Phase I study of axitinib combined with paclitaxel, docetaxel or capecitabine in patients with advanced solid tumours

Receptor tyrosine kinase inhibitors: Are they real tumor killers?

Inhibiting tumor growth by targeting the tumor vasculature was first proposed by Judah Folkman almost 40 years ago. Since then, different approaches and numerous drugs and agents have been developed to achieve this goal, either with the aim of inhibiting tumor neoangiogenesis or normalizing the tumor vasculature. Among the most promising therapeutic targets are receptor tyrosine kinases (RTKs), some of which are predominantly expressed on tumor endothelial cells, although they are sometimes also present on tumor cells. The majority of RTK inhibitors investigated over the past two decades competes with ATP at the active site of the kinase and therefore block the phosphorylation of intracellular targets. Some of these drugs have been approved for therapy, whereas others are still in clinical trials. Here, we discuss the scientific basis, current status, problems and future prospects of RTK inhibition in anti-tumor therapy.

Impact of pazopanib on docetaxel exposure: results of a phase I combination study with two different docetaxel schedules

PURPOSE

There are several reasons why combining an inhibitor of the vascular endothelial and the platelet-derived growth factor receptor with a taxane might induce synergistic antitumor activity. This phase I study aimed to determine the maximal tolerated dose (MTD) of the combination of pazopanib with two different schedules of docetaxel.

METHODS

In a 3 + 3 + 3 design, patients with advanced solid tumors received escalating doses of oral pazopanib combined with docetaxel given either every 3 weeks (D3w) or weekly at days 1, 8, and 15 every 28 days (D1w). Pharmacokinetic data of docetaxel and pazopanib were obtained through extensive sampling and WinNonlin modeling.

RESULTS

Forty-six patients were enrolled to six dose levels. Both schedules of docetaxel could be combined with 400 mg/day pazopanib. The MTD of D3w docetaxel was 50 mg/m(2), while for D1w MTD, it was 20 mg/m(2). In the D3w schedule, the administration of pazopanib led to a 33% lower docetaxel clearance (mean 31.5 vs 21.1 L/h/m(2); P = 0.019) and >50% increase in AUC(0-∞) (mean 1,602 vs 2,414 ng*h/mL; P = 0.029) compared with docetaxel single-agent data. Data for the D1w schedule were comparable.

CONCLUSIONS

Both treatment schedules of docetaxel combined with pazopanib are feasible but at doses for both drugs that are considerably lower than the recommended single-agent doses. This is largely due to a clinically relevant pharmacokinetic interaction with pazopanib, substantially increasing docetaxel exposure. This interaction is most likely due to CYP3A4 and OATP1B1 inhibition.

Population pharmacokinetic analysis of axitinib in healthy volunteers

AIMS

Axitinib is a potent and selective second generation inhibitor of vascular endothelial growth factor receptors 1, 2 and 3 approved for second line treatment of advanced renal cell carcinoma. The objectives of this analysis were to assess plasma pharmacokinetics and identify covariates that may explain variability in axitinib disposition following single dose administration in healthy volunteers.

METHODS

Plasma concentration-time data from 337 healthy volunteers in 10 phase I studies were analyzed, using non-linear mixed effects modelling (nonmem) to estimate population pharmacokinetic parameters and evaluate relationships between parameters and food, formulation, demographic factors, measures of renal and hepatic function and metabolic genotypes (UGT1A1*28 and CYP2C19).

RESULTS

A two compartment structural model with first order absorption and lag time best described axitinib pharmacokinetics. Population estimates for systemic clearance (CL), central volume of distribution (Vc ), absorption rate constant (ka ) and absolute bioavailability (F) were 17.0 l h(-1) , 45.3 l, 0.523 h(-1) and 46.5%, respectively. With axitinib Form IV, ka and F increased in the fasted state by 207% and 33.8%, respectively. For Form XLI (marketed formulation), F was 15% lower compared with Form IV. CL was not significantly influenced by any of the covariates studied. Body weight significantly affected Vc , but the effect was within the estimated interindividual variability for Vc .

CONCLUSIONS

The analysis established a model that adequately characterizes axitinib pharmacokinetics in healthy volunteers. Vc was found to increase with body weight. However, no change in plasma exposures is expected with change in body weight; hence no dose adjustment is warranted.

The design and discovery of water soluble 4-substituted-2,6-dimethylfuro[2,3-d]pyrimidines as multitargeted receptor tyrosine kinase inhibitors and microtubule targeting antitumor agents

The design, synthesis and biological evaluations of fourteen 4-substituted 2,6-dimethylfuro[2,3-d]pyrimidines are reported. Four compounds (11-13, 15) inhibit vascular endothelial growth factor receptor-2 (VEGFR-2), platelet-derived growth factor receptor β (PDGFR-β), and target tubulin leading to cytotoxicity. Compound 11 has nanomolar potency, comparable to sunitinib and semaxinib, against tumor cell lines overexpressing VEGFR-2 and PDGFR-β. Further, 11 binds at the colchicine site on tubulin, depolymerizes cellular microtubules and inhibits purified tubulin assembly and overcomes both βIII-tubulin and P-glycoprotein-mediated drug resistance, and initiates mitotic arrest leading to apoptosis. In vivo, its HCl salt, 21, reduced tumor size and vascularity in xenograft and allograft murine models and was superior to docetaxel and sunitinib, without overt toxicity. Thus 21 affords potential combination chemotherapy in a single agent.

Clinical pharmacology of axitinib

Axitinib is a potent and selective second-generation inhibitor of vascular endothelial growth factor receptors 1, 2, and 3 that is approved in the US and several other countries for treatment of patients with advanced renal cell carcinoma after failure of one prior systemic therapy. The recommended clinical starting dose of axitinib is 5 mg twice daily, taken with or without food. Dose increase (up to a maximum of 10 mg twice daily) or reduction is permitted based on individual tolerability. Axitinib pharmacokinetics are dose-proportional within 1-20 mg twice daily, which includes the clinical dose range. Axitinib has a short effective plasma half-life (range 2.5-6.1 h), and the plasma accumulation of axitinib is in agreement with what is expected based on the plasma half-life of the drug. Axitinib is absorbed relatively rapidly, reaching maximum observed plasma concentrations (C max) within 4 h of oral administration. The mean absolute bioavailability of axitinib is 58 %. Axitinib is highly (>99 %) bound to human plasma proteins with preferential binding to albumin and moderate binding to α1-acid glycoprotein. In patients with advanced renal cell carcinoma, at the 5-mg twice-daily dose in the fed state, the geometric mean (% coefficient of variation) C max and area under the plasma concentration-time curve (AUC) from time 0-24 h (AUC24) were 27.8 ng/mL (79 %) and 265 ng·h/mL (77 %), respectively. Axitinib is metabolized primarily in the liver by cytochrome P450 (CYP) 3A4/5 and, to a lesser extent (<10 % each), by CYP1A2, CYP2C19, and uridine diphosphate glucuronosyltransferase (UGT) 1A1. The two major human plasma metabolites, M12 (sulfoxide product) and M7 (glucuronide product), are considered pharmacologically inactive. Axitinib is eliminated via hepatobiliary excretion with negligible urinary excretion. Although mild hepatic impairment does not affect axitinib plasma exposures compared with subjects with normal hepatic function, there was a 2-fold increase in AUC from time zero to infinity (AUC∞) following a single 5-mg dose in subjects with moderate hepatic impairment. In the presence of ketoconazole, a strong CYP3A4/5 inhibitor, axitinib C max and AUC∞ increased by 1.5- and 2-fold, respectively, whereas co-administration of rifampin, a strong CYP3A4/5 inducer, resulted in a 71 and 79 % decrease in the C max and AUC∞, respectively. Axitinib does not inhibit CYP3A4/5, CYP1A2, CYP2C8, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, or UGT1A1 at concentrations obtained with the clinical doses and is not expected to have major interactions with drugs that are metabolized by these enzymes. Axitinib is an inhibitor of the efflux transporter P-glycoprotein (P-gp) in vitro, but is not expected to inhibit P-gp at therapeutic plasma concentrations. A two-compartment population pharmacokinetic model with first-order absorption and lag time was used to describe axitinib pharmacokinetics. No clinically relevant effects of age, sex, body weight, race, renal function, UGT1A1 genotype, or CYP2C19 inferred phenotype on the clearance of axitinib were identified.

Inhibition of OATP1B1 by tyrosine kinase inhibitors: in vitro-in vivo correlations

BACKGROUND

Several tyrosine kinase inhibitors (TKIs) can decrease docetaxel clearance in patients by an unknown mechanism. We hypothesised that these interactions are mediated by the hepatic uptake transporter OATP1B1.

METHODS

The influence of 16 approved TKIs on transport was studied in vitro using HEK293 cells expressing OATP1B1 or its mouse equivalent Oatp1b2. Pharmacokinetic studies were performed with Oatp1b2-knockout and OATP1B1-transgenic mice.

RESULTS

All docetaxel-interacting TKIs, including sorafenib, were identified as potent inhibitors of OATP1B1 in vitro. Although Oatp1b2 deficiency in vivo was associated with increased docetaxel exposure, single- or multiple-dose sorafenib did not influence docetaxel pharmacokinetics.

CONCLUSION

These findings highlight the importance of identifying proper preclinical models for verifying and predicting TKI-chemotherapy interactions involving transporters.

Axitinib for the treatment of advanced renal cell carcinoma

INTRODUCTION

Advanced understanding of the pathogenesis of renal cell carcinoma (RCC) has led to development and approval of several molecularly targeted therapies since 2005. Axitinib is a potent and selective inhibitor of vascular endothelial growth factor receptors 1, 2 and 3. In the randomized Phase III AXIS trial, axitinib significantly prolonged progression-free survival compared with sorafenib, respectively (6.7 vs 4.7 months; p < 0.0001), and improved objective response rate (19 vs 9%; p = 0.0001), resulting in its approval for advanced or metastatic RCC after failure of one systemic therapy. However, overall survival was similar with axitinib and sorafenib. Common adverse events associated with axitinib include diarrhea, hypertension and fatigue.

AREAS COVERED

The properties, clinical efficacy, adverse events, pharmacokinetics and pharmacodynamics of axitinib are summarized and its position in the overall therapeutic landscape for metastatic RCC among several targeted therapies is described.

EXPERT OPINION

Axitinib is generally well-tolerated and provides definitive clinical benefits in patients with advanced or metastatic RCC as second-line therapy. However, as with other tyrosine kinase inhibitors of the same class, axitinib does not prolong overall survival; therefore, selection of second-line tyrosine kinase inhibitor therapy, including axitinib, must be carefully considered to maximize outcomes for each patient.

Phase I trial of axitinib combined with platinum doublets in patients with advanced non-small cell lung cancer and other solid tumours

Background:

This phase I dose-finding trial evaluated safety, efficacy and pharmacokinetics of axitinib, a potent and selective second-generation inhibitor of vascular endothelial growth factor receptors, combined with platinum doublets in patients with advanced non-small cell lung cancer (NSCLC) and other solid tumours.

Methods:

In all, 49 patients received axitinib 5 mg twice daily (b.i.d.) with paclitaxel/carboplatin or gemcitabine/cisplatin in 3-week cycles. Following determination of the maximum tolerated dose, a squamous cell NSCLC expansion cohort was enroled and received axitinib 5 mg b.i.d. with paclitaxel/carboplatin.

Results:

Two patients experienced dose-limiting toxicities: febrile neutropenia (n=1) in the paclitaxel/carboplatin cohort and fatigue (n=1) in the gemcitabine/cisplatin cohort. Common nonhaematologic treatment-related adverse events were hypertension (36.7%), diarrhoea (34.7%) and fatigue (28.6%). No grade⩾3 haemoptysis occurred among 12 patients with squamous cell NSCLC. The objective response rate was 37.0% for patients receiving axitinib/paclitaxel/carboplatin (n=27) and 23.8% for patients receiving axitinib/gemcitabine/cisplatin (n=21). Pharmacokinetics of axitinib and chemotherapeutic agents were similar when administered alone or in combination.

Conclusion:

Axitinib 5 mg b.i.d. may be combined with standard paclitaxel/carboplatin or gemcitabine/cisplatin regimens without evidence of overt drug–drug interactions. Both combinations demonstrated clinical efficacy and were well tolerated.