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A peptide-based positron emission tomography probe for in vivo detection of caspase activity in apoptotic cells.

ABSTRACT: Apoptosis, or programmed cell death, can be leveraged as a surrogate measure of response to therapeutic interventions in medicine. Cysteine aspartic acid-specific proteases, or caspases, are essential determinants of apoptosis signaling cascades and represent promising targets for molecular imaging. Here, we report development and in vivo validation of [(18)F]4-fluorobenzylcarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone ([(18)F]FB-VAD-FMK), a novel peptide-based molecular probe suitable for quantification of caspase activity in vivo using positron emission tomography (PET).Supported by molecular modeling studies and subsequent in vitro assays suggesting probe feasibility, the labeled pan-caspase inhibitory peptide, [(18)F]FB-VAD-FMK, was produced in high radiochemical yield and purity using a simple two-step, radiofluorination. The biodistribution of [(18)F]FB-VAD-FMK in normal tissue and its efficacy to predict response to molecularly targeted therapy in tumors was evaluated using microPET imaging of mouse models of human colorectal cancer.Accumulation of [(18)F]FB-VAD-FMK was found to agree with elevated caspase-3 activity in response to Aurora B kinase inhibition as well as a multidrug regimen that combined an inhibitor of mutant BRAF and a dual PI3K/mTOR inhibitor in (V600E)BRAF colon cancer. In the latter setting, [(18)F]FB-VAD-FMK PET was also elevated in the tumors of cohorts that exhibited reduction in size.These studies illuminate [(18)F]FB-VAD-FMK as a promising PET imaging probe to detect apoptosis in tumors and as a novel, potentially translatable biomarker for predicting response to personalized medicine.

SUBMITTER: Hight MR

PROVIDER: S-EPMC3989451 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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A peptide-based positron emission tomography probe for in vivo detection of caspase activity in apoptotic cells.

Hight Matthew R MR Cheung Yiu-Yin YY Nickels Michael L ML Dawson Eric S ES Zhao Ping P Saleh Samir S Buck Jason R JR Tang Dewei D Washington M Kay MK Coffey Robert J RJ Manning H Charles HC

Clinical cancer research : an official journal of the American Association for Cancer Research 20140226 8

<h4>Purpose</h4>Apoptosis, or programmed cell death, can be leveraged as a surrogate measure of response to therapeutic interventions in medicine. Cysteine aspartic acid-specific proteases, or caspases, are essential determinants of apoptosis signaling cascades and represent promising targets for molecular imaging. Here, we report development and in vivo validation of [(18)F]4-fluorobenzylcarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone ([(18)F]FB-VAD-FMK), a novel peptide-based molecular probe suit ...[more]

PMID: 24573549

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Project description:Purpose: Positron emission tomography (PET) imaging of apoptosis is very important for early evaluation of tumor therapeutic efficacy. A stimuli-responsive probe based on the peptide sequence Asp-Glu-Val-Asp (DEVD), [18F]DEVD-Cys(StBu)-PPG(CBT)-AmBF3 ([18F]1), for PET imaging of tumor apoptosis was designed and prepared. This study aimed to develop a novel smart probe using a convenient radiosynthesis method and to fully examine the sensitivity and specificity of the probe response to the tumor treatment. Methods: The radiolabelling precursor DEVD-Cys(StBu)-PPG(CBT)-AmBF3 (1) was synthesized through multistep reactions. The reduction together with caspase-controlled macrocyclization and self-assembly of 1 was characterized and validated in vitro. After [18F]fluorination in the buffer (pH= 2.5), the radiolabelling yield (RLY), radiochemical purity (RCP) and stability of the probe [18F]1 in PBS and mouse serum were investigated by radio-HPLC. The sensitivity and specificity of [18F]1 for detecting the drug-induced apoptosis was fully evaluated in vitro and in vivo. The effect of cold precursor 1 on the cell uptake and tumor imaging of [18F]1 was also assessed. The level of activated caspase-3 in Hela cells and tumors with or without apoptosis induction was analyzed and compared by western blotting and histological staining. Results: The whole radiosynthesis process of [18F]1 was around 25 min with RLY of 50%, RCP of over 99% and specific activity of 1.45 ± 0.4 Ci/µmol. The probe was very stable in both PBS and mouse serum within 4 h. It can be activated by caspase-3 and then undergo an intermolecular cyclization to form nanosized particles. The retained [18F]1 in DOX-treated HeLa cells was 2.2 folds of that in untreated cells. Within 1 h microPET imaging of the untreated Hela-bearing mice, the injection of [18F]1 resulted in the increase of the uptake ratio of tumor to muscle (T/M) only from 1.74 to 2.18, while in the DOX-treated Hela-bearing mice T/M increased from 1.88 to 10.52 and the co-injection of [18F]1 and 1 even led to the increase of T/M from 3.08 to 14.81. Conclusions: A caspase-responsive smart PET probe [18F]1 was designed and prepared in a kit-like manner. Co-injection of [18F]1 and 1 generated remarkably enhanced tumor uptake and signal-to-noise ratio in the tumor-bearing mice with drug-induced apoptosis, which correlated well with the expression level of activated caspase-3. This early readout of treatment response ensured that the probe [18F]1 could serve as a promising PET imaging probe for timely and noninvasive evaluation of tumor therapy.

Project description:Fluorine-18-fluoro-2-deoxy-D-glucose (FDG) is widely used as positron-emission-tomography (PET) radiotracer for the detection and staging of human cancer. Tumor uptake of FDG varies substantially between different cancer types and between patients with the same tumor type. The molecular basis for this heterogeneity is unknown. Using cancer cell lines and primary human tumors of distinct histologic origins, we here show that increased FDG uptake is universally associated with coordinate upregulation of genes within the glycolysis, pentose-phosphate, and other related metabolic pathways. In primary human breast cancers, this FDG signature shows significant overlap with established breast cancer signatures for the “basal-like” disease subtype and “poor prognosis”. FDG high breast cancer showed significantly more gene copy number alterations genome wide than FDG low cancers. About 50 % of primary breast cancers with high FDG uptake and FDG gene expression signature show DNA copy gain encompassing the c-myc gene locus and express gene sets regulated by the transcription factor MYC. Our data shows that FDG-PET marks a distinct subset of “basal-like” human breast cancer which is characterized by MYC and prognostically unfavorable gene expression signatures, suggesting that FDG-PET imaging may be useful to risk-stratify patients with locally advanced breast cancer. Our general strategy to identify molecular determinants of FDG-retention through a genome-wide approach consisted of FDG uptake measurements in cancer cell lines and primary human tumors, the selection of samples with particularly high versus low FDG-retention, and subsequent pathway-based analysis of RNA expression data collected from these samples. Cell line RNA was extracted from a 10 cm plate seeded simultaneously and at the same density as the wells for FDG-uptake assays. For primary human tumor samples, RNA was extracted from macrodissected frozen tumor tissue. All cell line RNA samples and the astrocytoma RNA aliquots were hybridized to Affymetrix U133 Plus 2.0 arrays. All primary breast cancer RNA samples were hybridized to Affymetrix U133A arrays.

Dataset Information

A peptide-based positron emission tomography probe for in vivo detection of caspase activity in apoptotic cells.

Publications

A peptide-based positron emission tomography probe for in vivo detection of caspase activity in apoptotic cells.

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