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FDG-PET is a good biomarker of both early response and acquired resistance in BRAFV600 mutant melanomas treated with vemurafenib and the MEK inhibitor GDC-0973.

Baudy AR, Dogan T, Flores-Mercado JE, Hoeflich KP, Su F, van Bruggen N, Williams SP - EJNMMI Res (2012)

Bottom Line: We demonstrate that vemurafenib is equally effective at reducing FDG uptake in cell lines harboring either heterozygous or homozygous BRAFV600 but ineffective in cells with acquired resistance or having WT BRAF status.However, combination with GDC-0973 results in a highly significant increase of efficacy and inhibition of FDG uptake across all twenty lines.Vemurafenib and GDC-0973 combination efficacy was associated with decreased levels of hexokinase II, c-RAF, Ksr and p-MEK protein.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biomedical Imaging, Genentech Inc, 1 DNA Way, South San Francisco, CA, 94080, USA. williams.simon@gene.com.

ABSTRACT

Background: The BRAF inhibitor, vemurafenib, has recently been approved for the treatment of metastatic melanoma in patients harboring BRAFV600 mutations. Currently, dual BRAF and MEK inhibition are ongoing in clinical trials with the goal of overcoming the acquired resistance that has unfortunately developed in some vemurafenib patients. FDG-PET measures of metabolic activity are increasingly employed as a pharmacodynamic biomarker for guiding single-agent or combination therapies by gauging initial drug response and monitoring disease progression. However, since tumors are inherently heterogeneous, investigating the effects of BRAF and MEK inhibition on FDG uptake in a panel of different melanomas could help interpret imaging outcomes.

Methods: 18 F-FDG uptake was measured in vitro in cells with wild-type and mutant (V600) BRAF, and in melanoma cells with an acquired resistance to vemurafenib. We treated the cells with vemurafenib alone or in combination with MEK inhibitor GDC-0973. PET imaging was used in mice to measure FDG uptake in A375 melanoma xenografts and in A375 R1, a vemurafenib-resistant derivative. Histological and biochemical studies of glucose transporters, the MAPK and glycolytic pathways were also undertaken.

Results: We demonstrate that vemurafenib is equally effective at reducing FDG uptake in cell lines harboring either heterozygous or homozygous BRAFV600 but ineffective in cells with acquired resistance or having WT BRAF status. However, combination with GDC-0973 results in a highly significant increase of efficacy and inhibition of FDG uptake across all twenty lines. Drug-induced changes in FDG uptake were associated with altered levels of membrane GLUT-1, and cell lines harboring RAS mutations displayed enhanced FDG uptake upon exposure to vemurafenib. Interestingly, we found that vemurafenib treatment in mice bearing drug-resistant A375 xenografts also induced increased FDG tumor uptake, accompanied by increases in Hif-1α, Sp1 and Ksr protein levels. Vemurafenib and GDC-0973 combination efficacy was associated with decreased levels of hexokinase II, c-RAF, Ksr and p-MEK protein.

Conclusions: We have demonstrated that 18 F-FDG-PET imaging reflects vemurafenib and GDC-0973 action across a wide range of metastatic melanomas. A delayed post-treatment increase in tumor FDG uptake should be considered carefully as it may well be an indication of acquired drug resistance.

Trial registration: ClinicalTrials.gov NCT01271803.

No MeSH data available.


Related in: MedlinePlus

BRAF and MEK modulation of GLUT-1. BRAF and MEK inhibition results in changes in the amount of GLUT-1 at the cellular membrane associated with levels of FDG uptake. Immunofluorescent staining was performed for GLUT-1 (green) and nuclei (blue) on all panels of cells from Figure 1, which had been treated with drug for 3 days. (A) A375s, (B) resistant clone A375R1, (C) SK-Mel-30 melanomas and (D) HCT 116 colorectal cells.
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Figure 2: BRAF and MEK modulation of GLUT-1. BRAF and MEK inhibition results in changes in the amount of GLUT-1 at the cellular membrane associated with levels of FDG uptake. Immunofluorescent staining was performed for GLUT-1 (green) and nuclei (blue) on all panels of cells from Figure 1, which had been treated with drug for 3 days. (A) A375s, (B) resistant clone A375R1, (C) SK-Mel-30 melanomas and (D) HCT 116 colorectal cells.

Mentions: Immunofluorescent staining for GLUT-1 and GLUT-3 showed that GLUT-1 was the major transporter present across the panel of 20 in vitro cell lines. GLUT-3, a secondary glucose transporter in melanomas, displayed no observable staining, suggesting that increased levels may only be detectable in some patient biopsies and cells transfected with high levels of the protein (GLUT-3 positive staining control; Additional file 4: Figure S4) [28]. Furthermore, GLUT-1 mRNA expression levels are significantly higher than GLUT-3 in most cancers, including melanoma, and appear to be the dominant protein in the process of FDG uptake (glucose transport) and trapping (hexokinase II) [Additional file 5: Figure S5]. The relative levels of GLUT-1 on the cellular membrane directly corresponded with the observed drug-induced changes on intracellular FDG uptake that was previously shown (Figure 2).


FDG-PET is a good biomarker of both early response and acquired resistance in BRAFV600 mutant melanomas treated with vemurafenib and the MEK inhibitor GDC-0973.

Baudy AR, Dogan T, Flores-Mercado JE, Hoeflich KP, Su F, van Bruggen N, Williams SP - EJNMMI Res (2012)

BRAF and MEK modulation of GLUT-1. BRAF and MEK inhibition results in changes in the amount of GLUT-1 at the cellular membrane associated with levels of FDG uptake. Immunofluorescent staining was performed for GLUT-1 (green) and nuclei (blue) on all panels of cells from Figure 1, which had been treated with drug for 3 days. (A) A375s, (B) resistant clone A375R1, (C) SK-Mel-30 melanomas and (D) HCT 116 colorectal cells.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3405466&req=5

Figure 2: BRAF and MEK modulation of GLUT-1. BRAF and MEK inhibition results in changes in the amount of GLUT-1 at the cellular membrane associated with levels of FDG uptake. Immunofluorescent staining was performed for GLUT-1 (green) and nuclei (blue) on all panels of cells from Figure 1, which had been treated with drug for 3 days. (A) A375s, (B) resistant clone A375R1, (C) SK-Mel-30 melanomas and (D) HCT 116 colorectal cells.
Mentions: Immunofluorescent staining for GLUT-1 and GLUT-3 showed that GLUT-1 was the major transporter present across the panel of 20 in vitro cell lines. GLUT-3, a secondary glucose transporter in melanomas, displayed no observable staining, suggesting that increased levels may only be detectable in some patient biopsies and cells transfected with high levels of the protein (GLUT-3 positive staining control; Additional file 4: Figure S4) [28]. Furthermore, GLUT-1 mRNA expression levels are significantly higher than GLUT-3 in most cancers, including melanoma, and appear to be the dominant protein in the process of FDG uptake (glucose transport) and trapping (hexokinase II) [Additional file 5: Figure S5]. The relative levels of GLUT-1 on the cellular membrane directly corresponded with the observed drug-induced changes on intracellular FDG uptake that was previously shown (Figure 2).

Bottom Line: We demonstrate that vemurafenib is equally effective at reducing FDG uptake in cell lines harboring either heterozygous or homozygous BRAFV600 but ineffective in cells with acquired resistance or having WT BRAF status.However, combination with GDC-0973 results in a highly significant increase of efficacy and inhibition of FDG uptake across all twenty lines.Vemurafenib and GDC-0973 combination efficacy was associated with decreased levels of hexokinase II, c-RAF, Ksr and p-MEK protein.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biomedical Imaging, Genentech Inc, 1 DNA Way, South San Francisco, CA, 94080, USA. williams.simon@gene.com.

ABSTRACT

Background: The BRAF inhibitor, vemurafenib, has recently been approved for the treatment of metastatic melanoma in patients harboring BRAFV600 mutations. Currently, dual BRAF and MEK inhibition are ongoing in clinical trials with the goal of overcoming the acquired resistance that has unfortunately developed in some vemurafenib patients. FDG-PET measures of metabolic activity are increasingly employed as a pharmacodynamic biomarker for guiding single-agent or combination therapies by gauging initial drug response and monitoring disease progression. However, since tumors are inherently heterogeneous, investigating the effects of BRAF and MEK inhibition on FDG uptake in a panel of different melanomas could help interpret imaging outcomes.

Methods: 18 F-FDG uptake was measured in vitro in cells with wild-type and mutant (V600) BRAF, and in melanoma cells with an acquired resistance to vemurafenib. We treated the cells with vemurafenib alone or in combination with MEK inhibitor GDC-0973. PET imaging was used in mice to measure FDG uptake in A375 melanoma xenografts and in A375 R1, a vemurafenib-resistant derivative. Histological and biochemical studies of glucose transporters, the MAPK and glycolytic pathways were also undertaken.

Results: We demonstrate that vemurafenib is equally effective at reducing FDG uptake in cell lines harboring either heterozygous or homozygous BRAFV600 but ineffective in cells with acquired resistance or having WT BRAF status. However, combination with GDC-0973 results in a highly significant increase of efficacy and inhibition of FDG uptake across all twenty lines. Drug-induced changes in FDG uptake were associated with altered levels of membrane GLUT-1, and cell lines harboring RAS mutations displayed enhanced FDG uptake upon exposure to vemurafenib. Interestingly, we found that vemurafenib treatment in mice bearing drug-resistant A375 xenografts also induced increased FDG tumor uptake, accompanied by increases in Hif-1α, Sp1 and Ksr protein levels. Vemurafenib and GDC-0973 combination efficacy was associated with decreased levels of hexokinase II, c-RAF, Ksr and p-MEK protein.

Conclusions: We have demonstrated that 18 F-FDG-PET imaging reflects vemurafenib and GDC-0973 action across a wide range of metastatic melanomas. A delayed post-treatment increase in tumor FDG uptake should be considered carefully as it may well be an indication of acquired drug resistance.

Trial registration: ClinicalTrials.gov NCT01271803.

No MeSH data available.


Related in: MedlinePlus