"以贬抑的口吻" can be translated into English as "in a derogatory tone" or "with a condescending/disparaging manner".
"Derogatory tone" emphasizes the belittling or disrespectful nature of the speech.
"Condescending manner" conveys a sense of superiority or looking down upon others.
"Disparaging manner" highlights the act of speaking in a way that belittles or criticizes.
Choose the phrase that best fits the context of your sentence. For example:
"He spoke in a derogatory tone about his colleague."
"She responded with a condescending manner."