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Autotaxin and LPA receptors represent potential molecular targets for the radiosensitization of murine glioma through effects on tumor vasculature.

Schleicher SM, Thotala DK, Linkous AG, Hu R, Leahy KM, Yazlovitskaya EM, Hallahan DE - PLoS ONE (2011)

Bottom Line: In co-culture experiments using bEND.3 and mouse GL-261 glioma cells, treatment with BrP-LPA reduced Akt phosphorylation in both irradiated cell lines and decreased survival and migration of irradiated GL-261 cells.Using siRNA to knock down LPA receptors LPA1, LPA2 or LPA3 in HUVEC, we demonstrated that knockdown of LPA2 but neither LPA1 nor LPA3 led to increased viability and proliferation.However, knockdown of LPA1 and LPA3 but not LPA2 resulted in complete abrogation of tubule formation implying that LPA1 and LPA3 on endothelial cells are likely targets of BrP-LPA radiosensitizing effect.

View Article: PubMed Central - PubMed

Affiliation: School of Medicine, Vanderbilt University, Nashville, Tennessee, United States of America.

ABSTRACT
Despite wide margins and high dose irradiation, unresectable malignant glioma (MG) is less responsive to radiation and is uniformly fatal. We previously found that cytosolic phospholipase A2 (cPLA(2)) is a molecular target for radiosensitizing cancer through the vascular endothelium. Autotaxin (ATX) and lysophosphatidic acid (LPA) receptors are downstream from cPLA(2) and highly expressed in MG. Using the ATX and LPA receptor inhibitor, α-bromomethylene phosphonate LPA (BrP-LPA), we studied ATX and LPA receptors as potential molecular targets for the radiosensitization of tumor vasculature in MG. Treatment of Human Umbilical Endothelial cells (HUVEC) and mouse brain microvascular cells bEND.3 with 5 µmol/L BrP-LPA and 3 Gy irradiation showed decreased clonogenic survival, tubule formation, and migration. Exogenous addition of LPA showed radioprotection that was abrogated in the presence of BrP-LPA. In co-culture experiments using bEND.3 and mouse GL-261 glioma cells, treatment with BrP-LPA reduced Akt phosphorylation in both irradiated cell lines and decreased survival and migration of irradiated GL-261 cells. Using siRNA to knock down LPA receptors LPA1, LPA2 or LPA3 in HUVEC, we demonstrated that knockdown of LPA2 but neither LPA1 nor LPA3 led to increased viability and proliferation. However, knockdown of LPA1 and LPA3 but not LPA2 resulted in complete abrogation of tubule formation implying that LPA1 and LPA3 on endothelial cells are likely targets of BrP-LPA radiosensitizing effect. Using heterotopic tumor models of GL-261, mice treated with BrP-LPA and irradiation showed a tumor growth delay of 6.8 days compared to mice treated with irradiation alone indicating that inhibition of ATX and LPA receptors may significantly improve malignant glioma response to radiation therapy. These findings identify ATX and LPA receptors as molecular targets for the development of radiosensitizers for MG.

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Inhibition of ATX and LPA receptors represses tumor growth in irradiated GL261 mouse model.GL261 cells were injected into the hind limbs of nude mice. Tumors were irradiated with 3 Gy for 5 consecutive days for a total of 15 Gy. Mice were treated with 3 mg/kg BrP-LPA or vehicle control for 45 min prior to irradiation on days 1, 3, and 5. (A) Shown are mean tumor volumes with SEM from each treatment group of 5 mice. (B) Tumor growth delay was calculated as the number of days for tumors to reach a 6-fold volume increase compared to control. Shown is a bar graph representing the mean tumor growth delay with SEM from each treatment group of 5 mice; * p<0.05.
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pone-0022182-g007: Inhibition of ATX and LPA receptors represses tumor growth in irradiated GL261 mouse model.GL261 cells were injected into the hind limbs of nude mice. Tumors were irradiated with 3 Gy for 5 consecutive days for a total of 15 Gy. Mice were treated with 3 mg/kg BrP-LPA or vehicle control for 45 min prior to irradiation on days 1, 3, and 5. (A) Shown are mean tumor volumes with SEM from each treatment group of 5 mice. (B) Tumor growth delay was calculated as the number of days for tumors to reach a 6-fold volume increase compared to control. Shown is a bar graph representing the mean tumor growth delay with SEM from each treatment group of 5 mice; * p<0.05.

Mentions: To determine the efficacy of ATX and LPA receptor inhibition in vivo, a heterotopic mouse brain tumor model was used. GL261 cells (1×105) were injected s.c. into the right hind limbs of nude mice. Tumor-bearing mice were then treated with vehicle alone, irradiation alone (5 fractions of 3 Gy), 3 mg/kg BrP-LPA alone, or 3 mg/kg BrP-LPA for 45 min followed by irradiation (5 fractions of 3 Gy). Treatment with either BrP-LPA or irradiation alone delayed tumor growth relative to control (1.2 days and 12.0 days, respectively; Fig. 7). The most pronounced tumor growth delay, however, was observed in mice receiving a combination of BrP-LPA and irradiation. In this treatment group, the tumor growth delay was 6.8 days relative to treatment with irradiation alone (p = 0.03). This difference remained statistically significant (p = 0.0005) after using Holm's correction for multiple comparisons, and a 22 factorial design study of tumor growth delay revealed an additive interaction between BrP-LPA and irradiation.


Autotaxin and LPA receptors represent potential molecular targets for the radiosensitization of murine glioma through effects on tumor vasculature.

Schleicher SM, Thotala DK, Linkous AG, Hu R, Leahy KM, Yazlovitskaya EM, Hallahan DE - PLoS ONE (2011)

Inhibition of ATX and LPA receptors represses tumor growth in irradiated GL261 mouse model.GL261 cells were injected into the hind limbs of nude mice. Tumors were irradiated with 3 Gy for 5 consecutive days for a total of 15 Gy. Mice were treated with 3 mg/kg BrP-LPA or vehicle control for 45 min prior to irradiation on days 1, 3, and 5. (A) Shown are mean tumor volumes with SEM from each treatment group of 5 mice. (B) Tumor growth delay was calculated as the number of days for tumors to reach a 6-fold volume increase compared to control. Shown is a bar graph representing the mean tumor growth delay with SEM from each treatment group of 5 mice; * p<0.05.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3140496&req=5

pone-0022182-g007: Inhibition of ATX and LPA receptors represses tumor growth in irradiated GL261 mouse model.GL261 cells were injected into the hind limbs of nude mice. Tumors were irradiated with 3 Gy for 5 consecutive days for a total of 15 Gy. Mice were treated with 3 mg/kg BrP-LPA or vehicle control for 45 min prior to irradiation on days 1, 3, and 5. (A) Shown are mean tumor volumes with SEM from each treatment group of 5 mice. (B) Tumor growth delay was calculated as the number of days for tumors to reach a 6-fold volume increase compared to control. Shown is a bar graph representing the mean tumor growth delay with SEM from each treatment group of 5 mice; * p<0.05.
Mentions: To determine the efficacy of ATX and LPA receptor inhibition in vivo, a heterotopic mouse brain tumor model was used. GL261 cells (1×105) were injected s.c. into the right hind limbs of nude mice. Tumor-bearing mice were then treated with vehicle alone, irradiation alone (5 fractions of 3 Gy), 3 mg/kg BrP-LPA alone, or 3 mg/kg BrP-LPA for 45 min followed by irradiation (5 fractions of 3 Gy). Treatment with either BrP-LPA or irradiation alone delayed tumor growth relative to control (1.2 days and 12.0 days, respectively; Fig. 7). The most pronounced tumor growth delay, however, was observed in mice receiving a combination of BrP-LPA and irradiation. In this treatment group, the tumor growth delay was 6.8 days relative to treatment with irradiation alone (p = 0.03). This difference remained statistically significant (p = 0.0005) after using Holm's correction for multiple comparisons, and a 22 factorial design study of tumor growth delay revealed an additive interaction between BrP-LPA and irradiation.

Bottom Line: In co-culture experiments using bEND.3 and mouse GL-261 glioma cells, treatment with BrP-LPA reduced Akt phosphorylation in both irradiated cell lines and decreased survival and migration of irradiated GL-261 cells.Using siRNA to knock down LPA receptors LPA1, LPA2 or LPA3 in HUVEC, we demonstrated that knockdown of LPA2 but neither LPA1 nor LPA3 led to increased viability and proliferation.However, knockdown of LPA1 and LPA3 but not LPA2 resulted in complete abrogation of tubule formation implying that LPA1 and LPA3 on endothelial cells are likely targets of BrP-LPA radiosensitizing effect.

View Article: PubMed Central - PubMed

Affiliation: School of Medicine, Vanderbilt University, Nashville, Tennessee, United States of America.

ABSTRACT
Despite wide margins and high dose irradiation, unresectable malignant glioma (MG) is less responsive to radiation and is uniformly fatal. We previously found that cytosolic phospholipase A2 (cPLA(2)) is a molecular target for radiosensitizing cancer through the vascular endothelium. Autotaxin (ATX) and lysophosphatidic acid (LPA) receptors are downstream from cPLA(2) and highly expressed in MG. Using the ATX and LPA receptor inhibitor, α-bromomethylene phosphonate LPA (BrP-LPA), we studied ATX and LPA receptors as potential molecular targets for the radiosensitization of tumor vasculature in MG. Treatment of Human Umbilical Endothelial cells (HUVEC) and mouse brain microvascular cells bEND.3 with 5 µmol/L BrP-LPA and 3 Gy irradiation showed decreased clonogenic survival, tubule formation, and migration. Exogenous addition of LPA showed radioprotection that was abrogated in the presence of BrP-LPA. In co-culture experiments using bEND.3 and mouse GL-261 glioma cells, treatment with BrP-LPA reduced Akt phosphorylation in both irradiated cell lines and decreased survival and migration of irradiated GL-261 cells. Using siRNA to knock down LPA receptors LPA1, LPA2 or LPA3 in HUVEC, we demonstrated that knockdown of LPA2 but neither LPA1 nor LPA3 led to increased viability and proliferation. However, knockdown of LPA1 and LPA3 but not LPA2 resulted in complete abrogation of tubule formation implying that LPA1 and LPA3 on endothelial cells are likely targets of BrP-LPA radiosensitizing effect. Using heterotopic tumor models of GL-261, mice treated with BrP-LPA and irradiation showed a tumor growth delay of 6.8 days compared to mice treated with irradiation alone indicating that inhibition of ATX and LPA receptors may significantly improve malignant glioma response to radiation therapy. These findings identify ATX and LPA receptors as molecular targets for the development of radiosensitizers for MG.

Show MeSH
Related in: MedlinePlus