The present invention relates to compositions useful in inhibiting Bcl-XL or MCL-1 and disrupting p53-MDM2 and p53-MDMX interactions, and methods of using those compositions for treating a subject for conditions responsive to increasing p53 mediated activity or promoting p53 independent apoptosis, such as treating cancer. In some aspects, the compositions of this invention relate to fusion polypeptides comprising a human serum polypeptide and a p53-peptide, which can be, in some aspects, a p53 derived peptide and/or a p53 activating peptide.