Abstract P4-08-18: Engineered Toxin Bodies Specific for TROP2 Positive Cancers

Engineered Toxin Bodies Specific for TROP2 Positive Cancers Authors: Garrett L. Cornelison, Ileana Pedraza, Kendra Garrison, Elizabeth M. Kapeel, Channing Pletka, Abdul Khan, Jessica Momb, Rebecca Martin, Adam Bartos, Joseph D. Dekker, Jay Zhao, John Majercak, Garrett L. Robinson Molecular Templates, Austin, TX Lanier Biotherapeutics, Bogart, GA Molecular Templates produces next generation immunotoxins called Engineered toxin bodies (ETBs). ETBs are comprised of a proprietarily engineered form of Shiga-like Toxin A subunit (SLT-A) genetically fused to antibody-like binding domains. ETBs work through novel mechanisms of action and are capable of forced internalization, undergoing retrograde translocation to the cytosol, and inducing potent cell-kill via the enzymatic and permanent inactivation of ribosomes resulting in the inhibition of protein synthesis and induction of apoptosis. In addition, Molecular Templates has expanded the ETB platform to include Antigen Seeding Technology (AST) to generate ETBs with the ability to deliver foreign protein antigen to targeted populations of tumor cells. This mechanism of action allows for the intracellular processing of antigen and subsequent surface MHC-I presentation required for activation of a re-directed T lymphocyte response and the capacity to restore a functional immune clearance program against the tumor. Three ETBs are in clinical development (MT-5111 targeting HER2, MT-0169 targeting CD38, and AST enabled MT-6402 targeting PD-L1). The novel mechanisms of action have potential benefit in different indications including in the relapsed setting, when disease has progressed after chemotherapies and other targeted therapies, and additionally may be able to combine with standard of care. ETBs are being developed that target other cell surface receptors expressed on solid tumors including tumor-associated calcium signal transducer 2 (TROP2). TROP2 is a clinically validated target in metastatic triple-negative breast cancer (mTNBC) and other cancers such as metastatic urothelial carcinoma (mUC) using antibody drug conjugate (ADC) therapies such as sacituzumab govitecan (Trodelvy®). In vitro, ETBs targeting TROP2 specifically and directly kill tumor cells expressing TROP2 with picomolar activity. ETBs can bind to TROP2 in the presence of the Trodelvy parent monoclonal antibody, sacituzumab, and ETBs retain potency on TROP2 positive cell lines in the presence of clinically relevant concentrations of sacituzumab. AST enabled Trop2 targeted ETBs retain direct cell killing activity and can deliver multiple viral antigens to induce cytokine secretion and T-cell mediated killing in a co-culture assay of TROP2 target cells with antigen matched HLA type and antigen specific T-cells. In vivo, TROP2 targeted ETBs demonstrate good tolerability in a murine HCC1806 triple-negative breast cancer xenograft model and significantly reduce tumor burden relative to vehicle control. These pre-clinical in vitro and in vivo data suggest AST enabled Trop2 targeted ETBs have the potential to deplete Trop2 positive malignancies through multiple unique mechanisms of action.

Citation Format: Garrett L. Cornelison, Ileana Pedraza, Kendra Garrison, Elizabeth M. Kapeel, Channing Pletka, Abdul Khan, Jessica Momb, Rebecca Martin, Adam Bartos, Joseph D. Dekker, Jay Zhao, John Majercak, Garrett L. Robinson. Engineered Toxin Bodies Specific for TROP2 Positive Cancers [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-08-18.

Abstract 2579: Improving immunotoxin-based therapeutics for cancer with de-immunized engineered toxin bodies

Engineered Toxin Bodies (ETBs) represent a unique therapeutic strategy for fighting cancer by targeting and selectively destroying cancer cells or cancer-promoting immune cells. Featuring an antibody-based targeting domain fused with the cytotoxic, ribosome inactivating Shiga-like toxin A subunit (SLTA), ETBs enable killing of target expressing cells. Although immunotoxins have been explored for decades as promising cancer therapeutics, activation of innate immunity limited this approach. MTEM has developed 1st, 2nd, and 3rd generation ETBs with iterative improvements to reduce immunogenicity and add mechanisms of action. Here, we describe the development of an ex vivo cytokine release assay used to enhance the safety, tolerance, and therapeutic index (TI) of ETBs as cancer therapeutics. MT-3724, a 1st gen CD20 targeting ETB comprising wild type SLTA (WT SLTA) genetically fused to a CD20 targeting scFv, displayed efficacy as monotherapy in relapsed/refractory non-Hodgkin lymphoma. However, a subset of MT-3724-treated patients experienced capillary leak syndrome (CLS), likely driven by innate immune recognition of specific components of WT SLTA. Adverse events were also associated with a particular lot of MT-3724 that contained a higher proportion of aggregated species. Therefore, next gen ETBs were de-immunized by replacing surface exposed residues of WT SLTA while retaining cytotoxicity and were designed to have reduced propensity for aggregation. An ex vivo cytokine release assay, developed to triage candidate ETBs that generate innate immune activation, was validated by probing WT-SLTA and aggregated MT-3724. Cancer free human peripheral blood mononuclear cells (PBMCs) or PBMCs depleted of B cells were treated with positive and negative controls, non-targeted SLTAs, and ETBs. Cytokine concentrations were quantified by Luminex. The positive control TLR4 agonist lipopolysaccharide (LPS) activated robust release of proinflammatory cytokines including IL-1β, TNFα, and IL-6, as well as CCL3, CCL4, GM-CSF, IL-10, IFNγ, and Granzyme B. Non-targeted WT SLTA displayed a similar, but not identical, pattern of cytokine release. Conversely, the de-immunized (DI) SLTA did not activate cytokine or chemokine release, remaining at levels equal to PBS, indicating that scrubbing WT SLTA of immunogenic components can improve the safety profile and TI of our 2nd gen ETBs. Aggregated MT-3724 induced moderate increases in TNFα, IL-6, CCL3, and CCL4 relative to a non-aggregated MT-3724 lot. Removal of B cells from PBMCs did not alter cytokine release patterns of LPS, WT SLTA, or aggregated MT-3724. These data suggest that cytokines were released in response to WT SLTA and protein aggregates in an off-target manner. This assay will be used to evaluate ETB safety by testing candidate ETBs for likelihood of cytokine release and/or innate immune activation prior to selection as candidates for clinical trials.

Citation Format: Rachael M. Orlandella, Elizabeth M. Kapeel, Brigitte Brieschke, Garrett L. Robinson, Joseph D. Dekker, Chris B. Moore. Improving immunotoxin-based therapeutics for cancer with de-immunized engineered toxin bodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2579.

Abstract 326: Engineered toxin bodies (ETBs) targeting Trop2

Engineered toxin bodies (ETBs) are comprised of a proprietarily engineered form of Shiga-like Toxin A subunit (SLT-A) genetically fused to antibody-like binding domains. ETBs work through novel mechanisms of action and are capable of forced internalization, undergoing retrograde translocation to the cytosol, and inducing potent cell-kill via the enzymatic and permanent inactivation of ribosomes resulting in the inhibition of protein synthesis and induction of apoptosis through ribotoxic stress mechanisms.

Additionally, Molecular Templates has developed the Antigen Seeding Technology (AST) platform to generate ETBs with the unique ability to deliver foreign protein antigen to targeted populations of tumor cells. This MOA allows for the intracellular processing of antigen and subsequent surface MHC-I presentation required for activation of a re-directed T lymphocyte response and the capacity to restore a functional immune clearance program against the tumor.

Three ETBs are in clinical development (MT-5111 targeting HER2, MT-0169 targeting CD38, and AST enabled MT-6402 targeting PD-L1). The novel mechanisms of action have potential benefit in different indications including in the relapsed setting, when disease has progressed after chemotherapies and other targeted therapies, and additionally may be able to combine with standard of care.

ETBs are being developed that target other cell surface receptors expressed on solid tumors including tumor-associated calcium signal transducer 2 (Trop2). Trop2 is a clinically validated target of antibody drug conjugate (ADC) therapy in metastatic triple-negative breast cancer (mTNBC) and other cancers such as metastatic urothelial carcinoma (mUC).

In vitro, tumor cells expressing Trop2 are effectively, specifically, and directly killed with picomolar activity by targeted ETBs. AST enabled Trop2 targeted ETBs are capable of delivering viral antigens for multiple HLA types and inducing cytokine secretion and T-cell mediated killing in a co-culture assay of Trop2 target cells with antigen matched HLA type and antigen specific T-cells. These pre-clinical in vitro data suggest AST enabled Trop2 targeted ETBs have the potential to deplete Trop2 positive malignancies through multiple unique mechanisms of action.

Citation Format: Garrett L. Cornelison, Adam Bartos, Brigitte Brieschke, Jessica Momb, Ileana Pedraza, Elizabeth M. Kapeel, Rebecca Martin, Channing Pletka, Adrian Gonzalez, Joseph D. Dekker, Jay Zhao, John Majercak, Garrett L. Robinson. Engineered toxin bodies (ETBs) targeting Trop2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 326.

Abstract 3543: Altering tumor immunophenotypes with PD-L1 engineered toxin bodies

Targeting of PD-L1 checkpoint has shown clinical efficacy in multiple solid tumor indications. Currently approved PD-L1 targeted approaches rely on the blocking activity of monoclonal antibodies (mAbs) which sterically inhibit PD-L1 thus preventing PD-1 mediated immune checkpoint activity. Although these mAbs have shown activity in the clinic, the need for pre-existing tumor specific immunity and tumor immune infiltration precludes responses in some patients and leads to resistance in others. Therefore, there remains a need for new modalities and treatment paradigms. Molecular Templates has developed MT-6402, an engineered toxin body (ETB) targeting PD-L1 designed to overcome the challenges of current PD-L1 targeting approaches by 1) directly depleting PD-L1 positive tumor or immunosuppressive immune cells displaying PD-L1 and 2) alteration of the tumor immunophenotype through the cytoplasmic delivery of an HLA:A*02 restricted cytomegalovirus (CMV) antigen. Delivery of this antigen is meant to leverage recruitment of existing CMV-restricted cytotoxic T lymphocytes (CTLs) for cell-mediated cytotoxic depletion (antigen seeding technology, AST) of CMV antigen presenting tumor cells. MT-6402 is currently in a phase I open-label, dose escalation and expansion study in subjects with advanced solid cancers that express PD-L1 (NCT04795713). Initial assessment of pharmacodynamic markers for PD-L1 and CMV-mediated ETB activity in a subject with confirmed PD-L1+ tumor cells, CMV positivity, and HLA:A*02 restriction has shown serum phenotypes associated with robust checkpoint inhibitor activity and full extravasation of circulating CMV-specific T cells. In addition to assessing early clinical data from the HLA: A*02 restricted MT-6402 trials, expansion of ETB AST to a broader patient population requires testing of ETBs engineered with the ability to deliver CMV antigens across a broad range of HLA restriction, including HLA:A*01, HLA:A*03, and HLA:A*24. To this end, ETBs were benchmarked against MT-6402 to identify candidates that retain comparable specificity, selectivity, and activity. Substitution of peptide antigens did not alter specificity or selectivity of ETBs compared to MT-6402. Candidate ETB binding profiles and potency were comparable to MT-6402. ETBs delivered an antigen seeding response in a PD-L1 dependent and HLA specific manner. In vivo efficacy of candidate ETBs was comparable in a murine efficacy xenograft model with MT-6402. An ex vivo cytokine release assay in a co-culture setting using HLA matched CTLs and PD-L1+ target cells, treatment with AST capable ETBs resulted in secretion of antigen specific T cell mediated immune cytokines compared to AST null controls. These cytokines overlap with cytokine signatures observed after dosing MT-6402 in HLA:A*02 patients. Preclinical assessment of the safety profile of candidates is ongoing and further development is slated for 2021.

Citation Format: Swati Khanna, Elizabeth M. Kapeel, Lauren R. Byrne, Elizabeth Saputra, Steven Rivera, Lindsey Aschenbach, Lilia A. Rabia, Garrett L. Cornelison, Rachael M. Orlandella, Brigitte Brieschke, Michaela Sousares, Jay Zhao, Garrett L. Robinson, Chris Moore, Joseph D. Dekker. Altering tumor immunophenotypes with PD-L1 engineered toxin bodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3543.

Abstract 335: c-KIT targeted ETBs for cancer therapy and HSC transplant conditioning

Engineered toxin bodies (ETBs) are next-generation immunotoxins that harbor an antibody-derived targeting domain and a cytotoxic payload derived from Shiga-like toxin-1 catalytic subunit A (SLTA). SLTA has been engineered to reduce innate immunogenicity and therefore increase the safety of ETBs whilst retaining potent cytotoxic properties. When targeted via a binding domain, SLTA is internalized and routes to the cytosol leading to irreversible ribosome inactivation and ultimately cell death.

ETBs have been developed to treat a wide variety of cancers, including breast, lymphoma, multiple myeloma and PD-L1 positive solid tumors. This technology holds promise for non-oncology indications as well, particularly as a targeted and non-genotoxic conditioning regimen for hematopoietic stem cell (HSC) ablation to prepare patients for autologous stem cell transplant.

c-KIT (CD117) is a well-known marker of hematopoietic stem and progenitor cells and is overexpressed in a high percentage of certain cancers including GIST, SCLC and AML. While tyrosine kinase inhibitors such as imatinib are effective therapies for c-KIT mutant GIST, resistance often occurs by the development of secondary mutations in the intracellular signaling domains. Thus, c-KIT represents a potential ETB target for both oncological and HSC transplant conditioning indications. Here we present data highlighting the in vitro potency and efficacy of CD117-targeting ETBs on cancer cell lines as well as on primary human CD34+ HSCs. CD117-targeted ETBs demonstrate exquisite specificity in vitro by killing only target positive CD34+ cells at picomolar potency while sparing the progenitors that lack CD117 expression. However, relatively low CD117 receptor levels on CD34+ HSCs prevent complete killing in vitro, limiting the observed efficacy. To overcome this challenge, an additional cytotoxic payload was conjugated to the ETB molecule to capitalize on ETBs’ unique internalization and routing properties to deliver a secondary mechanism of action. ETB-drug conjugates (ETB-DCs) exhibited improved cytotoxicity in vitro, especially in CD117-low target cells. Moving forward, we plan to explore both the ETB and the ETB-DC therapeutic index in vivo with a series of CD117+ tumor efficacy and HSC depletion models.

Citation Format: Caleigh Howard, Shu Wiley, Wenzhao Dong, Andrea Mendiola, Veronica Partridge, Sara LeMar, Paul Amador, Amit K. Chaudhary, Joseph D. Dekker, Jay Zhao, Ross Durland, Aimee Iberg. c-KIT targeted ETBs for cancer therapy and HSC transplant conditioning [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 335.

Abstract 1628: Engineered toxin bodies targeting PD-L1 to alter tumor immunophenotypes and deliver broad antigenic diversity and patient coverage

Targeting PD-L1 has shown clinical efficacy in multiple solid tumor indications. Currently approved PD-L1 targeted approaches rely on monoclonal antibodies which sterically inhibit PD-L1 and prevent PD-1 mediated checkpoint activity. While these molecules have shown great activity in the clinic, the need for pre-existing tumor specific immunity and immune infiltration precludes responses in some patients and leads to resistance in others. Therefore, there remains a need for new modalities and treatment paradigms in these indications.

Molecular Templates has developed MT-6402, an engineered toxin body (ETB) targeting PD-L1, as a single agent immunotoxin designed to overcome the challenges of current PD-L1 targeting approaches by 1) directly depleting PD-L1 positive tumor cells or immunosuppressive immune cells displaying PD-L1 in the tumor microenvironment and 2) delivery of an HLA: A*02 restricted viral peptide to alter the tumor immunophenotype for recruitment of CMV-restricted CTLs to target the tumor for depletion (antigen seeding). MT-6402 is slated for clinical development in 2021.

Here we describe the preclinical characterization of several ETB candidates derived from MT-6402 delivering antigenic peptides restricted to the most prevalent MHC haplotypes in the U.S. population to broaden the patient population suitable for antigen seeding. ETBs were engineered with the ability to deliver viral peptides across a range of HLA restriction, including HLA: A*01, HLA: A*03, and HLA: A*24. ETBs were screened and benchmarked against MT-6402 and candidates were identified that retain comparable specificity, selectivity, and potency. Alteration of peptide antigen did not change the specificity or selectivity of ETBs which retained similar PD-L1 binding profiles to MT-6402. Binding profiles correlated to targeted potency and ETBs with varied HLA restricted peptides were found to target tumor and immune cells for depletion with similar potency to MT-6402. ETBs delivered an antigen seeding response in a PD-L1 dependent manner and only in conditions in which tumor cell and CTLs shared a matched HLA to the delivered antigenic peptide specificity. Preclinical assessment of the in vivo efficacy and safety profile of candidates is ongoing and further development is slated for 2021.

Citation Format: Joseph D. Dekker, Swati Khanna, Elizabeth Saputra, Wenzhao Dong, Lindsey Aschenbach, Lilia A. Rabia, Garrett L. Cornelison, Michaela Sousares, Jay Zhao, Garrett L. Robinson, Betty Chang, Hilario J. Ramos. Engineered toxin bodies targeting PD-L1 to alter tumor immunophenotypes and deliver broad antigenic diversity and patient coverage [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1628.

Foxp1 Regulates Neural Stem Cell Self-Renewal and Bias Toward Deep Layer Cortical Fates

The laminar architecture of the mammalian neocortex depends on the orderly generation of distinct neuronal subtypes by apical radial glia (aRG) during embryogenesis. Here, we identify critical roles for the autism risk gene Foxp1 in maintaining aRG identity and gating the temporal competency for deep-layer neurogenesis. Early in development, aRG express high levels of Foxp1 mRNA and protein, which promote self-renewing cell divisions and deep-layer neuron production. Foxp1 levels subsequently decline during the transition to superficial-layer neurogenesis. Sustained Foxp1 expression impedes this transition, preserving a population of cells with aRG identity throughout development and extending the early neurogenic period into postnatal life. FOXP1 expression is further associated with the initial formation and expansion of basal RG (bRG) during human corticogenesis and can promote the formation of cells exhibiting characteristics of bRG when misexpressed in the mouse cortex. Together, these findings reveal broad functions for Foxp1 in cortical neurogenesis.

Abstract 521: CD45 targeted engineered toxin bodies deplete hematopoietic and malignant cells

CD45 is highly expressed on the cell surface of all nucleated hematopoietic cells, including malignant cells of B, T and myeloid lineage. CD45, a receptor tyrosine phosphatase that has important roles in antigen receptor signaling, has multiple isoforms that are differentially expressed on immune cell subsets. Targeting of CD45 with antibody-based therapies, tested in conjunction with reduced dose chemotherapy and radiation regimens, has shown promise in preclinical models and clinical trials as a conditioning therapy for bone marrow transplant (BMT), although these approaches are associated with safety limitations. A single agent, targeted conditioning method could increase patient safety and eliminate genotoxic effects associated with the conditioning regimens. Conditioning therapy by depletion of CD45 positive cells specifically has potential applications in oncology as well as non-oncologic, hematopoietic disease settings where engraftment of donor or modified stem cells could provide benefit. Engineered toxin bodies (ETBs) are comprised of a proprietarily engineered form of Shiga-like Toxin A subunit (SLT-A) genetically fused to antibody-like binding domains. ETBs work through novel mechanisms of action and are capable of forcing internalization, self-routing through intracellular compartments to the cytosol, and inducing potent cell-kill via the enzymatic and permanent inactivation of ribosomes. Targeted ETBs are being developed to specifically target and destroy CD45 expressing cells. ETBs targeting CD45 specifically bind to, internalize into and then trigger cell death of the target cells in vitro. ETBs have been designed using antibody fragments that recognize all isoforms of CD45. The CD45 targeted ETB has shown high potency in immortalized blood cancer cell lines of T cell, B-cell and eosinophil origin, including leukemia and lymphoma cell lines. Additionally, the ability of the CD45 targeted ETBs to deplete primary cells from healthy donors has been demonstrated. The direct cell kill activity of the CD45 targeted ETBs have the potential to deplete immune cells in the periphery and the bone marrow, as well as to deplete malignant hematological cells expressing CD45. In vivo depletion of human immune cells in murine models by CD45 targeted ETBs will be evaluated.

Citation Format: Aimee Iberg, Garrett L. Robinson, Sara LeMar, Joseph D. Dekker, Jay Zhao, Hilario J. Ramos, Melissa M. Singh, Erin K. Willert. CD45 targeted engineered toxin bodies deplete hematopoietic and malignant cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 521.

Abstract 3366: In vivo efficacy of a PD-L1 targeted, antigen seeding engineered toxin body

Engineered toxin bodies (ETBs) comprised of a proprietarily engineered Shiga-like Toxin A subunit (SLTA) genetically fused to antibody-like binding domains work through novel mechanisms of action and can force internalization, self-route through intracellular compartments to the cytosol, and induce potent cell-kill via the enzymatic and permanent inactivation of ribosomes. Our PD-L1 targeted ETB, MT-6402, includes antigen seeding technology (AST), and additionally delivers a viral antigen for presentation in complex with MHC-I to resident viral-specific cytotoxic T lymphocytes (CTLs). The fusion protein provides a powerful, dual mechanism of action to specifically target and destroy PD-L1 positive tumor and inhibitory immune cells. In vitro testing of human tumor cell lines has demonstrated that cell surface PD-L1 expression is required for activity of the PD-L1 targeted ETBs. MT-6402 demonstrated effective depletion of PD-L1 expressing cells across a panel of immortalized cancer cell lines from multiple origins, including lung, skin, breast, and ovary. In a co-culture assay of PD-L1 target cells and antigen specific T-cells, PD-L1 targeted MT-6402 delivers a viral antigen to the target cells and can activate cytokine secretion and T-cell mediated killing. Additionally, MT-6402 treatment of human peripheral blood mononuclear cells (PBMCs) leads to selective depletion of PD-L1 positive cells (IFN-γ stimulated monocytes) in the absence of depletion of PD-L1 low/negative lymphocytes. Murine models, including patient derived xenografts, have demonstrated that the PD-L1 targeted ETBs are efficacious in vivo. Additional in vivo tumor models to further describe the effect of MT-6402 are being explored. Exploratory studies in a primate model have shown that MT-6402 can be tolerated at levels shown to induce T cell activation (type 1 cytokines). MT-6402 delivers a powerful and unique dual mechanism of action. The combination of a PD-L1 specific direct cell kill and redirection of a robust effector T cell response to the tumor has potential benefit in solid tumor indications, including in the relapsed setting, when disease has progressed after checkpoint and/or other therapies.

Citation Format: Hilario J. Ramos, Brigitte Brieschke, Sara LeMar, Joseph D. Dekker, Aimee Iberg, Garrett L. Robinson, Asis Sarkar, Banmeet Anand, Melissa M. Singh, Jay Zhao, Jack P. Higgins, Erin K. Willert. In vivo efficacy of a PD-L1 targeted, antigen seeding engineered toxin body [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3366.

Abstract 2278: CTLA-4 targeted engineered toxin bodies designed to deplete regulatory T cells (Tregs)

Tumor resident regulatory T cells (Tregs) are important mediators of an immunosuppressive tumor microenvironment (TME) promoting tumor immune evasion. The presence of Tregs, and a higher ratio of Tregs to effector T cells in the TME, are associated with poor prognosis. The depletion of Tregs in the TME is expected to re-expose the tumor to the immune system to allow for tumor control. CLTA-4 is expressed on the cell surface of Tregs and is a clinically validated target. Better responses to CTLA-4 monoclonal antibody (mAb) treatment are correlated with stronger ADCC-mediated Treg depletion in preclinical models, and patient FcγR polymorphism has been reported to correlate with response to CTLA-4 mAb therapy. Towards improving on current therapies, many efforts to increase effective depletion of Tregs (such as by Fc effector modification) are being pursued. Engineered toxin bodies (ETBs) are comprised of a proprietarily engineered form of Shiga-like Toxin A subunit (SLT-A) genetically fused to antibody-like binding domains. ETBs work through novel mechanisms of action and are capable of forcing internalization, self-routing through intracellular compartments to the cytosol, and inducing potent cell-kill via the enzymatic and permanent inactivation of ribosomes. Targeted ETBs are being developed to specifically target and destroy CTLA-4 expressing cells. In vitro, cells expressing CTLA-4 are effectively and specifically killed by targeted ETBs. This direct cell kill activity of the ETB has the potential to deplete Tregs in the TME without a requirement for ADCC mechanisms. ETBs have been designed to bind various CTLA-4 epitopes, and to comprise of different targeting domains formats, including monomeric and diabody single chain variable fragments (scFvs) as well as single domain and biparatopic antibody fragments. The development of a CTLA-4 targeted ETB is ongoing. The entry of a protein with direct cell kill properties into the therapeutic space represents a differentiated mechanism of action to deplete Tregs for ultimate re-invigoration of the anti-tumor immune response, and has the potential to provide benefit to patients, including in the relapsed or refractory setting.

Citation Format: Aimee Iberg, Edith Acquaye-Seedah, Lilia A. Rabia, Garrett L. Robinson, Hilario J. Ramos, Joseph D. Dekker, Jay Zhao, Erin K. Willert. CTLA-4 targeted engineered toxin bodies designed to deplete regulatory T cells (Tregs) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2278.

The lysine methyltransferase SMYD2 is required for normal lymphocyte development and survival of hematopoietic leukemias

The 5 membered SET and MYND Domain-containing lysine methyltransferase (SMYD) family plays pivotal roles in development and proliferation. Initially characterized within the cardiovascular system, one such member, SMYD2, has been implicated as an oncogene in leukemias deriving from flawed hematopoietic stem cell (HSC) differentiation. We show here that conditional SMYD2 loss disrupts hematopoiesis at and downstream of the HSC via both apoptotic loss and transcriptional deregulation of HSC proliferation and disruption of Wnt-β-Catenin signaling. Yet previously documented SMYD2 cell cycle targets were unscathed. Turning our analysis to human leukemias, we observed that SMYD2 is highly expressed in CML, MLLr-B-ALL, AML, T-ALL and B-ALL leukemias and its levels in B-ALL correlate with poor survival. SMYD2 knockdown results in apoptotic death and loss of anchorage-independent transformation of each of these hematopoietic leukemias. These data provide an underlying mechanism by which SMYD2 acts during normal hematopoiesis and as a proto-oncogene in leukemia.

Loss of the FOXP1 Transcription Factor Leads to Deregulation of B Lymphocyte Development and Function at Multiple Stages

The FOXP1 transcription factor is expressed throughout B cell development until its extinction just prior to terminal differentiation. Foxp1 nulls die of cardiac defects at midgestation, but adult rescue via fetal liver transfer led to a strong pre-B cell block. To circumvent these limitations and to investigate FOXP1 function at later stages of B cell differentiation, we generated and analyzed floxed (F) Foxp1 alleles deleted at pro-B, transitional (T) 1, and mature B cell stages. Mb-1cre-mediated deletion of Foxp1^F/F confirmed its requirement for pro-B to pre-B transition. Cd21- and Cd19cre deletion led to significant reduction of germinal center formation and a second block in differentiation at the T2/marginal zone precursor stage. T-dependent and -independent immunization of FOXP1 mutants led to reduction of Ag-specific IgM, whereas responses of class-switched Abs were unimpaired. Yet, unexpectedly, plasmablast and plasma cell numbers were significantly increased by in vitro BCR stimulation of Foxp1^F/F splenic follicular B cells but rapidly lost, as they were highly prone to apoptosis. RNA sequencing, gene set enrichment analysis, and chromatin immunoprecipitation sequencing analyses revealed strong enrichment for signatures related to downregulation of immune responses, apoptosis, and germinal center biology, including direct activation of Bcl6 and downregulation of Aicda/AID, the primary effector of somatic hypermutation, and class-switch recombination. These observations support a role for FOXP1 as a direct transcriptional regulator at key steps underlying B cell development in the mouse.

Abstract 3900: The Safety and efficacy profile of a PD-L1 directed, Engineered Toxin Body, as a novel targeted direct-cell kill approach for the treatment of PD-L1 expressing cancers

Engineered Toxin Bodies (ETBs) are comprised of a deimmunized Shiga-like toxin subunit A (SLTA) genetically fused to an antibody-like targeting domain. The antibody targeting domain allows for specific targeting of cancer cells while the SLTA component promotes self-internalization of ETBs, an activity that allows for the delivery of an enzymatic and permanent ribosomal destruction against targeted cells even in the context of non-or-poorly internalizing receptor targets. Molecular Templates has developed PD-L1-targeting ETBs as an approach to directly target tumor cells and overcome resistance mechanisms against PD-1 and PD-L1 antibodies. The cytotoxicity delivered by PD-L1-specific ETBs is engineered to be independent of a requirement for tumor infiltrating lymphocytes (TILs), high tumor mutational burden, or modulatory effects of the tumor microenvironment. Further, the activity is not dependent on blockade of the PD-1/PD-L1 checkpoint axis. Thus, PD-L1 targeting ETBs represent a distinct class of therapeutics with direct cell-kill mechanism of action and ability for activity in patients who have progressed on current standard of care or checkpoint therapy. In this study, we highlight the efficacy and safety profile of MT-6020, a human and cynomolgus cross-reactive, PD-L1 targeted, ETB. MT-6020 retains potent catalytic activity and mediates enzymatic destruction of ribosomes at comparable levels to wild-type SLTA in a cell free model. In addition, MT-6020 binds to human NSCLC, Melanoma, and TNBC tumor cell lines with nM affinity and mediates cellular cytotoxicity via ribosomal destruction at low nM to sub-nM potency. MT-6020 binds to cell lines expressing non-human primate (NHP)-PD-L1 and elicits cytotoxic responses comparable to those observed on human tumor target cells. MT-6020 demonstrated pharmacodynamic and pharmacokinetic effects and displayed a favorable tolerability profile in a repeat dose NHP study at doses that are above the presumed therapeutically active concentration. Further our lead PD-L1 ETB, MT-6035, is built upon the MT-6020 scaffold and can deliver a viral peptide for cell surface presentation to and targeting by a specific antiviral CTL population (antigen seeding technology (AST)) for a second and complementary mechanism for tumor cell destruction. MT-6020 and MT-6035 represent a novel approach to targeting and destroying tumors expressing PD-L1 that is unlikely to be inhibited by resistance mechanisms to current checkpoint inhibitors, is well tolerated in relevant toxicity models, and has the capacity for activity in indications where standard of care has failed. Molecular Templates is poised to initiate clinical development of the PD-L1 targeted-ETB (AST), MT-6035, in 2H - 2019.

Citation Format: Hilario J. Ramos, Asis K. Sarkar, Sara Le Mar, Brigitte Brieschke, Joseph D. Dekker, Veronica R. Partridge, Pablo A. Maceda, Michaela M. Sousares, Garrett L. Robinson, Aimee Iberg, Shaoyou Chu, Jensing Liu, Jack P. Higgins, Erin K. Willert. The Safety and efficacy profile of a PD-L1 directed, Engineered Toxin Body, as a novel targeted direct-cell kill approach for the treatment of PD-L1 expressing cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3900.

Engineered Toxin Bodies delivering immunogenic MHC class I peptides to tumor cells summon polyfunctional and relevant CTL responses against cancers

Immunotherapeutic approaches such as CAR-T and T cell engaging bispecific antibodies have shown positive clinical outcomes and demonstrate the value of harnessing cytotoxic T lymphocyte (CTL) activity for tumor intervention. Here we describe Engineered Toxin Bodies (ETBs) with Antigen Seeding Technology (AST) as a unique tumor targeted therapeutic approach to recruit endogenous polyfunctional memory CTL responses against cancers.

Molecular Templates’ ETB platform combines antibody domains with a proprietary form of the Shiga like Toxin A (SLTA) subunit to specifically target cells and exploit SLTA’s intrinsic ability to self-internalize and destroy ribosomes. With the addition of a foreign class I antigenic peptide fused to an ETB (AST), antigens present in complex with endogenous MHC I to initiate a high avidity T cell response to target cells. Utilizing this approach, we demonstrate ETBs targeted to clinically relevant markers can seed antigenic peptides to hematological tumor, solid tumor, and primary cells.

Expanded CTLs from donors with preexisting Human Cytomegalovirus (CMV) reactivity phenotypically resembled memory expansion from natural infection. We next delivered class I CMV peptide to tumor cells by AST with ETBs targeted to PD-L1 and co-cultured tumor cells with expanded CTLs. This led to activation of CMV specific T cells, direct tumor-T cell engagement, and potent cell kill activity above that of parental ETBs. CTL phenotyping and cytokine profiling revealed polyfunctional T cell activation driven by AST enabled ETBs. Thus, ETBs delivering peptide via AST provide additive mechanisms of action: direct cell kill via ribosomal destruction, and antigen specific polyfunctional memory CTL activation.

Common lymphoid progenitor derivation of a conserved dendritic cell subtype is mediated by Bcl11a

Plasmacytoid dendritic cells (pDCs) are a distinct subset of dendritic cell that specializes in the production of type I interferons (IFNs) upon engagement of pattern recognition receptors to promote antiviral immune responses. They have been implicated in the pathogenesis of autoimmune diseases that are characterized by a type I IFN signature, yet, pDC also can induce tolerogenic immune responses. Whereas an understanding of pDC physiology, immune function, and clinical significance has increased considerably, their development has not been unequivocally traced to either lymphoid or myeloid lineages nor has its transcriptional regulatory network been fully clarified. We observed that mb1-Cre mediated deletion of the Bcl11a transcription factor in common lymphoid progenitors (CLP) resulted in a ~15% reduction in pDC cellularity. Adoptive transfer of bone marrow from Bcl11aF/Fmb1-Cre mice recapitulated partial pDC loss. Mb1-Cre:YFP+ reporter mice contained ~85% YFP− and ~15% YFP+ pDCs, indicating a myeloid–lymphoid dichotomy of pDC generation. As compared with myeloid pDC, CLP-derived pDC (termed B-pDC) display a B cell-like gene expression profile, including hallmark targets directly transactivated by Bcl11a in B cells. B-pDCs demonstrate preferential homing to secondary lymphoid organs, are inherently activated compared to myeloid pDC, expand more rapidly upon TLR9 engagement, and are genetically and phenotypically homologous to a DC subtype recently discovered in human blood. We conclude that the pDC compartment comprises two cell types with overlapping but distinct functions that are conserved between mouse and man.

The Force Awakens: Illuminating the role of kynurenine in cancer progression and treatment

Cancer is the second leading cause of death in the US and, despite progress in treatment options, there is a critical need for novel treatments that specifically target cancerous cells. Our immune system routinely identifies potential cancer cells and eliminates them without the need for clinical intervention. However, to evade immune clearance, many cancers elevate tryptophan catabolism in the tumor microenvironment (TME) by upregulating the enzymes indoleamine 2, 3-dioxygenase (IDO) or, alternatively, tryptophan 2, 3- dioxygenase (TDO). This results in greater tryptophan turnover, accumulation of IDO/TDO product, kynurenine (L-kyn), and immune suppression in the TME. Whether the resulting immunosuppression arises from tryptophan depletion or L-kyn accumulation remains highly controversial. This work aims to (1) clarify L-kyn’s effect on T-cells and (2) whether its depletion can relieve tumor burden. Exposing T cells to L-kyn in vitro results in gene expression changes consistent with regulatory T-cell generation and the suppression of naïve T-cell proliferation; establishing L-kyn as a key therapeutic target for depletion to relieve TME immune suppression. Using a pharmacologically optimized kynureninase (KynU) enzyme, we tested L-kyn depletion therapy in murine cancers. KynU administration potently inhibits tumor growth, reduces L-kyn concentration, and results in a significant increase in the infiltration and proliferation of polyfunctional T-lymphocytes. Our ongoing study of KynU’s efficacy and L-kyn’s in vitro effects will illuminate details of L-kyn’s elusive mechanism of action, resolving critical mechanisms of tumor tolerance while creating a more innovative and effective cancer treatment strategy.

Forkhead Box Protein P1 Is Dispensable for Retina but Essential for Lens Development

Purpose

Forkhead box protein P1 (Foxp1) is a transcriptional repressor expressed in many tissues. We identified Foxp1 as a highly expressed gene in retinal progenitor cells and investigated its roles during eye development.

Methods

Mouse eyes with Foxp1 gain- or loss-of-function were established in vitro and in vivo.

Results

Foxp1 overexpression in retinal progenitor cells resulted in reduced rod and increased cone photoreceptors. However, retina-specific knockout of Foxp1 was not associated with retinal differentiation abnormalities. Foxp1 was highly expressed in the lens during early development, and continued to be expressed in epithelial and cortical fiber cells until adulthood. At birth, analyses of Foxp1 lens-specific knockout (Foxp1-L-CKO) mice showed no gross morphologic changes in germinal or central epithelial cell compared to the controls. However, the numbers of proliferating and apoptotic cells were significantly increased in Foxp1-L-CKO mice. In addition, clear Y-structures were not observed in either the posterior or anterior sutures of the Foxp1-L-CKO lenses. Mature lenses of Foxp1-L-CKO mice were small and opaque. The fiber cell structure in the core and the cortical fiber cell columns were disturbed in Foxp1-L-CKO mice at postnatal day 14, potentially accounting for the opacity. In addition, epithelial cells were not aligned into columns along the transition zone in Foxp1-L-CKO mice. Taken together, these results suggest that Foxp1 has a role during lens growth in epithelial and differentiating fiber cells.

Conclusions

Loss of Foxp1 results in loss of suture and fiber cell alignment, which eventually causes lens opacity, suggesting that Foxp1 has a key role in establishing cortical lens architecture.

FOXP1 controls mesenchymal stem cell commitment and senescence during skeletal aging

A hallmark of aged mesenchymal stem/progenitor cells (MSCs) in bone marrow is the pivot of differentiation potency from osteoblast to adipocyte coupled with a decrease in self-renewal capacity. However, how these cellular events are orchestrated in the aging progress is not fully understood. In this study, we have used molecular and genetic approaches to investigate the role of forkhead box P1 (FOXP1) in transcriptional control of MSC senescence. In bone marrow MSCs, FOXP1 expression levels declined with age in an inverse manner with those of the senescence marker p16INK4A. Conditional depletion of Foxp1 in bone marrow MSCs led to premature aging characteristics, including increased bone marrow adiposity, decreased bone mass, and impaired MSC self-renewal capacity in mice. At the molecular level, FOXP1 regulated cell-fate choice of MSCs through interactions with the CEBPβ/δ complex and recombination signal binding protein for immunoglobulin κ J region (RBPjκ), key modulators of adipogenesis and osteogenesis, respectively. Loss of p16INK4A in Foxp1-deficient MSCs partially rescued the defects in replication capacity and bone mass accrual. Promoter occupancy analyses revealed that FOXP1 directly represses transcription of p16INK4A. These results indicate that FOXP1 attenuates MSC senescence by orchestrating their cell-fate switch while maintaining their replicative capacity in a dose- and age-dependent manner.

FoxP1 orchestration of ASD-relevant signaling pathways in the striatum

In this study, Araujo et al. demonstrate that Foxp1 plays a role in the transcriptional regulation of autism-related pathways as well as genes involved in neuronal activity by identifying the gene expression program regulated by FoxP1 in both human neural cells and patient-relevant heterozygous Foxp1 mouse brains.

Mutations in the transcription factor Forkhead box p1 (FOXP1) are causative for neurodevelopmental disorders such as autism. However, the function of FOXP1 within the brain remains largely uncharacterized. Here, we identify the gene expression program regulated by FoxP1 in both human neural cells and patient-relevant heterozygous Foxp1 mouse brains. We demonstrate a role for FoxP1 in the transcriptional regulation of autism-related pathways as well as genes involved in neuronal activity. We show that Foxp1 regulates the excitability of striatal medium spiny neurons and that reduction of Foxp1 correlates with defects in ultrasonic vocalizations. Finally, we demonstrate that FoxP1 has an evolutionarily conserved role in regulating pathways involved in striatal neuron identity through gene expression studies in human neural progenitors with altered FOXP1 levels. These data support an integral role for FoxP1 in regulating signaling pathways vulnerable in autism and the specific regulation of striatal pathways important for vocal communication.

Spinal Locomotor Circuits Develop Using Hierarchical Rules Based on Motorneuron Position and Identity

The coordination of multi-muscle movements originates in the circuitry that regulates the firing patterns of spinal motorneurons. Sensory neurons rely on the musculotopic organization of motorneurons to establish orderly connections, prompting us to examine whether the intraspinal circuitry that coordinates motor activity likewise uses cell position as an internal wiring reference. We generated a motorneuron-specific GCaMP6f mouse line and employed two-photon imaging to monitor the activity of lumbar motorneurons. We show that the central pattern generator neural network coordinately drives rhythmic columnar-specific motorneuron bursts at distinct phases of the locomotor cycle. Using multiple genetic strategies to perturb the subtype identity and orderly position of motorneurons, we found that neurons retained their rhythmic activity-but cell position was decoupled from the normal phasing pattern underlying flexion and extension. These findings suggest a hierarchical basis of motor circuit formation that relies on increasingly stringent matching of neuronal identity and position.

Foxp1 Regulates the Proliferation of Hair Follicle Stem Cells in Response to Oxidative Stress during Hair Cycling

Hair follicle stem cells (HFSCs) in the bugle circularly generate outer root sheath (ORS) through linear proliferation within limited cycles during anagen phases. However, the mechanisms controlling the pace of HFSC proliferation remain unclear. Here we revealed that Foxp1, a transcriptional factor, was dynamically relocated from the nucleus to the cytoplasm of HFSCs in phase transitions from anagen to catagen, coupled with the rise of oxidative stress. Mass spectrum analyses revealed that the S468 phosphorylation of Foxp1 protein was responsive to oxidative stress and affected its nucleocytoplasmic translocation. Foxp1 deficiency in hair follicles led to compromised ROS accrual and increased HFSC proliferation. And more, NAC treatment profoundly elongated the anagen duration and HFSC proliferation in Foxp1-deficient background. Molecularly, Foxp1 augmented ROS levels through suppression of Trx1-mediated reductive function, thereafter imposing the cell cycle arrest by modulating the activity of p19/p53 pathway. Our findings identify a novel role for Foxp1 in controlling HFSC proliferation with cellular dynamic location in response to oxidative stress during hair cycling.

Smyd1 facilitates heart development by antagonizing oxidative and ER stress responses

Smyd1/Bop is an evolutionary conserved histone methyltransferase previously shown by conventional knockout to be critical for embryonic heart development. To further explore the mechanism(s) in a cell autonomous context, we conditionally ablated Smyd1 in the first and second heart fields of mice using a knock-in (KI) Nkx2.5-cre driver. Robust deletion of floxed-Smyd1 in cardiomyocytes and the outflow tract (OFT) resulted in embryonic lethality at E9.5, truncation of the OFT and right ventricle, and additional defects consistent with impaired expansion and proliferation of the second heart field (SHF). Using a transgenic (Tg) Nkx2.5-cre driver previously shown to not delete in the SHF and OFT, early embryonic lethality was bypassed and both ventricular chambers were formed; however, reduced cardiomyocyte proliferation and other heart defects resulted in later embryonic death at E11.5-12.5. Proliferative impairment prior to both early and mid-gestational lethality was accompanied by dysregulation of transcripts critical for endoplasmic reticulum (ER) stress. Mid-gestational death was also associated with impairment of oxidative stress defense—a phenotype highly similar to the previously characterized knockout of the Smyd1-interacting transcription factor, skNAC. We describe a potential feedback mechanism in which the stress response factor Tribbles3/TRB3, when directly methylated by Smyd1, acts as a co-repressor of Smyd1-mediated transcription. Our findings suggest that Smyd1 is required for maintaining cardiomyocyte proliferation at minimally two different embryonic heart developmental stages, and its loss leads to linked stress responses that signal ensuing lethality.

Foxp1/2/4 regulate endochondral ossification as a suppresser complex

Osteoblast induction and differentiation in developing long bones is dynamically controlled by the opposing action of transcriptional activators and repressors. In contrast to the long list of activators that have been discovered over past decades, the network of repressors is not well-defined. Here we identify the expression of Foxp1/2/4 proteins, comprised of Forkhead-box (Fox) transcription factors of the Foxp subfamily, in both perichondrial skeletal progenitors and proliferating chondrocytes during endochondral ossification. Mice carrying loss-of-function and gain-of-function Foxp mutations had gross defects in appendicular skeleton formation. At the cellular level, over-expression of Foxp1/2/4 in chondroctyes abrogated osteoblast formation and chondrocyte hypertrophy. Conversely, single or compound deficiency of Foxp1/2/4 in skeletal progenitors or chondrocytes resulted in premature osteoblast differentiation in the perichondrium, coupled with impaired proliferation, survival, and hypertrophy of chondrocytes in the growth plate. Foxp1/2/4 and Runx2 proteins interacted in vitro and in vivo, and Foxp1/2/4 repressed Runx2 transactivation function in heterologous cells. This study establishes Foxp1/2/4 proteins as coordinators of osteogenesis and chondrocyte hypertrophy in developing long bones and suggests that a novel transcriptional repressor network involving Foxp1/2/4 may regulate Runx2 during endochondral ossification.

Bright/Arid3A acts as a barrier to somatic cell reprogramming through direct regulation of Oct4, Sox2, and Nanog

We show here that singular loss of the Bright/Arid3A transcription factor leads to reprograming of mouse embryonic fibroblasts (MEFs) and enhancement of standard four-factor (4F) reprogramming. Bright-deficient MEFs bypass senescence and, under standard embryonic stem cell (ESC) culture conditions, spontaneously form clones that in vitro express pluripotency markers, differentiate to all germ lineages, and in vivo form teratomas and chimeric mice. We demonstrate that BRIGHT binds directly to the promoter/enhancer regions of Oct4, Sox2, and Nanog to contribute to their repression in both MEFs and ESCs. Thus, elimination of the BRIGHT barrier may provide an approach for somatic cell reprogramming.

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Loss of Bright can alone reprogram or enhance conventional four-factor reprogramming

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Bright directly represses Oct4, Sox2, and Nanog

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Bright may function in somatic and embryonic stem cells to enforce differentiation

Foxp1 maintains hair follicle stem cell quiescence through regulation of Fgf18

Hair follicles cyclically degenerate and regenerate throughout adult life and require regular stem cell activation to drive the cycle. In the resting phase of the hair cycle, hair follicle stem cells are maintained in a quiescent state until they receive signals to proliferate. We found that the forkhead transcription factor Foxp1 is crucial for maintaining the quiescence of hair follicle stem cells. Loss of Foxp1 in skin epithelial cells leads to precocious stem cell activation, resulting in drastic shortening of the quiescent phase of the hair cycle. Conversely, overexpression of Foxp1 in keratinocytes prevents cell proliferation by promoting cell cycle arrest. Finally, through both gain- and loss-of-function studies, we identify fibroblast growth factor 18 (Fgf18) as the key downstream target of Foxp1. We show that exogenously supplied FGF18 can prevent the hair follicle stem cells of Foxp1 null mice from being prematurely activated. As Fgf18 controls the length of the quiescent phase and is a key downstream target of Foxp1, our data strongly suggest that Foxp1 regulates the quiescent stem cell state in the hair follicle stem cell niche by controlling Fgf18 expression.

Foxp1/4 control epithelial cell fate during lung development and regeneration through regulation of anterior gradient 2

The molecular pathways regulating cell lineage determination and regeneration in epithelial tissues are poorly understood. The secretory epithelium of the lung is required for production of mucus to help protect the lung against environmental insults, including pathogens and pollution, that can lead to debilitating diseases such as asthma and chronic obstructive pulmonary disease. We show that the transcription factors Foxp1 and Foxp4 act cooperatively to regulate lung secretory epithelial cell fate and regeneration by directly restricting the goblet cell lineage program. Loss of Foxp1/4 in the developing lung and in postnatal secretory epithelium leads to ectopic activation of the goblet cell fate program, in part, through de-repression of the protein disulfide isomerase anterior gradient 2 (Agr2). Forced expression of Agr2 is sufficient to promote the goblet cell fate in the developing airway epithelium. Finally, in a model of lung secretory cell injury and regeneration, we show that loss of Foxp1/4 leads to catastrophic loss of airway epithelial regeneration due to default differentiation of secretory cells into the goblet cell lineage. These data demonstrate the importance of Foxp1/4 in restricting cell fate choices during development and regeneration, thereby providing the proper balance of functional epithelial lineages in the lung.

Controlled inactivation of recombinant viruses with vitamin B2

Inactivated viruses are important tools for vaccine development and gene transfer. 8-Methoxypsoralen (8-MOP) and long-wavelength ultraviolet irradiation (LWUVI) inactivates many viruses. Toxicity limits its use in animals and humans. Toxicological and photosensitizing properties of riboflavin make it suitable for virus inactivation in preparations for biological use. Viruses expressing beta-galactosidase were mixed with either 8-MOP (1.5mM) or riboflavin (50 microM) and exposed to LWUVI (365 nm) for 2 h. Virus activity was determined by limiting dilution. The half-life of the adenovirus preparation treated with 8-MOP was 8.28 ns(-1) and 36.5 ns(-1) after treatment with riboflavin. Despite the difference in half-life, both preparations were completely inactivated within 45 min. In contrast, the half-lives for adeno-associated virus (AAV) preparations were similar (63 ns(-1) 8-MOP vs. 67 ns(-1) riboflavin). Each AAV preparation was fully inactivated within 90 min. The half-life of lentivirus was 193.4 ns(-1) after treatment with 8-MOP and 208 ns(-1) after exposure to riboflavin. Virus treated with riboflavin was inactivated within 20 min. Virus exposed to 8-MOP was inactivated in 90 min. DNA and RNA viruses can be inactivated by riboflavin and LWUVI and used in physiological systems sensitive to other photochemicals.

Gene promoter methylation in plasma and sputum increases with lung cancer risk

PURPOSE

Lung cancer is the leading cause of cancer mortality in the United States, due in part to the lack of a validated and effective screening approach for early detection. The prevalence for methylation of seven and three genes was examined in DNA from sputum and plasma, respectively, from women at different risk for lung cancer.

EXPERIMENTAL DESIGN

Lung cancer survivors (n = 56), clinically cancer-free smokers (n = 121), and never smokers (n = 74) comprised the study population. Plasma was collected from all three groups, whereas sputum was collected from lung cancer survivors and smokers.

RESULTS

Methylation was detected in plasma DNA from 10 of 74 women who never smoked. Prevalence for methylation of the p16 gene in plasma was highest in lung cancer survivors. Lung cancer survivors showed a significant increase in the odds of having at least one or more genes methylated in plasma (odds ratio, 3.6; 95% confidence interval, 1.9-9.1) than never smokers. The prevalence for methylation of the O(6)-methylguanine-DNA methyltransferase, ras effector homologue 1, death associated protein kinase, and PAX5alpha genes in sputum was significantly higher in lung cancer survivors compared with smokers. Lung cancer survivors had 6.2-fold greater odds (95% confidence interval, 2.1-18.5) for methylation of three or more genes in sputum compared with smokers. Methylation was more commonly detected in sputum than plasma for O(6)-methylguanine-DNA methyltransferase and ras effector homologue 1, but not p16, in lung cancer survivors.

CONCLUSION

Concomitant methylation of multiple gene promoters in sputum is strongly associated with lung cancer risk.