Kinase Inhibitors: The Reality Behind the Success

Tremendous progress has been made by utilizing kinase inhibitors in oncology, and these agents continue to pave the way into other areas of medicine. There are, however, many challenges to the application of kinase inhibitors due to inherent shortcomings of the drugs and lack of comprehensive understanding of tumor and disease biology. The future fate of kinase inhibitors, however, is bright, as evidenced from ongoing efforts to increase their efficacy while remediating their weaknesses in order to provide the best quality of care to patients.

Identification of OAT1/OAT3 as Contributors to Cisplatin Toxicity

Cisplatin is among the most widely used anticancer drugs and known to cause a dose‐limiting nephrotoxicity, which is partially dependent on the renal uptake carrier OCT2. We here report a previously unrecognized, OCT2‐independent pathway of cisplatin‐induced renal injury that is mediated by the organic anion transporters OAT1 and OAT3. Using transporter‐deficient mouse models, we found that this mechanism regulates renal uptake of a mercapturic acid metabolite of cisplatin that acts as a precursor of a potent nephrotoxin. The function of these two transport systems can be simultaneously inhibited by the tyrosine kinase inhibitor nilotinib through noncompetitive mechanisms, without compromising the anticancer properties of cisplatin. Collectively, our findings reveal a novel pathway that explains the fundamental basis of cisplatin‐induced nephrotoxicity, with potential implications for its therapeutic management.

Influence of OATP1B1 Function on the Disposition of Sorafenib-β-D-Glucuronide

The oral multikinase inhibitor sorafenib undergoes extensive UGT1A9-mediated formation of sorafenib-β-D-glucuronide (SG). Using transporter-deficient mouse models, it was previously established that SG can be extruded into bile by ABCC2 or follow a liver-to-blood shuttling loop via ABCC3-mediated efflux into the systemic circulation, and subsequent uptake in neighboring hepatocytes by OATP1B-type transporters. Here we evaluated the possibility that this unusual process, called hepatocyte hopping, is also operational in humans and can be modulated through pharmacological inhibition. We found that SG transport by OATP1B1 or murine Oatp1b2 was effectively inhibited by rifampin, and that this agent can significantly increase plasma levels of SG in wildtype mice, but not in Oatp1b2-deficient animals. In human subjects receiving sorafenib, rifampin acutely increased the systemic exposure to SG. Our study emphasizes the need to consider hepatic handling of xenobiotic glucuronides in the design of drug-drug interaction studies of agents that undergo extensive phase II conjugation.

Predicting transporter-mediated drug interactions: Commentary on: "Pharmacokinetic evaluation of a drug transporter cocktail consisting of digoxin, furosemide, metformin and rosuvastatin" and "Validation of a microdose probe drug cocktail for clinical drug interaction assessments for drug transporters and CYP3A"

Transporters, expressed in various tissues, govern the absorption, distribution, metabolism, and excretion of drugs, and consequently their inherent safety and efficacy profiles. Drugs may interact with a transporter as a substrate and/or an inhibitor. Understanding transporter-mediated drug-drug interactions (DDIs), in addition to enzyme-mediated DDIs, is an integral part of risk assessment in drug development and regulatory review because the concomitant use of more than one medication in patients is common.

Drug Transporters: Advances and Opportunities

Drug transporter research conducted over the last several decades has led to a greatly advanced understanding of the mechanisms underlying the principles of drug absorption and disposition. Although many transporters remain poorly characterized, there is ample evidence that the drug transporter field will ultimately provide vital support to routine patient management, and will play a key role in the discovery, development, and evaluation of innovative, cutting-edge therapies.

Inherited variation in OATP1B1 is associated with treatment outcome in acute myeloid leukemia

Using broad interrogation of clinically relevant drug absorption, distribution, metabolism, and excretion (ADME) genes on the DMET platform, we identified a genetic variant in SLCO1B1 (rs2291075; c.597C>T), encoding the transporter OATP1B1, associated with event-free (P = 0.006, hazard ratio = 1.74) and overall survival (P = 0.012, hazard ratio = 1.85) in children with de novo acute myeloid leukemia (AML). Lack of SLCO1B1 expression in leukemic blasts suggested the association might be due to an inherited rather than a somatic effect. rs2291075 was in strong linkage with known functional variants rs2306283 (c.388A>G) and rs4149056 (c.521T>C). Functional studies in vitro determined that four AML-directed chemotherapeutics (cytarabine, daunorubicin, etoposide, and mitoxantrone) are substrates for OATP1B1 and the mouse ortholog Oatp1b2. In vivo pharmacokinetic studies using Oatp1b2-deficient mice further confirmed our results. Collectively, these findings demonstrate an important role for OATP1B1 in the systemic pharmacokinetics of multiple drugs used in the treatment of AML and suggest that inherited variability in host transporter function influences the effectiveness of therapy.

ABCC4 Is a Determinant of Cytarabine-Induced Cytotoxicity and Myelosuppression

Resistance to cytarabine remains a major challenge in the treatment of acute myeloid leukemia (AML). Based on previous studies implicating ABCC4/MRP4 in the transport of nucleosides, we hypothesized that cytarabine is sensitive to ABCC4‐mediated efflux, thereby decreasing its cytotoxic response against AML blasts. The uptake of cytarabine and its monophosphate metabolite was found to be facilitated in ABCC4‐expressing vesicles and intracellular retention was significantly impaired by overexpression of human ABCC4 or mouse Abcc4 (P < 0.05). ABCC4 was expressed highly in AML primary blasts and cell lines, and cytotoxicity of cytarabine in cells was increased in the presence of the ABCC4 inhibitors MK571 or sorafenib, as well as after ABCC4 siRNA. In Abcc4‐null mice, cytarabine‐induced hematological toxicity was enhanced and ex vivo colony‐forming assays showed that Abcc4‐deficiency sensitized myeloid progenitors to cytarabine. Collectively, these studies demonstrate that ABCC4 plays a protective role against cytarabine‐mediated insults in leukemic and host myeloid cells.

Conjunctive therapy of cisplatin with the OCT2 inhibitor cimetidine: influence on antitumor efficacy and systemic clearance

The organic cation transporter 2 (OCT2) regulates uptake of cisplatin in proximal tubules, and inhibition of OCT2 protects against severe cisplatin-induced nephrotoxicity. However, it remains uncertain whether potent OCT2 inhibitors, such as cimetidine, can influence the antitumor properties and/or disposition of cisplatin. Using an array of preclinical assays, we found that cimetidine had no effect on the uptake and cytotoxicity of cisplatin in ovarian cancer cells with high OCT2 mRNA levels (IGROV-1 cells). Moreover, the antitumor efficacy of cisplatin in mice bearing luciferase-tagged IGROV-1 xenografts was unaffected by cimetidine (P = 0.39). Data obtained in 18 patients receiving cisplatin (100 mg/m(2)) in a randomized crossover fashion with or without cimetidine (800 mg × 2) revealed that cimetidine did not alter exposure to unbound cisplatin, a marker of antitumor efficacy (4.37 vs. 4.38 µg·h/ml; P = 0.86). These results support the future clinical exploration of OCT2 inhibitors as specific modifiers of cisplatin-induced nephrotoxicity.

OATP1B1 polymorphism as a determinant of erythromycin disposition

Previous studies have demonstrated that the pharmacokinetic profile of erythromycin, a probe for CYP3A4 activity, is affected by inhibitors or inducers of hepatic solute carriers. We hypothesized that these interactions are mediated by OATP1B1 (gene symbol, SLCO1B1), a polypeptide expressed on the basolateral surface of hepatocytes. Using stably transfected Flp-In T-Rex293 cells, erythromycin was found to be a substrate for OATP1B1*1A (wild type) with a Michaelis-Menten constant of ~13 µmol/l, and that its transport was reduced by ~50% in cells expressing OATP1B1*5 (V174A). Deficiency of the ortholog transporter Oatp1b2 in mice was associated with a 52% decrease in the metabolic rate of erythromycin (P = 0.000043). In line with these observations, in humans the c.521T>C variant in SLCO1B1 (rs4149056), encoding OATP1B1*5, was associated with a decline in erythromycin metabolism (P = 0.0072). These results suggest that impairment of OATP1B1 function can alter erythromycin metabolism, independent of changes in CYP3A4 activity.

Environmental and genetic factors affecting transport of imatinib by OATP1A2

The bioavailability of orally administered imatinib is >90%, although the drug is monocationic under the acidic conditions in the duodenum. In vitro, we found that imatinib is transported by the intestinal uptake carrier organic anion transporting polypeptide (OATP1A2) and that this process is sensitive to pH, rosuvastatin, and genetic variants. However, in a study in patients with cancer, imatinib absorption was not associated with OATP1A2 variants and was unaffected by rosuvastatin. These findings highlight the importance of verifying in a clinical setting the drug-transporter interactions observed in in vitro tests.

Effect of ABCC2 (MRP2) transport function on erythromycin metabolism

The macrolide antiobiotic erythromycin undergoes extensive hepatic metabolism and is commonly used as a probe for cytochrome P450 (CYP) 3A4 activity. By means of a transporter screen, erythromycin was identified as a substrate for the transporter ABCC2 (MRP2) and its murine ortholog, Abcc2. Because these proteins are highly expressed on the biliary surface of hepatocytes, we hypothesized that impaired Abcc2 function may influence the rate of hepatobiliary excretion and thereby enhance erythromycin metabolism. Using Abcc2 knockout mice, we found that Abcc2 deficiency was associated with a significant increase in erythromycin metabolism, whereas murine Cyp3a protein expression and microsomal Cyp3a activity were not affected. Next, in a cohort of 108 human subjects, we observed that homozygosity for a common reduced-function variant in ABCC2 (rs717620) was also linked to an increase in erythromycin metabolism but was not correlated with the clearance of midazolam. These results suggest that impaired ABCC2 function can alter erythromycin metabolism, independent of changes in CYP3A4 activity.

Influence of solute carriers on the pharmacokinetics of CYP3A4 probes

We hypothesized that the assessment of baseline CYP3A4 activity is influenced by probe-specific differences in hepatocellular uptake mechanisms. There was no significant correlation between the erythromycin breath test (ERMBT) parameters and midazolam clearance in 30 cancer patients (R(2) < 0.01), regardless of their CYP3A5 genotype status. In cellular models overexpressing 10 different solute carriers, erythromycin uptake was significantly increased by OATP1A2 (P < 0.005) and OATP1B3 (P < 0.01). Midazolam was not a substrate for any of the tested transporters. In a separate cohort of 119 patients, 6 nonsynonymous variants in the OATP1B3 gene SLCO1B3 were identified. Individuals carrying two copies of the T allele at the 334 locus had a 2.4-fold lower value for ERMBT 1/T(max) (P = 0.001), a measure reflecting more rapid hepatic uptake. These findings suggest that differential affinities for solute carriers should be considered when selecting an appropriate phenotypic probe to allow tailored dosing of pharmaceuticals that are CYP3A4 substrates.

Modulation of erlotinib pharmacokinetics in mice by a novel cytochrome P450 3A4 inhibitor, BAS 100

Administration of BAS 100, a novel mechanism-based CYP3A4 inhibitor isolated from grapefruit juice, resulted in a 2.1-fold increase in erlotinib exposure following oral administration to wild-type and humanised CYP3A4 transgenic mice. This study illustrates the potential of BAS 100 to increase the low and variable oral bioavailability of erlotinib in cancer patients.

Germline polymorphisms in EGFR and survival in patients with lung cancer receiving gefitinib

The purpose of this study was to evaluate associations between germline epidermal growth factor receptor (EGFR) variants involved in transcriptional regulation and overall survival in white patients with non-small-cell lung cancer (NSCLC) treated with the EGFR tyrosine kinase inhibitor, gefitinib. Of 175 consecutive patients treated with oral gefitinib (250 mg/day), 170 (median age: 67 years; 72% men) were evaluable for genotyping and survival. Fifty-five patients (33%) had stable disease and 17 (10%) had an objective response. The most common of four haplotypes was G-C (EGFR*1) at the EGFR -216G>T and -191C>A loci (frequency, 0.45). After adjusting for performance status, previous platinum-containing chemotherapy and occurrence of skin rash or diarrhea during the first treatment cycle in patients with performance status 0 or 1 (N=139), the absence of EGFR*1 was associated with significantly better survival (hazard ratio: 0.54; 95% confidence interval: 0.32-0.91; P=0.015). The results may help identify patients with NSCLC who can benefit from gefitinib treatment.

Cigarette smoking during irinotecan therapy: Effects on pharmacokinetics and neutropenia

2506

Background: Irinotecan is mainly metabolized by CYP3A-mediated oxidation to form inactive substances and by esterase- cleavage to form its active metabolite SN-38, which is further conjugated by UGT1A-isozymes. Variability in the pharmacokinetics of irinotecan is extensive and largely unexplained. Several constituents of cigarette smoke are known to interact with drug metabolizing enzymes, e.g. CYPs and UGTs, and potentially affect treatment outcome with substrate drugs. Here, we retrospectively explored the effects of cigarette smoking on the pharmacokinetics and adverse effects of irinotecan. Methods: A total of 190 patients (49 smokers and 141 non-smokers) were eligible and had received irinotecan as a 3-weekly 90-minute infusion. Individual pharmacokinetic parameters were obtained using NONMEM. Complete toxicity data were available in a subset of 134 patients receiving the registered dose of 350 mg/m2 irinotecan or its flat- fixed dose-equivalent of 600 mg. Results: In smokers, the dose-normalized area under the plasma-concentration versus time curve of irinotecan was significantly lower (15% reduction: median, 28.7 versus 33.9 ng×h/mL/mg; P =.001) compared with non-smokers. In addition, smokers showed an almost 40% lower exposure to SN-38 (median, 0.54 versus 0.87 ng×h/mL/mg; P<.001), and a higher relative extent of glucuronidation of SN-38 into SN-38G (median, 6.6 versus 4.5; P=.006). Smokers experienced considerable less hematological toxicity. In particular, the incidence of grade 3–4 neutropenia was 6% in smokers versus 38% in non-smokers (OR, 0.10; 95%CI, 0.02–0.43; P<.001). There was a non-significant 60% lower incidence of delayed-onset diarrhea in smokers (6% versus 15%; OR, 0.34; 95%CI, 0.07–1.57; P=.149). Conclusions: This study indicates that smoking cigarettes significantly affects both the pharmacokinetic and toxicity profile of irinotecan. Although the underlying mechanism is not entirely clear, modulation of CYP3A and UGT1A may be part of the explanation. The data suggest that further investigation is warranted to determine whether smokers are at increased risk for treatment failure indeed, as is suggested by the lower exposure to the active metabolite SN-38 and by the lower incidence of SN-38 exposure related neutropenia in smokers.

No significant financial relationships to disclose.

Irinotecan-induced diarrhea: functional significance of the polymorphic ABCC2 transporter protein

Interindividual pharmacokinetic variability of the anticancer agent irinotecan is high. Life-threatening diarrhea is observed in up to 25% of patients receiving irinotecan and has been related with irinotecan pharmacokinetics and UGT1A1 genotype status. Here, we explore the association of ABCC2 (MRP2) polymorphisms and haplotypes with irinotecan disposition and diarrhea. A cohort of 167 Caucasian cancer patients who were previously assessed for irinotecan pharmacokinetics (90-min infusion given every 21 days), toxicity, and UGT1A1*28 genotype were genotyped for polymorphisms in ABCC2 using Pyrosequencing. Fifteen ABCC2 haplotypes were identified in the studied patients. The haplotype ABCC2*2 was associated with lower irinotecan clearance (28.3 versus 31.6 l/h; P=0.020). In patients who did not carry a UGT1A1*28 allele, a significant reduction of severe diarrhea was noted in patients with the ABCC2*2 haplotype (10 versus 44%; odds ratio, 0.15; 95% confidence interval, 0.04-0.61; P=0.005). This effect was not observed in patients with at least one UGT1A1*28 allele (32 versus 20%; odds ratio, 1.87; 95% confidence interval, 0.49-7.05; P=0.354). This study suggests that the presence of the ABCC2*2 haplotype is associated with less irinotecan-related diarrhea, maybe as a consequence of reduced hepatobiliary secretion of irinotecan. As the association was seen in patients not genetically predisposed at risk for diarrhea due to UGT1A1*28, confirmatory studies of the relationships of ABCC2 genotypes and irinotecan disposition and toxicity are warranted.

Variants in the SLCO1B3 Gene: Interethnic Distribution and Association with Paclitaxel Pharmacokinetics

To explore retrospectively the relationships between paclitaxel pharmacokinetics and three known, non-synonymous single-nucleotide polymorphisms (SNPs) in SLCO1B3, the gene encoding organic anion transporting polypeptide (OATP)1B3. Accumulation of [(3)H]paclitaxel was studied in Xenopus laevis oocytes injected with cRNA of Oatp1b2, OATP1A2, OATP1B1, OATP1B3, OAT1, OAT3, OCT1, and NTCP. The 334T>G (Ser112Ala), 699G>A (Met233Ile), and 1564G>T (Gly522Cys) loci of SLCO1B3 were screened in 475 individuals from five ethnic groups and 90 European Caucasian cancer patients treated with paclitaxel. Only OATP1B3 was capable of transporting paclitaxel to a significant extent (P=0.003). The 334T>G and 699G>A SNPs were less common in the African-American and Ghanaian populations (P<0.000001). Paclitaxel pharmacokinetics were not associated with the studied SNPs or haplotypes (P>0.3). The studied SNPs in SLCO1B3 appear to play a limited role in the disposition of paclitaxel, although their clinical significance in other ethnic populations remains to be investigated.

Dexamethasone as a probe for CYP3A4 metabolism: evidence of gender effect

BACKGROUND

A study was conducted to evaluate prospectively the correlation between docetaxel clearance and pharmacokinetics of dexamethasone previously obtained in 21 patients.

PATIENTS AND METHODS

Dexamethasone pharmacokinetics were performed in 17 patients 24 h before docetaxel treatment as monochemotherapy. Dexamethasone and docetaxel plasma concentrations were determined by HPLC methods. Determination of docetaxel unbound fraction in plasma was performed using microequilibrium dialysis.

RESULTS

Significant correlation was observed between observed plasma docetaxel clearances (CL(docetaxel)) and values predicted from dexamethasone plasma clearance (CL(dexa)), unbound plasma docetaxel fraction estimated from serum alpha1-acid glycoprotein level (fu(alpha1-AAG)), and hepatic metastasis status. However, after splitting of the prospective data set according to gender, no correlation was observed for males (R(2) = 0.08, NS, n = 10), then strong correlation was observed for females (R(2) = 0.78, P < 0.01, n = 7). Multivariate analysis was performed from data obtained in the women included in the first study and those of this prospective study (n = 18). Docetaxel CL was significantly correlated with CL(dexa) (P = 0.001) and fu(alpha1-AAG) (P = 0.01) according to the relationship (with +/-95% confidence intervals): CL(docetaxel) (l/h) = 1.92 (+/-0.94) x CL(dexa) (l/h) + 2.68 (+/-1.95) x fu(alpha1-AAG) (%) (R(2) = 0.68).

CONCLUSION

Dexamethasone may be used to predict docetaxel clearances in females, but not in males.

Pharmacogenetic influence of OATP1B1 variants *1b and *15 on irinotecan disposition in Asian and Caucasian cancer patients

13069

Background: The objective of this study was to evaluate the impact of OATP1B1 (SLCO1B1; OATP-C) functional variants on the disposition of irinotecan in Asian and Caucasian cancer patients. Methods: Irinotecan pharmacokinetic parameters and OATP1B1*1a, *1b, *5 and *15 genotyping data were obtained from Asian (N=71) and Caucasian (N=30) cancer patients receiving the drug as a 90-minute i.v. infusion. Genotypic-phenotypic correlations were assessed in cancer patients from each ethnic group. Results: The *1a/*1a genotype and the *15/*15 diplotype were absent in Caucasian cancer patients but present in Asians (*1a/*1a, N=6; *15/*15, N=1). Statistically insignificant differences were observed between patients carrying *1a/*1b and *1b/*1b genotypes and also between *1b/*15, *15/*15 and *15/*15 diplotypes. Compared to wild-type patients (N=6), total irinotecan clearance normalized by BSA was 2- and 3-fold lower in Asian patients carrying at least one *1b (*1a/*1b + *1b/*1b; N=54; P=0.055) and one *15 (*1b/*15 + *5/*15 + *15/*15; N=11; P=0.001) allele, respectively. Significant differences were also present between Asian patients carrying the *15 diplotype and wild-type patients with regard to exposure levels (Cmax/dose/BSA) to irinotecan (P=0.007), SN-38 (P=0.009) and SN-38G (P=0.004) as well as REC (P=0.005) and REG (0.001). The REG was 5-fold (P=0.022) and 27-fold (P=0.001) lower in Asian cancer patients carrying at least one *1b allele and at least one *15 haplotype, respectively, when compared with wild-type patients. No significant differences in pharmacokinetic parameters were found when comparing Caucasian cancer patients carrying at least one *1b allele and those carrying at least one *15 allele (P>0.05). Conclusions: The genotype and diplotype frequencies of the studied OATP1B1 variants were ethnically dependent, and OATP1B1 genotype status accounts, at least in part, for the observed differences in irinotecan disposition in Asian cancer patients. The lack of significant influence of OATP1B1 variants on irinotecan disposition in Caucasian cancer patients is not clear but may have resulted from the small patient population.

No significant financial relationships to disclose.

A pharmacokinetic study of Genetaxyl (G) together with cyclosporin A (CsA) administered orally in cancer patients

12002

Background: Oral administration of paclitaxel given with CsA has shown promising activity in Phase II trials, but the apparent bioavailability is low and dose-dependent due to the presence of high concentrations of Cremophor EL (CrEL). We hypothesized that the use of a novel oral paclitaxel formulation containing only 20% CrEL (Genetaxyl [G]; Genovate Biotechnology Ltd., Taiwan), given with CsA is associated with an improved pharmacokinetic (PK) profile. Methods: Cohorts of 6 patients with cancer were treated with oral G at a dose of 60, 120, or 180 mg/m2 and 10 mg/kg of oral CsA in cycle 1. In cycle 2, patients received IV G (175 mg/m2, 3-h infusion). Three additional patients received generic IV paclitaxel (GIP). Serial blood samples were analyzed by LC/MS/MS and equilibrium dialysis, to determine total and unbound paclitaxel PK. Results: The mean (± SD) total paclitaxel AUCs were 1299±189, 1682±636, and 2204±1407 ng.h/mL at the 3 consecutive dose levels, suggesting nonlinear PK. However, based on unbound AUC, the oral bioavailability was dose-independent (P=.62), with a mean value of 37.2±18.6% (n=15). As expected, the total paclitaxel AUC following IV G (9024±4648 ng·h/mL) was lower than that for IV GIP (13,732±3983 ng·h/mL), as a result of increased clearance (39.6 vs 18.3 L/h) and a larger volume of distribution (768 vs 268 L). Interestingly, the unbound paclitaxel AUC was similar between the two IV formulations (P=.25), as the ratio of unbound/total paclitaxel for G was 2.5 times higher than that for GIP (12.5 vs 4.9%). Toxicity profiles were mild, with only 2 patients experiencing ≥ Gr 3 myelosuppression following oral G at 180 mg/m2. Conclusions: The mean bioavailability of paclitaxel following oral Genetaxyl with CsA was about 37%, which is higher than that observed previously with paclitaxel (range, 21–31%). Further clinical exploration of oral Genetaxyl in taxane-sensitive diseases is warranted.

[Table: see text]

Phase I trial of the oral histone deacetylase inhibitor MS-275 administered with food

13036

Background: The histone deacetylase (HDAC) inhibitor MS-275, a synthetic benzamide derivative, has demonstrated antitumor activity in vitro & in vivo. After determining maximum tolerable dose (MTD = 2 mg/m2) & dose limiting toxicity (DLT) for MS-275 given to fasting patients (pts) weekly ×4 q6 weeks, we explored toxicity profile, MTD, & pharmacokinetics (PK) of MS-275 when given po on the same schedule with food. Methods: MS-275 at 2, 4, or 6 mg/m2 was administered to pts with advanced malignancy & PS ≤2, LFTs ≤2.5 × normal, adequate hematopoietic & renal function, & normal resting MUGA. PK samples were analyzed by LC-MS. Data for pts in the fed state were compared to data obtained in previous cohorts of pts treated in the fasting state. Protein acetylation assessed by a novel flow cytometric assay & HDAC enzymatic activity were measured in peripheral blood mononuclear cells (PBMC). Results: 16 pts received a median of 2 cycles (1–5) of MS-275 2–6 mg/m2 with food. No DLT occurred on 2 or 6 mg/m2 (n = 3 each), while 1 pt on 4 mg/m2 (n = 10) had a DLT: grade 3 hypophosphatemia. For 2–6 mg/m2 other grade 3 toxicities were neutropenia & lymphopenia. Grade 1–2 toxicities in >1 pt were leucopenia, anemia, thrombocytopenia, fatigue, nausea, vomiting, headache, hypoalbuminemia, hypophosphatemia, hyponatremia, & hypocalcemia. MTD has not been reached; current dose level is 8 mg/m2. Comparing PK for fasting & fed pts on 2–4 mg/m2, there was no difference in Tmax (0.5h); average Cmax & AUC were 35% & 25% lower, respectively, in fed pts; this difference is not statistically significant. Interindividual variability in exposure to MS-275 increased from 52% in fasting pts to 100% in fed pts. PBMC protein acetylation & HDAC inhibition were seen at all dose levels (2–6 mg/m2) in fed pts. Of 9 pts evaluable for response (2–4 mg/m2), 2 of 6 pts on 4 mg/m2 had stable disease. Conclusions: MTD has not yet been established for MS-275 given with food on this schedule but is ≥4 mg/m2 weekly x4 q6 weeks. Interindividual variability in exposure increases with food. Whether intestinal absorption is decreased when MS-275 is given with food requires further evaluation with additional patients. Drug-related protein hyperacetylation & HDAC inhibition were observed.

[Table: see text]

Phase I study of lenalidomide, a novel thalidomide analog, in patients with refractory metastatic cancer

13038

Background: Lenalidomide (L), CC5013, is a thalidomide (T) analog that has shown activity in multiple myeloma and myelodysplastic syndromes (MDS); including activity in pts refractory to T. Preclinical studies suggest L has more potent immunomodulatory and antiangiogenic activity than T. We have conducted a phase I clinical trial of L to determine the maximum-tolerated dose (MTD), characterize the side-effects, characterize pharmacokinetics (PK) in pts with solid tumors. Methods: Pts with refractory metastatic cancer were treated on a modified Fibonacci dose-escalation scheme with an oral daily dose of L. Therapy was continued until MTD or disease progression. Results: Forty-five pts have been enrolled (M/F: 37/8). Median age 68 yrs (range, 25–89 yrs). Tumor types include prostate cancer (36 pts), adrenal carcinoma (3 pt), renal cell carcinoma (1 pt), choleangiocarcinoma (1 pt), small intestine cancer (1 pt), colon cancer (2 pt), and melanoma (1 pt). Dose levels were: 5 mg (n = 3), 10 mg (n = 6), 15 mg (n = 3), 20 mg (n = 3 + 7), 25 mg (n = 6), 30 mg (n = 8), 35 mg (n = 6) and 40 mg (n = 3). Due to side effects the dosing schedule was modified from daily dosing to daily dosing for 21 out of 28 days. Therapy has been well tolerated with most frequent gr 1 and gr 2 toxicities include nausea (43%), myalgia (38%), pruritis/rash (54%), and fatigue (38%), neutropenia (30%) with gr 3 diarrhea (n = 1), hypotension (n = 1), pulmonary effusions (n = 1), thromboses (n = 2) and gr 4 neutropenia (n = 2), arrhythmias (n = 1), hemolysis (n = 1). Dose escalation continues. There were no differences observed between dose levels for either oral clearance values (p = 0.47) or the apparent volume of distribution (Vz) values (p = 0.23). Dose-normalized AUC(0-∞), dose-normalized peak concentrations (Cmax), or half-life (t1/2) did not vary between dose levels (p > 0.12). Conclusion: L has been well tolerated up to 35 mg/d (21 days on; 7 days off), doses higher than the recently FDA-approved doses of 5 and 10 mg/d. In this dose range L exhibits linear PK. Tolerability to myelosuppression the dose-limiting toxicity in pts with MDS may therefore be improved in pts without hematological malignancies.

No significant financial relationships to disclose.

Prophylactic treatment of irinotecan-induced diarrhea with neomycin (a randomized, placebo-controlled, double-blind study)

3626

Background: Delayed-type diarrhea is a common side-effect of irinotecan, and is associated with a bacterial-mediated formation of the active irinotecan metabolite SN-38 from its glucuronide conjugate in the intestines. We hypothesized that concomitant administration of the aminoglycoside antibiotic neomycin would diminish exposure of the gut to SN-38, ameliorating the incidence of diarrhea. Methods: Patients were treated with irinotecan in a randomized, placebo-controlled, double-blind trial. In arm A, patients received irinotecan (350 mg/m2 i.v. for 90 minutes once every 3 weeks) combined with neomycin (660 mg orally 3 times daily for 3 consecutive days, starting 2 days before chemotherapy). In arm B, patients received the same irinotecan regimen with placebo. To detect a 50% reduction to less than grade 2 diarrhea (power=.80; P=.05), 60 patients had to be studied. Blood samples for additional pharmacokinetic and pharmacogenetic analyses were obtained after separate informed consent. Results: Sixty-two patients were evaluable for toxicity analysis. Relevant baseline patient characteristics (P>.06), SN-38 plasma concentrations (P=.80; N=43), and UGT1A1*28 genotype status (P=.58; N=52) were similar in both arms. Distribution, severity, and duration of diarrhea did not differ significantly between both arms (P>.32), although grade 3 diarrhea tended to be less frequent in the neomycin arm (45% reduction; P=.19). Grade 2 nausea was more common in this arm (39% vs. 9%; P<.01). The presence of at least one UGT1A1*28 allele was strongly related to the incidence of grade 2–3 diarrhea (69% vs. 34%; P=.01). Conclusions: Our results do not suggest a role for neomycin in the prophylactic treatment of irinotecan-induced diarrhea. In addition, neomycin does not influence systemic SN-38 pharmacokinetics. Also, it is suggested that each patient’s UGT1A1*28 genotype status could be used as a prospective screening tool to prevent severe diarrhea.

No significant financial relationships to disclose.

Potential for improvement of docetaxel-based chemotherapy: a pharmacological review

Since the introduction of docetaxel, research has focused on various approaches to overcome treatment limitations and improve outcome. This review discusses the pharmacological attempts at treatment optimisation, which include reducing interindividual pharmacokinetic and pharmacodynamic variability, optimising schedule, route of administration, reversing drug resistance and the development of structurally related second-generation taxanes.

A phase I and pharmacologic study of the MDR converter GF120918 in combination with doxorubicin in patients with advanced solid tumors

BACKGROUND

Resistance to chemotherapy can partly be explained by the activity of membrane bound P-glycoprotein. Competitive inhibition of P-glycoprotein, by multidrug resistance (MDR) converters, may overcome this MDR. Previously studied MDR converters either have serious intrinsic side effects or considerably influence the pharmacokinetics of cytotoxic agents at concentrations theoretically required to convert MDR. GF120918 is a third-generation MDR converter with high affinity for P-glycoprotein and can be given orally. We performed a phase 1 study with escalating doses of GF120918 in combination with doxorubicin.

PATIENTS AND METHODS

The study group comprised 46 patients with advanced solid tumors. Doxorubicin was administered on day 1 (cycle 1), GF120918 on days 22-24 (cycle 2), and on days 29-33 with doxorubicin administered on day 31 (cycle 3). Pharmacokinetics of both GF120918 and doxorubicin were studied. The starting daily dose of GF120918 was 50 mg and was to be increased in subsequent cohorts until a steady state plasma level of 100 ng/ml was reached. The starting dose of doxorubicin was 50 mg/m2 and was to be increased after reaching the target dose level of GF120918.

RESULTS

In 37 of the 46 patients, full pharmacokinetic data from the three scheduled cycles were obtained. Pharmacokinetics of GF120918 showed a less than linear increase in Cmax with increasing doses, with considerable interpatient variation. The target steady-state plasma level for GF120918 was exceeded in 12 out of 19 patients who received 400 mg GF120918 alone twice daily and in 12 of 17 patients who received 400 mg GF120918 twice daily in combination with doxorubicin. GF120918 pharmacokinetics were not influenced by coadministration of doxorubicin. The doxorubicin AUC was only marginally influenced by GF120918 and only at the highest dose levels. In these patients there was a significant increase in the AUC of doxorubicinol in cycle 3 as compared to cycle 1. Hematologic toxicity mainly consisted of neutropenia and was more severe in cycle 3 than in cycle 1 (13 vs 5 patients with grade 4 neutropenia, P=0.003). Neutropenic fever was the dose-limiting toxicity at a doxorubicin dose of 75 mg/m2 with 400 mg GF120918 twice daily. The toxicity of GF120918 was limited to somnolence in eight patients and occasional gastrointestinal complaints.

CONCLUSION

GF120918 is an MDR converter with only minimal side effects at a dose level yielding concentrations able to convert the action of P-glycoprotein in vitro. A doxorubicin dose of 60 mg/m2 on day 3 in combination with 400 mg GF120918 twice daily on days 1-5 is an acceptable regimen for further clinical trials.