Next, it was shown that PpIX increases p73 protein levels in p53-null cancer cells, induces TAp73-dependent transcription and activates apoptotic NOXA and PUMA. Additionally, PpIX ablated the MDM2/MDMX/p73/ITCH complex and inhibited tumor growth of p53-null subcutaneous xenografts via activation of p73 and Poly (ADP-ribose) polymerase (PARP) cleavage [143] (Figure 4). Here, TP53 is linked to cancer.