Debian 8 に python3-pip をインストールできない

python3-pipをインストールしたいのですが、常にエラーが発生します。

sudo apt-get install python3-pip

The following packages have unmet dependencies:
 python3-pip : Depends: python3-setuptools but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

sudo apt-get install python-setuptools


The following packages have unmet dependencies:
 python3-setuptools : Depends: python3-pkg-resources (= 5.5.1-1) but 33.1.1-1~bpo8+1 is to be installed
E: Unable to correct problems, you have held broken packages.

sudo apt-get install python3-pkg-resources


Reading package lists... Done
Building dependency tree
Reading state information... Done
python3-pkg-resources is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.

更新/アップグレードしましたが、まだ機能しません。