Abstract
The vitamin A metabolite all-trans retinoic acid (ATRA; tretinoin) has anticancer potential. However, lack of clinical success has prevented its approval for solid tumours. Herein, we propose combining short-term low-dose ATRA preconditioning with fimaporfin-based photodynamic therapy (ATRA+PDT) for the improved treatment of solid cancers. Compared to monotherapies, ATRA+PDT induced synergistic cytotoxic responses including promotion of apoptosis in colon and breast carcinoma cell lines. Neither enhanced activity of alkaline phosphatase (ALP) nor increased expression of CD133 was detected after ATRA treatment indicating that ATRA+PDT cause cell death independent of differentiation. In the human colorectal adenocarcinoma cell line HT-29, the effect of ATRA+PDT on gene expression was evaluated by RNA sequencing (RNA-seq). We identified 1129 differentially expressed genes (DEGs) after ATRA+PDT compared to PDT. Ingenuity Pathway Analysis (IPA) predicted the unfolded protein response (UPR), interferon (IFN) signaling and retinoic acid-mediated apoptosis signaling as strongly activated canonical pathways after ATRA+PDT compared to PDT. A validation of the RNA-sec data by RT-qPCR revealed that ATRA+PDT elevated mRNA expression of early growth response 1 (EGR1) and strongly the stress-induced activating transcription factor 3 (ATF3), of which was confirmed on the protein level. In addition, ATRA+PDT abolished mRNA expression of regenerating islet-derived protein 4 (REG4). During the first 20 days post-ATRA+PDT, we obtained significant anti-tumour responses in HT-29 xenografts, including complete responses in 2/5 mice. In conclusion, ATRA+PDT represent a novel combination therapy for solid tumours that should be further tested in immunocompetent preclinical models.
Competing Interest Statement
P.K.S. and J.J.W.W. has filed a patent (US 63/282,267, 2021) on the ATRA+PDT method. P.K.S. is a co-inventor on several patents and patent applications related to the PCI technology. S.L. declares no conflict of interest.
Footnotes
Minor revision of text of manuscript. Inclusion of supplementary data.
Abbreviations
- ALDH1A1
- aldehyde dehydrogenase 1 family member A1
- ALP
- alkaline phosphatase
- ATF3
- activating transcription factor 3
- ATRA
- all-trans retinoic acid (tretinoin)
- ATRA+PDT
- ATRA preconditioning with fimaporfin-based photodynamic therapy
- DEG
- differentially expressed gene
- EGR1
- early growth response 1
- GSEA
- gene set enrichment analysis
- HDAC9
- histone deacetylase 9
- IFN
- interferon
- IGFBP6
- insulin-like growth factor-binding protein 6
- IPA
- Ingenuity pathway analysis
- LCN2
- lipocalin 2
- LD50
- light-dose inducing 50% reduction of cell viability
- LPS
- lipopolysaccharide
- PCI
- photochemical internalisation
- PDT
- photodynamic therapy
- RAR
- retinoic acid receptor
- REG4
- regenerating islet-derived protein 4
- RNA-seq
- RNA sequencing
- ROS
- reactive oxygen species
- UPR
- unfolded protein response
- TNF
- tumour necrosis factor
- TPCS2a
- disulfonated tetraphenyl chlorin (fimaporfin)
- TUNEL
- Terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labelling