To cite SPIA package in publications use:

  Adi L. Tarca, Sorin Draghici, Purvesh Khatri, Sonia S Hassan, Pooja
  Mittal, Jung-sun Kim, Chong Jai Kim, Juan Pedro Kusanovic, Roberto
  Romero, A novel signaling pathway impact analysis,
  Bioinformatics,25(1), 2008.

A BibTeX entry for LaTeX users is

  @Article{,
    author = {Adi L. Tarca and Sorin Draghici and Purvesh Khatri and Sonia S Hassan and Pooja Mittal and Jung-sun Kim and Chong Jai Kim and Juan Pedro Kusanovic and Roberto Romero},
    title = {A novel signaling pathway impact analysis},
    journal = {Bioinformatics},
    year = {2008},
    volume = {25},
    number = {1},
  }