Align list ignoring negative sign of the first number in items

What i do is to redefine \item inside the environment to examine the first token of \item (following an optional argument). If it is a - token, I \mathllap it and then continue, else I just typeset it directly.

\documentclass{article}
\usepackage{enumitem,mathtools}
\let\svitem\item
\newenvironment{alternativas}[1][0]
{
  \renewcommand\item[2][\relax]{%
    \ifx\relax##1\def\next{}\else\def\next{[##1]}\fi
    \ifx-##2\def\nnext{$\mathllap{##2}$}\else\def\nnext{##2}\fi
    \expandafter\svitem\next\nnext}
    \begin{enumerate}[label={\Alph*)}, itemsep=#1cm, topsep = 0.5cm, 
      wide=0pt, labelwidth=.5cm,leftmargin=!,labelsep=10pt]
}
{
    \end{enumerate}
}
\begin{document}
\begin{alternativas}
\item -1
\item 4
\item -5
\item 6
\end{alternativas}
\end{document}

ADDENDUM

OP clarified in comments that all numbers are entered in math mode (via leading $). However, not all items begin with math. So, some revisions were required:

\documentclass{article}
\usepackage{enumitem,mathtools}
\let\svitem\item
\newenvironment{alternativas}[1][0]
{
  \renewcommand\item[3][\relax]{%
    \ifx\relax##1\def\next{}\else\def\next{[##1]}\fi
    \ifx$##2\ifx-##3\def\nnext{##2\mathllap{##3}}\else\def\nnext{##2##3}\fi
      \else\def\nnext{##2##3}\fi
    \expandafter\svitem\next\nnext}
    \begin{enumerate}[label={\Alph*)}, itemsep=#1cm, topsep = 0.5cm, 
      wide=0pt, labelwidth=.5cm,leftmargin=!,labelsep=10pt]
}
{
    \end{enumerate}
}
\begin{document}
\begin{alternativas}
\item $-1$
\item $4$
\item $-\frac{5}{7}$
\item $\frac{6}{11}$
\item text
\end{alternativas}
\end{document}

You can load mathtools (needless to load amsmath in this case) to use its \mathllap command and slightly increase \labelsep:

\documentclass{article}

\usepackage{enumitem}
\usepackage{mathtools}
\newenvironment{alternativas}[1][0]
{
    \begin{enumerate}[label={\Alph*)}, itemsep=#1cm, topsep = 0.5cm, labelsep=6pt, wide=0pt,labelwidth=.5cm,leftmargin=!]
}
{
    \end{enumerate}
}

\begin{document}

 \begin{alternativas}
    \item $\mathllap{-}1 $
    \item $ 4 $
    \item $ \mathllap{-}5 $
    \item $ 6 $
    \end{alternativas}

\end{document}