You can use the titletoc
package for this:
The code:
\documentclass{book}
\usepackage{titletoc}
\renewcommand\thechapter{\Alph{chapter}}
\renewcommand{\thesection}{\arabic{section}}
\titlecontents*{subsubsection}
[7em]
{\small}
{\thecontentslabel}
{}
{}
[~---\ ]
\setcounter{tocdepth}{3}
\begin{document}
\tableofcontents
\chapter{A test chapter}
\section{A test section}
\subsection{A test subsection}
\subsubsection{Test subsubsection one one}
\subsubsection{Test subsubsection one two}
\subsubsection{Test subsubsection one three}
\subsubsection{Test subsubsection one four}
\subsection{Another test subsection}
\subsubsection{Test subsubsection two one}
\subsubsection{Test subsubsection two two}
\subsubsection{Test subsubsection two three}
\subsubsection{Test subsubsection two four}
\subsubsection{Test subsubsection two five}
\subsection{Yet another test subsection}
\subsubsection{Test subsubsection three one}
\end{document}
Update
In a comment it's been requested to add the page number after the title; here's one way to do it; I added a comma and an unbreakable space between the title and the page number (adjust according to needs):
\documentclass{book}
\usepackage{titletoc}
\renewcommand\thechapter{\Alph{chapter}}
\renewcommand{\thesection}{\arabic{section}}
\titlecontents*{subsubsection}
[7em]
{\small}
{\thecontentslabel}
{}
{,~\thecontentspage}
[~---\ ]
\setcounter{tocdepth}{3}
\begin{document}
\tableofcontents
\chapter{A test chapter}
\section{A test section}
\subsection{A test subsection}
\subsubsection{Test subsubsection one one}
\subsubsection{Test subsubsection one two}
\subsubsection{Test subsubsection one three}
\subsubsection{Test subsubsection one four}
\subsection{Another test subsection}
\subsubsection{Test subsubsection two one}
\subsubsection{Test subsubsection two two}
\subsubsection{Test subsubsection two three}
\subsubsection{Test subsubsection two four}
\subsubsection{Test subsubsection two five}
\subsection{Yet another test subsection}
\subsubsection{Test subsubsection three one}
\end{document}