Cancer-Associated Fibroblasts Facilitate Squamous Cell Carcinoma Lung Metastasis in Mice by Providing TGFß-Mediated Cancer Stem Cell Niche.

Cancer-associated fibroblasts (CAFs) have been shown to enhance squamous cell carcinoma (SCC) growth, but it is unclear whether they promote SCC lung metastasis. We generated CAFs from K15.KrasG12D.Smad4-/- mouse SCCs. RNA expression analyses demonstrated that CAFs had enriched transforming growth factor-beta (TGFß) signaling compared to normal tissue-associated fibroblasts (NAFs), therefore we assessed how TGFß-enriched CAFs impact SCC metastasis. We co-injected SCC cells with CAFs to the skin, tail vein, or the lung to mimic sequential steps of lung metastasis. CAFs increased SCC volume only in lung co-transplantations, characterized with increased proliferation and angiogenesis and decreased apoptosis compared to NAF co-transplanted SCCs. These CAF effects were attenuated by a clinically relevant TGFß receptor inhibitor, suggesting that CAFs facilitated TGFß-dependent SCC cell seeding and survival in the lung. CAFs also increased tumor volume when co-transplanted to the lung with limiting numbers of SCC cancer stem cells (CSCs). In vitro, CSC sphere formation and invasion were increased either with co-cultured CAFs or with CAF conditioned media (which contains the highest TGFß1 concentration) and these CAF effects were blocked by TGFß inhibition. Further, TGFß activation was higher in primary human oral SCCs with lung metastasis than SCCs without lung metastasis. Similarly, TGFß activation was detected in the lungs of mice with micrometastasis. Our data suggest that TGFß-enriched CAFs play a causal role in CSC seeding and expansion in the lung during SCC metastasis, providing a prognostic marker and therapeutic target for SCC lung metastasis.

RIPK1-mediated induction of mitophagy compromises the viability of extracellular-matrix-detached cells.

For cancer cells to survive during extracellular matrix (ECM) detachment, they must inhibit anoikis and rectify metabolic deficiencies that cause non-apoptotic cell death. Previous studies in ECM-detached cells have linked non-apoptotic cell death to reactive oxygen species (ROS) generation, although the mechanistic underpinnings of this link remain poorly defined. Here, we uncover a role for receptor-interacting protein kinase 1 (RIPK1) in the modulation of ROS and cell viability during ECM detachment. We find that RIPK1 activation during ECM detachment results in mitophagy induction through a mechanism dependent on the mitochondrial phosphatase PGAM5. As a consequence of mitophagy, ECM-detached cells experience diminished NADPH production in the mitochondria, and the subsequent elevation in ROS levels leads to non-apoptotic death. Furthermore, we find that antagonizing RIPK1/PGAM5 enhances tumour formation in vivo. Thus, RIPK1-mediated induction of mitophagy may be an efficacious target for therapeutics aimed at eliminating ECM-detached cancer cells.

Paradoxical roles of TGF-ß signaling in suppressing and promoting squamous cell carcinoma.

Transforming growth factor ß (TGF-ß) signaling either promotes or inhibits tumor formation and/or progression of many cancer types including squamous cell carcinoma (SCC). Canonical TGF-ß signaling is mediated by a number of downstream proteins including Smad family proteins. Alterations in either TGF-ß or Smad signaling can impact cancer. For instance, defects in TGF-ß type I and type II receptors (TGF-ßRI and TGF-ßRII) and in Smad2/3/4 could promote tumor development. Conversely, increased TGF-ß1 and activated TGF-ßRI and Smad3 have all been shown to have tumor-promoting effects in experimental systems of human and mouse SCCs. Among TGF-ß/Smad signaling, only TGF-ßRII or Smad4 deletion in mouse epithelium causes spontaneous SCC in the mouse model, highlighting the critical roles of TGF-ßRII and Smad4 in tumor suppression. Herein, we review the dual roles of the TGF-ß/Smad signaling pathway and related mechanisms in SCC, highlighting the potential benefits and challenges of TGF-ß/Smad-targeted therapies.

Design and evaluation of a peptide-based immunotoxin for breast cancer therapeutics.

Immunotoxins are chimeric proteins comprising a specific cellular targeting domain linked to a cytotoxic factor. Here we describe the design and use of a novel, peptide-based immunotoxin that can initiate selective cytotoxicity on ErbB2-positive cells. ErbB2 is a receptor tyrosine kinase that is overexpressed in the tumor cells of approximately 30% of breast cancer patients. Immunotoxin candidates were designed to incorporate a targeting ligand with affinity for ErbB2 along with a membrane lysin-based toxin domain. One particular peptide candidate, NL1.1-PSA, demonstrated selective cytotoxicity towards ErbB2-overexpressing cell lines. We utilized a bioengineering strategy to show that recombinant NL1.1-PSA immunotoxin expression by Escherichia coli also conferred selective cytotoxicity towards ErbB2-overexpressing cells. Our findings hold significant promise for the use of effective immunotoxins in cancer therapeutics.

Cancer cell survival during detachment from the ECM: multiple barriers to tumour progression.

Epithelial cells require attachment to the extracellular matrix (ECM) for survival. However, during tumour progression and metastasis, cancerous epithelial cells must adapt to and survive in the absence of ECM. During the past 20 years, several cellular changes, including anoikis, have been shown to regulate cell viability when cells become detached from the ECM. In this Opinion article, we review in detail how cancer cells can overcome or take advantage of these specific processes. Gaining a better understanding of how cancer cells survive during detachment from the ECM will be instrumental in designing chemotherapeutic strategies that aim to eliminate ECM-detached metastatic cells.

CAF-secreted IGFBPs regulate breast cancer cell anoikis.

UNLABELLED: Carcinoma-associated fibroblasts (CAFs) are now widely appreciated for their contributions to tumor progression. However, the ability of CAFs to regulate anoikis, detachment-induced cell death, has yet to be investigated. Here, a new role for CAFs in blocking anoikis in multiple cell lines, facilitating luminal filling in three-dimensional cell culture, and promoting anchorage-independent growth is defined. In addition, a novel mechanism underlying anoikis inhibition is discovered. Importantly, it was demonstrated that CAFs secrete elevated quantities of insulin-like growth factor-binding proteins (IGFBPs) that are both necessary for CAF-mediated anoikis inhibition and sufficient to block anoikis in the absence of CAFs. Furthermore, these data reveal a unique antiapoptotic mechanism for IGFBPs: the stabilization of the antiapoptotic protein Mcl-1. In aggregate, these data delineate a novel role for CAFs in promoting cell survival during detachment and unveil an additional mechanism by which the tumor microenvironment contributes to cancer progression. These results also identify IGFBPs as potential targets for the development of novel chemotherapeutics designed to eliminate detached cancer cells. IMPLICATIONS: The ability of CAF-secreted IGFBPs to block anoikis in breast cancer represents a novel target for the development of therapeutics aimed at specifically eliminating extracellular matrix-detached breast cancer cells.

Iron chelation and multiple sclerosis.

Histochemical and MRI studies have demonstrated that MS (multiple sclerosis) patients have abnormal deposition of iron in both gray and white matter structures. Data is emerging indicating that this iron could partake in pathogenesis by various mechanisms, e.g., promoting the production of reactive oxygen species and enhancing the production of proinflammatory cytokines. Iron chelation therapy could be a viable strategy to block iron-related pathological events or it can confer cellular protection by stabilizing hypoxia inducible factor 1α, a transcription factor that normally responds to hypoxic conditions. Iron chelation has been shown to protect against disease progression and/or limit iron accumulation in some neurological disorders or their experimental models. Data from studies that administered a chelator to animals with experimental autoimmune encephalomyelitis, a model of MS, support the rationale for examining this treatment approach in MS. Preliminary clinical studies have been performed in MS patients using deferoxamine. Although some side effects were observed, the large majority of patients were able to tolerate the arduous administration regimen, i.e., 6-8 h of subcutaneous infusion, and all side effects resolved upon discontinuation of treatment. Importantly, these preliminary studies did not identify a disqualifying event for this experimental approach. More recently developed chelators, deferasirox and deferiprone, are more desirable for possible use in MS given their oral administration, and importantly, deferiprone can cross the blood-brain barrier. However, experiences from other conditions indicate that the potential for adverse events during chelation therapy necessitates close patient monitoring and a carefully considered administration regimen.

Rapid vascular responses to anthrax lethal toxin in mice containing a segment of chromosome 11 from the CAST/Ei strain on a C57BL/6 genetic background.

Host allelic variation controls the response to B. anthracis and the disease course of anthrax. Mouse strains with macrophages that are responsive to anthrax lethal toxin (LT) show resistance to infection while mouse strains with LT non-responsive macrophages succumb more readily. B6.CAST.11M mice have a region of chromosome 11 from the CAST/Ei strain (a LT responsive strain) introgressed onto a LT non-responsive C57BL/6J genetic background. Previously, B6.CAST.11M mice were found to exhibit a rapid inflammatory reaction to LT termed the early response phenotype (ERP), and displayed greater resistance to B. anthracis infection compared to C57BL/6J mice. Several ERP features (e.g., bloat, hypothermia, labored breathing, dilated pinnae vessels) suggested vascular involvement. To test this, Evan's blue was used to assess vessel leakage and intravital microscopy was used to monitor microvascular blood flow. Increased vascular leakage was observed in lungs of B6.CAST.11M mice compared to C57BL/6J mice 1 hour after systemic administration of LT. Capillary blood flow was reduced in the small intestine mesentery without concomitant leukocyte emigration following systemic or topical application of LT, the latter suggesting a localized tissue mechanism in this response. Since LT activates the Nlrp1b inflammasome in B6.CAST.11M mice, the roles of inflammasome products, IL-1ß and IL-18, were examined. Topical application to the mesentery of IL-1ß but not IL-18 revealed pronounced slowing of blood flow in B6.CAST.11M mice that was not present in C57BL/6J mice. A neutralizing anti-IL-1ß antibody suppressed the slowing of blood flow induced by LT, indicating a role for IL-1ß in the response. Besides allelic differences controlling Nlrp1b inflammasome activation by LT observed previously, evidence presented here suggests that an additional genetic determinant(s) could regulate the vascular response to IL-1ß. These results demonstrate that vessel leakage and alterations to blood flow are part of the rapid response in mice resistant to B. anthracis infection.