Single-nucleotide polymorphisms associated with outcome in metastatic renal cell carcinoma treated with sunitinib.

BACKGROUND: There are no validated markers that predict response in metastatic renal cell cancer (RCC) patients treated with sunitinib. We aim to study the impact of single-nucleotide polymorphisms (SNPs) that have recently been proposed as predictors of outcome to anti-VEGF-targeted therapy in metastatic RCC in an independent cohort of patients. METHODS: We genotyped 16 key SNPs in 10 genes involved in sunitinib pharmacokinetics, pharmacodynamics and VEGF-independent angiogenesis in patients with metastatic clear-cell RCC treated with sunitinib as the first-line targeted therapy. Association between SNPs, progression-free survival (PFS) and overall survival (OS) were studied by multivariate Cox regression using relevant clinical factors associated with PFS and OS as covariates. RESULTS: In a series of 88 patients, both PFS and OS were associated significantly with SNP rs1128503 in ABCB1 (P=0.027 and P=0.025), rs4073054 in NR1/3 (P=0.025 and P=0.035) and rs307821 in VEGFR3 (P=0.032 and P=0.011). Progression-free survival alone was associated with rs2981582 in FGFR2 (P=0.031) and rs2276707 in NR1/2 (P=0.047), whereas OS alone was associated with rs2307424 in NR1/3 (P=0.048) and rs307826 in VEGFR3 (P=0.013). CONCLUSION: Our results confirm former communications regarding the association between SNPs in ABCB1, NR1/2, NR1/3 and VEGFR3 and sunitinib outcome in clear-cell RCC. Prospective validation of these SNPs is now required.

Concomitant oral tyrosine kinase inhibitors and bisphosphonates in advanced renal cell carcinoma with bone metastases.

BACKGROUND: The presence of bone metastases in patients with metastatic renal cell carcinoma treated with oral tyrosine kinase inhibitors (TKIs) is associated with poorer outcome as compared with patients without bone involvement. Concomitant bisphosphonates could probably improve outcomes but also induce osteonecrosis of the jaw (ONJ). METHODS: Retrospective study on all the renal cell carcinoma patients with bone metastases treated with sunitinib or sorafenib between November 2005 and June 2012 at the University Hospitals Leuven and AZ Groeninge in Kortrijk. RESULTS: Seventy-six patients were included in the outcome analysis: 49 treated with concomitant bisphosphonates, 27 with TKI alone. Both groups were well balanced in terms of prognostic and predictive markers. Response rate (38% vs 16% partial responses, P=0.028), median progression-free survival (7.0 vs 4.0 months, P=0.0011) and median overall survival (17.0 vs 7.0 months, P=0.022) were significantly better in patients receiving bisphosphonates. The incidence of ONJ was 10% in patients treated with TKI and bisphosphonates. CONCLUSION: Concomitant use of bisphosphonates and TKI in renal cell carcinoma patients with bone involvement probably improves treatment efficacy, to be confirmed by prospective studies, but is associated with a high incidence of ONJ.

The effects of receptor density and cell shape on epidermal growth factor binding.

In this paper we describe the effects of receptor density and cell shape on the binding of epidermal growth factor (EGF) to its receptor. Association kinetics of EGF binding to cells with a high receptor density was done using A431 cells. The association rate of EGF binding was apparently independent of the EGF concentration, most likely due to diffusion limited EGF binding as result of high receptor density. The effect of receptor density on EGF association rate was examined by reducing the number of functional EGF receptors on A431 cells. Preincubation of the cells with a monoclonal antibody directed against the EGF receptor and isolation of the cytoskeletons of A431 cells which both leaves only EGF binding to high affinity receptors revealed an EGF concentration dependent association rate. These results were confirmed in HeLa cells with 40 times less receptor numbers than A431 cells demonstrating the effect of receptor density on EGF binding. The influence of shape of the cell on EGF binding was examined by comparing the EGF association to monolayer cells with that of suspension cells. EGF association to suspended A431 cells was EGF concentration dependent. In conclusion we have shown that binding of EGF to A431 cells is dependent not only on the intrinsic rate constants but in addition on both receptor numbers per cell and the shape of cells. These results are in agreement with the hypothesis that EGF binding can be restricted by limited diffusion.

Three classes of epidermal growth factor receptors on HeLa cells.

The kinetics of 125I-labeled epidermal growth factor (EGF) binding to receptors on HeLa cells were investigated. Scatchard analysis revealed the presence of 22,000 high affinity receptors (Kd = 0.12 nM) and 25,000 low affinity receptors per cell (Kd = 9.2 nM). The kinetic analysis of EGF binding to high affinity receptors was performed with cells pretreated with the monoclonal antibody 2E9, which prevents specifically EGF binding to low affinity receptors. The study of EGF binding to only low affinity receptors was performed with cells pretreated with the phorbol ester phorbol 12-myristate 13-acetate, which induces a conversion of high affinity receptors to low affinity receptors. This kinetic analysis of EGF binding to HeLa cells revealed the presence of three types of receptors. High affinity receptors were found to consist of one receptor type (type I) with a kinetic association constant (kass) of 6.2 x 10(5) M-1.s-1 and a kinetic dissociation constant (kdis) of 3.5 x 10(-4) s-1. The low affinity receptors were found to consist of two kinetic distinguishable sites: type II or fast sites with kass = 3.3 x 10(6) M-1.s-1 and kdis = 8.1 x 10(-3) s-1 and the type III or slow sites with kass = 3.2 x 10(4) M-1.s-1 and kdis = 1.6 x 10(-4) s-1. The regulatory mechanism which may determine the EGF binding characteristics is discussed.

Membrane vesicles of A431 cells contain one class of epidermal growth factor binding sites.

Epidermoid carcinoma A431 cells exhibit two classes of epidermal growth factor (EGF) receptors as deduced from Scatchard analysis. Steady-state binding of EGF to isolated A431 membranes indicated, however, the presence of only one class of EGF binding sites. The apparent dissociation constant (Kd) of these sites was approx. 0.45 nM which is similar to that of the high-affinity receptor of intact A431 cells. These results suggest that the vesicle receptor population consists only of high-affinity receptors. However, further studies indicated that the binding sites were similar to the low-affinity class, since binding of EGF could be blocked entirely by 2E9, a monoclonal anti-EGF receptor antibody which is able to inhibit specifically EGF binding to low-affinity receptors in A431 cells. The difference in affinity of the receptors in membrane vesicles as compared to intact cells may be explained by differences in biophysical parameters such as diffusion-limited EGF binding and receptor distribution. Based upon these considerations, it is concluded that membrane vesicles of A431 cells contain one class of EGF receptors which are apparently identical to the low-affinity receptors of intact cells.