MEET US AT ACCESS! 2019 – AAM ANNUAL MEETING
Thereby, melanoma together with kidney and lung cancer are natural targets for immunotherapeutic approaches, because both tumor types are frequently infiltrated with CD8+ T-lymphocytes, and occasionally undergo spontaneous regression. Tumor-specific CD8+ T-lymphocytes are believed to particularly mediate these anti-tumor effects.
The broad approval granted in March 2011 by the FDA for use of the drug ipilimumab for patients with late-stage metastatic melanoma, either as initial therapy or after relapse, was a major breakthrough in the immunotherapy for melanoma. This not only brought a clear survival advantage observed for a patient group with no other therapeutic options, but also employs a mechanism of action which is virtually certain to involve the modulation of endogenous T-cell responses.
Ipilimumab is a monoclonal antibody to CTLA4 (cytotoxic T-lymphocyte antigen-4). The latter is an immune checkpoint regulator protein and negative regulator of the immune response. Under physiological conditions, CTLA4 attenuates the chances for chronic autoimmune inflammation, but also inhibits the development of an active immune response by acting primarily at the level of T cell development and proliferation. Blocking of CTLA4 with an antibody overcomes the negative regulation. This, following a current rationale, gives rise to activation of pre-existing anticancer T-cell responses and possibly triggers new responses.
A second immune checkpoint, PD-1 (programmed cell death-1), has garnered significant interest since the blockade of PD-1 with a single agent was associated with objective responses in melanoma, kidney cancer and lung cancer.
However, despite of the significant progress recently obtained, cancer immunotherapy is still suffering a number of limitations. In case of ipilimumab challenges are a significant rate of on-site toxicity effects, leading to serious colitis and hypophysitis due to induced inflammation in up to 23 % of the patients. In co-therapy with dacarbazine, significant elevations in liver function tests in 20 % of the so treated patients were observed. Moreover, the stimulation of T-cell response with ipilimumab may take several months to occur, while treatment with conventional cytotoxic therapies may trigger rapid tumor shrinkage due to direct killing of cancer cells. The adverse effects with PD-1 blockade seem to be less pronounced, than with CTLA-4 blockade.
Both, for antibody-based therapy or for cancer vaccines, the search for human tumor antigens as potential immunotherapeutic targets has been a continuous task in the field of tumor immunology. For tumor antigens to be potential immunotherapeutic targets, the antigen must have no or highly restricted expression in normal tissues so that autoimmunity can be prevented.
Tumor Associated Antigens
The first TAA recognized by cytotoxic CD8+ T-lymphocytes was described in 1991. Since then, researchers utilize expression cloning of TAA cDNAs as well as novel strategies such as reverse immunology, biochemical methods, genetic approaches, and serological analysis of recombination expression libraries (SEREX) to identify TAAs. This led to more than 400 T-cell-defined human tumor antigens registered in a relevant data base in 2013. Categories of tumor antigens can be discriminated according to their expression in neoplastic and normal tissues (Table 1).
Since most TAAs used for immunotherapy are considered to be ‘‘self’’-antigens, one of the main challenges is to develop methods that can effectively and safely break tolerance to TAA. Peptides can be used for example in a simple and inexpensive strategy for vaccination, utilizing the host’s endogenous antigen presenting cells to present TAA peptides. For this, the peptides are generally delivered in an adjuvant, required for effective activation of dendritic cells.
|TAA Categories||Antigen Characteristics||Genes|
|Cancer-testis||Expressed in various tumors but not normal tissues except in testis and placenta||MAGE, GAGE, BAGE, NY-ESO-1|
|Differentiation||Antigens shared between tumors and normal tissues from which they arose||Tyrosinase, Melan-A/ MART-1, gp100, TRP-1, TRP-2|
|Tumor-specific||Antigens generated by point mutations or splicing aberrations in ubiquitous genes||p53, Ras, CDK4, β-catenin, TRP-2/INT2|
|Widely occurring over-expressed||Proteins over-expressed in histologically different types of tumors||Survivin, MUC1/2, AFP and EphA2|
Cancer/testis antigens (CTs or CTAs) (Table 2) are protein antigens with normal expression restricted to adult testicular germ cells, but are aberrantly activated and expressed in some human cancers. Thereby, melanoma, ovarian and bladder cancer as well as lung cancer, particularly in case of the squamous cell type, have been found to have the highest frequency of CT expression and sometimes are referred to as “CT-rich” tumor types. Since the early 1980s, about 70 families of CT antigens have been identified with over 140 members, including for example the melanoma-associated antigens MAGE, BAGE, GAGE, PRAME, NY-ESO-I and HOMMEL-40 (SSX-2).
As well-known and intensively studied biomarkers in cancer, the MAGE (melanoma antigen gene) family may provide novel targets to develop cancer-specific therapies for a broad range of cancers because of their relatively restricted expression and antigenicity. This family of proteins includes more than 50 identified members in humans, all of which containing a highly conserved MAGE homology domain (MHD) with a length of around 170 to 200 amino acids and multiple tandem winged-helix motifs.
As the first human tumor-associated antigen found to be specifically recognized by CD8+ T-cells, MAGE-A3 is promising for antigen-specific immunotherapy of malignant cells. Along with encouraging results obtained in mouse model, tests performed in non-small cell lung carcinoma patients and metastatic melanoma patients showed that patients receiving recombinant MAGEA3- based vaccine will develop MAGE-A3-specific antibodies and have more clinical benefits than the placebo-treated group. However, one of the largest-ever phase III lung cancer trials trying to investigate the efficacy of MAGE-A3 antigen-specific cancer immunotherapeutic agents in preventing cancer relapse, turned out to have no improvement in progression-free survival.
|Target Antigen||Restricting HLA||Epitope||Sequence / Prod. No.|
Differentiation antigens (Table 3) are tissue-specific tumor antigens with higher expression in cancer cells compared with normal cells. However, only a low immunogenicity is assigned to the melanocyte differentiation antigens, because of the development of an immunological tolerance for the potential epitopes of these “self” proteins. Differentiation antigens include tyrosinase, Melan-A/MART-1, gp100, tyrosinase-related proteins-1 (TRP-1/gp75) and -2 (TRP-2).
Tyrosinase consists of 529 amino acid residues and is involved in the synthesis of melanin. In general, the generation of a tyrosinase-specific response in a melanoma patient is a relatively infrequent event and is usually only seen in patients showing a high response to several melanoma-associated antigens.
Melan-A/MART-1 (melanoma antigen A/melanoma antigen recognized by T cells 1) is a relatively small transmembrane protein consisting of 118 amino acid residues. It is expressed in most melanoma cells, but cannot be observed in other tumors. The Melan-A/MART-1 gene codes for antigens that are recognized by HLA-A2-restricted cytotoxic T lymphocytes (CTLs) and, among the family of melanocyte differentiation antigens, Melan-A/MART-1 seems to represent the highest relative immunogenicity.
The glycoprotein gp100 was originally identified as a melanocyte lineage-specific antigen by the monoclonal antibodies NKI/ beteb, HMB45 and HMB50. These antibodies are used as diagnostic markers for human melanoma.
Gp100 alone has been shown to induce an immune response, but has limited antitumor activity. A multi-center phase II clinical trial in patients with advanced melanoma showed that the gp100 peptide vaccine plus interleukin-2 (IL-2) group had a significant improvement in centrally verified overall clinical response and longer progression-free survival, compared with the IL-2-only group (16 % versus 6 %), but without overall survival benefit.
|Target Antigen||Restricting HLA||Epitope||Sequence / Prod. No.|
HLA-DR1, 3, 4
In contrast to other types of tumor-specific antigens, neoantigens are novel peptides that are not normally found in the host and are unique to a particular cancer (Table 4). These peptides are not subject to central tolerance and hence appear as ideal targets for cancer immunotherapy. They may also contribute to the understanding of the molecular mechanisms of malignant transformation. Neoantigens can arise from somatic mutations (or other genetic alterations) that result in the production of a novel peptide, or from viral peptides in virally induced cancers. These antigens have been identified predominantly in melanoma, likely due to their relatively high mutation rate, but also in other tumor types including lung and renal cancers.
One major concern with regard to the suitability of neoantigens for tumor therapy is the heterogeneity of tumors. Neoantigens may be expressed in some, but not all tumor cells in an individual patient, leading to tumor escape from immunotherapy. Potential approaches to address this concern are to target multiple neoantigens at the same time, so all tumor cells expressing at least one neoantigen can be destroyed, or to target a single neoantigen, which is ideally expressed in all tumor cells within a patient.
|Target Antigen||Restricting HLA||Epitope||Sequence / Prod. No.|
Melanoma still is a live-threatening disease, for which, besides preventive measurements and conventional therapies, immunotherapies based on peptide epitopes give hope for future therapies. Significant clinical breakthroughs have already been obtained with immune checkpoint inhibitors, and therapeutic approaches like vaccination have the potential to further improve the prognosis for the patients.
However, future research will need to address a broad variety of open questions. Optimal combinations of antigens, adjuvants and delivery vehicles need to be determined, and combinations of complementary immunotherapies are required to induce robust and sustained anti-tumor responses. It is important to overcome immune tolerance and immune suppression.
Appropriate pharmacodynamic biomarkers and diagnostics as well as new metrics for evaluating the effectiveness of immunotherapies will need to be implemented. The metrics of immunotherapies thereby differ significantly from those of conventional cytotoxic drugs. Another important scientific topic will be the use of optimum adjuvants, which might not have been optimally selected in initial trials with melanoma vaccines, and are important constituents in current strategies for immunotherapy of melanoma.
Melanoma is an aggressive form of skin cancer that affects populations worldwide. The number of melanoma cases is expected to rise from approximately 165,650 in 2016 to 206,720 in 2026 among adults living in major markets including the United States, France, Germany, Italy, Spain, the United Kingdom and Australia (1). Surgery is often a successful treatment option for early-stage melanomas but advanced melanomas are more difficult to treat. New immunotherapies such as the checkpoint inhibitors pembrolizumab (Keytruda®), nivolumab (Opdivo®) and ipilimumab (Yervoy®) have shown promise in treating melanomas. In addition, drugs that target the BRAF protein are being used to treat advanced melanomas that are positive for the BRAF gene and melanoma vaccines are being studied as potential treatments (2). As shown in Table 5, there are several peptides in clinical development for the treatment of melanoma. Furthermore, there are over fifteen peptides known to be in preclinical development for the treatment of melanoma.
|Product Name||Active Ingredient||Condition Treated||Highest Phase|
|LTX-315||--||Head And Neck Cancer; Metastatic Breast Cancer; Metastatic Melanoma; Soft Tissue Sarcoma; Solid Tumor||Phase II|
|MMD-37K||--||Bladder Cancer; Colorectal Cancer; Esophageal Cancer; Gastric Cancer; Glioblastoma Multiforme (GBM); Liver Cancer; Melanoma; Pancreatic Cancer||Phase II|
|LL-37||--||Metastatic Melanoma||Phase II|
|Debio 8200||Triptorelin||Melanoma||Phase I|
Lytix Biopharma AS is developing LTX-315 for the treatment of soft tissue sarcoma, melanoma, breast cancer and head and neck cancer. LTX-315 is a membrane-active host defense peptide that binds to tumor cell membranes causing lysis and immunostimulating activities. In April 2018, Lytix announced that recruitment was completed for its Phase I/II study of LTX-315 in patients with advanced solid tumors. Patients will receive LTX-315 as a monotherapy for multiple tumor types, in combination with ipilimumab for malignant melanoma, or in combination with pembrolizumab for triple negative breast cancer (1).
MetaMax Ltd is developing MMD-37K for the treatment of glioblastoma, melanoma and other cancers. MMD-37K is a chimeric recombinant peptide developed based on cell-penetrating peptide technology. This drug candidate inhibits the activity of CDK4 and CDK6, two kinases involved in allowing cells to divide and multiply. In 2014, the company announced that it had enrolled the first patients in a Phase I/IIa trial of MMD-37K to treat malignant neoplasms (1).
LL-37 is under development by the University of Texas MD Anderson Cancer Center for the treatment of metastatic melanoma. LL-37 is an antimicrobial peptide with wound healing properties that is part of the human antimicrobial protein known as cathelicidin. In 2015, a Phase I/II trial of LL-37 was initiated to evaluate the safety, efficacy of LL-37 and to find the appropriate dose of LL-37 (2).
Debiopharm is developing Debio 8200 (triptorelin) as a treatment for patients with advanced melanoma in combination with nivolumab, a Programmed Cell Death Protein 1 (PD-1) inhibitor. Triptorelin acts as a gonadotropin-releasing hormone (GnRH) agonist. The peptide reduces the production of luteinizing hormone and follicle stimulating hormone to slow down the development of cancer. Debio 8200 is currently being tested in a Phase I trial in combination with nivolumab in patients with advanced melanoma (1).
Peptides are playing a key role in the development of new treatment options for melanoma. To support researchers and organizations focused on this field, Bachem offers a custom peptide synthesis service, the production of New Chemical Entities and Generic Active Pharmaceutical Ingredients (APIs). In addition, we offer a selection of peptides for cancer research including melanoma peptides.
(1) GlobalData (2018)
(2) What’s New in Melanoma Skin Cancer Research? American Cancer Society (2018)
(3) Intratumoral Injections of LL37 for Melanoma. ClinicalTrials.gov (2014)
(4) Medtrack (2018)
What is your official job title at Bachem?
I am a Marketing Specialist in the Science Marketing Team.
How long have you been with Bachem? Where did you work before Bachem?
I started at Bachem in June 2018, so I have been here for six months now. Before Bachem, I studied Chemistry at ETH Zurich.
Briefly, what do you do at Bachem?
I handle the scientific support, which means that I assist our customers as well as our sales team, if any questions come up – especially about our catalog products. Additionally, I work on the revision of our monographs and the creation of new marketing material. There is also an IT-component to my job at Bachem, since I work on the website and the database of our catalog products.
What is your academic background/degrees or training?
I have a PhD in Chemistry, which I obtained in March 2018.
What do you like most about your job?
Every day I am learning something new about peptides. By supporting our customers with their applications for our products and during the revision of our publications, I am always in contact with the newest publications in various fields of research.
What do you do for fun?
I like to meet with friends over a beer or two or to just stay at home playing video games.
What is your preferred peptide?
Since I come from the synthetic side of chemistry, I am a big fan of pseudoprolines and isoacyldipeptides. I think these compounds are a very elegant and powerful tool in the synthesis of difficult peptide sequences.
Thank you very much Erik.
Interesting news about peptides in basic research and pharmaceutical development:
Synthetic antimicrobial peptide can destroy biofilms in CF patients, study reports-Cystic Fibrosis News Today
Radiolabeled peptide offers surgical method for assessing NETs-Cancer Network
Deadly Australian funnel-web spiders can also kill melanoma cancer cells, study shows-Australian Broadcasting Corporation News