Get other properties attributes while validating a custom attribute

I have created a validation attribute. And the IsValid method is as follows

<AttributeUsage(AttributeTargets.Field Or AttributeTargets.Property, AllowMultiple:=True)> _
Public NotInheritable Class BlaBlaAttribute
        Inherits ValidationAttribute

        Private ReadOnly _typeId As New Object()
        ...........

        Protected Overrides Function IsValid(value As Object, validationContext As ValidationContext) As ValidationResult

               Dim otherProperties = validationContext.ObjectType.GetProperties(BindingFlags.IgnoreCase Or BindingFlags.Public Or BindingFlags.Instance).ToList()

               For Each item In otherProperties
                    Dim propItem = item
                    Dim attr As DisplayNameAttribute = DirectCast(Attribute.GetCustomAttribute(propItem, GetType(DisplayNameAttribute)), DisplayNameAttribute)
                    If attr Is Nothing Then
                    ............
                    End If
               Next
               Return ValidationResult.Success
        End Function
End Class

Thought, there are some display attributes but "attr" is always nothing. How to get other properties custom attributes? Any help would be highly appriciated