^99mTc‐labeled NGR‐chlorambucil conjugate, ^99mTc‐HYNIC‐CLB‐c(NGR) for targeted chemotherapy and molecular imaging

Abstract

Targeted delivery of chemotherapeutic drug at the tumor site enhances the efficacy with minimum systemic exposure. Towards this, drugs conjugated with peptides having affinity towards a particular molecular target are recognized as affective agents for targeted chemotherapy. Thus, in the present study, tumor-homing asparagine-glycine-arginine (NGR) peptide ligand was conjugated to DNA alkylating nitrogen mustard, chlorambucil (CLB). The peptide-drug conjugate (PDC), CLB-c(NGR), was radiolabeled with Tc-HYNIC core to trace its pharmacokinetics and biodistribution pattern. In vitro cell-binding studies of Tc-HYNIC-CLB-c(NGR) were conducted in murine melanoma B16F10 cells. The cytotoxicity studies conducted by incubation of the peptide/drug/PDC with B16F10 cells demonstrated enhanced cytotoxic effect of PDC in comparison to either the peptide or the drug alone. In vivo biodistribution studies in C57BL6 mice bearing melanoma tumor showed maximum tumor uptake at 30 minutes pi (2.45 ± 0.28% ID/g), which reduced to 0.77 ± 0.1% ID /g at 3 hours pi. The radiotracer being hydrophilic cleared rapidly from the heart, lungs, liver, and muscle. The tumor-to-blood and tumor-to-muscle ratios improved with time. This study opens avenues for conjugation of other targeting peptides with the drug CLB for enhanced toxicity at the diseased site.

Research Progress of Radiolabeled Asn-Gly-Arg (NGR) Peptides for Imaging and Therapy

“…Chlorambucil (CLB), a DNA-alkylating nitrogen mustard, is widely used to treat chronic lymphocytic leukemia, lymphomas, breast, and ovarian carcinoma and a variety of other solid tumors. To address the systemic toxicity and various other side effects caused by its low specificity, Vats K et al 41 explored the targeted chemotherapy ability of CLB-cNGR and used 99m Tc to monitor its pharmacokinetics and biodistribution through the chelator 6-hydra-zinonicotinic acid (HYNIC). Drugs conjugated with the targeting vectors NGR peptides can act as conduits for site-specific delivery and can then overcome the nonspecific accumulation in normal tissues.…”

Molecular Imaging of Aminopeptidase N in Cancer and Angiogenesis

“…A chemotherapeutic drug, chlorambucil (CLB), was conjugated to cCNGRC and functionalized with a HYNIC chelator for radiolabeling with 99m Tc. The targeted 99m Tc-HYNIC-CLB-cCNGRC probe inhibited cancer cell growth, and its high hydrophilicity promoted rapid clearance from nontarget organs [ 57 ]. In an attempt to change the pharmokinectic profile, a PEG2 linker was added to the structure, but no change was observed [ 58 ].…”

Design, synthesis, and comparative evaluation of 99mTc(CO)3‐labeled N‐terminal and C‐terminal modified asparagine–glycine–arginine peptide constructs

“…The CD13 receptors specifically recognize asparagine–glycine–arginine (NGR) motif containing peptides . Radiometalated NGR peptide constructs are hence being explored as molecular imaging probes for detection and monitoring of CD13 receptor‐expressing malignant sites . According to a literature report, carboxyl terminal of cyclic NGR [cCNGRC] peptide is a favorable position for tagging radioisotopes/drugs rather than N‐terminal that plays more important role in receptor binding .…”

“…Radiometalation of NGR peptides has been reported with 64 Cu, 68 Ga, and 99m Tc for diagnostic purpose . However, single‐photon emission computed tomography (SPECT) radioisotope, 99m Tc has wider coverage in nuclear medicine hospitals because of lower infrastructure and financial requirement in comparison with positron emission tomography (PET) isotopes, 64 Cu and 68 Ga .…”

“…15,23 Radiometalation of NGR peptides has been reported with 64 Cu, 68 Ga, and 99m Tc for diagnostic purpose. [7][8][9][10][11][12] However, single-photon emission computed tomography (SPECT) radioisotope, 99m Tc has wider coverage in nuclear medicine hospitals because of lower infrastructure and financial requirement in comparison with positron emission tomography (PET) isotopes, 64 Cu and 68 Ga. 24,25 The nuclear (E γ = 140 keV, 89%) and physical (t ½ = 6 h) properties of 99m Tc are ideally suited for carrying out labeling and imaging procedures. The diverse redox chemistry of 99m Tc offers ample options of oxidation states and metal cores to choose for peptide labeling.…”