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Convergent synthesis and evaluation of (18)F-labeled azulenic COX2 probes for cancer imaging.

Nolting DD, Nickels M, Tantawy MN, Yu JY, Xie J, Peterson TE, Crews BC, Marnett L, Gore JC, Pham W - Front Oncol (2013)

Bottom Line: After exploring numerous synthetic routes, the final target molecule and precursor PET compounds were prepared successfully using convergent synthesis.This observation was supported after successfully using an (18)F labeling strategy that employed a much milder phosphate buffer.A biodistribution study and Western blot analysis corroborate with the imaging data.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology, Institute of Imaging Science, Vanderbilt University Nashville, TN, USA.

ABSTRACT
The overall objectives of this research are to (i) develop azulene-based positron emission tomography (PET) probes and (ii) image COX2 as a potential biomarker of breast cancer. Several lines of research have demonstrated that COX2 is overexpressed in breast cancer and that its presence correlates with poor prognoses. While other studies have reported that COX2 inhibition can be modulated and used beneficially as a chemopreventive strategy in cancer, no viable mechanism for achieving that approach has yet been developed. This shortfall could be circumvented through in vivo imaging of COX2 activity, particularly using sensitive imaging techniques such as PET. Toward that goal, our laboratory focuses on the development of novel (18)F-labled COX2 probes. We began the synthesis of the probes by transforming tropolone into a lactone, which was subjected to an [8 + 2] cycloaddition reaction to yield 2-methylazulene as the core ring of the probe. After exploring numerous synthetic routes, the final target molecule and precursor PET compounds were prepared successfully using convergent synthesis. Conventional (18)F labeling methods caused precursor decomposition, which prompted us to hypothesize that the acidic protons of the methylene moiety between the azulene and thiazole rings were readily abstracted by a strong base such as potassium carbonate. Ultimately, this caused the precursors to disintegrate. This observation was supported after successfully using an (18)F labeling strategy that employed a much milder phosphate buffer. The (18)F-labeled COX2 probe was tested in a breast cancer xenograft mouse model. The data obtained via successive whole-body PET/CT scans indicated probe accumulation and retention in the tumor. Overall, the probe was stable in vivo and no defluorination was observed. A biodistribution study and Western blot analysis corroborate with the imaging data. In conclusion, this novel COX2 PET probe was shown to be a promising agent for cancer imaging and deserves further investigation.

No MeSH data available.


Related in: MedlinePlus

Analysis of COX2 expression and quantity in murine breast cancer cells. Western blot analysis was performed to verify the presence and relative intensity of COX2 in C57GM cells compared to other cells. β-actin served as a loading control (left). RT-PCR data were used to quantify the level of COX2 expression after normalization.
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Figure 3: Analysis of COX2 expression and quantity in murine breast cancer cells. Western blot analysis was performed to verify the presence and relative intensity of COX2 in C57GM cells compared to other cells. β-actin served as a loading control (left). RT-PCR data were used to quantify the level of COX2 expression after normalization.

Mentions: To confirm and quantify COX2 expression in the C57MG cell line, we selected two other cells, 4T1 and 67NR, which are also murine breast cancer cell lines. It has been demonstrated previously that the 4T1 (Harmey et al., 2002) and 67NR cells (Nagler et al., 2011) were positive and negative, respectively, for COX2. As shown in Figure 3, Western blot analysis on cell lysate indicated a very low level of COX2 in 67NR cells. In contrast, C57MG possesses a high constitutive level of COX2. Furthermore, real-time PCR data demonstrated that COX2 was expressed at a rate approximately 31-fold higher in C57MG cells compared to 67NR.


Convergent synthesis and evaluation of (18)F-labeled azulenic COX2 probes for cancer imaging.

Nolting DD, Nickels M, Tantawy MN, Yu JY, Xie J, Peterson TE, Crews BC, Marnett L, Gore JC, Pham W - Front Oncol (2013)

Analysis of COX2 expression and quantity in murine breast cancer cells. Western blot analysis was performed to verify the presence and relative intensity of COX2 in C57GM cells compared to other cells. β-actin served as a loading control (left). RT-PCR data were used to quantify the level of COX2 expression after normalization.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3539664&req=5

Figure 3: Analysis of COX2 expression and quantity in murine breast cancer cells. Western blot analysis was performed to verify the presence and relative intensity of COX2 in C57GM cells compared to other cells. β-actin served as a loading control (left). RT-PCR data were used to quantify the level of COX2 expression after normalization.
Mentions: To confirm and quantify COX2 expression in the C57MG cell line, we selected two other cells, 4T1 and 67NR, which are also murine breast cancer cell lines. It has been demonstrated previously that the 4T1 (Harmey et al., 2002) and 67NR cells (Nagler et al., 2011) were positive and negative, respectively, for COX2. As shown in Figure 3, Western blot analysis on cell lysate indicated a very low level of COX2 in 67NR cells. In contrast, C57MG possesses a high constitutive level of COX2. Furthermore, real-time PCR data demonstrated that COX2 was expressed at a rate approximately 31-fold higher in C57MG cells compared to 67NR.

Bottom Line: After exploring numerous synthetic routes, the final target molecule and precursor PET compounds were prepared successfully using convergent synthesis.This observation was supported after successfully using an (18)F labeling strategy that employed a much milder phosphate buffer.A biodistribution study and Western blot analysis corroborate with the imaging data.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology, Institute of Imaging Science, Vanderbilt University Nashville, TN, USA.

ABSTRACT
The overall objectives of this research are to (i) develop azulene-based positron emission tomography (PET) probes and (ii) image COX2 as a potential biomarker of breast cancer. Several lines of research have demonstrated that COX2 is overexpressed in breast cancer and that its presence correlates with poor prognoses. While other studies have reported that COX2 inhibition can be modulated and used beneficially as a chemopreventive strategy in cancer, no viable mechanism for achieving that approach has yet been developed. This shortfall could be circumvented through in vivo imaging of COX2 activity, particularly using sensitive imaging techniques such as PET. Toward that goal, our laboratory focuses on the development of novel (18)F-labled COX2 probes. We began the synthesis of the probes by transforming tropolone into a lactone, which was subjected to an [8 + 2] cycloaddition reaction to yield 2-methylazulene as the core ring of the probe. After exploring numerous synthetic routes, the final target molecule and precursor PET compounds were prepared successfully using convergent synthesis. Conventional (18)F labeling methods caused precursor decomposition, which prompted us to hypothesize that the acidic protons of the methylene moiety between the azulene and thiazole rings were readily abstracted by a strong base such as potassium carbonate. Ultimately, this caused the precursors to disintegrate. This observation was supported after successfully using an (18)F labeling strategy that employed a much milder phosphate buffer. The (18)F-labeled COX2 probe was tested in a breast cancer xenograft mouse model. The data obtained via successive whole-body PET/CT scans indicated probe accumulation and retention in the tumor. Overall, the probe was stable in vivo and no defluorination was observed. A biodistribution study and Western blot analysis corroborate with the imaging data. In conclusion, this novel COX2 PET probe was shown to be a promising agent for cancer imaging and deserves further investigation.

No MeSH data available.


Related in: MedlinePlus