Hyaluronan-induced masking of ErbB2 and CD44-enhanced trastuzumab internalisation in trastuzumab resistant breast cancer

Die hard: are cancer stem cells the Bruce Willises of tumor biology?

In recent years, an exponentially growing number of studies have focused on identifying cancer stem cells (CSC) in human malignancies. The rare CSCs could be crucial in controlling and curing cancer: through asymmetric division CSCs supposedly drive tumor growth and evade therapy with the help of traits shared with normal stem cells such as quiescence, self-renewal ability, and multidrug resistance pump activity. Here, we give a brief overview of techniques used to confirm the stem cell-like behavior of putative CSCs and discuss markers and methods for identifying, isolating, and culturing them. We touch on the limitations of each marker and why the combined use of CSC markers, in vitro and in vivo assays may still fail to identify all relevant CSC populations. Finally, the various experimental findings supporting and contradicting the CSC hypothesis are summarized. The large number of tumor types thus far with a subpopulation of uniquely tumorigenic and therapy resistant cells suggests that despite the unanswered questions and inconsistencies, the CSC hypothesis has a legitimate role to play in tumor biology. At the same time, experimental evidence supporting the established alternative theory of clonal evolution can be found as well. Therefore, a model that describes cancer initiation and progression should combine elements of clonal evolution and CSC theory.

Hyaluronan in human tumors: pathobiological and prognostic messages from cell-associated and stromal hyaluronan

Cancers are supported by a distinct type of connective tissue stroma, crucial for tumor survival and advancement. Hyaluronan is a major matrix molecule in the stroma of many common tumors, and involved in their growth and spreading. Here we focus in recent data on stromal hyaluronan in human tumors, and that on the surface of the malignant cells. Hyaluronan accumulation is most conspicuous in malignancies that develop in cells and tissues normally devoid of hyaluronan, such as single layered epithelia and their hyaluronan-poor connective tissue stroma. The magnitude of the hyaluronan accumulation in the malignant epithelium itself (e.g. colon and gastric cancers) or tumor stroma (breast, ovarian, prostate cancers) strongly correlates with an unfavorable prognosis of the patient, i.e. advancement of the malignancy. A completely different pattern arises from stratified epithelia that normally produce hyaluronan and are surrounded by a hyaluronan-rich stroma. The cell surface of the latter group of tumors (e.g. squamous cell carcinomas of skin, mouth, larynx and esophagus, and skin melanoma) show abundant hyaluronan which tends to get reduced and patchy in the most advanced stages of the tumors, suggesting enhanced turnover. While the assays of human tumors represent snapshots of currently unknown processes and kinetics of hyaluronan metabolism, it is obvious that hyaluronan accumulation at some stage is an inherent feature in most of the common epithelial malignant tumors. The possible contributions of inflammatory cells, stem cells, mutated stromal cells, or otherwise deranged growth factor exchange between stromal and cancer cells are discussed as possible explanations to hyaluronan abundance in the tumors. The importance of hyaluronan in human tumor progression will be further clarified when drugs become available to modify hyaluronan metabolism.

Breast tumor microenvironment: proteomics highlights the treatments targeting secretome

Tumor secreted substances (secretome), including extracellular matrix (ECM) components, act as mediators of tumor-host communication in the breast tumor microenvironment. Proteomic analysis has emphasized the value of the secretome as a source of prospective markers and drug targets for the treatment of breast cancers. Utilizing bioinformatics, our recent studies revealed global changes in protein expression after the activation of ECM-mediated signaling in breast cancer cells. A newly designed technique integrating a capillary ultrafiltration (CUF) probe with mass spectrometry was demonstrated to dynamically sample and identify in vivo and pure secretome from the tumor microenvironment. Such in vivo profiling of breast cancer secretomes may facilitate the development of novel drugs specifically targeting secretome.

Trastuzumab decreases the number of circulating and disseminated tumor cells despite trastuzumab resistance of the primary tumor

We have recently shown that despite of the fact that the ErbB2-positive JIMT-1 human breast cancer cells intrinsically resistant to trastuzumab in vitro, trastuzumab inhibited the outgrowth of early phase JIMT-1 xenografts in SCID mice via antibody-dependent cellular cytotoxicity (ADCC). Here we show that trastuzumab significantly reduces the number of circulating and disseminated tumor cells (CTCs and DTCs) in this xenograft model system at a time when the primary tumor is already unresponsive to trastuzumab. This observation suggests that ErbB2 positive CTCs and DTCs might be sensitive to trastuzumab-mediated ADCC even if when the primary tumor is already non-responsive. Thus, trastuzumab treatment might also be beneficial in the case of patients with breast cancer that is already trastuzumab resistant.