required for evaluating the potential role of screening for asymptomatic CNS lesions and of more aggressive CNS-M treatment in Lum/HER2+ subtype.

HER2-positive breast cancer cells resistant to trastuzumab and lapatinib lose reliance upon HER2 and are sensitive to the multitargeted kinase inhibitor sorafenib

Trastuzumab has changed the prognosis of HER2 positive breast cancers. Despite this progress, resistance to trastuzumab occurs in most patients. Newer anti-HER2 therapies, like the dual tyrosine-kinase inhibitor (TKI) lapatinib, show significant antitumor activity, indicating that HER2 can be still exploited as a target after trastuzumab failure. However, since a high proportion of patients fail to respond to these alternative strategies, it is possible that cell escape from HER2 targeting may rely on HER2 independent pathways. The knowledge of these pathways deserve to be exploited to develop new therapies. We characterized two human HER2 overexpressing breast cancer cell lines resistant to trastuzumab and lapatinib (T100 and JIMT-1) from a molecular and biological point of view. Indeed, we assessed both in vitro and in vivo the activity of the multitarget inhibitor sorafenib. In both cell lines, the previously proposed mechanisms did not explain resistance to HER2 inhibitors. Notably, silencing HER2 by shRNA did not affect the growth of our cells, suggesting loss of reliance upon HER2. Moreover, we identified alterations in two antiapoptotic proteins Mcl-1 and Survivin which are known to be targets of the multikinase inhibitor sorafenib. Moreover, sorafenib, strongly inhibited the in vitro growth of T100 and JIMT-1 cells, through the downregulation of both Mcl-1 and Survivin. Similar results were obtained in JIMT-1 xenografts subcutaneously injected in NOD SCID mice. We provide preclinical evidence that tumor cells resistant to trastuzumab and lapatinib may rely on HER2 independent pathways that can be efficiently inhibited by sorafenib.

Potential biomarkers of long-term benefit from single-agent trastuzumab or lapatinib in HER2-positive metastatic breast cancer

In 2009 a prospective, randomized Phase II trial (NCT00842998) was initiated to evaluate the activity of HER2‐targeting agents without chemotherapy (CT) in HER2‐positive metastatic breast cancer (MBC) patients. The primary tumors of the patients enrolled in this study offered a unique opportunity to identify biomarkers that could predict durable clinical benefit from CT‐free anti‐HER2 therapy.