Franny Jongbloed

65 3 PROTECTION OF FASTING ON IRINOTECAN TOXICITY Table 2. (continued) Canonical Pathway Pathway classification P- value Genes Ratio Z-score B Cell Activating Factor Signaling Humoral Immune Response; Cellular Growth, Proliferation and Development 7.34 E -05 12/41 (29.3%) +2.111 CD27 Signaling in Lymphocytes Apoptosis; Cellular Immune Response 2.68 E -04 13/53 (24.5%) +2.111 Pancreatic Adenocarcinoma Signaling Cancer 3.34 E -03 19/118 (16.1%) +2.111 NF-kB Signaling Organismal Growth and Development; Humoral Immune Response; Cytokine Signaling; Cellular Immune Response 3.98 E -06 34/181 (18.8%) +2.058 IL-6 Signaling Cytokine Signaling; Cellular Immune Response 1.03 E -04 24/128 (18.8%) +2.041 PPARa-RXRa Activation Nuclear Receptor Signaling 1.26 E -06 35/180 (19.4%) -2.121 All canonical pathways with a z-score of ≤-1.000 or ≥+1.000 are listed in table A. Due to the high number of differentially regulated pathways, in table 2B only the canonical pathways with z-score ≤-2.000 or ≥+2.000 are listed. Pathways with a significant z-score of ≤-2.000 or ≥+2.000 are depicted in bold. Genes ratio= the number and percentage of genes differentially expressed in ratio to the total number of genes involved in the pathway. Using the AL vehicle group as reference, the analysis in the liver revealed activation of mRNA expression of carboxylesterase 1 ( Ces1 ) and Ces2 in both fasting groups, i.e. with and without irinotecan, while both genes were inhibited in the AL irinotecan group. Ces3 expression was activated by fasting alone and significantly inhibited by irinotecan alone. In combination, the net effect of Ces3 expression by irinotecan and fasting was practically cancelled out. In tumor tissue, regulation of the carboxylesterases was not distinctly present. Carboxylesterases one to three are needed to convert irinotecan in to its active metabolite SN-38 (Figure 4). Cyp3a16 , the mouse homolog of Cyp3a4 , was not regulated in any of the groups, while other members of the cytochrome P450 family involved in drug metabolism appeared to be higher expressed in the fasting groups. Both Ugt1a1 and Abcc1 , genes involved in the transport of SN-38 out of the cell, were higher expressed in the fasting irinotecan group compared to the AL irinotecan group. DISCUSSION In this study, we confirm that three days of fasting prior to treatment with irinotecan is able to reduce liver toxicity as well as bone marrow depression in mice carrying subcutaneous colorectal carcinoma. Previously, we showed that these signs of somatic resistance to irinotecan were accompanied by a reduction in other side effects as body weight reduction and diarrhea without compromising the antitumor effect 7,10 . Here we set out to retrieve mechanistic insights in the chemoprotective effects of fasting through transcriptomic analyses of healthy liver and tumor tissue after an irinotecan challenge.