Thymidine kinase 1 and thymidine phosphorylase expression in non-small-cell lung carcinoma in relation to angiogenesis and proliferation

Abstract

The thymidine salvage pathway enzymes thymidine kinase 1 (TK1) and thymidine phosphorylase (TP) compete for thymidine as a substrate and catalyze opposing synthetic and catabolic reactions that have been implicated in the control of proliferation and angiogenesis, respectively. We investigated the relationship between the expression of TK1 and TP as they relate to proliferation (Ki-67 labeling index) and angiogenesis (Chalkley count of CD31-stained blood vessels) in a series of 110 non-small-cell lung cancer (NSCLC) tumors from patients prospectively enrolled in an imaging trial. TK1 and TP exhibited similar patterns of immunohistochemical distribution, in that each was found in both the nucleus and the cytoplasm of tumor cells. Each enzyme exhibited a significant positive correlation between its levels of nuclear and cytoplasmic expression. A significant positive correlation between TK1 expression and the Ki-67 labeling index (r = 0.53, p<0.001) was observed. TP was significantly positively correlated with Chalkley scoring of CD31 staining in high vs low Chalkley scoring samples (mean TP staining of 115.8 vs 79.9 scoring units, p<0.001), respectively. We did not observe a substantial inverse correlation between the TP and TK1 expression levels in the nuclear compartment (r = -0.17, p=0.08). Tumor size was not found to be associated with TK1, TP, Ki-67, or Chalkley score. These findings provide additional evidence for the role of thymidine metabolism in the complex interaction of proliferation and angiogenesis in NSCLC.

Figure 1

Thymidine plays a central role in both proliferation and angiogenesis. TP, thymidine phosphorylase; TK1, thymidine kinase 1; dTMPK, thymidine monophosphate kinase; NDPK, nucleotide diphsophate kinase; dTTP, thymidine triphosphate; dTMP, thymidine monophosphate (thymidylate); 2-dR-1-P, 2-deoxyribose-1-phosphate. Unequal reversible reaction arrows indicate that thymidine catabolism is usually the energetically preferred direction of bidirectional TP catalysis.

Figure 2

Representative examples of immunohistochemical staining. (A) TP-low composite score. (B) TP-high composite score. (C) TK1-low composite score. (D) TK1-high composite score. (E) CD31 staining. (F) Ki-67 staining. Bar = 50 μm.

Figure 3

Nuclear TP staining vs cytoplasmic TP staining. Cytoplasmic TP staining was strongly correlated with (r = 0.85, p<0.001) and significantly greater than (p<0.001) nuclear TP staining.

Figure 4

Nuclear TK1 staining vs cytoplasmic TK1 staining. Cytoplasmic TK1 staining was strongly correlated with (r = 0.78, p<0.001) and significantly greater than (p<0.001) nuclear TK1 staining.

Figure 5

Cytoplasmic TK1 staining vs Ki-67 labeling index. Cytoplasmic TK1 staining was significantly correlated with the Ki-67 labeling index (r = 0.53, p<0.001).

Figure 6

Boxplot of cytoplasmic TP vs CD31. Cytoplasmic TP staining was significantly greater for those with high (>6) compared with low (≤6) Chalkley score for CD31 staining (mean cytoplasmic TP staining, 115.8 vs 79.9, respectively, p<0.001). The length of the box represents the interquartile data range (the distance between the 25th and the 75th percentiles). The plus symbol in the box interior denotes the data mean, and the horizontal line in the box interior represents the data median. Vertical lines extending from the box mark the minimum and maximum observed values.