- Trillium Therapeutics' lead compound is SIRPαFc, which blocks CD47, the "don’t eat me" signal on cancer cells which prevents immune-mediated cancer cell killing.
- The fusion protein SIRPαFc may have a superior safety profile compared to antibody approaches of blocking CD47, due to reduced red blood cell binding.
- An IND for acute myeloid leukemia is expected in mid-2015, but SIRPαFc has broad anti-cancer potential as a monotherapy and used in combination.
- In December 2013, Trillium Therapeutics raised $33M from a private placement with prominent US healthcare funds, which is expected to fund SIRPαFc through IND-enabling studies, manufacturing, and Phase 1 clinical.
By Elton Chan, Henok Eyob, Ph.D., Armen Mekhdjian, Dimitre Simeonov, and Evan Markegard
Trillium Therapeutics (OTCQX:OTCQX:SCTPF, TSX: TR) is a life sciences company focused on cancer immunotherapy, and trades on the Toronto Stock Exchange (TSX) under the ticker TR and also on the OTC market under the ticker SCTPF. Trillium Therapeutics is located in Toronto, Canada, has 14 employees, and a market cap of 43.5 million CAD ($43.3 million). It has a share price of 0.35 CAD ($0.34), with shares outstanding of 124.4 million. Although the fully diluted share count is 360 million, meaning fully diluted market cap is 126 million CAD ($118 million). In June 2014, the company voted to consolidate shares, which should provide increased visibility. At the June 2014 meeting, Stem Cell Therapeutics voted to changed its name to Trillium Therapeutics to properly reflect its business strategy. In April of 2013, Stem Cell Therapeutics merged with Trillium Therapeutics and obtained Trillium's anti-CD47 cancer immunotherapy compound SIRPαFc, but kept the Stem Cell Therapeutics name. Previously, Stem Cell therapeutics was focused on stem cell therapy, such as the stem cell stimulator NTx-265, which failed in Phase 2 clinical trials of acute stroke in 2010. By merging with Trillium Therapeutics, the company is now focused on anti-CD47 cancer immunotherapy. Cancer immunotherapy is a hot field and is expected to become a very large industry, $35B by 2023, according to a Citigroup analyst.
Trillium Therapeutics' lead compound is SIRPαFc, which blocks CD47, the "don't eat me" signal that is overexpressed on cancer cells. This signal prevents immune-mediated cancer cell killing, mostly through macrophages. SIRPαFc is still in preclinical studies, with an IND expected mid-2015. Although the company is focused on SIRPαFc, it does have other programs in its pipeline, including Tigecycline, TTI-1612, and an anti-CD200 antibody, which will be discussed below. Trillium Therapeutics is very early in development with SIRPαFc, but it has the potential to improve acute myeloid leukemia (AML) treatment as a monotherapy, and also has broad anti-cancer potential when combined with chemotherapy, antibody therapy, immune stimulatory agents, and other cancer therapies.
CD47 is a cell surface protein that has many functions and roles, ranging from cell migration to T-cell and dendritic cell (DC) activation, and brain development. In immunity, CD47 functions as a "don't eat me" signal and a marker of self when it interacts with SIRPα on the macrophage. Cells that have lower levels of CD47 are removed by the immune system, whereas cells expressing elevated levels of CD47 are resistant to destruction. Memory immune cells are long-lived and have high levels of CD47, which protects them from clearance by macrophages. When bound to thrombospondin-1, CD47 also regulates cell migration, adhesion, cell proliferation, death, vascularization, and inflammation. A clinically relevant example of the thrombospondin-1/CD47 system is the inhibition of nitric oxide signaling, resulting in ischemia reperfusion injury (IRI). This injury contributes to delayed graft function and graft loss. Therefore, blocking CD47, and subsequently preventing nitric oxide activity, may improve IRI in organ transplantation. Vasculox, a private biotechnology company, is actively pursuing this aspect of CD47 therapy, attesting to the importance of CD47 in multiple pathologies.
Irving Weissman, professor of Pathology and Developmental Biology at Stanford University, has pioneered studies demonstrating CD47 overexpression on multiple human tumor types, including acute myeloid leukemia (AML), chronic myeloid leukemia (NYSE:CML), acute lymphoblastic leukemia (NYSE:ALL), non-Hodgkin's lymphoma (NHL), multiple myeloma (MM), and bladder cancer. This overexpression has several consequences: 1) increased CD47 expression shields the tumor from the immune system. 2) High levels of CD47 in hematologic malignancies and solid tumors are associated with a reduced survival time. 3) AML patients with high CD47 are also resistant to standard chemotherapies. When CD47 is overexpressed in head and neck squamous carcinomas, the tumors evade the immune system. CD47 regulates tumor metastasis and dissemination in both MM and NHL. In a mouse model of MM, tumor metastasis to bone was decreased in mice that have no CD47, when compared to controls. Inhibition of CD47 in human NHL reduces dissemination and spread to major organs in xenografted mice.
Inhibiting CD47 on the surface of AML cells might increase macrophage-mediated cancer killing of AML cells. Irv Weissman's group at Stanford University is using an antibody approach to block CD47, with clinical trials expected to start in the summer or fall of 2014. In June of 2012, Inhibrx announced an option and license agreement with Celgene (NASDAQ:CELG) worth up to $500M for its antibody program. Although targets were not disclosed, some have speculated one target could be CD47. The Ukrainian Antitumor Center previously had a Phase 1 clinical trial registered on clinical trials.gov with an anti-CD47 antibody against solid tumors, but it has recently been withdrawn due to lack of funding.
Increased expression of CD47 on many cancer types and CD47's role as a "don't eat me" signal suggest that targeting CD47 can be a viable cancer immunotherapy. Antibodies and fusion peptides against CD47 have demonstrated preclinical activity against many different human cancers (AML, ALL, NHL, MM, bladder cancer, and breast cancer) both in vitro and in mouse models. This strong scientific rationale has prompted the development of multiple anti-CD47 compounds. Some are likely to enter the clinic over the next few years, with the Stanford group being the first. However, clinical drug development programs take many years to complete, and investors do not yet know which compound will become the most successful. Interest from multiple companies provides some level of validation to the CD47 target for cancer treatment.
SIRPαFc Fusion Protein (anti-CD47)
Unlike the antibody approach that many others have taken, Trillium Therapeutics is using a fusion protein called SIRPαFc (formerly TTI-621) to block CD47. SIRPαFc combines a fragment of the SIRPα, which is naturally CD47's ligand (target), with a region of the human antibody, the Fc region. Not only does SIRPαFc bind to CD47 (diminishing the "do not eat" signal), the Fc portion further enhances anti-leukemic activity by engaging the immune system (antibody-dependent cellular cytotoxicity and complement activation-ADCC).
While Trillium Therapeutics is developing SIRPαFc for AML, it has broad anti-cancer potential. Studies have shown that AML cells over-expresses CD47 and deactivate macrophages that would phagocytose (kill) AML cells. CD47 on the surface of AML binds SIRPα on the surface of macrophages' and prevents phagocytosis. Thus, the strategy is to block AML's CD47 so that the macrophage will kill the cancer cells (no CD47-SIRPα binding). This idea is supported by data in the clinic: patients' expression level of CD47 is correlated with overall survival of many cancers - higher CD47 signal (more "do not eat" signal) correlated with worse prognosis for the patient.
Trillium Therapeutics AACR poster "Cancer Immunotherapy Targeting CD47: Wild Type SIRPαFc is the Ideal CD47-Blocking Agent to Minimize Unwanted Erythrocyte Binding"
In a co-culture of AML cells with macrophages, treatment with SIRPαFc significantly enhances phagocytosis (eating and killing) of AML cells.
SIRPαFc enhances macrophage-mediated phagocytosis of AML cells. Macrophages are shown in red and AML cells are shown in green. Trillium Therapeutics Corp. 26th Annual ROTH Conference, March 9-12, 2014.
That normal cells also express CD47 motivates two concerns for using SIRPαFc as a treatment to a whole organism. First, does SIRPαFc cause macrophage-mediated phagocytosis of normal cells? Second, could CD47 expression on normal cells act as an "antigen sink" that bind to SIRPαFc and sequester it away from CD47 on the cancer cells?
Demonstrating that SIRPαFc does not promote killing of normal cells was shown using a co-culture of normal cells with macrophages where SIRPαFc did not show phagocytosis, while that of co-culture with AML showed greater than a 200-fold effect. Thus, Trillium concluded that SIRPαFc discriminately promotes phagocytosis (death) of AML. This was explained by an extra pro-phagocytic signal on the surface on a cancer cell: AML's calreticulin engages the macrophage receptor, LRP. In fact, chemotherapy can cause the tumor to expose calreticulin, giving justification to explore potential combination therapy using chemotherapy and SIRPαFc for complementary and synergistic effects in the future.
SIRPαFc enhances macrophage-mediated phagocytosis of AML cells, but not normal cells. Macrophages are shown in red and AML cells or normal cells are shown in green. Trillium Therapeutics Corp. 26th Annual ROTH Conference, March 9-12, 2014.
A murine proof-of-concept study has demonstrated that the in vitro "petri dish" results apply to a living organism (in vivo). Mice were engrafted with AML cells and treated with SIRPαFc, resulting in a lower level of AML at all sites - at the bone marrow site of the injection, at a different bone marrow site, and at the spleen. Furthermore, antigen sink concerns does not appear to be an issue - even with a mouse version of SIRPαFc that can bind to both normal mouse CD47 and AML's CD47, SIRPαFc still exhibits anti-leukemic activity.
In immunodeficient mouse models of human AML, anti-CD47 treatment with SIRPαFc or an anti-CD47 antibody reduces AML cell number. Percent human AML cancer cells on the y-axis with negative control IgG antibody and anti-CD47 treatment on the x-axis. RF, right femur, BM, bone marrow, SP, spleen.
An Enhanced Effect with a Complete Immune System?
The AML immunodeficient mouse model (no T-, B-, or NK cells) is useful here to aid in the establishment of human AML cells. But, anti-cancer responses might be enhanced with the full immune cell repertoire. The Weissman group published that CD47 blocking macrophage-mediated phagocytosis led to an increase in activated CD8+ T cells (cytotoxic T cells), which also have anti-cancer effector functions. Additionally, CD4+ T regulatory cells, known to dampen the immune response, showed decreased activation. Therefore, when given to AML patients, SIRPαFc could have even greater efficacy than what has been observed in immunodeficient mouse models, due to activation of cytotoxic T cells and inactivation of T regulatory cells.
With strong preclinical efficacy, Trillium moved forward with the development of SIRPαFc. Although CD47 is overexpressed on cancer cells (see figure below from Irv Weissman's lab), safety is a concern, since CD47 is also expressed on healthy cells. Safe levels of anti-CD47 peptides were established in monkeys, and were significantly higher than the predicted efficacious dose. Primary adverse events were anemia and thrombocytopenia, but these are reversible and may not be recapitulated in humans for reasons described below. While SIRPαFc is likely to also bind CD47 on healthy cells, as well as cancer cells, if cancer cells express more CD47, hopefully there will be chance for a therapeutic window where SIRPαFc therapy leads to more cancer cell killing than healthy cell killing.
CD47 is highly expressed on patient solid cancer cells than normal cells.
Human red blood cells (RBCs) also express CD47, making CD47-targeting a potential cause of hematological toxicity, anemia, a loss of RBCs. Remarkably, while commercially available and property anti-CD47 antibodies have high binding affinity for RBCs, SIRPαFc appears to have a lower RBC binding affinity, which may prevent anemia.
SIRPαFc binds with high binding affinity to AML and other CD47+ cells, but not to RBCs, unlike multiple anti-CD47 antibodies. Binding affinity in Fl units on the y-axis, anti-CD47 antibodies in blue, SIRPαFc in red, negative control Fc in black. Trillium Therapeutics AACR poster "Cancer Immunotherapy Targeting CD47: Wild Type SIRPαFc is the Ideal CD47-Blocking Agent to Minimize Unwanted Erythrocyte Binding".
Stronger isn't always better, Christopher Garcia's lab at Stanford University engineered a high-affinity (50,000-fold) SIRPα variant, but this high-affinity variant also bound RBCs and caused chronic anemia in mouse models. A single dose in cynomolgus macaques also led to a significant drop in RBCs, although slow dose escalation did not. SIRPαFc does not bind human RBCs with high affinity, but it does appear to bind RBCs of cynomolgus macaque and mice, meaning both these model systems may not accurately recapitulate RBC binding and anemia in humans. SIRPαFc appears to be the ideal CD47 blocking agent with targeted effects that spare healthy RBCs.
Potential for Anti-Cancer Synergy
SIRPαFc is being developed as a monotherapy and as a combination therapy. In non-Hodgkin's lymphoma, combination therapy of rituximab and anti-CD47 antibody synergizes to promote phagocytosis and eradicate lymphoma. In addition, previous work reported that combination therapy of CD47-blockade and chemotherapy (ara-c or Cytarabine) could effectively eliminate AML. There may be potential for SIRPαFc to become part of the current standard of care to enhance the therapeutic benefit of chemotherapy.
Potential synergy with SIRPαFc and other anti-cancer antibodies as described in "Engineered SIRPα Variants as Immunotherapeutic Adjuvants to Anticancer Antibodies".
Background on Acute myelogenous Leukemia (AML)
AML is a cancer of myeloid white blood cells that fill the bone marrow, and interferes with normal white blood cell production. In 2013 in the US, there were 18,860 adults diagnosed with AML and 10,460 deaths. The current standard of care begins with an induction chemotherapy, anthracycline and cytarabine. As high as 60%-80% of adult patients <60 yrs. of age will attain a complete remission (NYSE:CR). However, without additional cytotoxic therapy, virtually all of these patients will relapse within a median time of 4-8 months. Even patients who receive post-remission therapy, such as high-dose chemotherapy (cytarabine), bone marrow transplant, or other measures, may expect four-year survival rates of around 40%. These treatment options clearly highlight the unmet medical need in AML.
SIRPαFc Development Timeline. Trillium Therapeutics Corp. 26th Annual ROTH Conference, March 9-12, 2014.
In addition to SIRPαFc, Trillium Therapeutics has 3 other drugs in early stages of its pipeline, although we see very little value in these programs.
Trillium Therapeutics Pipeline. Trillium Therapeutics Corp. 26th Annual ROTH Conference, March 9-12, 2014.
SIRPαFc has Broad Clinical Potential. Bloom Burton & Co. Healthcare Investor Conference June 18, 2014.
Tigecycline (acute myeloid leukemia)
Tigecycline is an antibiotic used in hospitals to treat a variety of serious infections. Repurposing of this small molecule has shown strong activity in AML by targeting leukemia cells by inhibiting mitochondrial protein synthesis and thus shutting down the cells' energy supply. Dosing for AML greatly exceeds the amount approved for anti-infective use, and is well within the range of doses that have demonstrated anti-cancer activity in published preclinical studies. Tigecycline reduces leukemia in preclinical models, but does not affect normal hematopoiesis. Tigecycline synergizes with AML chemotherapies such as danorubicin, and preferentially accumulates in bone marrow, where liquid tumors arise. In October of 2013, Trillium Therapeutics was granted orphan drug designation by the US FDA for the use of tigecycline in the treatment of AML. Trillium Therapeutics is licensing Tigecycline from the University Health Network (NYSEARCA:UHN) located in Toronto, Canada, for common shares and common shares purchase warrants. Trillium Therapeutics is nearing completion of the multi-center Phase I clinical trial in patients with relapsed or refractory AML. The cost of the study is covered by the UHN. Although the trial was expected to complete in mid-2013, a protocol amendment delayed patient enrollment, and completion is now expected in 2014. The goal of the study is to determine the MTD dose for Phase 2 studies.
TTI-1612 (interstitial cystitis)
TTI-1612 is a recombinant soluble form of heparin-binding epidermal growth factor-like growth factor (HB-EGF). It is being developed as a treatment for interstitial cystitis (IC), a chronic bladder disease characterized by low urinary HB-EGF levels and a dysfunctional, "leaky" bladder epithelium. TTI-1612 is designed to target the root cause of IC-dysfunction of the bladder urothelium by remedying the low levels of HB-EGF, and stimulating proliferation of bladder epithelial cells and reducing their permeability. The current competition in IC includes drugs in various trials that are largely palliative, such as pain-killers, and are unlikely to alter the IC treatment landscape. This program was developed by Trillium Therapeutics and was obtained by Stem Cell Therapeutics during the merger. In May 2013, the Phase I study of TTI-1612 in patients with interstitial cystitis/bladder pain syndrome (IC/BPS) was completed through Trillium. The data from the trial indicate that the drug has good safety and pharmacokinetic profiles. TTI-1612 has orphan designation in the US and Europe for the prevention of necrotizing enterocolitis (NEC). Trillium Therapeutics is seeking a development partner to move this program forward into Phase 2 testing.
CD200 mAb (cancer)
CD200 mAb is a human monoclonal antibody against CD200. CD200 is an immunosuppressive molecule expressed by many hematological and solid tumours. Disruption in the CD200-CD200R pathway leads to enhanced immune activity in animal models of cancer and autoimmunity. This mechanism of action is similar to SIRPαFc, because it eliminates the suppressive properties of CD200 that shield cancer cells from the immune system. The development of CD200 is halted due to limited resources.
Trillium Therapeutics currently has a market cap of $43M, with $32M in cash. Most of the capital came from a $33M private placement raise in December of 2013 from prominent US healthcare funds. These funds include an impressive group, Special Situations Funds, Ridgeback Capital, Merlin Nexus, Sabby Capital, venBio, Opaleye Management, and HSMR Advisors. The cash provided much-needed capital to fund development of SIRPαFc through IND-enabling studies, manufacturing, and Phase 1 clinical trials. Trillium Therapeutics' operating costs and expenses totaled $4.3M in 2013, although spending (burn rate) is expecting to increase as the SIRPαFc program advances. Trillium's cash is expected to last for 36-42 months, through completion of Phase 1 trials of SIRPαFc.
The $33M private placement from December 2013 provides enough cash to fund the company for approximately 3 years and fund SIRPαFc through Phase 1 trials. So in ~2017, Trillium is expected to raise cash again to fund operations, as is common in early-stage life sciences companies.
SIRPαFc is very early in development, and although preclinical efficacy and safety look promising, it could fail at any stage of clinical development. The average time from IND to FDA approval for an oncology biologic is ~7 years, so revenue from SIRPαFc isn't expected until ~2022.
Oncology biologics with similar mechanisms of action are familiar to regulatory agencies. So, the regulatory pathway for SIRPαFc should be clear.
Small life sciences companies often do not have the experience and capital to successfully commercialize their products. Therefore, we expect Trillium to partner SIRPαFc once it is further along in development to maximize the commercial opportunity.
- 2014 Q2 Tigecycline reformulation status/initiate NCE program
- 2014 Q3 SIRPαFc Pre-IND meeting with the FDA
- 2014 Q3 SIRPαFc CMC engineering run
- 2014 TTI-1612 Publish Phase I clinical results
- 2014 TTI-1612 Looking to out-license
- 2014 Tigecycline Phase 1 data
- 2015 Q1 SIRPαFc GLP toxicology studies
- 2015-mid SIRPαFc IND filing
Trillium Therapeutics is an early-stage cancer immunotherapy company with the promising anti-CD47 fusion peptide, SIRPαFc. CD47 has been validated in multiple preclinical models as an attractive anti-cancer target. Preclinical models validate SIRPαFc-CD47 binding affinity and macrophage-mediated AML cancer cell clearance. SIRPαFc could offer a superior safety profile, specifically anemia, compared to anti-CD47 antibody approaches by Stanford University and others. Trillium Therapeutics recently received a major cash infusion from prominent US healthcare funds, which allowed it to advance the SIRPαFc through Phase 1 clinical trials. An IND in AML for SIRPαFc is expected in mid-2015, but SIRPαFc has broad anti-cancer potential as a monotherapy and in combination with other cancer therapy. Trillium Therapeutics is trading near cash, so long term-oriented investors who understand the risks involved with SIRPαFc might see value in this overlooked, microcap Canadian cancer immunotherapy company.
Disclosure: The author is long SCTPF. The author wrote this article themselves, and it expresses their own opinions. The author is not receiving compensation for it (other than from Seeking Alpha). The author has no business relationship with any company whose stock is mentioned in this article.
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