Activation of an IL6 inflammatory loop mediates trastuzumab resistance in HER2+ breast cancer by expanding the cancer stem cell population.

Although inactivation of the PTEN gene has been implicated in the development of resistance to the HER2 targeting antibody trastuzumab, the mechanisms mediating this resistance remain elusive. We generated trastuzumab resistant cells by knocking down PTEN expression in HER2 overexpressing breast cancer cell lines and demonstrate that development of trastuzumab resistance in these cells is mediated by activation of an IL6 inflammatory feedback loop leading to expansion of the cancer stem cell (CSC) population. Long term trastuzumab treatment generates highly enriched CSCs which display an EMT phenotype secreting over 100-fold more IL6 than parental cells. An IL6 receptor antibody interrupted this inflammatory feedback loop reducing the cancer stem cell population resulting in decreased tumor growth and metastasis in mouse xenographs. These studies demonstrate that trastuzumab resistance may be mediated by an IL6 inflammatory loop and suggest that blocking this loop may provide alternative strategy to overcome trastuzumab resistance.

Effects of Chronic Low-Dose Radiation on Human Neural Progenitor Cells.

The effects of chronic low-dose radiation on human health have not been well established. Recent studies have revealed that neural progenitor cells are present not only in the fetal brain but also in the adult brain. Since immature cells are generally more radiosensitive, here we investigated the effects of chronic low-dose radiation on cultured human neural progenitor cells (hNPCs) derived from embryonic stem cells. Radiation at low doses of 31, 124 and 496 mGy per 72 h was administered to hNPCs. The effects were estimated by gene expression profiling with microarray analysis as well as morphological analysis. Gene expression was dose-dependently changed by radiation. By thirty-one mGy of radiation, inflammatory pathways involving interferon signaling and cell junctions were altered. DNA repair and cell adhesion molecules were affected by 124 mGy of radiation while DNA synthesis, apoptosis, metabolism, and neural differentiation were all affected by 496 mGy of radiation. These in vitro results suggest that 496 mGy radiation affects the development of neuronal progenitor cells while altered gene expression was observed at a radiation dose lower than 100 mGy. This study would contribute to the elucidation of the clinical and subclinical phenotypes of impaired neuronal development induced by chronic low-dose radiation.

Molecular interactions of B-CAM (basal-cell adhesion molecule) and laminin in epithelial skin cancer.

Molecular events underlying the progression of malignant tumors through the surrounding tissue are largely mediated by membrane-bound adhesion molecules. Basal-cell adhesion molecule (B-CAM), a 90-kDa laminin receptor of the immunoglobulin superfamily, is induced in some epithelial malignancies. Its function in these tumors, however, still remains obscure. We demonstrated that expression of B-CAM is very weak, if detectable at all, in normal epidermis but is strongly induced in both basal cell carcinomas and squamous cell carcinomas of the skin, and most pronounced at the basal surface of the tumor nests. Interestingly, the only known B-CAM ligand, laminin, was markedly upregulated within corresponding microanatomical sites surrounding the tumor nests, suggesting that both molecules may interact there. Consistent with this hypothesis, we were able to directly demonstrate binding of a B-CAM/Fc chimeric molecule to the peritumoral stroma in situ. Finally, in proof-of-principle experiments, human B-CAM was overexpressed both in murine and in human fibroblasts. The haptotactic migration of these novel B-CAM+ cell populations on a laminin matrix was significantly increased (P = 0.02) as compared to mock-transfected cells when integrin-mediated adhesion was blocked by chelation of divalent cations. Thus, our findings provide the first direct experimental evidence that interactions of B-CAM and laminin may be involved in progression of epithelial skin tumors.

HER2 drives luminal breast cancer stem cells in the absence of HER2 amplification: implications for efficacy of adjuvant trastuzumab.

Although current breast cancer treatment guidelines limit the use of HER2-blocking agents to tumors with HER2 gene amplification, recent retrospective analyses suggest that a wider group of patients may benefit from this therapy. Using breast cancer cell lines, mouse xenograft models and matched human primary and metastatic tissues, we show that HER2 is selectively expressed in and regulates self-renewal of the cancer stem cell (CSC) population in estrogen receptor-positive (ER(+)), HER2(-) luminal breast cancers. Although trastuzumab had no effects on the growth of established luminal breast cancer mouse xenografts, administration after tumor inoculation blocked subsequent tumor growth. HER2 expression is increased in luminal tumors grown in mouse bone xenografts, as well as in bone metastases from patients with breast cancer as compared with matched primary tumors. Furthermore, this increase in HER2 protein expression was not due to gene amplification but rather was mediated by receptor activator of NF-κB (RANK)-ligand in the bone microenvironment. These studies suggest that the clinical efficacy of adjuvant trastuzumab may relate to the ability of this agent to target the CSC population in a process that does not require HER2 gene amplification. Furthermore, these studies support a CSC model in which maximal clinical benefit is achieved when CSC targeting agents are administered in the adjuvant setting. Cancer Res; 73(5); 1635-46. ©2012 AACR.

B-CAM/LU expression and the role of B-CAM/LU activation in binding of low- and high-density red cells to laminin in sickle cell disease.

Red blood cells from patients with sickle cell disease (SS RBC) adhere to laminin and over-express the high-affinity laminin receptor basal cell adhesion molecule/Lutheran protein (B-CAM/LU). This receptor has recently been shown to undergo activation in vitro through a protein kinase A-dependent mechanism. Low-density SS RBC express two-thirds more B-CAM/LU than high-density SS RBC. However, high-density SS RBC have been identified as most adherent to laminin under flow conditions. We investigated the ability of low- and high-density SS RBC to interact with laminin under various conditions and explored factors that might be responsible for the differences in B-CAM/LU-laminin interaction between high- and low-density SS RBC. We confirmed that high-density SS RBC adhere to laminin more strongly than low-density SS RBC under flow conditions. However, low-density SS RBC bind soluble laminin most strongly and are the most adherent to laminin under static conditions. Soluble recombinant Lutheran extracellular domain protein completely blocked SS RBC adhesion to laminin under both static and flow conditions. The protein kinase A inhibitor 14-22 amide inhibited adhesion to laminin during flow by high-density SS RBC from patients with strongly adherent cells but had no effect on adhesion observed after a static phase. Deletion of the cytoplasmic domain of B-CAM as well as mutation of the juxtamembranous tyrosine residue failed to reduce B-CAM-mediated adhesion to laminin by transfected MEL cells. These studies confirm that B-CAM/LU is the most critical receptor mediating adhesion to laminin under both static and flow conditions. Dense SS RBC are most adherent to laminin despite bearing fewer laminin receptors, apparently due to a reversible protein kinase A-dependent process that is unlikely to involve direct phosphorylation of B-CAM/LU. Our results also suggest that the nature of the interaction of B-CAM/LU with laminin may be different under static and flow conditions.

Novel epinephrine and cyclic AMP-mediated activation of BCAM/Lu-dependent sickle (SS) RBC adhesion.

The vasoocclusive crisis is the major clinical feature of sickle cell anemia, which is believed to be initiated or sustained by sickle (SS) red blood cell (RBC) adhesion to the vascular wall. SS RBCs, but not unaffected (AA) RBCs, adhere avidly to multiple components of the vascular wall, including laminin. Here we report a novel role for epinephrine and cyclic adenosine monophosphate (cAMP) in the regulation of human SS RBC adhesiveness via the laminin receptor, basal cell adhesion molecule/Lutheran (BCAM/Lu). Our data demonstrate that peripheral SS RBCs contain greater than 4-fold more cAMP than AA RBCs under basal conditions. Forskolin or the stress mediator epinephrine further elevates cAMP in SS RBCs and increases adhesion of SS RBCs to laminin in a protein kinase A (PKA)-dependent manner, with the low-density population being the most responsive. Epinephrine-stimulated adhesion to laminin, mediated primarily via the beta 2-adrenergic receptor, occurred in SS RBC samples from 46% of patients and was blocked by recombinant, soluble BCAM/Lu, implicating this receptor as a target of cAMP signaling. Thus, these studies demonstrate a novel, rapid regulation of SS RBC adhesion by a cAMP-dependent pathway and suggest that components of this pathway, particularly PKA, the beta 2-adrenergic receptor, and BCAM/Lu, should be further explored as potential therapeutic targets to inhibit SS RBC adhesion.