SN-38 AUC Research Articles

Role of MRPs transporters in pharmacokinetics and intestinal toxicity of irinotecan

To identify additional genetic markers contributing to variability in CPT-11 disposition and toxicity, we assessed impact of the multiple drug-resistant transporters 1, 2, and 3 (MRP1, MRP2, and MRP3) on the intestinal toxicity, pharmacokinetics, tissue distribution and biliary excretion of CPT-11 using a knockout mouse model. Mrp1/3 knockout had minor impact on intestinal toxicity of CPT-11, tissue distribution, biliary excretion, and PK parameter of its active metabolites SN38. Conversely, Mrp2−/− mice, with low carboxylesterase activity, displayed insensitivity to CPT-11 toxicity due to reduced intestinal exposure to SN38. In PK studies, Mrp1/2 knockout significantly increased the AUC of CPT-11 compared to their AUC in FVB mice. However, the AUC of SN38 in Mrp2 −/− mice was decreased by 3.25-fold. Mrp3 knockout only slightly increased SN38 plasma exposure. Lastly, Mrp2/3 knockout increased biliary excretion amount of CPT-11 by 67.2% and 48.5% compared to wild-type mice, respectively. Consequently, Mrp1/3 deficiency didn't change SN38 tissue distribution. Finally, correlation analysis demonstrated that tissue exposure to SN38 was better correlated with toxicity than plasma AUC of SN38. Mrp1/2/3 deficiency showed a minor impact on PK, biliary excretion, distribution and intestinal exposure of SN38, and as a result, did not affect the intestinal toxicity of CPT-11.

Evaluation of SN-38 PK profile in patients with RAS wild-type metastatic colorectal cancer treated with a combination of SCO-101 and FOLFIRI.

185 Background: The FOLFIRI regimen (5-fluorouracil, leucovorin and irinotecan) is a predominant treatment regimen for metastatic colorectal cancer. To optimize the benefit for the patients, it would be desirable to increase the efficacy of irinotecan by increasing the exposure of SN-38 (the active metabolite of irinotecan) to the cancer cells, while maintaining a good safety profile. The oral drug SCO-101, that is currently being developed by Scandion Oncology A/S, was tested in an early clinical trial (CORIST-trial, ClinicalTrials.gov identifier: NCT04247256). SCO-101 is an inhibitor of ABCG2, UGT1A1 and SRPK1. The CORIST trial was set up to address the safety, tolerability, and efficacy of SCO-101 given orally for 6 days followed by FOLFIRI at varying doses from day 5 to 7, in a biweekly schedule, in patients with metastatic colorectal cancer who have formerly been treated with FOLFIRI and afterwards progressed. The first part of the study was a dose-finding study, where the impact of SCO-101 on the pharmacokinetics (PK) of SN-38 was studied. Methods: 12 patients from the dose-finding part of the CORIST study received 150 mg SCO-101 for 6 days and 45 – 80% of the recommended dose of FOLFIRI. 6 of the patients had RAS wild-type tumors and these patients are the subject of the current analysis. Blood for PK analysis was sampled from the patients at 1, 2, 4, 8, 24, 48, and 96 hours after treatment with FOLFIRI and SCO-101. The blood samples were analyzed for Cmax, T½ and AUC (0-24h) of SCO-101, irinotecan and SN-38. Results: The PK of SN-38 from the patients in the study, normalized to a dose of irinotecan of 90 mg/m2 showed a T½ day 5 of 19 hours (SD 5,7) a Cmax of 60 ng/ml (SD 20,6) and an AUC_0-24h of 1415 hxng/ml (SD: 670). The results were compared to SN-38 data from treatment with irinotecan at 180 mg/m2, which is used in standard doses of FOLFIRI and the data is presented in the table. The data analysis showed an increased T½, increased Cmax and increased AUC of SN-38 when combining SCO-101 with 90 mg/m2 irinotecan, compared to SN-38 PK data from standard irinotecan treatment of 180 mg/m2. The toxicity profile of the patients treated with 90 mg irinotecan/m2 (50% FOLFIRI) showed only grade 1 and 2 adverse events. Conclusions: SCO-101 in combination with FOLFIRI has demonstrated the ability to modulate the PK profile of SN-38 in mCRC patients with RAS wild-type tumors, by significantly increasing the half-life, the peak plasma concentration, and area under the curve of SN-38. The combined treatment was well tolerated, and the drug is now being tested for efficacy in the CORIST trial.[Table: see text]

Effect of UGT1A1, CYP3A and CES Activities on the Pharmacokinetics of Irinotecan and its Metabolites in Patients with UGT1A1 Gene Polymorphisms.

Irinotecan (CPT-11) is metabolized to an active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38) by carboxylesterase (CES). SN-38 is then converted to the inactive metabolite SN-38 glucuronide (SN-38G) by glucuronosyltransferase 1A1 (UGT1A1). Genetic polymorphisms in UGT1A1 have been associated with altered SN-38 pharmacokinetics, which increase the risk of toxicity in patients. CPT-11 is also converted to 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycamptothecin (APC) and 7-ethyl-10-(4-amino-1-piperidino) carbonyloxycamptothecin (NPC) by cytochrome P450 3A (CYP3A), and this route also affects the plasma concentration of SN-38. We evaluated the activities of UGT1A1, CYP3A, and CES and the factors affecting the pharmacokinetics of plasma SN-38 in patients with UGT1A1 gene polymorphisms. Three male patients aged 56, 65, and 49 years were recruited for the analysis. All patients had pancreatic cancer, received FOLFIRINOX, and had UGT1A1*6/*6 (patients 1 and 3) or *6/*28 (patient 2) genetic polymorphisms. The rate constants for evaluating the enzyme activity were determined from the measured plasma concentration of CPT-11 and its metabolites using a two-compartment model by WinNonlin. The area under the plasma concentration-time curve (AUC) of SN-38 was patient 1 > patient 2 > patient 3. The rate constants obtained from the model analysis indicated the respective enzyme activities of UGT1A1 (k57), CYP3A (k13 + k19), and CES (k15). The order of values for UGT1A1 activity was patient 2 > patient 3 > patient 1. Since UGT1A1 activity was low in patient 1 with a high AUC of SN-38, it can be said that the increase in plasma concentration was due to a decrease in UGT1A1 activity. Conversely, the order of values for CYP3A and CES activities was patient 3 > patient 1 > patient 2 and patient 2 > patient 1 > patient 3, respectively. Patient 3 had the lowest AUC of SN-38, caused by a lower level of CES activity and increased CYP3A activity. In this study, we indicated that the plasma AUC of SN-38 and AUC ratio of SN-38G/SN-38 may depend on changes in the activities of CYP3A, CES, and UGT1A1. Using pharmacokinetic analysis, it is possible to directly evaluate enzyme activity and consider what kind of enzyme variation causes the increase in the AUC of SN-38.

Effects of inflammation on irinotecan pharmacokinetics and development of a best-fit PK model

Irinotecan is a chemotherapeutic drug used in the treatment of advanced colorectal cancer and elevated blood concentrations of its active metabolite, SN-38 leads to increased gastrointestinal (GI) toxicity and diarrhea in patients. In this study, we investigated the effects of inflammation on the pharmacokinetics (PK) of irinotecan (CPT-11) and its active metabolite, SN-38. Mice were i.p.-injected with either saline or lipopolysaccharide (LPS) to induce inflammation. After 16 h, irinotecan was administered orally. Blood was collected from the tail vein of mice from 0 to 24 h after dosing. Concentrations of irinotecan, SN-38 and SN-38G were analyzed using LC-MS/MS. The AUC, Cmax, and tmax were derived using WinNonlin® 5.2. A PK model was developed using Phoenix NLME® to describe the PK of irinotecan and SN-38 during inflammation. Results indicated a significant increase in the blood concentrations of irinotecan and SN-38 in mice during inflammation. The AUC of irinotecan and SN-38 in LPS group were 2.6 and 2-folds, respectively, of those in control saline-treated mice. The Cmax of irinotecan and SN-38 in LPS treated mice were 2.4 and 2.3-folds of those in saline-treated mice. The PK model was successfully developed and validated. The best-fit plots of individual PK analysis showed a good correlation between observed and predicted concentrations of irinotecan and SN-38. Together, this study reveals that SN-38 concentrations are elevated during inflammation, which may increase the GI toxicity and diarrhea in patients who receive irinotecan; and the developed PK model can quantitatively describe the PK of irinotecan and SN-38 during inflammation.

Selective TACE with irinotecan-loaded 40 \u03bcm microspheres and FOLFIRI for colorectal liver metastases: phase I dose escalation pharmacokinetic study

BackgroundEfficacy of treatments for colorectal liver metastases after failure of first-line chemotherapy is limited. The aim of this study was to prospectively evaluate the feasibility, tolerability, and pharmacokinetics of selective transarterial chemoembolization (TACE) with irinotecan-loaded 40 μm microspheres combined with systemic FOLFIRI for colorectal liver metastases refractory to oxaliplatin regimen.MethodsThe dose escalation study was conducted in three patient groups with different amounts of irinotecan loaded (50, 75 and 100 mg per mL-microspheres). Selective catheterization was performed to embolize subsegments or segments of located tumors using TACE navigation system. FOLFIRI was administrated 7 days after TACE. Plasma concentration was measured before and time points after administration.ResultsNine patients successfully underwent a total of 22 TACE procedures. Dose-limiting toxicity did not appear at any level. The overall response rate was 55.6%. The median progression free and overall survival were 8.1 and 18.2 months, respectively. The AUC and Cmax of plasma SN-38 per 1 mg injected irinotecan dose were significantly higher in irinotecan-loaded microspheres compared with FOLFIRI (P = 0.009 and P < 0.001, respectively).ConclusionSelective TACE using 40 μm irinotecan-loaded microspheres combined with systemic FOLFIRI was feasible and safe even when a high dose of irinotecan was loaded. Irinotecan-loaded microspheres resulted in a higher plasma concentration and AUC of SN-38 than treatment with FOLFIRI. Further large scale trials to evaluate the efficacy are mandatory.Trial registrationUniversity Hospital Medical Information Network (UMIN) Clinical Trials Registry, Registration number; UMIN000015367; Registered date; 08,10,2014.

Pazopanib interacts with irinotecan by inhibiting UGT1A1-mediated glucuronidation, but not OATP1B1-mediated hepatic uptake, of an active metabolite SN-38.

Pazopanib is an orally active, multi-targeted tyrosine kinase inhibitor. A previous phase I study demonstrated that coadministration of pazopanib with irinotecan increases the area under the plasma concentration-time curve (AUC) for SN-38, an active metabolite of irinotecan. To clarify the possible mechanism underlying that drug-drug interaction, we investigated the potential for pazopanib to inhibit UDP-glucuronosyltransferase (UGT)1A1 and organic anion-transporting polypeptide (OATP)1B1, which are involved in detoxification and hepatic uptake of SN-38, respectively. Human liver microsomes (HLMs) and recombinant human UGT1A1, and HEK293 cells stably transfected with OATP1B1 were used to evaluate the inhibitory effects of pazopanib against glucuronidation, and hepatic uptake of SN-38, respectively. Kinetic analysis was performed to estimate inhibition constants, which were corrected for non-specific binding to enzyme sources (Ki,u values). Concentration-dependent inhibition of SN-38 glucuronidation was observed in the HLMs and recombinant human UGT1A1 experiments: Pazopanib noncompetitively inhibited SN-38 glucuronidation by HLMs (Ki,u = 1.6 ± 0.05µM) and recombinant human UGT1A1 (Ki,u = 0.69 ± 0.02µM). Pazopanib-induced increases in SN-38 AUC estimated using Ki,u values were comparable to those observed in patients of the phase I study who received both irinotecan and pazopanib. Such results suggest that the drug-drug interaction is at least partially mediated by inhibition of UGT1A1. In contrast, pazopanib did not inhibit OATP1B1-mediated SN-38 uptake at concentrations up to 60µM. Results showed that pazopanib inhibits UGT1A1-mediated SN-38 glucuronidation, but not OATP1B1-mediated SN-38 uptake.

Abstract 3734: Pharmacokinetics of sacituzumab govitecan (IMMU-132), an antibody-drug conjugate (ADC) targeting Trop-2, in patients with diverse advanced solid tumors

Abstract BACKGROUND: Sacituzumab govitecan (IMMU-132), an ADC targeting Trop-2, an antigen present in many solid tumors, uses SN-38, a topoisomerase I inhibitor that has nanomolar potency derived from irinotecan (IRI), and a pH sensitive linker that releases SN-38 gradually (in vitro, 50% released per 1 day in serum). Clinical studies in patients (pts) with diverse solid tumors have shown manageable toxicity (dose-limiting neutropenia, diarrhea but lower incidence than IRI) and encouraging efficacy. METHODS: Conjugate and IgG were monitored in pts given 8 (N = 24) or 10 mg/kg (N = 29) by ELISA. SN-38 and glucuronidated SN-38 (SN-38G) were measured by reversed-phase HPLC. SN-38 and SN-38G levels are expressed as the amount of drug dissociated from the conjugate (i.e., Free SN-38) and the amount bound to the IgG (Total SN-38). UGT1A1 status was determined in baseline blood sample from 146 pts. RESULTS: IMMU-132 cleared with a half-life of 11.7-18.9 h, depending on the assay, while the IgG half-life was 4-5 days, which agrees with in vitro drug-release data. Levels of Free SN-38 at 30 min or 1 d after injection were &amp;lt;2% and ~ 5% of Total SN-38, respectively, indicating most SN-38 in serum is bound to the conjugate. Free SN-38 clears with a half-life of ~20 h, which is consistent with SN-38 clearance in IRI therapy. No correlation was found between Free SN-38 in serum at 30 min and the incidence of severe neutropenia. Total and Free levels of SN-38G were similar, supporting in vitro results indicating that SN-38 is not glucuronidated while bound to the IgG. Free SN-38G levels were lower than Free SN-38 (SN-38G/SN-38 AUC ratio = 0.52), explaining the lower incidence of severe diarrhea. PK parameters for 8 and 10 mg/kg group were similar; no major differences in toxicity. UGT1A1 status showed 43% and 44% with *1*1 and *1*28 haplotype, respectively, and 13% with *28*28 haplotype, which is associated with higher risk of severe neutropenia and diarrhea for IRI therapy. With IMMU-132, 58% of the *28*28 pts had severe neutropenia compared to ~40% of the *1*1 and *1*28 pts, and 16% of the *28*28 pts had grade 3 diarrhea compared to 5-8% of the *1*1 and *1*28. In 3 of 4 cancer indications, objective response rate and clinical benefit ratio favored the 10 mg/kg group. CONCLUSION: IMMU-132 cleared as predicted from in vitro serum stability data, with no difference between the 8 and 10 mg/kg groups. Current data show neutropenia did not correlate with Free SN-38 levels in serum at 30 min, and low SN-38G levels support the lower incidence of severe diarrhea. While pts with the *28*28 haplotype had a somewhat higher incidence of severe neutropenia or diarrhea than *1*1 and *1*28 pts, the overall incidence of each is small, suggesting toxicity management rather than screening is appropriate. With no major difference in safety and PK, but improved responses with 10 mg/kg, 10 mg/kg is selected for future clinical studies. Citation Format: Robert M. Sharkey, Allyson J. Ocean, Alexander N. Starodub, Aditya Bardia, Michael Guarino, Wells A. Messersmith, Jordan D. Berlin, Vincent J. Picozzi, Rebecca Moroose, William A. Wegener, Pius Maliakal, Serengulam V. Govindan, David M. Goldenberg. Pharmacokinetics of sacituzumab govitecan (IMMU-132), an antibody-drug conjugate (ADC) targeting Trop-2, in patients with diverse advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3734. doi:10.1158/1538-7445.AM2017-3734

The utility of genomics and functional imaging to predict irinotecan pharmacokinetics and pharmacodynamics: The PREDICT IR study.

2564 Background: BSA-based dosing of Irinotecan (IR), does not account for its pharmacokinetic (PK) and pharmacodynamic (PD) variability. Given IR’s unique metabolism, functional hepatic nuclear imaging (HNI) with probes for hepatic transporters correlated with its PK. This study further evaluated the utility of HNI combined with extensive excretory/metabolic/PD pharmacogenomics (PG) to predict IR PK and PD in patients (pts) treated with FOLFIRI to enable dose individualization. Methods: Eligible pts had advanced colorectal cancer, suitable for 1st/2nd-line FOLFIRI± Bevacizumab. Pts had blood analyzed by Affymetrix DMET™ Plus Array and additional SNPs were genotyped. For HNI, pts were given IV 250MBq 99mTc-IDA and imaging data analyzed for hepatic extraction/excretion parameters (clearance [CL], 1hour retention [1hRET], deconvulutional CL [DeCL], hepatic extraction fraction [HEF]). Pts treated with chemotherapy, q2-weekly, and restaged after 4 cycles. Blood taken for IR and metabolite (SN38, SN38G) analysis on day 1 cycle 1, PK parameters derived by non-compartmental analysis. Statistical correlations were evaluated between (i) IDA HNI and (2) PGs, with IR PK, toxicity, objective response (ORR) and progression-free survival (PFS). Results: 32 pts analysed, 31 pts completed 4 cycles. (1) PK correlates: (a) HNI CL and 1hRET with SN38 Metabolic CL, (P = 0.04) and (b) HNI DeCL with IR AUC(0-∞) (P = 0.04). (2) Grade 3+ diarrhea (N = 4, 13%) predicted by SN38 AUC(0-∞) and Metabolic CL (P = 0.04), and gene variants for SCL22A2 and -28A3, ABCC2, UGT2B17, CYP2C18 and DPYD (P &lt; 0.05). (3) Grade 3+ neutropenia (N = 9, 28%) predicted by SN38 PK exposure (P &lt; 0.02), HNI CL and 1hRET (P &lt; 0.0001) and variants for SLC7A7-, SLC22A2-, CHST1-, UGT1A1-, -2B7, ABCB1. (4) ORR (N = 6, 20%) predicted by Methylene tetrahydrofolate reductase (MTHFR) 677C &gt; T (P = 0.002), SN38 exposure (P &lt; 0.003), and variants in metabolic/transporter genes (P &lt; 0.05). (5) PFS by SN38 PK exposure, MTHFR 677C &gt; T, HNI CL, HNI HEF and variants in PK genes (P &lt; 0.05). Conclusions: Hepatic functional imaging with extensive pharmacogenomics correlate with Irinotecan PK and PD enabling the development of nomograms to individualize dosing. Clinical trial information: ACTRN12610000898055.

Etirinotecan pegol administration is associated with lower incidences of neutropenia compared to irinotecan administration

PurposeThe relationship between incidences of neutropenia and 10-hydroxy-7-ethyl camptothecin (SN38) exposure was explored using SN38 pharmacokinetic and neutrophil count data from toxicology studies of etirinotecan pegol (EP) and irinotecan in beagle dogs.MethodsDogs received four weekly intravenous infusions of either vehicle control (n = 22), EP (6, 15, 20, 25, 40/25 mg/kg; n = 3–9 dogs/dose group/sex; n = 48), or irinotecan (20 or 25 mg/kg n = 3–4 dogs/dose group/sex; n = 14). Blood samples were collected up to 50 days post-dose for characterization of SN38 pharmacokinetics. Two separate models were created describing SN38 concentration time profiles after either irinotecan or EP administrations to project the AUC0–168h after Day 1 and Day 22 doses. The relationship between incidence of neutropenia and SN38 exposure was explored using logistic regression.ResultsThe incidence of neutropenia in dogs receiving weekly doses of irinotecan or EP was strongly correlated with maximum plasma SN38 concentration (Cmax), but not SN38 area under the concentration–time curve (AUC). Neutropenia occurred in approximately 80% of dogs receiving irinotecan (mean SN38 Cmax of 13.5 and 26.3 ng/mL for 20 and 25 mg/kg, respectively). No neutropenia occurred in dogs receiving EP at doses up to and including 25 mg/kg (mean SN38 Cmax of 3.4 and 4.9 ng/mL for 20 and 25 mg/kg, respectively), despite 2.5–3.6 times greater SN38 AUC after EP compared to irinotecan at equivalent doses.ConclusionsEP administration avoids both high SN38 Cmax values and development of dose-limiting neutropenia observed after irinotecan, while maintaining greater and sustained SN38 exposure between doses.

Increased Plasma Concentrations of Unbound SN-38, the Active Metabolite of Irinotecan, in Cancer Patients with Severe Renal Failure.

Delayed plasma concentration profiles of the active irinotecan metabolite SN-38 were observed in cancer patients with severe renal failure (SRF), even though SN-38 is eliminated mainly via the liver. Here, we examined the plasma concentrations of unbound SN-38 in such patients. Plasma unbound concentrations were examined by ultrafiltration. Physiologically-based pharmacokinetic (PBPK) models of irinotecan and SN-38 were established to quantitatively assess the principal mechanism for delayed SN-38 elimination. The area under the plasma unbound concentration-time curve (AUC(u)) of SN-38 in SRF patients was 4.38-fold higher than that in normal kidney patients. The unbound fraction of SN-38 was also 2.6-fold higher in such patients, partly because SN-38 protein binding was displaced by the uremic toxin 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF). This result was supported by correlation of the unbound fraction of SN-38 with the plasma CMPF concentration, which negatively correlated with renal function. PBPK modeling indicated substantially reduced influx of SN-38 into hepatocytes and approximately one-third irinotecan dose for SRF patients to produce an unbound concentration profile of SN-38 similar to normal kidney patients. The AUC(u) of SN-38 in SRF cancer patients is much greater than that of normal kidney patients primarily because of the reduced hepatic uptake of SN-38.

Inhibition of SN-38 glucuronidation by gefitinib and its metabolite.

Drug combinations including irinotecan and gefitinib have been evaluated in clinical trials. SN-38 is the active metabolite of irinotecan, and the increase in its concentration due to drug interactions will result in increased clinical toxicity. We aimed to investigate the effects of gefitinib and its predominant metabolite observed in human plasma, O-desmethyl-gefitinib (DMG), on SN-38 glucuronidation. Our data indicated that both gefitinib and DMG are potent inhibitors of SN-38 glucuronidation via UGT1A1 inhibition. It is predicted from in vitro data that gefitinib administered at 700mg/day may result in about 149% increase in SN-38 AUC, but there is no significant effects on SN-38 AUC at lower concentrations. Our prediction study provides a basis for design of clinical studies for the development and optimization of this combination.

P-glycoprotein-dependent pharmacokinetics of irinotecan and its active metabolite, SN-38 in rats: Effect of verapamil

We have recently demonstrated that the oral bioavailability of irinotecan (80 mg/kg) can be increased at least 7-fold by co-administration of the P-gp blocker verapamil (25 mg/kg, Oral). As a result, co-treatment with P-gp inhibitor could be a useful strategy for bioavailability enhancement. However, in view of narrow therapeutic index, the co-administration of irinotecan and verapamil may result in unanticipated toxicities. Therefore, dose optimisation studies of irinotecan were performed when it is given in conjunction with a P-gp inhibitor. For dose optimization study, the bioavailability and pharmacokinetic parameters were studied in rats after oral administration of irinotecan at three doses (i.e. 20, 40 and 80 mg/kg) alone and in combination with verapamil (25 mg/kg, oral). The area under the plasma-concentration time curve (AUC) of irinotecan at 20, 40 and 80 mg/kg was 3.51 ± 1.20, 8.81 ± 1.93 and 14.03 ± 2.18 h µg/ml, respectively which after treatment with verapamil, increased dose dependently to 7.84 ± 1.20, 19.94 ± 2.39 and 61.71 ± 15.0 h µg/ml, respectively. In addition to irinotecan, plasma concentrations of SN-38, one of the major active metabolite of irinotecan, were also monitored. The less than proportional increase in SN-38 AUC from 20 to 80 mg/kg is consistent with the saturation of carboxylesterase. Our results indicate that oral drug treatment of irinotecan in presence of temporary P-gp inhibition could be as equally safe and effective as intravenous administration. Nevertheless, safe P-gp inhibitors need to be identified as alternatives to verapamil for development of efficacious oral irinotecan formulations.

Cetuximab increases concentrations of irinotecan and of its active metabolite SN-38 in plasma and tumour of human colorectal carcinoma-bearing mice

In a previous study, we showed that cetuximab, a monoclonal antibody directed towards epidermal growth factor receptor, could inhibit P-glycoprotein (P-gp), an efflux protein of ATP-binding cassette family, and lead to an increased P-gp substrate intracellular concentration. Cetuximab is given with irinotecan to patients with metastasis colorectal cancer who did not respond to irinotecan-based therapy. The mechanism of this successful clinical reversion remains unknown. As irinotecan is a P-gp substrate, we tested here whether cetuximab could modify irinotecan concentration in mice. Therefore, concentrations of irinotecan and of its active metabolite SN-38 were measured by HPLC in plasma and tumour of mice bearing a human colorectal carcinoma xenograft when irinotecan is given orally alone or after a pretreatment with cetuximab. Pharmacokinetic analysis showed no significant modification of irinotecan concentrations but a significant increase (1.7-fold) in SN-38 AUCs in plasma and in tumour after a pretreatment with cetuximab. Those results suggest that cetuximab influence irinotecan distribution into tissues probably due to inhibition of P-gp. As SN-38 is 200-fold more potent than irinotecan, cetuximab could reverse irinotecan resistance by an effect on its active metabolite. Inhibiting SN-38 efflux by P-gp drug transporters in biliary system and tumour can lead to pharmacokinetic modification and a higher anticancer efficacy.

Total bilirubin as a predictive marker for irinotecan-induced toxicity in patients with gastrointestinal cancer.

68 Background: Irinotecan (CPT-11) is widely used for the treatment of patients with gastrointestinal cancer. However, CPT-11 can cause severe neutropenia and diarrhea.It has been reported that the AUC of SN-38, an active metabolite of CPT-11, correlated with Pre-treatment serum total bilirubin level (PTB), but there is no criteria of dose setting based on the PTB. Therefore, we retrospectively searched the PTB which can serve as an indicator for dose setting of CPT-11. Methods: We investigated the incidence of neutropenia and diarrhea at the first 28 days in patients with gastrointestinal cancer who were administered CPT-11 alone in Osaka National Hospital from June 2006 to July 2013. Correlation between PTB and grade 3-4 neutropenia or diarrhea were assessed. When toxicity of correlation exists, ROC (receiver operating characteristic) analysis was conducted to explore the cut-off value of the PTB. In addition, the incidence of febrile neutropenia (FN) in the cut-off value was compared. Results: 87 patients were analyzed. Of these, 65 were gastric cancer, 22 were colorectal cancer. Although PTB was significantly higher in patients who experienced grade 3-4 neutropenia than those who didn’t (p&lt;0.001), PTB was not associated with grade 3-4 diarrhea. As the results of ROC analysis, cut-off value of PTB associated with grade 3-4 neutropenia was determined to 0.8 mg/dL. The incidence of FN was significantly higher in 20% of patients with PTB ≥ 0.8 mg/dL compared with 1.6% of patients with PTB &lt; 0.8 mg/dL (OR: 15.5, p=0.01). On the other hand, in subgroup analysis showed no difference in the incidence of FN and neutropenia in patients whose dose was less than 100 mg/m². Conclusions: PTB was a predictive marker for CPT-11-induced severe neutropenia and FN. Results of this study suggested needs of dose reduction to less than 100 mg/m2 in patients with PTB ≥ 0.8mg/dL.

A UGT1A1 genotype-guided dosing study of irinotecan in metastatic colorectal cancer (mCRC) patients (pts) treated with FOLFIRI plus bevacizumab (BEV).

562 Background: Dosing based on UGT1A1*28 genotyping has been demonstrated to reduce irinotecan-related adverse events. Previous data (Toffoli et al. JCO, 2010) showed that mCRC pts treated with first-line FOLFIRI tolerated higher doses (310 mg/m2 for *1/*28; 370 mg/m2 for *1/*1) of irinotecan than the standard 180 mg/m2. The aims of this study (NCT01183494; supported by Eudract 2009-012227-28) were to define the maximally-tolerated dose (MTD) of irinotecan in FOLFIRI plus BEV as first-line therapy in mCRC pts and to determine whether BEV alters irinotecan pharmacokinetics (PK). Methods: Pts were accrued at 3 sites: Chicago (USA), Aviano (Italy), Rome (Italy). In *1/*28 and *1/*1 pts (*28/*28 pts were excluded), irinotecan was administered at an initial dose of 260 mg/m2 IV every 2 weeks. The dose was escalated to 310 and 370 mg/m2 if 0/3, &lt;2/6, or &lt;3/10 pts had a DLT (grade 3-4 non-hematologic or grade 4 hematologic toxicity during the first 28-day cycle). MTD was defined as the highest dose at which &lt;4/10 pts had a DLT. 5-FU was administered as a 400 mg/m2 IV bolus followed by 2400 mg/m2 IV over 46 hours, plus 200 mg/m2leucovorin. BEV was administered at 5 mg/kg IV on day 3 (2 days after irinotecan) and on day 15 (before irinotecan), then every 2 weeks. Irinotecan PK were collected on days 1-3 (in absence of BEV) and on days 15-17 (in presence of BEV). Results: 44 pts (23 *1/*28; 21 *1/*1) were enrolled and 43 were evaluable for DLTs during cycle 1 (Table). Neutropenia and diarrhea were the most common DLTs and were each observed in 5 of 11 (45%) pts with DLTs. The MTD is 260 mg/m2 in the *1/*28 cohort and at least 310 mg/m2in the *1/*1 cohort. In a preliminary analysis of 22 pts, BEV decreased the AUC of SN-38, the active metabolite of irinotecan (p = 0.026 by Wilcoxon matched pairs signed rank test). Conclusions: In first-line therapy of mCRC with FOLFIRI plus BEV, irinotecan doses higher than the standard dose can be safely administered based on UGT1A1 genotype. The impact of this genotype-guided dosing approach on survival will be established in future trials. Clinical trial information: NCT01183494. [Table: see text]

A genotype-directed study to optimize dosing of irinotecan according to the UGT1A1 genotype.

2570 Background: The risk of severe neutropenia from irinotecan (I) is in part related to UGT1A1*28, a polymorphism that reduces the elimination of SN-38, the active metabolite of I. We aimed to identify the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) of I in advanced solid tumor patients (pts) stratified by*1/*1, *1/*28, and *28/*28 genotypes. We hypothesized that *1/*1 pts would tolerate a higher MTD than the standard 350 mg/m2 dose and that *28/*28 pts would require dose reduction. Methods: 68 pts (30 lung, 30 gastrointestinal, 8 other cancers) received q3w, flat-dose I. Genotype frequencies were 46% (*1/*1), 41% (*1/*28), and 13% (*28/*28). Pts (66% males, median age 68 years) had 0-1 PS (only one pt had PS 2). 82% were Caucasians, 13% African Americans, and 4% Hispanics. The I starting dose was 700 mg in *1/*1 and *1/*28 pts, and 500 mg in *28/*28 pts. Pharmacokinetics was obtained at cycle 1. DLT at cycle 1 was defined as grade (G) 4 neutropenia (N) for ≥4 days, G≥3N on a treatment day, G≥3 febrile N, G4 anemia or thrombocytopenia, or G≥3 non-hematological toxicity. Results: In *1/*1 pts, the MTD was 850 mg (4 DLTs/16 pts), and 1000 mg was not tolerated (2 DLTs/6). In *1/*28 pts, the MTD was 700 mg (5 DLTs/22) and 850 mg was not tolerated (4 DLTs/6). In *28/*28 pts, the MTD was 400 mg (1 DLT/6) and 500 mg was not tolerated (3 DLTs/3). DLTs were mainly G4N, G≥3 febrile N, and G3 diarrhea. I clearance followed linear kinetics. I and SN-38 AUCs were associated with decreased log10ANC nadir (r2 0.27 and 0.30, respectively, p&lt;0.0001). At the MTD, I AUC in *28/*28 pts was 50% and 62% lower than that of *1/*28 and *1/*1 pts (16.8±4.4, 33.4±11.9, 44.2±11.3 h*ug/ml [mean±SD], respectively). At the MTD, SN-38 AUC in *28/*28 pts was 30% and 26% lower than that of *1/*28 and *1/*1 pts (620±407, 881±715, 841±888 h*ng/ml). 3 PRs were observed (NSCLC-700 mg-*1/*28, gastric-850 mg-*1/*1, small bowel-850 mg-*1/*28). Conclusions: In a heavily pretreated population, UGT1A1*28 information can be used to individualize dosing of I. Additional studies should evaluate the effect of genotype-guided dosing on efficacy in pts receiving I. Clinical trial information: NCT00708773.

Chronomodulated hepatic artery infusion (HAI) of irinotecan, 5-fluorouracil (5-FU), and oxaliplatin (l-OHP) plus intravenous (iv) cetuximab (Cet) (Chrono-Optiliv) in patients with unresectable liver metastases from wt KRAS colorectal cancer (LM-CRC) after treatment failure (European Phase II trial NCT 00852228).

3606 Background: Hepatic artery triplet chronotherapy is an effective salvage therapy for pretreated LM-CRC (Bouchahda et al. Cancer 2009). The combination of iv Cet with chrono or conventional triplet HAI allowed complete macroscopic resection (R0-R1) of previously unresectable LM-CRC in 28% of the pts, and median progression-free (PFS) and overall survival (OS) of 8.7 and 25.7 months respectively, despite prior chemotherapy (Lévi et al. ASCO-GI 2013). Purpose: To relate tolerability and efficacy of Chrono-Optiliv to pharmacokinetics (PK). Methods: 18/64 registered patients received iv Cet (500 mg/m²) and chrono HAI of Irinotecan (180 mg/m²), 5-FU (2800 mg/m²), and l-OHP (85 mg/m²) q2 weeks. Liver surgery was performed according to q6wks reviews. The systemic exposure to the 4 drugs was determined on 1st course in 11 pts, through 16 samples over 56h. Results: 8F, 10M, aged 33-72 years had good PS (0/1: 83%/17%), a median of 7 LM-CRC (2-50) in 6 segments (1-8) with median largest diameter of 47 mm (15-130). LM-CRC were bilateral in 13 pts (72%); 10 pts (56%) got Chrono-Optiliv as 3rd-4th line. Main grade 3-4 toxicities were neutropenia (56%), abdominal pain (44%), diarrhea and fatigue (22%). The rate of objective responses was 50% [26.9-73.1], and that of R0-R1 33.3% [11.5 -55.1], resulting in median PFS and OS (months) of 12.6 [8.8 -16.1] and 21.9 [7.4-36.4] respectively. Plasma PK revealed the expected Cet levels and a relevant systemic exposure to the HAI drugs, with median trapezoidal AUC’s of 12.4 µg*mn/mL (2.6-38.5) for SN-38, 142 µg*mn/mL (96- 434) for 5-FU and 100 µg*mn/mL (37-189) for free l-OHP. A significant correlation was found between free l-OHP AUC and abdominal pain (p=0.016) and between SN38 AUC and both neutropenia (p=0.018) and response (p=0.028). Conclusions: The significant systemic exposure to the HAI drugs together with iv Cet could explain efficacy and lack of early progression on Chrono-Optiliv. The results call for upfront testing of optimized Chrono-Optiliv. Clinical trial information: NCT 00852228.

P-0177 Effect of Bevacizumab on P-Glycoprotein Activity and on the Pharmacokinetics of Irinotecan and its Main Active Metabolite (SN-38) in Vivo

ABSTRACT Introduction Bevacizumab (BVZ; Avastin®) is an anti-VEGF antibody associated with irinotecan for the treatment of metastatic colorectal cancer. P-glycoprotein (P-gp) has a major role in the multidrug resistance (MDR) phenomenon, responsible for the resistance of cancer cells to chemotherapy. The aim of this study was to assess the influence of BVZ on the functionality of P-gp in vitro, and to document the effect of a BVZ intra peritoneal pretreatment on pharmacokinetics (PK) of irinotecan and SN-38 in plasma after oral administration in Swiss Nude mice. Methods IGR-OV1 cancer cells were incubated with 10 µM doxorubicin during 2 hours. Two concentrations of BVZ were tested: 1 mg/ml and 5 mg/ml. Verapamil, a P-gp inhibitor, was used as the control at 10µM. Functionality of P-gp was assessed by flowcytometry. For the in vivo study, Swiss Nude mice (n=48) were randomly assigned into two groups receiving irinotecan 40 mg/kg orally on day 4 (n=24) or irinotecan 40 mg/kg orally on day 4 with a pretreatment by BVZ 5 mg/kg intraperitoneally on day 1 and day 3 (n=24). The total PK sampling time in each group was 8 points (0.25 hr, 0.5 hr, 1 hr, 2 hr, 3 hr, 4 hr, 6 hr, 8 hr) and we used 3 mice for each time. Samples were analyzed using high performance liquid chromatography. Results BVZ significantly inhibited P-gp activity in vitro in a dose dependant manner. In vivo, pretreatment with BVZ did not modify the plasma irinotecan and SN-38 AUC. However, SN-38 trough concentration (T+8h) was significantly greater with BVZ pretreatment (p=0.034); the same trend was observed for irinotecan, although the difference was not significant (p=0.084). Pretreatment with BVZ resulted in a SN-38 splitted absorption peak in two parts, whereas the absorption of irinotecan was unaffected. Terminal half-life of irinotecan and SN-38 were not affected by BVZ. Conclusion BVZ did not affect the plasma AUC of irinotecan and SN-38. However, BVZ pretreatment allowed an increase in SN-38 trough concentration: this may be due to an inhibition of the P-gp biliary excretion of SN-38 by BVZ. To complete these results, we are currently studying different administration schedules for BVZ. Table 1 .

Correlation of pharmacokinetics of CPT-11 in FOLFIRI with phenotyping of CYP3A4 and UGT1A1 activity.

e13002 Background: CPT-11 has complex PK and PD; genotyping of UGT1A1 is recommended for higher doses in *28 carriers (Caucasian) and *6 carriers (Asian) because of a higher risk of toxicity. Raltegravir is mainly metabolized to raltegravir glucuronide by UGT1A1. CPT-11 is mainly eliminated by cytochrome P450 isoform 3A (CYP3A)-mediated oxidation and by esterase cleavage to form SN-38, which is further conjugated by uridine-diphosphate glucuronosyltransferase (UGT) isozymes to the inactive SN-38 glucuronide. We prospectively explored the correlation of midazolam and raltegravir PK with CPT-11 clearance (CL) and SN-38 levels respectively and toxicity in patients undergoing chemotherapy with CPT-11. Methods: Twenty-five Asian patients with advanced cancer received CPT-11 as a 2-weekly 90-minute infusion (180 mg/m2) as part of the FOLFIRI regimen. Subjects were administered raltegravir 400 mg orally (as a UGT1A1 probe) and intravenous midazolam 1 mg (as a CYP3A4 probe) one day before the first dose of their chemotherapy. Blood sampling for drug concentrations was performed for 2 days after probe drug administration. Non-compartmental PK analyses were performed using WinNonLin. Genomic DNA was isolated and screened for the known genetic variants in UGT1A1*6. Results: One patient developed grade 3 diarrhea and 16 developed grade 3-4 neutropenia. The mean CPT-11 CL was 21.9 + 7.8L/h. SN-38G/SN-38 AUC ratio was highly correlated with Raltegravir glucuronide/ Raltegravir AUC ratio (r=0.784 p&lt;0.01). Midazolam CL was highly correlated with CPT-11 CL (r=0.563 p&lt;0.01). SN38 AUC correlated well with neutropenia (Log10Nadir Absolute Neutrophil Count (ANC) (r=-0.397 p&lt;0.05). Neither CPT-11 nor midazolam CL correlated with Log10 Nadir ANC. Of the 24 patients with genotyping of UGT1A1*6 done, 17 were wild type (GG), 7 heterozygotes (AG) and 0 were mutant (AA). No differences in toxicity or SN38 pharmacokinetics were observed in the UGT1A1*6 variants. Conclusions: Raltegravir glucuronide ratio is a good predictor of SN-38 glucuronidation, and has potential to predict neutropenia from FOLFIRI treatment. Prospective studies with dose adjustments should be done to develop raltegravir as a probe to optimize CPT-11 therapy.

Genotype‐directed, dose‐finding study of irinotecan in cancer patients with UGT1A1*28 and/or UGT1A1*6 polymorphisms

Irinotecan-induced severe neutropenia is associated with homozygosity for the UGT1A1*28 or UGT1A1*6 alleles. In this study, we determined the maximum-tolerated dose (MTD) of irinotecan in patients with UGT1A1 polymorphisms. Patients who had received chemotherapy other than irinotecan for metastatic gastrointestinal cancer were enrolled. Patients were divided into three groups according to UGT1A1 genotypes: wild-type (*1/*1); heterozygous (*28/*1, *6/*1); or homozygous (*28/*28, *6/*6, *28/*6). Irinotecan was given every 2 weeks for two cycles. The wild-type group received a fixed dose of irinotecan (150 mg/m(2)) to serve as a reference. The MTD was guided from 75 to 150 mg/m(2) by the continual reassessment method in the heterozygous and homozygous groups. Dose-limiting toxicity (DLT) and pharmacokinetics were evaluated during cycle 1. Of 82 patients enrolled, DLT was assessable in 79 patients (wild-type, 40; heterozygous, 20; and homozygous, 19). Dose-limiting toxicity occurred in one patient in the wild-type group, none in the heterozygous group, and six patients (grade 4 neutropenia) in the homozygous group. In the homozygous group, the MTD was 150 mg/m(2) and the probability of DLT was 37.4%. The second cycle was delayed because of neutropenia in 56.3% of the patients given the MTD. The AUC(0-24 h) of SN-38 was significantly greater (P < 0.001) and more widely distributed in the homozygous group. Patients homozygous for the UGT1A1*28 or UGT1A1*6 allele can receive irinotecan in a starting dose of 150 mg/m(2), but many required dose reductions or delayed treatment in subsequent cycles. UMIN Clinical Trial Registration number: UMIN000000618.