Figure 6

Concentration of free receptors and matrix components and relative probabilities of VEGF binding. The diseased compartment represents a 4-cm diameter tumor. Vascular permeability of the healthy tissue, $k_p^N$ = 4 × 10^-8 cm/s; vascular permeability in the tumor $k_p^D$ = 4 × 10^-7 cm/s; VEGF plasma clearance c _V = 0.0206 min^-1 [28]; VEGFR1 = 10,000 and VEGFR2 = 10,000 molecules/endothelial cell; NRP1 = 10,000 molecules/endothelial cell in the healthy tissue; VEGF₁₆₅ secretion rate in healthy tissue q _N = 0.102 molecule/cell/s; tumor VEGF₁₆₅ secretion rate q _D = 0.076 or 0.025 molecule/cell/s for 10,000 (black bars) or 100,000 (dark yellow bars) NRP1 in tumor respectively. A, Concentration of free receptors and matrix components. For the same NRP1 density in both tissues, the healthy tissue and tumor have the same concentration of free receptors. The occupancy of the matrix components (ECM, PBM, EBM) is insensitive to the NRP1 density in the tumor. B, Relative probabilities of VEGF binding to receptors and matrix components (concentration/K_d). The propensity to bind to receptors is much higher in healthy tissue than in tumor. The likelihood of binding to the matrix components, however, is very similar in the healthy tissue and tumor regardless of the NRP1 density.