Effects of Cancer Presence and Therapy on the Platelet Proteome.

Platelets are involved in tumor angiogenesis and cancer progression. Previous studies indicated that cancer could affect platelet content. In the current study, we investigated whether cancer-associated proteins can be discerned in the platelets of cancer patients, and whether antitumor treatment may affect the platelet proteome.

Hypoxia Impairs Initial Outgrowth of Endothelial Colony Forming Cells and Reduces Their Proliferative and Sprouting Potential.

Vascular homeostasis and regeneration in ischemic tissue relies on intrinsic competence of the tissue to rapidly recruit endothelial cells for vascularization. The mononuclear cell (MNC) fraction of blood contains circulating progenitors committed to endothelial lineage. These progenitors give rise to endothelial colony-forming cells (ECFCs) that actively participate in neovascularization of ischemic tissue.

A functional bioassay to determine the activity of anti-VEGF antibody therapy in blood of patients with cancer.

Background: Only a small proportion of patients respond to anti-VEGF therapy, pressing the need for a reliable biomarker that can identify patients who will benefit. We studied the biological activity of anti-VEGF antibodies in patients' blood during anti-VEGF therapy by using the Ba/F3-VEGFR2 cell line, which is dependent on VEGF for its growth.

Methods: Serum samples from 22 patients with cancer before and during treatment with bevacizumab were tested for their effect on proliferation of Ba/F3-VEGFR2 cells.

Sunitinib activates Axl signaling in renal cell cancer.

Mass spectrometry-based phosphoproteomics provides a unique unbiased approach to evaluate signaling network in cancer cells. The tyrosine kinase inhibitor sunitinib is registered as treatment for patients with renal cell cancer (RCC). We investigated the effect of sunitinib on tyrosine phosphorylation in RCC tumor cells to get more insight in its mechanism of action and thereby to find potential leads for combination treatment strategies.

Evaluation of different phospho-tyrosine antibodies for label-free phosphoproteomics.

Background: Mass spectrometry based phosphoproteomics emerged as advantageous approach for the analysis of tyrosine phosphorylation on proteins and tyrosine kinase signaling. Immunoaffinity purification is required for comprehensive analysis. Here we compared the performance of two antibodies for label-free phosphotyrosine-based phosphoproteomics.

Cross-resistance to clinically used tyrosine kinase inhibitors sunitinib, sorafenib and pazopanib.

Purpose: When during cancer treatment resistance to a tyrosine kinase inhibitor (TKI) occurs, switching to another TKI is often considered as a reasonable option. Previously, we reported that resistance to sunitinib may be caused by increased lysosomal sequestration, leading to increased intracellular lysosomal storage and, thereby, inactivity. Here, we studied the effect of several other TKIs on the development of (cross-) resistance.

Acquired tumor cell resistance to sunitinib causes resistance in a HT-29 human colon cancer xenograft mouse model without affecting sunitinib biodistribution or the tumor microvasculature.

Acquired resistance to anti-angiogenic tyrosine kinase inhibitors is an important clinical problem in treating various cancers. To what extent acquired resistance is determined by microenvironmental host-factors or by tumor cells directly is unknown. We previously found that tumor cells can become resistant to sunitinib in vitro.

Analysis of AKT and ERK1/2 protein kinases in extracellular vesicles isolated from blood of patients with cancer.

Background: Extracellular vesicles (EVs) are small nanometre-sized vesicles that are circulating in blood. They are released by multiple cells, including tumour cells. We hypothesized that circulating EVs contain protein kinases that may be assessed as biomarkers during treatment with tyrosine kinase inhibitors.

Predictive biomarkers in renal cell cancer: insights in drug resistance mechanisms.

Introduction: VEGF-targeted therapy is currently the first line treatment for patients with metastatic clear cell renal cell carcinoma (ccRCC), but most patients either display primary (intrinsic) resistance or acquire drug resistance. In recent years multiple mechanisms of resistance to VEGF-targeted therapy emerged from preclinical research, but it is currently unknown to what extent these drug resistance modalities play a role in the clinic. Here we reviewed the current literature on biomarkers that predict treatment outcome in patients with ccRCC to gain insight in clinical drug resistance mechanisms.

Lysosomal sequestration of sunitinib: a novel mechanism of drug resistance.

Purpose: Resistance to antiangiogenic tyrosine kinase inhibitors such as sunitinib is an important clinical problem, but its underlying mechanisms are largely unknown. We analyzed tumor sunitinib levels in mice and patients and studied sensitivity and resistance mechanisms to sunitinib.

Experimental Design: Intratumoral and plasma sunitinib concentrations in mice and patients were determined.

Sunitinib-induced changes in circulating endothelial cell-related proteins in patients with metastatic renal cell cancer.

Vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitors are effective agents in the treatment of metastatic renal cell cancer (mRCC). We here investigated whether inhibition of VEGFR signalin by sunitinib causes changes in plasma proteins associated with tumor endothelium. Forty-three patients with mRCC received sunitinib 50 mg/day in a 4-weeks on 2-weeks off schedule.

Nanomedicine for targeted cancer therapy: towards the overcoming of drug resistance.

Anticancer drug resistance almost invariably emerges and poses major obstacles towards curative therapy of various human malignancies. In the current review we will distinguish between mechanisms of chemoresistance that are predominantly mediated by ATP-driven multidrug resistance (MDR) efflux transporters, typically of the ATP-binding cassette (ABC) superfamily, and those that are independent of such drug efflux pumps. In recent years, multiple nanoparticle (NP)-based therapeutic systems have been developed that were rationally designed to overcome drug resistance by neutralizing, evading or exploiting various drug efflux pumps and other resistance mechanisms.

Understanding the causes of multidrug resistance in cancer: a comparison of doxorubicin and sunitinib.

Multiple molecular, cellular, micro-environmental and systemic causes of anticancer drug resistance have been identified during the last 25 years. At the same time, genome-wide analysis of human tumor tissues has made it possible in principle to assess the expression of critical genes or mutations that determine the response of an individual patient's tumor to drug treatment. Why then do we, with a few exceptions, such as mutation analysis of the EGFR to guide the use of EGFR inhibitors, have no predictive tests to assess a patient's drug sensitivity profile.

Increased numbers of small circulating endothelial cells in renal cell cancer patients treated with sunitinib.

Mature circulating endothelial cell (CEC) as well as endothelial progenitor populations may reflect the activity of anti-angiogenic agents on tumor neovasculature or even constitute a target for anti-angiogenic therapy. We investigated the behavior of CECs in parallel with hematopoietic progenitor cells (HPCs) in the blood of renal cell cancer patients during sunitinib treatment. We analyzed the kinetics of a specific population of small VEGFR2-expressing CECs (CD45(neg)/CD34(bright)), HPCs (CD45(dim)/CD34(bright)), and monocytes in the blood of 24 renal cell cancer (RCC) patients receiving 50 mg/day of the multitargeted VEGF inhibitor sunitinib, on a 4-week-on/2-week-off schedule.

Proteomics of the TRAP-induced platelet releasate.

Upon stimulation, platelets release the soluble content of their cytoplasmic granules along with microparticles. This sub-proteome is of interest since many of its constituents are associated with coagulation, (tumor) angiogenesis, cell growth and adhesion. Previously, differential - antibody-based - serum analysis has yielded information on the proteins released from platelets upon stimulation.

Sunitinib-induced myeloid lineage redistribution in renal cell cancer patients: CD1c+ dendritic cell frequency predicts progression-free survival.

Purpose: A disturbed myeloid lineage development with abnormally abundant neutrophils and impaired dendritic cell (DC) differentiation may contribute to tumor immune escape. We investigated the effect of sunitinib, a tyrosine kinase inhibitor of fms-like tyrosine kinase-3, KIT, and vascular endothelial growth factor receptors, on myeloid differentiation in renal cell cancer (RCC) patients.

Experimental Design: Twenty-six advanced RCC patients were treated with sunitinib in a 4-week on/2-week off schedule.

Anticancer therapeutics: a surge of new developments increasingly target tumor and stroma.

The Annual Meeting of the American Association for Cancer Research (AACR) brings together research in fundamental biology, translational science, drug development and clinical testing of emerging anticancer therapies. Among the highlights of the 2007 Annual Meeting were major research themes on drug action, drug resistance and new drug development. Instead of striving for a comprehensive overview, we showcase several trends, concepts and research areas that exemplify the complexity of drug resistance and its reversal as we currently understand it.

VEGFR2 expressing circulating (progenitor) cell populations in volunteers and cancer patients.

Circulating cells of several lineages are thought to participate in angiogenesis and tumor growth. Experimental studies in tumor-bearing mice have pointed to the potential importance of VEGF-responding circulating (endothelial) progenitor cells in tumor growth. We have studied circulating CD31- and/or CD34-positive cell populations with a low to moderate VEGFR2 expression in human volunteers and cancer patients.

Celecoxib enhances doxorubicin-induced cytotoxicity in MDA-MB231 cells by NF-kappaB-mediated increase of intracellular doxorubicin accumulation.

Non-steroidal anti-inflammatory drugs (NSAIDs) and cyclo-oxygenase (COX) inhibitors are anti-inflammatory agents that have also shown to be useful in anticancer therapy. In the present study, we show that the specific COX-2 inhibitor celecoxib enhances the inhibitory effect of doxorubicin (dox) on human MDA-MB231 breast tumour growth in vivo and in vitro. We also found that celecoxib increased the intracellular accumulation and retention of dox in vitro.

Anticancer therapeutics: "Addictive" targets, multi-targeted drugs, new drug combinations.

The annual meeting of the American Association for Cancer Research (AACR) provided a panoramic view of new developments and trends in cancer research. In the area of new drug development, a recurrent theme was receptor tyrosine kinase (TK) inhibitors, with multi-targeted, small molecule inhibitors - highly potent against a family of receptors such as vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor (PDGFR) and the receptor tyrosine kinase KIT - taking centre stage. Several agents interfering with intracellular targets that are components of key oncogenic signaling pathways, such as RAF kinase, phosphatidylinositol 3-kinase (PI3K)/Akt or Src, are in preclinical and early clinical development.

New cancer therapeutics: target-specific in, cytotoxics out?

The International Conference on Molecular Targets and Therapeutics, jointly sponsored by the American Association for Cancer Research (AACR), National Cancer Institute (NCI) and European Organization for Research and Treatment of Cancer (EORTC), was held in Boston on November 17-21, 2003. It offered updates of the latest developments and emerging trends in anti-cancer research. One of the most exciting areas was the development of molecular target-specific therapeutics that have the potential to maximize therapeutic benefit while minimizing toxicity to normal cells.

Reduced growth, increased vascular area, and reduced response to cisplatin in CD13-overexpressing human ovarian cancer xenografts.

Purpose: Expression of aminopeptidase N/CD13 can be detected in several solid tumor types. Thus far, the role of CD13 in ovarian cancer has not been studied. We have investigated the expression pattern and biological function of CD13 in ovarian cancer.

Aminopeptidase inhibitor bestatin stimulates microvascular endothelial cell invasion in a fibrin matrix.

The aminopeptidase inhibitor bestatin has been shown to have anti-angiogenic effects in a number of model systems. These effects are thought to result from inhibition of CD13 activity. Because tumor angiogenesis can evolve in a fibrin-rich stroma matrix we have studied for the first time the effects of bestatin on microvascular endothelial capillary-like tube formation in a fibrin matrix.

Multidrug-resistant tumor cells remain sensitive to a recombinant interleukin-4-Pseudomonas exotoxin, except when overexpressing the multidrug resistance protein MRP1.

Tumor cells may become resistant to conventional anticancer drugs through the occurrence of transmembrane transporter proteins such as P-glycoprotein (ABCB1), breast cancer resistance protein (ABCG2), or members of the multidrug resistance-associated protein family (MRP1-MRP5; ABCC1-ABCC5). In this report, we studied whether tumor cells that are cytostatic drug resistant because of overexpression of one of the above mentioned proteins are sensitive to a new anticancer agent, interleukin-4 toxin (IL-4 toxin). IL-4 toxin is a fusion protein composed of circularly permuted IL-4 and a truncated form of Pseudomonas exotoxin (PE) [IL-4(38-37)-PE38KDEL].