Eliciting anti-cancer immunity by genetically engineered multifunctional exosomes.

Exosomes are cell-derived nanovesicles involved in regulating intercellular communications. In contrast to conventional nanomedicines, exosomes are characterized by unique advantages for therapeutic development. Despite their major successes in drug delivery, the full potential of exosomes for immunotherapy remains untapped. Herein we designed genetically engineered exosomes featured with surfaced-displayed antibody targeting groups and immunomodulatory proteins. Through genetic fusions with exosomal membrane proteins, Expi293F cell-derived exosomes were armed with monoclonal antibodies specific for human T-cell CD3 and epidermal growth factor receptor (EGFR) as well as immune checkpoint modulators, programmed death 1 (PD-1) and OX40 ligand (OX40L). The resulting genetically engineered multifunctional immune-modulating exosomes (GEMINI-Exos) can not only redirect and activate T cells toward killing EGFR-positive triple negative breast cancer (TNBC) cells but also elicit robust anti-cancer immunity, giving rise to highly potent inhibition against established TNBC tumors in mice. GEMINI-Exos represent candidate agents for immunotherapy and may offer a general strategy for generating exosome-based immunotherapeutics with desired functions and properties.

Site-specific antibody-drug conjugates with variable drug-to-antibody-ratios for AML therapy.

Random conjugations of chemotherapeutics to monoclonal antibodies result in heterogeneous antibody-drug conjugates (ADCs) with suboptimal pharmacological properties. We recently developed a new technology for facile generation of homogeneous ADCs by harnessing human CD38 catalytic domain and its dinucleotide-derived covalent inhibitor, termed ADP-ribosyl cyclase-enabled ADCs (ARC-ADCs). Herein we advance this technology by designing and synthesizing ARC-ADCs with customizable drug-to-antibody ratios (DARs). Through varying numbers and locations of CD38 fused to an antibody targeting human C-type lectin-like molecule-1 (hCLL-1), ARC-ADCs featuring DARs of 2 and 4 were rapidly generated via a single step with cytotoxic monomethyl auristatin F (MMAF) as payloads. In contrast to anti-hCLL-1 ARC-ADC carrying 2 drug molecules, anti-hCLL-1 ARC-ADC with a DAR of 4 shows highly potent activity in killing hCLL-1-positive acute myeloid leukemia (AML) cells both in vitro and in vivo. This work provides novel ADC candidates for combating AML and supports ARC-ADC as a general and versatile approach for producing site-specific ADCs with defined DARs.

VprBP directs epigenetic gene silencing through histone H2A phosphorylation in colon cancer.

Histone modification is aberrantly regulated in cancer and generates an unbalanced state of gene transcription. VprBP, a recently identified kinase, phosphorylates histone H2A on threonine 120 (T120) and is involved in oncogenic transcriptional dysregulation; however, its specific role in colon cancer is undefined. Here, we show that VprBP is overexpressed in colon cancer and directly contributes to epigenetic gene silencing and cancer pathogenesis. Mechanistically, the observed function of VprBP is mediated through H2AT120 phosphorylation (H2AT120p)-driven transcriptional repression of growth regulatory genes, resulting in a significantly higher proliferative capacity of colon cancer cells. Our preclinical studies using organoid and xenograft models demonstrate that treatment with the VprBP inhibitor B32B3 impairs colonic tumor growth by blocking H2AT120p and reactivating a transcriptional program resembling that of normal cells. Collectively, our work describes VprBP as a master kinase contributing to the development and progression of colon cancer, making it a new molecular target for novel therapeutic strategies.

The structure-function relationship of oncogenic LMTK3.

Elucidating signaling driven by lemur tyrosine kinase 3 (LMTK3) could help drug development. Here, we solve the crystal structure of LMTK3 kinase domain to 2.1Å resolution, determine its consensus motif and phosphoproteome, unveiling in vitro and in vivo LMTK3 substrates. Via high-throughput homogeneous time-resolved fluorescence screen coupled with biochemical, cellular, and biophysical assays, we identify a potent LMTK3 small-molecule inhibitor (C28). Functional and mechanistic studies reveal LMTK3 is a heat shock protein 90 (HSP90) client protein, requiring HSP90 for folding and stability, while C28 promotes proteasome-mediated degradation of LMTK3. Pharmacologic inhibition of LMTK3 decreases proliferation of cancer cell lines in the NCI-60 panel, with a concomitant increase in apoptosis in breast cancer cells, recapitulating effects of LMTK3 gene silencing. Furthermore, LMTK3 inhibition reduces growth of xenograft and transgenic breast cancer mouse models without displaying systemic toxicity at effective doses. Our data reinforce LMTK3 as a druggable target for cancer therapy.

Synthesis of site-specific antibody-drug conjugates by ADP-ribosyl cyclases.

Most of the current antibody-drug conjugates (ADCs) in clinic are heterogeneous mixtures. To produce homogeneous ADCs, established procedures often require multiple steps or long reaction times. The introduced mutations or foreign sequences may cause high immunogenicity. Here, we explore a new concept of transforming CD38 enzymatic activity into a facile approach for generating site-specific ADCs. This was achieved through coupling bifunctional antibody-CD38 fusion proteins with designer dinucleotide-based covalent inhibitors with stably attached payloads. The resulting adenosine diphosphate-ribosyl cyclase-enabled ADC (ARC-ADC) with a drug-to-antibody ratio of 2 could be rapidly generated through single-step conjugation. The generated ARC-ADC targeting human epidermal growth factor receptor 2 (HER2) displays excellent stability and potency against HER2-positive breast cancer both in vitro and in vivo. This proof-of-concept study demonstrates a new strategy for production of site-specific ADCs. It may provide a general approach for the development of a novel class of ADCs with potentially enhanced properties.

Genetically Engineered Cell-Derived Nanoparticles for Targeted Breast Cancer Immunotherapy.

Exosomes are nanosized membranous vesicles secreted by a variety of cells. Due to their unique and pharmacologically important properties, cell-derived exosome nanoparticles have drawn significant interest for drug development. By genetically modifying exosomes with two distinct types of surface-displayed monoclonal antibodies, we have developed an exosome platform termed synthetic multivalent antibodies retargeted exosome (SMART-Exo) for controlling cellular immunity. Here, we apply this approach to human epidermal growth factor receptor 2 (HER2)-expressing breast cancer by engineering exosomes through genetic display of both anti-human CD3 and anti-human HER2 antibodies, resulting in SMART-Exos dually targeting T cell CD3 and breast cancer-associated HER2 receptors. By redirecting and activating cytotoxic T cells toward attacking HER2-expressing breast cancer cells, the designed SMART-Exos exhibited highly potent and specific anti-tumor activity both in vitro and in vivo. This work demonstrates preclinical feasibility of utilizing endogenous exosomes for targeted breast cancer immunotherapy and the SMART-Exos as a broadly applicable platform technology for the development of next-generation immuno-nanomedicines.

CBP/ß-Catenin/FOXM1 Is a Novel Therapeutic Target in Triple Negative Breast Cancer.

Background: Triple negative breast cancers (TNBCs) are an aggressive BC subtype, characterized by high rates of drug resistance and a high proportion of cancer stem cells (CSC). CSCs are thought to be responsible for tumor initiation and drug resistance. cAMP-response element-binding (CREB) binding protein (CREBBP or CBP) has been implicated in CSC biology and may provide a novel therapeutic target in TNBC. Methods: RNA Seq pre- and post treatment with the CBP-binding small molecule ICG-001 was used to characterize CBP-driven gene expression in TNBC cells. In vitro and in vivo TNBC models were used to determine the therapeutic effect of CBP inhibition via ICG-001. Tissue microarrays (TMAs) were used to investigate the potential of CBP and associated proteins as biomarkers in TNBC. Results: The CBP/ß-catenin/FOXM1 transcriptional complex drives gene expression in TNBC and is associated with increased CSC numbers, drug resistance and poor survival outcome. Targeting of CBP/ß-catenin/FOXM1 with ICG-001 eliminated CSCs and sensitized TNBC tumors to chemotherapy. Immunohistochemistry of TMAs demonstrated a significant correlation between FOXM1 expression and TNBC subtype. Conclusion: CBP/ß-catenin/FOXM1 transcriptional activity plays an important role in TNBC drug resistance and CSC phenotype. CBP/ß-catenin/FOXM1 provides a molecular target for precision therapy in triple negative breast cancer and could form a rationale for potential clinical trials.

Reprogramming Exosomes as Nanoscale Controllers of Cellular Immunity.

Exosomes are naturally occurring membranous vesicles secreted by various types of cells. Given their unique and important biological and pharmacological properties, exosomes have been emerging as a promising form of nanomedicine acting via efficient delivery of endogenous and exogenous therapeutics. Here we explore a new concept of utilizing endogenously derived exosomes as artificial controllers of cellular immunity to redirect and activate cytotoxic T cells toward cancer cells for killing. This was achieved through genetically displaying two distinct types of antibodies on exosomal surface. The resulting synthetic multivalent antibodies retargeted exosomes (SMART-Exos), which express monoclonal antibodies specific for T-cell CD3 and cancer cell-associated epidermal growth factor receptor (EGFR), were shown to not only induce cross-linking of T cells and EGFR-expressing breast cancer cells but also elicit potent antitumor immunity both in vitro and in vivo. This proof-of-concept study demonstrates a novel application of exosomes in cancer immunotherapy and may provide a general and versatile approach for the development of a new class of cell-free therapy.

Characterization of Imatinib Resistant CML Leukemic Stem/Initiating Cells and Their Sensitivity to CBP/Catenin Antagonists.

BACKGROUND AND OBJECTIVE: The development of the tyrosine kinase inhibitor Imatinib (IM) represents a milestone in CML (Chronic Myeloid Leukemia) treatment. However, it is not curative and patients develop IM resistance. IM resistance has been previously correlated with the emergence of drug-resistant LIC/LSC (Leukemia Initiating Cell/Leukemia Stem Cell) and increased nuclear catenin levels and enhanced Wnt signaling. It has been demonstrated previously that drug resistant CML LIC/LSC can be safely eliminated both in vitro and in vivo via disruption of the CBP/catenin interaction, utilizing the highly biochemically selective small molecule CBP/catenin antagonist ICG- 001. METHODS: Here, we utilized an in vitro IM selection of primary CML patients' samples to identify drug-resistant LIC/LSC populations. In this report, we characterized the drug-resistant CML LIC/LSC population using FACS, Smartchip qPCR and colony assays to analyze cell surface markers, transcriptomics and function. RESULTS: As opposed to previous characterization of the CML leukemic stem cell population as being either CD34+CD38- or CD34+CD38+, the in vitro selected Imatinib resistant (IM-R) CML LSC population was consistently CD34-CD38-. In Long-Term Culture Initiating Cell assay (LTC-IC, a surrogate assay for long term repopulating stem cells), our results suggest that the CBP/catenin antagonist ICG- 001 sensitizes LIC/LSC to IM treatment by forced differentiative elimination of the CML LIC/LSC population. CONCLUSION: In vitro selected IM resistant cells are negative for both CD34 and CD38 by FACS analysis. These cells acquire CD34/CD38 expression after co-culture with stromal cells. CBP/catenin antagonist ICG-001 facilitates IM function in eliminating these cells.

Small molecule p300/catenin antagonist enhances hematopoietic recovery after radiation.

There is currently no FDA approved therapeutic agent for ARS mitigation post radiation exposure. Here we report that the small molecule YH250, which specifically antagonizes p300/catenin interaction, stimulates hematopoiesis in lethally or sublethally irradiated mice. A single administration of YH250 24 hours post irradiation can significantly stimulate HSC proliferation, improve survival and accelerate peripheral blood count recovery. Our studies suggest that promotion of the expansion of the remaining HSC population via stimulation of symmetric non-differentiative proliferation is at least part of the mechanism of action.

Novel cell lines established from pediatric brain tumors.

The paucity of cell culture models for childhood brain tumors prompted us to establish pediatric cell lines for use in biological experiments and preclinical developmental therapeutic studies. Three cell lines were established, CHLA-200 (GBM), CHLA-259 (anaplastic medulloblastoma) and CHLA-266 (atypical teratoid rhabdoid tumor, AT/RT). Consistent with an AT/RT origin, CHLA-266 lacked INI1 expression and had monosomy 22. All lines had unique DNA short tandem repeat "fingerprints" matching that of the patient's tumor tissue and were adherent on tissue culture plastic, but differed in morphology and doubling times. CHLA-200 had a silent mutation in TP53. CHLA-259 and CHLA-266 had wild-type TP53. All three lines were relatively resistant to multiple drugs when compared to the DAOY medulloblastoma cell line, using the DIMSCAN fluorescence digital image microscopy cytotoxicity assay. RNA expression of MYC and MYCN were quantified using RT-PCR (Taqman). CHLA-200 expressed MYC, DAOY and CHLA-259 expressed MYCN, and CHLA-266 expressed both MYCN and MYC. CHLA-200 was only tumorigenic subcutaneously, but CHLA-259 and CHLA-266 were tumorigenic both subcutaneously and in brains of NOD/SCID mice. Immunohistochemistry of the xenografts revealed GFAP staining in CHLA-200 and PGP 9.5 staining in CHLA-259 and CHLA-266 tumors. As expected, INI1 expression was lacking in CHLA-266 (AT/RT). These three new cell lines will provide useful models for research of pediatric brain tumors.

Metabolism of orthotopic mouse brain tumor models.

We used magnetic resonance spectroscopy to determine whether orthotopic mouse brain tumors grown as xenografts in immunocompromised mice either from human brain tumor cells implanted immediately after surgery or from cultured human tumor lines show metabolic profiles comparable to those of the original tumors. Using a 7 T scanner, spectra were acquired from mice with a human atypical teratoid/rhabdoid tumor (AT/RT) either implanted directly from the surgical specimen or first grown in culture, directly implanted choroid plexus carcinoma (CPC), and two medulloblastoma cell lines. The results were compared with spectra from these same tumors or tumor types in patients and with controls. Metabolic variability of tumors from a single cell line was also evaluated using the medulloblastoma lines. The main metabolic features of human tumors were qualitatively replicated in xenografts. AT/RTs in mice exhibited choline, creatine, and myo-inositol levels comparable to those observed in the patient. As in patients, choline was prominent in experimental CPC. Tumors from a single cell line were comparable. Significant correlations were found with key metabolites in humans and mice; however, differences including lower lipids in the implanted AT/RTs than in patient spectra and taurine observed in all animal spectra were also noted. The causes of these dissimilarities warrant further investigation.

Expansion of multipotent and lymphoid-committed human progenitors through intracellular dimerization of Mpl.

Self-renewal capacity is rapidly lost during differentiation of hematopoietic stem cells to lineage-committed progenitors. We demonstrate here that regulated intracellular signaling through the cytokine receptor Mpl induces profound expansion of not only multipotent (ie, lymphomyeloid) but also lymphoid-committed human hematopoietic progenitors. A fusion protein containing the intracellular signaling domain of Mpl and a dimerization domain was constitutively expressed in populations enriched in human lymphomyeloid progenitor/stem cells (CD34(+)CD38(-)Lin(-)CD7(-)) and multilymphoid progenitors (CD34(+)CD38(-)Lin(-)CD7(+)). Intracellular dimerization of Mpl in target cells was induced by in vitro or in vivo administration of a diffusible synthetic ligand. In vitro, Mpl dimerization produced divisions of clonogenic, multilineage CD34(+) cells able to engraft immunodeficient mice. When dimerization was induced in vivo after transplantation of either lymphomyeloid or multilymphoid progenitors, donor-derived hematopoiesis was sustained for at least 12 weeks and primitive CD34(+)Lin(-) progenitors were expanded more than 1000-fold. Lineage potential of progenitors was not altered and differentiation was not prevented by synthetically induced Mpl signaling. These data demonstrate that dimerization of a single cytokine receptor can deliver a profound expansion signal in both uncommitted and lymphoid-committed human hematopoietic progenitors.