ChAcNLS, a Novel Modification to Antibody-Conjugates Permitting Target Cell-Specific Endosomal Escape, Localization to the Nucleus, and Enhanced Total Intracellular Accumulation

Local delivery of accutox® synergises with immune-checkpoint inhibitors at disrupting tumor growth

BACKGROUND

The Accum® platform was initially designed to accumulate biomedicines in target cells by inducing endosomal-to-cytosol escape. Interestingly however, the use of unconjugated Accum® was observed to trigger cell death in a variety of cancer cell lines; a property further exploited in the development of Accum®-based anti-cancer therapies. Despite the impressive pro-killing abilities of the parent molecule, some cancer cell lines exhibited resistance. This prompted us to test additional Accum® variants, which led to the identification of the AccuTOX® molecule.

METHODS

A series of flow-cytometry and cell-based assays were used to assess the pro-killing properties of AccuTOX® along with its ability to trigger the production of reactive oxygen species (ROS), endosomal breaks and antigen presentation. RNA-seq was also conducted to pinpoint the most prominent processes modulated by AccuTOX® treatment in EL4 T-cell lymphoma. Finally, the therapeutic potency of intratumorally-injected AccuTOX® was evaluated in three different murine solid tumor models (EL4, E0771 and B16) both as a monotherapy or in combination with three immune-checkpoint inhibitors (ICI).

RESULTS

In total, 7 Accum® variants were screened for their ability to induce complete cell death in 3 murine (EL4, B16 and E0771) and 3 human (MBA-MD-468, A549, and H460) cancer cell lines of different origins. The selected compound (hereafter refereed to as AccuTOX®) displayed an improved killing efficiency (~ 5.5 fold compared to the parental Accum®), while retaining its ability to trigger immunogenic cell death, ROS production, and endosomal breaks. Moreover, transcriptomic analysis revealed that low dose AccuTOX® enhances H2-Kb cell surface expression as well as antigen presentation in cancer cells. The net outcome culminates in impaired T-cell lymphoma, breast cancer and melanoma growth in vivo especially when combined with anti-CD47, anti-CTLA-4 or anti-PD-1 depending on the animal model.

CONCLUSIONS

AccuTOX® exhibits enhanced cancer killing properties, retains all the innate characteristics displayed by the parental Accum® molecule, and synergizes with various ICI in controlling tumor growth. These observations will certainly pave the path to continue the clinical development of this lead compound against multiple solid tumor indications.

A1-reprogrammed mesenchymal stromal cells prime potent antitumoral responses

Mesenchymal stromal cells (MSCs) have been modified via genetic or pharmacological engineering into potent antigen-presenting cells-like capable of priming responding CD8 T cells. In this study, our screening of a variant library of Accum molecule revealed a molecule (A1) capable of eliciting antigen cross-presentation properties in MSCs. A1-reprogrammed MSCs (ARM) exhibited improved soluble antigen uptake and processing. Our comprehensive analysis, encompassing cross-presentation assays and molecular profiling, among other cellular investigations, elucidated A1's impact on endosomal escape, reactive oxygen species production, and cytokine secretion. By evaluating ARM-based cellular vaccine in mouse models of lymphoma and melanoma, we observe significant therapeutic potency, particularly in allogeneic setting and in combination with anti-PD-1 immune checkpoint inhibitor. Overall, this study introduces a strong target for developing an antigen-adaptable vaccination platform, capable of synergizing with immune checkpoint blockers to trigger tumor regression, supporting further investigation of ARMs as an effective and versatile anti-cancer vaccine.

Nuclear localization signal-tagged systems: relevant nuclear import principles in the context of current therapeutic design

Nuclear targeting of therapeutics provides a strategy for enhancing efficacy of molecules active in the nucleus and minimizing off-target effects. 'Active' nuclear-directed transport and efficient translocations across nuclear pore complexes provide the most effective means of maximizing nuclear localization. Nuclear-targeting systems based on nuclear localization signal (NLS) motifs have progressed significantly since the beginning of the current millennium. Here, we offer a roadmap for understanding the basic mechanisms of nuclear import in the context of actionable therapeutic design for developing NLS-therapeutics with improved treatment efficacy.

Intratumoral administration of unconjugated Accum™ impairs the growth of pre-established solid lymphoma tumors

The Accum™ technology was initially designed to enhance the bioaccumulation of a given molecule in target cells. It does so by triggering endosomal membrane damages allowing endocytosed products to enter the cytosol, escaping the harsh environmental cues of the endosomal lumen. In an attempt to minimize manufacturing hurdles associated with Accum™ conjugation, we tested whether free Accum™ admixed with antigens could lead to outcomes similar to those obtained with conjugated products. Surprisingly, unconjugated Accum™ was found to promote cell death in vitro, an observation further confirmed on various murine tumor cell lines (EL4, CT-26, B16, and 4 T1). At the molecular level, unconjugated Accum™ triggers the production of reactive oxygen species and elicits immunogenic cell death while retaining its innate ability to cause endosomal damages. When administered as a monotherapy to animals with pre-established EL4 T-cell lymphoma, Accum™ controlled tumor growth in a dose-dependent manner, and its therapeutic effect relies on CD4 and CD8 T cells. Although unconjugated Accum™ synergizes with various immune checkpoint inhibitors (anti-CTLA4, anti-PD-1, or anti-CD47) at controlling tumor growth, its therapeutic potency could not be further enhanced when combined with all three tested immune checkpoint inhibitors at once due to its dependency on a specific dosing regimen. In sum, we report in this study an unprecedented new function for unconjugated Accum™ as a novel anticancer molecule. These results could pave the path for a new line of investigation aimed at exploring the pro-killing properties of additional Accum™ variants as a mean to develop second-generation anticancer therapeutics.

Accum™ Technology: A Novel Conjugable Primer for Onco-Immunotherapy

Compromised activity is a common impediment for biologics requiring endosome trafficking into target cells. In cancer cells, antibody-drug conjugates (ADCs) are trapped in endosomes or subsequently pumped extracellularly, leading to a reduction in intracellular accumulation. In subsets of dendritic cells (DCs), endosome-engulfed antigens face non-specific proteolysis and collateral damage to epitope immunogenicity before proteasomal processing and subsequent surface presentation. To bypass these shortcomings, we devised Accum™, a conjugable biotechnology harboring cholic acid (ChAc) and a nuclear localization signal (NLS) sequence for endosome escape and prompt nuclear targeting. Combined, these mechanisms culminate in enhanced intracellular accumulation and functionalization of coupled biologics. As proof-of-principle, we have biochemically characterized Accum, demonstrating its adaptability to ADCs or antigens in different cancer settings. Additionally, we have validated that endosome escape and nuclear routing are indispensable for effective intracellular accumulation and guaranteed target cell selectivity. Importantly, we have demonstrated that the unique mechanism of action of Accum translates into enhanced tumor cytotoxicity when coupled to ADCs, and durable therapeutic and prophylactic anti-cancer immunogenicity when coupled to tumor antigens. As more pre-clinical evidence accumulates, the adaptability, unique mechanism of action, and high therapeutic potency of Accum signal a promising transition into clinical investigations in the context of onco-immunotherapy.

Promoting antigen escape from dendritic cell endosomes potentiates anti-tumoral immunity

The cross-presenting capacity of dendritic cells (DCs) can be limited by non-specific degradation during endosome maturation. To bypass this limitation, we present in this study a new Accum-based formulation designed to promote endosome-to-cytosol escape. Treatment of primary DCs with Accum linked to the xenoantigen ovalbumin (OVA) triggers endosomal damages and enhances protein processing. Despite multiple challenges using ascending doses of tumor cells, DC prophylactic vaccination results in complete protection due to increased levels of effector CD4 and CD8 T cells as well as high production of pro-inflammatory mediators. When combined with anti-PD-1, therapeutic vaccination using both syngeneic and allogeneic Accum-OVA-pulsed DCs triggers potent anti-tumoral responses. The net outcome culminates in increased CD11c, CD8, and NK infiltration along with a high CD8/Treg ratio. These highly favorable therapeutic effects highlight the promising potential of Accum as a distinct and potent technology platform suitable for the design of next generation cell cancer vaccines.

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Accum-linked antigen enhances antigen processing and presentation

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Pulsed dendritic cells elicit potent effector T cell responses

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Therapeutic vaccination using allogeneic DCs controls pre-established tumors

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The vaccine boosts tumor-infiltrating lymphocytes and increases the CD8/Treg ratio

Targeted Radionuclide Therapy Using Auger Electron Emitters: The Quest for the Right Vector and the Right Radionuclide

Auger electron emitters (AEEs) are attractive tools in targeted radionuclide therapy to specifically irradiate tumour cells while sparing healthy tissues. However, because of their short range, AEEs need to be brought close to sensitive targets, particularly nuclear DNA, and to a lower extent, cell membrane. Therefore, radioimmunoconjugates (RIC) have been developed for specific tumour cell targeting and transportation to the nucleus. Herein, we assessed, in A-431_CEA-luc and SK-OV-3_1B9 cancer cells that express low and high levels of HER2 receptors, two ¹¹¹In-RIC consisting of the anti-HER2 antibody trastuzumab conjugated to NLS or TAT peptides for nuclear delivery. We found that NLS and TAT peptides improved the nuclear uptake of ¹¹¹In-trastuzumab conjugates, but this effect was limited and non-specific. Moreover, it did not result in a drastic decrease of clonogenic survival. Indium-111 also contributed to non-specific cytotoxicity in vitro due to conversion electrons (30% of the cell killing). Comparison with [¹²⁵I]I-UdR showed that the energy released in the cell nucleus by increasing the RIC’s nuclear uptake or by choosing an AEE that releases more energy per decay should be 5 to 10 times higher to observe a significant therapeutic effect. Therefore, new Auger-based radiopharmaceuticals need to be developed.

Lysosomal escaped protein nanocarriers for nuclear-targeted siRNA delivery

In the process of drug carrier design, lysosome degradation in cells is often neglected, which makes a considerable number of drugs not play a role. Here, we have constructed a tumor treatment platform (Apn/siRNA/NLS/HA/Apt) with unique lysosomal escape function and excellent cancer treatment effect. Apoferritin (Apn) has attracted more and more attention because of its high uniformity, modifiability, and controllability. Meanwhile, its endogenous nature can avoid the risk of immune response being eliminated. We used aptamer modified iron deficient protein nanocages (Apn) to tightly encapsulate the combination of siRNA and NLS (siRNA/NLS) with influenza virus hemagglutinin (HA peptide). After Apn/siRNA/NLS/HA/Apt was targeted into cells, the acidic environment of lysosome led to the cleavage of Apn nanocages, and the release of siRNA/NLS and HA peptide. HA peptide can destroy lysosome membrane, make siRNA/NLS escape lysosome, and enter the nucleus under the action of NLS, resulting in efficient gene silencing effect. This kind of cancer treatment strategy based on Apn nanocage shows high biocompatibility and unique lysosome escape property, which significantly improves the drug delivery and treatment efficiency. Lysosomal escape protein nanocarriers for nuclear-targeted siRNA delivery.

A Novel Proteomic Method Reveals NLS Tagging of T-DM1 Contravenes Classical Nuclear Transport in a Model of HER2-Positive Breast Cancer

The next breakthrough for protein therapeutics is effective intracellular delivery and accumulation within target cells. Nuclear localization signal (NLS)-tagged therapeutics have been hindered by the lack of efficient nuclear localization due to endosome entrapment. Although development of strategies for tagging therapeutics with technologies capable of increased membrane penetration has resulted in proportional increased potency, nonspecific membrane penetration limits target specificity and, hence, widespread clinical success. There is a long-standing idea that nuclear localization of NLS-tagged agents occurs exclusively via classical nuclear transport. In the present study, we modified the antibody-drug conjugate trastuzumab-emtansine (T-DM1) with a classical NLS linked to cholic acid (cell accumulator [Accum]) that enables modified antibodies to escape endosome entrapment and increase nuclear localization efficiency without abrogating receptor targeting. In parallel, we developed a proteomics-based method to evaluate nuclear transport. Accum-modified T-DM1 significantly enhanced cytotoxic efficacy in the human epidermal growth factor receptor 2 (HER2)-positive SKBR3 breast cancer system. We discovered that efficacy was dependent on the nonclassical importin-7. Our evaluation reveals that when multiple classical NLS tagging occurs, cationic charge build-up as opposed to sequence dominates and becomes a substrate for importin-7. This study results in an effective target cell-specific NLS therapeutic and a general approach to guide future NLS-based development initiatives.

Delivery systems exploiting natural cell transport processes of macromolecules for intracellular targeting of Auger electron emitters

The presence of Auger electrons (AE) among the decay products of a number of radionuclides makes these radionuclides an attractive means for treating cancer because these short-range electrons can cause significant damage in the immediate vicinity of the decomposition site. Moreover, the extreme locality of the effect provides a potential for selective eradication of cancer cells with minimal damage to adjacent normal cells provided that the delivery of the AE emitter to the most vulnerable parts of the cell can be achieved. Few cellular compartments have been regarded as the desired target site for AE emitters, with the cell nucleus generally recognized as the preferred site for AE decay due to the extreme sensitivity of nuclear DNA to direct damage by radiation of high linear energy transfer. Thus, the advantages of AE emitters for cancer therapy are most likely to be realized by their selective delivery into the nucleus of the malignant cells. To achieve this goal, delivery systems must combine a challenging complex of properties that not only provide cancer cell preferential recognition but also cell entry followed by transport into the cell nucleus. A promising strategy for achieving this is the recruitment of natural cell transport processes of macromolecules, involved in each of the aforementioned steps. To date, a number of constructs exploiting intracellular transport systems have been proposed for AE emitter delivery to the nucleus of a targeted cell. An example of such a multifunctional vehicle that provides smart step-by-step delivery is the so-called modular nanotransporter, which accomplishes selective recognition, binding, internalization, and endosomal escape followed by nuclear import of the delivered radionuclide. The current review will focus on delivery systems utilizing various intracellular transport pathways and their combinations in order to provide efficient targeting of AE to the cancer cell nucleus.

Antibody-Drug Conjugate that Exhibits Synergistic Cytotoxicity with an Endosome-Disruptive Peptide

Antibody-drug conjugates are an important class of cancer therapeutics. These agents generally bind a specific cell surface receptor, undergo receptor-mediated endocytosis, and enter the endosomal-lysosomal system, where the environment in these organelles facilitates the release of a membrane-permeable cytotoxin. By using a membrane-impermeable cytotoxin, we describe here a method that allows the cytotoxicity of an antibody conjugate to be triggered by co-administration with an endosome-disruptive peptide that exhibits low toxicity. This approach was validated by conjugation of an anionic derivative of the tubulin-binding cytotoxin colchinol methyl ether to lysine residues of the HER2-targeting antibody trastuzumab (Herceptin) via a disulfide. When this antibody binds HER2 on SKBR3 breast cancer cells and undergoes endocytosis, the membrane-impermeable cytotoxin is released, but it becomes trapped in endosomes, resulting in relatively low cytotoxicity (IC50 > 1 μM). However, co-administration with an essentially nontoxic (IC50 > 10 μM) cholesterol-linked endosome-disruptive peptide promotes the release of this small molecule into the cytoplasm, conferring subnanomolar cytotoxic potency (IC50 = 0.11 ± 0.07 nM). Studies of a structurally related fluorophore conjugate revealed that the endosome-disruptive peptide does not substantially enhance cleavage of the disulfide (t 1/2 = 8 ± 2 h) within endosomes, suggesting that the mechanism of endosomal escape involves the efflux of some small molecules without facilitating substantial influx of reduced glutathione.

Initial Evaluation of Antibody-conjugates Modified with Viral-derived Peptides for Increasing Cellular Accumulation and Improving Tumor Targeting

Antibody-conjugates (ACs) modified with virus-derived peptides are a potentially powerful class of tumor cell delivery agents for molecular payloads used in cancer treatment and imaging due to increased cellular accumulation over current ACs. During early AC in vitro development, fluorescence techniques and radioimmunoassays are sufficient for determining intracellular localization, accumulation efficiency, and target cell specificity. Currently, there is no consensus on standardized methods for preparing cells for evaluating AC intracellular accumulation and localization. The initial testing of ACs modified with virus-derived peptides is critical especially if several candidates have been constructed. Determining intracellular accumulation by fluorescence can be affected by background signal from ACs at the cell surface and complicate the interpretation of accumulation. For radioimmunoassays, typically treated cells are fractionated and the radioactivity in different cell compartments measured. However, cell lysis varies from cell to cell and often nuclear and cytoplasmic compartments are not adequately isolated. This can produce misleading data on payload delivery properties. The intravenous injection of radiolabeled virus-derived peptide-modified ACs in tumor bearing mice followed by radionuclide imaging is a powerful method for determining tumor targeting and payload delivery properties at the in vivo phase of development. However, this is a relatively recent advancement and few groups have evaluated virus-derived peptide-modified ACs in this manner. We describe the processing of treated cells to more accurately evaluate virus-derived peptide-modified AC accumulation when using confocal microscopy and radioimmunoassays. Specifically, a method for trypsinizing cells to remove cell surface bound ACs. We also provide a method for improving cellular fractionation. Lastly, this protocol provides an in vivo method using positron emission tomography (PET) for evaluating initial tumor targeting properties in tumor-bearing mice. We use the radioisotope ⁶⁴Cu (t1/2 = 12.7 h) as an example payload in this protocol.

NLS-Cholic Acid Conjugation to IL-5Rα-Specific Antibody Improves Cellular Accumulation and In Vivo Tumor-Targeting Properties in a Bladder Cancer Model

Receptor-mediated internalization followed by trafficking and degradation of antibody-conjugates (ACs) via the endosomal-lysosomal pathway is the major mechanism for delivering molecular payloads inside target tumor cells. Although a mainstay for delivering payloads with clinically approved ACs in cancer treatment and imaging, tumor cells are often able to decrease intracellular payload concentrations and thereby reduce the effectiveness of the desired application. Thus, increasing payload intracellular accumulation has become a focus of attention for designing next-generation ACs. We developed a composite compound (ChAcNLS) that enables ACs to escape endosome entrapment and route to the nucleus resulting in the increased intracellular accumulation as an interleukin-5 receptor α-subunit (IL-5Rα)-targeted agent for muscle invasive bladder cancer (MIBC). We constructed ⁶⁴Cu-A14-ChAcNLS, ⁶⁴Cu-A14-NLS, and ⁶⁴Cu-A14 and evaluated their performance by employing mechanistic studies for endosome escape coupled to nuclear routing and determining whether this delivery system results in improved ⁶⁴Cu cellular accumulation. ACs consisting of ∼20 ChAcNLS or NLS moieties per ⁶⁴Cu-A14 were prepared in good yield, high monomer content, and maintaining high affinity for IL-5Rα. Confocal microscopy analysis demonstrated ChAcNLS mediated efficient endosome escape and nuclear localization. ⁶⁴Cu-A14-ChAcNLS increased ⁶⁴Cu cellular accumulation in HT-1376 and HT-B9 cells relative to ⁶⁴Cu-A14 and ⁶⁴Cu-A14-NLS. In addition, we tested ⁶⁴Cu-A14-ChAcNLS in vivo to evaluate its tissue distribution properties and, ultimately, tumor uptake and targeting. A model of human IL-5Rα MIBC was developed by implanting NOD/SCID mice with subcutaneous HT-1376 or HT-B9MIBC tumors, which grow containing high and low IL-5Rα-positive tumor cell densities, respectively. ACs were intravenously injected, and daily blood sampling, biodistribution at 48 and 96 h, and positron emission tomography (PET) at 24 and 48 h were performed. Region of interest (ROI) analysis was also performed on reconstructed PET images. Pharmacokinetic analysis and biodistribution studies showed that ⁶⁴Cu-A14-ChAcNLS had faster clearance rates from the blood and healthy organs relative to ⁶⁴Cu-A14. However, ⁶⁴Cu-A14-ChAcNLS maintained comparable tumor accumulation relative to ⁶⁴Cu-A14. This resulted in ⁶⁴Cu-A14-ChAcNLS having superior tumor/normal tissue ratios at both 48 and 96 h biodistribution time points. Visualization of AC distribution by PET and ROI analysis confirmed that ⁶⁴Cu-A14-ChAcNLS had improved targeting of MIBC tumor relative to ⁶⁴Cu-A14. In addition, ⁶⁴Cu-A14 modified with only NLS had poor tumor targeting. This was a result of poor tumor uptake due to extremely rapid clearance. Thus, the overall findings in this model of human IL-5Rα-positive MIBC describe an endosome escape-nuclear localization cholic-acid-linked peptide that substantially enhances AC cellular accumulation and tumor targeting.

Targeting IL-5Rα with antibody-conjugates reveals a strategy for imaging and therapy for invasive bladder cancer

Despite the high interest and concern due to an increasing incidence and death rate, patients who develop muscle invasive bladder cancer (MIBC) have few options available. However, the past decade has produced many candidate bladder tumor-specific markers but further development of these markers is still needed for creating effective targeted medications to solve this urgent need. Interleukin-5 receptor α-subunit (IL-5Rα) has recently been reported to be involved in MIBC progression. Thus, we aimed to validate IL-5Rα as a target for antibody-conjugates to better manage patients with MIBC. Patients were recruited and their tumors were processed for IL-5Rα immunohistochemical analysis. NOD/SCID mice were also heterotopically implanted with the human MIBC HT-1376 and HT-B9 cell lines and established xenografts immunohistochemically evaluated for IL-5Rα and compared against patient tumors. Using the mAb A14, an antibody-drug conjugate (ADC) and a radiolabeled immunoconjugate (RIC) were developed by conjugating to vinblastine and to the positron emitter copper-64 (⁶⁴Cu), respectively. As a proof-of-concept for ADC and RIC efficacy, in vitro cytotoxicity and in vivo positron emission tomography (PET) imaging in tumor-bearing mice were performed, respectively. In addition, as rapid internalization and accumulation are important components for effective antibody-conjugates, we evaluated these aspects in response to IL-5 and ⁶⁴Cu-A14 treatments. Our findings suggest that although IL-5Rα protein expression is preferentially increased in MIBC, it is rapid IL-5Rα-mediated internalization allowing vinblastine-A14 to have cytotoxic activity and ⁶⁴Cu-A14 to detect MIBC tumors in vivo. This is the first report to elucidate the potential of IL-5Rα as an attractive MIBC target for antibody-conjugate applications.

Development of a Novel Covalent Folate-Albumin-Photosensitizer Conjugate

There is considerable interest in the development of novel and more efficient delivery systems for improving the efficacy of photodynamic therapy (PDT). The authors in this highlighted issue describe the synthesis and the photobiological characterizations of two photosensitizer (PS) conjugates based on β-carboline derivatives covalently conjugated to folic acid (FA) coupled to bovine serum albumin (BSA) as a carrier system specifically targeting cancer cells overexpressing FA receptor alpha (FRα). Accordingly, only the FA-BSA-β-carboline conjugates are internalized specifically in FRα-positive cells and are proved to be phototoxic. On the other hand, albumin-β-carboline conjugates without FA or β-carboline derivatives alone are not internalized and nontoxic. This conjugate is among the first to produce a conjugate composed of a PS and FA molecules that are directly conjugated to BSA. In addition, the in vitro studies are the first evidence that directly conjugated FA-BSA can be used as carriers to selectively enhance cytotoxicity by PDT relative to unmodified PS or nontargeted BSA-PS. This strategy is a positive step forward for the covalent design and construction of a photodynamic nanomedicine for FR-positive tumors.