Browsing by Subject "MDM2"

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Open Access
Fluorine-18 Labeling of the MDM2 Inhibitor RG7388 for PET Imaging: Chemistry and Preliminary Evaluation.
(Molecular pharmaceutics, 2021-09-15) Zhou, Zhengyuan; Zalutsky, Michael R; Chitneni, Satish K
RG7388 (Idasanutlin) is a potent inhibitor of oncoprotein murine double minute 2 (MDM2). Herein we investigated the feasibility of developing ¹⁸F-labeled RG7388 as a radiotracer for imaging MDM2 expression in tumors with positron emission tomography (PET). Two fluorinated analogues of RG7388, 6 and 7, were synthesized by attaching a fluoronicotinyl moiety to RG7388 via a polyethylene glycol (PEG₃) or a propyl linker. The inhibitory potency (IC₅₀) of 6 and 7 against MDM2 was determined by a fluorescence polarization (FP)-based assay. Next, compound 6 was labeled with ¹⁸F using a trimethylammonium triflate precursor to obtain [¹⁸F]FN-PEG₃-RG7388 ([¹⁸F]6), and its properties were evaluated in MDM2 expressing wild-type p53 tumor cell lines (SJSA-1 and HepG2) in vitro and in tumor xenografts in vivo. The FP assays revealed an IC₅₀ against MDM2 of 119 nM and 160 nM for 6 and 7, respectively. ¹⁸F-labeling of 6 was achieved in 50.3 ± 7.5% radiochemical yield. [¹⁸F]6 exhibited a high uptake (∼70% of input dose) and specificity in SJSA-1 and HepG2 cell lines. Saturation binding assays revealed a binding affinity (K_d) of 128 nM for [¹⁸F]6 on SJSA-1 cells. In mice, [¹⁸F]6 showed fast clearance from blood with a maximum tumor uptake of 3.80 ± 0.85% injected dose per gram (ID/g) in HepG2 xenografts at 30 min postinjection (p.i.) and 1.32 ± 0.32% ID/g in SJSA-1 xenografts at 1 h p.i. Specificity of [¹⁸F]6 uptake in tumors was demonstrated by pretreatment of mice with SJSA-xenografts with a blocking dose of RG7388 (35 mg/kg body weight, i.p.). In vivo stability studies in mice using HPLC showed ∼60% and ∼30% intact [¹⁸F]6 remaining in plasma at 30 min and 1 h p.i., respectively, with the remaining activity attributed to polar peaks. Our results suggest that RG7388 is a promising molecular scaffold for ¹⁸F-labeled probe development for MDM2. Additional labeling strategies and functionalizing locations on RG7388 are under development to improve binding affinity and in vivo stability of the ¹⁸F-labeled compound to make it more amenable for PET imaging of MDM2 in vivo.
Open Access
Stapled peptides as scaffolds for developing radiotracers for intracellular targets: Preliminary evaluation of a radioiodinated MDM2-binding stapled peptide in the SJSA-1 osteosarcoma model.
(Bioorganic & medicinal chemistry letters, 2022-04-15) Zhou, Zhengyuan; Zalutsky, Michael R; Chitneni, Satish K
Stapled peptides are promising scaffolds for inhibiting protein-protein interactions in cells, including between the intracellular oncoprotein MDM2 and p53. Herein, we have investigated the potential utility of a stapled peptide, VIP116, for developing radiolabeled agents targeting MDM2. VIP116 was radioiodinated using the prosthetic agent N-succinimidyl-3-[*I]iodobenzoate ([*I]SIB). The resulting labeled peptide [*I]SIB-VIP116 exhibited high uptake (165.3 ± 27.7%/mg protein) and specificity in SJSA-1 tumor cells. Tissue distribution studies of [*I]SIB-VIP116 revealed a peak tumor uptake of 2.19 ± 0.56 percent injected dose per gram (%ID/g) in SJSA-1 xenografts at 2 h post-injection, which was stable until 6 h. [*I]SIB-VIP116 exhibited high activity (8.33 ± 1.18%ID/g) in the blood pool but had high tumor-to-muscle ratios (12.0 ± 5.7), at 30 min. Metabolic stability studies in mice indicated that about 80% of the activity in plasma was intact [*I]SIB-VIP116 at 4 h. Our results confirm the cell permeability and specific binding of [*I]SIB-VIP116 to MDM2 and the suitability of the VIP116 scaffold for radiolabeled probe development.
Open Access
The Intersection of DNA Damage Response and Ferroptosis-A Rationale for Combination Therapeutics.
(Biology, 2020-07-23) Chen, Po-Han; Tseng, Watson Hua-Sheng; Chi, Jen-Tsan
Ferroptosis is a novel form of iron-dependent cell death characterized by lipid peroxidation. While the importance and disease relevance of ferroptosis are gaining recognition, much remains unknown about its interaction with other biological processes and pathways. Recently, several studies have identified intricate and complicated interplay between ferroptosis, ionizing radiation (IR), ATM (ataxia-telangiectasia mutated)/ATR (ATM and Rad3-related), and tumor suppressor p53, which signifies the participation of the DNA damage response (DDR) in iron-related cell death. DDR is an evolutionarily conserved response triggered by various DNA insults to attenuate proliferation, enable DNA repairs, and dispose of cells with damaged DNA to maintain genome integrity. Deficiency in proper DDR in many genetic disorders or tumors also highlights the importance of this pathway. In this review, we will focus on the biological crosstalk between DDR and ferroptosis, which is mediated mostly via noncanonical mechanisms. For clinical applications, we also discuss the potential of combining ionizing radiation and ferroptosis-inducers for synergistic effects. At last, various ATM/ATR inhibitors under clinical development may protect ferroptosis and treat many ferroptosis-related diseases to prevent cell death, delay disease progression, and improve clinical outcomes.