**5. Requirements for biosimilar monoclonal antibody clinical trials**

Since the first monoclonal antibody have come off patent protection, regulatory agencies like European of Medicines Agency (EMA), FDA, Health Canada, Australian government Therapeutic Goods Administration (TGA) as well as the World Health Organization (WHO), developed guidance to manufactures interested in submitting applications for biosimilar products approval. Principles for designing, conducting, and reporting the results from clinical trials are set by these guidelines.

Clinical pharmacology studies are a critical part of demonstrating biosimilarity by supporting a demonstration that there are no clinically meaningful differences between the proposed biosimilar product and the reference product [21].

The comparison of the pharmacokinetics properties of the biosimilar and the reference product forms the first step of a biosimilar monoclonal antibodies' development [29]. It is critical to use the appropriate bioanalytical methods to evaluate pharmacokinetics and pharmacodynamics properties [21]. They need to be accurate, precise, specific, sensitive, and reproducible.

The design of the study depends on some factors, including clinical context, safety, and the pharmacokinetics characteristics of the antibody [29]. Two study designs are of particular relevance: single dose crossover designs and parallel study designs. For pharmacokinetics similarity assessments, a single dose study, randomized, crossover study in healthy volunteers, is generally preferred [21, 29].

Pharmacokinetics and pharmacodynamics studies of trastuzumab (CT-P6 drug) [31] and bevacizumab (SB8 drug) [32] were developed with healthy participants. On the other hand, rituximab (PF-05280586) [33] were conducted with patients (rheumatoid arthritis or lymphoma). A study in healthy subjects is considered to be more sensitive in evaluating the product similarity because it is likely to produce less pharmacokinetics and/or pharmacodynamics variability compared with a study in patients with potential confounding factors [21].

Single dose study is recommended for a product with a short half-life, a rapid pharmacodynamics response, and a low anticipated incidence of immunogenicity [21]. To biological products with a long half-life, e.g., the mean serum half-life of rituximab is 59.8 hours after the first infusion [34], to evaluate clinical pharmacokinetics and pharmacodynamics similarity, a parallel group design is more appropriate for this kind of product [21, 29].

To demonstrate comparable clinical efficacy of the biosimilar and the reference product, an adequately powered, randomized, parallel group comparative clinical trial, preferably double-blind, by using efficacy endpoints is usually necessary [19].

Confirmatory trials (superiority trials) for new drugs should demonstrate that the investigational product provides clinical benefit. In this way, FDA and EMA have published guidance to applicants, providing background information and general regulatory principles for cancer clinical trials [7, 35]. Acceptable primary clinical endpoints in this kind of trial include cure rate, overall survival (OS), progression free survival (PFS), disease free survival (DFS) [7, 35].

### *Monoclonal Antibodies for Cancer Treatment DOI: http://dx.doi.org/10.5772/intechopen.97915*

While clinical trials of originator products aim to demonstrate patient benefit, in the biosimilar comparable studies the intention is to compare the biosimilar product with the reference product to exclude clinically relevant product-specific differences [36]. In this case, the most appropriate study design is the equivalence study, and in some specific cases, non-inferiority trial may be accepted after to discuss with regulatory authorities [19, 23, 29]. For this, the manufacturer needs justify on the basis of a strong scientific rationale.

OS is considered the most reliable cancer endpoint because is precise, easy to measure and the bias is not a factor to worried. It is defined as the time from randomization until death from any cause. It is measured in the intent-to-treat population [29, 35]. As it is necessary to perform the study with long follow-up periods in large trials, this endpoint is not usually expected to be present in the biosimilar studies and it is not required by the regulatory agencies.

In the comparable studies, it is not necessary to use the same primary efficacy endpoints as those that were used in the marketing authorization application of the reference product [19, 37]. However, EMA advises to include some common endpoints to facilitate comparisons to the clinical trials conducted with the reference product [19].

At moment, a large number of studies with bevacizumab, rituximab and trastuzumab biosimilar are using the ORR as the primary endpoint, and EFS, PFS as the secondary endpoint (**Table 3**). OS is less frequently used.

ORR is defined by the regulatory agencies as the proportion of patients with tumor size reduction of a predefined amount and for a minimum time period. The FDA has defined ORR as the sum of partial responses plus complete responses (CRs) [35]. ORR is a direct measure of a drug antitumor activity and should be assessed using a standardized criterion to determine the response [35]. The most common is the Response Evaluation Criteria in Solid Tumors (RECIST) guideline [55].

Beyond the pharmacokinetics and pharmacodynamics analyses, and clinical results, immunogenicity data should be collected and evaluated too. The goal is to investigate presence of an immune response to the therapeutic protein and its clinical impact [56].

The risk of immunogenicity varies between products and product categories, as well, between individuals and patient groups [56]. The consequences of an immune reaction to a therapeutic protein range from transient presence of anti-drug antibody (ADA) without any clinical significance to severe life-threatening conditions [56]. Immune responses to therapeutic protein products have the potential to affect product pharmacokinetic, pharmacodynamics, safety, and efficacy [56, 57].

When an ADA binds to or near the active site of a therapeutic protein or induces conformational changes, binding to relevant receptors will not happen and it will affect efficacy of the product. Besides these conformational-based effects, in addition immune-based adverse effects can happen. This includes injection-site and infusion reactions [56].

Among the product-related factors we have the protein origin (e.g. human or animal) and nature of the active substance (endogenous protein, post-translational modifications), significant modifications in the molecule structure, process-related impurities, formulation (excipients) and the interactions between the drug and/or formulation with the primary product packaging [56].

Immunogenicity testing of the biosimilar and the reference product should be conducted within the biosimilar comparability exercise by using the same assay format and sampling schedule which must meet all current standards [56, 58]. Assays used to detect antibodies against monoclonal antibody are often more problematic, difficult and can be technically challenging than for other proteins less complex [59].


### *Biosimilars*


*Legend: ORR, overall response rate; pCR, pathological complete response.*

### **Table 3.**

*Study design and primary endpoint for biosimilar monoclonal antibodies for cancer treatment.*
