Treatment of experimental pancreatic cancer with 213-Bismuth-labeled chimeric antibody to single-strand DNA

A Theranostic Approach to Imaging and Treating Melanoma with 203Pb/212Pb-Labeled Antibody Targeting Melanin

Metastatic melanoma is a deadly disease that claims thousands of lives each year despite the introduction of several immunotherapeutic agents into the clinic over the past decade, inspiring the development of novel therapeutics and the exploration of combination therapies. Our investigations target melanin pigment with melanin-specific radiolabeled antibodies as a strategy to treat metastatic melanoma. In this study, a theranostic approach was applied by first labeling a chimeric antibody targeting melanin, c8C3, with the SPECT radionuclide 203Pb for microSPECT/CT imaging of C57Bl6 mice bearing B16-F10 melanoma tumors. Imaging was followed by radioimmunotherapy (RIT), whereby the c8C3 antibody is radiolabeled with a 212Pb/212Bi "in vivo generator", which emits cytotoxic alpha particles. Using microSPECT/CT, we collected sequential images of B16-F10 murine tumors to investigate antibody biodistribution. Treatment with the 212Pb/212Bi-labeled c8C3 antibody demonstrated a dose-response in tumor growth rate in the 5-10 µCi dose range when compared to the untreated and radiolabeled control antibody and a significant prolongation in survival. No hematologic or systemic toxicity of the treatment was observed. However, administration of higher doses resulted in a biphasic tumor dose response, with the efficacy of treatment decreasing when the administered doses exceeded 10 µCi. These results underline the need for more pre-clinical investigation of targeting melanin with 212Pb-labeled antibodies before the clinical utility of such an approach can be assessed.

Radioimmunotherapy of Pancreatic Ductal Adenocarcinoma: A Review of the Current Status of Literature

Pancreatic ductal adenocarcinoma (PDAC) has long been associated with low survival rates. A lack of accurate diagnostic tests and limited treatment options contribute to the poor prognosis of PDAC. Radioimmunotherapy using α- or β-emitting radionuclides has been identified as a potential treatment for PDAC. By harnessing the cytotoxicity of α or β particles, radioimmunotherapy may overcome the anatomic and physiological factors which traditionally make PDAC resistant to most conventional treatments. Appropriate selection of target receptors and the development of selective and cytotoxic radioimmunoconjugates are needed to achieve the desired results of radioimmunotherapy. The aim of this review is to examine the growing preclinical and clinical trial evidence regarding the application of α and β radioimmunotherapy for the treatment of PDAC. A systematic search of MEDLINE® and Scopus databases was performed to identify 34 relevant studies conducted on α or β radioimmunotherapy of PDAC. Preclinical results demonstrated α and β radioimmunotherapy provided effective tumour control. Clinical studies were limited to investigating β radioimmunotherapy only. Phase I and II trials observed disease control rates of 11.2%-57.9%, with synergistic effects noted for combination therapies. Further developments and optimisation of treatment regimens are needed to improve the clinical relevance of α and β radioimmunotherapy in PDAC.

Evaluation of novel highly specific antibodies to cancer testis antigen Centrin-1 for radioimmunoimaging and radioimmunotherapy of pancreatic cancer

Background

Pancreatic ductal adenocarcinoma (PDAC) accounts for >90% of pancreatic malignancies, and has median survival of <6 months. There is an urgent need for diagnostic and therapeutic options for PDAC. Centrin1 (CETN1) is a novel member of Cancer/Testis Antigens, with a 25‐fold increase of CETN1 gene expression in PDX from PDAC patients. The absence of selective anti‐CETN1 antibodies is hampering CETN1 use for diagnosis and therapy. Here we report the generation of highly specific for CETN1 antibodies and their evaluation for radioimmunoimaging and radioimmunotherapy (RIT) of experimental PDAC.

Methods

The antibodies to CETN1 were generated via mice immunization with immunogenic peptide distinguishing CETN1 from CETN2. Patient tumor microarrays were used to evaluate the binding of the immune serum to PDAC versus normal pancreas. The antibodies were tested for their preferential binding to CETN1 over CETN2 by ELISA. Mice bearing PDAC MiaPaCa2 xenografts were imaged with microSPECT/CT and treated with ²¹³Bi‐ and ¹⁷⁷Lu‐labeled antibodies to CETN1.

Results

Immune serum bind to 50% PDAC cases on patient tumor microarrays with no specific binding to normal pancreas. Antibodies demonstrated preferential binding to CETN1 versus CETN2. Antibody 69‐11 localized to PDAC xenografts in mice in vivo and ex vivo. RIT of PDAC xenografts with ²¹³Bi‐labeled antibodies was effective, safe, and CETN1‐specific.

Conclusions

The results demonstrate the ability of these novel antibodies to detect CETN1 both in vitro and in vivo; as well, the RIT treatment of experimental PDAC when radiolabeled with ²¹³Bi is highly efficient and safe. Further evaluation of these novel reagents for diagnosis and treatment of PDAC is warranted.

Updated developments on molecular imaging and therapeutic strategies directed against necrosis

Cell death plays important roles in living organisms and is a hallmark of numerous disorders such as cardiovascular diseases, sepsis and acute pancreatitis. Moreover, cell death also plays a pivotal role in the treatment of certain diseases, for example, cancer. Noninvasive visualization of cell death contributes to gained insight into diseases, development of individualized treatment plans, evaluation of treatment responses, and prediction of patient prognosis. On the other hand, cell death can also be targeted for the treatment of diseases. Although there are many ways for a cell to die, only apoptosis and necrosis have been extensively studied in terms of cell death related theranostics. This review mainly focuses on molecular imaging and therapeutic strategies directed against necrosis. Necrosis shares common morphological characteristics including the rupture of cell membrane integrity and release of cellular contents, which provide potential biomarkers for visualization of necrosis and necrosis targeted therapy. In the present review, we summarize the updated joint efforts to develop molecular imaging probes and therapeutic strategies targeting the biomarkers exposed by necrotic cells. Moreover, we also discuss the challenges in developing necrosis imaging probes and propose several biomarkers of necrosis that deserve to be explored in future imaging and therapy research.

Selectivity Conversion of Protease Inhibitory Antibodies

Solid tumors are inherently difficult to treat because of large regions of hypoxia and are often chemotherapy- or radiotherapy-resistant. It seems that cancer stem cells reside in hypoxic and adjacent necrotic tumor areas. Therefore, new treatments that are highly selective for tumors and can eradicate cells in both hypoxic and necrotic tumor regions are desirable. Antibody α-radioconjugates couple an α-emitting radionuclide with the specificity of a tumor-targeting monoclonal antibody. The large mass and energy of α-particles result in radiation dose delivery within a smaller area independent of oxygen concentration, thus matching key criteria for killing hypoxic tumor cells. With advances in radionuclide production and chelation chemistry, α-radioconjugate therapy is regaining interest as a cancer therapy. Here, we will review current literature examining radioconjugate therapy specifically targeting necrotic and hypoxic tumor cells and outline how α-radioconjugate therapy could be used to treat tumor regions harboring more resistant cancer cell types.

Statement of Significance

Tumor-targeting antibodies are excellent vehicles for the delivery of toxic payloads directly to the tumor site. Tumor hypoxia and necrosis promote treatment recurrence, resistance, and metastasis. Targeting these areas with antibody α-radioconjugates would aid in overcoming treatment resistance.

Selectivity Conversion of Protease Inhibitory Antibodies

Background: Proteases are one of the largest pharmaceutical targets for drug developments. Their dysregulations result in a wide variety of diseases. Because proteolytic networks usually consist of protease family members that share high structural and catalytic homology, distinguishing them using small molecule inhibitors is often challenging. To achieve specific inhibition, this study described a novel approach for the generation of protease inhibitory antibodies. As a proof of concept, we aimed to convert a matrix metalloproteinase (MMP)-14 specific inhibitor to MMP-9 specific inhibitory antibodies with high selectivity. Methods: An error-prone single-chain Fv (scFv) library of an MMP-14 inhibitor 3A2 was generated for yeast surface display. A dual-color competitive FACS was developed for selection on MMP-9 catalytic domain (cdMMP-9) and counter-selection on cdMMP-14 simultaneously, which were fused/conjugated with different fluorophores. Isolated MMP-9 inhibitory scFvs were biochemically characterized by inhibition assays on MMP-2/-9/-12/-14, proteolytic stability tests, inhibition mode determination, competitive ELISA with TIMP-2 (a native inhibitor of MMPs), and paratope mutagenesis assays. Results: We converted an MMP-14 specific inhibitor 3A2 into a panel of MMP-9 specific inhibitory antibodies with dramatic selectivity shifts of 690-4,500 folds. Isolated scFvs inhibited cdMMP-9 at nM potency with high selectivity over MMP-2/-12/-14 and exhibited decent proteolytic stability. Biochemical characterizations revealed that these scFvs were competitive inhibitors binding to cdMMP-9 near its reaction cleft via their CDR-H3s. Conclusions: This study developed a novel approach able to convert the selectivity of inhibitory antibodies among closely related protease family members. This methodology can be directly applied for mAbs inhibiting many proteases of biomedical importance.

212Pb-labeled B7-H3-targeting antibody for pancreatic cancer therapy in mouse models

INTRODUCTION

We recently validated monoclonal antibody (mAb) 376.96 as an effective carrier for targeted α-particle radioimmunotherapy (RIT) with ²¹²Pb in ovarian cancer mouse models. In this study, we tested the binding of radiolabeled mAb 376.96 to human pancreatic ductal adenocarcinoma (PDAC) cells and localization in xenografts in immune-deficient mice and evaluated ²¹²Pb-labeled 376.96 (²¹²Pb-376.96) for PDAC therapy.

METHODS

In vitro Scatchard assays assessed the specific binding of ²¹²Pb-376.96 to human PDAC3 adherent differentiated cells and non-adherent cancer initiating cells (CICs) dissociated from tumorspheres. In vitro clonogenic assays were used to measure the proliferation of adherent PDAC3 cells and CIC-enriched tumorspheres treated with ²¹²Pb-376.96 or the irrelevant isotype-matched ²¹²Pb-F3-C25. Mice bearing patient derived pancreatic cancer Panc039 xenografts were i.v. injected with 0.17-0.70 MBq ²¹²Pb-376.96 or isotype control ²¹²Pb-F3-C25, and used for biodistribution and tumor growth inhibition studies. Mice bearing orthotopic PDAC3 xenografts were i.v. co-injected with ^99mTc-376.96 and ¹²⁵I-F3-C25 and used for biodistribution studies.

RESULTS

²¹²Pb-376.96 specifically bound to PDAC3 adherent and dissociated tumorsphere CICs; K_d values averaged 9.0 and 21.7 nM, respectively, with 10⁴-10⁵ binding sites/cell. ²¹²Pb-376.96 inhibited the clonogenic survival of PDAC3 cells or CICs dissociated from tumorspheres 3-6 times more effectively than isotype-matched control ²¹²Pb-F3-C25. Panc039 s.c. tumors showed significantly higher uptake of ²¹²Pb-376.96 (14.0 ± 2.1% ID/g) compared to ²¹²Pb-F3-C25 (6.5 ± 0.9% ID/g, p < .001) at 24 h after dosing. Orthotopic PDAC3 tumors showed significantly higher uptake of ^99mTc-376.96 (6.4 ± 1.8% ID/g) compared to ¹²⁵I-F3-C25 (3.9 ± 0.9% ID/g, p < .05) at 24 h after dosing. Panc039 tumor growth was significantly inhibited by ²¹²Pb-376.96 compared to ²¹²Pb-F3-C25 or non-treated control tumors (p < .05).

CONCLUSION

Our results provide evidence for the efficacy of B7-H3 targeted RIT against preclinical models of pancreatic ductal adenocarcinoma (PDAC) and support future studies with ²¹²Pb-376.96 in combination with chemotherapy to potentiate efficacy against PDAC.

Cathepsin S-cleavable, multi-block HPMA copolymers for improved SPECT/CT imaging of pancreatic cancer

This work continues our efforts to improve the diagnostic and radiotherapeutic effectiveness of nanomedicine platforms by developing approaches to reduce the non-target accumulation of these agents. Herein, we developed multi-block HPMA copolymers with backbones that are susceptible to cleavage by cathepsin S, a protease that is abundantly expressed in tissues of the mononuclear phagocyte system (MPS). Specifically, a bis-thiol terminated HPMA telechelic copolymer containing 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Three maleimide modified linkers with different sequences, including cathepsin S degradable oligopeptide, scramble oligopeptide and oligo ethylene glycol, were subsequently synthesized and used for the extension of the HPMA copolymers by thiol-maleimide click chemistry. All multi-block HPMA copolymers could be labeled by (177)Lu with high labeling efficiency and exhibited high serum stability. In vitro cleavage studies demonstrated highly selective and efficient cathepsin S mediated cleavage of the cathepsin S-susceptible multi-block HPMA copolymer. A modified multi-block HPMA copolymer series capable of Förster Resonance Energy Transfer (FRET) was utilized to investigate the rate of cleavage of the multi-block HPMA copolymers in monocyte-derived macrophages. Confocal imaging and flow cytometry studies revealed substantially higher rates of cleavage for the multi-block HPMA copolymers containing the cathepsin S-susceptible linker. The efficacy of the cathepsin S-cleavable multi-block HPMA copolymer was further examined using an in vivo model of pancreatic ductal adenocarcinoma. Based on the biodistribution and SPECT/CT studies, the copolymer extended with the cathepsin S susceptible linker exhibited significantly faster clearance and lower non-target retention without compromising tumor targeting. Overall, these results indicate that exploitation of the cathepsin S activity in MPS tissues can be utilized to substantially lower non-target accumulation, suggesting this is a promising approach for the development of diagnostic and radiotherapeutic nanomedicine platforms.

Relevance of radiobiological concepts in radionuclide therapy of cancer

PURPOSE

Radionuclide therapy (RNT) is a rapidly growing area of clinical nuclear medicine, wherein radionuclides are employed to deliver cytotoxic dose of radiation to the diseased cells/tissues. During RNT, radionuclides are either directly administered or delivered through biomolecules targeting the diseased site. RNT has been clinically used for diverse range of diseases including cancer, which is the focus of the review.

CONCLUSIONS

The major emphasis in RNT has so far been given towards developing peptides/antibodies and other molecules to conjugate a variety of therapeutic radioisotopes for improved targeting/delivery of radiation dose to the tumor cells. Despite that, many of the RNT approaches have not achieved their desired therapeutic success probably due to poor knowledge about complex and dynamic (i) fate of radiolabeled molecules; (ii) radiation dose delivered; (iii) cellular heterogeneity in tumor mass; and (iv) cellular radiobiological response. Based on understanding gathered during recent years, it may be stated that besides the absorbed dose, the net radiobiological response of tumor/normal cells also determines the clinical response of radiotherapeutic modalities including RNT. The radiosensitivity of tumor/normal cells is governed by radiobiological phenomenon such as radiation-induced bystander effect, genomic instability, adaptive response and low dose hyper-radiosensitivity. These concepts have been well investigated in the context of external beam radiotherapy, but their clinical implications during RNT have received meagre attention. In this direction, a few studies performed using in vitro and in vivo models envisage the possibilities of exploiting the radiobiological knowledge for improved therapeutic outcome of RNT.

Beta emitters rhenium-188 and lutetium-177 are equally effective in radioimmunotherapy of HPV-positive experimental cervical cancer

Cervical cancer caused by the infection with the human papillomavirus (HPV) remains the fourth leading killer of women worldwide. Therefore, more efficacious treatments are needed. We are developing radioimmunotherapy (RIT) of HPV‐positive cervical cancers by targeting E6 and E7 viral oncoproteins expressed by the cancer cells with the radiolabeled monoclonal antibodies (mAbs). To investigate the influence of different radionuclides on the RIT efficacy—we performed RIT of experimental cervical cancer with Rhenium‐188 (¹⁸⁸Re) and Lutetium‐177 (¹⁷⁷Lu)‐labeled mAb C1P5 to E6. The biodistribution of ¹⁸⁸Re‐ and ¹⁷⁷Lu‐labeled C1P5 was performed in nude female mice bearing CasKi cervical cancer xenografts and the radiation dosimetry calculations for the tumors and organs were carried out. For RIT the mice were treated with 7.4 MBq of either ¹⁸⁸Re‐C1P5 or ¹⁷⁷Lu‐C1P5 or left untreated, and observed for their tumor size for 28 days. The levels of ¹⁸⁸Re‐ and ¹⁷⁷Lu‐C1P5 mAbs‐induced double‐strand breaks in CasKi tumors were compared on days 5 and 10 post treatment by staining with anti‐gamma H2AX antibody. The radiation doses to the heart and lungs were similar for both ¹⁷⁷Lu‐C1P5 and ¹⁸⁸Re‐C1P5. The dose to the liver was five times higher for ¹⁷⁷Lu‐C1P5. The doses to the tumor were 259 and 181 cGy for ¹⁷⁷Lu‐C1P5 and ¹⁸⁸Re‐C1P5, respectively. RIT with either ¹⁷⁷Lu‐C1P5 or ¹⁸⁸Re‐C1P5 was equally effective in inhibiting tumor growth when each was compared to the untreated controls (P = 0.001). On day 5 there was a pronounced staining for gamma H2AX foci in ¹⁷⁷Lu‐C1P5 group only and on day 10 it was observed in both ¹⁷⁷Lu‐C1P5 and ¹⁸⁸Re‐C1P5 groups. ¹⁸⁸Re‐ and ¹⁷⁷Lu‐labeled mAbs were equally effective in arresting the growth of CasKi cervical tumors. Thus, both of these radionuclides are candidates for the clinical trials of this approach in patients with advanced, recurrent or metastatic cervical cancer.

Targeted radionuclide therapies for pancreatic cancer

Pancreatic malignancies, the fourth leading cause of cancer deaths, have an aggressive behavior with poor prognosis, resulting in a 5-year survival rate of only 4%. It is typically a silent malignancy until patients develop metastatic disease. Targeted radionuclide therapies of cancer such as radiolabeled peptides, which bind to the receptors overexpressed by cancer cells and radiolabeled antibodies to tumor-specific antigens provide a viable alternative to chemotherapy and external beam radiation of metastatic cancers. Multiple clinical trials of targeted radionuclide therapy of pancreatic cancer have been performed in the last decade and demonstrated safety and potential efficacy of radionuclide therapy for treatment of this formidable disease. Although a lot of progress has been made in treatment of pancreatic neuroendocrine tumors with radiolabeled (90)Y and (177)Lu somatostatin peptide analogs, pancreatic adenocarcinomas remain a major challenge. Novel approaches such as peptides and antibodies radiolabeled with alpha emitters, pre-targeting, bispecific antibodies and biological therapy based on the radioactive tumorlytic bacteria might offer a potential breakthrough in treatment of pancreatic adenocarcinomas.

Naive and radiolabeled antibodies to E6 and E7 HPV-16 oncoproteins show pronounced antitumor activity in experimental cervical cancer

BACKGROUND

In spite of profound reduction in incidence, cervical cancer claims >275,000 lives annually. Previously we demonstrated efficacy and safety of radioimmunotherapy directed at HPV16 E6 oncoprotein in experimental cervical cancer.

MATERIALS & METHODS

We undertook a direct comparison of targeting E7 and E6 oncoproteins with specific (188)Rhenium-labeled monoclonal antibodies in CasKi subcutaneous xenografts of cervical cancer cells in mice.

RESULTS

The most significant tumor inhibition was seen in radioimmunotherapy-treated mice, followed by the unlabeled monoclonal antibodies to E6 and E7. No hematological toxicity was observed. Immunohistochemistry suggests that the effect of unlabeled antibodies is C3 complement mediated.

CONCLUSION

We have demonstrated for the first time that radioimmunotherapy directed toward E7 oncoprotein inhibits experimental tumors growth, decreases E7 expression and may offer a novel approach to cervical cancer therapy.

Radioimmunotherapy--a potential novel tool for pancreatic cancer therapy?

Pancreatic cancer is one of the most severe cancers and is predicted to rise up to the number two cancer killer by 2030. The ineffective treatment options available and that the cancer is silent until very late in its course are the main reasons for the poor outcome of the disease. Surgery is the only curative option but only available for 10-15 % of the patients, but even then many relapse due to metastases. Many new treatments are under way, and one of the promising ones is radioimmunotherapy (RIT). This review includes clinical trials with RIT in pancreatic cancer as well as a review of adverse events observed during treatment of other solid tumors. Additionally, preclinical studies are reviewed with emphasis on effect, adverse events, the tumor targeting as well as isotope function. Four clinical trials with pancreatic cancer have been conducted with positive results, and one phase III trial is underway. The use of RIT in patients with solid tumors has proven to be well tolerated, and the adverse effects are almost exclusively hematological. Multiple targets and isotopes have been evaluated preclinically, alone, or in combination with existing drug options. Smaller tumors have in several studies completely regressed, while larger ones have stabilized or progressed more slowly. Pancreatic cancer is one of the solid tumors where RIT have reached the longest. The tumor heterogeneity will most likely leave room for more than one treatment option, and several aspiring therapies are under way. RIT may become part of multimodality tumor-directed therapy for pancreatic cancer.