Vaccines are one of the best achievements in the pharmaceutical industry. They have largely contributed to eradicating multiple devastating diseases and saved millions of lives.
There are two categories of vaccines:
- Prophylactic vaccines: they are designed to prevent a disease or an infection from occurring. Prophylactic vaccines are disease / infection derived antigens administered to healthy people to trigger an immune response against foreign antigens.
- Therapeutic vaccines: they are administered to sick patients to cure or alleviate a diagnosed disease. The immune response is directed against self-antigens.
Although the first peptide vaccine investigated goes back to the 1980s, when peptide epitopes from virus-derived CD8 T-cells were used, the main research activities in the field have taken place in the last 15 years.
Looking at the therapeutic vaccine pipeline, cancer vaccines are by far the most investigated. In 2014, therapeutic vaccines generated USD 3.1 billion, of which cancer vaccines represented USD 2.9 billion. By 2019 total sales are expected to reach USD 4.3 billion, with the US market dominating nearly USD 2 billion of that in sales.
As of today only one cancer vaccine has been approved by the USFDA. In 2014 Dendreon’s Provenge®
(Sipuleucel-T) sales were USD 224 million (BioMedtracker, February 2015). Provenge®
is prescribed for patients with metastatic prostate cancer. Some of the infectious agents (viruses, bacteria, parasites) are associated with 15-20% of cancers. Several preventive cancer treatments have been developed, and two of them are currently marketed: Gardasil®
. Both vaccines are directed against Human Papilloma Virus (HPV), which is responsible for ~70% of worldwide incidents of cervical cancer. Cancer vaccines are leading the race of overall therapeutic vaccines in clinical trials.
Peptide vaccines are designed to activate B-cells and killer T-cells to recognize cancer cells as foreign agents. Cancer cells have surface protein modifications such as phosphorylations and glycosylations that differentiate them from healthy cells. The peptide epitopes used are usually fragments from these modified proteins. These “cocktails” of peptide fragments can be further engineered to increase their immune activity and plasma half-life by constraining the peptide backbone through introduction of cyclization or non-natural amino acids in the sequence. Multiple biotechnology companies use peptide cocktails in their clinical pipeline (e.g. Ac Immune, Anergis, Ultimovacs, CellDex, MedVax, Circassia, Immune Targeting Systems, Immatics).
Reducing the antigen to protein fragments (peptides) can lead to a decrease in the expected immune response, thereby requiring the use of adjuvants. Some peptide drug delivery systems can be used as adjuvants as well, e.g. nanoparticles, liposomes, carbohydrates, and lipids.
Besides their low toxicity, peptide vaccines offer multiple advantages such as an increase in the specificity and longevity of the immune response, which leads to significant cost-saving compared to conventional therapies. Furthermore, cancer is a dynamic disease associated with mutations that render conventional drugs less effective. Vaccines could overcome the mutation barrier by using appropriate epitopes from proteins (over-)expressed in cancer cells, thus triggering the immune response against cancer cells despite the mutations.
Developing therapeutic vaccines is also associated with many challenges, such as varying immune response between individuals. The approach of using epitopes from modified cancer cell-based proteins is rather “young” and is not backed up by decades of successful data. Thus Big Pharma companies mostly show their appetite for this segment when the vaccine has demonstrated efficacy and safety in Phase 1/2 studies. Biotech companies own almost 80% of the current therapeutic vaccine pipeline. The number of therapeutic vaccines in clinical trials is estimated at 290 products, 125 of which are in Phase 1, 110 in Phase 2 and 55 in Phase 3. Nearly 40% (113 products) of the total are investigated for cancer treatment.
Peptide Vaccines: Chemistry Manufacturing Control (CMC) Challenges
Peptide drugs have a high affinity and specificity for their target. It is not unusual to produce a peptide vaccine where only a few hundred milligrams to a few grams can cover a full clinical study. In some cases the quantity of the Active Pharmaceutical Ingredient (API) used for analytical testing and ICH-stability exceeds the amount used for clinical trials.
Drug Substance Manufacturing Challenges:
With the limited amount of APIs required, the most straightforward synthetic strategy is solid-phase peptide synthesis. The production costs are clearly labor-driven and the costs of raw materials are less significant. Producing a peptide vaccine API consisting of multiple epitopes can be a real challenge in many aspects. For example, the case of a vaccine consisting of 5 peptides would translate into the following process tasks. To shorten the delivery time, most of the tasks have to be carried out in parallel:
Process development for 5 peptide sequences
cGMP production of 5 peptides
Analytical method development for 5 peptides (synergies especially for HPLC methods can be found here but it is critical to have a robust stability indicating an HPLC method for each peptide)
Process and analytical validations: 5 validation programs for 5 different peptides
ICH stability program on 5 peptides (testing all of them at each time-point in parallel)
Lengthy CMC package for filing (including a robust CMC section comprising all synthetic and analytical testing details)
All of these tasks are labor-intensive and require more resources than conventional APIs. Also, streamlined project management and clear communication are absolutely necessary to carry out multiple vaccine projects in parallel. The CDMO must have a high level of flexibility and enough resources to accommodate such a complex program. The level of resources required can be easily accommodated by a large CDMO with potentially multiple locations to absorb the amount of work within the shortest time possible. CordenPharma overcomes this difficulty by offering formulation development and drug product manufacturing services.
Drug Product Manufacturing Challenges:
Formulating a cocktail peptide vaccine is very complex. The behavior of each component in the formulation mix adds to the known technical issues associated with peptide stability and aggregation/gelling properties. Different peptides can mutually interact with each other and trigger aggregation through electrostatic interactions. The overall peptide mix ionic charge may also impact the solubility and stability of the vaccine drug product. These aspects need to be investigated during formulation development.
Testing a drug product containing a cocktail of peptides can be rather challenging for multiple reasons:
HPLC Methods: Multiple HPLC methods have potentially been used for the drug substance testing to reflect each peptide component purity; all the peptide components are now in one single vial; the HPLC purity testing method has to quantify all the peptides in the vaccine; since each peptide may have a different response factor, ideally an internal standard for each peptide composing the vaccine has to be qualified, which should reveal the exact composition of each peptide in the vaccine drug product.
Limit of Quantification: the amount of peptide in each vial of drug product is sometimes very low; monitoring the level of impurities in stability samples can be a challenge; the HPLC method needs to be complemented by other techniques.
Stability Studies: the main difficulty here is not only to detect the impurities but also associate each potential impurity to the peptide from which it is derived; mass spectrometry techniques are necessary to fully trace back each impurity and determine its corresponding peptide.
To summarize, the challenges encountered in manufacturing peptide cocktail vaccines are variable. Drug substance complexity is mainly driven by the amount of resources necessary to accomplish the manufacturing and testing within a short time frame, whereas the drug product manufacturing challenges are intrinsic to the drug product properties such as stability and testing complexity.
The increasing number of peptide vaccines in clinical trials reflects a growing interest in the field. Peptide vaccines have multiple advantages and are designed to overcome some of the limitations observed with conventional drugs. The approach of designing a peptide cocktail vaccine based on protein epitopes to treat various diseases is supported by promising clinical data. However, although the process of peptide synthesis at any scale has made huge progress, managing the manufacturing of a peptide vaccine is much more complex than a standard API. Efficiently addressing all of the manufacturing and analytical tasks required in a timely manner is a very important point for drug development companies to consider. Particular expertise in analytical services and seamless project management are a must.
Read the full cover story here.
Read the online Chemica Oggi Oligo & Peptide Supplement April 2015 full issue here.