Endothelial cell–specific LAT1 ablation normalizes tumor vasculature
Jun-ichi Suehiro, Toru Kimura, Toshiyuki Fukutomi, Hisamichi Naito, Yasuharu Kanki, Youichiro Wada, Yoshiaki Kubota, Nobuyuki Takakura, Hiroyuki Sakurai
Jun-ichi Suehiro, Toru Kimura, Toshiyuki Fukutomi, Hisamichi Naito, Yasuharu Kanki, Youichiro Wada, Yoshiaki Kubota, Nobuyuki Takakura, Hiroyuki Sakurai
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Research Article Angiogenesis Vascular biology

Endothelial cell–specific LAT1 ablation normalizes tumor vasculature

Abstract

Some endothelial cells in the tumor vasculature express a system L amino acid transporter, LAT1. To elucidate the role of LAT1 in tumor-related endothelial cells, tumor cells were injected into endothelial cell–specific LAT1 conditional knockout mice (Slc7a5flox/flox; Cdh5-Cre-ERT2), and we found that the shape of the tumor vasculature was normalized and the size and numbers of lung metastasis was reduced. TNF-α–induced expression of VCAM1 and E-selectin at the surface of HUVEC, both of which are responsible for enhanced monocyte attachment and premetastatic niche formation, was reduced in the presence of LAT1 inhibitor, nanvuranlat. Deprivation of tryptophan, a LAT1 substrate, mimicked LAT1 inhibition, which led to activation of MEK1/2-ERK1/2 pathway and subsequent cystathionine γ lyase (CTH) induction. Increased production of hydrogen sulfide (H2S) by CTH was at least partially responsible for tumor vascular normalization, leading to decreased leakiness and enhanced delivery of chemotherapeutic agents to the tumor.

Authors

Jun-ichi Suehiro, Toru Kimura, Toshiyuki Fukutomi, Hisamichi Naito, Yasuharu Kanki, Youichiro Wada, Yoshiaki Kubota, Nobuyuki Takakura, Hiroyuki Sakurai

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Figure 6

Endothelial cell–specific LAT1 ablation led to improved drug delivery to primary tumor mediated by vascular normalization.

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Endothelial cell–specific LAT1 ablation led to improved drug delivery to...
(A) Tumor vessel perfusion was examined in subcutaneous Ex-3LLC bearing mice by intravenous injection of FITC conjugated tomato lectin. The ratio (mean ± SEM, control; n = 8, Slc7a5iEC–KO mice; n = 10) of lectin positive cells/PECAM1 positive cells were counted and normalized to that of control mice (the mean of the control mice was calculated as 1). (B) Tumor vessel perfusion was examined in subcutaneous B16F10 bearing control or Slc7a5iEC–KO mice by intravenous injection of FITC-conjugated tomato lectin. Semiquantification of lectin positivity (mean ± SEM, control; n = 12, Slc7a5iEC–KO mice; n = 12) was done as in A. (C) Tumor vessel perfusion was examined in subcutaneous Ex-3LLC–bearing mice by intravenous injection of doxorubicin. Fluorescent intensity of doxorubicin (mean ± SEM) was calculated from 4 randomly selected slices and normalized to that of control (= 1). (D) Tumor vessel perfusion was examined in subcutaneous B16F10-bearing control or Slc7a5iEC–KO mice by intravenous injection of doxorubicin. Fluorescent intensity of doxorubicin (mean ± SEM) was calculated from 4 or 5 randomly selected slices and normalized to that of control (= 1). (E) Ex-3LLC solid tumor growth in control or Slc7a5iEC–KO mice in the presence or absence of 10 mg/kg cisplatin at day 26. (F) Ex-3LLC tumor volume in each condition were estimated from the radius of the tumor. (mean ± SEM, control; n = 7, control + cisplatin; n = 7, Slc7a5iEC–KO mice; n = 6, Slc7a5iEC–KO + cisplatin; n = 6). (G) Ex-3LLC tumor weights at day 26 were shown. (H) B16F10 solid tumor growth in control or Slc7a5iEC–KO mice in the presence or absence of 10 mg/kg cisplatin at day 15. (I) B16F10 tumor volume in each condition were estimated from the radius of the tumor. (mean ± SEM, control; n = 12, control + cisplatin; n = 10, Slc7a5iEC–KO mice; n = 9, Slc7a5iEC–KO + cisplatin; n = 10). (J) B16F10 tumor weights at 15 days were shown. (A–D) P values were determined by 2-tailed, unpaired t test. (F–I) P values were determined by 1-way ANOVA with Tukey-Kramer’s multiple comparisons test compared to control at each time point. *P < 0.05. Scale bars: 200 μm (A and B); 100 μm (C and D); 1 cm (E and H).