Five Prime (FPRX) recently held a quarterly conference call and, importantly, all of the company's timelines remain on track; it has developed a broad pipeline with five drug candidates now in human clinical development, observes John McCamant, biotech expert and editor of The Medical Technology Stock Letter.
Five Prime spent some time on the call discussing an intriguing early stage asset, FPT155, that has in our view, significant potential.
FPT155 is not an antibody, but a CD80-Fc fusion protein. CD80 is a co-stimulatory ligand of CD28, which is the dominant co-stimulatory pathway by which T-cells are activated.
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FPT155 is a first-in-class CD80-Fc fusion protein that is expected to potently enhance anti-tumor immunity as a monotherapy. The drug candidate was discovered using an in vivo screen of approximately 800 immune-associated, secreted and extracellular domain proteins from FPRX’ immunome library.
The proteins are screened individually in tumor-bearing mice to identify those that inhibit tumor growth by immune-dependent mechanisms. This program is now in a Phase Ia dose escalation trial in solid tumors.
FPT155 is a fusion protein created to optimize its pharmacologic and PK properties.
This drug candidate does two things. First, it’s the natural binding partner for CD28, the key co-stimulatory receptor needed in addition to the T-cell receptor for effective activation of T-cells.
Importantly, we don’t see super agonism with its accompanying cytokine release that we’ve seen with the CD28 targeted antibody. This is because FPT155 requires co-engagement of the T-cell antigen receptor in addition to CD28 binding for its activity.
Secondly, FPT155 blocks CTLA-4 from competing for endogenous CD80, allowing CD28 signaling to prevail in T-cell activation. FPT155 behaves differently than CTLA-4 antibodies, such as ipilimumab and tremelimumab, because it directly interacts with CD28.
In contrast with CTLA- 4 antibodies, FPT155 is not dependent on endogenous expression of CD28 ligands for its activity. FPT155 can co-stimulate T-cells in the tumor micro environment where the CD28 ligands are often limiting.
In preclinical models, FPT155 has demonstrated strong single-agent activity across a wide range of syngeneic tumor models, including the B16F10 model, which is notoriously refractory to immunotherapies that include single-agent anti-CTLA-4 or anti-PD-1.
FPRX believes this is a very different drug compared to anti-CTLA-4s and could represent an important addition to I/O treatment options. We will have to wait until November’s SITC meeting for the first FPT155 data. At that meeting we expect to see Phase Ia solid tumor POC data.
In our view, positive POC data for FPT155 would serve as a significant stock catalyst. Before FPT155 data, we expect two additional catalysts with FPA150 Phase Ia data anticipated at ASCO in June.
The second catalyst will be Phase Ia/Ib data at ESMO in September. From a big picture perspective, we are impressed with Five Prime's ability to build a pipeline which is positioned for multiple potential catalysts in 2019.
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