INT131 targets inflammation and activates neuroprotective pathways
Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of highly conserved family of transcription factors that are expressed over a wide range of tissues. The specificity of PPARγ -mediated gene transcription is dependent upon transcriptional cofactors and ligands that direct PPARγ activity. INT131 is a highly selective PPARγ agonist that activates a very restricted subset of PPARγ -dependent activities in a small number of tissues, including anti-inflammatory and anti-oxidative stress pathways, as well as neuroprotective activities. This limited activation is a major advancement in the evolution of PPARγ activating drugs, which include the older diabetes drugs Actos® and Avandia®. These earlier compounds are non-selective and thus they activate a wide range of PPARγ -mediated pathways, including pathways beneficial in controlling blood sugar levels, as well as other, undesirable, off-target effects that include edema and fat accumulation. These off-target effects have led to FDA-mandated black box warnings for these compounds.
INT131 is the result of rational drug design
Understanding the structure function relationship of INT131 bound to its cognate receptor PPARγ was the result of a concerted effort to generate a drug that activated only selected PPARγ-regulated pathways without activating the edemagenic and lipogenic cascades that are stimulated by the thiazolidinedione (TDZ or glitazone) drugs Actos® and Avandia®. In specific, INT131 was selected from approximately 100 co-crystals of drug candidates and the PPARγ binding pocket. These co-crystals were evaluated for binding within the drug binding pocket without binding PPARγ helix-12. The glitazones binding to PPARγ helix-12 results in the fluid retention and fat accumulation that has been widely described for the TDZ drugs (figure 1). Extensive preclinical testing and clinical trials have confirmed the positive effects of INT131 with none of the edema-inducing or weight gain that is associated with the glitazone drugs.
Figure 1. INT131 (purple) binds in the PPARγ drug-binding pocket without contacting helix-12. In contrast, Rosiglitazone (gray) binds in the same pocket, but in doing so, it contacts helix-12, thereby activating edemagenic and lipogenic pathways.
SPPARM Rationale (Selective PPAR-γ Modulation)
Full PPAR-γ agonists activate changes in expression across a large number of genes, including those that are responsible for desirable efficacy, such as anti-inflammatory and antioxidative cascades, and other, undesirable side effects, such as congestive heart failure and weight gain. Not surprisingly, the greater the extent of agonist-mediated gene activation correlates with an increasing array of undesirable side effects, resulting in a poor clinical profile for these compounds.
Figure 2. INT131 is a selective pparg agonist that activates a restricted set of pathways without causing the unwanted side effects seen with the full pparg or mixed agonists.
The strategy used in the design of INT-131 was to develop a selective, high affinity PPAR-γ agonist that would activate a limited number of the PPAR-γ-modulated genes activities without activating helix-12 mediated gene expression. Such a molecule would retain the positive results of PPAR-γ activation while eliminating the unwanted side effects (figure 2).
There is a strong precedent for the success of this modulator approach for another nuclear receptor: both tamoxifen and its successor raloxifene are selective estrogen receptor modulators (SERMs) that are designed to optimize the therapeutic actions of estrogen receptor activation while minimizing side effects. As a genuine SPPARM, INT-131 acts in a context dependent manner (depending on the tissue and the environment) to alter expression of a subset of PPAR-γ genes, and is thereby able to separate therapeutic benefits from unwanted side effects. INT-131 is not structurally related to the TZD class and thus represents a new chemical class of PPAR-γ ligands.
INT131 is a high potency selective PPAR-γ modulator.
INT-131 binds to PPAR-γ with a potency of ~10 nM, which makes it >20-fold more potent than either rosiglitazone or pioglitazone. Characterization of binding beyond potency reveals the efficacy of INT-131 for inducing PPAR-γ receptor activities. In cell-based reporter assays designed to detect full agonist activity, INT-131 activates PPAR-γ with a maximal activity of only 5-10% of that of rosiglitazone (Figure 1, left). Similarly, in fluorescence resonance energy transfer assays, INT-131 causes recruitment of selected coactivators with a maximal activity of about 10% of that of rosiglitazone (Figure 3, below).
Figure 3. INT-131 is a potent selective PPAR-γ modulator. Left panel. Cell-based reporter assays were performed with increasing concentrations of INT-131 (green line) and rosiglitazone (black line). Right panel. Fluorescence resonance energy transfer (FRET) assays were performed with PPAR-γ and a fragment of the co-activator DRIP205 in the presence of increasing concentrations of INT-131 (blue line) and rosiglitazone (black line).
INT131 does not promote adipocyte differentiation in-vitro:
Consistent with its high potency/low activity profile in the full agonist cell-based reporter and FRET assays, INT131 causes virtually no adipocyte differentiation or triglyceride accumulation in human and mouse pre-adipocytes in vitro (Figure 4). Moreover, INT131 blocks most of the potent effects of rosiglitazone to promote fat cell differentiation. Thus, INT131 has the desired, non-adipogenic profile.
Figure 4. INT131 does not promote adipocyte differentiation. Human (left panel) or mouse (not shown) preadipocyte cells were treated with INT131 or rosiglitazone and lipid accumulation was measured. The cartoon at the right shows that INT131 blocks pre-adipocyte/adipocyte differentiation of mesenchymal stem/progenitor cells, while allowing osteoblast differentiation to proceed.
Demonstrated safety in preclinical and clinical settings
The data shown above are highly suggestive that INT131 is a safe drug. This prediction has been confirmed in both preclinical and clinical studies.
It is well established that the fluid retention seen in animal models is predictive of this side effect in humans. The subsequent cardiac effects of TDZ treatment seen in animal models are also thought to translate to humans. Preclinical models with the TDZ drugs resulted in plasma volume expansion, as manifested by a decrease in hematocrit, within the first months of TZD treatment in both animal models and human patients. Consistent with this are the secondary increases in heart size and heart weight observed in animals. Longer exposures are marked by cardiac hypertrophy and sometimes death in a dose- and time-dependent fashion. In contrast, treatment with INT131 resulted in neither edema, nor changes in heart size in animals, including nonhuman primates as well as in over 400 individuals treated with INT131 to date. In fact, there were no drug-induced serious adverse events seen in the seven (7) clinical trials of INT131 that have occurred to date.
By all measures, INT131 is an exceptionally safe and efficacious drug. This safety is almost certainly the result of the careful drug design that was instituted at the outset of INT131 development, and the thoughtful and extensive testing that has occurred to date.