Prevalidation of a model for predicting acute neutropenia by colony forming unit granulocyte/macrophage (CFU-GM) assay

This report describes an international prevalidation study conducted to opt imise the Standard Operating Procedure (SOP) for detecting myelosuppressive agents by CFU-GM assay and to study a model for predicting (by means of th is in vitro hematopoietic assay) the acute xenobiotic exposure levels that cause maximum tolerated decreases in absolute neutrophil counts (ANC). In t he first phase of the study (Protocol Refinement), two SOPs were assessed, by using two cell culture media (Test A, containing GMCSF; and Test B, cont aining G-CSF, GM-CSF, IL-3, IL-6 and SCF), and the two tests were applied t o cells from both human (bone marrow and umbilical cord blood) and mouse (b one marrow) CFU-GM. In the second phase (Protocol Transfer), the SOPs were transferred to four laboratories to verify the linearity of the assay respo nse and its interlaboratory reproducibility. After a further phase (Protoco l Performance), dedicated to a training set of six anticancer drugs (adriam ycin, flavopindol, morpholino-doxorubicin, pyrazoloacridine, taxol and topo tecan), a model for predicting neutropenia was verified. Results showed tha t the assay is linear under SOP conditions, and that the in vitro endpoints used by the clinical prediction model of neutropenia are highly reproducib le within and between laboratories. Valid tests represented 95% of all test s attempted. The 90% inhibitory concentration values (IC90) from Test A and Test B accurately predicted the human maximum tolerated dose (MTD) for fiv e of six and for four of six myelosuppressive anticancer drugs, respectivel y, that were selected as prototype xenobiotics. As expected, both tests fai led to accurately predict the human MTD of a drug that is a likely protoxic ant. It is concluded that Test A offers significant cost advantages compare d to Test B, without any loss of performance or predictive accuracy. On the basis of these results, we proposed a formal Phase II validation study usi ng the Test A SOP for 16-18 additional xenobiotics that represent the spect rum of haematotoxic potential, (C) 2001 Elsevier Science Ltd. All rights re served.