The role of p53 in combination radioimmunotherapy with 64Cu-DOTA-cetuximab and cisplatin in a mouse model of colorectal cancer

Synergism of 64Cu-Labeled RGD with Anti-PD-L1 Immunotherapy for the Long-Acting Antitumor Effect

We put forward a novel targeting-triggering-therapy (TTT) scheme that combines ⁶⁴Cu-based targeted radionuclide therapy (TRT) with programmed death-ligand 1 (PD-L1)-based immunotherapy for enhancing therapeutic efficacy. The α_vβ₃ integrin-targeted ⁶⁴Cu-DOTA-EB-cRGDfK (⁶⁴Cu-DER) was synthesized. Flow cytometry, immunofluorescence staining, and RT-qPCR were performed to verify PD-L1 upregulation after irradiation with ⁶⁴Cu-DER. Positron emission tomography imaging was performed to investigate the prominent tumor retention property of ⁶⁴Cu-DER. In the MC38 tumor model, anti-PD-L1 antibody (αPD-L1 mAb) was delivered in a concurrent or sequential manner after ⁶⁴Cu-DER was injected, followed by the testing of changes in tumor microenvironment (TME). PD-L1 was upregulated in a time- and dose-dependent manner after being induced by ⁶⁴Cu-DER. The combination of ⁶⁴Cu-DER TRT (925 MBq/kg) and αPD-L1 mAb (10 mg/kg) resulted in significant delay in tumor growth and protected against tumor rechallenge. Blockade of PD-L1 at 4 h after ⁶⁴Cu-DER TRT (⁶⁴Cu-DER + αPD-L1 mAb @ 4 h combination group) was able to achieve 100% survival rate, prevent tumor relapse, and evidently prolong the survival of mice. In summary, the combination of ⁶⁴Cu-DER and αPD-L1 mAb in a time-dependent manner could be a promising approach to improve therapeutic efficacy. Understandably, this strategy has the potential to extend the scope of ⁶⁴Cu-based TTT and merits translation into clinical practice for the better management of immune checkpoint blockade immunotherapy.

Derivation and Clinical Validation of a Redox-Driven Prognostic Signature for Colorectal Cancer

Colorectal cancer (CRC), a seriously threat that endangers public health, has a striking tendency to relapse and metastasize. Redox-related signaling pathways have recently been extensively studied in cancers. However, the study and potential role of redox in CRC remain unelucidated. We developed and validated a risk model for prognosis and recurrence prediction in CRC patients via identifying gene signatures driven by redox-related signaling pathways. The redox-driven prognostic signature (RDPS) was demonstrated to be an independent risk factor for patient survival (including OS and RFS) in four public cohorts and one clinical in-house cohort. Additionally, there was an intimate association between the risk score and tumor immune infiltration, with higher risk score accompanied with less immune cell infiltration. In this study, we used redox-related factors as an entry point, which may provide a broader perspective for prognosis prediction in CRC and have the potential to provide more promising evidence for immunotherapy.

A Critical Review of Second-Generation Anti-EGFR Monoclonal Antibodies in Metastatic Colorectal Cancer

BACKGROUND

Anti-EGFR monoclonal antibodies (mAbs) have become a relevant solution for the treatment of patients with metastatic colorectal cancer. Current anti-EGFR monoclonal antibodies face a series of problems, including resistance and non-durable response, and RAS and BRAF mutations serve as exclusion criteria for treatment with anti-EGFR mAbs. Advances in molecular tumor profiling and information on subsequent pathways responsible for disease progression and drug resistance helped develop a new generation of anti-EGFR mAbs. These second-generation mAbs have been developed to overcome existing resistance mechanisms and to limit common side effects. For the moment, existing literature suggests that these novel anti-EGFR mAbs are far from finding their way to clinical practice soon.

OBJECTIVE

In this review, we summarize and evaluate current data regarding ongoing research and completed clinical trials for different second-generation anti-EGFR monoclonal antibodies.

CONCLUSION

Anti-EGFR mAbs exhibit efficacy in advanced colorectal cancer, but second-generation mAbs failed to prove their benefit in the treatment of metastatic colorectal cancer. Understanding the biological basis of primary and acquired drug resistance could allow scientists to design better clinical trials and develop improved second-generation mAbs.

A Pretargeted Imaging Strategy for EGFR-Positive Colorectal Carcinoma via Modulation of Tz-Radioligand Pharmacokinetics

PURPOSE

Previously, we successfully developed a pretargeted imaging strategy (atezolizumab-TCO/[^99mTc]HYNIC-PEG₁₁-Tz) for evaluating programmed cell death ligand-1 (PD-L1) expression in xenograft mice. However, the surplus unclicked [^99mTc]HYNIC-PEG₁₁-Tz is cleared somewhat sluggishly through the intestines, which is not ideal for colorectal cancer (CRC) imaging. To shift the excretion of the Tz-radioligand to the renal system, we developed a novel Tz-radioligand by adding a polypeptide linker between HYNIC and PEG₁₁.

PROCEDURES

Pretargeted molecular probes [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz and cetuximab-TCO were synthesized. [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz was evaluated for in vitro stability and in vivo blood pharmacokinetics. In vitro ligation reactivity of [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz towards cetuximab-TCO was also tested. Biodistribution assay and imaging of [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz were performed to observe its excretion pathway. Pretargeted biodistribution was measured at three different accumulation intervals to determine the optimal pretargeted interval time. Pretargeted (cetuximab-TCO 48 h/[^99mTc]HYNIC-PEG₁₁-Tz 6 h) and (cetuximab-TCO 48 h/[^99mTc]HYNIC-Polypeptide-PEG₁₁-Tz 6 h) imagings were compared to examine the effect of the excretion pathway on tumor imaging.

RESULTS

[^99mTc]HYNIC-polypeptide-PEG₁₁-Tz showed favorable in vitro stability and rapid blood clearance in mice. SEC-HPLC revealed almost complete reaction between cetuximab-TCO and [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz in vitro, with the 8:1 Tz-to-mAb reaction providing a conversion yield of 87.83 ± 3.27 %. Biodistribution and imaging analyses showed that the Tz-radioligand was cleared through the kidneys. After 24, 48, and 72 h of accumulation in HCT116 tumor, the tumor-to-blood ratio of cetuximab-TCO was 0.83 ± 0.13, 1.40 ± 0.31, and 1.15 ± 0.21, respectively. Both pretargeted (cetuximab-TCO 48 h/[^99mTc]HYNIC-PEG₁₁-Tz 6 h) and (cetuximab-TCO 48 h/[^99mTc]HYNIC-polypeptide-PEG₁₁-Tz 6 h) clearly delineated HCT116 tumor. Pretargeted imaging strategy using cetuximab-TCO/[^99mTc]HYNIC-polypeptide-PEG₁₁-Tz could be used for diagnosing CRC, as the surplus unclicked [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz was cleared through the urinary system, leading to low abdominal uptake background.

CONCLUSION

Our novel pretargeted imaging strategy (cetuximab-TCO/[^99mTc]HYNIC-polypeptide-PEG₁₁-Tz) was useful for imaging CRC, broadening the application scope of pretargeted imaging strategy. The pretargeted imaging strategy clearly delineated HCT116 tumor, showing that its use could be extended to selection of internalizing antibodies.

Cation Exchange Protocols to Radiolabel Aqueous Stabilized ZnS, ZnSe, and CuFeS2 Nanocrystals with 64Cu for Dual Radio- and Photo-Thermal Therapy

Here, cation exchange (CE) reactions are exploited to radiolabel ZnSe, ZnS, and CuFeS2 metal chalcogenide nanocrystals (NCs) with 64Cu. The CE protocol requires one simple step, to mix the water-soluble NCs with a 64Cu solution, in the presence of vitamin C used to reduce Cu(II) to Cu(I). Given the quantitative cation replacement on the NCs, a high radiochemical yield, up to 99%, is reached. Also, provided that there is no free 64Cu, no purification step is needed, making the protocol easily translatable to the clinic. A unique aspect of the approach is the achievement of an unprecedentedly high specific activity: by exploiting a volumetric CE, the strategy enables to concentrate a large dose of 64Cu (18.5 MBq) in a small NC dose (0.18 µg), reaching a specific activity of 103 TBq g-1. Finally, the characteristic dielectric resonance peak, still present for the radiolabeled 64Cu:CuFeS2 NCs after the partial-CE reaction, enables the generation of heat under clinical laser exposure (1 W cm-2). The synergic toxicity of photo-ablation and 64Cu ionization is here proven on glioblastoma and epidermoid carcinoma tumor cells, while no intrinsic cytotoxicity is seen from the NC dose employed for these dual experiments.

64Cu-Intraperitoneal Radioimmunotherapy: A Novel Approach for Adjuvant Treatment in a Clinically Relevant Preclinical Model of Pancreatic Cancer

Pancreatic cancer (PC) has a very poor prognosis. Surgery is the primary treatment for patients with resectable PC; however, local recurrence, hepatic metastasis, and peritoneal dissemination often occur even after extensive surgery. Adjuvant chemotherapy, typically with gemcitabine, has been used clinically but with only a modest survival benefit. To achieve a better outcome, we investigated the efficacy of 64Cu-intraperitoneal radioimmunotherapy (ipRIT) with 64Cu-labeled antiepidermal growth factor receptor antibody cetuximab as an adjuvant treatment after PC surgery using an orthotopic xenografted mouse model. Methods: The efficacy of adjuvant 64Cu-ipRIT was investigated in a human PC mouse model harboring orthotopic xenografts of xPA-1-DC cells. To reproduce the clinical situation, PC xenografts were surgically resected when pancreatic tumors were readily visible but not metastatic tumors. Increasing doses of 64Cu-cetuximab were intraperitoneally injected, and the mice were monitored for toxicity to determine the safe therapeutic dose. For adjuvant 64Cu-ipRIT, the day after tumor resection, the mice were intraperitoneally administered 22.2 MBq of 64Cu-PCTA-cetuximab and the survival was compared with that in surgery-only controls. For comparison, adjuvant chemotherapy with gemcitabine was also examined using the same model. Results: The mouse model not only developed primary tumors in the pancreas but also subsequently reproduced local recurrence, hepatic metastasis, and peritoneal dissemination after surgery, which is similar to the manifestations that occur with human PC. Adjuvant 64Cu-ipRIT with 64Cu-labeled cetuximab after surgery effectively suppressed local recurrence, hepatic metastasis, and peritoneal dissemination in this model. Significant improvement of the survival with minimal toxicity was achieved by adjuvant 64Cu-ipRIT compared with that in control mice that underwent surgery only. Adjuvant chemotherapy with gemcitabine nominally prolonged the survival, but the effect was not statistically significant. Conclusion:64Cu-ipRIT with cetuximab can be an effective adjuvant therapy after PC surgery.

Synthesis and evaluation of 64Cu-radiolabeled NOTA-cetuximab (64Cu-NOTA-C225) for immuno-PET imaging of EGFR expression

Objective

Epidermal growth factor receptor (EGFR) is overexpressed in a wide variety of solid tumors, serving as a well-characterized target for cancer imaging or therapy. In this study, we aimed to design and synthesize a radiotracer, ⁶⁴Cu-NOTA-C225, targeting EGFR for tumor positron emission tomography (PET) imaging.

Methods

Cetuximab (C225) was conjugated to a bifunctional chelator, p-isothiocyanatobenzyl-1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), and further radiolabeled with copper-64 for PET imaging. ⁶⁴Cu-NOTA-IgG and Cy5.5-C225 were also synthesized as control probes. A431 and A549 mouse models were established for micro-PET and/or near-infrared fluorescence (NIRF) imaging.

Results

⁶⁴Cu-NOTA-C225 exhibited stability in vivo and in vitro up to 24 h and 50 h post-injection, respectively. A431 tumors with average standard uptake values (SUVs) of 5.61±0.69, 6.68±1.14, 7.80±1.51 at 6, 18 and 36 h post-injection, respectively, which were significantly higher than that of moderate EGFR expressing tumors (A549), with SUVs of 0.89±0.16, 4.70±0.81, 2.01±0.50 at 6, 18 and 36 h post-injection, respectively. The expression levels of A431 and A549 were confirmed by western blotting. Additionally, the tracer uptake in A431 tumors can be blocked by unlabeled cetuximab, suggesting that tracer uptake by tumors was receptor-mediated. Furthermore, NIRF imaging using Cy5.5-C225 showed that the fluorescence intensity in tumors increased with time, with a maximal intensity of 8.17E+10 (p/s/cm²/sr)/(μW/cm²) at 48 h post-injection, which is consistent with the paradigm from micro-PET imaging in A431 tumor-bearing mice.

Conclusions

The ⁶⁴Cu-NOTA-C225 PET imaging may be able to specifically and sensitively differentiate tumor models with different EGFR expression levels. It offers potentials as a PET radiotracer for imaging of tracer EGFR-positive tumors.

Biodistribution, pharmacokinetics and radioimmunotherapy of 188Re-cetuximab in NCI-H292 human lung tumor-bearing nude mice

Background Cetuximab is a fully humanized IgG1 subclass monoclonal that binds specifically to the human epidermal growth factor receptor (EGFR). Although EGFR is expressed in normal cells, the overexpression of EGFR is detected in many human cancers, such as colon, rectum and lung tumors. In this study, cetuximab with a combination of radiotherapy nuclear ¹⁸⁸Re achieved better therapeutic effect on lung cancer. Methods¹⁸⁸Re-cetuximab administered by the i.v. route in human NCI-H292 lung tumor-bearing mice was investigated. NanoSPECT/CT images were taken to evaluate the distribution and tumor targeting of ¹⁸⁸Re-cetuximab in mice. The anti-tumor effect of ¹⁸⁸Re-cetuximab was assessed by the tumor growth inhibition, survival ratio. Results For nanoSPECT/CT imaging, a significant uptake in tumor was observed at 24 and 48 h following the injection of ¹⁸⁸Re-cetuximab. The anti-tumor effect of ¹⁸⁸Re-cetuximab was assessed by tumor growth inhibition and the survival ratio. The tumor-bearing mice treated with ¹⁸⁸Re-cetuximab showed a better mean tumor growth inhibition rate (MGI = 0.049) and longer median survival time and lifespan (62.50 d; 70.07%) than those treated with ¹⁸⁸Re-perrhenate and cetuximab only by single injection. A synergistic effect of tumor growth inhibition was observed with the combination index exceeding one for ¹⁸⁸Re-cetuximab (CI = 6.135 and 9.276). Conclusion The tumor targeting and localization of 188Re-cetuximab were confirmed in this study. Synergistic therapeutic efficacy was demonstrated for the radioimmunotherapy of ¹⁸⁸Re-cetuximab. The results of this study reveal the potential advantage and benefit obtained from ¹⁸⁸Re-cetuximab for diagnosis and therapy of oncology applications in the future.

Combined external beam radiotherapy with carbon ions and tumor targeting endoradiotherapy

External beam radiotherapy (EBRT) with carbon ions and endoradiotherapy using radiolabeled tumor targeting agents are emerging concepts in precision cancer therapy. We report on combination effects of these two promising strategies.

Tumor targeting ¹³¹I-labelled anti-EGFR-antibody (Cetuximab) was used in the prototypic EGFR-expressing A431 human squamous cell carcinoma xenograft model. A ¹³¹I-labelled melanin-binding benzamide derivative was utilized targeting B16F10 melanoma in an orthotopic syngeneic C57bl6 model. Fractionated EBRT was performed using carbon ions in direct comparison with conventional photon irradiation.

Tumor uptake of ¹³¹I-Cetuximab and ¹³¹I-Benzamide was enhanced by fractionated EBRT as determined by biodistribution studies. This effect was independent of radiation quality and significant for the small molecule ¹³¹I-Benzamide, i.e., >30% more uptake in irradiated vs. non-irradiated melanoma was found (p<0.05). Compared to each monotherapy, dual combination with ¹³¹I-Cetuximab and EBRT was most effective in inhibiting A431 tumor growth. A similar trend was seen for ¹³¹I-Benzamide and EBRT in B16F10 melanoma model. Addition of ¹³¹I-Benzamide endoradiotherapy to EBRT altered expression of genes related to DNA-repair, cell cycle and cell death. In contrast, immune-response related pathways such as type 1 interferon response genes (ISG15, MX1) were predominantly upregulated after combined ¹³¹I-Cetuximab and EBRT. The beneficial effects of combined 131I-Cetuximab and EBRT was further attributed to a reduced microvascular density (CD31) and decreased proliferation index (Ki-67).

Fractionated EBRT could be favorably combined with endoradiotherapy. ¹³¹I-Benzamide endoradiotherapy accelerated EBRT induced cytotoxic effects. Activation of immune-response by carbon ions markedly enhanced anti-EGFR based endoradiotherapy suggesting further evaluation of this novel and promising radioimmunotherapy concept.

Integrated treatment using intraperitoneal radioimmunotherapy and positron emission tomography-guided surgery with 64Cu-labeled cetuximab to treat early- and late-phase peritoneal dissemination in human gastrointestinal cancer xenografts

Peritoneal dissemination is a common cause of death from gastrointestinal cancers and is difficult to treat using current therapeutic options, particularly late-phase disease. Here, we investigated the feasibility of integrated therapy using ⁶⁴Cu-intraperitoneal radioimmunotherapy (ipRIT), alone or in combination with positron emission tomography (PET)-guided surgery using a theranostic agent (⁶⁴Cu-labeled anti-epidermal growth factor receptor antibody cetuximab) to treat early- and late-phase peritoneal dissemination in mouse models. In this study, we utilized the OpenPET system, which has open space for conducting surgery while monitoring objects at high resolution in real time, as a novel approach to make PET-guided surgery feasible. ⁶⁴Cu-ipRIT with cetuximab inhibited tumor growth and prolonged survival with little toxicity in mice with early-phase peritoneal dissemination of small lesions. For late-phase peritoneal dissemination, a combination of ⁶⁴Cu-ipRIT for down-staging and subsequent OpenPET-guided surgery for resecting large tumor masses effectively prolonged survival. OpenPET clearly detected tumors (≥3 mm in size) behind other organs in the peritoneal cavity and was useful for confirming the presence or absence of residual tumors during an operation. These findings suggest that integrated ⁶⁴Cu therapy can serve as a novel treatment strategy for peritoneal dissemination.

Tetraspanin 8 (TSPAN 8) as a potential target for radio-immunotherapy of colorectal cancer

Tetraspanin 8 (TSPAN8) overexpression is correlated with poor prognosis in human colorectal cancer (CRC). A murine mAb Ts29.2 specific for human TSPAN8 provided significant efficiency for immunotherapy in CRC pre-clinical models. We therefore evaluate the feasability of targeting TSPAN8 in CRC with radiolabeled Ts29.2. Staining of tissue micro-arrays with Ts29.2 revealed that TSPAN8 espression was restricted to a few human healthy tissues. DOTA-Ts29.2 was radiolabeled with 111In or 177Lu with radiochemical purities >95%, specific activity ranging from 300 to 600 MBq/mg, and radioimmunoreactive fractions >80%. The biodistribution of [111In]DOTA-Ts29.2 in nude mice bearing HT29 or SW480 CRC xenografts showed a high specificity of tumor localization with high tumor/blood ratios (HT29: 4.3; SW480-TSPAN8: 3.9 at 72h and 120h post injection respectively). Tumor-specific absorbed dose calculations for [177Lu]DOTA-Ts29.2 was 1.89 Gy/MBq, establishing the feasibility of using radioimmunotherapy of CRC with this radiolabeled antibody. A significant inhibition of tumor growth in HT29 tumor-bearing mice treated with [177Lu]DOTA-Ts29.2 was observed compared to control groups. Ex vivo experiments revealed specific DNA double strand breaks associated with cell apoptosis in [177Lu]DOTA-Ts29.2 treated tumors compared to controls. Overall, we provide a proof-of-concept for the use of [111In/177Lu]DOTA-Ts29.2 that specifically target in vivo aggressive TSPAN8-positive cells in CRC.

Targeted α-Particle Radiation Therapy of HER1-Positive Disseminated Intraperitoneal Disease: An Investigation of the Human Anti-EGFR Monoclonal Antibody, Panitumumab

Identifying molecular targets and an appropriate targeting vehicle, i.e., monoclonal antibodies (mAb) and their various forms, for radioimmunotherapy (RIT) remains an active area of research. Panitumumab, a fully human and less immunogenic mAb that binds to the epidermal growth factor receptor (Erb1; HER1), was evaluated for targeted α-particle radiation therapy using ²¹²Pb, an in vivo α generator. A single dose of ²¹²Pb-panitumumab administered to athymic mice bearing LS-174T intraperitoneal (i.p.) tumor xenografts was found to have greater therapeutic efficacy when directly compared with ²¹²Pb-trastuzumab, which binds to HER2. A dose escalation study determined a maximum effective working dose of ²¹²Pb-panitumumab to be 20 μCi with a median survival of 35 days versus 25 days for the untreated controls. Pretreatment of tumor-bearing mice with paclitaxel and gemcitabine 24 hours prior to injection of ²¹²Pb-pantiumumab at 10 or 20 μCi resulted in the greatest enhanced therapeutic response at the higher dose with median survivals of 106 versus 192 days, respectively. The greatest therapeutic impact, however, was observed in the animals that were treated with topotecan 24 hours prior to RIT and then again 24 hours after RIT; the best response from this combination was also obtained with the lower 10-μCi dose of ²¹²Pb-panitumumab (median survival >280 days). In summary, ²¹²Pb-panitumumab is an excellent candidate for the treatment of HER1-positive disseminated i.p. disease. Furthermore, the potentiation of the therapeutic impact of ²¹²Pb-pantiumumab by chemotherapeutics confirms and validates the importance of developing a multimodal therapy regimen.

Evaluation of cetuximab as a candidate for targeted α-particle radiation therapy of HER1-positive disseminated intraperitoneal disease

Although the epidermal growth factor receptor (EGFR), also known as HER1, has been studied for over a decade, it continues to be a molecule of great interest and focus of investigators for development of targeted therapies. The marketed monoclonal antibody cetuximab binds to HER1, and thus might serve as the basis for creation of imaging or therapies that target this receptor. The potential of cetuximab as a vehicle for the delivery of α-particle radiation was investigated in an intraperitoneal tumor mouse model. The effective working dose of 10 μCi of (212)Pb-cetuximab was determined from a dose (10-50 μCi) escalation study. Toxicity, as indicated by the lack of animal weight loss, was not evident at the 10 μCi dose of (212)Pb-cetuximab. A subsequent study demonstrated (212)Pb-cetuximab had a therapeutic efficacy similar to that of (212)Pb-trastuzumab (p = 0.588). Gemcitabine given 24 h prior to (212)Pb-cetuximab increased the median survival from 174 d to 283 d, but carboplatin suppressed the effectiveness of (212)Pb-cetuximab. Notably, concurrent treatment of tumor-bearing mice with (212)Pb-labeled cetuximab and trastuzumab provided therapeutic benefit that was greater than either antibody alone. In conclusion, cetuximab proved to be an effective vehicle for targeting HER1-expressing tumors with α-radiation for the treatment of disseminated intraperitoneal disease. These studies provide further evidence that the multimodality therapy regimens may have greater efficacy and benefit in the treatment of cancer patients.

PET of EGFR with (64) Cu-cetuximab-F(ab')2 in mice with head and neck squamous cell carcinoma xenografts

Overexpression of the epidermal growth factor receptor (EGFR) is linked to an adverse outcome in various solid tumors. Cetuximab is an EGFR inhibitor, which in combination with radiotherapy improves locoregional control and survival in a subgroup of patients with head and neck squamous cell carcinomas (HNSCCs). The aim of this study was to develop and characterize an EGFR-directed PET tracer, (64) Cu-cetuximab-F(ab')2, to determine the systemic accessibility of EGFR. Mice with HNSCC xenografts, UT-SCC-8 (n = 6) or UT-SCC-45 (n = 6), were imaged 24 h post injection with (64) Cu-NODAGA-cetuximab-F(ab')2 using PET/CT. One mouse for each tumor model was co-injected with excess unlabeled cetuximab 3 days before radiotracer injection to determine non-EGFR-mediated uptake. Ex vivo biodistribution of the tracer was determined and tumors were analyzed by autoradiography and immunohistochemistry. The SUVmax of UT-SCC-8 tumors was higher than that of UT-SCC-45: 1.5 ± 1.0 and 0.8 ± 0.2 (p < 0.05), respectively. SUVmax after in vivo blocking of EGFR with cetuximab was 0.4. Immunohistochemistry showed that UT-SCC-8 had a significantly higher EGFR expression than UT-SCC-45: 0.50 ± 0.19 versus 0.12 ± 0.08 (p < 0.005), respectively. Autoradiography indicated that (64) Cu-cetuximab-F(ab')2 uptake correlated with EGFR expression in both tumors: r = 0.86 ± 0.06 (UT-SCC-8) and 0.90 ± 0.06 (UT-SCC-45). (64) Cu-cetuximab-F(ab')2 is a promising PET tracer to determine expression of EGFR in vivo. Clinically, this tracer has the potential to be used to determine cetuximab targeting of tumors and possibly to non-invasively monitor the response to EGFR-inhibitor treatment.

Semaphoring mAb: a new guide in RIT in inhibiting the proliferation of human skin carcinoma

Semaphoring is a transmembrane receptor which participates in many cytokine-mediated signal pathways that are closely related to the angiogenesis, occurrence and development of carcinoma. The present study was designed to access the effect of mono-antibody (mAb) guided radioimmunotherapy (RIT) on skin carcinoma and investigate the potential mechanisms. Semaphoring mAb was acquired from mice (Balb/c), purified with rProtein A column; purity, concentration and activity were tested with SDS-PAGE and indirect ELISA; specificity and expression on the cutanuem carcinoma line and tissue were tested by Western blotting; morphology change was assessed by microscopy. MTT assay and colony inhibition tests were carried out to test the influence on the proliferation of tumor cells; Western blotting was also carried out for expression of apoptosis-associated (caspase-3, Bax, Bcl-2) and proliferation-related (PI3K, p-Akt, Akt, p-ERK1/2, ERK1/2) proteins and analyse the change in signal pathways (PI3K/Akt and MEK/ERK). The purity of purified semaphorin mAb was 96.5% and the titer is about 1?106. Western blotting showed semaphoring mAb to have specifically binding stripes with semaphoring b1b2 protein, B16F10, and A431 cells at 39KDa, 100KDa and 130KDa, respectively. Positive expression was detected both in cutanuem carcinoma line and tissue and it mostly located in cell membranes. MMT assay revealed dose-relate and time-relate inhibitory effect of semaphorin mAb on A431 and B16F10. Colony inhibition tests also showed dose-relate inhibitory effects. Western blotting demonstrated the expression of apoptosis and proliferation-related protein and changes in signal pathway. In conclusion, we demonstrated that semaphorin is highly expressed on the tumor cell-surfaces and RIT with semaphorin mAb has effect in inhibiting proliferation and accelerating apoptosis of tumor cells.

Hypofractionated radiotherapy induces miR-34a expression and enhances apoptosis in human nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) is a relatively radiosensitive disease. However, the therapeutic effects of radiotherapy are not always satisfactory due to radioresistance. The hypofractionated schema is currently widely used in clinical practice. In the present study, we investigated the effects of hypofractionated radiotherapy on NPC cells and explored the mechanisms involved. In addition, we aimed to determine the role of miR-34a in the effects of hypofractionated radiotherapy and whether these effects occur in a p53-dependent manner. For this purpose, we used CNE1 and CNE2 NPC cells which were subjected to hyperfractionated and hypofractionated radiotherapy. The viability of the cells was measured by MTT assay and acridine orange (AO) and ethidium bromide (EB) staining was used to observe morphological changes. In addition, Annexin V-propidium iodide (PI) staining and flow cytometry were used to determine the number of apoptotic cells and mRNA and protein expression was measured by qPCR and western blot analysis, respectively. The results revealed that hypofractionated radiotherapy enhanced apoptosis and increased the expression of miR-34a and p53 in the NPC cells. In addition, it stimulated p53 promoter activity and downregulated the protein expression of c-Myc in the human NPC cells. Furthermore, the knockdown of miR-34a suppressed the growth inhibitory effects induced by hypofractionated radiotherapy. Thus, our results suggest that the enhanced apoptosis of NPC cells may be associated with the miR-34a-mediated suppression of c-Myc in a p53-dependent manner.

Anti-L1CAM radioimmunotherapy is more effective with the radiolanthanide terbium-161 compared to lutetium-177 in an ovarian cancer model

PURPOSE

The L1 cell adhesion molecule (L1CAM) is considered a valuable target for therapeutic intervention in different types of cancer. Recent studies have shown that anti-L1CAM radioimmunotherapy (RIT) with (67)Cu- and (177)Lu-labelled internalising monoclonal antibody (mAb) chCE7 was effective in the treatment of human ovarian cancer xenografts. In this study, we directly compared the therapeutic efficacy of anti-L1CAM RIT against human ovarian cancer under equitoxic conditions with the radiolanthanide (177)Lu and the potential alternative (161)Tb in an ovarian cancer therapy model.

METHODS

Tb was produced by neutron bombardment of enriched (160)Gd targets. (161)Tb and (177)Lu were used for radiolabelling of DOTA-conjugated antibodies. The in vivo behaviour of the radioimmunoconjugates (RICs) was assessed in IGROV1 tumour-bearing nude mice using biodistribution experiments and SPECT/CT imaging. After ascertaining the maximal tolerated doses (MTD) the therapeutic impact of 50 % MTD of (177)Lu- and (161)Tb-DOTA-chCE7 was evaluated in groups of ten mice by monitoring the tumour size of subcutaneous IGROV1 tumours.

RESULTS

The average number of DOTA ligands per antibody was 2.5 and maximum specific activities of 600 MBq/mg were achieved under identical radiolabelling conditions. RICs were stable in human plasma for at least 48 h. (177)Lu- and (161)Tb-DOTA-chCE7 showed high tumour uptake (37.8-39.0 %IA/g, 144 h p.i.) with low levels in off-target organs. SPECT/CT images confirmed the biodistribution data. (161)Tb-labelled chCE7 revealed a higher radiotoxicity in nude mice (MTD: 10 MBq) than the (177)Lu-labelled counterpart (MTD: 12 MBq). In a comparative therapy study with equitoxic doses, tumour growth inhibition was better by 82.6 % for the (161)Tb-DOTA-chCE7 than the (177)Lu-DOTA-chCE7 RIT.

CONCLUSIONS

Our study is the first to show that anti-L1CAM (161)Tb RIT is more effective compared to (177)Lu RIT in ovarian cancer xenografts. These results suggest that (161)Tb is a promising candidate for future clinical applications in combination with internalising antibodies.

The production of radionuclides for nuclear medicine from a compact, low-energy accelerator system

INTRODUCTION

The field of nuclear medicine is reliant on radionuclides for medical imaging procedures and radioimmunotherapy (RIT). The recent shut-downs of key radionuclide producers have highlighted the fragility of the current radionuclide supply network, however. To ensure that nuclear medicine can continue to grow, adding new diagnostic and therapy options to healthcare, novel and reliable production methods are required. Siemens are developing a low-energy, high-current - up to 10 MeV and 1 mA respectively - accelerator. The capability of this low-cost, compact system for radionuclide production, for use in nuclear medicine procedures, has been considered.

METHODOLOGY

The production of three medically important radionuclides - (89)Zr, (64)Cu, and (103)Pd - has been considered, via the (89)Y(p,n), (64)Ni(p,n) and (103)Rh(p,n) reactions, respectively. Theoretical cross-sections were generated using TALYS and compared to experimental data available from EXFOR. Stopping power values generated by SRIM have been used, with the TALYS-generated excitation functions, to calculate potential yields and isotopic purity in different irradiation regimes.

RESULTS

The TALYS excitation functions were found to have a good agreement with the experimental data available from the EXFOR database. It was found that both (89)Zr and (64)Cu could be produced with high isotopic purity (over 99%), with activity yields suitable for medical diagnostics and therapy, at a proton energy of 10MeV. At 10MeV, the irradiation of (103)Rh produced appreciable quantities of (102)Pd, reducing the isotopic purity. A reduction in beam energy to 9.5MeV increased the radioisotopic purity to 99% with only a small reduction in activity yield.

CONCLUSION

This work demonstrates that the low-energy, compact accelerator system under development by Siemens would be capable of providing sufficient quantities of (89)Zr, (64)Cu, and (103)Pd for use in medical diagnostics and therapy. It is suggested that the system could be used to produce many other isotopes currently useful to nuclear medicine.

Comparison of conjugation strategies of cross-bridged macrocyclic chelators with cetuximab for copper-64 radiolabeling and PET imaging of EGFR in colorectal tumor-bearing mice

Epidermal growth-factor receptor (EGFR) is overexpressed in a wide variety of solid tumors and has served as a well-characterized target for cancer imaging and therapy. Cetuximab was the first mAb targeting EGFR approved by the FDA for the treatment of metastatic colorectal and head and neck cancers. Previous studies showed that (64)Cu (T1/2 = 12.7 h; β(+) (17.4%)) labeled DOTA-cetuximab showed promise for PET imaging of EGFR-positive tumors; however the in vivo stability of this compound has been questioned. In this study, two recently developed cross-bridged macrocyclic chelators (CB-TE1A1P and CB-TE1K1P) were conjugated to cetuximab using standard NHS coupling procedures and/or strain-promoted azide-alkyne cycloaddition (SPAAC) methodologies. The radiolabeling and in vitro/vivo evaluation of the resulting cetuximab conjugates were compared. Improved Cu-64 labeling efficiency and high specific activity (684 kBq/μg, decay corrected to the end of bombardment) were obtained with the CB-TE1K1P-PEG4-click-cetuximab conjugate. Saturation binding assays indicated that the prepared cetuximab conjugates had comparable affinity (1.32-2.00 nM) in the HCT116 human colorectal tumor cell membranes. In the subsequent in vivo evaluation, (64)Cu-CB-TE1K1P-PEG4-click-cetuximab demonstrated more rapid renal clearance with a higher tumor/nontumor ratio than other (64)Cu-labeled cetuximab conjugates, and it shows the greatest promise for imaging and therapy of EGFR-positive tumors.

⁶⁴Cu-labeled inhibitors of prostate-specific membrane antigen for PET imaging of prostate cancer

Prostate-specific membrane antigen (PSMA) is a well-recognized target for identification and therapy of a variety of cancers. Here we report five (64)Cu-labeled inhibitors of PSMA, [(64)Cu]3-7, which are based on the lysine-glutamate urea scaffold and utilize a variety of macrocyclic chelators, namely NOTA(3), PCTA(4), Oxo-DO3A(5), CB-TE2A(6), and DOTA(7), in an effort to determine which provides the most suitable pharmacokinetics for in vivo PET imaging. [(64)Cu]3-7 were prepared in high radiochemical yield (60-90%) and purity (>95%). Positron emission tomography (PET) imaging studies of [(64)Cu]3-7 revealed specific accumulation in PSMA-expressing xenografts (PSMA+ PC3 PIP) relative to isogenic control tumor (PSMA- PC3 flu) and background tissue. The favorable kinetics and high image contrast provided by CB-TE2A chelated [(64)Cu]6 suggest it as the most promising among the candidates tested. That could be due to the higher stability of [(64)Cu]CB-TE2A as compared with [(64)Cu]NOTA, [(64)Cu]PCTA, [(64)Cu]Oxo-DO3A, and [(64)Cu]DOTA chelates in vivo.

Radiolabeled Cetuximab Conjugates for EGFR Targeted Cancer Diagnostics and Therapy

The epidermal growth factor receptor (EGFR) has evolved over years into a main molecular target for the treatment of different cancer entities. In this regard, the anti-EGFR antibody cetuximab has been approved alone or in combination with: (a) chemotherapy for treatment of colorectal and head and neck squamous cell carcinoma and (b) with external radiotherapy for treatment of head and neck squamous cell carcinoma. The conjugation of radionuclides to cetuximab in combination with the specific targeting properties of this antibody might increase its therapeutic efficiency. This review article gives an overview of the preclinical studies that have been performed with radiolabeled cetuximab for imaging and/or treatment of different tumor models. A particularly promising approach seems to be the treatment with therapeutic radionuclide-labeled cetuximab in combination with external radiotherapy. Present data support an important impact of the tumor micromilieu on treatment response that needs to be further validated in patients. Another important challenge is the reduction of nonspecific uptake of the radioactive substance in metabolic organs like liver and radiosensitive organs like bone marrow and kidneys. Overall, the integration of diagnosis, treatment and monitoring as a theranostic approach appears to be a promising strategy for improvement of individualized cancer treatment.