Current strategies in the non-clinical safety assessment of biologics: New targets, new molecules, new challenges.

Nonclinical safety testing of biopharmaceuticals can present significant challenges to human risk assessment with these innovative and often complex drugs. Emerging topics in this field were discussed recently at the 2016 Annual US BioSafe General Membership meeting. The presentations and subsequent discussions from the main sessions are summarized. The topics covered included: (i) specialty biologics (oncolytic virus, gene therapy, and gene editing-based technologies), (ii) the value of non-human primates (NHPs) for safety assessment, (iii) challenges in the safety assessment of immuno-oncology drugs (T cell-dependent bispecifics, checkpoint inhibitors, and costimulatory agonists), (iv) emerging therapeutic approaches and modalities focused on microbiome, oligonucleotide, messenger ribonucleic acid (mRNA) therapeutics, (v) first in human (FIH) dose selection and the minimum anticipated biological effect level (MABEL), (vi) an update on current regulatory guidelines, International Council for Harmonization (ICH) S1, S3a, S5, S9 and S11 and (vii) breakout sessions that focused on bioanalytical and PK/PD challenges with bispecific antibodies, cytokine release in nonclinical studies, determining adversity and NOAEL for biologics, the value of second species for toxicology assessment and what to do if there is no relevant toxicology species.

Derivation and Preclinical Characterization of CYT-303, a Novel NKp46-NK Cell Engager Targeting GPC3.

Glypican-3 (GPC3) is an oncofetal antigen that is highly expressed in multiple solid tumors, including hepatocellular carcinoma, and is barely expressed in adult normal tissues except the placenta. NKp46 activation receptor is expressed in all-natural killer (NK) cells, including tumor-infiltrating NK cells. FLEX-NKTM is a platform for the production of tetravalent multifunctional antibody NK cell engagers (NKE). CYT-303 was designed using the FLEX-NK scaffold, incorporating a novel humanized NKp46 binder that does not induce NKp46 internalization and a humanized GPC3 binder that targets the membrane-proximal lobe to mediate NK cell-redirected killing of HCC tumors. CYT-303 shows sub-nanomolar binding affinities to both GPC3 and NKp46. CYT-303 was highly potent and effective in mediating NK cell-redirected cytotoxicity against multiple HCC tumor cell lines and tumor spheroids. More interestingly, it can reverse the dysfunction induced in NK cells following repeated rounds of serial killing of tumors. It also mediated antibody-dependent cellular phagocytosis (ADCP) and complement-dependent cytotoxicity against GPC3-expressing HCC tumors. In vivo, CYT-303 showed no toxicity or cytokine release in cynomolgus monkeys up to the highest dose (60 mg/kg), administered weekly by intravenous infusion for 28 days. These results demonstrate the potential of CYT-303 to be a safe and effective therapy against HCC.

KIR3DL3 Is an Inhibitory Receptor for HHLA2 that Mediates an Alternative Immunoinhibitory Pathway to PD1.

Blockade of the PD1 pathway is a broadly effective cancer therapy, but additional immune-inhibitory pathways contribute to tumor immune evasion. HERV-H LTR-associating 2 (HHLA2; also known as B7H5 and B7H7) is a member of the B7 family of immunoregulatory ligands that mediates costimulatory effects through its interaction with the CD28 family member transmembrane and immunoglobulin domain containing 2 (TMIGD2). However, HHLA2 has also been known to have inhibitory effects on T cells. Here, we report that we have identified killer cell immunoglobulin-like receptor, three immunoglobulin domains and long cytoplasmic tail 3 (KIR3DL3) as an inhibitory receptor for HHLA2 in T cells and natural killer (NK) cells and have generated HHLA2 and KIR3DL3 antibodies that block the immune-inhibitory activity of HHLA2, preserving the costimulatory signal. It is known that HHLA2 is frequently expressed in several tumor types, including clear cell renal cell carcinoma (ccRCC). We found that HHLA2 expression was nonoverlapping with PDL1 expression in ccRCC, suggesting that HHLA2 mediates a mechanism of tumor immune evasion that is independent from PDL1. Blockade of both the PD1 and KIR3DL3 pathways may be a more effective way to reverse tumor immune evasion.See related Spotlight on p. 128.

Formation of human IFN-beta complex with the soluble type I interferon receptor IFNAR-2 leads to enhanced IFN stability, pharmacokinetics, and antitumor activity in xenografted SCID mice.

Interferon-beta (IFN-beta) is biologically unstable under physiologic conditions in vitro and is cleared rapidly from the bloodstream on administration in vivo. In the present study, we demonstrate that a soluble recombinant form of the type I IFN receptor subunit, sIFNAR-2, can neutralize the bioactivity of type I IFNs at high concentrations and, at lower concentrations, causes an enhancement of IFN-beta-mediated antiviral activity. The in vitro enhancement is due to the specific interaction of IFN-beta with sIFNAR-2, followed by dissociation of IFN-beta from the complex over time in culture. In vivo, the serum half-life of IFN-beta is extended from minutes to hours when administered intravenously in mice as a sIFNAR-2-associated complex. Moreover, the antitumor effect of IFN-beta is increased by between 9-fold and 27-fold when injected as an sIFNAR-2-associated complex, as demonstrated by an increase in the mean survival time of immunodeficient mice challenged with human Burkitt lymphoma cell (Daudi) xenografts (sIFNAR-2-complexed vs. free IFN-beta treatment). These results show that on association with sIFNAR-2, IFN-beta is more stable in vitro and exhibits increased efficacy when administered in vivo. Administration as a complex with sIFNAR-2 may, therefore, provide a method of enhancing the delivery and effectiveness of type I IFNs.