[gdpawel]

There are any number of variables that affect drugs. These include the rate of excretion of the drugs by the kidneys and liver, protein binding and a myriad of other biological factors.

Some anticancer drugs are actually pro-drugs: they need to be first activated in the liver before becoming biologically active. So in vitro testing must administer the active forms of these agents, not the pro-drug form that is given to patients.

In the body, these cells interact with and supported by other living cells, both malignant and non-malignant cells. That is why cell-death functional profiling assays study cancer cells in small clusters, or microspheroids.

Analysis of these microspheroids provides a snapshot of cancer's behavior within the human body and provides a more accurate representation of how cancer cells are likely to respond to treatment in the clinic.

It is crucial that there is no manipulation of isolated cancer cells to make them grow, which was an important point of distinction with earlier cell-growth assays.

Drs. Larry Weisenthal and Robert Nagourney adopted this concept and began applying the term microclusters.

Real-life cancers grow as a complex organism that includes both malignant and non-malignant components. It may include fibrous tissue, mesothelial cells, fibroblasts, endothelial cells, etc.

In order to exhibit its most characteristic behavior patterns, a cancer cell needs to be surrounded by a colony of other cells, both normal and malignant.

Human tumors represent micro-ecosystems composed of transformed cells, stroma, fibroblasts, vascular elements, extra-cellular protein matrices and inflammatory elements.

The behavior of human cancers and their reponse to therapy reflect the complex interplay between humoral, vascular, adhesion and cytokine-mediated events acting in concert.

Tumors are very complex organisms. Ignoring this complexity, most studies of human cancer in culture have focused upon individual tumor cells that have been removed from their complex microenvironoment.

Cells are routinely broken up by mechanical and enzymatic means, which alters their subsequent behavior. Some previous methods of assays limited their analysis only to isolated tumor cells and failed to incorporate the crucial contribution of non-tumorous elements to the cancer phenomenon.

When allowed to grow in vitro, living cancer cells develop into these tiny micro-spheroid clusters that form a complex biosystem in which each malignant cell reacts upon its fellow colonists in subtle but important ways.

Each of these microspheres contains all the complex elements of tumor biosytems that are found in the human body and which can impact clinical reponse.

Source: Nagourney RA, Kollin CA, Sommers B, Su Y-Z, Evans SS. Functional profiling of human tumors in primary culture: a platform for drug discovery and therapy selection, AACR abstract #1546, 2008