Elsevier

European Journal of Cancer

Volume 66, October 2016, Pages 47-54
European Journal of Cancer

Original Research
Sunitinib uptake inhibits platelet function in cancer patients

https://doi.org/10.1016/j.ejca.2016.07.016Get rights and content

Highlights

  • Sunitinib is sequestered by blood platelets in vitro and in patients on treatment.

  • Sunitinib inhibits platelet activation, aggregation and thrombus formation.

  • Sunitinib treatment moderately but significantly decreases platelet count.

  • Together, this may contribute to the higher bleeding tendency observed during treatment.

  • Clinicians need to be aware of the antiplatelet effects of sunitinib therapy.

Abstract

Background

Sunitinib is an oral tyrosine kinase inhibitor used for cancer treatment. Patients treated with sunitinib are at higher bleeding risk. As tyrosine kinases are essential for platelet signalling, the effects of sunitinib on platelet function in vitro and in cancer patients on treatment were investigated.

Patients and methods

Blood samples were collected from eight healthy volunteers and eight patients diagnosed with metastatic renal cell cancer (RCC) before and 2 weeks on treatment with sunitinib. Platelets from 15 additional healthy individuals were preincubated with sunitinib or vehicle to perform in vitro experiments. Immunofluorescence imaging, western blotting, light transmission aggregometry, whole blood perfusion over collagen, flow cytometry and ELISA were performed.

Results

Confocal microscopy indicated that platelets sequester sunitinib in vitro and in patients. In platelets from healthy controls, tyrosine phosphorylation was inhibited by sunitinib. Also, sunitinib dose dependently reduced collagen- and ADP-induced aggregation, collagen-dependent thrombus formation and collagen-induced secretion of platelet-derived growth factor and β-thromboglobulin. In blood from RCC patients before treatment, thrombus formation and procoagulant activity under flow were 47% and 80% higher than in healthy controls. After 14 d of sunitinib treatment, platelet count was moderately, but significantly decreased (from 243 to 144 × 109/l). At the same time, collagen-induced platelet aggregation as well as thrombus formation and phosphatidylserine exposure under flow were significantly reduced (by 45%, 16% and 61%, respectively).

Conclusions

Sunitinib uptake by platelets inhibits collagen receptor-induced aggregation and thrombus formation via reduction of protein tyrosine phosphorylation and α-granule secretion. This dysfunction may contribute to the higher bleeding tendency observed in sunitinib-treated patients.

Introduction

Inhibition of protein tyrosine kinases has shown considerable anticancer activity in patients with malignancies [1]. The multitarget tyrosine kinase inhibitor (TKI) sunitinib has been approved for the treatment of advanced renal cell cancer (RCC) and for imatinib-resistant gastrointestinal and pancreatic neuroendocrine tumours [2]. The effect of sunitinib in the management of several other malignancies is currently being explored in several trials (ClinicalTrials.gov Identifiers: NCT02074878, NCT01396148, NCT02058901 and NCT00753727).

Although treatment with sunitinib has shown anticancer effects and improves progression-free survival, patients treated with this TKI may also encounter bleeding. Overall, bleeding occurs in approximately 19% of sunitinib-treated patients; about 3% of the bleeding incidents are life threatening [3]. The mechanism underlying this higher bleeding diathesis in patients treated with sunitinib is still poorly understood. Haemostasis upon vessel wall injury is an intricate process in which platelets play a major role; it involves activation of platelets by multiple exogenous and autocrine agonists and their receptors [4]. Exposed extracellular matrix proteins, including collagen and von Willebrand Factor (vWF), first mediate platelet adhesion and activation, as a prerequisite for ensuing aggregation and thrombus formation. A subpopulation of activated platelets exposes phosphatidylserine which promotes thrombin generation and fibrin formation [5], [6]. Platelets contain multiple active protein tyrosine kinases [4] that are essential for platelet functioning in haemostasis. Moreover, platelets also play an important role in tumour angiogenesis and cancer progression [7]. The role of platelets in sunitinib-induced toxicity has not been explored.

The current study examined the hypothesis that sunitinib treatment of cancer patients impairs platelet haemostatic function, explaining the higher occurrence of bleeding in patients undergoing this treatment. We investigated the effects of sunitinib on platelet activation, aggregation and thrombus formation both in vitro and in patients with RCC.

Section snippets

Patients

The study was approved by the medical ethics committee from Maastricht University Medical Centre+ (MUMC+, The Netherlands). Informed consent was obtained from all participants in accordance with the declaration of Helsinki. At the department of Medical Oncology of MUMC+, blood samples were obtained from eight patients diagnosed with metastatic RCC and eight healthy donors who were similar in age and gender to the RCC patients. The patients included were treated with sunitinib (Sutent®, Pfizer,

Sunitinib is sequestered by platelets and inhibits collagen-induced protein tyrosine phosphorylation

Visualisation by confocal microscopy of washed platelets from healthy individuals that were treated with 10 μM sunitinib showed that platelets accumulate sunitinib and sequester this fluorescent compound in granules (Fig. 1A). This uptake of sunitinib from the environment was observed within minutes after exposure. Platelets contain several tyrosine kinases implicated in platelet functioning, mostly acting in the collagen-induced signalling pathway [4]. Western blotting was used to investigate

Discussion

The present study shows that the multi-TKI sunitinib is taken up by platelets and inhibits collagen receptor-induced integrin activation, secretion, aggregation and thrombus formation. Protein tyrosine kinases are abundantly expressed in platelets and play important roles in platelet activation and haemostasis [9]. It has been shown that sunitinib also affects tyrosine kinases that are expressed in platelets [10]. This may explain that sunitinib treatment was accompanied by bleeding episodes in

Funding

This research is financially supported by the Netherlands Organization for Scientific Research (NWO) under project number 017.008.143, granted to Siamack Sabrkhany, and by the Cardiovascular Centre Maastricht (Thrombosis Expertise Centre) to Johan Heemskerk and Marijke Kuijpers.

Conflict of interest statement

None declared.

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