Characterizing emerging companies in computational drug development.

Computation promises to accelerate, de-risk and optimize drug research and development. An increasing number of companies have entered this space, specializing in the design of new algorithms, computing on proprietary data, and/or development of hardware to improve distinct drug pipeline stages. The large number of such companies and their unique strategies and deals have created a highly complex and competitive industry. We comprehensively analyze the companies in this space to highlight trends and opportunities, identifying highly occupied areas of risk and currently underrepresented niches of high value.

Targeted chain-exchange-mediated reconstitution of a split type-I cytokine for conditional immunotherapy.

Antibody-cytokine fusions targeted against tumor-associated antigens (TAAs) are promising cancer immunotherapy agents, with many such molecules currently undergoing clinical trials. However, due to the limited number of tumor-specific targets, on-target off-tumor effects can lead to systemic toxicity. Additionally, targeted cytokines can be scavenged by cytokine receptors on peripheral cells, decreasing tumor penetration. This study aims at overcoming these issues by engineering a platform for targeted conditionally active type I cytokines. Building on our previously reported PACE (Prodrug-Activating Chain Exchange) platform, we split the type I cytokine interleukin-4 (IL-4) to create two inactive IL-4 prodrugs, and fused these split IL-4 counterparts to the C-termini of antibody-like molecules that undergo proximity-induced chain exchange. In doing so, we developed IL-4 prodrugs that preferentially reconstitute into active IL-4 on target cells. We demonstrate that pre-assembled split IL-4 (without additional inactivation) retains activity and present two different strategies of splitting and inactivating IL-4. Using an IL-4 responsive cell-line, we show that IL-4 prodrugs are targeted to TAAs on target cells and regain activity upon chain exchange, primarily in a cis-activation setting. Furthermore, we demonstrate that split IL-4 complementation is also possible in a trans-activation setting, which opens up the possibility for activation of immune cells in the tumor vicinity. We demonstrate that targeted on-cell prodrug conversion is more efficient than nonspecific activation in-solution. Due to the structural similarity between IL-4 and other type I cytokines relevant in cancer immunotherapy such as IL-2, IL-15, and IL-21, cytokine-PACE may be expanded to develop a variety of targeted conditionally active cytokines for cancer immunotherapy.

Prodrug-Activating Chain Exchange (PACE) converts targeted prodrug derivatives to functional bi- or multispecific antibodies.

Driven by the potential to broaden the target space of conventional monospecific antibodies, the field of multi-specific antibody derivatives is growing rapidly. The production and screening of these artificial proteins entails a high combinatorial complexity. Antibody-domain exchange was previously shown to be a versatile strategy to produce bispecific antibodies in a robust and efficient manner. Here, we show that the domain exchange reaction to generate hybrid antibodies also functions under physiological conditions. Accordingly, we modified the exchange partners for use in therapeutic applications, in which two inactive prodrugs convert into a product with additional functionalities. We exemplarily show the feasibility for generating active T cell bispecific antibodies from two inactive prodrugs, which per se do not activate T cells alone. The two complementary prodrugs harbor antigen-targeting Fabs and non-functional anti-CD3 Fvs fused to IgG-CH3 domains engineered to drive chain-exchange reactions between them. Importantly, Prodrug-Activating Chain Exchange (PACE) could be an attractive option to conditionally activate therapeutics at the target site. Several examples are provided that demonstrate the efficacy of PACE as a new principle of cancer immunotherapy in vitro and in a human xenograft model.

SnoopLigase-Mediated Peptide-Peptide Conjugation and Purification.

Covalently linking together different proteins can enhance functionality for a range of applications. We have developed the SnoopLigase peptide-peptide conjugation method to easily and specifically link proteins fused to the peptides SnoopTagJr or DogTag via an isopeptide bond. SnoopLigase conjugation has been applied for enhancing enzyme resilience and for antigen oligomerization to enhance vaccine efficacy. Following conjugation, SnoopLigase and unreacted substrates can be removed by solid-phase immobilization of SnoopLigase, yielding purified protein-protein conjugates. Here, we describe procedures for designing tag-fused proteins, SnoopLigase purification, and ligation of SnoopTagJr and DogTag. We further define steps for the purification of the ligated product and quantification of ligation success.

Format chain exchange (FORCE) for high-throughput generation of bispecific antibodies in combinatorial binder-format matrices.

Generation of bispecific antibodies (bsAbs) requires a combination of compatible binders in formats that support desired functionalities. Here, we report that bsAb-matrices can be generated by Format Chain Exchange (FORCE), enabling screening of combinatorial binder/format spaces. Input molecules for generation of bi/multi-valent bsAbs are monospecific entities similar to knob-into-hole half-antibodies, yet with complementary CH3-interface-modulated and affinity-tagged dummy-chains. These contain mutations that lead to limited interface repulsions without compromising expression or biophysical properties of educts. Mild reduction of combinations of educts triggers spontaneous chain-exchange reactions driven by partially flawed CH3-educt interfaces resolving to perfect complementarity. This generates large bsAb matrices harboring different binders in multiple formats. Benign biophysical properties and good expression yields of educts, combined with simplicity of purification enables process automation. Examples that demonstrate the relevance of screening binder/format combinations are provided as a matrix of bsAbs that simultaneously bind Her1/Her2 and DR5 without encountering binder or format-inflicted interferences.

SnoopLigase peptide-peptide conjugation enables modular vaccine assembly.

For many infectious diseases there is still no vaccine, even though potential protective antigens have been identified. Suitable platforms and conjugation routes are urgently needed to convert the promise of such antigens into broadly protective and scalable vaccines. Here we apply a newly established peptide-peptide ligation approach, SnoopLigase, for specific and irreversible coupling of antigens onto an oligomerization platform. SnoopLigase was engineered from a Streptococcus pneumoniae adhesin and enables isopeptide bond formation between two peptide tags: DogTag and SnoopTagJr. We expressed in bacteria DogTag linked to the self-assembling coiled-coil nanoparticle IMX313. This platform was stable over months at 37 °C when lyophilized, remaining reactive even after boiling. IMX-DogTag was efficiently coupled to two blood-stage malarial proteins (from PfEMP1 or CyRPA), with SnoopTagJr fused at the N- or C-terminus. We also showed SnoopLigase-mediated coupling of a telomerase peptide relevant to cancer immunotherapy. SnoopLigase-mediated nanoassembly enhanced the antibody response to both malaria antigens in a prime-boost model. Including or depleting SnoopLigase from the conjugate had little effect on the antibody response to the malarial antigens. SnoopLigase decoration represents a promising and accessible strategy for modular plug-and-display vaccine assembly, as well as providing opportunities for robust nanoconstruction in synthetic biology.

SnoopLigase Catalyzes Peptide-Peptide Locking and Enables Solid-Phase Conjugate Isolation.

Simple, efficient reactions for connecting biological building-blocks open up many new possibilities. Here we have designed SnoopLigase, a protein that catalyzes site-specific transamidation, forming an isopeptide bond with more than 95% efficiency between two peptide tags, SnoopTagJr and DogTag. We initially developed these components by three-part splitting of the Streptococcus pneumoniae adhesin RrgA. The units were then engineered, guided by structure, bioinformatic analysis of sequence homology, and computational prediction of stability. After engineering, SnoopLigase demonstrated high-yield coupling under a wide range of buffers and temperatures. SnoopTagJr and DogTag were functional at the N- or C-terminus, while DogTag was also functional at internal sites in proteins. Having directed reaction of SnoopTagJr and DogTag, SnoopLigase remained stably bound to the ligated product, thus reconstituting the parent domain. Separating products from unreacted starting material and catalyst is often as challenging as reactions themselves. However, solid-phase immobilization of SnoopLigase enabled the ligated SnoopTagJr-DogTag product to be eluted with high purity, free from SnoopLigase or unligated substrates. The solid-phase catalyst could then be reused multiple times. In search of a generic route to improve the resilience of enzymes, we fused SnoopTagJr to the N-terminus and DogTag to the C-terminus of model enzymes, allowing cyclization via SnoopLigase. While wild-type phytase and ß-lactamase irreversibly aggregated upon heating, cyclization using SnoopLigase conferred exceptional thermoresilience, with both enzymes retaining solubility and activity following heat treatment up to 100 °C. SnoopLigase should create new opportunities for conjugation and nanoassembly, while illustrating how to harness product inhibition and extend catalyst utility.

Dual Plug-and-Display Synthetic Assembly Using Orthogonal Reactive Proteins for Twin Antigen Immunization.

Engineering modular platforms to control biomolecular architecture can advance both the understanding and the manipulation of biological systems. Icosahedral particles uniformly displaying single antigens stimulate potent immune activation and have been successful in various licensed vaccines. However, it remains challenging to display multiple antigens on a single particle and to induce broader immunity protective across strains or even against distinct diseases. Here, we design a dually addressable synthetic nanoparticle by engineering the multimerizing coiled-coil IMX313 and two orthogonally reactive split proteins. SpyCatcher protein forms an isopeptide bond with SpyTag peptide through spontaneous amidation. SnoopCatcher forms an isopeptide bond with SnoopTag peptide through transamidation. SpyCatcher-IMX-SnoopCatcher provides a modular platform, whereby SpyTag-antigen and SnoopTag-antigen can be multimerized on opposite faces of the particle simply upon mixing. We demonstrate efficient derivatization of the platform with model proteins and complex pathogen-derived antigens. SpyCatcher-IMX-SnoopCatcher was expressed in Escherichia coli and was resilient to lyophilization or extreme temperatures. For the next generation of malaria vaccines, blocking the transmission of the parasite from human to mosquito is an important goal. SpyCatcher-IMX-SnoopCatcher multimerization of the leading transmission-blocking antigens Pfs25 and Pfs28 greatly enhanced the antibody response to both antigens in comparison to the monomeric proteins. This dual plug-and-display architecture should help to accelerate vaccine development for malaria and other diseases.