CYCLO (ARG-GLY-ASP-D-PHE-LYS) is a cyclic pentapeptide whose core is the RGD sequence (Arg Gly Asp), which is the natural ligand recognition site for integrin receptors. The circular structure makes its conformation more rigid, significantly enhancing its affinity and selectivity for integrin receptors, while improving its stability in vivo. Its ability to resist protease degradation is superior to that of linear RGD peptides. Research has shown that Cyclo (RGDFK) TFA is a potent and selective inhibitor of integrin α v β 3, with an IC50 value of 0.94 nM. It can specifically bind to receptors such as integrin α v β 3 and α v β 5 on the cell surface through the RGD sequence, blocking the interaction between integrin and its natural ligands (such as fibronectin and fibronectin), thereby inhibiting tumor angiogenesis, tumor cell proliferation, migration, and invasion. Integrin α v β 3 is highly expressed in various tumor cells and neovascular endothelial cells, while its expression level is lower in normal tissues, providing a theoretical basis for targeted therapy.
What is the research progress of CYCLO (-RGDFK) in tumor targeted therapy?
CYCLO (RGDFK), as a cyclic pentapeptide, has shown great potential in the field of tumor targeted therapy due to its unique RGD sequence and cyclic structure. In recent years, this molecule has made significant progress in basic research, preclinical evaluation, and early clinical exploration.
1.Molecular characteristics and mechanism of action
The biggest feature of CYCLO (RGDFK) is that its core RGD sequence can specifically recognize integrin αvβ3, αvβ5 and other receptors. These receptors are highly expressed in many tumor cells and neovascular endothelial cells, but the expression level is low in normal tissues. The cyclic structure makes RGD sequence show a specific angle in space, which significantly enhances the affinity for integrin receptor, and at the same time improves the stability in vivo, and its anti-protease degradation ability is better than that of linear RGD peptide.
2.Breakthrough in preclinical research
In preclinical studies, CYCLO (RGDFK) has demonstrated excellent targeting and therapeutic efficacy. The ⁶⁸ Ga DOTA cyclo (RGDfK) PET imaging probe showed a tumor site radioactive uptake of 12.8-18.5% ID/g and a tumor/muscle ratio of 12.5-28.6 in a tumor bearing animal model 1 hour after Add. ¹⁷⁷ Lu-DOTA-cyclo(RGDfK) In breast cancer model, a single dose of 111 MBq can achieve a tumor growth inhibition rate of 78%, and there is no significant weight loss or. In a melanoma mouse model, after 2 weeks of treatment, the tumor volume decreased by 70% without significant inhibition of bone marrow hematopoietic function.
3.Early clinical exploration
At present, radiopharmaceutical conjugates (RDCs) based on CYCLO (RGDFK) have entered the early clinical trial stage. As a PET imaging probe, ⁶⁸ Ga DOTA cyclo (RGDfK) was successfully used to locate tumor lesions in advanced solid tumor patients, with good patient tolerance and no serious adverse reactions. The Phase I clinical trial of ¹⁷⁷ Lu DOTA cyclo (RGDfK) for the treatment of advanced integrin positive tumors is currently underway, and its safety has been preliminarily validated. These studies have laid an important foundation for the clinical application of CYCLO (RGDFK).
What are the permeability and distribution characteristics of CYCLO (RGDFK) in the tumor microenvironment?
CYCLO (RGDFK) exhibits good permeability and targeted distribution characteristics in the tumor microenvironment, mainly through the active targeting mechanism mediated by integrin α v β 3 to achieve tumor tissue enrichment.
1. Permeability and distribution characteristics
Tumor tissue enrichment ability: CYCLO (RGDFK) exhibits significant tumor targeting in tumor bearing animal models. After 1 hour of use, the radioactive uptake of ⁶⁸ Ga DOTA cyclo (RGDfK) at the tumor site can reach 12.8-18.5% ID/g, and the tumor/muscle ratio (T/M) can reach 12.5-28.6, significantly higher than that of normal tissue. The half-life of the ¹⁷⁷ Lu-DOTA-cyclo(RGDfK) in tumor tissue is extended to 12.5 hours, which is beneficial for the accumulation of radiation dose.
Organizational distribution characteristics: The uptake of drugs in the liver, spleen, and intestine is comparable to that of tumors, but the renal uptake is relatively low (about 2.1-2.3% ID/g), indicating its high targeting and low renal toxicity. In the U87MG glioma model, the radioactive uptake at the tumor site is 5.6 times that of α v β 3-negative tumors.
Pharmacokinetic characteristics: The blood clearance half-life of ⁶⁸ Ga DOTA cycl0 (RGDfK) is approximately 1.2-1.8 hours, mainly excreted through the kidneys. In U87MG glioma and MDA-MB-435 breast cancer xenotransplantation models, tumor size was linearly related to tumor uptake of radioactive tracer.
2. The impact of structural optimization on permeability
PEGylation modification: Introducing polyethylene glycol (PEG) groups can significantly improve pharmacokinetic properties. The blood clearance half-life of PEG modified ¹⁷⁷ Lu DOTA cyclo (RGDfK) was extended from 1.2 hours to 3.5 hours, and the tumor uptake rate was increased by about 40%, while the normal liver tissue uptake rate was reduced by 30%.
Dimerization strategy: Two DOTA cyclo (RGDfK) molecules are coupled through a connecting arm to form a dimer. The affinity for the α v β 3 receptor (IC ₅₀=0.8 nM) is significantly higher than that of the monomer (IC ₅₀=5.2 nM). The tumor uptake reaches 18.5% ID/g, which is 1.4 times that of the monomer, and the blood clearance rate is slower (half-life 1.8 hours vs 0.9 hours).
PEG4 adapter optimization: The two PEG4 adapters between the RGD motif in HYNIC-2PEG4 Dimer (IC ₅₀=2.8 ± 0.5 nM) and HYNIC-3PEG4 Dimer (IC ₅₀=2.4 ± 0.7 nM) significantly improved the binding affinity for integrin α v β 3, with stronger affinity compared to HYNIC-PEG4 dimer (IC ₅₀=7.5 ± 2.3 nM).
3.Clinical application prospect
The radiopharmaceutical conjugate (RDC) based on CYCLO (RGDFK) has entered the early clinical trial. As a PET imaging probe, GA-DOTA-Cyclo (RGDFK) successfully located the tumor focus in patients with advanced solid tumors, and the patients were well tolerated. Phase I clinical trial of Lu-dota-Cyclo (RGDFK) in the treatment of advanced integrin-positive tumors is under way, and its safety has been preliminarily verified.
These results show that CYCLO (RGDFK) has good permeability and distribution characteristics in tumor microenvironment through the active targeting mechanism mediated by integrin αvβ3, which provides an important tool molecule for tumor targeted therapy and molecular imaging.
What are the limitations of pharmacokinetic studies of CYCLO (RGDFK) in tumor targeted therapy?
Cyclo(-Arg-Gly-Asp-D-Phe-Lys), a high-affinity and highly selective integrin αvβ3 inhibitor, shows great potential in fields such as tumor-targeted therapy, molecular imaging, and tissue engineering. Its cyclic structure provides excellent stability and targeting capabilities, and the lysine side chain facilitates functional modification. However, challenges remain in pharmacokinetics and targeting selectivity.
1. Insufficient in vivo metabolic stability
c(RGDfK) is easily degraded by peptidases in vivo, resulting in a short half-life (approximately 0.5-1 hour), which limits its sustained action time in the body. Although the cyclic structure improves stability compared to linear RGD peptides, it still faces the challenge of protease degradation. In preclinical studies, pharmacokinetic analysis of ¹³¹I-c(RGD)₂ showed a distribution phase half-life (t1/2α) of 15.364 minutes and an elimination phase half-life (t1/2β) of 123.125 minutes, indicating rapid drug clearance in the body.
2. Targeting selectivity needs improvement
Some normal tissues (such as activated vascular endothelial cells) also express low levels of αvβ3 integrin, which may lead to off-target effects. Although CYCLO (RGDFK) has high affinity for integrin αvβ3 (IC50 approximately 0.94 nM), it still exhibits cross-reactivity with other subtypes such as integrin αIIbβ3, which may cause side effects such as platelet aggregation.
3. Individual variability in pharmacokinetic parameters
In animal models, the pharmacokinetics of CYCLO (RGDFK) exhibit non-linear, target-mediated clearance characteristics, with significant differences in parameters such as clearance rate and distribution volume among different individuals. For example, in a 70 kg subject, key PK parameters include a clearance rate of 7.28 mL/h, central and peripheral compartment Vd of 3.01 liters and 1.18 liters respectively, and a terminal half-life of 19.3 days. These parameters are affected by factors such as body weight and liver and kidney function.
4. Limitations of Tissue Distribution Characteristics
Although CYCLO (RGDFK) exhibits high uptake in tumor sites (up to 12.8-18.5% ID/g), its uptake in the liver, spleen, and intestines is comparable to that in tumors, while kidney uptake is lower (approximately 2.1-2.3% ID/g). This tissue distribution characteristic may lead to drug accumulation in non-target tissues, increasing the risk of potential toxicity.
5. Challenges in Clinical Translation
Currently, most research on CYCLO (RGDFK) is in the preclinical stage, lacking large-scale clinical trial data to verify its pharmacokinetic characteristics in humans. Furthermore, key issues such as drug permeability in the tumor microenvironment, binding kinetics with target sites, and interactions with other therapeutic drugs still require further in-depth research.
Where is its future development headed?
To address the above limitations, researchers are optimizing its pharmacokinetic properties through strategies such as chemical modification to enhance peptide stability, constructing nanocarriers to protect peptides from degradation, and developing "smart responsive" RGD cyclic peptides. They are also developing "dual-target" products that simultaneously target integrin αvβ3 and other tumor markers to improve targeting efficiency in tumors with low expression levels.
Multi-target strategy: Developing bispecific or multispecific molecules that simultaneously target integrin αvβ3 and other tumor markers (such as EGFR, HER2) to improve targeting efficiency and therapeutic effect.
Smart responsive drugs: Constructing "smart responsive" RGD cyclic peptides that release drugs under the tumor microenvironment (e.g., low pH, high enzyme activity) to reduce toxic side effects on normal tissues.
Combination therapy: Exploring the combined application of CYCLO (RGDFK) with traditional treatments such as immunotherapy, chemotherapy, and radiotherapy to achieve synergistic effects.
Personalized treatment: Based on the detection of integrin expression levels, screening patient groups suitable for CYCLO (RGDFK) targeted therapy to achieve precision medicine.
Why choose our CYCLO (RGDFK)?
Choosing c(RGDfK) from Xi'an faithful BioTech Co.,Ltd is not only because of its purity of ≥ 98.5%, but also because it meets international pharmacopoeial standards such as CP, USP, and EP. Moreover, we currently adopt the most advanced production technology, which not only meets the regulatory requirements of major global markets, but also reduces production costs. Can meet your different types of development and experimentation needs.
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