Non-human Primate Toxicology Studies Research Articles

Effects of LRRK2 Inhibitors in Nonhuman Primates.

Toxicology studies in nonhuman primates were conducted to evaluate selective, brain penetrant inhibitors of LRRK2. GNE 7915 was limited to 7-day administration in cynomolgus monkeys at 65 mg/kg/day or limited to 14 days in rhesus at 22.5 mg/kg b.i.d. due to physical signs. Compound 25 demonstrated acceptable tolerability at 50 and 225 mg/kg b.i.d. for 7 days in rhesus monkeys. MK-1468 was tolerated during 7-day administration at 100, 200 or 800 mg/kg/day or for 30-day administration at 30, 100, or 500 mg/kg b.i.d. in rhesus monkeys. The lungs revealed hypertrophy of type 2 pneumocytes, with accumulation of intra-alveolar macrophages. Transmission electron microscopy confirmed increased lamellar structures within hypertrophic type 2 pneumocytes. Hypertrophy and hyperplasia of type 2 pneumocytes with accumulation of intra-alveolar macrophages admixed with neutrophils were prominent at peripheral lungs of animals receiving compound 25 or MK-1468. Affected type 2 pneumocytes were immuno-positive for pro-surfactant C, but negative for CD11c, a marker for intra-alveolar macrophages. Accumulation of collagen within alveolar walls, confirmed by histochemical trichrome stain, accompanied changes described for compound 25 and MK-1468. Following a 12-week treatment-free interval, animals previously receiving MK-1468 for 30 days exhibited remodeling of alveolar structure and interstitial components that did not demonstrate reversibility.

830-P: Preclinical Development of ALN-KHK, an Investigational RNAi Therapeutic for Type 2 Diabetes Mellitus

Fructose consumption is implicated in increased rates of metabolic syndrome and type 2 diabetes worldwide. In the liver, ketohexokinase (KHK) is required for fructose metabolism, phosphorylating fructose to fructose-1-phosphate (F1P), a substrate for synthesis of fatty acids, contributing to nonalcoholic fatty liver. Excess liver fat is associated with insulin resistance and loss of glycemic control. Lowering KHK expression should reduce fatty acid synthesis and thus reduce insulin resistance and improve glycemic control in obese individuals with T2DM. We developed a robust RNAi therapeutics platform for delivery of siRNAs to liver using GalNAc conjugates to specifically silence hepatocyte-expressed genes. Liver-directed silencing of KHK improved insulin sensitivity in pre-clinical models of T2DM. ALN-KHK was selected based on in vitro assessment of a large set of GalNAc-siRNAs targeting human and primate KHK. ALN-KHK demonstrated suppression of liver KHK mRNA and protein in cynomolgus macaques after a single subcutaneous (SC) injection with potent and durable reduction in KHK protein (94.1% lowering through day 85 at the 10 mg/kg dose) supporting evaluation of infrequent dosing in the clinic. To evaluate impact of KHK silencing on fructose metabolism and establish circulating biomarkers of pharmacology, cynomolgus macaques were administered an oral fructose bolus on Day 30 following SC injection of ALN-KHK of 0.3, 3 or 10 mg/kg. ALN-KHK treatment resulted in a dose-dependent increase in circulating fructose with a 4.6-fold increase and a 10.7-fold decrease in FGF21 (which is regulated by liver F1P), at 2 hr post fructose bolus, associated with 90.7% KHK liver protein reduction. These data suggest monitoring of circulating fructose and FGF21 to assess KHK silencing in the clinic. In IND-enabling rat and non-human primate toxicology studies ALN-KHK was safe and well tolerated, supporting the planned initiation of first-in-human studies in obese healthy volunteers. Disclosure L. Noetzli: Employee; Alnylam Pharmaceuticals, Inc. Stock/Shareholder; Alnylam Pharmaceuticals, Inc. A. Borodovsky: Employee; Alnylam Pharmaceuticals, Inc. Stock/Shareholder; Alnylam Pharmaceuticals, Inc. X. Chua: Employee; Alnylam Pharmaceuticals, Inc. Stock/Shareholder; Alnylam Pharmaceuticals, Inc. R. Tymon: Employee; Alnylam Pharmaceuticals, Inc. Stock/Shareholder; Alnylam Pharmaceuticals, Inc. J. Darcy: None. S. Belozerova: Employee; Alnylam Pharmaceuticals, Inc. Stock/Shareholder; Alnylam Pharmaceuticals, Inc. M. Keibler: Employee; Alnylam Pharmaceuticals, Inc. Stock/Shareholder; Alnylam Pharmaceuticals, Inc. H. Tu: Employee; Alnylam Pharmaceuticals, Inc. Stock/Shareholder; Alnylam Pharmaceuticals, Inc. E. Maratos-Flier: Employee; Novartis, Alnylam Pharmaceuticals, Inc.

VIP943 Is a Novel CD123 Antibody Drug Conjugate with in Vitro and In Vivo Efficacy in Acute Myeloid Leukemia (AML) Models

Background: Current treatment options (cytarabine with anthracyclines) for patients with acute myeloid leukemia (AML) are often associated with severe and barely tolerable toxicities. In patients who tolerate induction therapy, the complete remission rate is 60%-80%; however, 50% of patients relapse due to the presence of leukemic stem cells (LSC). Antibody-drug conjugates (ADCs) are putatively designed to deliver potent drugs directly to cancer cells while sparing normal tissue; however, first-generation ADCs are associated with severe bone marrow and liver toxicity. VIP943 is a CD123-targeting ADC which uses a kinesin spindle protein inhibitor (KSPi) as a new payload class and a unique legumain linker designed to overcome liabilities of currently approved ADC therapies. The payload is delivered with a drug-antibody ratio of 6. It consists of the KSPi warhead which is modified with a CellTrapperTM moiety so it accumulates within the CD123-targeted tumor cell and cannot enter normal cells. Non-human primate toxicology studies demonstrated a highly favorable and differentiated safety profile for VIP943 (Kirchhoff et al, Cancers 2020). Here we characterize VIP943 in various patient-derived AML models. Methods: For co-localization experiments, MOLM-13 AML cell line was stained with labelled anti-CD123 antibody or isotype control and CytoPainter LysoGreen indicator reagent and analyzed by imaging flow cytometry. AML primary patient mononuclear cells from blood and bone marrow were treated with VIP943 for 24, 48, and 72 hours. Flow cytometry immunophenotyping for AML blasts and CD34+/CD38- LSCs was used to analyze these populations. An in vivo patient-derived AML PDX mouse model was treated with VIP943 (5 mg/kg IV every 7 days) or in combination with 5-azacytidine (2.5 mg/kg SC days 1-5 x 3) and venetoclax (50 mg/kg PO days 1-5 x 3). Cytokine release syndrome was analyzed comparing VIP943 to isotype control ADC, anti-CD123 antibody, and positive comparator antibodies by in vitro cytokine release assays (CRA) in two different assay formats using whole blood and isolated mononuclear cells from 10 healthy donors. Flow cytometric lymphocyte and leukemic immunophenotyping was performed from blood of non-human primates. A leukemia cell line panel drug screen with VIP943 was evaluated and baseline genomic features were correlated with response. Results: Co-localization studies confirm specific internalization and efficient intracellular trafficking to the lysosome of VIP943. In vitro treatment with VIP943 (66 nM, continuous exposure) delivers blast reductions of 37% after a 24h incubation with VIP943, 45% after 48h incubation and 83% after an 72h incubation. In the CD34+/CD38- cell population, a reduction of 71% was achieved. In a patient-derived AML model, VIP943 with 5-azacytidine and venetoclax led to complete tumor growth inhibition after 21 days showing superiority of this triplet therapy (complete regression: 8/9 mice) with high tolerability (maximum body weight loss -4.8 %). The immunotoxicological evaluation in both CRA formats and with the tested antibody concentrations (100µg, 10µg, 1µg) exerts no induction of cytokines by VIP943 compared to controls. Immunophenotyping demonstrates no impact of VIP943 treatment on lymphocytic subpopulations, whereas the CD123-positive basophils are reduced after 24h followed by an almost complete recovery. VIP943 IC50 ranges from 0.1nM-300nM in a leukemia cell line panel screen and features associated with sensitivity are investigated. Conclusions: VIP943 is a next-generation ADC with a differentiated safety profile from currently approved ADCs, including lack of in vitro cytokine release. In vitro and in vivo studies using patient-derived AML cells show VIP943 has favorable monotherapy and combination efficacy including targeting of leukemic stem cells, which drive relapse. These findings warrant evaluating VIP943 in clinical trials.

Abstract 907: XMT-1660, a B7-H4-targeted Dolasynthen antibody-drug conjugate for the treatment of breast cancer

Abstract XMT-1660 is a novel Dolasynthen-based antibody drug conjugate carrying a DolaLock payload with controlled bystander effect and targeting B7-H4, a tumor antigen that is broadly expressed on the cell surface in breast, ovarian and endometrial cancers. B7-H4 (VTCN1) exerts immunosuppressive effects by suppression of T cell proliferation and is expressed on tumor-associated macrophages (TAMs) as well as epithelial tumor cells. XMT-1660 is comprised of an anti-B7-H4 antibody site-specifically conjugated to Dolasynthen, with a total of 6 DolaLock Auristatin F-HPA (AF-HPA) anti-tubulin payloads per antibody (DAR-6). To select the optimal ADC, three ADCs using the same antibody and DolaLock payload were compared: site-specific Dolasynthen-based DAR-2 and DAR-6 ADCs, and a stochastically conjugated Dolaflexin-based DAR-12 ADC. In vitro, no significant differences were observed among the 3 ADCs: all exhibited specific recognition of B7-H4 and elicited potent cytotoxicity against B7-H4-expressing cancer cells. In vivo, XMT-1660 consistently exhibited more anti-tumor activity than the other ADCs in TNBC models and ER+/HER2- models after single, equivalent doses based on payload. XMT-1660 demonstrated dose-dependent anti-tumor activity and induced sustained tumor regressions after a single administration. XMT-1660 and the Dolasynthen DAR-2 ADC both exhibited improved pharmacokinetics in mouse relative to the Dolaflexin DAR 12 ADC. These data indicate that XMT-1660 exhibited a superior preclinical profile to the other ADCs and more generally demonstrate the importance of DAR-ranging studies to identify the optimal antibody-drug conjugate for a given target. These results, as well as results from exploratory toxicology studies in non-human primates, strongly support the clinical development of XMT-1660. Citation Format: Shawn P. Fessler, Jason Wang, Scott D. Collins, LiuLiang Qin, Kenneth Avocetien, Ling Xu, Ronald Eydelloth, Steven Vonderfecht, Chen-Ni Chin, Steven Bradley, Susan Clardy, Anouk Dirksen, Elizabeth Ditty, Bingfan Du, Dokyong Kim, Rebecca Mosher, Elena Ter-Ovanesyen, Kelly Slocum, Alex Uttard, Phonphimon Wongthida, Jeffrey Zurita, Dorin Toader, Marc Damelin, Timothy B. Lowinger. XMT-1660, a B7-H4-targeted Dolasynthen antibody-drug conjugate for the treatment of breast cancer [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 907.

Abstract 694: Novel conditionally active bispecific EpCAM x CD3 T cell engagers targeting solid tumors

Abstract Epithelial cell adhesion molecule (EpCAM) is a transmembrane glycoprotein that plays many roles in cancer biology. EpCAM is an attractive therapeutic target due to its expression on most solid tumors. However, targeting of EpCAM protein has been limited since it is also expressed on normal epithelial tissues. In fact, initial attempts to develop EpCAM-specific T cell engagers were not successful due to severe cytokine release effects as well as serious on-target off-tumor drug related toxicities. Conditionally Active Biologic (CAB) technology is a proprietary platform that generates bispecific antibodies which have no or very little binding to CD3 or to the target antigen in healthy tissue (normal physiological conditions), but have strong binding in the context of diseased tissues (tumor microenvironment) based on the glycolytic tumor metabolism (Warburg effect). Using our CAB technology, we have developed CD3 mono-CAB (WT EpCAM x CAB CD3) and CD3/EpCAM dual-CAB (CAB EpCAM x CAB CD3) bispecific antibodies. In vitro and in vivo efficacy data as well as toxicology studies in non-human primates for mono- and dual-CAB EpCAM x CD3 bispecific antibodies targeting EpCAM will be presented. Our data demonstrate that both mono- and dual-CAB EpCAM x CD3 bispecific antibodies have potent anti-tumor activities in vivo and have much lower toxicity compared to non-CAB bispecific antibodies. The mono- and dual-CAB EpCAM x CD3 bispecific antibodies generated by the CAB technology represent a new class of potent, effective T-cell engagers with potential for increased safety margin and therapeutic index in the clinic. Citation Format: Ana Paula G. Cugnetti, Haizhen Liu, Jing Wang, Charles Xing, Christina Wheeler, Matthew Lucas, Cathy Chang, Gerhard Frey, William Boyle, Jay Short. Novel conditionally active bispecific EpCAM x CD3 T cell engagers targeting solid tumors [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 694.

ALX148 Is a High Affinity Sirpα Fusion Protein That Blocks CD47, Enhances the Activity of Anti-Cancer Antibodies and Checkpoint Inhibitors, and Has a Favorable Safety Profile in Preclinical Models

CD47 is a widely expressed cell surface protein thought to function as an immune checkpoint in cancer. CD47 binds SIRPα on myeloid cells, suppressing tumor cell phagocytosis and other innate immune functions. CD47-SIRPα signaling has also been implicated in the suppression of adaptive antitumor responses, but the relevant cellular functions have yet to be elucidated. Abundant CD47 expression has been observed in tumors and may aid tumor cells in the evasion of immune surveillance.Therapeutic blockade of the CD47 pathway may stimulate antitumor immunity and improve cancer therapy. To this end, the novel CD47-blocking molecule ALX148 was generated by fusing a modified SIRPα N-terminal D1 domain to an inactive Fc. Surface plasmon resonance analysis demonstrated that ALX148 binds human and murine CD47 with high affinity, with respective KDs of 0.14 nM and 12 nM. ALX148 also bound multiple CD47-expressing cell populations in flow cytometry assays. ALX148 blocks the interaction between CD47 and wild type SIRPα, enhancing antibody-dependent phagocytosis of hematologic tumor cell lines by daratumumab, rituximab, and obinutuzumab.ALX148 increased the efficacy of antibodies targeting hematologic tumors, such as rituximab and obinutuzumab, in xenograft models of hematologic malignancies. Because ALX148 also binds murine CD47 with high affinity, syngeneic tumor models were used to examine the activity of ALX148 in the context of an intact immune system. ALX148 enhanced the antitumor activities of checkpoint inhibitors. Specifically, the immune response induced by ALX148 bridged innate and adaptive immune responses. ALX148 stimulated antitumor properties of innate immune cells, promoting dendritic cell activation and a shift of tumor associated macrophages toward a proinflammatory phenotype. ALX148 in combination with checkpoint inhibitors caused increased cytotoxic T cell infiltrates, with greater CD8 to Treg ratios, and greater amounts of interferon gamma production by T cells in both tumors and the spleen. These findings reveal multiple mechanisms by which adaptive immunity is stimulated by CD47 blockade.Notably, ALX148 had no adverse effect on CD47-expressing red blood cells and platelets. In vitro, ALX148 did not induce erythrocyte hemagglutination. In non-human primate toxicology studies, ALX148 multi-dose administration was well tolerated and did not affect levels of circulating red blood cells, white blood cells, or platelets. This is in contrast to other published CD47-blocking molecules, which have caused anemia and thrombocytopenia in preclinical and clinical studies. Thus, ALX148 may have minimal hematologic toxicity in humans.ALX148 enhances adaptive and innate immune responses, demonstrates enhanced preclinical anti-tumor activity in combination with multiple standard of care cancer therapies, and is well tolerated. It is currently being investigated in a first-in-patient, phase 1 dose escalation/expansion, multi-center study in patients with advanced solid tumors and lymphoma. (NCT03013218). DisclosuresKauder:Alexo Therapeutics: Employment. Kuo:Alexo Therapeutics: Employment. Chen:Alexo Therapeutics: Employment. Harrabi:Alexo Therapeutics: Employment. Rocha:Alexo Therapeutics: Employment. Doyle:Alexo Therapeutics: Employment. Bollini:Alexo Therapeutics: Employment. Han:Alexo Therapeutics: Employment. Sangalang:Novartis: Employment; Alexo Therapeutics: Employment. Sim:Alexo Therapeutics: Employment. Randolph:VenBio: Consultancy; Carrick Therapeutics: Membership on an entity's Board of Directors or advisory committees; Alexo Therapeutics: Employment. Pons:Alexo Therapeutics: Employment, Equity Ownership. Wan:Alexo Therapeutics: Employment; Pfizer: Equity Ownership.

PCA062, a P-cadherin Targeting Antibody-Drug Conjugate, Displays Potent Antitumor Activity Against P-cadherin-expressing Malignancies.

The cell surface glycoprotein P-cadherin is highly expressed in a number of malignancies, including those arising in the epithelium of the bladder, breast, esophagus, lung, and upper aerodigestive system. PCA062 is a P-cadherin specific antibody-drug conjugate that utilizes the clinically validated SMCC-DM1 linker payload to mediate potent cytotoxicity in cell lines expressing high levels of P-cadherin in vitro, while displaying no specific activity in P-cadherin-negative cell lines. High cell surface P-cadherin is necessary, but not sufficient, to mediate PCA062 cytotoxicity. In vivo, PCA062 demonstrated high serum stability and a potent ability to induce mitotic arrest. In addition, PCA062 was efficacious in clinically relevant models of P-cadherin-expressing cancers, including breast, esophageal, and head and neck. Preclinical non-human primate toxicology studies demonstrated a favorable safety profile that supports clinical development. Genome-wide CRISPR screens reveal that expression of the multidrug-resistant gene ABCC1 and the lysosomal transporter SLC46A3 differentially impact tumor cell sensitivity to PCA062. The preclinical data presented here suggest that PCA062 may have clinical value for treating patients with multiple cancer types including basal-like breast cancer.

SGN-CD30C, an Investigational CD30-Directed Camptothecin Antibody-Drug Conjugate (ADC), Shows Strong Anti Tumor Activity and Superior Tolerability in Preclinical Studies

SGN-CD30C, an investigational CD30-directed ADC, utilizes a potent novel camptothecin derivative as the cytotoxic payload. SGN-CD30C targets the same antigen as brentuximab vedotin (BV), though the payload has a different mechanism of action, namely inhibiting topoisomerase I rather than disrupting microtubules. Unlike monomethyl auristatin E, camptothecin-based therapies do not cause peripheral neuropathy clinically, suggesting that SGN-CD30C may have the potential to avoid one of the most common adverse events associated with BV. In preclinical studies, SGN-CD30C demonstrated strong monotherapy activity, inducing durable tumor regressions in multiple lymphoma models and eliciting cures in a BV-resistance tumor model (Figure 1). Moreover, SGN-CD30C exhibits many of the desirable attributes associated with BV, notably, bystander activity and CD30+ T regulatory cell (Treg) depletion. Using an admixed model of CD30+ and CD30-tumor cells, SGN-CD30C demonstrated robust anti-tumor activity in vivo, confirming SGN-CD30C can induce bystander killing of antigen-negative tumor cells in CD30-heterogeneous tumors. Additionally, SGN-CD30C depleted CD30+ Treg cells in vitro (Figure 2), suggesting it has the potential to exert activity through multiple mechanisms of action. SGN-CD30C was well-tolerated in non-human primate toxicology studies and demonstrated ~6-fold higher maximum tolerated dose when compared to BV. The primary toxicity for SGN-CD30C in non-human primates (NHP) studies was anemia due primarily to bone marrow suppression of erythropoiesis. SGN-CD30C had no effect on neutrophil counts and caused only minimal to mild decreases in platelets. The lack of significant neutropenia seen with SGN-CD30C contrasts with BV, indicating the two ADCs may have non-overlapping dose limiting toxicities. Hematology parameters show SGN-CD30C is tolerated at a 10-fold higher dose than BV with weekly dosing, suggesting SGN-CD30C may offer the potential for increased dose density. In summary, our data show SGN-CD30C is a compelling therapeutic candidate for CD30-positive malignancies. The distinct mechanism of action, strong anti-tumor activity, and enhanced tolerability provide a strong rationale to clinically investigate SGN-CD30C across the CD30-expressing lymphoma landscape. A Phase 1 clinical trial is planned to investigate SGN-CD30C in relapsed and refractory lymphoma. Disclosures Heiser: Seattle Genetics: Current Employment, Current equity holder in publicly-traded company. Grogan:Seattle Genetics: Current Employment, Current equity holder in publicly-traded company. Jin:Seattle Genetics: Current Employment, Current equity holder in publicly-traded company. Conerly:Seattle Genetics: Current Employment, Current equity holder in publicly-traded company.

Abstract 5698: Novel conditionally active bispecific T cell engagers targeting solid tumors

Abstract The use of CD3/target bispecific molecules has great therapeutic potential in oncology. This potential, however, is diminished due to serious on-target drug-related toxicities, restricting the development of bispecific T cell engagers to targets that have limited expression in normal tissues. Conditionally Active Biologic (CAB) technology is a proprietary platform that generates antibodies which have no or very little binding to the target antigen in healthy tissue (normal physiological conditions), but have strong binding in the context of diseased tissues (tumor microenvironment) based on the glycolytic tumor metabolism (including Warburg effect). Using our CAB technology, we have developed CD3/target bispecific antibodies that bind to recombinant CD3 and to CD3 expressing cells under in vitro tumor microenvironment conditions, but not in physiologic conditions (CAB CD3). CAB CD3 bispecific antibodies were generated against various well-established tumor associated antigens (TAA), including EpCAM, B7-H3, HER-2 and EGFR. All of these molecules play important roles in cancer biology and are attractive targets for the development of therapeutic bispecific antibodies. In addition, we have also developed CAB TAA / CAB CD3 bispecific antibodies. In vitro and in vivo efficacy data as well as toxicology studies in non-human primates for CAB-T cell engagers will be presented. Our data demonstrates that CAB bispecific antibodies are efficacious in vivo and have lower toxicity comparing to non-CAB bispecific antibodies. The CAB technology will allow the generation of a new class of T-cell engagers with increased safety margin and therapeutic index in the clinic. Citation Format: Ana Paula G. Cugnetti, Haizhen Liu, Jing Wang, Charles Xing, Christina Wheeler, Matthew Lucas, Cathy Chang, Gerhard Frey, William J. Boyle, Jay M. Short. Novel conditionally active bispecific T cell engagers targeting solid tumors [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 5698.

Biophysical and Immunological Characterization and In Vivo Pharmacokinetics and Toxicology in Nonhuman Primates of the Anti-PD-1 Antibody Pembrolizumab.

The programmed cell death 1 (PD-1) pathway represents a major immune checkpoint, which may be engaged by cells in the tumor microenvironment to overcome active T-cell immune surveillance. Pembrolizumab (Keytruda®, MK-3475) is a potent and highly selective humanized mAb of the IgG4/kappa isotype designed to directly block the interaction between PD-1 and its ligands, PD-L1 and PD-L2. This blockade enhances the functional activity of T cells to facilitate tumor regression and ultimately immune rejection. Pembrolizumab binds to human and cynomolgus monkey PD-1 with picomolar affinity and blocks the binding of human and cynomolgus monkey PD-1 to PD-L1 and PD-L2 with comparable potency. Pembrolizumab binds both the C'D and FG loops of PD-1. Pembrolizumab overcomes human and cynomolgus monkey PD-L1-mediated immune suppression in T-cell cultures by enhancing IL2 production following staphylococcal enterotoxin B stimulation of healthy donor and cancer patient cells, and IFNγ production in human primary tumor histoculture. Ex vivo and in vitro studies with human and primate T cells show that pembrolizumab enhances antigen-specific T-cell IFNγ and IL2 production. Pembrolizumab does not mediate FcR or complement-driven effector function against PD-1-expressing cells. Pembrolizumab displays dose-dependent clearance and half-life in cynomolgus monkey pharmacokinetic and toxicokinetic studies typical for human IgG4 antibodies. In nonhuman primate toxicology studies, no findings of toxicologic significance were observed. The preclinical data for pembrolizumab are consistent with the clinical anticancer activity and safety that has been demonstrated in human clinical trials.

Abstract DDT01-05: First-in-class T cell-redirecting bispecific antibody targeting glypican-3: a highly tumor-selective antigen

Abstract Immune checkpoint inhibitors such as anti-PD1 antibodies have shown promising clinical responses in several solid tumors, however there remain patients who do not show an adequate response. Recent biomarker studies have revealed that the presence of neoantigens in the tumor can determine the level of response, and thus the next challenge will be how to target tumors with a neoantigen level that is too low to be recognized by endogenous cytotoxic T cells. Hope in this area is offered by a T cell-redirecting antibody (TRAB), which bispecifically engages CD3 and a tumor antigen, even at very low expression levels, to activate the inherent cytolytic potential of T cells against target tumor cells. A TRAB is highly potent because T cells are activated only in the presence of the targeted antigens and are not restricted by the specificity of the T cell receptor. Given this very potent cytotoxicity, the key to successfully achieving strong antitumor efficacy while avoiding on-target off-tumor toxicity is to select a highly tumor-selective antigen. Our fully humanized IgG TRAB recognizes CD3 and a highly tumor-selective antigen, glypican-3 (GPC3), which is a fetal protein expressed in a wide variety of tissues during development but suppressed in most adult tissues. On the other hand, an inct101e in GPC3 expression has been reported in hepatocellular carcinoma, gastric cancer, lung squamous cell carcinoma, and other cancers. In nonclinical in vitro pharmacology studies, the anti-GPC3 TRAB elicited activation and proliferation of T cells and T cell-dependent cellular cytotoxicity against a wide variety of GPC3-expressing tumor cells, and showed long-lasting in vivo efficacy against tumor expressing very low levels of GPC3 at a few thousand molecules per cell. Furthermore, in an immunocompetent mouse model using human CD3 transgenic mice, anti-GPC3 TRAB showed strong antitumor efficacy against poorly immunogenic tumors, whereas both the immune checkpoint inhibitors and a conventional ADCC-inducing antibody recognizing GPC3 did not show significant efficacy. Pharmacokinetics and toxicology studies in nonhuman primates showed a plasma half-life comparable to a standard IgG drug, allowing a QW or Q2W regimen in humans, with toxicity which was manageable and reversible; the main observations of transient cytokine elevation and associated clinical symptoms were markedly reduced by steroid premedication. Our anti-GPC3 TRAB, which is supported by proprietary antibody engineering technology (ART-Ig) that enables large-scale GMP manufacturing, has promise as a new approach in cancer immunotherapy. Citation Format: Takahiro Ishiguro, Yasuko Kinoshita, Yuji Sano, Yumiko Azuma, Toshiaki Tsunenari, Natsuki Ono, Yoko Kayukawa, Mika Kamata-Sakurai, Hirotake Shiraiwa, Akihisa Kaneko, Werner Frings, Shunichiro Komatsu, Junichi Nezu, Mika Endo. First-in-class T cell-redirecting bispecific antibody targeting glypican-3: a highly tumor-selective antigen. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr DDT01-05.

Abstract 641: Trastuzumab-dolaflexin, a highly potent Fleximer-based antibody-drug conjugate, demonstrates a favorable therapeutic index in exploratory toxicology studies in multiple species

Abstract Antibody-drug conjugates (ADCs) represent a promising drug class that relies on monoclonal antibody recognition of specific cancer-associated antigens for targeted delivery of chemotherapeutic agents. Fleximer® ADCs utilize a polymer-based conjugation platform to enable high drug-antibody ratios (DAR) and significantly greater anti-tumor potency compared to ADCs with DAR 3-4. We previously showed that trastuzumab-dolaflexin (T-dolaflexin), a HER2-targeted ADC comprised of the antibody trastuzumab conjugated to ∼15 proprietary auristatin molecules via Fleximer, has excellent pharmacokinetics and efficacy in mouse models (AACR 2014 Abstract #2645). T-dolaflexin is efficacious at a single dose of 0.67 mg/kg in mouse xenograft models, and achieves prolonged tumor-free survival after a single 2 mg/kg dose in a low HER2-expressing model that is insensitive to ado-trastuzumab emtansine (T-DM1). We sought to test the tolerability of T-dolaflexin in exploratory mouse, rat and non-human primate toxicology studies. Cohorts of 6 mice were treated with a single dose of vehicle or T-dolaflexin at 20, 30 or 40 mg/kg and followed for 21 days. The 20 and 30 mg/kg doses were well-tolerated based on body weight loss and mortality and achieved a therapeutic index (TI) in mouse >40X. Cohorts of 4 female cynomolgus monkeys were treated with a single dose of vehicle or T-dolaflexin at 0.67, 1.34 or 2.68 mg/kg (payload doses 600, 1200 and 2400 μg/m2, respectively). Day 3 necropsy was performed on 2 animals per cohort, with recovery necropsy on Day 22 in the remaining 2 animals. All animals survived until scheduled necropsy with limited body weight loss. There were no test-article related findings on gross pathology. Most notable clinical pathology findings were transaminase elevations (primarily AST), and decreased platelet counts at Day 8. One high dose animal demonstrated laboratory findings consistent with hepatic injury with full recovery by Day 22 and no findings on gross or microscopic pathology at necropsy. There was no evidence of myelosuppression. Microscopic pathology findings were limited, with no test-article related findings in HER2-expressing organs including heart, lungs and GI tract. All doses were considered well-tolerated. Toxicokinetics demonstrated good stability of drug conjugate in plasma with t1/2 ∼5 days (comparable to antibody t1/2) and minimal exposure to free payload. Plasma exposure at the 2.68 mg/kg dose in cyno was several fold higher than mouse exposure at the minimally efficacious dose of 0.67 mg/kg, and was comparable to the mouse exposure associated with prolonged tumor free survival after a single 2mg/kg dose. Trastuzumab-dolaflexin, a highly potent Fleximer-based ADC, demonstrates a favorable TI in tumor models with low HER2 expression where current HER2-directed therapies are inactive. Citation Format: Natalya Bodyak, Alex Yurkovetskiy, Peter U. Park, Dmitry R. Gumerov, Michael DeVit, Mao Yin, Joshua D. Thomas, LiuLiang Qin, Timothy B. Lowinger, Donald A. Bergstrom. Trastuzumab-dolaflexin, a highly potent Fleximer-based antibody-drug conjugate, demonstrates a favorable therapeutic index in exploratory toxicology studies in multiple species. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 641. doi:10.1158/1538-7445.AM2015-641

Effects of group housing on ECG assessment in conscious cynomolgus monkeys

IntroductionAssessing the cardiovascular safety of new chemical or biological entities is important during pre-clinical development. Electrocardiogram (ECG) assessments in non-human primate (NHP) toxicology studies are often made using non-invasive telemetry systems. We investigated whether ECG recording was feasible during group housing of NHPs, rather than the usual single housed arrangement, and whether it would impact the data collected or affect the ability to detect drug-induced changes in QTc interval. MethodsFollowing a period of acclimatisation to jackets, cynomolgus monkeys (3 males and 3 females) were housed in same sex groups of 3. Female monkeys were administered 4 doses of vehicle while male monkeys were administered vehicle, 15, 45, and 135mg/kg moxifloxacin. Each dose was administered on a separate dosing day. The same dosing protocol was repeated with the animals singly housed and the results from the two phases were compared including assessment of statistical power. ResultsHeart rate (HR) was significantly lower, and PR and QT intervals were significantly higher, at multiple time points when the animals were group housed compared with the singly housed phase. QRS duration and QTc interval were less affected. Moxifloxacin increased QT and QTc intervals but had no consistent effect on HR, QRS duration or PR interval under group housed or singly housed conditions. Power analysis suggested that group housing did not adversely affect the magnitude of detectable changes of ECG parameters. In general, detection of slightly smaller changes was achieved under conditions of group housing. DiscussionThe current study shows group housing to be technically possible during non-invasive ECG recording, resulting in lower resting heart rates and small improvements in sensitivity of detection of drug-induced effects. Given the psychological benefits of group housing for NHPs, it is a refinement that should be considered when conducting ECG assessments in NHP toxicology studies.

Effects of group housing on ECG assessment in conscious cynomolgus monkeys.

Assessing the cardiovascular safety of new chemical or biological entities is important during pre-clinical development. Electrocardiogram (ECG) assessments in non-human primate (NHP) toxicology studies are often made using non-invasive telemetry systems. We investigated whether ECG recording was feasible during group housing of NHPs, rather than the usual single housed arrangement, and whether it would impact the data collected or affect the ability to detect drug-induced changes in QTc interval. Following a period of acclimatisation to jackets, cynomolgus monkeys (3 males and 3 females) were housed in same sex groups of 3. Female monkeys were administered 4 doses of vehicle whilst male monkeys were administered vehicle, 15, 45 and 135mg/kg moxifloxacin. Each dose was administered on a separate dosing day. The same dosing protocol was repeated with the animals singly housed and the results from the two phases were compared including assessment of statistical power. Heart rate (HR) was significantly lower, and PR and QT interval significantly higher, at multiple time points when the animals were group housed compared with the singly housed phase. QRS duration and QTc interval were less affected. Moxifloxacin increased QT and QTc intervals but had no consistent effect on HR, QRS duration or PR interval under group housed or singly housed conditions. Power analysis suggested that group housing did not adversely affect the magnitude of detectable changes of ECG parameters. In general, detection of slightly smaller changes was achieved under conditions of group housing. The current study shows group housing to be technically possible during non-invasive ECG recording, resulting in lower resting heart rates and small improvements in sensitivity of detection of drug-induced effects. Given the psychological benefits of group housing for NHPs, it is a refinement that should be considered when conducting ECG assessments in NHP toxicology studies.

Aln-CC5, an Investigational RNAi Therapeutic Targeting C5 for Complement Inhibition

Excessive complement activation plays a pivotal role in a variety of disorders. Complement component C5 is a clinically validated therapeutic target for treatment of both paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic-uremic syndrome.We developed a robust RNAi therapeutics platform for the delivery of siRNAs to the liver using trivalent GalNAc conjugates, enabling specific silencing of hepatocyte-expressed genes following subcutaneous (SC) injection. The liver produces essentially the entirety of C5 and other complement pathway proteins. We are developing ALN-CC5, an investigational RNAi therapeutic targeting human, primate and rodent C5. C5 silencing and complement activity inhibition were examined in rodents and primates. Multi-dose SC ALN-CC5 treatment resulted in sustained lowering of cyno serum C5 with ≤3% residual protein remaining. C5 reduction was associated with >90% and >95% inhibition of classical and alternative complement pathways as measured by ELISA-based assays. Additionally, >80% lowering of complement serum hemolytic activity was observed. ALN-CC5 was safe and well tolerated in both rat and non-human primate toxicology studies. In addition to wild type animals, ALN-CC5 was tested in several animal models of disease in which complement activation plays a prominent role. Silencing of murine C5 was highly efficacious in a model of anti-collagen antibody-induced arthritis with a disease modifying activity equivalent to that of an anti-C5 antibody. Furthermore, C5 silencing was effective at reducing proteinuria in a rat model of membranous nephropathy. Up-regulation of C5 expression, observed in both models, had no effect on the extent of C5 silencing, suggesting that ALN-CC5 could be efficacious in the context of inflammation. These data demonstrate a prominent role for circulating, liver-derived C5 in mediating pathology at extrahepatic sites and the potential utility of an RNAi therapeutic targeting C5.In summary, RNAi-mediated silencing of liver-derived C5 is a promising novel therapeutic approach for inhibiting systemic complement activity, with the potential to enable, low volume, subcutaneous treatment for patients with PNH and other disorders where complement activation plays a role in disease progression. DisclosuresBorodovsky:Alnylam: Employment. Yucius:Alnylam: Employment. Sprague:Alnylam: Employment. Banda:Alnylam: Research Funding. Holers:Alnylam: Research Funding. Vaishnaw:Alnylam Pharmaceuticals: Employment, Equity Ownership. Maier:Alnylam: Employment. Kallanthottathil:Alnylam: Employment. Charisse:Alnylam: Employment. Kuchimanchi:Alnylam: Employment. Manoharan:Alnylam: Employment. Salant:Alnylam: Honoraria. Fitzgerald:Alnylam: Employment. Meyers:Alnylam: Employment. Sorensen:Alnylam Pharmaceuticals: Employment, Equity Ownership.

Developmental and reproductive toxicology studies in nonhuman primates

Developmental and reproductive toxicology testing in nonhuman primates (NHPs) has become more common due to the increasing number of biopharmaceuticals in drug development, since NHPs are frequently the only species to express pharmacologic responses similar to humans. NHPs may also be used to help resolve issues associated with small-molecule reproductive toxicology in traditional species (rodents and rabbits). Adequate designs in NHP are presented for developmental toxicity (embryo-fetal development, pre-postnatal development, enhanced pre-postnatal development), reproductive toxicity (male and female), and juvenile toxicity studies. Optional parameters that may be included in these studies are discussed, as are new study designs that consolidate multiple aspects of the reproductive assessment and thereby conserve the limited supply of sexually mature NHPs available for testing. The details described will assist scientists in pharmaceutical, regulatory, and contract research organizations who are involved in conducting these unique studies to optimize their design based on case-by-case considerations.

A phase I study of MORAb-003, a fully humanized monoclonal antibody against folate receptor alpha, in advanced epithelial ovarian cancer

5553 Background: Folate receptor alpha (FRA) is over-expressed in the majority of epithelial ovarian cancers (EOC) but is largely absent from normal tissue. MORAb-003 is a humanized monoclonal antibody (MAb) to FRA. Binding of MORAb-003 to FRA can prevent phosphorylation of substrates specific for Lyn kinase, suppress proliferation of cells over-expressing FRA, mediate FRA-positive tumor cell killing via antibody-dependent cellular and complement-dependent mechanisms, and suppress tumor growth in vivo of FRA-expressing tumors in rodent xenograft models. Toxicology studies in non-human primates found no evidence of toxicity with MORAb-003 at supra- pharmacological doses. This open-label, multiple-infusion, first-in-human, dose-escalation trial evaluates the safety, pharmacokinetics (PK), and anti-tumor activity of MORAb-003 in patients with platinum-resistant EOC. Methods: Sequential cohorts of patients received four weekly infusions at escalating dose levels of MORAb-003 from 12.5 mg/m2 to 400 mg/m2. Eligible patients had platinum-resistant EOC, acceptable organ function, KPS = 70%, and measurable disease by GOG-RECIST criteria. A subset of subjects received a tracer dose of 111In-labelled MORAb-003 and SPECT-CT and planar imaging. Human anti-human antibody (HAHA) and PK analyses were performed. Results: To date, 18 subjects have been dosed with up to 200 mg/m2. No dose limiting toxicity or significant related adverse events have been observed. Four subjects had rigors (2 grade 1) or fevers (3 grade 1, 1 grade 2) following the first infusion. Nine subjects have had radiologically stable disease, and 7 subjects have had stable or declining CA125. Two subjects have received extended therapy for an apparent clinical benefit. Radiolabelled tracer studies have demonstrated significant tumor uptake of labeled MORAb-003. The 400 mg/m2 dose cohort is currently enrolling. Conclusions: The FRA-specific MAb MORAb-003 appears to be well tolerated in patients with EOC and may have activity in platinum-resistant patients. These results support further evaluation of the efficacy of MORAb-003 in a phase 2 study which is ongoing. [Table: see text]

Phase I study of MORAb-003, a humanized anti-folate receptor-alpha monoclonal antibody, in platinum resistant ovarian cancer

5027 Background: Folate receptor alpha (FRA) is over-expressed in the majority of epithelial ovarian cancers (EOC) but largely absent from normal tissue. MORAb-003 (M3) is a humanized monoclonal antibody (MAb) to FRA. Binding of M3 to FRA can prevent phosphorylation of substrates specific for the Lyn kinase; suppress proliferation of cells over-expressing FRA; mediate FRA-positive tumor cell killing via antibody-dependent cellular and complement-dependent mechanisms; and suppress tumor growth in vivo of FRA-expressing tumors in rodent xenograft models. Toxicology studies in non-human primates found no evidence of toxicity with M3 at supra-pharmacological doses. This open-label, multiple-infusion, first-in-human, dose-escalation trial evaluates the safety, pharmacokinetics (PK), and antitumor activity of M3 in patients with platinum-resistant EOC. Methods: Sequential cohorts of patients receive four weekly infusions at escalating dose levels of M3, from 12.5 mg/m2 to 100 mg/m2. Human anti-human antibody (HAHA) and PK analyses are performed. Eligible patients have EOC that relapsed < 6 months after platinum-based therapy, acceptable organ function, Karnofsky Performance Status ≥ 70%, and measurable disease by GOG-RECIST criteria. Patients undergo pulmonary function testing (PFT) at baseline, and at end of study. Results: To date, 7 women have been treated with M3: 3 at the 12.5 mg/m2 dose, 3 at 25 mg/m2, and 1 at 37.5 mg/m2. Median age was 60. Neither dose limiting toxicity nor HAHA has been observed. Grade 1 rash occurred in 1 patient. Grade 1/2 fever following drug administration occurred in 2 patients. Grade 2 FEV1 decrease was observed in a patient with likely pulmonary lymphangitic metastasis. One subject at 25 mg/m2 had radiographically stable disease. At low doses, the PK analysis demonstrated the half-life to be shorter than anticipated based on animal studies, possibly due to tumor binding. Radiolableled imaging studies are underway to determine the distribution of M3. Conclusions: The FRA-specific MAb MORAb-003 appears to be well tolerated in patients with EOC. Enrollment continues and updated results will be presented. No significant financial relationships to disclose.

Production and purification of refolded recombinant human IL-7 from inclusion bodies

A recombinant form of human rhIL-7 was overexpressed in Escherichia coli HMS174 (DE3) pLysS under the control of a T7 promoter. The resulting insoluble inclusion bodies were separated from cellular debris by cross-flow filtration and solubilized by homogenization with 6 M guanidine HCl. Attempts at refolding rhIL-7 from solubilized inclusion bodies without prior purification of monomeric, denatured rhIL-7 were not successful. Denatured, monomeric rhIL-7 was therefore initially purified by size-exclusion chromatography using Prep-Grade Pharmacia Superdex 200. Correctly folded rhIL-7 monomer was generated by statically refolding the denatured protein at a final protein concentration of 80–100 μg/mL in 100 mM Tris, 2 mM EDTA, 500 mM l-arginine, pH 9.0, buffer with 0.55 g/L oxidized glutathione at 2–8 °C for at least 48 h. The refolded rhIL-7 was subsequently purified by low-pressure liquid chromatography, using a combination of hydrophobic interaction, cation-exchange, and size-exclusion chromatography. The purified final product was >95% pure by SDS–PAGE stained with Coomassie brilliant blue, high-pressure size-exclusion chromatography (SEC-HPLC), and reverse-phase HPLC. The endotoxin level was <0.05 EU/mg. The final purified product was biologically active in a validated IL-7 dependent pre-B-cell bioassay. In anticipation of human clinical trials, this material is currently being evaluated for safety and efficacy in non-human primate toxicology studies.