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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

FDG-PET imaging. FDG-PET imaging is effective for monitoring vemurafenib and GDC-0973 combination drug action in BRAFV600E mutant and resistant xenografts. (A) A375- and (B) A375 R1-resistant KRAS mutant melanomas were implanted in athymic nude mice and were administered vehicle, vemurafenib (50 mg/kg BID) or vemurafenib (50 mg/kg BID) and GDC-0973 (7.5 mg/kg QD). Dynamic FDG-PET imaging was performed at baseline, day 3 and day 6 after treatment. A reduction in Ki and MRGlucMAX was induced on day 6 of imaging by both vemurafenib and 0973 combination treatment (Student's t test showing standard error of the mean A375: MRGlucMax − vemuraf; *p = 0.02, combination; **p = 0.01, Ki − vemuraf; *p = 0.02, combination; **p = 0.001, tumor volume; ***p = 0.001. A375R1: MRGlucMax − vemuraf; *p = 0.04, tumor volume; ***p = 0.001). White arrow points at the tumor.
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Figure 3: FDG-PET imaging. FDG-PET imaging is effective for monitoring vemurafenib and GDC-0973 combination drug action in BRAFV600E mutant and resistant xenografts. (A) A375- and (B) A375 R1-resistant KRAS mutant melanomas were implanted in athymic nude mice and were administered vehicle, vemurafenib (50 mg/kg BID) or vemurafenib (50 mg/kg BID) and GDC-0973 (7.5 mg/kg QD). Dynamic FDG-PET imaging was performed at baseline, day 3 and day 6 after treatment. A reduction in Ki and MRGlucMAX was induced on day 6 of imaging by both vemurafenib and 0973 combination treatment (Student's t test showing standard error of the mean A375: MRGlucMax − vemuraf; *p = 0.02, combination; **p = 0.01, Ki − vemuraf; *p = 0.02, combination; **p = 0.001, tumor volume; ***p = 0.001. A375R1: MRGlucMax − vemuraf; *p = 0.04, tumor volume; ***p = 0.001). White arrow points at the tumor.

Mentions: Vemurafenib treatment induced significant reductions in the dynamic FDG uptake parameters Ki and MRGLUCMAX in A375 xenografts over the course of 6 days (Figure 3). Similar to earlier in vitro results, the addition of GDC-0973 also significantly improved FDG response. Both treatments also lead to reductions in tumor volumes and did not result in any significant changes in body weight. Vemurafenib treatment of the resistant A375R1 tumors resulted in a significant increase in dynamic FDG uptake over the period of drug treatment, indicating the effect as a sign of vemurafenib drug resistance. An increase in FDG uptake was also observed with 6 days of vemurafenib treatment in vitro [Additional file 6: Figure S6A] [10]. The addition of GDC-0973 overcame drug resistance as demonstrated by reductions in Ki, MRGLUCMAX and tumor volume. Histological analysis of the tumor xenografts demonstrated parallels between GLUT-1 membrane intensity and FDG uptake, and also confirmed the significant efficacy enhancement with the addition of GDC-0973 (Figure 4). Increases in GLUT-1 levels in vemurafenib-treated A375R1s were apparent using a more sensitive immunofluorescent histological approach [Additional file 6: Figure S6B].


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)

FDG-PET imaging. FDG-PET imaging is effective for monitoring vemurafenib and GDC-0973 combination drug action in BRAFV600E mutant and resistant xenografts. (A) A375- and (B) A375 R1-resistant KRAS mutant melanomas were implanted in athymic nude mice and were administered vehicle, vemurafenib (50 mg/kg BID) or vemurafenib (50 mg/kg BID) and GDC-0973 (7.5 mg/kg QD). Dynamic FDG-PET imaging was performed at baseline, day 3 and day 6 after treatment. A reduction in Ki and MRGlucMAX was induced on day 6 of imaging by both vemurafenib and 0973 combination treatment (Student's t test showing standard error of the mean A375: MRGlucMax − vemuraf; *p = 0.02, combination; **p = 0.01, Ki − vemuraf; *p = 0.02, combination; **p = 0.001, tumor volume; ***p = 0.001. A375R1: MRGlucMax − vemuraf; *p = 0.04, tumor volume; ***p = 0.001). White arrow points at the tumor.
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Figure 3: FDG-PET imaging. FDG-PET imaging is effective for monitoring vemurafenib and GDC-0973 combination drug action in BRAFV600E mutant and resistant xenografts. (A) A375- and (B) A375 R1-resistant KRAS mutant melanomas were implanted in athymic nude mice and were administered vehicle, vemurafenib (50 mg/kg BID) or vemurafenib (50 mg/kg BID) and GDC-0973 (7.5 mg/kg QD). Dynamic FDG-PET imaging was performed at baseline, day 3 and day 6 after treatment. A reduction in Ki and MRGlucMAX was induced on day 6 of imaging by both vemurafenib and 0973 combination treatment (Student's t test showing standard error of the mean A375: MRGlucMax − vemuraf; *p = 0.02, combination; **p = 0.01, Ki − vemuraf; *p = 0.02, combination; **p = 0.001, tumor volume; ***p = 0.001. A375R1: MRGlucMax − vemuraf; *p = 0.04, tumor volume; ***p = 0.001). White arrow points at the tumor.
Mentions: Vemurafenib treatment induced significant reductions in the dynamic FDG uptake parameters Ki and MRGLUCMAX in A375 xenografts over the course of 6 days (Figure 3). Similar to earlier in vitro results, the addition of GDC-0973 also significantly improved FDG response. Both treatments also lead to reductions in tumor volumes and did not result in any significant changes in body weight. Vemurafenib treatment of the resistant A375R1 tumors resulted in a significant increase in dynamic FDG uptake over the period of drug treatment, indicating the effect as a sign of vemurafenib drug resistance. An increase in FDG uptake was also observed with 6 days of vemurafenib treatment in vitro [Additional file 6: Figure S6A] [10]. The addition of GDC-0973 overcame drug resistance as demonstrated by reductions in Ki, MRGLUCMAX and tumor volume. Histological analysis of the tumor xenografts demonstrated parallels between GLUT-1 membrane intensity and FDG uptake, and also confirmed the significant efficacy enhancement with the addition of GDC-0973 (Figure 4). Increases in GLUT-1 levels in vemurafenib-treated A375R1s were apparent using a more sensitive immunofluorescent histological approach [Additional file 6: Figure S6B].

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