Aims. We study the formation and evolution of a failed filament eruption observed in NOAA active region 11121 near the southeast limb on November 6, 2010. Methods. We used a time series of SDO/AIA 304, 171, 131, 193, 335, and 94 Å images, SDO/HMI magnetograms, as well as ROSA and ISOON Hα images to study the erupting active region. Results. We identify coronal loop arcades associated with a quadrupolar magnetic configuration, and show that the expansion and cancellation of the central loop arcade system over the filament is followed by the eruption of the filament. The erupting filament reveals a clear helical twist and develops the same sign of writhe in the form of inverse γ-shape. Conclusions. The observations support the "magnetic breakout" process in which the eruption is triggered by quadrupolar reconnection in the corona. We propose that the formation mechanism of the inverse γ-shape flux rope is the magnetohydrodynamic helical kink instability. The eruption has failed because of the large-scale, closed, overlying magnetic loop arcade that encloses the active region. © 2013 ESO.