Including next-gen antibodies in pharma pipelines is considered essential for future success.
By Cynthia A. Challener
Next-generation antibodies are designed to be more specific and are often more potent than traditional monoclonal antibodies (mAbs). As a result, their commercial potential is significant. The global market for next-generation antibodies, including antibody drug conjugates (ADCs), engineered antibodies, bispecific antibodies, antibody fragments, antibody-like proteins and biosimilar antibody therapies, is estimated by Vision Gain to reach $11.6 billion in 2020 (1). Both large and small pharmaceutical and biotech companies are pursuing these newer therapies. A few have already been approved, and many more are in preclinical and clinical development. There are numerous challenges that need to be overcome first, however, and the full impact of next-generation antibodies will likely not be observed for many years.
Many technologies
Next-generation antibody formats include ADCs, other bioconjugates, bispecific (multispecific) antibodies, nanobodies, engineered antibodies, antibody fragments, and antibody-like proteins. Based on discussions with partners, Catalent sees ADCs, other bioconjugates, and bispecific antibodies as being the most prevalent technologies, according to Mike Riley, vice-president and general manager at Catalent Biologics.
The various formats can be placed into four main categories. One involves technologies designed to improve the effector function and/or extend the half-lives of traditional mAbs through modification of the back end, or Fc (fragment crystallizable) region. “This approach aims to optimize the killing potential (i.e., impart more antibody-dependent cell-mediated cytotoxicity [ADCC] activity), so that target cells are killed more effectively,” notes Tony de Fougerolles, chief scientific officer with Ablynx. Two products developed using glycoengineering have been approved (Gazyva and Poteligeo). MacroGenics is taking an alternative approach with the substitution of amino acids in the Fc region.
The second category consists of antibodies that have additional specificities for targeting. Most are bispecific, and thus have two targets, but tri-specific and other multi-specific therapies are being explored, according to de Fougerolles. Various technologies are being used to develop these products, such as the joining of two different heavy and two different light chains together to produce a substance that can attack two different targets. Two bispecific antibodies have been approved to date (Removab and Blincyto).
The third category includes drugs made from smaller antibody fragments or other protein-based scaffolds. These encode much smaller target-binding molecules (in the case of Nanobodies, these are 1/10th the size of a traditional antibody) and as such can be easily genetically linked together to encode for bi- and multi-specific drugs.
The fourth category is conjugates, including ADCs and others. While the potential of ADCs has been widely touted, to date only two products have been approved (Adcetris and Kadcyla). Drug developers are, however, improving linker technologies and the specificity of newer ADC products, such as the targeting of dividing cells vs. non-dividing cells, and Scott Koenig, president, CEO, and director of MacroGenics expects to see a new wave of products reach the market in the coming years.
Some of these technologies, such as ADCs and bispecific antibodies, were initially proposed decades ago but, at the time, the technical capabilities required to make them commercially feasible were lacking, according to Koenig. “Today there is a whole set of technologies in pre-clinical and clinical trials with tremendous promise,” he notes.
Many therapeutic targets
Oncology continues to be a key focus for next-generation antibody therapies, but Catalent is also seeing an interest in new modalities, such as conjugates, for other indications, according to Riley. “Novel antibody platforms have primarily been applied to cancers because immunogenicity and potential unforeseen clinical effects that might be better tolerated for cancer treatment than for chronic treatment in non-oncologic diseases,” agrees Andrew Chan, senior-vice-president of research biology at Genentech. He notes that bispecific and multispecific antibodies have also been broadly applied in oncology for the neutralization of multiple antigens, the fusion of binding proteins to antibodies, and cell recruiting therapeutics in cancer immunology to recruit T cells to facilitate tumor killing (e.g., T cell-directed bispecific antibodies).
The development of next-generation monoclonal antibodies has expanded beyond oncology into all therapeutic areas. “For instance, ADCs were initially focused primarily on cancer, but Genentech has applied the lessons learned to infectious diseases, leading to the discovery and development of THIOMAB antibiotic conjugates (TACs) for the treatment of methicillin-resistant Staphylococcus aureus (MRSA),” says Chan. In addition, he observes that the use of fragment antigen-binding (Fab) and other antibody fragments and nanotechnologies have expanded to ophthalmologic indications, where intravitreal injection volumes are limited requiring small molecular mass therapeutics with high potency. Application bispecific antibodies are also being applied to diseases of the central nervous system with the development of brain-penetrant antibodies.
“Hence, next-generation biotherapeutic technologies have potential in virtually all human diseases,” Chan asserts.
Real advantages
These new antibody formats are attracting attention because they have several advantages over current monoclonal antibody therapies. “These new modalities very often can be more targeted and potent than traditional technologies, and in some cases can access new targets or combinations of targets,” Riley explains.
“With multispecific antibodies in particular,” adds de Fougerolles, “it is possible to block multiple pathways with a single molecule, which provides development cost and cost of goods advantages in addition to enhanced therapeutic effects. In some cases, synergistic results have been obtained, with bi-specific drugs providing better results than even the use of both mono-specific drugs in combination.”
For instance, MacroGenics has shown preclinically that a bispecific antibody containing two check-point inhibitors has an even more dramatic effect than the use of two separate antibodies, according to Koenig. He adds that molecules that interact in multiple ways with the same target cell, such as bispecific antibodies with components that are physically close together in the same molecule, can result in unmasking biological functions that cannot be activated with conventional mAbs. He also notes that Fc-engineering can lead to mitigation of the body’s natural checkpoint mechanisms, which modulate the expression of T cells, resulting in amplification of cytolytic effects.
“The key is that these next-generation antibodies are offering new biological activities that cannot be achieved with traditional mAbs while at the same time adding greater specificity to their targeting mechanisms for improved potency and reduced potential toxicities and side effects,” Koenig states.
Commercial potential
Typically, it takes 10-12 years or more between the advent of a new technology and the first approval, sometimes several decades for complex technologies, according to Paul Carter, senior director and staff scientist of antibody engineering at Genentech. For example, the concepts of antibody drug conjugates and bispecific antibodies were first described in 1960 and the early 1970s, respectively. “Industry interest in next-generation antibodies has grown substantially in recent years, fueled by the commercial success of first-generation antibodies and the widespread goal of developing best-in-class antibodies. Many of the more recent next-generation approaches are, however, still early in clinical development at the proof-of-concept stage,” he observes.
Each of the next-generation antibody technologies has its pros and cons, according to de Fougerolles. “Improving the Fc region, for instance, is a useful step in improving on existing products, but isn’t helping to uncover new target biology. They could, however, be very commercially interesting as second-generation products. Multi-specific antibodies, on the other hand, have the potential to unlock new mechanism of action and afford significantly improved efficacy. As a new technology with many different approaches, commercial success will need to be proven on a product-by-product basis,” he notes.
Of technologies currently in research and development, Carter believes that bispecific and multispecific antibodies have perhaps the broadest range of potential clinical applications across many areas of medicine, and for this reason greatest potential for success. “Having said that,” he comments, “only two bispecific antibodies have been approved with 50+ in clinical development. It will be years, perhaps another decade or more, before we realize the full potential of bispecific and multispecific antibodies.”
One bispecific technology of interest is bispecific T-cell engaging antibodies (BiTEs), which was developed by Micromet based on research conducted at the University of Munich. The company has since been acquired by Amgen. BiTes are designed to direct the body’s T cells to attack tumor cells.
Ablynx’s Nanobody technology is another. Nanobodies are based on naturally occurring heavy-chain-only antibodies first discovered in the serum of camelids and, according to de Fougerolles, upon sequence optimization and humanization maintain their extremely robust physical properties, making them excellent therapeutic drug candidates that can be delivered via multiple routes of administration, including inhalation. The company recently submitted a marketing authorization application to the European Medicines Agency for aplacizumab, its anti-vWF Nanobody for the treatment of acquired thrombotic thrombocytopenic purpura. De Fougerolles expects Ablynx to report results of an on-going Phase III study in the second half of 2017 and be at the approval stage in 2018.
“There are very few limitations when it comes to the use of smaller fragments, particularly with our Nanobody platform,” de Fougerolles asserts. The company also has a drug in development (ALX-0171) for the treatment of respiratory syncytial virus (RSV) infection in infants. This product is attractive because it is sufficiently stable for administration via inhalation directly into the lungs, and offers the potential to be the first drug aimed at treating on-going RSV infection.
Nanobodies also have manufacturing advantages over other bispecific technologies, according to de Fougerolles. Because they involve a simple single heavy-chain immunoglobulin (Ig) domain, there are no heavy/light chain pairing issues seen with other mAb-based bi-specific platforms. It is possible to genetically string together any number of different Nanobodies to form multispecific antibodies that have well-behaved, simple structures. From the discovery perspective, he adds that a combinatorial approach can be used to readily construct and screen large numbers of different bispecific combinations.
MacroGenics’ dual-affinity re-targeting (DART) technology, which can target multiple disease-causing cells or different disease-causing pathways with one antibody, is also a bispecific antibody approach. DARTs have a proprietary minimal linker size and a content that reduces the potential for immune reactions, according to Koenig. In January 2017, FDA granted orphan drug status to the company’s candidate MGD006 (also known as S80880), a DART molecule for the investigational treatment of acute myeloid leukemia.
The company is also developing trispecific candidates, including one product that targets two different antigens on the same cancer cell and also modulates the activity of immune cells, recruiting them to help fight the targeted cells. “There is no reason we cannot combine out bispecific antibodies with other elements, such as Fc engineering and incorporation of ADCs. All of these approaches are being explored today,” Koenig comments.
Riley concludes that “there is potential across a variety of next-generation antibody formats. ADCs, bi-specifics and other novel formats have already been commercially approved and preclinical and clinical pipelines continue to expand. As technologies for creating these types of molecules continue to advance, companies are able to develop the right molecule for a given target.”
Not without hurdles
The key is the continued advancement of technologies from the discovery to commercial manufacturing stages. “The development of next-generation antibodies typically involves more uncertainty, complexity, and risk than well-established IgG (immunoglobulin G) technology on both the clinical side and with respect to commercial manufacturing. For these reasons, it is highly desirable preclinically to demonstrate some significant benefit of the next-generation approach versus a traditional IgG,” Carter explains.
For instance, for bispecifics consisting of multiple heavy and light chains, it is essential to ensure that the right components are connected together, according to de Fougerolles. The synthesis of these molecules can be complex and involve extensive purification to obtain the desired structure.
“The further removed these molecules are from conventional antibody structures, the more challenging their development and commercialization can be. As they get more structurally complex, there are concerns about expression, protein folding, etc.,” Koenig notes. It is necessary, he adds, to be able to show both scalability and manufacturability, particularly that these products can be produced in large quantities with relative ease in order to meet the treatment needs of large patient populations. “These issues also create opportunities for companies that can develop effective solutions.”
Delivery of next-generation antibodies is also an important issue for consideration, according to Koenig. “Traditional mAbs are administered via injection or subcutaneously. For next-generation products, delivery methods that give the best therapeutic effects, safety profiles, and convenience for the patient, the latter becoming increasingly important, should be the goal,” he asserts. That will require the use of new technologies. The very high potency of some next-generations antibodies--on the nanogram level--may provide opportunities to explore alternative delivery methods. “Because only very small quantities of the active drug substance must be delivered to the patient, there is the possibility of using newer delivery devices such as micro delivery systems,” says Koenig.
Additional analytical and regulatory demands
Next-generation antibodies also have their own set of analytical and regulatory challenges. With respect to analytical methods, each format/target combination can require novel methods.
As mass spectrometry techniques have advanced in sensitivity over the years, researchers have the capability of pinpointing modifications to determine the location of conjugation sites for ADCs and ensuring the correct pairings of subunits with novel formats, according to John Joly, senior director of analytical development and quality control with Genentech. He adds that formats have been engineered to engage T cells directly through the use of CD3 binding domains coupled to specific targets. It is important in these cases to demonstrate that undesirable side products such as CD3 homodimers are low in the final purified product through multiple assays including physicochemical tests and in-vitro biological assays. Biological assays demonstrating the intended mechanism-of-action are crucial for ensuring engineered formats have the desired activities (e.g., target engagement plus T-cell activation or target engagement and cytokine activity for cytokine fusions). “These new types of formats have forced the sharpening of analytical toolboxes and the analytical labs have kept pace with the challenges. The wide diversity of antibody formats found in all phases of clinical development is evidence of their continuing advancement,” Joly asserts.
The high potency of next-generation antibodies is also creating the need for the development of analytical methods with much higher sensitivities, down to picomolar levels, according to Koenig. “It is necessary to be able to detect and analyze extremely low levels of these actives at the site of action and wherever they end up in the body,” he notes.
On the regulatory front, there are additional requirements for next-generation antibody treatments that involve modulation of immune responses. Problems observed with early CAR T-cell therapies with respect to overly aggressive immune responses have led regulators to require treatments that involve immune responses be started at very low doses, with the dosage then increased slowly until the actual therapeutic level is reached, according to Koenig. It can therefore take considerable time to see a pharmacological effect and ensure an acceptable safety profile is, which extends clinical trials times.
More growth expected
Most large pharmaceutical and biotechnology companies have recognized the importance of next-generation antibody therapies and have multiple products under development, whether ADCs, multispecific antibodies, or engineered products, according to Koenig. “Some of this work is being conducted in-house, while other technologies are being accessed through relationships with emerging/smaller pharmaceutical companies focused on next-generation antibodies,” he notes.
There are, for instance, roughly a dozen well-established companies in the bispecific antibody space, according to de Fougerolles. He notes that a few like Ablynx have multiple products in advanced-stage clinical trials, but most are earlier stage companies with just one or two products in man. Many of these smaller companies are funded by venture capital firms.
“Recent years have witnessed major growth in the variety of next-generation antibody approaches. We expect this trend to continue with no single next-generation antibody strategy in particular becoming dominant over the next few years,” concludes Carter.
Reference
1. Visiongain, “Next Generation Antibody Therapies Market Forecast 2016-2026,” Press Release, May 11, 2016.