Background

The vast majority of low back pain (LBP) is self-limited or successfully treated conservatively, whereas a small proportion of patients develop chronic LBP intractable to nonsurgical treatments. These patients present an increasing medical and socioeconomic problem [1]. Intervertebral disc degeneration (IVDD) is emphasized as an important cause of LBP [2, 3]. With progressive degeneration, the effectiveness of the nutrition mechanism of the intervertebral disc decreases; in consequence, the nucleus pulposus cells lose their ability to produce proteoglycan and other important extracellular matrix proteins, which results in disc desiccation and progressive instability [4]. Most treatment approaches, for example, the aggressive removal of the pathological disc or spondylodesis, do not address options of restoring structural or biological deteriorations when IVDD is the underlying problem. However, cell retransplantation and restoration, as a procedure used in this trial, would offer a less invasive and biological alternative to lumbar fusion in an attempt to obviate the LBP associated with IVDD earlier in the degenerative cascade. Until now, an intervertebral disc may only be repaired biologically after a herniation through the transplantation of the patient’s disc chondrocytes [5–8].

Results of the application of ADCT showed that cellular revitalization of the intervertebral disc is possible [8], and the results of a prospective randomized and controlled multicenter trial for ADCT were promising [9]. For the survival and the adaptation of the cultivated cells to the harsh environment in the disc space, the availability of nutrients, the number of injected cells required to avoid nutritional problems due to cell overpopulation, and the pro-inflammatory environment play a crucial role. These problems should be overcome with a suitable biomaterial, which is used in this study [10].

By using an initially liquid biomaterial, which polymerizes after being injected, the cells adhere much better to the disc tissue. NOVOCART™ Disc plus (NDplus), an autologous cell compound for autologous disc chondrocyte transplantation (ADCT), was developed to provide rehydration and maintain the biological integrity of degenerative lumbar discs to prevent secondary diseases such as recurrent lumbar disc herniation, osteochondrosis, or segmental instability. The important properties of NDplus are anti-inflammatory, antiangiogenic and antiosteogenic. Moreover, NDplus is hydrophilic, supports cell morphology, and stabilizes the chrondrogenic phenotype.

In this phase-I/II study, NDplus is being investigated for its clinical applicability, safety, and efficacy in the repair of herniated, nucleotomized discs and of adjacent degenerated discs, if present.

The objective of this clinical study is to provide the basis for a confirmatory study design (endpoints and methodologies) (phase II) and to develop a safety profile for the surgical procedure as well as for NDplus (phase I). This study further aims at developing and validating known and new biologic markers for the quality and clinical efficacy of NDisc plus as requested in the context of identity, purity, and potency characteristics of the medicinal/investigational product.

Methods/design

Study design

The NOVOCART™ Disc study is a nonconfirmatory, prospective, multicenter, unmasked, randomized study with two phases aimed at gathering preliminary clinical information on NOVOCART™ Disc plus and NOVOCART™ Disc basic used in the treatment of a herniated disc. Phase I aimed to develop a safety profile of the investigational medicinal product NOVOCART™ Disc plus. The objectives of phase II are mainly to provide a basis for a confirmatory clinical trial design and proof of concept. Twelve trial sites are planned to participate in this combined phase-I/II study; three of them have already participated in phase I. In total, 120 patients meeting the inclusion criteria will be randomized, treated according to the randomization, and followed up for 5 years. The primary study endpoint of the phase II is the difference in the Oswestry Disability Index (ODI) between treatment groups 2 years after the intervention. This index has emerged as the most commonly recommended condition-specific outcome measure for spinal disorders. It is a self-administered questionnaire divided into 10 sections designed to assess the limitations of various activities of daily living [11, 12]. The Short Form-36 (SF-36) questionnaire and EuroQuality of Life-5 Dimension (EQ-5D) are applied to assess changes in health status and quality of life [13, 14]. Moreover, changes in leg and back pain are assessed by the Visual Analog Scale (VAS) [15]. Numerical measurements in the disc height, volumetry, and signal intensity of index and adjacent discs and categorical evaluations, such as degeneration scale and the presence or absence of stenosis, are determined by magnetic resonance imaging (MRI). Neurological and functional status and the quantity of current pain medication and time to return to work after surgery are documented. The serology of HIV, hepatitis and Treponema palladium are determined preoperatively. Laboratory values (IL-6, Leukotriene, and CRP) as safety vales are being evaluated only in phase I of the study. Adverse events and serious adverse events are documented. Histological investigation of the explanted tissue is performed. Primary and secondary outcome parameters are outlined in more detail in Table 1.

Table 1 Primary and secondary outcome parameters
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Trial organization, registration, and ethical aspects

Ethics approval was attained in Germany from the National Physician Board, “Landesärztekammer” Sachsen-Anhalt and in Austria from the committee of the Medical University Innsbruck. Furthermore, the clinical trial approval was obtained from the Paul-Ehrlich-Institute (Langen, Germany) and the Austrian Agency for Health and Food Safety (Vienna, Austria). The ethical bodies that approved the study in the various centers are listed in Table 2.

Table 2 Ethical bodies of the various centers
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The study complies with the World Medical Association Declaration of Helsinki Ethical Principles for Medical Research Involving Human Subjects, Good Clinical Practice (GCP), national pharmaceutical acts in the participating countries (Austria and Germany), and European guidelines for the conduct of clinical trials with medicinal products for human use. The trial is initiated and sponsored by TETEC Ag (B|Braun Aesculap AG shared company, Reutlingen, Germany), which is responsible for management and registration (EudraCT No: 2010-023830-22, ID NCT01640457). CenTrial GmbH (Tuebingen, Germany) is responsible for clinical trial submission, independent clinical monitoring, and pharmacovigilance. Mediri GmbH (Heidelberg, Germany), as a core imaging lab, is responsible for the development of the MRI protocols, data storage and analyses. Laboratory values are investigated centrally by Synlab Services GmbH (Synlab MVZ, Leinfelden-Echterdingen, Germany). Accovion GmbH (Eschborn, Germany) is responsible for data management, biometrics, and medial writing. Quality assurance is being done in cooperation with participating clinical research organizations (CRO).

Study population

The N-Disc trial aims to include patients who qualify for lumbar sequestrectomy because of a lumbar disc herniation. The target population consists of patients with symptomatic lumbar disc herniation who failed adequate conservative or interventional treatment approaches in accordance with the guidelines of DGNC and DGOOC. Additionally, an MRI-determined lesion at treatment level needs to correlate with the primary symptoms. To minimize risk factors, patients with significant comorbidities have been excluded from the study. Written informed consent has been obtained from each patient. Inclusion and exclusion criteria are outlined in more detail in Table 3.

Table 3 Inclusion and exclusion criteria
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Timetable

The visit plan is outlined in Fig. 1. In phase I, close monitoring of the safety parameters and additional assessment of the MRI will occur.

Fig. 1
figure 1

Visit plan. In phase I, close monitoring of the safety parameters and an additional assessment of the magnetic resonance imaging (MRI) will occur

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Investigational medicinal product

NOVOCART™ Disc plus (NDisc), an autologous cell compound for ADCT, was developed to provide rehydration and maintain the biological integrity of degenerative lumbar discs to prevent secondary diseases such as recurrent lumbar disc herniation, osteochondrosis, or segmental instability. NDisc plus is an injectable, in situ-polymerizing, modified albumin, hyaluronic acid gel with ex vivo-expanded autologous disc derived chondrocyte cells as the active ingredient. NDisc plus is composed of two components: Component A is a suspension with 3.6 to 4.4 million autologous intervertebral disc cells contained in a solution of modified human albumin, human serum, culture media components, chondroitin sulfate, and hyaluronic acid. The total volume is 4 ml suspension placed in a 6 ml glass vial. Component B is a bis thio-polyethylene glycol (BTPEG) solution; the total volume is 1 ml in a 2 ml glass vial. Components A and B polymerize in situ using a dedicated application system (special dual-chamber syringe) to form the desired hydrogel. The preparation is for single use during the ADCT. The dosage is individual, and the volume of injection is, depending on the capacity of the treated disc, between 0.5 and 2 ml cell suspension volume. NDisc basic is used as the placebo in the NDisc study and is the cell-free hydrogel carrier material with an identical composition but without growth factors.

Sequestrectomy

Surgery is performed by two trial-designated surgeons with the assistance of an operating microscope while the patient is under general endotracheal anesthesia and in a prone position. Depending on the location of the disc herniation, the spinal canal harboring the sequestrated disc material is exposed by either a minimal interlaminar fenestration or a translaminar approach [16]. In case of a lateral lumbar disc herniation, a lateral extraforaminal approach is performed [17]. Immediately after extraction, the disc tissue is transferred into a sterile transport vial and provided to TETEC AG for the GMP compliant manufacturing of the investigational medicinal product NDisc.

Adjacent disc disease

The presents or absence of an adjacent degenerative disc is thought to be a potential factor affecting the prophylactic treatment capacity of NDisc plus. Analyses of primary and secondary efficacy variables will be performed separately for these two patient subgroups in addition to the overall analysis.

Transplantation

Transplantation is performed 90 days after sequestrectomy. N Disc plus (NDplus) or N Disc basic (NDbasic) is applied via an injection with a dual-needle technique directly at the intended site of action. NDplus or NDbasic is to be transplanted in a comfortable lateral or abdominal position. After the treatment level is localized and local anesthesia is performed, the puncture of the intervertebral disc concerned takes place contralaterally to the disc surgery. An injection needle is placed in the center of the disc space under image guidance, and the medicinal product is injected. In case of an ADD (adjacent disc degeneration), positioning of the needles and the mandrin takes place simultaneously to minimize radiation exposure (Fig. 2).

Fig. 2
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Transplantation. An injection needle is placed in the center of the disc space contra-laterally to the side of the disc surgery. In case of an adjacent disc disease, positioning of the needle takes place simultaneously to minimize radiation exposure

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Randomization

Randomization is performed intraoperatively by envelope and separately for phase I and phase II of the study. In phase I, 24 patients are randomly assigned to NDplus and NDbasic in a 1:1 allocation ratio. In phase II, 96 patients are randomly assigned to NDplus, NDbasic or follow the standard of care treatment (surgery only, SC). The allocation ratio in phase II is 2:1:1. Altogether, 60 patients will be assigned to NDplus, 36 to NDbasic, and 24 to SC (Fig. 3). Two randomization schedules are generated by CROs using Rando™ (CRO’s proprietary randomization software). The randomization schedule is kept at the CRO by the randomization code administrator, who is independent from the study team. A copy of the randomization schedule is provided to TETEC AG.

Fig. 3
figure 3

Randomization. Randomization is performed separately for phase I and phase II of the study

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Sample size and power calculation

The sample size calculation is based on the primary endpoint of the study, which is the group difference in the ODI. A change of 10 units is considered as a clinically meaningful difference. Moreover, a standard deviation of 12 is assumed, based on results of a previous trial (Hägg, Fritzell, Nordwall, 2003). A sample size calculation was performed based on a two-group t-test (nQuery Advisor™ Software, version 7.0). The width of the respective confidence intervals were calculated using a large sample approximation, with 60 patients to be enrolled in the NDplus group, 36 patients in the NDbasic group, and 24 patients in the SC arm (120 patients in total). A detailed power calculation is shown in Table 4.

Table 4 Power calculation
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Statistical analysis

Efficacy variables

The analysis of efficacy variables will focus on estimation of treatment effects and differences between treatment groups. For this purpose, it is assumed that effects of treatment with SC, NDbasic, and NDplus are additive so that treatment effects can be assessed by location shifts (like mean change or median change) between treatment groups. Differences between NDbasic and SC are the total effect of NDbasic, the transplantation/implantation procedure to inject the NDbasic, and the time interval between tissue harvest and transplantation/implantation. Observed differences between NDplus and SC are the total effect of NDplus, the chondrocytes, the transplantation procedure to inject the NDplus, and the time interval between tissue harvest and cell transplantation. Consequently, observed differences between NDplus and NDbasic are assumed the sole effect of chondrocytes. All efficacy data will be presented for patients in the Full Analysis Set (FAS). Primary and secondary efficacy variables and their changes from baseline will be summarized by treatment group. An analysis of variance with factors treatment and the presence or absence of a degenerative adjacent disc (ADD/HD) will be used to evaluate continuous and quasi-continuous, approximately normal data. Confidence intervals will be based on estimated means (least square means) and the corresponding t-statistic. Additional covariates, such as baseline measurements, will be included in the model as appropriate. VAS readings will be summarized by treatment group and visit over the course of the study. MRI parameters and variables to assess functional neurological status will be summarized descriptively. Survival analysis will be used to evaluate time to return to work after surgery. The Kaplan-Meier product-limit estimator will be used to estimate the probability to return to work over time by treatment group for all patients in the FAS. Imputation of missing data has not been planned.

Safety variables

Adverse events (AEs) will be coded according to the latest Medical Dictionary for Regulatory Activities (MedDRA™) version available at the day of database closure. The analysis of adverse events will focus on treatment-emergent adverse events (TEAE). The frequency and percentage of TEAEs and possibly related TEAEs (that is, any possibly, probably, or definitely related TEAEs) will be summarized according to primary system organ class and preferred term and tabulated by treatment group. All laboratory values will be classified as normal or abnormal according to the laboratories’ normal ranges. Morphological parameters like the Modic Score, the detection of an extra discal fluid collection and re-herniation of the treated disc will be monitored by a MRI protocol. An independent data safety monitoring board (DSMB) has reviewed the phase I data, and no concerns have been raised. An ongoing evaluation by the DSMB will be undertaken during phase II. If relevant concerns should be detectable like increased reherniation rates, a discontinuation of the trial must be considered.

Interim and final analysis

Data collected in the study may be analyzed and reviewed continuously. Early findings may be used to stop the study in case of safety concerns or lack of efficacy or futility with regard to a positive outcome in the NDplus group. To ensure the efficient use of clinical data, interim analyses are being performed (see Table 5).

Table 5 Interim and final analyses
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Discussion

Next to the high prevalence of lumbar back pain caused by degenerative disc disease and the increasing number of spinal interventions [1], the major advantage of disc repair procedures is the ability to address the source of low back pain with a minimally invasive technique. Autologous chondrocyte cell transplantation has been shown to reduce intervertebral disc degeneration in animal models, as well as to be safely applicable in humans [9, 18, 19].

The avascularity of the lumbar disc is a promising precondition for autologous chondrocyte cell transplantation. Limited blood flow inhibits cell migration and provides an immunologically privileged environment [20]. Controversially, transplanted cells must survive in a limited blood supply and in a mechanically stressful environment that can cause a loss of native chondrocyte cells and leads to a decreased extracellular matrix production [4]. Therefore, the choice of biomaterial is important.

By using an initially liquid biomaterial, which polymerizes after being injected into the intervertebral disc, the cells adhere much better to the disc tissue. In an animal experiment, a significant increase in the survival rate of cells that were injected into the intervertebral disc was achieved with a polymerizing biomaterial as opposed to the application in a watery solution [10].

The use of hyaluronic acid and chondroitin sulfate in a defined concentration and composition stabilizes the phenotype of the expanded cells and allows an environmental conditioning, a more balanced nutrient distribution, and ultimately a higher cell survival rate after transplantation, by anti-inflammatory and osmotic effects [21–23]. Furthermore, the polymerizing hydrogel has anti-osteogenic and anti-angiogenic effects [24].

The hydrodynamic properties of hyaluronic acid have been known for many years [25]. Glycosaminoglycan plays a major role in the extracellular matrix of the healthy human intervertebral disc [26]. In an intervertebral disc with degenerative changes, however, the proteoglycans, the level of hyaluronic acid, and subsequently, the fluid content are already substantially reduced [27, 28]. Besides a high bio- and cell compatibility, a polymerizable biomaterial must also possess other important properties in order to be suitable for the biological disc reconstruction. It must ensure that the biomaterial stays in the disc after its in vivo polymerization and during the remobilization of the patient, that is, during increased physical stress [29].

The goal of ADCT is to reduce the degenerative sequelae after lumbar disc surgery or to prophylactically avoid degeneration in adjacent discs. Injection of material into the disc, however, theoretically carries several risks, such as extrusion of the injected material, increased intradiscal pressure, potentially provoking disc herniations, and local or systemic inflammatory reactions.

Trial status

Phase I of the trial started in October 2012 with one site in Austria (the Department of Neurosurgery, Medical University Innsbruck), followed by two sites in Germany (the Department of Neurosurgery, BG Clinic Halle-Bergmannstrost (February 2013) and Department of Neurosurgery, BG-Clinic Murnau (March 2013)). Phase I revealed no relevant safety issues as reviewed by an independent DSMB. Thus, phase-II was planned with the following nine sites in Germany and Austria contributing: the Department of Neurosurgery, Medical University Düsseldorf; Department of Orthopedics-II, St. Franziskus Hospital Muenster; Department of Neurosurgery, Medical University Charité Berlin; Center of Spine Surgery, DRK Clinic Berlin Westend; Department of Neurosurgery, City Clinic Karlsruhe; Department of Neurosurgery, SHG Clinic Idar-Oberstein; Department of Trauma Surgery, Medical University Göttingen; Department of Neurosurgery, Medical University Schlewig-Holstein (Kiel); and Department of Spine Surgery, Orthopedic Hospital Speising.