Muvalaplin, an Oral Small Molecule Inhibitor of Lipoprotein(a) Formation: A Randomized Clinical Trial

Importance

Lipoprotein(a) (Lp[a]) is associated with atherosclerotic disease and aortic stenosis. Lp(a) forms by bonding between apolipoprotein(a) (apo[a]) and apo B100. Muvalaplin is an orally administered small molecule that inhibits Lp(a) formation by blocking the apo(a)-apo B100 interaction while avoiding interaction with a homologous protein, plasminogen.

Objective

To determine the safety, tolerability, pharmacokinetics, and pharmacodynamic effects of muvalaplin.

Design, Setting, and Participants

This phase 1 randomized, double-blind, parallel-design study enrolled 114 participants (55 assigned to a single-ascending dose; 59 assigned to a multiple-ascending dose group) at 1 site in the Netherlands.

Interventions

The single ascending dose treatment evaluated the effect of a single dose of muvalaplin ranging from 1 mg to 800 mg or placebo taken by healthy participants with any Lp(a) level. The multiple ascending dose treatment evaluated the effect of taking daily doses of muvalaplin (30 mg to 800 mg) or placebo for 14 days in patients with Lp(a) levels of 30 mg/dL or higher.

Main Outcomes and Measures

Outcomes included safety, tolerability, pharmacokinetics, and exploratory pharmacodynamic biomarkers.

Results

Among 114 randomized (55 in the single ascending dose group: mean [SD] age, 29 [10] years, 35 females [64%], 2 American Indian or Alaska Native [4%], 50 White [91%], 3 multiracial [5%]; 59 in the multiple ascending dose group: mean [SD] age 32 [15] years; 34 females [58%]; 3 American Indian or Alaska Native [5%], 6 Black [10%], 47 White [80%], 3 multiracial [5%]), 105 completed the trial. Muvalaplin was not associated with tolerability concerns or clinically significant adverse effects. Oral doses of 30 mg to 800 mg for 14 days resulted in increasing muvalaplin plasma concentrations and half-life ranging from 70 to 414 hours. Muvalaplin lowered Lp(a) plasma levels within 24 hours after the first dose, with further Lp(a) reduction on repeated dosing. Maximum placebo-adjusted Lp(a) reduction was 63% to 65%, resulting in Lp(a) plasma levels less than 50 mg/dL in 93% of participants, with similar effects at daily doses of 100 mg or more. No clinically significant changes in plasminogen levels or activity were observed.

Conclusion

Muvalaplin, a selective small molecule inhibitor of Lp(a) formation, was not associated with tolerability concerns and lowered Lp(a) levels up to 65% following daily administration for 14 days. Longer and larger trials will be required to further evaluate safety, tolerability, and effect of muvalaplin on Lp(a) levels and cardiovascular outcomes.

Trial Registration

ClinicalTrials.gov Identifier: NCT04472676.

Abemaciclib does not increase the corrected QT interval in healthy participants

Abemaciclib is an orally administered, potent, and selective small molecule inhibitor of cyclin-dependent kinases 4 and 6, approved for advanced or metastatic breast cancer. This study aimed to use an exposure-response approach to investigate the effect of abemaciclib and its active metabolites (M2 and M20) on QTc interval and delay in cardiac repolarization at clinically relevant exposures. This was a single-blind, randomized, and placebo-controlled study of ascending doses of abemaciclib. Thirty-five healthy participants were administered a single dose of 200-600 mg abemaciclib. Twelve-lead electrocardiogram tracings and pharmacokinetic samples were collected serially pre- and post-dose. The primary objective was to study the relationship between abemaciclib and its active metabolites (M2 and M20) and QTc interval following ascending oral doses of abemaciclib. The secondary objective included evaluating the safety and tolerability of single ascending doses of abemaciclib in healthy participants. Exposure-response analysis demonstrated that there was no significant relationship between placebo-corrected change from baseline QTcF (ΔΔQTcF), abemaciclib, and metabolite plasma concentrations. Additionally, the ΔΔQTcF slopes of abemaciclib, its metabolites, and total analyte concentrations were not statistically different from zero. Single doses of abemaciclib, up to 400 mg, were well-tolerated by healthy participants; however, at the 600 mg dose (three times the highest registered dose), the frequency and severity of treatment-related gastrointestinal events (primarily diarrhea, nausea, and vomiting) increased. In conclusion, single doses of abemaciclib, up to 400 mg, had no statistically or clinically relevant effects on QTc, and abemaciclib was well tolerated up to a dose of 400 mg in this study.

Abemaciclib in combination with endocrine therapy for East Asian patients with HR+, HER2- advanced breast cancer: MONARCH 2 & 3 trials

This post hoc analysis of MONARCH 2 and MONARCH 3 assesses the efficacy, safety, and pharmacokinetics (PK) of abemaciclib in combination with endocrine therapy (ET) in East Asian patients with hormone receptor positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer. MONARCH 2 and MONARCH 3 are global, randomized, double-blind, phase 3 studies of abemaciclib/placebo + fulvestrant and abemaciclib/placebo + nonsteroidal aromatase inhibitor (NSAI, anastrozole or letrozole), respectively. The East Asian population comprised 212 (31.7%) of the 669 intent-to-treat (ITT) population in the MONARCH 2 trial and 144 (29.2%) of the 493 ITT patients in the MONARCH 3 trial. In the East Asian population, median progression-free survival (PFS) was significantly prolonged in the abemaciclib arm compared with placebo in both MONARCH 2 (hazard ratio [HR], 0.520; 95% confidence interval [CI], 0.362 to 0.747; P < .001; median: 21.2 vs 11.6 months) and MONARCH 3 (HR, 0.326; 95% CI, 0.200 to 0.531, P < .001; median: not reached vs 12.82 months). Diarrhea (MONARCH 2: 90%; MONARCH 3: 88%) and neutropenia (MONARCH 2: 68%; MONARCH 3: 58%) were the most frequent adverse events observed in the East Asian populations. Abemaciclib exposures and PK were similar in East Asians and the non-East Asian populations of both trials. Abemaciclib in combination with ET in the East Asian populations of MONARCH 2 and MONARCH 3 provided consistent results with the ITT populations, demonstrating improvements in efficacy with generally tolerable safety profiles for patients with HR+, HER2- advanced breast cancer.

Development and Application of a Mechanistic Population Modeling Approach to Describe Abemaciclib Pharmacokinetics

Abemaciclib is an oral anticancer drug that inhibits cyclin dependent kinases 4 and 6 and is metabolized by cytochrome P450 3A in the intestines and liver to active metabolites. The objectives were (1) to develop a mechanistic model to characterize the pharmacokinetics (PK) of the active moieties and investigate the effect of patient factors and (2) apply the model to dat from two phase III breast cancer trials of abemaciclib in combination with endocrine therapy. To develop the model, data from seven phase I studies and two phase II studies including 421 patients with cancer and 65 healthy individuals were pooled for nonlinear mixed effects modeling. The PK was similar between patients and healthy subjects, and the effects of diarrhea, formulation, race, and patient covariates on exposure were negligible. Application of the model confirmed its predictive performance and that abemaciclib PK did not change when coadministered with endocrine therapy.

Predicting Clinical Effects of CYP3A4 Modulators on Abemaciclib and Active Metabolites Exposure Using Physiologically Based Pharmacokinetic Modeling

Abemaciclib, a selective inhibitor of cyclin‐dependent kinases 4 and 6, is metabolized mainly by cytochrome P450 (CYP)3A4. Clinical studies were performed to assess the impact of strong inhibitor (clarithromycin) and inducer (rifampin) on the exposure of abemaciclib and active metabolites. A physiologically based pharmacokinetic (PBPK) model incorporating the metabolites was developed to predict the effect of other strong and moderate CYP3A4 inhibitors and inducers. Clarithromycin increased the area under the plasma concentration‐time curve (AUC) of abemaciclib and potency‐adjusted unbound active species 3.4‐fold and 2.5‐fold, respectively. Rifampin decreased corresponding exposures 95% and 77%, respectively. These changes influenced the fraction metabolized via CYP3A4 in the model. An absolute bioavailability study informed the hepatic and gastric availability. In vitro data and a human radiolabel study determined the fraction and rate of formation of the active metabolites as well as absorption‐related parameters. The predicted AUC ratios of potency‐adjusted unbound active species with rifampin and clarithromycin were within 0.7‐ and 1.25‐fold of those observed. The PBPK model predicted 3.78‐ and 7.15‐fold increases in the AUC of the potency‐adjusted unbound active species with strong CYP3A4 inhibitors itraconazole and ketoconazole, respectively; and 1.62‐ and 2.37‐fold increases with the concomitant use of moderate CYP3A4 inhibitors verapamil and diltiazem, respectively. The model predicted modafinil, bosentan, and efavirenz would decrease the AUC of the potency‐adjusted unbound active species by 29%, 42%, and 52%, respectively. The current PBPK model, which considers changes in unbound potency‐adjusted active species, can be used to inform dosing recommendations when abemaciclib is coadministered with CYP3A4 perpetrators.

Abemaciclib Inhibits Renal Tubular Secretion Without Changing Glomerular Filtration Rate

Abemaciclib, an inhibitor of cyclin dependent kinases 4 and 6, is indicated for metastatic breast cancer treatment. Reversible increases in serum creatinine levels of ~15-40% over baseline have been observed following abemaciclib dosing. This study assessed the in vitro and clinical inhibition of renal transporters by abemaciclib and its metabolites using metformin (a clinically relevant transporter substrate), in a clinical study that quantified glomerular filtration and iohexol clearance. In vitro, abemaciclib inhibited metformin uptake by organic cation transporter 2, multidrug and toxin extrusion (MATE)1, and MATE2-K transporters with a half-maximal inhibitory concentration of 0.4-3.8 μM. Clinically, abemaciclib significantly increased metformin exposure but did not significantly affect measured glomerular filtration rate, serum neutrophil gelatinase-associated lipocalin (NGAL), serum cystatin-C, or the urinary markers of kidney tubular injury, NGAL and kidney injury molecule-1.

Physiologically Based Pharmacokinetic Modelling of Cytochrome P450 2C9-Related Tolbutamide Drug Interactions with Sulfaphenazole and Tasisulam

Background and Objectives

Cytochrome P450 2C9 (CYP2C9) is involved in the biotransformation of many commonly used drugs, and significant drug interactions have been reported for CYP2C9 substrates. Previously published physiologically based pharmacokinetic (PBPK) models of tolbutamide are based on an assumption that its metabolic clearance is exclusively through CYP2C9; however, many studies indicate that CYP2C9 metabolism is only responsible for 80–90% of the total clearance. Therefore, these models are not useful for predicting the magnitude of CYP2C9 drug–drug interactions (DDIs). This paper describes the development and verification of SimCYP^®-based PBPK models that accurately describe the human pharmacokinetics of tolbutamide when dosed alone or in combination with the CYP2C9 inhibitors sulfaphenazole and tasisulam.

Methods

A PBPK model was optimized in SimCYP^® for tolbutamide as a CYP2C9 substrate, based on published in vitro and clinical data. This model was verified to replicate the magnitude of DDI reported with sulfaphenazole and was further applied to simulate the DDI with tasisulam, a small molecule investigated for the treatment of cancer. A clinical study (CT registration # NCT01185548) was conducted in patients with cancer to assess the pharmacokinetic interaction of tasisulum with tolbutamide. A PBPK model was built for tasisulam, and the clinical study design was replicated using the optimized tolbutamide model.

Results

The optimized tolbutamide model accurately predicted the magnitude of tolbutamide AUC increase (5.3–6.2-fold) reported for sulfaphenazole. Furthermore, the PBPK simulations in a healthy volunteer population adequately predicted the increase in plasma exposure of tolbutamide in patients with cancer (predicted AUC ratio = 4.7–5.4; measured mean AUC ratio = 5.7).

Conclusions

This optimized tolbutamide PBPK model was verified with two strong CYP2C9 inhibitors and can be applied to the prediction of CYP2C9 interactions for novel inhibitors. Furthermore, this work highlights the utility of mechanistic models in navigating the challenges in conducting clinical pharmacology studies in cancer patients.

Abemaciclib in Combination with Single-Agent Options in Patients with Stage IV Non-Small Cell Lung Cancer: A Phase Ib Study

Purpose: Abemaciclib, a dual inhibitor of cyclin-dependent kinases 4 and 6, has demonstrated preclinical activity in non-small cell lung cancer (NSCLC). A multicenter, nonrandomized, open-label phase Ib study was conducted to test safety, MTD, pharmacokinetics, and preliminary antitumor activity of abemaciclib in combination with other therapies for treatment in patients with metastatic NSCLC.Patients and Methods: An initial dose escalation phase was used to determine the MTD of twice-daily oral abemaciclib (150, 200 mg) plus pemetrexed, gemcitabine, or ramucirumab, followed by an expansion phase for each drug combination. Pemetrexed and gemcitabine were administered according to label. The abemaciclib plus ramucirumab study examined two dosing schedules.Results: The three study parts enrolled 86 patients; all received ≥1 dose of combination therapy. Across arms, the most common treatment-emergent adverse events were fatigue, diarrhea, neutropenia, decreased appetite, and nausea. The trial did not identify an abemaciclib MTD for the combination with pemetrexed or gemcitabine but did so for the combination of abemaciclib with days 1 and 8 ramucirumab (8 mg/kg). Plasma sample analysis showed that abemaciclib did not influence the pharmacokinetics of the combination agents and the combination agents did not affect abemaciclib exposure. The disease control rate was 57% for patients treated with abemaciclib-pemetrexed, 25% for abemaciclib-gemcitabine, and 54% for abemaciclib-ramucirumab. Median progression-free survival was 5.55, 1.58, and 4.83 months, respectively.Conclusions: Abemaciclib demonstrated an acceptable safety profile when dosed on a continuous twice-daily schedule in combination with pemetrexed, gemcitabine, or ramucirumab. Abemaciclib exposures remained consistent with those observed in single-agent studies. Clin Cancer Res; 24(22); 5543-51. ©2018 AACR.

Abemaciclib for the treatment of brain metastases (BM) secondary to hormone receptor positive (HR+), HER2 negative breast cancer

1019

Background: Abemaciclib is an oral selective CDK4 and CDK6 inhibitor administered on a continuous dosing schedule, which has demonstrated clinical activity and an acceptable safety profile in patients (pts) with heavily pre-treated HR+ metastatic breast cancer (MBC). Abemaciclib has been shown preclinically to cross the blood-brain barrier, providing rationale for testing this agent in pts with BM. Furthermore, as previously presented, levels of abemaciclib similar to plasma were detected in resected BM in a subset of pts with HR+, HER2- MBC in this study. Methods: Study I3Y-MC-JPBO is an open-label, Phase 2, Simon 2-Stage trial evaluating the safety and efficacy of abemaciclib 200 mg BID in pts with new or progressive BM secondary to HR+ MBC, NSCLC, or melanoma. Eligible pts in Part B (the focus of this presentation) include pts with HR+, HER2- MBC who have ≥1 measurable brain lesion. The primary objective was objective intracranial (IC) response rate as defined by Response Assessment in Neuro-Oncology BM response criteria. Secondary objectives (IC related) include best overall response, duration of response, disease control rate, and clinical benefit rate. Exploratory objectives include assessment of drug concentrations in resected tumors. Safety, tolerability, and PK of abemaciclib were also assessed. Stage 1 includes 23 pts; if < 2 of the 23 pts respond to abemaciclib, futility is met. However, if ≥2 respond, 33 additional pts are to be enrolled to Stage 2. Results: This Stage 1 efficacy analysis included 23 pts; 32 pts were included in the safety analysis. Although 5 pts were considered nonevaluable, 2 pts (8.7%) had confirmed partial response (PR) (meeting the predefined threshold for advancement to Stage 2); enrollment is ongoing. At the time of the analysis, the 2 pts with PR had completed 14 and 15 cycles each (21d cycles) of therapy. The majority of adverse events were gastrointestinal in nature, consistent with previous studies of abemaciclib. Conclusions: This study has provided preliminary evidence that abemaciclib penetrated BM in pts with HR+, HER2- MBC and had antitumor activity in this population. Final results will be presented following Stage 2 analyses. Clinical trial information: NCT02308020.

A First-in-Human Phase I Study of a Bivalent MET Antibody, Emibetuzumab (LY2875358), as Monotherapy and in Combination with Erlotinib in Advanced Cancer

Purpose: The MET/HGF pathway regulates cell proliferation and survival and is dysregulated in multiple tumors. Emibetuzumab (LY2875358) is a bivalent antibody that inhibits HGF-dependent and HGF-independent MET signaling. Here, we report dose escalation results from the first-in-human phase I trial of emibetuzumab.Experimental Design: The study comprised a 3+3 dose escalation for emibetuzumab monotherapy (Part A) and in combination with erlotinib (Part A2). Emibetuzumab was administered i.v. every 2 weeks (Q2W) using a flat dosing scheme. The primary objective was to determine a recommended phase II dose (RPTD) range; secondary endpoints included tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and antitumor activity.Results: Twenty-three patients with solid tumors received emibetuzumab monotherapy at 20, 70, 210, 700, 1,400, and 2,000 mg and 14 non-small cell lung cancer (NSCLC) patients at 700, 1,400, and 2,000 mg in combination with erlotinib 150 mg daily. No dose-limiting toxicities and related serious or ≥ grade 3 adverse events were observed. The most common emibetuzumab-related adverse events included mild diarrhea, nausea, and vomiting, and mild to moderate fatigue, anorexia, and hypocalcemia in combination with erlotinib. Emibetuzumab showed linear PK at doses >210 mg. Three durable partial responses were observed, one for emibetuzumab (700 mg) and two for emibetuzumab + erlotinib (700 mg and 2,000 mg). Both of the responders to emibetuzumab + erlotinib had progressed to prior erlotinib and were positive for MET protein tumor expression.Conclusions: Based on tolerability, PK/PD analysis, and preliminary clinical activity, the RPTD range for emibetuzumab single agent and in combination with erlotinib is 700 to 2,000 mg i.v. Q2W. Clin Cancer Res; 23(8); 1910-9. ©2016 AACR.

Understanding Disease-Drug Interactions in Cancer Patients: Implications for Dosing Within the Therapeutic Window

The human inflammatory response can result in the alteration of drug clearance through effects on metabolizing enzymes or transporters. In this article we briefly review the theory of how cancer can lead to indirect changes in drug metabolism, review acute phase proteins and cytokines as markers of changes in cytochrome P450 (CYP) activity in cancer patients, and provide clinical case examples of how the inflammation in advanced cancer patients can lead to altered CYP-mediated drug clearance.

A randomized, open-label clinical trial of tasisulam sodium versus paclitaxel as second-line treatment in patients with metastatic melanoma

BACKGROUND

Tasisulam sodium (hereafter referred to as tasisulam) is a novel, highly albumin-bound agent that demonstrated activity in a phase 2 melanoma study.

METHODS

In this open-label phase 3 study, patients with AJCC stage IV melanoma received tasisulam (targeting an albumin-corrected exposure of 1200-6400 h (hour).μg/mL on day 1) or paclitaxel (80 mg/m(2) on days 1, 8, and 15) every 28 days as second-line treatment.

RESULTS

The study was placed on clinical hold after randomization of 336 patients when a safety review indicated an imbalance of possibly drug-related deaths in the tasisulam arm. Efficacy results for tasisulam versus paclitaxel revealed a response rate of 3.0% versus 4.8%, a median progression-free survival of 1.94 months versus 2.14 months (P = .048), and a median overall survival of 6.77 months versus 9.36 months (P = .121). The most common drug-related grade ≥3 laboratory toxicities (graded according to Common Terminology for Adverse Events [version 3.0]) were thrombocytopenia (18.9%) for patients treated with tasisulam and neutropenia/leukopenia (8.7%) among those receiving paclitaxel. There were 13 possibly related deaths reported to occur on the study, with the majority occurring during cycle 2 in the setting of grade 4 myelosuppression, all in the tasisulam arm. Investigation of the unexpectedly high rate of hematologic toxicity revealed a subset of patients with low tasisulam clearance, leading to drug accumulation and high albumin-corrected exposure in cycle 2.

CONCLUSIONS

Although the study was stopped early because of safety issues in the tasisulam arm, tasisulam was considered unlikely to be superior to paclitaxel, and paclitaxel activity in the second-line treatment of melanoma was much lower than expected. The toxicity imbalance was attributed to an unexpectedly low tasisulam clearance in a subset of patients, underscoring the importance of pharmacokinetic monitoring of compounds with complex dosing, even in late-phase studies.

Tasisulam-sodium in combination with liposomal doxorubicin in patients with ovarian cancer

5551

Background: Tasisulam-sodium (TASI) is a novel, highly albumin-bound small molecule that induces tumor cell apoptosis and has antiangiogenic activity. This phase 1b study was designed as a dose-finding study for TASI in combination with liposomal doxorubicin (DX) in patients (pts) with advanced solid tumors, followed by a dose-confirmation phase in platinum-resistant DX-naïve ovarian cancer (OvCa) pts. However, the study was stopped early for business reasons. Nonetheless, the dataset allowed partial characterization of the safety and antitumor activity of TASI + DX among OvCa pts who achieved an albumin-corrected exposure (AUCalb) within a hypothesized therapeutic range identified in phase II monotherapy trials. Methods: In the dose-escalation phase (3+3 schema), pts received TASI (escalating Cmax targets of 300-380 μg/mL, 2-h IV) plus DX (40 mg/m2, 1-h IV) every 28 days. Pharmacokinetic and safety analyses identified an AUCalb target of 3500 h*μg/mL for the dose-confirmation phase. We analyzed data for OvCa pts from both phases who achieved TASI AUCalbof 1200-6400 h*μg/mL in cycle 1. Results: Of the 13 OvCa pts who completed the dose-escalation phase and 6 OvCa pts who completed the dose-confirmation phase, 10 had AUCalbof 1200-6400 h*μg/mL in cycle 1. For these pts, the most common possibly drug-related Grade 3-4 adverse event was neutropenia (see table). Although no pt achieved complete response, 2 pts achieved partial response. Data from the other OvCa pts will also be presented. Conclusions: The early closure of the study did not allow complete assessment of TASI in combination with DX; however, acceptable tolerability and some antitumor activity were observed for OvCa pts with TASI AUCalbwithin the hypothesized therapeutic range. Clinical trial information: NCT01214668. [Table: see text]

Development and validation of limited sampling models for topotecan lactone pharmacokinetic studies in children

PURPOSE

To develop and validate a pharmacokinetic limited sampling model (LSM) for intravenous and oral topotecan pharmacokinetic studies in children.

METHODS

Topotecan lactone concentration-time data from five trials were used to develop and validate LSM for intravenous and oral topotecan. Based on full sampling from one intravenous study (30 patients; 195 studies), a LSM for intravenous topotecan was determined using a modification of the D-optimality algorithm. For oral topotecan we used full sampling data from one oral topotecan study (27 patients; 47 studies) to develop an LSM. Accuracy and bias of each LSM were determined relative to the full sampling method. Predictive performance of the LSM was validated using additional data and Monte-Carlo simulations based on these data.

RESULTS

LSM for intravenous topotecan includes: 5 min, 1.5, and 2.5 h after the end of the 30 min infusion. The median accuracy (absolute predicted error) and bias (predicted error) are < or =8% and < or =6.1%, respectively. For oral topotecan, the optimal LSM includes: 15 min, 1.5, and 6 h. The median accuracy and bias are 6% and 4%, respectively.

CONCLUSIONS

Our results indicate that the optimal sampling times for the intravenous LSM for topotecan in children consist of: predose, and 5 min, 1.5, and 2.5 h after the end of infusion. For oral topotecan the sample times are predose, 15 min, 1.5, and 6 h after dose administration. These LSM are invaluable to children receiving topotecan because it minimizes inconvenience and blood collection.

Interferon-gamma pharmacokinetics and pharmacodynamics in patients with colorectal cancer

PURPOSE

The study objectives were to define subcutaneous (s.c.) interferon gamma (IFN-gamma) disposition in patients with gastrointestinal malignancies receiving 5-fluorouracil (5-FU) and leucovorin (LV) and to examine the relationship between IFN-gamma exposures and Fas upregulation in vivo and in vitro.

METHODS

Patients received IFN-gamma (10, 25, 50, 75, and 100 microg/m(2)) with LV and 5-FU, and serial samples were collected after the first dose. IFN-gamma concentrations were measured by ELISA. A linear one-compartment model with a lag was fitted to the IFN-gamma plasma concentration-time data. To examine the relationship between IFN-gamma systemic exposure and biological activity in vivo, cell surface Fas upregulation was assessed in peripheral blood mononuclear cell (PBMC) subcompartments.

RESULTS

The median (range) apparent IFN-gamma clearance was 46 l/m(2) per hour (2.6-92 l/m(2) per hour). With increasing IFN-gamma dosages, the area under the concentration-time curve (AUC(0--> infinity )) and C(max) increased; however, significant interpatient variability was observed. IFN-gamma AUC(0--> infinity ) and time above 33.3 pg/ml significantly correlated with Fas upregulation in several PBMC compartments, but dosage was significantly correlated with this pharmacodynamic marker only in CD4(+) and CD56(+) cells. In vitro studies in HT29 cells demonstrated that clinically relevant IFN-gamma concentrations (1 to 10 U/ml for 6.5 h) with 5-FU/LV upregulated Fas expression 3.5-fold, similar to that in PBMC in vivo.

CONCLUSIONS

We characterized IFN-gamma disposition and developed a limited sampling model for use in future pharmacokinetic studies. Our results showed that IFN-gamma upregulates Fas in PBMC in vivo and in HT29 cells in vitro at tolerable, clinically relevant exposures and that monitoring IFN-gamma pharmacokinetics/pharmacodynamics may be warranted in IFN-gamma clinical use.

Topoisomerase I interactive agents

Elucidation of the crystal structure of topoisomerase I will enhance the rational development of topoisomerase I interactive agents. Although the first topoisomerase I interactive agents were camptothecin derivatives, future drugs may be designed to take advantage of the knowledge of the mechanism of interaction with topoisomerase I to increase the therapeutic index. Preclinical studies designed to determine the precise mechanism by which the topoisomerase I interactive agents lead to cell death will be essential. Future clinical trials must rationally utilize the results of preclinical studies in the design of combination regimens, both with other cytotoxics and with the newer cytostatics. Moreover, the optimum schedule of administration for irinotecan and topotecan are not known, although results of preclinical studies clearly point to protracted dosing of these S-phase-specific agents. Future clinical trials should evaluate these schedules in an effort to optimize the currently available agents, prior to introducing new analogs, which may not provide any therapeutic benefit over the current agents properly dosed. Finally, many investigators are trying to better understand the mechanism(s) of the dose-limiting toxicities observed with the currently available topoisomerase I interactive agents (e.g., glucuronidation for irinotecan diarrhea). The results of these studies may also enable the maximal dosing of the currently available agents. Even though the first priority must be to determine the therapeutic potential of the currently available agents, it is reassuring to know that many topoisomerase I interactive agents are currently under development. However, it is essential that these agents have the proper preclinical studies performed and that they be rationally developed.

Topoisomerase I interactive agents

Increased insight into the mechanism of interaction of topoisomerase I interactive agents will maximize the therapeutic index and enhance the development of additional agents. Preclinical studies designed to elucidate mechanisms by which the topoisomerase I interactive agents induce cell death will be essential. The role of ABC transporters in resistance to topoisomerase I interactive agents has been recently appreciated and future studies should be directed at circumventing this resistance. The results of preclinical studies must be translated into the design of clinical trials so that these agents can be used rationally. In this regard results of preclinical studies have clearly pointed to the enhanced antitumor activity from protracted dosing of topoisomerase I interactive agents and results of clinical trials are now supporting these preclinical findings. Finally, investigators are trying to understand better the mechanism(s) of the dose-limiting toxicities observed with the currently available topoisomerase I interactive agents in an effort to enable the optimal dosing of these agents. Even though the first priority must be to determine the therapeutic potential of the currently available agents, it is reassuring to know that other topoisomerase I interactive agents are currently under development.

Modulation of the Fas signaling pathway by IFN-gamma in therapy of colon cancer: phase I trial and correlative studies of IFN-gamma, 5-fluorouracil, and leucovorin

Potentiation of 5-fluorouracil/leucovorin (FUra/LV) cytotoxicity by IFN-gamma in colon carcinoma cells is dependent on FUra-induced DNA damage, the Fas death receptor, and independent of p53 and RNA-mediated FUra toxicity, which occurs in normal gastrointestinal tissues. This provides a rationale for enhancing the selective action of FUra/LV by IFN-gamma in the treatment of colorectal carcinoma. Based on results from our preclinical studies we designed a Phase I trial combining FUra (370 mg/m2) and LV (200 mg/m2), i.v. bolus daily x 5 days, with escalating doses of IFN-gamma (10-100 micro g/m2) s.c. on days 1, 3, and 5, every 28 days. Twenty-five patients with carcinomas were enrolled; 6 patients received IFN-gamma on days 1 and 3 only. The dose-limiting toxicity, stomatitis, occurred most frequently at 100 micro g/m2 IFN-gamma. Minor response or SD was observed in 2 of 9 patients and in 4 of 12 patients at dose levels of < or =50 micro g/m2 and > or =75 micro g/m2 IFN-gamma, respectively. Three evaluable chemonaive patients demonstrated partial response (2) or complete response (1). Serial plasma samples revealed peak FUra concentrations of >100 micro M; at 100 micro g/m2 IFN-gamma plasma concentrations >5 units/ml persisted for 6.5 h and >1 unit/ml for 28.5 h. The pharmacokinetic parameters of IFN-gamma correlated with a 2-3-fold up-regulation of Fas expression at 24 h in CD15+ cells in peripheral blood samples. Furthermore, clinically relevant IFN-gamma concentrations up-regulated Fas expression and sensitized HT29 colon carcinoma cells in vitro to FUra/LV cytotoxicity. On the basis of the modulation of Fas signaling, FUra/LV combined with IFN-gamma has shown activity in a Phase I trial in colorectal carcinoma and warrants additional evaluation in Phase II.

Assessment of toxicity reduction in wastewater effluent flowing through a treatment wetland using Pimephales promelas, Ceriodaphnia dubia, and Vibrio fischeri

Effluent toxicity is regularly assessed with Ceriodaphnia dubia short-term chronic and Vibrio fischeri toxicity tests. Condition factor and hemotocrit of fish have recently been used to assess fish health following exposure to xenoestrogens in complex municipal effluents. To assess the ability of a treatment wetland to reduce or remove toxicity of a municipal effluent, we compared C. dubia and V. fischeri bioassays to Pimephales promelas responses in situ. Final whole effluent was diverted to a constructed wetland and effluent samples were taken daily from four sites, at incremental distances from the inflow, for a 3-week study. Overlapping 7-day C. dubia tests and V. fischeri assays were conducted with samples from each wetland site concurrent with a 3-week fish exposure. C. dubia survival and fecundity were significantly (< 0.0001) reduced at the inflow, but steadily improved with distance from the inflow. Fish condition and hematocrit were lower (alpha < 0.05) at wetland sites closer to the inflow than other wetland sites and laboratory controls. However, effluent toxicity was not detected by V. fischeri bioassays. Our findings indicate that 7-day C. dubia bioassays were most sensitive to effluent toxicity and suggest that other bioassays should be used concurrent with V. fischeri assays for municipal effluent toxicity testing.