132 Intermittent dosing of the MEK inhibitor, GDC-0973, and the PI3K inhibitor, GDC-0941, results in prolonged accumulation of Bim and causes strong tumor growth inhibition in vivo

The biology and clinical development of MEK inhibitors for cancer

The mitogen-activated protein kinase kinases (MAPKK) MEK1 and MEK2 are integral members of the MAPK/ERK signaling pathway and are of interest in the development of anti-cancer therapeutics. The MAPK/ERK pathway is dysregulated in more than 30 % of cancers, predominately by mutations in RAS and BRAF proteins, and MEK serves as a potential downstream target for both of these. The biology of MEK inhibition is complex, as the molecule is differentially regulated by upstream RAS or RAF. This has impacted on the past development of MEK inhibitors as treatments for cancer and may be exploited in more rational, molecularly selected drug development plans in the future. The role of MEK in cancer and the mechanism of action of MEK inhibitors is reviewed. Furthermore, MEK inhibitors that are available in standard practice, as well as those most advanced in clinical development, are discussed. Finally, next steps in the development of MEK inhibitors are considered.

PK-PD modeling of combination efficacy effect from administration of the MEK inhibitor GDC-0973 and PI3K inhibitor GDC-0941 in A2058 xenografts

PURPOSE

Mutations and activations of the MEK and PI3K pathways are associated with the development of many cancers. GDC-0973 and GDC-0941 are inhibitors of MEK and PI3K, respectively, currently being evaluated clinically in combination as anti-cancer treatment. The objective of these studies was to characterize the relationship between the plasma concentrations of GDC-0973 and GDC-0941 administered in combination and efficacy in A2058 melanoma xenograft.

METHODS

GDC-0973 and GDC-0941 were administered to A2058 tumor-bearing mice daily (QD) or every third day (Q3D) either as single agents or in combination. A semi-mechanistic population anti-cancer model was developed to simultaneously describe the tumor growth following QD/Q3D single-agent and QD combination treatments. The interaction terms ψ included in the model were used to assess whether the combination was additive. Using this model, data from the Q3D combination regimen were simulated and compared with the observed tumor volumes.

RESULTS

The model consisting of saturable tumor growth provided the best fit of the data. The estimates for ψ were not significantly different from 1, suggesting an additive effect of GDC-0973 and GDC-0941 on tumor growth inhibition. The population rate constants associated with tumor growth inhibition for GDC-0973 and GDC-0941 were 0.00102 and 0000651 μM(-1) h(-1), respectively. Using the model based on single-agent and QD combination efficacy data, simulations adequately described the tumor growth from the Q3D combination regimen.

CONCLUSIONS

These findings suggest that, based on minimal data, it is possible to predict the effects of various combinations preclinically and also assess the potential clinical efficacy of combinations using human pharmacokinetic inputs.

Preclinical disposition of GDC-0973 and prospective and retrospective analysis of human dose and efficacy predictions

[3,4-Difluoro-2-(2-fluoro-4-iodo-phenylamino)-phenyl]-((S)-3-hydroxy-3-piperidin-2-yl-azetidin-1-yl)-methanone (GDC-0973) is a potent and highly selective inhibitor of mitogen-activated protein kinase(MAPK)/extracellular signal-regulated kinase (ERK) 1/2 (MEK1/2), a MAPK kinase that activates ERK1/2. The objectives of these studies were to characterize the disposition of GDC-0973 in preclinical species and to determine the relationship of GDC-0973 plasma concentrations to efficacy in Colo205 mouse xenograft models. The clearance (CL) of GDC-0973 was moderate in mouse (33.5 ml · min(-1) · kg(-1)), rat (37.9 ± 7.2 ml · min(-1) · kg(-1)), and monkey (29.6 ± 8.5 ml · min(-1) · kg(-1)). CL in dog was low (5.5 ± 0.3 ml · min(-1) · kg(-1)). The volume of distribution across species was large, 6-fold to 15-fold body water; half-lives ranged from 4 to 13 h. Protein binding in mouse, rat, dog, monkey, and human was high, with percentage unbound, 1 to 6%. GDC-0973-related radioactivity was rapidly and extensively distributed to tissues; however, low concentrations were observed in the brain. In rats and dogs, [(14)C]GDC-0973 was well absorbed (fraction absorbed, 70-80%). The majority of [(14)C]GDC-0973-related radioactivity was recovered in the bile of rat (74-81%) and dog (65%). The CL and volume of distribution of GDC-0973 in human, predicted by allometry, was 2.9 ml · min(-1) · kg(-1) and 9.9 l/kg, respectively. The predicted half-life was 39 h. To characterize the relationship between plasma concentration of GDC-0973 and tumor growth inhibition, pharmacokinetic-pharmacodynamic modeling was applied using an indirect response model. The KC(50) value for tumor growth inhibition in Colo205 xenografts was estimated to be 0.389 μM, and the predicted clinical efficacious dose was ∼10 mg. Taken together, these data are useful in assessing the disposition of GDC-0973, and where available, comparisons with human data were made.