figures legends, tables, and references. There are six figures and one table. The supplemental information contains an additional seven figures and seven tables. Research.

Background: A major determinant of the risk of myocardial infarction is the stability of the atherosclerotic plaque. Macrophage-rich plaques are more vulnerable to rupture, since macrophages excrete an excess of matrix-degrading enzymes over their inhibitors, reducing collagen content and thinning the fibrous cap. Several genetic studies have shown that disruption of signalling by the chemokine monocyte chemoattractant protein 1 reduced the lipid lesion area and macrophage accumulation in the vessel wall. Methods: We have tested whether a similar reduction in macrophage accumulation could be achieved pharmacologically by treating apolipoprotein-E-deficient mice with the chemokine inhibitor NR58-3.14.3. Results: Mice treated for various periods of time (from several days to 6 months) with NR58-3.14.3 (approximately 30 mg/kg/day) consistently had 30–40% fewer macrophages in vascular lesions, compared with mice treated with the inactive control NR58-3.14.4 or PBS vehicle. Similarly, cleaved collagen staining was lower in mice treated for up to 7 days, although this effect was not maintained when treatment time was extended to 12 weeks. The vascular lipid lesion area was unaffected by treatment, but total collagen I staining and smooth muscle cell number were both increased, suggesting that a shift to a more stable plaque phenotype had been achieved. Conclusions: Strategies, such as chemokine inhibition, to attenuate macrophage accumulation may therefore be useful to promote stabilization of atherosclerotic plaques.

Metastatic, castrate-resistant prostate cancer (mCRPC) is diagnosed in up to 50,000 patients each year in the US alone, and roughly 27,000 patients will succumb to it every year. Once metastasized beyond regional lymph nodes, the 5-year survival rate is 30%. While novel therapeutics like abiraterone and enzalutamide have improved the treatment options for mCRPC, no curative treatment is available, and new therapies are urgently needed. HPN424 is a ~50-kDa antibody derivative called TriTAC (Tri-specific T cell Activating Construct) under development for the treatment of mCRPC. It is designed to simultaneously bind to CD3ε on T cells and to prostate specific membrane antigen (PSMA, FOLH1) on prostate cancer cells. A third domain of HPN424 binds non-covalently to serum albumin for extension of serum half-life. PSMA is expressed in >90% of malignant lesions of patients, and outside the central nervous system, its expression on normal tissue is largely restricted to the prostate. HPN424 binds human PSMA with sub-nanomolar affinity. When incubated in co-cultures with resting, human T cells and prostate cancer cells, it activates T cells and induces cytokine production, proliferation and redirected target cell killing with EC50 values in the single digit picomolar range. When administered to mice bearing human prostate cancer xenografts and human T cells, HPN424 eradicates subcutaneous tumors. The affinities of HPN424 for human and cynomolgus monkey CD3 and albumin are comparable, while HPN424 binds only marginally to cynomolgus PSMA. HPN424 is very well tolerated in non-human primates, even at high doses, indicating that CD3-binding has little if any pharmacological effect in the absence of target binding. Pharmacokinetic analysis supports weekly administration in humans. Our preclinical data suggest that HPN424 will be highly efficacious, safe and convenient for the treatment of patients with mCRPC. Citation Format: Bryan Lemon, Wade Aaron, Richard Austin, Patrick Baeuerle, Manasi Barath, Adrie Jones, Susan D. Jones, Kathryn Kwant, Che-Leung Law, Anna Muchnik, Kenneth Sexton, Laurie Tatalick, Holger Wesche, Timothy Yu. HPN424, a half-life extended, PSMA/CD3-specific TriTAC for the treatment of metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1773.

Mesothelin (MSLN) is a GPI-linked tumor antigen overexpressed in a variety of solid tumors, including ovarian, pancreatic, lung and triple-negative breast cancer. Normal tissue expression is restricted to single-cell, mesothelial layers lining the pleural, pericardial, and peritoneal cavities. Overexpression of MSLN is associated with poor prognosis in lung adenocarcinoma and triple-negative breast cancer. MSLN has been used as cancer target antigen for numerous modalities, including immunotoxins, vaccines, antibody drug conjugates and CAR-T cells. Early signs of clinical efficacy have validated MSLN as target, but therapies with improved efficacy are still needed to address the significant, unmet medical need posed by MSLN-expressing cancers. HPN536 is a ~50-kDa antibody derivative called TriTAC (Tri-specific T cell Activating Construct) designed to simultaneously bind to MSLN on tumor cells and to CD3ε on T cells with an affinity of 1 nM and 14 nM, respectively. Transient bispecific binding leads to the formation of an immunological cytolytic synapse, T cell activation and redirected tumor cell killing. A third domain of HPN536 binds non-covalently to serum albumin with an affinity of 8 nM to extend serum half-life life. Because TriTACs are built using single domain antibodies, TriTACs are much smaller than full size antibodies and are anticipated to demonstrate improved penetration of human tumors compared to full sized antibodies. HPN536 is produced by eukaryotic cell culture and secreted as a highly stable, single polypeptide. It binds with similar affinity to human and cynomolgus MSLN, albumin and CD3. When incubated in co-cultures with resting, human or cynomolgus T cells and human tumor cells, T cells are induced to release cytokines, to proliferate, and to specifically lyse MSLN-positive target cells with EC50 values at single-digit picomolar concentrations. In an exploratory toxicological study in non-human primates, HPN536 was well tolerated and showed pharmacokinetics in support of weekly dosing in humans. Preclinical characterization suggests that HPN536 is an efficacious and safe novel therapeutic candidate for the convenient treatment of patients with MSLN-expressing malignancies. Citation Format: Richard Austin, Wade Aaron, Patrick Baeuerle, Manasi Barath, Adrie Jones, Susan D. Jones, Che-Leung Law, Kathryn Kwant, Bryan Lemon, Anna Muchnik, Kenneth Sexton, Laurie Tatalick, Holger Wesche, Timothy Yu. HPN536, a T cell-engaging, mesothelin/CD3-specific TriTAC for the treatment of solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1781.

Interleukin-2 (IL-2) and interleukin-15 (IL-15) promote anti-tumor immune activity by stimulating effector T and NK cells expressing the β and γ subunits of the IL-2 and IL-15 receptors. However, preferential activation of off-target cell populations expressing the high-affinity α subunit (including regulatory T cells, eosinophils, and endothelial cells) has limited the safety, therapeutic benefit, and widespread clinical use of these cytokines. Recently, we used sophisticated computational methods to create Neoleukin-2/15 (Neo-2/15), an entirely de novo α-independent agonist of both the IL-2 and IL-15 receptors. Unlike strategies that attempt to sterically inhibit or mutate the α-binding region of IL-2 or IL-15, Neo-2/15 was computationally designed to have no α-binding interface, while also having increased affinity for the β and γ signaling subunits. As a result, Neo-2/15 stimulates effector T and NK cells more potently and selectively than IL-2 or IL-15. Here, we report on the preclinical development and pharmacology of NL-201, a long-circulating variant of Neo-2/15 that is intended for clinical applications. NL-201 was derived from Neo-2/15 via the site-specific conjugation of a single PEG molecule and is manufactured using a simple and scalable process. NL-201 has a prolonged blood half-life and a sustained pharmacodynamic effect while retaining the high potency, selectivity, and thermodynamic stability of Neo-2/15. Preclinical studies demonstrate the robust antitumor activity of NL-201 as a single agent across a wide range of syngeneic murine tumor models, including those that do not respond well to checkpoint inhibitors. Due to its stability, high potency, and selectivity, NL-201 may overcome the long-standing challenges associated with the clinical use of IL-2 and IL-15 for cancer immunotherapy. Citation Format: Carl D. Walkey, Paul Hara, Laurie Tatalick, Umut Ulge, Jonathan Drachman, Daniel-Adriano Silva. Pre-clinical development of NL-201: A de novo α-independent IL-2/IL-15 agonist [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 4518.

No abstract

NL-201 is a potent, selective, and long-acting computationally designed alpha-independent agonist of the IL-2 and IL-15 receptors that is being developed as an immunotherapy for cancer. NL-201 binds to the beta and gamma subunits, selectively stimulating dose-dependent expansion and tumor infiltration of cytotoxic CD8+ T cells and natural killer (NK) cells, thereby enhancing the immune response to the tumor. Absence of binding to the IL-2 alpha subunit reduces the undesirable effects of traditional IL-2 therapies, such as vascular leak syndrome and expansion of immunosuppressive regulatory T cells. In this abstract, we demonstrate that NL-201, alone or in combination, demonstrates robust antitumor activity in preclinical models of non-Hodgkin lymphoma (NHL). We have previously demonstrated that NL-201 has marked antitumor activity in multiple syngeneic tumor models, including the A20 lymphoma model. These observations in lymphoma have been extended to explore the effects of NL-201 in combination with anti-mPD-1 checkpoint inhibitor therapy in vivo. In this model, NL-201 and anti-mPD-1 demonstrated tumor growth inhibition and increased median survival (21 days each vs 17 days as observed in control) when given alone. In combination, NL-201 and anti-mPD-1 resulted in increased antitumor activity and significant prolongation of survival (>51 days). We have also demonstrated that NL-201 does not directly induce signaling or cell death in B cell−derived NHL, suggesting that the observed antitumor activity is due to activation of non-malignant host immune cells. Additional in vitro and in vivo NHL models are being tested to enhance understanding of the interaction between NL-201 and other approved therapies within the hematopoietic tumor microenvironment. These data will be used to design future clinical trials of NL-201 in novel regimens to treat hematological malignancies. Disclosures Huard: Neoleukin Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company, Patents & Royalties. Tatalick: Neoleukin Therapeutics, Inc.: Consultancy, Current equity holder in publicly-traded company, Other: Independent paid nonclinical consultant for Neoleukin. Walkey: Neoleukin Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company, Current holder of stock options in a privately-held company. Swanson: Neoleukin Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties.

BackgroundNL-201 is a potent, selective, and long-acting computationally designed alpha-independent agonist of the IL-2 and IL-15 receptors that is being developed as an immunotherapy for cancer. Intravenous NL-201 administration is active in numerous pre-clinical tumor models. Here, we report data demonstrating favorable tolerability, pharmacokinetics, and antitumor activity of NL-201 after intratumoral (IT) administration in syngeneic murine tumor models.MethodsMice were implanted with syngeneic colorectal tumors in a single tumor (right flank) or bilateral tumor model (right and left flank). Once tumors were established, mice were randomized to receive IT or intravenous (IV) NL-201, or IV vehicle as control. Tumor volumes (mm3) and bodyweights were measured twice weekly, and mice were monitored for abnormal clinical signs. Blood samples were collected at pre-specified time points, and serum was analyzed for NL-201 concentration using a ligand-binding assay. Toxicokinetic parameters were determined using a non-compartmental model consistent with the IT and IV routes. Animals were sacrificed if tumor sizes reached 2000 mm3 or if body weight loss was >20%. In the bilateral tumor models, surviving tumor-free animals from both the IT and IV treatment arms were rechallenged with tumor cells after a washout period to assess antitumor immune responses.ResultsIT NL-201 demonstrated dose-dependent antitumor activity and was well tolerated based on a lack of clinical observations and body weight changes at doses up to 10 µg/mouse. Comparable antitumor activity was observed in mice receiving 3 μg/mouse NL-201 via IV or IT routes, but reduced systemic exposure and better tolerability were observed after IT administration. The estimated absolute bioavailability following 3 µg/mouse IT administration was 19.4%–66.5% of the NL-201 IV exposure. In the bilateral tumor model, IT NL-201 resulted in significant antitumor activity in both the treated and untreated tumors. Surviving animals from both IT and IV groups in which the initial tumors regressed rejected engraftment of the same tumor cell line upon rechallenge.ConclusionsIT NL-201 administration resulted in dose-dependent antitumor activity in both injected and uninjected tumors while demonstrating markedly reduced systemic exposure and improved tolerability compared to systemic administration at equivalent dose levels. Rechallenged animals failed to develop tumors, demonstrating durable tumor-specific immunity after IT NL-201 treatment. Results of this study support planned clinical investigation of IT NL-201 administration to increase NL-201 concentrations in accessible lesions.Ethics ApprovalThis study was approved by the Institutional Animal Care and Use Committee (IACUC) of CrownBio.