Fluorouracil Enhances Photodynamic Therapy of Squamous Cell Carcinoma via a p53-Independent Mechanism that Increases Protoporphyrin IX levels and Tumor Cell Death

Abstract

Photodynamic therapy (PDT), using 5-aminolevulinic acid (ALA) to drive synthesis of protoporphryin IX (PpIX) is a promising, scar-free alternative to surgery for skin cancers, including squamous cell carcinoma (SCC) and SCC precursors called actinic keratoses (AK). In the United States, PDT is only FDA approved for treatment of AK; this narrow range of indications could be broadened if PDT efficacy were improved. Toward that goal, we developed a mechanism-based combination approach using 5-fluorouracil (5-FU) as a neoadjuvant for ALA-based PDT. In mouse models of SCC (orthotopic UV-induced lesions, and subcutaneous A431 and 4T1 tumors), pretreatment with 5-FU for 3 days followed by ALA for 4 hours led to large, tumor-selective increases in PpIX levels, and enhanced cell death upon illumination. Several mechanisms were identified that might explain the relatively improved therapeutic response. Firstly, the expression of key enzymes in the heme synthesis pathway was altered, including upregulated coproporphyrinogen oxidase and downregulated ferrochelatase. Secondly, a 3- to 6-fold induction of p53 in 5-FU pretreated tumors was noted. The fact that A431 contains a mutant form p53 did not prevent the development of a neoadjuvantal 5-FU effect. Furthermore, 5-FU pretreatment of 4T1 tumors (cells that completely lack p53), still led to significant beneficial inductions, i.e., 2.5-fold for both PpIX and PDT-induced cell death. Thus, neoadjuvantal 5-FU combined with PDT represents a new therapeutic approach that appears useful even for p53-mutant and p53-null tumors.

5-Fluorouracil Enhances Protoporphyrin IX Accumulation and Lesion Clearance during Photodynamic Therapy of Actinic Keratoses: A Mechanism-Based Clinical Trial

“…In our studies in murine models of UV-induced skin cancer, a brief period of 5FU application (only 3 days) was sufficient to increase PpIX levels and improve the tumor treatment response. PpIX elevations were accompanied by significant changes in CPO and FC enzyme levels, as well as in E-cadherin (21,26). In addition, p53 was increased after 5FU pretreatment.…”

Augmentation of 5-aminolevulinic Acid Treatment of Glioblastoma by Adding Ciprofloxacin, Deferiprone, 5-fluorouracil and Febuxostat: The CAALA Regimen

“…5-FU enhances 5-ALA photocytotoxicity. In a study of rats with UV induced squamous cell carcinoma, sequential 3 days of 5-FU followed by 4 hrs of 5-ALA gave a 2 to 4 fold increase of intracellular PpIX compared to rats not given 5-FU pretreatment [46]. Perhaps even more importantly, normal non-irradiated skin showed no difference in intracellular PpIX with either sequential 5-FU plus 5-ALA or when given 5-ALA alone compared to skin cells exposed to neither [46].…”

“…In a study of rats with UV induced squamous cell carcinoma, sequential 3 days of 5-FU followed by 4 hrs of 5-ALA gave a 2 to 4 fold increase of intracellular PpIX compared to rats not given 5-FU pretreatment [46]. Perhaps even more importantly, normal non-irradiated skin showed no difference in intracellular PpIX with either sequential 5-FU plus 5-ALA or when given 5-ALA alone compared to skin cells exposed to neither [46]. Human clinical use in using sequential topical 5-FU, followed by 5-ALA PDT compared with 5-ALA PDT alone in treating actinic keratoses indicate that pretreatment with 5-FU increases 5-ALA PDT effectiveness [47,48].…”

Vitamin D and Other Differentiation‐promoting Agents as Neoadjuvants for Photodynamic Therapy of Cancer

“…To test the idea of using 5‐FU as a neoadjuvant for ALA‐based PDT, Anand et al (32) pursued a mechanism‐based approach. In several mouse models of squamous cell carcinoma, including skin lesions induced by UV light or subcutaneously implanted carcinoma cells (A431 and 4T1), a 5‐FU pretreatment was administered for 3 days, followed by ALA for 4 h. This led to enhanced PpIX levels within tumor cells and to greater cell death upon illumination.…”