Barts-MS rose-tinted-odometer: ★★ (mid-week sepia = #704214)
In my post on rebound disease activity in a person with secondary progressive MS switching from fingolimod to siponimod, someone asked whether there is any logic in switching DMTs within the class of S1P modulators. Two or three years ago I would have said no, but now I would say yes. There are well defined and clear differences between the two compounds that may explain their different effects as DMTs in people with more advanced or progressive MS (see figure and table below).
The fact that fingolimod works on a broader spectrum of S1P receptors may explain why it has a greater effect on peripheral immune function, i.e. its action on S1P4 may explain why it disrupts antibody responses to new vaccines. S1P4 plays an important role in the functioning of germinal centres (GCs) in lymph nodes and other secondary lymphoid organs, i.e. so-called follicular T-helper cells use S1P4 for migration signals. If these cells can’t enter the GCs they can’t help B-cells make good antibody responses. I, therefore, predict that vaccine responses in response to the COVID-19 vaccines will be better preserved with siponimod, ozanimod and ponesimod because this new generation of S1P modulators has less or no activity on S1P4 receptors.
Fingolimod needs to be phosphorylated to become active, in comparison siponimod is active already. This may explain why siponimod has greater activity on the S1P5 receptor within the central nervous system (CNS) and explains its greater apparent effects on cells within the central nervous system (CNS). It is clear that when you look at the results of the fingolimod in the PPMS trial there was very little evidence that fingolimod was having any effect on the end-organ, i.e. there was no impact on brain volume loss and no difference across any of the clinical endpoints in the PPMS trial. In comparison, siponimod has a clear CNS signal compared to placebo in subjects with SPMS. Compared to placebo, patients on siponimod have less whole brain, grey matter and thalamic volume loss, preservation of brain tissue integrity on MTR, an MRI marker of myelination, and these effects correlated with better preservation of cognition. On the downside, siponimod was associated with a small but significant risk of seizures, which seems to be more common than with fingolimod in adults with MS.
I have interpreted these results as showing fingolimod as being a more powerful peripheral immunosuppressive therapy but has fewer direct CNS effects. In comparison, siponimod is likely to be less immunosuppressive, but have more direct CNS effects. So based on these differences I think there is a rationale for switching someone on fingolimod to siponimod who has more advanced MS or has transitioned to SPMS. The downside of this switch is that in the NHS you will have to label someone as having SPMS to be able to prescribe siponimod. Using our current criteria SPMS is a one-way street, i.e. once you are labelled as having SPMS you can’t be undiagnosed and converted back to RRMS. As there are no other DMTs currently licensed for SPMS you are therefore theoretically stuck with siponimod. This is why I refer to siponimod as the cul de sac DMT.
The other issue is that to be eligible for siponimod you have to have active SPMS, i.e. relapses or MRI activity (new or enlarging lesions) in the last 2 years. Most people who develop SPMS on fingolimod have inactive SPMS, which means they are not eligible for siponimod. To become eligible under NHS England guidelines you would have to stop fingolimod and hope you develop rebound disease activity that will then allow you to be eligible for siponimod. I have previously stated that I think this is unethical based on our current biological understanding of MS. In any case, once you label someone as having SPMS on fingolimod you are meant to stop their fingolimod in the NHS; the latter is one of the NHS England’s stopping criteria.
So based on the above if you have transitioned to SPMS on fingolimod would you (1) want to switch to siponimod and (2) would you be prepared to stop fingolimod so that your SPMS became active, i.e. developed rebound disease activity?
|MOA: Targets S1P1, S1P3, S1P4 & S1P5||MOA: Targets S1P1 & S1P5|
|No baseline pharmacogenomics||Baseline pharmacogenomics (CYP2C9 genotyping)CYP2C9 Genotypes *1/*1, *1/*2, or *2/*2 = 2 mg/dayCYP2C9 Genotypes *1/*3 or *2/*3 = 1 mg /dayModerate CYP2C9 and strong CYP3A4 inducers are not recommended (e.g. rifampin, carbamazepine)|
|First dose monitoring for all patients||First dose monitoring in patients with certain pre-existing cardiac conditions|
|Half life of 6-9 days||Half life of approximately 30 hours|
|Lymphocyte counts progressively return to normal range within 1-2 months of stopping therapy in most patients||Lymphocyte counts return to the normal range within 10 days of stopping therapy in the vast majority (90%) of patients|
|Prodrug – needs to phosphorylated||Active compound no need for activation|
General Disclaimer: Please note that the opinions expressed here are those of Professor Giovannoni and do not necessarily reflect the positions of the Barts and The London School of Medicine and Dentistry nor Barts Health NHS Trust.