Biodistribution and planar gamma camera imaging of 123I- and 131I-labeled F(ab′)2 and Fab fragments of monoclonal antibody 14C5 in nude mice bearing an A549 lung tumor

Macrocyclic-Albumin Conjugates for Precise Delivery of Radionuclides and Anticancer Drugs to Tumors

Precise delivery of radionuclides and anticancer drugs to tumor tissue is crucial to ensuring drug synergism and optimal therapeutic effects in radionuclide-based combination radio-chemotherapy. However, current codelivery vectors often rely on physical embedment/adsorption to load anticancer drugs, which lacks precise mechanisms for drug loading and release, resulting in unpredictable combination effects. Herein, a macrocyclic-albumin conjugate (MAC) that enables precise loading and controlled release of anticancer drugs is presented. By conjugating multiple macrocyclic hosts (sulfonate azocalix[4]arenes, SAC4A) to albumin molecules, the MAC facilitates the precise loading of anticancer drugs through host-guest interactions and site-specific labeling of radionuclides. Furthermore, the MAC degrades under hypoxic conditions, enabling the release of loaded drugs upon reaching tumor tissues. Through precise loading and targeted delivery of radionuclides and anticancer drugs, MAC achieves efficient cancer diagnosis and combined radio-chemotherapy in breast cancer cell (4T1)-bearing mice. Considering that SAC4A can load many anticancer drugs, MAC may provide a promising platform for effective combination radio-chemotherapy.

Albumin-Templated Manganese Dioxide Nanoparticles for Enhanced Radioisotope Therapy

Although nanoparticle-based drug delivery systems have been widely explored for tumor-targeted delivery of radioisotope therapy (RIT), the hypoxia zones of tumors on one hand can hardly be reached by nanoparticles with relatively large sizes due to their limited intratumoral diffusion ability, on the other hand often exhibit hypoxia-associated resistance to radiation-induced cell damage. To improve RIT treatment of solid tumors, herein, radionuclide ¹³¹ I labeled human serum albumin (HSA)-bound manganese dioxide nanoparticles (¹³¹ I-HSA-MnO₂ ) are developed as a novel RIT nanomedicine platform that is responsive to the tumor microenvironment (TME). Such ¹³¹ I-HSA-MnO₂ nanoparticles with suitable sizes during blood circulation show rather efficient tumor passive uptake owing to the enhanced permeability and retention effect, as well as little retention in other normal organs to minimize radiotoxicity. The acidic TME can trigger gradual degradation of MnO₂ and thus decomposition of ¹³¹ I-HSA-MnO₂ nanoparticles into individual ¹³¹ I-HSA with sub-10 nm sizes and greatly improves intratumoral diffusion. Furthermore, oxygen produced by MnO₂ -triggered decomposition of tumor endogenous H₂ O₂ would be helpful to relieve hypoxia-associated RIT resistant for those tumors. As the results, the ¹³¹ I-HSA-MnO₂ nanoparticles appear to be a highly effective RIT agent showing great efficacy in tumor treatment upon systemic administration.

High contrast tumor imaging with radio-labeled antibody Fab fragments tailored for optimized pharmacokinetics via PASylation

Although antigen-binding fragments (Fabs) of antibodies constitute established tracers for in vivo radiodiagnostics, their functionality is hampered by a very short circulation half-life. PASylation, the genetic fusion with a long, conformationally disordered amino acid chain comprising Pro, Ala and Ser, provides a convenient way to expand protein size and, consequently, retard renal filtration. Humanized αHER2 and αCD20 Fabs were systematically fused with 100 to 600 PAS residues and produced in E. coli. Cytofluorimetric titration analysis on tumor cell lines confirmed that antigen-binding activities of the parental antibodies were retained. The radio-iodinated PASylated Fabs were studied by positron emission tomography (PET) imaging and biodistribution analysis in mouse tumor xenograft models. While the unmodified αHER2 and αCD20 Fabs showed weak tumor uptake (0.8% and 0.2% ID/g, respectively; 24 h p.i.) tumor-associated radioactivity was boosted with increasing PAS length (up to 9 and 26-fold, respectively), approaching an optimum for Fab-PAS₄₀₀. Remarkably, 6- and 5-fold higher tumor-to-blood ratios compared with the unmodified Fabs were measured in the biodistribution analysis (48 h p.i.) for αHER2 Fab-PAS₁₀₀ and Fab-PAS₂₀₀, respectively. These findings were confirmed by PET studies, showing high imaging contrast in line with tumor-to-blood ratios of 12.2 and 5.7 (24 h p.i.) for αHER2 Fab-PAS₁₀₀ and Fab-PAS₂₀₀. Even stronger tumor signals were obtained with the corresponding αCD20 Fabs, both in PET imaging and biodistribution analysis, with an uptake of 2.8% ID/g for Fab-PAS₁₀₀vs. 0.24% ID/g for the unmodified Fab. Hence, by engineering Fabs via PASylation, plasma half-life can be tailored to significantly improve tracer uptake and tumor contrast, thus optimally matching reagent/target interactions.

Tumor necrosis targeted radiotherapy of non-small cell lung cancer using radioiodinated protohypericin in a mouse model

Lung cancer is the leading cause of cancer-related death. About 80% of lung cancers are non-small cell lung cancers (NSCLC). Radiotherapy is widely used in treatment of NSCLC. However, the outcome of NSCLC remains unsatisfactory. In this study, a vascular disrupting agent (VDA) combretastatin-A4-phosphate (CA4P) was used to provide massive necrosis targets. (131)I labeled necrosis-avid agent protohypericin ((131)I-prohy) was explored for therapy of NSCLC using tumor necrosis targeted radiotherapy (TNTR). Gamma counting, autoradiography, fluorescence microscopy and histopathology were used for biodistribution analysis. Magnetic resonance imaging (MRI) was used to monitor tumor volume, ratios of necrosis and tumor doubling time (DT). The biodistribution data revealed 131I-prohy was delivered efficiently to tumors. Tracer uptake peaked at 24 h in necrotic tumor of (131)I-prohy with and without combined CA4P (3.87 ± 0.38 and 2.96 ± 0.34%ID/g). (131)I-prohy + CA4P enhanced the uptake of (131)I-prohy in necrotic tumor compared to (131)I-prohy alone. The TNTR combined with CA4P prolonged survival of tumor bearing mice relative to vehicle control group, CA4P control group and (131)I-prohy control group with median survival of 35, 20, 22 and 27 days respectively. In conclusion, TNTR appeared to be effective for the treatment of NSCLC.

In Vitro and In Vivo Pre-Clinical Analysis of a F(ab')(2) Fragment of Panitumumab for Molecular Imaging and Therapy of HER1 Positive Cancers

BACKGROUND

The objective of this study was to characterize the in vitro and in vivo properties of the F(ab')(2) fragment of panitumumab and to investigate its potential for imaging and radioimmunotherapy.

METHODS

The panitumumab F(ab')(2) was generated by enzymatic pepsin digestion. After the integrity and immunoreactivity of the F(ab')(2) was evaluated, the fragment was radiolabeled. In vivo studies included direct quantitation of tumor targeting and normal organ distribution of the radiolabeled panitumumab F(ab')(2) as well as planar γ-scintigraphy and PET imaging.

RESULTS

The panitumumab F(ab')(2) was successfully produced by peptic digest. The F(ab')(2) was modified with the CHX-A"-DTPA chelate and efficiently radiolabeled with either (111)In or (86)Y. In vivo tumor targeting was achieved with acceptable uptake of radioactivity in the normal organs. The tumor targeting was validated by both imaging modalities with good visualization of the tumor at 24 h.

CONCLUSIONS

The panitumumab F(ab')(2) fragment is a promising candidate for imaging of HER1 positive cancers.

Generation and in vivo characterization of a chimeric αvβ5-targeting antibody 14C5 and its derivatives

Background

Previous studies showed that radiolabeled murine monoclonal antibody (mAb) 14C5 and its Fab and F(ab')₂ fragments, targeting α_vβ₅ integrin, have promising properties for diagnostic and therapeutic applications in cancer. To diminish the risk of generating a human anti-mouse antibody response in patients, chimeric variants were created. The purpose of this study was to recombinantly produce chimeric antibody (chAb) derivatives of the murine mAb 14C5 and to evaluate the in vitro and in vivo characteristics.

Methods

In vitro stability, specificity, and affinity of radioiodinated chAb and fragments (Iodo-Gen method) were examined on high-expressing α_vβ₅ A549 lung tumor cells. In vivo biodistribution and pharmacokinetic characteristics were studied in A549 lung tumor-bearing Swiss Nu/Nu mice.

Results

Saturation binding experiments revealed high in vitro affinity of radioiodinated chAb, F(ab')₂, and Fab, with dissociation constants (K_D) of 1.19 ± 0.19, 0.68 ± 0.10, and 2.11 ± 0.58 nM, respectively. ChAb 14C5 showed highest tumor uptake (approximately 10%ID/g) at 24 h post injection, corresponding with other high-affinity Abs. ChF(ab')₂ and chFab fragments showed faster clearance from the blood compared to the intact Ab.

Conclusions

The chimerization of mAb 14C5 and its fragments has no or negligible effect on the properties of the antibody. In vitro and in vivo properties show that the chAb 14C5 is promising for radioimmunotherapy, due to its high maximum tumor uptake and its long retention in the tumor. The chF(ab')₂ fragment shows a similar receptor affinity and a faster blood clearance, causing less non-specific retention than the chAb. Due to their fast blood clearance, the fragments show high potential for radioimmunodiagnosis.

PET imaging of CD105/endoglin expression with a ⁶¹/⁶⁴Cu-labeled Fab antibody fragment

PURPOSE

The goal of this study was to generate and characterize the Fab fragment of TRC105, a monoclonal antibody that binds with high affinity to human and murine CD105 (i.e., endoglin), and investigate its potential for PET imaging of tumor angiogenesis in a small-animal model after (61/64)Cu labeling.

METHODS

TRC105-Fab was generated by enzymatic papain digestion. The integrity and CD105 binding affinity of TRC105-Fab was evaluated before NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) conjugation and (61/64)Cu labeling. Serial PET imaging and biodistribution studies were carried out in the syngeneic 4T1 murine breast cancer model to quantify tumor targeting efficiency and normal organ distribution of (61/64)Cu-NOTA-TRC105-Fab. Blocking studies with unlabeled TRC105 were performed to confirm CD105 specificity of the tracer in vivo. Immunofluorescence staining was also conducted to correlate tracer uptake in the tumor and normal tissues with CD105 expression.

RESULTS

TRC105-Fab was produced with high purity through papain digestion of TRC105, as confirmed by SDS-PAGE, HPLC analysis, and mass spectrometry. (61/64)Cu labeling of NOTA-TRC105-Fab was achieved with about 50 % yield (specific activity about 44 GBq/μmol). PET imaging revealed rapid uptake of (64)Cu-NOTA-TRC105-Fab in the 4T1 tumor (3.6 ± 0.4, 4.2 ± 0.5, 4.9 ± 0.3, 4.4 ± 0.7, and 4.6 ± 0.8 %ID/g at 0.5, 2, 5, 16, and 24 h after injection, respectively; n = 4). Since tumor uptake peaked soon after tracer injection, (61)Cu-labeled TRC105-Fab was also able to provide tumor contrast at 3 and 8 h after injection. CD105 specificity of the tracer was confirmed with blocking studies and histological examination.

CONCLUSION

We report PET imaging of CD105 expression using (61/64)Cu-NOTA-TRC105-Fab, which exhibited prominent and target-specific uptake in the 4T1 tumor. The use of a Fab fragment led to much faster tumor uptake (which peaked at a few hours after tracer injection) compared to radiolabeled intact antibody, which may be translated into same-day immunoPET imaging for clinical investigation.

Comparison of (99m)Tc-labeled PR81 and its F(ab')₂ fragments as radioimmunoscintigraphy agents for breast cancer imaging

OBJECTIVE

We digested anti-MUC1 monoclonal antibody PR81 to produce F(ab')₂ fragments. A comparison was performed between the two radiolabeled PR81 and F(ab')₂ fragments for breast tumor imaging in a mouse model.

METHODS

The optimum conditions for pepsin digestion of PR81 were investigated in terms of enzymes: antibody ratio, digestion time duration and preserved immunoreactivity of the produced fragments. The F(ab')₂ fragments were labeled with Technetium-99m using HYNIC as a chelator and tricine as a co-ligand. The immunoreactivity of the complexes was assessed by radioimmunoassay using MCF7 cells. Biodistribution and imaging studies were performed in female BALB/c mice with breast tumor xenograft at 4, 8 and 24 h post-administration. The PR81 was labeled with technetium-99m in the same way for comparison.

RESULTS

The optimum time duration for PR81 digestion was found to be 28 h at an enzyme:antibody weight ratio of 1:20 that resulted in 95.2 ± 4.7% purity. The labeling of intact PR81 and its F(ab')₂ fragments were 87.6 ± 4.2 and 76.1 ± 3.3% after 1 h, respectively (p value <0.05). The percentage of immunoreactivity of F(ab')₂ fragments and intact PR81 were 75.4 ± 2.1% and 85.7 ± 2.9%, respectively (p value <0.05). The biodistribution and imaging studies demonstrated localization of the fragments at 4 h post-administration with high sensitivity and specificity.

CONCLUSION

The results showed that F(ab')₂ fragment of PR81 is more suitable than intact PR81 for safer and more rapid detection of human breast cancer.

Localization, mechanism and reduction of renal retention of technetium-99m labeled epidermal growth factor receptor-specific nanobody in mice

BACKGROUND

Nanobodies are single-domain antigen binding fragments derived from functional heavy-chain antibodies elicited in Camelidae. They are powerful probes for radioimmunoimaging, but their renal uptake is relatively high. In this study we have evaluated the role of megalin on the renal uptake of anti-EGFR (99m)Tc-7C12 nanobody and the potency of gelofusine and/or lysine to reduce renal uptake of (99m)Tc-7C12.

METHODS

First we compared the renal uptake of (99m)Tc-7C12 in megalin-deficient and megalin-wild-type mice using pinhole SPECT/microCT and ex vivo analysis. The effect of gelofusine and lysine administration on renal accumulation of (99m)Tc-7C12 was analyzed in CD-1 mice divided into lysine preload at 30 min before tracer injection (LysPreload), LysPreload + gelofusine coadministration (LysPreload + GeloCoad), lysine coadministration (LysCoad), gelofusine coadministration (GeloCoad) and LysCoad + GeloCoad. The combined effect of gelofusine and lysine on tumor uptake was tested in mice xenografts.

RESULTS

Renal uptake of (99m)Tc-7C12 was 44.22 ± 3.46% lower in megalin-deficient compared with megalin-wild-type mice. In CD-1 mice, lysine preload had no effect on the renal retention whereas coinjection of lysine or gelofusine with the tracer resulted in 25.12 ± 2.99 and 36.22 ± 3.07% reduction, respectively. The combined effect of gelofusine and lysine was the most effective, namely a reduction of renal retention of 45.24 ± 2.09%. Gelofusine and lysine coadministration improved tumor uptake.

CONCLUSION

Megalin contributes to the renal accumulation of (99m)Tc-7C12. Gelofusine and lysine coinjection with the tracer reduces the renal uptake while tumor uptake is improved. Although this methodology allows for optimization of imaging protocol using nanobodies, further improvements are needed before using these molecules for radionuclide therapy.

Preclinical evaluation of monoclonal antibody 14C5 for targeting pancreatic cancer

The use of radiolabeled antibodies that are able to target primary tumors as well as metastatic tumor sites with minimal reactivity to normal tissues is a promising approach for treating pancreatic cancer. In this study, the integrin alpha(v)beta(5) is studied as a target for the diagnosis of and potential therapy for human pancreatic cancer by using the radiolabeled murine monoclonal antibody (mAb) 14C5. Biopsy specimens from human pancreatic tumors were examined for the expression of the integrin alpha(v)beta(5). The pancreatic tumor cell line Capan-1 was used to test the in vitro targeting potency of mAb 14C5 labeled with 125/131-iodine and 111-indium. Internalization, retention, and metabolism were investigated in cellular radioimmunoassays. Biodistribution and tumor-targeting characteristics were studied in Capan-1 xenografts. All tumor sections were positive for the integrin alpha(v)beta(5), with an extensive positive staining of the stroma. Saturation binding experiments showed high affinity with comparable K(d)s. In vitro internalization experiments showed a longer intracellular retention of (111)In-p-benzyl isothiocyanate-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (p-SCN-Bz-DOTA)-14C5 in comparison to (125)I-14C5 and (111)In-p-isothiocyanatobenzyl diethylenetriaminepentaacetic acid (p-SCN-Bz-DTPA)-14C5. In vivo radioisotope tumor uptake was maximum at 48-72 hours, with the uptake of (111)In-p-SCN-Bz-DOTA-14C5 (35.84 +/- 8.64 percentage of injected dose per g [%ID/g]) being 3.9- and 2.2-folds higher than (131)I-14C5 (12.16 +/- 1.03%ID/g) and (111)In-p-SCN-Bz-DTPA-14C5 (14.30 +/- 3.76%ID/g), respectively. Planar gamma imaging with mAb 14C5 indicated clear localization of the pancreatic tumors versus minimal normal tissue uptake. mAb 14C5 is a promising new antibody for targeting the integrin alpha(v)beta(5) for the diagnosis of and potential therapy for pancreatic cancer.

Imaging of alpha(v)beta(3) expression by a bifunctional chimeric RGD peptide not cross-reacting with alpha(v)beta(5)

PURPOSE

To test whether a novel bifunctional chimeric peptide comprising a cyclic Arg-Gly-Asp pentapeptide covalently bound to an echistatin domain can discriminate alpha(v)beta(3) from alpha(v)beta(5) integrin, thus allowing the in vivo selective visualization of alpha(v)beta(3) expression by single-photon and positron emission tomography (PET) imaging.

EXPERIMENTAL DESIGN

The chimeric peptide was preliminarily tested for inhibition of alpha(v)beta(3)-dependent cell adhesion and competition of 125I-echistatin binding to membrane of stably transfected K562 cells expressing alpha(v)beta(3) (Kalpha(v)beta(3)) or alpha(v)beta(5) (Kalpha(v)beta(5)) integrin. The chimeric peptide was then conjugated with diethylenetriaminepentaacetic acid and labeled with 111In for single-photon imaging, whereas a one-step procedure was used for labeling the full-length peptide and a truncated derivative, lacking the last five C-terminal amino acids, with 18F for PET imaging. Nude mice bearing tumors from Kalpha(v)beta(3), Kalpha(v)beta(5), U87MG human glioblastoma, and A431 human epidermoid cells were subjected to single-photon and PET imaging.

RESULTS

Adhesion and competitive binding assays showed that the novel chimeric peptide selectively binds to alpha(v)beta(3) integrin and does not cross-react with alpha(v)beta(5). In agreement with in vitro findings, single-photon and PET imaging studies showed that the radiolabeled chimeric peptide selectively localizes in tumor xenografts expressing alphavbeta3 and fails to accumulate in those expressing alpha(v)beta(5) integrin. When 18F-labeled truncated derivative was used for PET imaging, alphavbeta3- and alpha(v)beta(5)-expressing tumors were visualized, indicating that the five C-terminal amino acids are required to differentially bind the two integrins.

CONCLUSION

Our findings indicate that the novel chimeric Arg-Gly-Asp peptide, having no cross-reaction with alphavbeta5 integrin, allows highly selective alphavbeta3 expression imaging and monitoring.

Engineering therapeutic monoclonal antibodies

During last two decades, the chimerization and humanization of monoclonal antibodies (mAbs) have led to the approval of several for the treatment of cancer, autoimmune diseases, and transplant rejection. Additional approaches have been used to further improve their in vivo activity. These include combining them with other modalities such as chemotherapy and redesigning them for improved pharmacokinetics, effector function, and signaling activity. The latter has taken advantage of new insights emerging from an increased understanding of the cellular and molecular mechanisms that are involved in the interaction of immunoglobulin G with Fc receptors and complement as well as the negative signaling resulting from the hypercrosslinking of their target antigens. Hence, mAbs have been redesigned to include mutations in their Fc portions, thereby endowing them with enhanced or decreased effector functions and more desirable pharmacokinetic properties. Their valency has been increased to decrease their dissociation rate from cells and enhance their ability to induce apoptosis and cell cycle arrest. In this review we discuss these redesigned mAbs and current data concerning their evaluation both in vitro and in vivo.

Monoclonal antibody 14C5 targets integrin alphavbeta5

This study identifies and characterizes the antigen recognized by monoclonal antibody (mAb) 14C5. We compared the expression of antigen 14C5 with the expression of eight integrin subunits (alpha1, alpha2, alpha3, alphav, beta1, beta2, beta3, and beta4) and three integrin heterodimers (alphavbeta3, alphavbeta5, and alpha5beta1) by flow cytometry. Antigen 14C5 showed a similar expression to alphavbeta5 in eight different epithelial cancer cell lines (A549, A2058, C32, Capan-2, Colo16, HT-1080, HT-29, and SKBR-3). Specific binding of P1F6, an anti-alphavbeta5 specific antibody, was blocked by mAb 14C5. After transient expression of alphavbeta5 in 14C5-negative Colo16 cells, mAb 14C5 was able to bind a subpopulation of alphavbeta5-positive cells. We evaluated the tissue distribution of the 14C5 antigen in colon (n = 20) and lung (n = 16) cancer tissues. The colon carcinoma cells stained positive for 14C5 in 50% of tumors analyzed, whereas bronchoalveolar lung carcinoma and typical carcinoid were not positive for the antigen. More common types of non-small cell lung cancer, i.e., squamous (n = 5) and adenocarcinoma (n = 3), stained positive in 2 of 5 squamous carcinomas and in 1 of 3 investigated adenocarcinoma. Colon (95%) and lung (50%) carcinoma tissues showed extensive expression of antigen 14C5 in the stroma surrounding the tumor cells and on the membrane of the adjacent fibroblasts. We show for the first time that mAb 14C5 binds the vascular integrin alphavbeta5, suggesting that mAb 14C5 can be used as a screening agent to select colon and lung cancer patients that are eligible for anti-alphavbeta5-based therapies.