Avastin (bevacizumab)-induced tumor calcifications can be elicited in glioblastoma

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Endothelial Massive Calcium Accumulation Death (MCAD): Mechanism, Target, and Predictive Biomarker for Anti-Angiogenic Therapy.

When you culture endothelial cells (either pure cultures of endothelial cells or endothelial cells associated with fresh human tumor microclusters) with Avastin, all of the VEGF gets pulled out of the culture medium and the endothelial cells undergo what is called "massive calcium accumulation death."

Cytotoxic anticancer drugs (topotecan, vinorelbine, melphalan, doxorubicin, cisplatin) antagonize the ability of Avastin to kill endothelial cells through this specific cell death mechanism. The standard, traditional cytotoxic drugs all inhibited Avastin, but the new, "targeted" drugs either don't inhibit it or actually enhance it (e.g. lapatinib, erlotinib).

Clinical trials have shown that the combination of chemotherapy with Avastin generally works better than either alone (that is, in situations where Avastin works at all). But this is because Avastin has a very long half life (weeks) and it has the opportunity to work at times when the drug levels of the standard anticancer drugs go down to undetectable levels (where they won't antagonize the ability of low VEGF to cause death of the tumor endothelial cells).

It would be predictive that continuous chemotherapy with a drug like Taxol would be antagonistic; so that intermittent, lower dose therapy might actually work much better than continuous high dose therapy. This is a theoretical extrapolation from cell culture data.

The mechanism of antagonism is that the "MCAD" (massive calcium accumulation death of endothelial cells) is a bioenergetically active process. I'm sure that there's a specific pathway for it that someone will eventually work out and that non-specific cytotoxins inhibit this active process and, thus, the withdrawal of VEGF can't trigger this active, MCAD form of endothelial cell death.

Bibliography relevant to AngioRx/Microvascular Viability assay (MVVA)

1. Weisenthal, L. M. Patel, N., Rueff-Weisenthal, C. (2008). "Cell culture detection of microvascular cell death in clinical specimens of human neoplasms and peripheral blood." J Intern Med 264(3): 275-287.

2. Weisenthal, L., Lee, DJ, and Patel, N. (2008). Antivascular activity of lapatinib and bevacizumab in primary microcluster cultures of breast cancer and other human neoplasms. ASCO 2008 Breast Cancer Symposium. Washington, D.C.: Abstract # 166. Slide presentation at: http://tinyurl.com/weisenthal-breast-lapatinib

3. Weisenthal, L. M. (2010). Antitumor and anti-microvascular effects of sorafenib in fresh human tumor culture in comparison with other putative tyrosine kinase inhibitors. J Clin Oncol 28, 2010 (suppl; abstr e13617)

4.Weisenthal, L., H. Liu, Rueff-Weisenthal, C. (2010). "Death of human tumor endothelial cells in vitro through a probable calcium-associated mechanism induced by bevacizumab and detected via a novel method." Nature Precedings 28 May 2010. from http://hdl.handle.net/10101/npre.2010.4499.1

5. Weisenthal, Larry. Endothelial Massive Calcium Accumulation Death (MCAD): Mechanism, Target, and Predictive Biomarker for Anti-Angiogenic Therapy. 13th international symposium on anti-angiogenic therapy: recent advances and future directions in basic and clinical cancer research. LaJolla, CA. February 2011
Available from Nature Precedings http://dx.doi.org/10.1038/npre.2011.6647.1> (2011)

6. Weisenthal, L, Williamson, S, Ryan, K, Brunshwiler, C, and Rueff-Weisenthal, C. Massive calcium uptake in human endothelial cells, submitted for publication.

7.Bevacizumab-induced tumor calcifications can be elicited in glioblastoma microspheroid culture and represent massive calcium uptake death (MCAD) of tumor endothelial cells. Larry Weisenthal, Summer Williamson, Cindy Brunschwiler, and Constance Rueff-Weisenthal, 14th International Anti-Angiogenesis Symposium, LaJolla CA, Feb 2012. Available from Nature Precedings http://dx.doi.org/10.1038/npre.2012.7069.1> (2012)

Weisenthal, Larry. Endothelial Massive Calcium Accumulation Death (MCAD): Mechanism, Target, and Predictive Biomarker for Anti-Angiogenic Therapy. Available from Nature Precedings (2011)

http://dx.doi.org/10.1038/npre.2011.6647.1

Poster Presentation

http://precedings.nature.com/documen...20116647-1.pdf

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J Intern Med. 2008 Sep;264(3):275-87.

Cell culture detection of microvascular cell death in clinical specimens of human neoplasms and peripheral blood.

Weisenthal LM, Patel N, Rueff-Weisenthal C.

Weisenthal Cancer Group, Huntington Beach, CA 92647, USA. [email]mail@weisenthal.org

Abstract

BACKGROUND:

Angiogenesis studies are limited by the clinical relevance of laboratory model systems. We developed a new method for measuring dead microvascular (MV) cells in clinical tissue, fluid and blood specimens, and applied this system to make several potentially novel observations relating to cancer pharmacology.

METHODS:

Dead MV cells tend to have a hyperchromatic, refractile quality, further enhanced during the process of staining with Fast Green and counterstaining with either haematoxylin-eosin or Wright-Giemsa. We used this system to quantify the relative degree of direct antitumour versus anti-MV effects of cisplatin, erlotinib, imatinib, sorafenib, sunitinib, gefitinib and bevacizumab.

RESULTS:

Bevacizumab had striking anti-MV effects and minimal antitumour effects; cisplatin had striking antitumour effects and minimal anti-MV effects. The ;nib' drugs had mixed antitumour and anti-MV effects. Anti-MV effects of erlotinib and gefitinib were equal to those of sunitinib and sorafenib. There was no detectable VEGF in culture medium without cells; tumour cells secreted copious VEGF, reduced to undetectable levels by bevacizumab, greatly reduced by cytotoxic levels of cisplatin + anguidine, and variably reduced by DMSO and/or ethanol. We observed anti-MV additivity between bevacizumab and other drugs on an individual patient basis. Peripheral blood specimens had numerous MV cells which were strikingly visualized for quantification with public domain image analysis software using bevacizumab essentially as an imaging reagent.

CONCLUSIONS:

This system could be adapted for simple, inexpensive and sensitive/specific detection of tissue and circulating MV cells in a variety of neoplastic and non-neoplastic conditions, and for drug development and individualized cancer treatment.

PMID: 18793333 [PubMed - indexed for MEDLINE]

http://www.ncbi.nlm.nih.gov/pubmed/18793333

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It's neither. It gives a much better understanding of what happens when Avastin is used. In pharmacology, the term agonist-antagonist is used to refer to a drug which exhibits some properties of an agonist (a substance that fully activates the neuronal receptor that it attaches to) and some properties of an antagonist (a substance that attaches to a receptor but does not activate it or if it displaces an agonist at that receptor it seemingly deactivates it thereby reversing the effect of the agonist).

When you culture endothelial cells with Avastin, all the VEGF gets pulled out of the culture medium and the endothelial cells undergo what is called "massive calcium accumulation death." Cytotoxic anticancer drugs antagonize the ability of Avastin to kill endothelial cells through this specific cell death mechanism. What is unique is that standard, traditional cytotoxic drugs inhibit Avastin, but the new "targeted" drugs don't inhibit it.

Clinical trials have shown that the combination of conventional chemotherapy with Avastin generally works better than either alone. But this is because Avastin has a very long half life (weeks) and it has the opportunity to work at times when the drug levels of the standard anticancer drugs go down to undetectable levels, where they won't antagonize the ability of low VEGF to cause death of the tumor endothelial cells. In other words, intermittent, "low dose" therapy might actually work much better than continuous "high dose" therapy.

In cell-based functional profiling assays, conducted on human tumor samples utilizing native microspheroids (fresh, live cells, not cell lines) replete with vascular, stromal and inflammatory cells to analyze cellular responses in the context of the tumor microenvironment, this snapshot of cellular response recapitulates patient response to cytotoxic compounds, signal transduction inhibitors and growth factor agonists/antagonists in real time.

Source: Cell Function Analysis