Simplified schematics of the leukopoiesis and erythropoiesis model.

<p>Stem cells reside in the bone marrow, proliferate, mature and enter the circulation as fully functional leukocytes. Stem cells receive biochemical feedback for proliferation from the circulating blood. On treatment initiation, 6-MP enters the bone marrow and imparts cytotoxicity to the stem cells. Leukocytes and RBC MCV in the circulating blood are routinely measured and used as a dose-limiting parameter. A. Leukopoiesis, B. Erythropoiesis. Additional compartment for MCV was added to account for the dynamic changes following 6-MP treatment. Solid arrows represent cellular movement; dashed arrow represents property changes.</p

Leukopoiesis model fit to individual patient data obtained from literature.

<p>Solid dots indicate the individual patient WBC count and solid lines represent the model fit. The estimated patient-specific parameters are provided in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109623#pone-0109623-t005" target="_blank">Table 5</a>. The model mimics diverse behavior observed during 6-MP treatment.</p

List of parameters identified for individualization through GSA (in bold letters) together with other fixed parameters.

<p>List of parameters identified for individualization through GSA (in bold letters) together with other fixed parameters.</p

Glossary of state variables and parameters for leukopoiesis model.

<p>Glossary of state variables and parameters for leukopoiesis model.</p

Leukopoiesis model fit to average patient data.

<p>Solid dots represent average patient data and curve represent leukocyte model (Eqn. 4) fit. The model mimics the clinical observation during 6-MP treatment; Depletion of leukocytes following 6-MP dosing has been countered by the body's feed-back mechanism. Error bars represent standard error.</p

6-MP model fit to individual patient data obtained from literature.

<p>Solid dots indicate the individual patient 6-TGN concentration and the solid line represents the model fit. Patient # 8 was omitted from analysis as it is observed that the dosing was discontinued or substantially lowered. The estimated patient-specific parameters are provided in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109623#pone-0109623-t005" target="_blank">Table 5</a>.</p

MCV model fit to average patient MCV data.

<p>Solid dots represent the data from literature and the solid line shows the model (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109623#pone.0109623.e043" target="_blank">Eqn. 7</a>) fit with 6-TGN concentration of 158 pmol/8×10⁸ RBCs. The model fits the data well; it reaches the steady state and stays at ΔMCV of ∼8 fL, which is typically observed during 6-MP treatment at Riley Hospital for Children. Error bars represent standard error.</p

Average patient 6-MP model fit to literature data.

<p>A. Model fit to RBC 6-TGN concentration data. B. Model fit to RBC MeMP concentration data. Solid dots represent data points and curves represent 6-MP model (Eqn. 2) fit. Error bars represent standard error.</p

Virtual patient simulation for leukocyte and MCV model.

<p>Data for 6-MP model and leukocyte model are assumed to have originated from the same patient. The resultant estimated parameters for three representative patients are used to simulate the virtual patient response. It is apparent from the figure that different patients achieved different levels of response for the same dose, thereby achieving different treatment outcome. A. Leukocyte model, B. MCV model.</p

Optimal dosing based on leukocyte count and MCV as target.

<p>A. Evolution of leukocyte count in response to optimum 6-MP dosing. B. Evolution of ΔMCV response with optimum 6-MP dose. Dashed lines represent critical leukocyte and target MCV levels and solid dots represent clinical data for an average patient. C. Optimum 6-MP dosing profile predicted by NMPC. The standard daily 6-MP dosing is 75 mg/day.</p