Drenaje Profundo (2010)

After an accident in the Mexico City subway system, detective Ulises Elizalde (Juan Pablo Medina) is sent to investigate. Ulises follows after a suspicious man who knocks him out and dumps him into the city's sewer. He is rescued by Yamel (Ana Serradilla), a young woman who's hiding an enormous secret. Yamel and other people living in the sewers have been injected with an eternal-youth serum that was developed by a scientist named Igor, under the orders of multimillionaire Milosz, a notorious doctor from the late sixties who owns a large pharmaceutical company and hides his corrupt experiments deep beneath the city.