Chemotherapy synergizes with radioimmunotherapy targeting La autoantigen in tumors

Imaging of cell death in malignancy: Targeting pathways or phenotypes?

Cell death is fundamental in health and disease and resisting cell death is a hallmark of cancer. Treatment of malignancy aims to cause cancer cell death, however current clinical imaging of treatment response does not specifically image cancer cell death but assesses this indirectly either by changes in tumor size (using x-ray computed tomography) or metabolic activity (using 2-[18F]fluoro-2-deoxy-glucose positron emission tomography). The ability to directly image tumor cell death soon after commencement of therapy would enable personalised response adapted approaches to cancer treatment that is presently not possible with current imaging, which is in many circumstances neither sufficiently accurate nor timely. Several cell death pathways have now been identified and characterised that present multiple potential targets for imaging cell death including externalisation of phosphatidylserine and phosphatidylethanolamine, caspase activation and La autoantigen redistribution. However, targeting one specific cell death pathway carries the risk of not detecting cell death by other pathways and it is now understood that cancer treatment induces cell death by different and sometimes multiple pathways. An alternative approach is targeting the cell death phenotype that is "agnostic" of the death pathway. Cell death phenotypes that have been targeted for cell death imaging include loss of plasma membrane integrity and dissipation of the mitochondrial membrane potential. Targeting the cell death phenotype may have the advantage of being a more sensitive and generalisable approach to cancer cell death imaging. This review describes and summarises the approaches and radiopharmaceuticals investigated for imaging cell death by targeting cell death pathways or cell death phenotype.

The RNA-binding protein La/SSB associates with radiation-induced DNA double-strand breaks in lung cancer cell lines

BACKGROUND

Platinum-based chemotherapy and radiotherapy are standard treatments for non-small cell lung cancer, which is the commonest, most lethal cancer worldwide. As a marker of treatment-induced cancer cell death, we have developed a radiodiagnostic imaging antibody, which binds to La/SSB. La/SSB is an essential, ubiquitous ribonuclear protein, which is over expressed in cancer and plays a role in resistance to cancer therapies.

AIM

In this study, we examined radiation-induced DNA double strand breaks (DSB) in lung cancer cell lines and examined whether La/SSB associated with these DSB.

METHOD

Three lung cancer lines (A549, H460 and LL2) were irradiated with different X-ray doses or X-radiated with a 5 Gy dose and examined at different time-points post-irradiation for DNA DSB in the form of γ-H2AX and Rad51 foci. Using fluorescence microscopy, we examined whether La/SSB and γ-H2AX co-localise and performed proximity ligation assay (PLA) and co-immunoprecipitation to confirm the interaction of these proteins.

RESULTS

We found that the radio-resistant A549 cell line compared to the radio-sensitive H460 cell line showed faster resolution of radiation-induced γ-H2AX foci over time. Conversely, we found more co-localised γ-H2AX and La/SSB foci by PLA in irradiated A549 cells.

CONCLUSION

The co-localisation of La/SSB with radiation-induced DNA breaks suggests a role of La/SSB in DNA repair, however further experimentation is required to validate this.

Fc gamma receptor is not required for in vivo processing of radio- and drug-conjugates of the dead tumor cell-targeting monoclonal antibody, APOMAB®

The Fc region of a monoclonal antibody (mAb) can play a crucial role in its biodistribution and therapeutic activity. The chimeric mAb, chDAB4 (APOMAB®), which binds to dead tumor cells after DNA-damaging anticancer treatment, has been studied pre-clinically in both diagnostic and therapeutic applications in cancer. Given that macrophages contribute to the tumor accumulation of chDAB4 and its potency as an antibody drug conjugate in vivo, we next wanted to determine whether the Fc region of the chDAB4 mAb also contributed. We found that, regardless of prior labeling with chDAB4, dead EL4 lymphoma or Lewis Lung (LL2) tumor cells were phagocytosed equally by wild-type or Fcγ knock-down macrophage cell lines. A similar result was seen with bone marrow-derived macrophages from wild-type, Fcγ knock-out (KO) and NOTAM mice that express Fcγ but lack immunoreceptor tyrosine-based activation motif (ITAM) signaling. Among EL4 tumor-bearing wild-type, Fcγ KO or NOTAM mice, no differences were observed in post-chemotherapy uptake of ⁸⁹Zr-labeled chDAB4. Similarly, no differences were observed between LL2 tumor-bearing wild-type and Fcγ KO mice in post-chemotherapy uptake of ⁸⁹Zr-chDAB4. Also, the post-chemotherapy activity of a chDAB4-antibody drug conjugate (ADC) directed against LL2 tumors did not differ among tumor-bearing wild-type, Fcγ KO and NOTAM mice, nor did the proportions and characteristics of the LL2 tumor immune cell infiltrates differ significantly among these mice. In conclusion, Fc-FcγR interactions are not essential for the diagnostic or therapeutic applications of chDAB4 conjugates because the tumor-associated macrophages, which engulf the chDAB4-labelled dead cells, respond to endogenous 'eat me' signals rather than depend on functional FcγR expression for phagocytosis.

ImmunoPET imaging of hematological malignancies: From preclinical promise to clinical reality

Immuno-positron emission tomography (immunoPET) imaging is a paradigm-shifting imaging technique for whole-body and all-lesion tumor detection, based on the combined specificity of tumor-targeting vectors [e.g., monoclonal antibodies (mAbs), nanobodies, and bispecific antibodies] and the sensitivity of PET imaging. By noninvasively, comprehensively, and serially revealing heterogeneous tumor antigen expression, immunoPET imaging is gradually improving the theranostic prospects for hematological malignancies. In this review, we summarize the available literature regarding immunoPET in imaging hematological malignancies. We also highlight the pros and cons of current conjugation strategies, and modular chemistry that can be leveraged to develop novel immunoPET probes for hematological malignancies. Lastly, we discuss the use of immunoPET imaging in guiding antibody drug development.

Positron Emission Tomographic Imaging of Tumor Cell Death Using Zirconium-89-Labeled APOMAB® Following Cisplatin Chemotherapy in Lung and Ovarian Cancer Xenograft Models

PURPOSE

Early detection of tumor treatment responses represents an unmet clinical need with no approved noninvasive methods. DAB4, or its chimeric derivative, chDAB4 (APOMAB®) is an antibody that targets the Lupus associated antigen (La/SSB). La/SSB is over-expressed in malignancy and selectively targeted by chDAB4 in cancer cells dying from DNA-damaging treatment. Therefore, chDAB4 is a unique diagnostic tool that detects dead cancer cells and thus could distinguish between treatment responsive and nonresponsive patients.

PROCEDURES

In clinically relevant tumor models, mice bearing subcutaneous xenografts of human ovarian or lung cancer cell lines or intraperitoneal ovarian cancer xenografts were untreated or given chemotherapy followed 24h later by chDAB4 radiolabeled with [⁸⁹Zr]Zr^IV. Tumor responses were monitored using bioluminescence imaging and caliper measurements. [⁸⁹Zr]Zr-chDAB4 uptake in tumor and normal tissues was measured using an Albira SI Positron-Emission Tomography (PET) imager and its biodistribution was measured using a Hidex gamma-counter.

RESULTS

Tumor uptake of [⁸⁹Zr]Zr-chDAB4 was detected in untreated mice, and uptake significantly increased in both human lung and ovarian tumors after chemotherapy, but not in normal tissues.

CONCLUSION

Given that tumors, rather than normal tissues, were targeted after chemotherapy, these results support the clinical development of chDAB4 as a radiodiagnostic imaging agent and as a potential predictive marker of treatment response.

Improved non-invasive positron emission tomographic imaging of chemotherapy-induced tumor cell death using Zirconium-89-labeled APOMAB®

Purpose

The chimeric monoclonal antibody (mAb) chDAB4 (APOMAB®) targets the Lupus associated (La)/Sjögren Syndrome-B (SSB) antigen, which is over-expressed in tumors but only becomes available for antibody binding in dead tumor cells. Hence, chDAB4 may be used as a novel theranostic tool to distinguish between responders and nonresponders early after chemotherapy. Here, we aimed to ascertain which positron emitter, Zirconium-89 ([⁸⁹Zr]Zr^IV) or Iodine-124 ([¹²⁴I]I), was best suited to label chDAB4 for post-chemotherapy PET imaging of tumor-bearing mice and to determine which of two different bifunctional chelators provided optimal tumor imaging by PET using [⁸⁹Zr]Zr^IV-labeled chDAB4.

Methods

C57BL/6 J mice bearing subcutaneous syngeneic tumors of EL4 lymphoma were either untreated or given chemotherapy, then administered radiolabeled chDAB4 after 24 h with its biodistribution examined using PET and organ assay. We compared chDAB4 radiolabeled with [⁸⁹Zr] Zr^IV or [¹²⁴I] I, or [⁸⁹Zr]Zr-chDAB4 using either DFO-NCS or DFOSq as a chelator.

Results

After chemotherapy, [⁸⁹Zr]Zr-chDAB4 showed higher and prolonged mean (± SD) tumor uptake of 29.5 ± 5.9 compared to 7.8 ± 1.2 for [¹²⁴I] I -chDAB4. In contrast, antibody uptake in healthy tissues was not affected. Compared to DFO-NCS, DFOSq did not result in significant differences in tumor uptake of [⁸⁹Zr]Zr-chDAB4 but did alter the tumor:liver ratio in treated mice 3 days after injection in favour of DFOSq (8.0 ± 1.1) compared to DFO-NCS (4.2 ± 0.7).

Conclusion

ImmunoPET using chDAB4 radiolabeled with residualizing [⁸⁹Zr] Zr^IV rather than [¹²⁴I] I optimized post-chemotherapy tumor uptake. Further, PET imaging characteristics were improved by DFOSq rather than DFO-NCS. Therefore, the radionuclide/chelator combination of [⁸⁹Zr] Zr^IV and DFOSq is preferred for the imminent clinical evaluation of chDAB4 as a selective tumor cell death radioligand.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s41181-020-00109-6.

Tumour-associated macrophages process drug and radio-conjugates of the dead tumour cell-targeting APOMAB® antibody

APOMAB (chDAB4) is a dead tumour cell-targeting antibody which has been used preclinically as a diagnostic agent and therapeutically as a radioimmunotherapy and antibody drug conjugate (ADC). However, little is known of the intra-tumour processing of chDAB4 when bound to dead tumour cells. In this study we examine the role of macrophages in the in vitro and in vivo processing of radiolabelled chDAB4 and a chDAB4 ADC. We found that chDAB4 binds to macrophages in vitro, resulting in the killing of macrophages when using the ADC, chDAB4-SG3249. Free drug released by the macrophage processing of chDAB4-SG3249 could result in killing of 'bystander' Lewis lung (LL2) carcinoma cells. Furthermore, macrophages phagocytosed chDAB4-bound dead LL2 cells and were killed when they phagocytosed chDAB4-SG3249-bound dead LL2 cells in vitro. In vivo, we found markedly different tumour retention of chDAB4 in the LL2 tumour model depending on whether it was radiolabelled with a residualising radionuclide (⁸⁹Zr), which is retained intracellularly, or a non-residualising radionuclide (¹²⁴I), which can diffuse out of the cell. This prolonged retention of ⁸⁹Zr vs¹²⁴I indicated intra-tumoral processing of chDAB4 in vivo. The tumour uptake of ⁸⁹Zr-chDAB4 was reduced after macrophage depletion, which also reduced the efficacy of the chDAB4 ADC in vivo. This study shows that macrophages can process chDAB4 and chDAB4 ADC in vitro and shows the importance of tumour-associated macrophages in the tumour retention of chDAB4 and the efficacy of chDAB4 ADC in vivo.

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.

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.

Dendritic cell-based cancer immunotherapy for colorectal cancer

Colorectal cancer (CRC) is one of the most common cancers and a leading cause of cancer-related mortality worldwide. Although systemic therapy is the standard care for patients with recurrent or metastatic CRC, the prognosis is extremely poor. The optimal sequence of therapy remains unknown. Therefore, alternative strategies, such as immunotherapy, are needed for patients with advanced CRC. This review summarizes evidence from dendritic cell-based cancer immunotherapy strategies that are currently in clinical trials. In addition, we discuss the possibility of antitumor immune responses through immunoinhibitory PD-1/PD-L1 pathway blockade in CRC patients.

Targeted α-therapy using 227Th-APOMAB and cross-fire antitumour effects: preliminary in-vivo evaluation

Resistance to conventional cancer treatments is a major problem associated with solid tumours. Tumour hypoxia is associated with a poor prognosis and with poor treatment outcomes; therefore, there is a need for treatments that can kill hypoxic tumour cells. One potential option is targeted α-radioimmunotherapy, as α-particles can directly kill hypoxic tumour cells. The murine monoclonal antibody DAB4 (APOMAB), which binds dead tumour cells after DNA-damaging treatment, was conjugated and radiolabelled with the α-particle-emitting radionuclide thorium-227 (Th). Mice bearing Lewis lung tumours were administered Th-DAB4 alone or after chemotherapy and the tissue biodistribution of the radioimmunoconjugate was examined, as was the effect of these treatments on tumour growth and survival. Th-DAB4 accumulated in the tumour particularly after chemotherapy, whereas the distribution in healthy tissues did not change. Th-DAB4 as a monotherapy increased survival, with more pronounced responses observed when given after chemotherapy. We have shown that targeted α-therapy of necrotic tumour cells with Th-DAB4 had significant and surprising antitumour activity as it would occur only through a cross-fire effect.

90Y-Labeled Anti-ROBO1 Monoclonal Antibody Exhibits Antitumor Activity against Small Cell Lung Cancer Xenografts

INTRODUCTION

ROBO1 is a membrane protein that contributes to tumor metastasis and angiogenesis. We previously reported that 90Y-labeled anti-ROBO1 monoclonal antibody (90Y-anti-ROBO1 IgG) showed an antitumor effect against ROBO1-positive tumors. In this study, we performed a biodistribution study and radioimmunotherapy (RIT) against ROBO1-positive small cell lung cancer (SCLC) models.

METHODS

For the biodistribution study, 111In-labeled anti-ROBO1 monoclonal antibody (111In-anti-ROBO1 IgG) was injected into ROBO1-positive SCLC xenograft mice via the tail vein. To evaluate antitumor effects, an RIT study was performed, and SCLC xenograft mice were treated with 90Y-anti-ROBO1 IgG. Tumor volume and body weight were periodically measured throughout the experiments. The tumors and organs of mice were then collected, and a pathological analysis was carried out.

RESULTS

As a result of the biodistribution study, we observed tumor uptake of 111In-anti-ROBO1 IgG. The liver, kidney, spleen, and lung showed comparably high accumulation of 111In-labeled anti-ROBO1. In the RIT study, 90Y-anti-ROBO1 IgG significantly reduced tumor volume compared with baseline. Pathological analyses of tumors revealed coagulation necrosis and fatal degeneration of tumor cells, significant reduction in the number of Ki-67-positive cells, and an increase in the number of apoptotic cells. A transient reduction of hematopoietic cells was observed in the spleen, sternum, and femur.

CONCLUSIONS

These results suggest that RIT with 90Y-anti-ROBO1 IgG is a promising treatment for ROBO1-positive SCLC.

Autoradiography imaging in targeted alpha therapy with Timepix detector

There is a lack of data related to activity uptake and particle track distribution in targeted alpha therapy. These data are required to estimate the absorbed dose on a cellular level as alpha particles have a limited range and traverse only a few cells. Tracking of individual alpha particles is possible using the Timepix semiconductor radiation detector. We investigated the feasibility of imaging alpha particle emissions in tumour sections from mice treated with Thorium-227 (using APOMAB), with and without prior chemotherapy and Timepix detector. Additionally, the sensitivity of the Timepix detector to monitor variations in tumour uptake based on the necrotic tissue volume was also studied. Compartmental analysis model was used, based on the obtained imaging data, to assess the Th-227 uptake. Results show that alpha particle, photon, electron, and muon tracks were detected and resolved by Timepix detector. The current study demonstrated that individual alpha particle emissions, resulting from targeted alpha therapy, can be visualised and quantified using Timepix detector. Furthermore, the variations in the uptake based on the tumour necrotic volume have been observed with four times higher uptake for tumours pretreated with chemotherapy than for those without chemotherapy.

Gemcitabine and CHK1 inhibition potentiate EGFR-directed radioimmunotherapy against pancreatic ductal adenocarcinoma

PURPOSE

To develop effective combination therapy against pancreatic ductal adenocarcinoma (PDAC) with a combination of chemotherapy, CHK1 inhibition, and EGFR-targeted radioimmunotherapy.

EXPERIMENTAL DESIGN

Maximum tolerated doses were determined for the combination of gemcitabine, the CHK1 inhibitor PF-477736, and Lutetium-177 ((177)Lu)-labeled anti-EGFR antibody. This triple combination therapy was investigated using PDAC models from well-established cell lines, recently established patient-derived cell lines, and fresh patient-derived xenografts. Tumors were investigated for the accumulation of (177)Lu-anti-EGFR antibody, survival of tumor-initiating cells, induction of DNA damage, cell death, and tumor tissue degeneration.

RESULTS

The combination of gemcitabine and CHK1 inhibitor PF-477736 with (177)Lu-anti-EGFR antibody was tolerated in mice. This triplet was effective in established tumors and prevented the recurrence of PDAC in four cell line-derived and one patient-derived xenograft model. This exquisite response was associated with the loss of tumor-initiating cells as measured by flow cytometric analysis and secondary implantation of tumors from treated mice into treatment-naïve mice. Extensive DNA damage, apoptosis, and tumor degeneration were detected in the patient-derived xenograft. Mechanistically, we observed CDC25A stabilization as a result of CHK1 inhibition with consequent inhibition of gemcitabine-induced S-phase arrest as well as a decrease in canonical (ERK1/2 phosphorylation) and noncanonical EGFR signaling (RAD51 degradation) as a result of EGFR inhibition.

CONCLUSIONS

Our study developed an effective combination therapy against PDAC that has potential in the treatment of PDAC.

Postchemotherapy and tumor-selective targeting with the La-specific DAB4 monoclonal antibody relates to apoptotic cell clearance

Early identification of tumor responses to treatment is crucial for devising more effective and safer cancer treatments. No widely applicable, noninvasive method currently exists for specifically detecting tumor cell death after cytotoxic treatment and thus for predicting treatment outcomes.

METHODS

We have further characterized the targeting of the murine monoclonal antibody DAB4 specifically to dead tumor cells in vitro, in vivo, and in clinical samples. We found that sustained DAB4 binding to treated cells was closely associated with markers of intrinsic apoptosis and DNA double-strand break formation. In a competition binding assay, DAB4 bound EL4 murine thymic lymphoma cells in preference to the normal counterpart of murine thymocytes. Defective in vivo clearance of apoptotic cells augmented in vivo accumulation of DAB4 in tumors particularly after chemotherapy but was unchanged in normal tissues. Tumor targeting of DAB4 was selective for syngeneic murine tumors and for human tumor xenografts of prostate cancer (PC-3) and pancreatic cancer (Panc-1) before and more so after chemotherapy. Furthermore, DAB4 was shown to bind to dead primary acute lymphoblastic leukemic blasts cultured with cytotoxic drugs and dead epithelial cancer cells isolated from peripheral blood of small cell lung carcinoma patients given chemotherapy.

CONCLUSION

Collectively, these results further demonstrate the selectivity of DAB4 for chemotherapy-induced dead tumor cells. This postchemotherapy selectivity is related to a relative increase in the availability of DAB4-binding targets in tumor tissue rather than in normal tissues. The in vitro findings were translated in vivo to human xenograft models and to ex vivo analyses of clinical samples, providing further evidence of the potential of DAB4 as a marker of tumor cell death after DNA-damaging cytotoxic treatment that could be harnessed as a predictive marker of treatment responses.

Monte Carlo simulations of dose distributions with necrotic tumor targeted radioimmunotherapy

Radio-resistant hypoxic tumor cells are significant contributors to the locoregional recurrences and distant metastases that mark failure of radiotherapy. Due to restricted tissue oxygenation, chronically hypoxic tumor cells frequently become necrotic and thus there is often an association between chronically hypoxic and necrotic tumor regions. This simulation study is the first in a series to determine the feasibility of hypoxic cell killing after first targeting adjacent areas of necrosis with either an α- or β-emitting radioimmunoconjugate.

The La antigen is over-expressed in lung cancer and is a selective dead cancer cell target for radioimmunotherapy using the La-specific antibody APOMAB®

Background

The lupus-associated (La)-specific murine monoclonal antibody DAB4 (APOMAB®) specifically binds dead cancer cells. Using DAB4, we examined La expression in human lung cancer samples to assess its suitability as a cancer-selective therapeutic target. We evaluated the safety and effectiveness of radioimmunotherapy (RIT) using DAB4 radiolabeled with Lutetium-177 (¹⁷⁷Lu) in the murine Lewis Lung (LL2) carcinoma model, and determined whether combining RIT with DNA-damaging cisplatin-based chemotherapy, a PARP inhibitor (PARPi), or both alters treatment responses.

Methods

The expression of La mRNA in human lung cancer samples was analysed using the online database Oncomine, and the protein expression of La was examined using a TissueFocus Cancer Survey Tissue Microarray. The binding of DAB4 to cisplatin-treated LL2 cells was assessed in vitro. LL2 tumour-bearing mice were administered escalating doses of ¹⁷⁷Lu-DAB4 alone or in combination with chemotherapy, and tumour growth and survival measured. Biodistribution analysis was used to determine tissue uptake of ¹⁷⁷Lu-DAB4 or its isotype control (¹⁷⁷Lu-Sal5), when delivered alone or after chemotherapy. PARPi (rucaparib; AG-014699) was combined with chemotherapy and the effects of combined treatment on tumour growth, tumour cell DNA damage and death, and intratumoural DAB4 binding were also analysed. The effect of the triple combination of PARPi, chemotherapy and ¹⁷⁷Lu-DAB4 on tumour growth and survival of LL2 tumour-bearing mice was tested.

Results

La was over-expressed at both mRNA and protein levels in surgical specimens of human lung cancer and the over-expression of La mRNA conferred a poorer prognosis. DAB4 bound specifically to cisplatin-induced dead LL2 cells in vitro. An anti-tumour dose response was observed when escalating doses of ¹⁷⁷Lu-DAB4 were delivered in vivo, with supra-additive responses observed when chemotherapy was combined with ¹⁷⁷Lu-DAB4. Combining PARPi with chemotherapy was more effective than chemotherapy alone with increased tumour cell DNA damage and death, and intratumoural DAB4 binding. The combination of PARPi, chemotherapy and ¹⁷⁷Lu-DAB4 was well-tolerated and maximised tumour growth delay.

Conclusions

The La antigen represents a dead cancer cell-specific target in lung cancer, and DAB4 specifically targeted tumour tissue in vivo, particularly after chemotherapy. Tumour uptake of DAB4 increased further after the combination of PARPi and chemotherapy, which generated new dead tumour cell-binding targets. Consequently, combining ¹⁷⁷Lu-DAB4 with PARPi and chemotherapy produced the greatest anti-tumour response. Therefore, the triple combination of PARPi, chemotherapy and RIT may have broad clinical utility.

Treatment of triple-negative breast cancer using anti-EGFR-directed radioimmunotherapy combined with radiosensitizing chemotherapy and PARP inhibitor

Triple-negative breast cancer (TNBC) is associated with poor survival. Chemotherapy is the only standard treatment for TNBC. The prevalence of BRCA1 inactivation in TNBC has rationalized clinical trials of poly(adenosine diphosphate ribose) polymerase (PARP) inhibitors. Similarly, the overexpression of epidermal growth factor receptor (EGFR) rationalized anti-EGFR therapies in this disease. However, clinical trials using these 2 strategies have not reached their promise. In this study, we used EGFR as a target for radioimmunotherapy and hypothesized that EGFR-directed radioimmunotherapy can deliver a continuous lethal radiation dose to residual tumors that are radiosensitized by PARP inhibitors and chemotherapy.

METHODS

We analyzed EGFR messenger RNA in published gene expression array studies and investigated EGFR protein expression by immunohistochemistry in a cohort of breast cancer patients to confirm EGFR as a target in TNBC. Preclinically, using orthotopic and metastatic xenograft models of EGFR-positive TNBC, we investigated the effect of the novel combination of (177)Lu-labeled anti-EGFR monoclonal antibody, chemotherapy, and PARP inhibitors on cell death and the survival of breast cancer stem cells.

RESULTS

In this first preclinical study of anti-EGFR radioimmunotherapy in breast cancer, we found that anti-EGFR radioimmunotherapy is safe and that TNBC orthotopic tumors and established metastases were eradicated in mice treated with anti-EGFR radioimmunotherapy combined with chemotherapy and PARP inhibitors. We showed that the superior response to this triple-agent combination therapy was associated with apoptosis and eradication of putative breast cancer stem cells.

CONCLUSION

Our data support further preclinical investigations toward the development of combination therapies using systemic anti-EGFR radioimmunotherapy for the treatment of recurrent and metastatic TNBC.

An apoptosis-homing peptide-conjugated low molecular weight heparin-taurocholate conjugate with antitumor properties

Various angiogenesis inhibitors and apoptosis-targeting agents have been therapeutically applied in preclinical cancer models, some of which have been tested in clinical trials. In a previous study, we demonstrated that LHT7, a low molecular weight heparin (LMWH)-taurocholate conjugate, has strong antiangiogenic and tumor-suppressive activity and diminished anticoagulant properties. In this study, we developed LHT7-ApoPep-1, an apoptosis-homing peptide-conjugated variant of LHT7. LHT7-ApoPep-1 exhibited antiangiogenic activity in endothelial cell tube-formation assays and apoptotic cell-targeting ability in tumor cell binding assays; it also showed little toxicity toward healthy cells. Administration of LHT7-ApoPep-1 in mouse xenograft models of breast carcinoma delayed tumor growth compared to LHT7-only, and histological evaluations revealed decreased vessel formation and increased apoptotic area in tumor tissues. Moreover, an examination of LHT7-ApoPep-1-Cy7.5 localization within the body using in vivo live imaging showed accumulation at the tumor site of tumor-bearing mice, with a more prolonged circulation time and enhanced intensity compared to LHT7-Cy7.5. Inspection of the tumor microenvironment revealed that Cy5.5-labeled LHT7-ApoPep-1 was located on and near CD31-positive vessels in tumor tissue. We conclude that LHT7-ApoPep-1 has antiangiogenic and apoptosis-targeting properties and exerts antitumor effects by suppressing tumor vessel growth and homing to apoptotic cells within the tumor.

Cancer radioimmunotherapy

Targeting of radionuclides with antibodies, or radioimmunotherapy, has been an active field of research spanning nearly 50 years, evolving with advancing technologies in molecular biology and chemistry, and with many important preclinical and clinical studies illustrating the benefits, but also the challenges, which all forms of targeted therapies face. There are currently two radiolabeled antibodies approved for the treatment of non-Hodgkin lymphoma, but radioimmunotherapy of solid tumors remains a challenge. Novel antibody constructs, focusing on treatment of localized and minimal disease, and pretargeting are all promising new approaches that are currently under investigation.

Ambient oxygen promotes tumorigenesis

Oxygen serves as an essential factor for oxidative stress, and it has been shown to be a mutagen in bacteria. While it is well established that ambient oxygen can also cause genomic instability in cultured mammalian cells, its effect on de novo tumorigenesis at the organismal level is unclear. Herein, by decreasing ambient oxygen exposure, we report a ∼50% increase in the median tumor-free survival time of p53−/− mice. In the thymus, reducing oxygen exposure decreased the levels of oxidative DNA damage and RAG recombinase, both of which are known to promote lymphomagenesis in p53−/− mice. Oxygen is further shown to be associated with genomic instability in two additional cancer models involving the APC tumor suppressor gene and chemical carcinogenesis. Together, these observations represent the first report directly testing the effect of ambient oxygen on de novo tumorigenesis and provide important physiologic evidence demonstrating its critical role in increasing genomic instability in vivo.

Polo-like kinases mediate cell survival in mitochondrial dysfunction

Cancer cells often display defects in mitochondrial respiration, thus the identification of pathways that promote cell survival under this metabolic state may have therapeutic implications. Here, we report that the targeted ablation of mitochondrial respiration markedly increases expression of Polo-like kinase 2 (PLK2) and that it is required for the in vitro growth of these nonrespiring cells. Furthermore, we identify PLK2 as a kinase that phosphorylates Ser-137 of PLK1, which is sufficient to mediate this survival signal. In vivo, knockdown of PLK2 in an isogenic human cell line with a modest defect in mitochondrial respiration eliminates xenograft formation, indicating that PLK2 activity is necessary for growth of cells with compromised respiration. Our findings delineate a mitochondrial dysfunction responsive cell cycle pathway critical for determining cancer cell outcome.