Castellanos has left for West Ham, while Fenerbahce are closing the signing of Guendouzi today.
The decision to sell Guendouzi, particularly, was criticised by coach Maurizio Sarri after last night's 2-2 draw with Fiorentina.
Lotito later responded, stating: "My longevity is dictated by experience; I am the longest-serving president in the history of Italian football. Experience tells me that players who don't want to stay shouldn't be held back.
"Castellano wanted to leave, as did Guendouzi, so we let them go, and they were absolutely correct in their behaviour. They were attracted by other technical projects and other financial offers, but this doesn't mean the players are being sold off.
"The club has been selecting players for as long as anyone can remember. Sarri isn't a scout, and I think he'll be satisfied in the end.
"Both Castellanos and Guendouzi are two good guys, serious and honest. I have a team to safeguard; the team is giving everything, and I can't humiliate them by changing everyone."