How PS is a validated target despite bavi being the only drug in clinical development:
As recently mentioned with the Stimuvax cancer vaccine (NSCLC) failure, a clear mechanism of action is important when investing in risky biotech companies (Martin Shkreil, Seeking Alpha). I have to agree to some extent (although there are examples of anticancer drugs or other drugs that have unclear or unknown mechanisms that have been approved by the FDA). Nevertheless, I have spent a significant amount of time researching phosphatidylserine, the apoptotic pathway, and the tumor microenvironment. Just to add context on my background: I have a BS in Biology (minor chemistry) and a Doctorate in Pharmacy.
Before I go to the reason it is validated, let me just review our understanding of tumor-associated macrophages:
As discussed on this board before, macrophages (which comprise up to 50% of solid tumors such as those found in NSCLC) are controlled by cancer cells to produce immunosuppressive cytokines (chemical signals) such as IL-10, IL-6, PGE-2 and vascular growth factors (VEGF, endothelin-2, EMAD-11) important for new blood vessel growth and metastasis of tumor.
These cancer-supporting macrophages are referred to as tumor associated macrophages (TAMs) and exist primarily in the 'M2' state, which means they are producing immunosuppresive cytokines.
Because of this immune suppressive tumor microenvironment, it has been previously thought that inflammation in cancer is correlated with reduced survival. However, recent evidence indicates that tumor associated macrophages are 'plastic' and can be switched to a 'M1' state, where they will secrete inflammatory cytokines (e.g. IL-12, TNF-alpha, nitric oxide). Studies have shown that tumors with their TAM balance shifted to the M1 inflammatory state have increased patient survival (including NSCLC)
Now, the reason why PS is a validated target is two-fold: its role in the apoptotic pathway is well documented/understood and the cytokines impacted by blocking PS (whether increased or decreased) have established roles in shaping the tumor microenvironment, including shifting TAM state from M2 to M1. Additionally, there are other drugs in approved or in development that influence this M2 to M1 pathway at different targets. The best example is the already approved bortezomib (Velcade) for multiple myeloma. Bortezomib has NF-KB inhibitory effects, which is believed to help reprogram TAMs to M1 state (as well as inhibit degradation of pro-apoptotic pathways). Another example is STAT3, which is a transcription factor that when activated leads to production of immunosuppresive cytokines IL-6 and MFG-E8 that help support a M2 environment. Otsuka has a STAT3 that just completed Ph I in solid tumors.
These are just two examples of attacking the immunosuppressive microenvironment. Other targets include IL 10, CCL2, and Toll receptors. Pharma is just now realizing the potential of shifting the type and function of immune cells by way of influencing what cytokines are secreted. Macrophages, dendritic cells, T cells, and NK cells have all been indicated to be able to change role and function in cancer based on what cytokines are present. PS is one target, but it is a good one as it is found in multiple cell types and is consistently immunosuppressive in the microenvironment.
I don't see why bavi could not be active in multiple tumor types, starting with NSCLC. Looking forward to 2013 OS results.
