Leaping the hurdles in developing regenerative treatments for the intervertebral disc from preclinical to clinical

Chronic back and neck pain is a prevalent disability, often caused by degeneration of the intervertebral disc. Because current treatments for this condition are less than satisfactory, a great deal of effort is being applied to develop new solutions, including regenerative strategies. However, the path from initial promising idea to clinical use is fraught with many hurdles to overcome. Many of the keys to success are not necessarily linked to science or innovation. Successful translation to clinic will also rely on planning and awareness of the hurdles. It will be essential to plan your entire path to clinic from the outset and to do this with a multidisciplinary team. Take advice early on regulatory aspects and focus on generating the proof required to satisfy regulatory approval. Scientific demonstration and societal benefits are important, but translation cannot occur without involving commercial parties, which are instrumental to support expensive clinical trials. This will only be possible when intellectual property can be protected sufficiently to support a business model. In this manner, commercial, societal, medical, and scientific partners can work together to ultimately improve patient health. Based on literature surveys and experiences of the co‐authors, this opinion paper presents this pathway, highlights the most prominent issues and hopefully will aid in your own translational endeavors.

ethical permission for use of human tissues and clinical trial applications. 1 Furthermore, engagement with end users is often required during design of research phases for funding, especially within Europe.
The (regulatory) pathway to clinic is also important to consider from the outset, attention to appropriate laboratory tests to demonstrate proof of concept and initial toxicity and animal testing. Early considerations of commercialization, patenting and regulatory approvals are necessary to reduce delays to clinical trials and pathways to the clinic.
Throughout laboratory and animal testing, good laboratory practice (GLP) or similar is required to support findings, regulatory approvals and patent applications. This includes aspects of good record keeping to laboratory maintenance and quality control. 2 The design of clinical trials, stratification of patients and outcome measure design are all important to ensure that the correct questions are addressed at the appropriate time.
This review aims to map out the important aspects to consider during the development of regenerative therapies for the IVD. Covering the developmental stages for a diverse range of regenerative approaches including: gene, cell, biological factors, and biomaterial approaches to repair and regenerate the IVD, as a potential treatment for chronic back and neck pain.

| BENCH SIDE TESTING: IN VITRO AND EX VIVO TESTING
The first stage in developing a new regenerative therapy for the IVD is testing in vitro, often in mammalian cell culture. This stage is used to perform initial proof of principle studies and fundamental cellular toxicology (viability) studies on relevant cell types. Important aspects to consider during the design of in vitro and ex vivo testing includes: species, sources of cells and tissues, and culture conditions. The specific question being addressed and stage within the developmental pathway will require different levels of complexity ( Figure 1).

| Species and cell/tissue source
The choice of cell source is an important question. It is well known that species-specific responses can be observed 7,8 and as such, caution must be applied when using nonhuman cells in initial proof of principle testing. These differences could arise from differential species-dependent expression of proteins and receptors, cell types isolated from tissues (eg, notochordal cells), or the disease status of the tissues. [9][10][11] In view of the challenges in accessing human cells, the majority of animal cells utilized in initial experimental studies are from normal young adult animals, which do not represent the cellular phenotype seen within the degenerated (human) IVD, which are senescent and exhibit a catabolic phenotype which has implications on regenerative therapies. [12][13][14] Over the last 10 years, there has been increased research on human cell sources with approximately 50% of studies culturing IVD cells or cells for regeneration of the IVD sourced from human (Figure 2A,C). Accessibility to human tissues is more complex for tissue explant or organ culture studies with the majority of these utilizing animal tissues ( Figure 2B), especially cow tails, due to their ease of access and similarity in cell type and structure to human discs. 15 Similarities between animal and human disc tissues have been reviewed elsewhere. 15 The utilization of animal tissues can be useful for initial tests and studies have attempted to mimic the degenerate disc within such systems (see below). However, no animal tissue represents the human situation directly. Therefore, human tissues should be utilized wherever possible, which also enables patient variation to be determined. Prior to translation to animal testing, it is also essential to confirm results in vitro within the species of choice for in vivo experimentation to ensure these cell types respond in the same way as human cells prior to animal model selection, as indicated recently, for example, by species-specific responses to Link-N. 8

| Culture systems
Two-dimensional (monolayer) culture of nucleus pulposus (NP) cells is well known to lead to changes in cellular phenotype, characterized by rapid de-differentiation within the first passage, for example, loss of normal matrix synthesis (collagen type II and aggrecan) and gain of collagen type I. 14,16 Moreover, it acts as an oversimplification of the cellular environment, lacking cell-extracellular matrix (ECM) interactions. Two-dimensional (2D) culture systems for IVD studies are widely used ( Figure 3A). While 2D culture has its use, particularly in initial cellular toxicology studies and preliminary proof of concept studies, it is difficult to translate results from 2D culture directly to the in vivo environment. Three-dimensional culture systems such as pellet 17 or alginate 14 have been shown to restore the phenotype (with appropriate expression of IVD matrix molecules) of native NP cells and collagen scaffolds for annulus fibrosus (AF), 18 thus, are a useful model to study effects of gene therapy and biological factors. However, these systems are often limited to single cell types and with the exception of newly deposited matrix do not recapitulate the complexity of cellular and extracellular matrix components and interactions FIGURE 1 Recommended culture systems for developmental stages in regenerative therapy developments for the intervertebral disc (IVD). Regulatory classifications are shown in italics. ATMP, Advanced Therapeutic Medical Product. Images are representative images of culture systems: 2D culture: IVD cells in monolayer; 3D culture: IVD cells in alginate culture; tissue explants: explant culture systems; organ culture: examples of organ culture systems [3][4][5][6] thereof, which exist in vivo. The IVD regeneration field would benefit from defining a standard culture system such as alginate for NP and collagen for AF cells and its conditions ( Table 1) that would be used worldwide and as such enable comparison of efficacy results. However, the defined "gold standard" will still need adjustments depending on the clinical questions addressed, as conditions in the IVD differ depending on age, spinal level, health state and underlying disease process.
Until early in the 21st century, culture of IVD tissue explants, especially NP tissue explants, were hampered by tissue swelling, loss of extracellular matrix, cellular phenotype and viability. However, a number of culture systems are now available which can maintain tissue explants of animal and human tissue in culture for prolonged periods of time. These systems either constrain tissue volume, 3,27,28 culture tissue in raised osmotic pressures, 29 or under compressive loading, 30 which prevents tissue swelling, maintains tissue architecture and cellular phenotype. These systems are particularly useful as human tissue obtained from surgery can be utilized as small pieces of intact tissue and can be maintained in culture. Such systems have been employed to excellent effect to study proof of principle studies on regenerative approaches including biological, 31,32 cellular [33][34][35] , and injectable hydrogel systems. 36 These studies can provide useful initial data on local tissue responses, integration and delivery to tissues, which are essential in the pathway to clinic.
However, NP explants fail to model the interactions of different cell types within the disc and nutritional diffusion. Although this can be simulated to a certain extent by adjusting the nutrient supply in the media, this does not mimic the gradient seen in a whole IVD. Thus, a number of organ culture bioreactors have been developed which can maintain whole discs: mainly mouse, rabbit, sheep, cow, and goat discs. Recently, a long-term IVD organ culture model that retains the vertebral bone system was developed. 6 This model is useful for testing potential drugs on disc repair 37 and is based on the bovine IVD. To study repair, IVDs are maintained in organ culture and degradation is induced by injection with trypsin. The whole organ culture system used for the bovine work is to some extent applicable to human IVDs, but in this case degeneration is not truly reflective of the human IVD.
A number of systems have recently been developed which can maintain whole cadaveric human discs, which can allow investigations in naturally degenerate tissues. [38][39][40] These systems have been reviewed in a number of excellent reviews. 41,42

| Culture conditions
The native IVD in vivo is a hostile environment, characterized by low oxygen tension, low nutrition, high osmolality, low pH and exists under dynamic load 43,44 (Table 1). Yet the majority of in vitro studies are performed in nutrient-rich culture media, most commonly Dulbecco's Culture conditions are also essential to consider during expansion of cells for biobanking of IVD cells for regenerative approaches.
Expansion conditions, including passage number, oxygen tension, supplements, and osmolality have been shown to influence the cell phenotype and as such influence the regenerative capacity and differentiation of mesenchymal stromal cells 45 and NP cells. 46 These conditions can be tuned, either to achieve optimal regenerative performance or to achieve an NP phenotype that resembles better the NP cells present within a degenerative niche.
During testing of regenerative approaches, systems should be tested within conditions which mimic the native IVD environment (Table 1). However, key factors preventing many researchers from modulating culture conditions are the comparison to previously published data and facilities that are available. Some studies are indeed starting to modulate these conditions within in vitro culture studies ( Figure 3B). A key feature, however, which currently hampers in vitro culture modifications is accurate determination of actual levels seen in vivo. 47 Furthermore, these conditions are known to change during degeneration, but levels will vary between patients and across regions within the IVD, and these measures are very difficult to determine in vivo and often depend on computer modeling to provide suggested

| MODELING THE DEGENERATIVE NICHE IN VITRO
The degenerated IVD is a hostile environment for cells with further decrease in nutrients and pH and altered osmolarity compared to normal discs, which was recently reviewed by Sakai and Anderson. 43 The degenerated niche also contains abundant catabolic cytokines, degradative enzymes, matrix fragments increased levels of free calcium (Ca 2+ ), 6 neurotrophic and angiogenic factors, which together could alter the behavior of any proposed regenerative therapy. 48 For therapies which rely on the native cells of the IVD, these become senescent, 13 alter phenotype, and undergo apoptosis, which results in an altered and/or reduced cell source available to respond to potential gene and biological treatments. 48 While newly implanted cell sources may not survive and/or differentiate into the correct NP cell phenotype within the catabolic environment of the degenerate disc. 49 Hence, it is important to assess any potential regenerative therapy within an environment which mimics the degenerated niche as much as possible (Table 1) prior to progression to clinical trials. ex vivo tissue explant and organ culture systems have in part begun to re-create this niche with various degrees of success. Methods to mimic the changes observed in human IVD degeneration include enzymatic NP digestion, 50 surgical methods to create AF injury, 51 and overloading (by magnitude, duration, and frequency). 52 However, these systems can only replicate some morpho-histo-pathological and cellular changes and it is unknown how closely they mimic/induce in vivo degenerative mechanisms. To date, the best ex vivo model systems available are those based on human degenerative IVD tissue/organs, but even these do not fully recapitulate the full in vivo environment as they are decoupled from systemic interactions, for example, immune, nervous, and endocrine systems.
Efforts are underway to develop realistic computational models for the human IVD, so called "virtual human IVD", with the aim of diagnosing and understanding IVD degeneration. 53,54 As a step between simplified in vitro culture experiments and more sophisticated ex vivo culture employing tissue explants or even whole tissue organs, in silico modeling could provide an avenue to further identify essential environmental and cellular aspects that need to be considered in follow-up studies. Although the field is still in its infancy, 55 this may have the potential of performing in silico clinical trials and may help to optimize and guide the rational design of therapeutic interventions. 56

| PRECLINICAL ANIMAL MODELS
When promising (regenerative) treatment candidates have been established in vitro and/or in ex vivo tissue/organ cultures mimicking the degenerative disc niche, the next step would be to test these candidates in clinically relevant animal models for safety and efficacy prior to starting human clinical trials. To generate an overview of the types of efficacy outcome measures previously used, a literature search for papers published over the last 20 years on "regenerative treatments for the IVD in animal models" was performed. A total of 112 papers were reviewed and the outcome measures appeared to vary considerably between the different types of assessment (ie, histological, macroscopic, radiological, biochemical, mechanical, and pain assessment; Figure 4A,B). It is well known that IVD degeneration is a complex disease with cellular and biochemical matrix changes. 12,57,58 Therefore, the assessment of histological and biochemical outcome measures is essential to fully evaluate the native cell response and matrix regeneration capacity of any treatment strategy. Despite this, histological, biochemical and/or radiological changes indicative of degeneration can be found in patients in the absence of pain, demonstrating that the two do not always correlate. [59][60][61] Therefore, histological, biochemical and/or radiological improvements observed in animal models may not necessarily translate clinically into a reduction in disability and for this reason should not be used alone to indicate therapeutic success.
From a clinical point of view, the ultimate aim of any treatment developed for neck and back pain is to alleviate pain and restore the biomechanical function of the IVD. Interestingly, from the 112 papers reviewed, only 4% of these papers performed some kind of biomechanical assessment to determine the success of the therapy under investigation, and to the authors knowledge none of the papers reviewed had assessed pain as an outcome measure following administration of a regenerative therapy ( Figure 4). This is likely due to the fact that standardized methods to assess biomechanical function and pain in animal models are less well defined. Furthermore, it is a common practice in translational studies to employ more than one levels within in each animal in order to reduce the number of animals needed in an experiment (3Rs principle: reduction, replacement, refinement). This limits the ability to assess pain properly. As such, once a promising treatment candidate has been encountered in Note that for proper mimicking the degenerative environment in 3D hydrogel culture low density of cells should be employed; for explant and organ culture diffusion of oxygen and glucose into the disc should be considered and thus higher culture concentrations may be required to result in these internal concentrations.
studies with more than one spinal level injected with a different treatment, it would be recommended to perform an in vivo study on this treatment candidate injected at only one spinal level, enabling pain assessment.
Suitable methods to assess pain in animal models is still in its research infancy; for those that do exist, it is not clear whether these methods will relate to human neck and back pain, since the source of IVD-related pain in humans is not always defined. 62,63 A number of preclinical small animal models that mimic specific aspects that contribute to low back pain (LBP) has been recently reviewed by Shi et al. 64 Pain measurements in large animal models are primarily qualitative 65 and deduced from objective gait analysis that does not allow for the exact (spinal) localization. 66 Specifically in the case of dog patients with chronic back pain employed as a model for humans within the concept of "One Medicine," owners can fill in questionnaires regarding pain assessment aspects and inherent impairment of mobility as would humans entering a clinical trial. 67 Despite the difficulties, when evaluating the success of any potential therapy in animal models, it is recommended that some measure of biomechanical function and pain assessment, appropriate to the selected animal model, is performed. These outcome measures should be performed in combination with histological, biochemical and/or radiological outcome measures to evaluate the native IVD cell response, including production of catabolic/inflammatory factors, repair of matrix components and restoration of disc height. All outcomes should ideally be determined blindly and objectively, for example, by using quantitative scoring systems. This will improve knowledge concerning the efficacy of the therapeutic and may improve the translation of clinical findings within animal models to those found in humans. In this way, the chance of failure of the treatment candidate in human clinical trails would be reduced and translational success would be improved.
Commonly used experimental animal models for IVD degeneration include mice, rats, rabbits, dogs, sheep, goats, 15  IVDs, causing severe degenerative changes in the aging spine. 73 Most identified genes associated with LBP due to IVD degeneration code for proteins affecting ECM integrity, responsible for mechanical properties of the IVD. Thus far, animal studies on the genetics of IVD disease use mice. [74][75][76] Although far less well researched, also in larger animal models employed for in vivo studies, genetics can play an important role. 77 Therefore, researchers need to consider this when choosing a suitable animal model.

Differences in IVDs between human and animal species include
anatomical (size, shape), biomechanical, biochemical, aging/degeneration, nutritional, cellular, and loading variations as reviewed by Alini et al. 15 The difference in IVD size affects the type and number of readout parameters that can be measured: small IVDs cannot be used to evaluate multiple parameters and assay detection limits coincide with small samples. Also, limitations in relevant volume of therapeutics relative to tissue constructs are encountered. 78 Although for large animal models this is not a specific issue, safe injection volumes and pressure should be determined to avoid injection-induced accelerated degeneration. 79 In this respect, IVD organ cultures are useful for injection volume and extrusion testing before animal models are employed.  an IND-based on small animal models may make product development more affordable and shorten the time to market, but small animal models may insufficiently predict efficacy in man.
When combining IVD size and NP cell type, sheep and goats more closely resemble the human situation, but IVD degeneration also needs to be induced. The question remains how adequately animal models with induced IVD degeneration represent the cellular changes which occur during natural degeneration in humans. Therefore, NCD or CD dogs may more accurately resemble human IVD degeneration where degeneration is spontaneous. 120 Over the past few years, both human and veterinary medicine have recognized the importance of the "One Medicine" concept: bringing together human and animal

| REGULATION
Regulatory pathways for the Food and Drug Administration (FDA), and Medicines and Healthcare products Regulatory Agency approval, will depend on the therapeutic under investigation and whether it is defined as a drug, biologic or device. When considering the welldefined regulatory pathways for drugs, it is estimated that the average length of time from discovery to clinical application is approximately 12 to 15 years with an estimated cost of $800 million. 130 In contrast, the regulatory pathways for biological therapeutic approaches are often more complex and time consuming. The FDA have established that biological drugs include blood-derived products, vaccines, in vivo diagnostic allogenic products, immunoglobulin products, protein products and products containing cells or microorganisms. 131 Given the unique nature of biological therapeutics, the preclinical tests performed to evaluate the safety, purity, potency and efficacy of the therapeutic will often be specific to the biological therapeutic under investigation. It is therefore recommended that researchers have contact with their local regulatory authorities early on in the preclinical experimental design process to ensure that the necessary experiments are being performed in line with the requirements for an IND application and premarket approval (biologics license application). Consideration, early on during preclinical investigations, should also be given to the manufacturing processes of the therapeutic. In comparison to well-characterized synthetic small molecule drugs, regulatory authorities will often require additional clinical studies to demonstrate the identity, safety, purity, potency, and efficacy of the biologic following manufacturing processes. 132 Currently, there is an increasing research interest for the use of implantable biomaterial scaffolds to replace tissues of the IVD as a treatment strategy for LBP. 133,134 Where the biomaterial scaffold is delivered without cells or biological factors it will likely be classified as an implantable medical device, which are typically subject to the regulatory requirements of class III medical devices (90/385/EEC). 135 Again, it is essential that regulatory considerations are thought of early on, even while the initial in vitro investigations are being performed; this is because certain long-term surveillance studies may be required for regulatory approval, for example, long-term degradation and materials characterization studies in accordance with the ISO10993 standards. 136 Where cells are either incorporated within biomaterials scaffolds or used individually for regenerative purposes, the therapy will likely be classified as an Advanced Therapy Medicinal Product. 137 However, the classification of systems is different within each regulatory authority and is beyond the scope of this review to advise specific regulatory guidelines. Investigators are encouraged to contact their local regulatory bodies for advice as early as possible in the developmental pipeline, to enable appropriate investigations to be incorporated into development.

| CLINICAL TRIAL DESIGN
Translating a potential product with great preclinical data to clinical reality, that is, from the bench to bedside, requires numerous steps.
For a therapeutic agent that will be injected into the IVD under image guidance as a single dose, the pathway will be that for a new drug application, biological agent, medical device, or advanced therapy medical product. While the regulatory nuances can differ from one regime to another, some principles remain the same. Here, we describe numerous steps, documents, principles, and three-lettered    quantifiable measures with the advent of wearable devices and potentially using biomarkers for disc degeneration. 138 Radiological outcomes will be expected too, where the minimum will be a disc height measurement on a standing lateral X-ray in neu- with IVD disease, which often do not suffer from any comorbidities. 121 In both Phase II and III trails, data for safety has to be compulsorily obtained and preliminary efficacy can be tested in Phase II. Whether a regulatory agency will accept another expedient clinical trial model like a single arm study without a control will be dependent on the ability of the sponsor to demonstrate compelling socioeconomic reasons or "orphan-disease" status for their indication. Furthermore, varying dose studies, multiple disc levels treatment or a repeat injection study should best be addressed after market approval for the drug for one level and one dose; as incorporating these questions in a regulatory study will not only make the trial unwieldy, but also add un-sustainable cost and time. Such further studies can be investigator-initiated with or without regulatory oversight.
A complete statistical plan and data management plan are essential. The trial has to be listed at clinicaltrials.gov. Data from the IND (in case the therapy is a protein or a drug) has to be submitted for a NDA which requires multiple and stringent regulatory reviews that may include panels consisting of lay persons and experts. Other regulatory regimes have similar or slight variations. In case a scaffold is classified as a device an Investigational Device Exemption (IDE) study submission followed by a Pre Market Approval (PMA) will be needed.
The IDE may require a pilot, a pivotal or a comprehensive study based on what is being evaluated and in consultation with the FDA utilizing their pre-submission process. More importantly, regulatory harmonization between various countries can help to speed up regulatory FIGURE 6 Drug approval process from bench to bedside. Phase I may not be needed for intradiscal therapies. Direct entry to Phase II or Phase III will be suitable and appropriate for therapies that have a human physiological basis or derivation rather than a small molecule, drug or carrier that may be novel and not a known carrier. FDA, Food and Drug Administration; IND, investigational new drug application A clinical trial protocol has to consist of subjective (patient reported) and objective (investigator determined) outcome tools.  AnGes, Inc. NCT03263611 • Nuclear factor-κB Decoy oligodeoxynucleotide approvals. Intradiscal therapies that have undergone or are undergoing clinical trials are provided in Table 5. As one can deduce from the   154 In this respect, cell transplantation and growth factor dosing needs to take into consideration the demanding disc mileau. Once approved, post-market surveillance and other investigator-initiated studies will form the basis of systematic reviews and meta-analysis that will lead to further finetuning of indications and or dose regimes.

| INTELLECTUAL PROPERTY AND COMMERCIAL SUPPORT
Intellectual property (IP) is a term that describes creations of the mind, such as inventions; literary and artistic works; designs; and symbols, names, and images used in commerce. It is divided into industrial property and copyrights. IP protection allows the holder to exclude others from interfering with or using the property right in specified ways. The main forms of IP are patents, copyrights, trademarks, and trade secrets. 155 To obtain the grant of a patent, one must file a patent application at a patent office. It is important to file an application as soon as possible, because after the filing date, disclosing to the public no longer forms prior art and if a full patent application is granted provides protection for 20 years from the earliest filing date of the application, not from the date that the patent was granted. This is important because it is possible to spend considerable funds preparing and filing an application when there is prior art that will prevent a patent, or make the patent very narrow. 156,157 Those individuals within academic institutions will have a technology transfer office (or equivalent) within their institution who will normally manage this process and provide funding if deemed to have potential. Discussion with the local technology transfer office as soon as inventors feel they have something worth patenting is essential. Most technology transfer offices will have their own experiences of patenting and commercialization who will work with inventors to collect initial patent searches.
The knowledge from these searches will help with accentuating both the positive aspects of your invention and the differences that exist over the prior art, leading to a stronger patent application. 157 The next step is to file for a provisional patent application where the filing date is recorded officially with the assistance of a patent attorney and then within 12 months file a nonprovisional patent application. If inventors fail to submit the full application within 12 months of the provisional patent then this will automatically run out and any protection is lost. While, typically inventors do a search after the filing of the provisional patent application but before the filing of the nonprovisional patent application, 158 it is advised to complete this prior to filling the provisional. The reason not everyone chooses to do a patent search first is because of the high cost of hiring a patent attorney.
Certainly, recording your invention as quickly as possible and getting an early filing date has its advantages. However, the best course to follow, if funds are available, is doing a patent search first before any patent application is filed. By doing a patent search and receiving professional help from a patent attorney you will be able to determine whether it makes sense to move forward and what, if any, rights could be possibly obtained. Furthermore, inventors will search the database for themselves to be informed of the patent landscape so that they can determine whether it even makes sense to start or continue a project in a certain way and whether there may be some available space that they could target.
Do not disclose your inventions until the provisional patent application is on file as any public activity associated with the invention such as telling others at conferences, in abstracts or as a publication This is often done in exchange for a share of or exclusive transferrable license rights to the IP. As these incubators or engines can be highly specific to the medical field and hold much specific expertise, they are able to considerably accelerate the formation and maturation of spinouts in a successful manner. At the moment it can take millions of dollars and on average 12 years to get from bench to patients depending on the invention.

| DISCUSSION
Over the last two decades, there has been a vast amount of published literature on the preclinical development of novel therapies for IVD degeneration. However, to date we still do not have a therapy which addresses this unmet clinical need. Through scientific research, the IVD field has a greater understanding of the physiological and catabolic environment of the degenerate niche and the biological impact that it has on the cells and extracellular matrix. Research within the community has also uncovered key differences in cell behavior and phenotype with species and culture conditions. It is essential that this scientific knowledge is incorporated into the preclinical design to accelerate and improve translation of findings from preclinical development to clinical studies. It is accepted that the culture conditions used within preliminary proof of concept studies will depend on availability of resources and the research question being investigated.
However, at some point during the preclinical phase, novel therapies should be investigated using human cells/tissues within culture conditions that mimic those most closely seen within the degenerate human IVD (Table 1). Utilizing human cells/tissues early within the developmental pipeline will enable aspects such as patient variability to be explored and will require multiple patient samples to be investigated in vitro. These experiments will be the most clinically relevant and thus reduce risk of failure within clinical studies. Standardized approaches to preclinical investigations of novel therapies from 2D culture to organ culture systems, which mimic the in vivo IVD (Figure 1), will aid comparison with competing therapeutics, so that the best candidate therapies go forward to clinical testing and, thus, improve the chances of progression to clinical use. The therapeutics found to be most promising in the preclinical (in vitro/ex vivo) phase still need to be tested in animals before they can enter human clinical trials. As no single animal model will exactly match human IVD degeneration in all of its complex aspects, it is important to choose an appropriate animal model, based on the most important research questions and desired outcome parameters. Small animal (eg, rodent) models are very useful for fundamental/safety studies, whereas the more expensive large animal models are more suitable for translational/efficiency studies. In all animal models, however, the outcomes should be determined objectively, for example, by randomization, blinding, and quantitative scoring systems.
Scientists are often not well informed about the regulatory pathway. Hence, they should contact their local regulatory authority as early as possible to gain appropriate advice. To determine the pathway, the therapeutic under investigation should be classified which will define the preclinical work required for regulatory acceptance. As work proceeds, it must be fully documented in accordance with GLP procedures and entered in a treatment strategy file so that they can be submitted and reviewed as part of the regulatory process.
To obtain meaningful results from a clinical trial, regardless of its SMEs, valuable developmental resources include governmental valorization grants/loans and incubators/engines.
In conclusion, for successful translation of regenerative therapies to clinic, it is essential to plan your pathway to clinic from the outset, take advice early on regulatory and commercial aspects and consider the required proof of concept experiments required to satisfy regulatory approval for clinical trials. Do not delay too long, otherwise any protection will run out, which makes commercial interest difficult (and often this is the only way to fund expensive clinical trials).