68 Ga labeled Erlotinib: A novel PET probe for imaging EGFR over-expressing tumors

Design, synthesis and biological evaluation of small molecule fluorescent probes targeting EGFR for tumor detection and treatment

The epidermal growth factor receptor (EGFR) is a tyrosine kinase receptor that plays a crucial role in cell differentiation and tumor progression, and its overexpression is closely associated with the development and metastasis of multiple cancers. The development of a fluorescent probe capable of targeting EGFR while simultaneously integrating diagnostic and therapeutic functions could have a profound impact on the treatment of related cancers. In this study, we developed a series of EGFR-targeting probes that consisted of an environment-sensitive 1,8-naphthalimide fluorophore, a linker unit and a targeting unit (gefitinib), using a coupling strategy. The synthesized probes were first evaluated for their spectroscopic properties and cytotoxicities against different cell lines, which were selected based on their intrinsic EGFR expression levels. Remarkably, among the probes tested, GP1 showed outstanding environmental sensitivity and exhibited a specific response to tumor cells that overexpress EGFR. Furthermore, the representative probe GP1 was evaluated for its EGFR-specific targeting ability in live-cell fluorescence imaging and in vivo xenograft imaging, as well as its in vivo anti-tumor activity. The results showed that the probe GP1 had excellent EGFR-specific targeting ability, exhibited competitive replacement behavior towards the EGFR inhibitor gefitinib, and demonstrated potent anti-tumor effects in a CT-26 tumor-bearing mouse model. Overall, as a turn-on EGFR targeting fluorescent ligand, GP1 holds immense promise as a valuable tool for tumor detection and treatment.

Evaluation of Rhenium and Technetium-99m Complexes Bearing Quinazoline Derivatives as Potential EGFR Agents

Τhe Epidermal Growth Factor Receptor tyrosine kinase inhibitor (EGFR-TKI) 6-amino-4-[(3-bromophenyl) amino]quinazoline was derivatized with 6-bromohexanoyl-chloride and coupled with the tridentate chelating agents N-(2-pyridylmethyl) aminoethyl acetic acid (PAMA) and L(+)-cysteine bearing the donor atom set NNO and SNO, respectively. The rhenium precursors ReBr(CO)₅ and fac-[NEt₄]₂[ReBr₃(CO)₃] were used for the preparation of the Re complexes fac-[Re(NNO)(CO)₃] (5a) and fac-[Re(SNO)(CO)₃] (7a) which were characterized by NMR and IR spectroscopies. Subsequently, the new potential EGFR inhibitors were labeled with the fac-[^99mTc(CO)₃]⁺ core in high yield and radiochemical purity (>90%) by ligand exchange reaction using the fac-[^99mTc][Tc(OH₂)₃(CO)₃]⁺ precursor. The radiolabeled complexes were characterized by comparative HPLC analysis with the analogous rhenium (Re) complexes as references. In vitro studies in the A431 cell lines showed that both ligands and Re complexes inhibit A431 cell growth. Complex 5a demonstrated the highest potency (IC₅₀ = 8.85 ± 2.62 μM) and was further assessed for its capacity to inhibit EGFR autophosphorylation, presenting an IC₅₀ value of 26.11 nM. Biodistribution studies of the ^99mTc complexes in healthy mice showed high in vivo stability for both complexes and fast blood and soft tissue clearance with excretion occurring via the hepatobiliary system.

Pyrazole derivatives as potent EGFR inhibitors: synthesis, biological evaluation and in silico and biodistribution study

Aim: Synthesis of pyrazole derivatives as EGFR inhibitors. Materials & methods: Cytotoxicity and EGFR inhibitory effect were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and EGFR kits, respectively. The biodistribution of radioiodinated compound nanoparticles in tumor-bearing mice was studied. Results: The IC₅₀ values of compound 4a against HepG2 cells and EGFR were 0.15 ± 0.03 and 0.31 ± 0.008 μM, respectively, while those of erlotinib were 0.73 ± 0.04 and 0.11 ± 0.008 μM, respectively. The binding scores of compound 4a and erlotinib to EGFR were -9.52 and -10.23 Kcal/mol, respectively. The maximum tumor uptake of radioiodinated compound after intravenous nanoparticle injection was 6.7 ± 0.3% radioactivity/g. Conclusion: Compound 4a is a promising antitumor agent with a potential EGFR inhibitory effect.

A Novel Dextran-Based Dual Drug Conjugate Targeted Tumors with High Biodistribution Ratio of Tumors to Normal Tissues

PURPOSE

Most chemotherapeutic agents possess poor water solubility and show more significant accumulations in normal tissues than in tumor tissues, resulting in serious side effects. To this end, a novel dextran-based dual drug delivery system with high biodistribution ratio of tumors to normal tissues was developed.

METHODS

A bi-functionalized dextran was developed, and several negatively charged dextran-based dual conjugates containing two different types of drugs, docetaxel and docosahexaenoic acid (DTX and DHA, respectively) were synthesized. The structures of these conjugates were characterized using nuclear magnetic resonance and liquid chromatography/mass spectrometry (¹H-NMR and LC/MS, respectively) analysis. Cell growth inhibition, apoptosis, cell cycle distribution, and cellular uptake were measured in vitro. Drug biodistribution and pharmacokinetics were investigated in mice bearing 4T1 tumors using LC/MS analysis. Drug biodistribution was also explored by in vivo imaging. The effects of these conjugates on tumor growth were evaluated in three mice models.

RESULTS

The dextran-docosahexaenoic acid (DHA)- docetaxel (DTX) conjugates caused a significant enhancement of DTX water solubility and improvement in pharmacokinetic characteristics. The optimized dextran-DHA-DTX conjugate A treatment produced a 2.1- to 15.5-fold increase in intra-tumoral DTX amounts for up to 96 h compared to parent DTX treatment. Meanwhile, the concentrations of DTX released from conjugate A in normal tissues were much lower than those of the parent DTX. This study demonstrated that DHA could lead to an improvement in the efficacy of the conjugates and that the conjugate with the shortest linker displayed more activity than conjugates with longer linkers. Moreover, conjugate A completely eradicated all MCF-7 xenograft tumors without causing any obvious side effects and totally outperformed both the conventional DTX formulation and Abraxane in mice.

CONCLUSION

These dextran-based dual drug conjugates may represent an innovative tumor targeting drug delivery system that can selectively deliver anticancer agents to tumors.

Preparation of radiolabeled erlotinib analogues and analysis of the effect of linkers

Erlotinib is a first generation epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) which was granted Food and Drug administration (FDA) approval for treatment of patients with locally advanced or metastatic NSCLC. The present study aimed at development of radiolabeled erlotinib variants as tyrosine kinase inhibitors. Three DOTA-erlotinib conjugates were prepared for radiolabeling with ¹⁷⁷Lu. The terminal alkyne group of erlotinib was modified by performing Cu-catalyzed click chemistry and three different linkers were introduced which were then conjugated to the chelator, DOTA. The DOTA-erlotinib conjugates were characterized by ¹H NMR and ESI-MS. ¹⁷⁷Lu-DOTA-erlotinib complexes were characterized using ^natLu-DOTA-erlotinib conjugates. The ¹⁷⁷Lu-complexes exhibited high in vitro stability in human serum up to 48 h. They were highly hydrophilic in nature as observed from their log P_o/w values (¹⁷⁷Lu-DOTA-propyl-Er: -2.5 ± 0.1; ¹⁷⁷Lu-DOTA-PEG₃-Er: -3.0 ± 0.1; ¹⁷⁷Lu-DOTA-PEG₆-Er: -3.3 ± 0.1). The MTT assay in A431 human epidermoid carcinoma cell lines indicates that the chemical modification at the terminal alkyne group of the erlotinib molecule does not have significant effect on its TKI property. Biodistribution studies in normal Swiss mice demonstrated fast clearance and excretion of ¹⁷⁷Lu-labeled erlotinib complexes. These studies indicate that erlotinib variants with hydrophobic pharmacokinetic modifiers/chelators may enhance the retention of ¹⁷⁷Lu-labeled complexes in blood thereby increasing the probability to reach EGFR-expressing tumor.

PET Imaging of Lung Cancers in Precision Medicine: Current Landscape and Future Perspective

Despite the recent advances in cancer treatment, lung cancer remains the leading cause of cancer mortality worldwide. Immunotherapies using immune checkpoint inhibitors (ICIs) achieved substantial efficacy in nonsmall cell lung cancer (NSCLC). Currently, most ICIs are still a monoclonal antibody (mAb). Using mAbs or antibody derivatives labeled with radionuclide as the tracers, immunopositron emission tomography (immunoPET) possesses multiple advantages over traditional ¹⁸F-FDG PET in imaging lung cancers. ImmunoPET presents excellent potential in detecting, diagnosing, staging, risk stratification, treatment guidance, and recurrence monitoring of lung cancers. By using radiolabeled mAbs, immunoPET can visualize the biodistribution and uptake of ICIs, providing a noninvasive modality for patient stratification and response evaluation. Some novel targets and associated tracers for immunoPET have been discovered and investigated. This Review introduces the value of immunoPET in imaging lung cancers by summarizing both preclinical and clinical evidence. We also emphasize the value of immunoPET in optimizing immunotherapy in NSCLC. Lastly, immunoPET probes developed for imaging small cell lung cancer (SCLC) will also be discussed. Although the major focus is to summarize the immunoPET tracers for lung cancers, we also highlighted several small-molecule PET tracers to give readers a balanced view of the development status.

Impact of Selected Small-Molecule Kinase Inhibitors on Lipid Membranes

Small-molecule protein kinase inhibitors are used for the treatment of various diseases. Although their effect(s) on the respective kinase are generally quite well understood, surprisingly, their interaction with membranes is only barely investigated; even though these drugs necessarily come into contact with the plasma and intracellular membranes. Using biophysical methods such as NMR, ESR, and fluorescence spectroscopy in combination with lipid vesicles, we studied the membrane interaction of the kinase inhibitors sunitinib, erlotinib, idelalisib, and lenvatinib; these drugs are characterized by medium log p values, a parameter reflecting the overall hydrophobicity of the molecules, which is one important parameter to predict the interaction with lipid membranes. While all four molecules tend to embed in a similar region of the lipid membrane, their presence has different impacts on membrane structure and dynamics. Most notably, sunitinib, exhibiting the lowest log p value of the four inhibitors, effectively influences membrane integrity, while the others do not. This shows that the estimation of the effect of drug molecules on lipid membranes can be rather complex. In this context, experimental studies on lipid membranes are necessary to (i) identify drugs that may disturb membranes and (ii) characterize drug-membrane interactions on a molecular level. Such knowledge is important for understanding the efficacy and potential side effects of respective drugs.

Synthesis, characterization and evaluation of 68Ga labelled monomeric and dimeric quinazoline derivatives of the HBED-CC chelator targeting the epidermal growth factor receptor

Tyrosine kinase (TK) receptors including epidermal growth factor receptors (EGFRs) are known to be overexpressed in a wide variety of solid tumors associated with poor prognosis. The HBED-CC chelator N,N'-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid 1 was coupled via one or both its propionic acid moieties with the quinazoline EGFR-TK inhibiting pharmacophore 4-amino-N-(4-((3-bromophenyl)amino)quinazolin-6-yl)butanamide 3 resulting in either a monomeric 4 or a dimeric 5 species. Ligands 4 and 5 reacted with Ga³⁺ generating the corresponding complexes Ga4 and Ga5. Both ligands and complexes were characterized with mass spectrometry and NMR spectroscopy and evaluated in vitro with MTT assays in A431 cells, where they showed IC₅₀ values in the range 51.6 to 68.8 μM. Labeling of ligands 4 and 5 with the PET radionuclide ⁶⁸Ga was quantitative and resulted in tracers [⁶⁸Ga]Ga4 and [⁶⁸Ga]Ga5 with radiochemical purities greater than 98%, which were also characterised by comparative RP-HPLC studies with Ga4 and Ga5 respectively. Radiotracers [⁶⁸Ga]Ga4 and [⁶⁸Ga]Ga5 were stable (intact tracer over 98%) in the reaction mixture (120 min) and in human serum (30 min). Both tracers were evaluated in vivo with biodistribution experiments in SCID mice bearing A431 tumors presenting tumor uptake of 1.34 for [⁶⁸Ga]Ga4 and 1.01 %ID/g for [⁶⁸Ga]Ga5 at 5 min, which was slightly decreased at 60 min p.i. and then remained stable until 120 min p.i. To the best of our knowledge, this is the first report of monomeric and dimeric quinazoline conjugates with the chelator HBED-CC, which can serve as a basis for further development of EGFR-TKI targeting tracers.