Monte Carlo simulations of dose distributions with necrotic tumor targeted radioimmunotherapy

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.

Dosimetry in targeted alpha therapy. A systematic review: current findings and what is needed

Objective. A systematic review of dosimetry in Targeted Alpha Therapy (TAT) has been performed, identifying the common issues. Approach. The systematic review was performed in accordance with the PRISMA guidelines, and the literature was searched using the Scopus and PubMed databases. Main results. From the systematic review, three key points should be considered when performing dosimetry in TAT. (1) Biodistribution/Biokinetics: the accuracy of the biodistribution data is a limit to accurate dosimetry in TAT. The biodistribution of alpha-emitting radionuclides throughout the body is difficult to image directly, with surrogate radionuclide imaging, blood/faecal sampling, and animal studies able to provide information. (2) Daughter radionuclides: the decay energy of the alpha-emissions is sufficient to break the bond to the targeting vector, resulting in a release of free daughter radionuclides in the body. Accounting for daughter radionuclide migration is essential. (3) Small-scale dosimetry and microdosimetry: due to the short path length and heterogeneous distribution of alpha-emitters at the target site, small-scale/microdosimetry are important to account for the non-uniform dose distribution in a target region, organ or cell and for assessing the biological effect of alpha-particle radiation. Significance. TAT is a form of cancer treatment capable of delivering a highly localised dose to the tumour environment while sparing the surrounding healthy tissue. Dosimetry is an important part of treatment planning and follow up. Being able to accurately predict the radiation dose to the target region and healthy organs could guide the optimal prescribed activity. Detailed dosimetry models accounting for the three points mentioned above will help give confidence in and guide the clinical application of alpha-emitting radionuclides in targeted cancer therapy.

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.

Track structure model of microscopic energy deposition by protons and heavy ions in segments of neuronal cell dendrites represented by cylinders or spheres

Changes to cognition, including memory, following radiation exposure are a concern for cosmic ray exposures to astronauts and in Hadron therapy with proton and heavy ion beams. The purpose of the present work is to develop computational methods to evaluate microscopic energy deposition (ED) in volumes representative of neuron cell structures, including segments of dendrites and spines, using a stochastic track structure model. A challenge for biophysical models of neuronal damage is the large sizes (> 100µm) and variability in volumes of possible dendritic segments and pre-synaptic elements (spines and filopodia). We consider cylindrical and spherical microscopic volumes of varying geometric parameters and aspect ratios from 0.5 to 5 irradiated by protons, and ³He and ¹²C particles at energies corresponding to a distance of 1cm to the Bragg peak, which represent particles of interest in Hadron therapy as well as space radiation exposure. We investigate the optimal axis length of dendritic segments to evaluate microscopic ED and hit probabilities along the dendritic branches at a given macroscopic dose. Because of large computation times to analyze ED in volumes of varying sizes, we developed an analytical method to find the mean primary dose in spheres that can guide numerical methods to find the primary dose distribution for cylinders. Considering cylindrical segments of varying aspect ratio at constant volume, we assess the chord length distribution, mean number of hits and ED profiles by primary particles and secondary electrons (δ-rays). For biophysical modeling applications, segments on dendritic branches are proposed to have equal diameters and axes lengths along the varying diameter of a dendritic branch.

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.