Rat tumor response to the vascular-disrupting agent 5,6-dimethylxanthenone-4-acetic acid as measured by dynamic contrast-enhanced magnetic resonance imaging, plasma 5-hydroxyindoleacetic acid levels, and tumor necrosis

Abstract

The dose-dependent effects of 5,6-dimethylxanthenone-4-acetic acid (DMXAA) on rat GH3 prolactinomas were investigated in vivo. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was used to assess tumor blood flow/permeability pretreatment and 24 hours posttreatment with 0, 100, 200, or 350 mg/kg DMXAA. DCE-MRI data were analyzed using K(trans) and the integrated area under the gadolinium time curve (IAUGC) as response biomarkers. High-performance liquid chromatography (HPLC) was used to determine the plasma concentration of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) following treatment to provide an index of increased vessel permeability and vascular damage. Finally, tumor necrosis was assessed by grading hematoxylin and eosin-stained sections cut from the same tumors investigated by MRI. Both tumor K(trans) and IAUGC were significantly reduced 24 hours posttreatment with 350 mg/kg DMXAA only, with no evidence of dose response. HPLC demonstrated a significant increase in plasma 5-HIAA 24 hours posttreatment with 200 and 350 mg/kg DMXAA. Histologic analysis revealed some evidence of tumor necrosis following treatment with 100 or 200 mg/kg DMXAA, reaching significance with 350 mg/kg DMXAA. The absence of any reduction in K(trans) or IAUGC following treatment with 200 mg/kg, despite a significant increase in 5-HIAA, raises concerns about the utility of established DCE-MRI biomarkers to assess tumor response to DMXAA.

Figure 1

K^trans maps from a single slice through a GH3 prolactinoma (A) pretreatment and (B) 24 hours posttreatment with 350 mg/kg DMXAA.

Figure 2

(A) IAUGC and (B) K^trans histograms of a GH3 prolactinoma tumor model pretreatment and 24 hours posttreatment with vehicle only.

Figure 3

(A) IAUGC and (B) K^trans histograms of a GH3 prolactinoma pretreatment and 24 hours posttreatment with 350 mg/kg DMXAA.

Figure 4

Line series graphs showing K^trans values for individual rats (A) pretreatment and 24 hours posttreatment with 100 mg/kg DMXAA; (B) pretreatment and 4 hours posttreatment with 200 mg/kg DMXAA; (C) pretreatment and 24 hours posttreatment with 200 mg/kg DMXAA; and (D) pretreatment and 24 hours posttreatment with 350 mg/mg DMXAA.

Figure 5

Summary of the response of the biomarkers (A) K^trans and (B) IAUGC to 200 mg/kg DMXAA 4 hours posttreatment (200 mg/kg*) (n = 7) and to 0 mg/kg (n = 6), 100 mg/kg (n = 7), 200 mg/kg (n = 8), or 350 mg/kg (n = 7) DMXAA 24 hours posttreatment (data points are ± 1 SEM; ^#P < .05, Student's t test).

Figure 6

Summary of the concentration of 5-HIAA in rat plasma samples 4 hours posttreatment with 200 mg/kg DMXAA (200 mg/kg*) (n = 4) and 24 hours posttreatment with 0 mg/kg (n = 4), 100 mg/kg (n = 5), 200 mg/kg (n = 8), or 350 mg/kg (n = 4) DMXAA (data points are mean ± 1 SEM; ^#P < .05, Student's paired t test).

Figure 7

(A) A hematoxylin and eosin-stained section of a GH3 prolactinoma 24 hours posttreatment with vehicle. Grade 1, no necrosis. (B) A hematoxylin and eosin-stained section of a GH3 prolactinoma tumor model 24 hours posttreatment with 350 mg/kg DMXAA. Grade 4, extensive necrosis (v = viable tissue; n = necrosis).

Figure 8

Summary of necrosis grade in GH3 prolactinomas 4 hours posttreatment with 200 mg/kg DMXAA (200 mg/kg*) (n = 5) and 24 hours posttreatment with 0 mg/kg (n = 6), 100 mg/kg (n = 7), 200 mg/kg (n = 8), or 350 mg/kg (n = 7) DMXAA (data points are mean ± 1 SEM; ^#P < .05, Mann-Whitney U test).

Figure 9

Growth of GH3 prolactinomas posttreatment with either vehicle (▲; n = 4) or 350 mg/kg DMXAA (■; n = 4) (data points are mean ± 1 SEM; *P < .02, **P < .01, Student's t test).