Measuring Hemotoxicity

The different degrees of potential for proliferation by stem cells also cause it to be one of the most sensitive to the toxicity of drugs (Harper and Rich, 2013). Most stem ceUs are in a quiescent, nonproliferative state (Rich, 2015b) however, this does not mean that they are immune to potential toxicity. Small molecules may modulate quiescent cells, and for stem cells, this effect may not be evident until the cells reenter the cell cycle. Attenuations may also appear during cell development or differentiation as increased apoptosis or necrosis or other events that inhibit the system from establishing and/or maintaining homeostasis. 

In practice, such a high in vitro to in vivo concordance for myelotoxicity has been known for decades. The hematopoietic hierarchical organization (Fig. 11.1) and its regulation are, to a large part, based on animal and human perturbations (drugs, irradiation, etc.) that have been detected using in vitro methods such as the CFU/CFC assay. The term hemotoxicity, rather than myelotoxicity, will be used henceforth since the former imphes that the bone marrow is the adult site for toxicity and encompasses all cells of the hematopoietic system. 

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