Abstract 4627: Fasting reduces the systemic exposure to irinotecan and its active metabolite SN-38

Limitations to the use of chemotherapeutic agents are the often severe adverse side-effects which may lead to early discontinuation of treatment. Most anticancer agents have a narrow therapeutic index. In previous work we have shown that 72 hours of fasting prior to treatment with a high dose of irinotecan prevents the occurrence of adverse side effects in C26 colon carcinoma bearing mice, while the antitumor activity is not abrogated. To elucidate the mechanism of fasting induced resistance against adverse side effects, we have examined the pharmacokinetics of irinotecan in 72 hours fasted mice in plasma and liver.

Male BALB/c mice were divided into four groups (n=18/group). Two groups were fasted for 72 hours and two groups were fed ad libitum. After the fasting period, mice were fed ad libitum again. One group of ad libitum and fasted animals was treated with 50 mg/kg and the other with 100 mg/kg irinotecan intraperitoneally. Plasma and liver were collected at 1,4,8,12,24 and 48 hours after irinotecan injection. Tissues were homogenized in lithium heparinized plasma and concentrations of irinotecan (CPT-11) and the active metabolite SN-38 were determined using a validated reversed-phase high-performance liquid chromatography (HPLC) system with fluorescence detection. Pharmacokinetic parameters, including peak concentration, area under the plasma concentration-time curve (AUC), clearance (CL), and the half-life of the terminal disposition phase were calculated.

In the fasted group, plasma levels of SN-38 in the 50 mg/kg and 100 mg/kg group showed a 57% and 53% reduction, respectively, compared with ad libitum fed controls (AUC0-inf 5,149 vs. 2,242 ng*h/mL and 7,507 vs. 3,562 ng*h/mL). For CPT-11 the effects of fasting were smaller. An increase of 26% in the 50 mg/kg group and a reduction of 15% in the 100 mg/kg group were observed (AUC0-inf 9,715 vs. 12,235 and 37,360 vs. 31,924 ng*h/mL). In the liver, SN-38 levels in the 50 mg/kg and 100 mg/kg group showed a reduction of 51% and 30%, respectively, in the fasted animals (AUC0-inf 85.4 vs. 41.5 µg*h/g and 126 vs. 87.6 µg*h/g), while CPT-11 levels were reduced with 19% in the 50 mg/kg group and 28% in the 100 mg/kg group (AUC0-inf 218 vs. 177 µg*h/g and 712 vs. 512 µg*h/mg).

Our data demonstrate that 72 hours of fasting prior to irinotecan administration induces an important change in its metabolism. Plasma and liver levels of the pro-drug CPT-11 were only slightly reduced in fasted animals. Levels of the active metabolite SN-38 were considerably lower in fasted animals compared to ad libitum fed animals. These data suggest that the reduction of side effects by fasting is due to the lower systemic exposure to SN-38, and may have important clinical implications if also found in humans.

Citation Format: Sander A. Huisman, P de Bruijn, I.M. Ghobadi Moghaddam-Helmantel, J.N.M. IJzermans, E Wiemer, A.H.J. Mathijssen, R.W.F. de Bruin. Fasting reduces the systemic exposure to irinotecan and its active metabolite SN-38. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4627. doi:10.1158/1538-7445.AM2014-4627

Abrogation of DNA vector-based RNAi during apoptosis in mammalian cells due to caspase-mediated cleavage and inactivation of Dicer-1

RNA interference (RNAi) is used as a reverse-genetic tool to examine functions of a gene in different cellular processes including apoptosis. As key cellular proteins are inactivated during apoptosis, and as RNAi requires cooperation of many cellular proteins, we examined whether DNA vector-based RNAi would continue to function during apoptosis. The short hairpin RNA transcribed from the DNA vector is processed by Dicer-1 to form small interfering RNA that is incorporated in the RNA-induced silencing complex (RISC) to guide a sequence-specific silencing of the target mRNA. We report here that DNA vector-based RNAi of three different genes, namely poly(ADP-ribose) polymerase-1, p14(ARF) and lamin A/C are abrogated during apoptosis. The failure of DNA vector-based RNAi was not at the level of Ago-2 or RISC-mediated step of RNAi but due to catalytic inactivation of Dicer-1 on specific cleavage at the STTD(1476) and CGVD(1538) sites within its RNase IIIa domain. Using multiple approaches, caspase-3 was identified as the major caspase responsible for the cleavage and inactivation of Dicer-1. As Dicer-1 is also the common endonuclease required for formation of microRNA (miRNA) in mammalian cells, we observed decreased levels of mature forms of miR-16, miR-21 and let-7a. Our results suggest a role for apoptotic cleavage and inactivation of Dicer-1 in controlling apoptotic events through altered availability of miRNA.

Expression in hematological malignancies of a glucocorticoid receptor splice variant that augments glucocorticoid receptor-mediated effects in transfected cells

Glucocorticoids play an important role in the treatment of a number of hematological malignancies, such as multiple myeloma. The effects of glucocorticoids are mediated through the glucocorticoid receptor alpha, the abundance of which can be modulated by alternative splicing of the glucocorticoid receptor mRNA. Two splice variants of the glucocorticoid receptor mRNA have been described: glucocorticoid receptor beta, which reportedly has a dominant negative effect on the actions of the glucocorticoid receptor alpha, and glucocorticoid receptor P, of which the effects are unknown. In this study, we have investigated the expression levels of these two splice variants at the mRNA level in multiple myeloma cells and in a number of other hematological tumors. Although the glucocorticoid receptor beta mRNA was, if at all, expressed at very low levels, considerable amounts (up to 50% of the total glucocorticoid receptor mRNA) glucocorticoid receptor P mRNA was present in most hematological malignancies. In transient transfection studies in several cell types and in multiple myeloma cell lines, the glucocorticoid receptor P increased the activity of the glucocorticoid receptor alpha. These results suggest that the relative levels of the glucocorticoid receptor alpha and the glucocorticoid receptor P may play a role in the occurrence of glucocorticoid resistance in tumor cells during the treatment of hematological malignancies with glucocorticoids.

Consensus strategy to quantitate malignant cells in myeloma patients is validated in a multicenter study. Belgium-Dutch Hematology-Oncology Group

Recently the Belgium-Dutch Hematology-Oncology group initiated a multicenter study to evaluate whether myeloma patients treated with intensive chemotherapy benefit from additional peripheral stem cell transplantation. To determine treatment response accurately, we decided to quantitate malignant cells. To test a consensus quantitation strategy, 5 centers independently determined the immunoglobulin heavy chain sequences of patient tumor cells and developed allele-specific oligonucleotides (ASO) and ASO-polymerase chain reaction (PCR). We compared the reproducibility of real-time quantitation with quantitation using limiting dilutions. We distributed DNA samples with a 4-log range of tumor cell concentrations and found average quantitation values deviating 74% and 42% from the input values with real-time PCR (1 center) and limiting dilutions (4 centers), respectively. Within single centers we found an average variation coefficient of 0.74, with limiting dilutions not significantly different from the average 0.82 center-to-center variation coefficient. Within a single center, real-time quantitation proved more reproducible (average variation coefficient, 0.36). Quantification was confirmed in 3 patients during treatment in the protocol. This report shows that real-time PCR or limiting dilution assays can be used for quantitation in a single multicenter trial. We present a consensus strategy that allows an accurate comparison of quantitation data generated in independent centers.

The Mr 193,000 vault protein is up-regulated in multidrug-resistant cancer cell lines

Vaults are 13 megadalton ribonucleoprotein particles composed largely of the major vault protein (MVP) and two high molecular weight proteins, p240 and p193, and a small vault RNA (vRNA). Increased levels of MVP expression, vault-associated vRNA, and vaults have been linked directly to multidrug resistance (MDR). To further define the putative role of vaults in MDR, we produced monoclonal antibodies against the Mr 193,000 vault protein and studied its expression levels in various multidrug-resistant cell lines. We find that, like MVP, p193 mRNA and protein levels are increased in various multidrug-resistant cell lines. Subcellular fractionation of vault particles revealed that vault-associated p193 levels are increased in multidrug-resistant cells as compared with the parental, drug-sensitive cells. Furthermore, protein analysis of postnuclear supernatants and co-immunoprecipitation studies show that drug-sensitive MVP-transfected tumor cells lack this up-regulation in vault-associated p193. Our observations indicate that vault formation is limited not only by the expression of the MVP but also by the expression or assembly of at least one of the other vault proteins.

Inhibitors of multidrug resistance

P-glycoprotein expression on tumor cells is a frequent cause of pleiotropic drug resistance in cell lines and tumor specimens. Besides the multidrug resistance gene (MDR1), other mechanisms of increased drug extrusion have been described, such as the MDR-related protein and the lung resistance protein. In addition, other gene-regulated processes may lead to cell survival after exposure to cytostatic agents. It has been shown that p-glycoprotein can be circumvented in vitro by noncytotoxic agents such as verapamil and cyclosporin A, which interact pharmacologically with p-glycoprotein-mediated efflux. More recently, molecular approaches to downregulate p-glycoprotein expression or function have been studied. These approaches and the clinical results obtained so far will be discussed.

Assays for the analysis of P-glycoprotein in acute myeloid leukemia and CD34 subsets of AML blasts

Expression of the multidrug resistance (MDR) phenotype is an independent prognostic variable in acute myeloid leukemia. Approximately 43-57% of the patients have P-glycoprotein (P-gp) expression. A major drawback with the interpretation of P-gp data in AML is the lack of coherence with different analytical assays. We have focused our efforts of P-gp detection on flow cytometry using a dual technique of P-gp staining with antibodies for the extracellular epitope (MRK16) and a functional analysis of P-gp using the rhodamine efflux assay and the effect of P-gp inhibitors such as SDZ PSC 833. This technique was combined with the staining of lineage-specific antigens such as CD34, CD56 and c-kit. In this way, various subsets of AML cells can be identified such as MRK 16+/-, CD34+/- blasts. These cells can be sorted for further analysis, such as the molecular expression of P-gp and other pleiotropic drug resistance genes.