Evaluación de los extractos crudos permeados de la membrana de 10 kDa

As early as 1980 Chodak and Folkman demonstrated a positive angiogenic response in the

rabbit iris assay in 95% o f malignant and pre-malignant human bladder urothelial

specimens compared to less that 10% o f normal tissue having such a response (120). A

similar result was seen when malignant cell lines were compared with normal cells (121).

Furthermore Chodak also demonstrated increased stimulation o f endothelial cell migration

(an essential component o f angiogenesis) by urine from patients with bladder cancer over

removal of bladder tumours and increased several months later in patients who developed

recurrent tumours.

Further evidence o f the angiogenic potential o f bladder cancer has been demonstrated by

the finding o f raised mierovessel density as an independent prognostic indicator in

invasive bladder cancer (1,123,124). Abnormalities in the p53 tumour suppresser gene are

found in a number o f malignancies and predict a significant increased risk o f recurrence and

death in patients with TCC independent o f stage, grade and lymph node status (125).

When mierovessel density was analysed in association with p53 status additional

information was provided, identifying subgroups at greatest risk. Patients whose invasive

tumour had low mierovessel counts and no evidence o f p53 alterations had only a 3%

recurrence and an 88% survival rate 5 years after radical cystectomy. This compares with

61% recurrence and 43% overall survival for patients with high mierovessel densities but

still no p53 abnormalities (126).

Angiogenesis as indicated by mierovessel density has provided useful prognostic

information in patients with invasive bladder cancer but one group o f patients where such

information would be very valuable are those with superficial bladder cancer. Superficial

bladder cancer is a heterogeneous disease, any additional prognostic information would

help decide which tumours are high risk and should be treated early and aggressively and

which can be treated more conservatively. Due to the papillary structure o f many

although not impossible (127) and therefore attention has focused on angiogenic factors as

prognostic indicators. Once again the most extensively studied are basic FGF and VEGF.

Basic FGF has been isolated from the urine o f patients with bladder cancer (128). Levels

are higher in patients with active bladder cancer than in those with a history o f bladder

cancer but a clear cystoscopy (129,130). The levels were highest in those patients with

active metastatic disease (130). However, it must not be forgotten that urinary levels o f

angiogenic factors can be derived not only from tumours in the urogenital track but also

from systemic tumours. Urinary basic FGF is increased in patients with a wide spectrum

of malignancies (131) and also in patients with benign prostatic hyperplasia (129). This

lack o f specificity would appear to rule out urinary measurement o f basic FGF as a

screening tool, however it may be useful as a surrogate marker in patients with known

disease undergoing anti-angiogenic therapy.

We have previously demonstrated that vascular endothelial growth factor messenger RNA

(mRNA), detected by ribonuclease protection assay, is elevated 10 fold in superficial

bladder tumours compared with normal bladder and 4 fold in superficial tumours

compared with invasive tumours (2). Further investigation revealed that elevated VEGF

mRNA correlated with VEGF protein levels and that elevated mRNA was associated w ith

earlier recurrence and stage progression o f T1G1/T1G2 bladder tumours (3). In a study o f

261 patients urinary VEGF was significantly higher in patients with bladder tumours than

highest in patients with a positive check cystoscopy compared to those with a negative

check cystoscopy and a significant correlation existed between VEGF levels and

superficial bladder tumour recurrence rates (132).

Unlike VEGF expression with the highest levels in superficial tumours, thymidine

phosphorylase expression is greatest in invasive tumours. O ’Brien and colleagues

reported a 33 fold higher expression o f TP in invasive versus superficial bladder tumours

and a 260 fold higher expression in invasive tumours compared with normal bladder

specimens (2). Less dramatic, but still significant, differences have been reported in

another study (133) which also demonstrated that high TP expression also predicted

earlier recurrence for Ta tumours. The differences between VEGF and TP expression has

lead to the hypothesis that 2 distinct angiogenic pathways exist in superficial and invasive

bladder cancer consistent with the differing genetic pathways that typify this disease.

Other angiogenic stimulatory factors that are implicated in bladder cancer include midkine

which correlates with reduced patient survival (134) and scatter factor/hepatocyte growth

factor (135). Transforming growth factor p is elevated in the serum o f patients with

bladder cancer and acidic fibroblast growth factor is significantly elevated in the urine o f

patients with invasive TCC compared with controls (136).

It has recently been shown that EGF promotes bladder cancer cell invasion and this was

pivotal role in angiogenesis played by the extracellular matrix, in particular extracellular

matrix degradation allowing endothelial cell and tumour cell invasion, modification o f

EGF/ECM degradation may provide an important therapeutic target.

As has been demonstrated, angiogenesis is a dynamic balance o f stimulatory and

inhibitory factors. In human bladder cancer the most studied endogenous inhibitor is

thrombospondin-1 (TSP-1). Low TSP-1 expression in patients with invasive TCC was

significantly associated with increased recurrence rates and decreased overall survival.

Patients with low TSP-1 levels were also significantly more likely to have high M VD

(138). Experimentally in a mouse comeal neovascularization model, the human UBC

(urinary bladder carcinoma) cell line, growing as a subcutaneous xenograft, inhibited basic

FGF induced angiogenesis (139). The nature o f this inhibitory compound was unknown

but it proved the principle that bladder cancer cells can secrete endogenous inhibitors in

much the same way as Lewis lung carcinoma cells secrete angiostatin. Subsequently Noel

Bouck’s group has demonstrated that normal urothelial cells fail to stimulate an angiogenic

response due to secreted TSP-1 (140). The secretion by tumour cells o f TSP-1 was

significantly reduced. Despite this, they found that expression o f stimulatory factors,

principally VEGF and basic FGF, was similar between tumour and normal cells. This

suggested that down regulation o f an inhibitor, TSP-1, is at least as important as

upregulation o f angiogenic stimulators in the development o f an angiogenic phenotype in

cancer cells are injected directly into the bladder wall, transfection o f the bladder cancer

cells to express more TSP-1 significantly reduced tumour growth (141).

This evidence strongly suggests that as a therapeutic target we should not only attempt to

interfere with the angiogenic stimulators but also promote the activity o f angiogenic

inhibitors.