An in vivo role for Rho kinase activation in the tumour vascular disrupting activity of combretastatin A‐4 3‐O‐phosphate

Abstract

Background and PurposeCombretastatin A-4 3-O-phosphate (CA4P) is in clinical trial as a tumour vascular disrupting agent (VDA) but the cause of blood flow disruption is unclear. We tested the hypothesis that activation of Rho/Rho kinase (ROCK) is fundamental to the effects of this drug in vivo.Experimental ApproachMouse models of human colorectal carcinoma (SW1222 and LS174T) were used. Effects of the ROCK inhibitor, Y27632, alone or in combination with CA4P, on ROCK activity, vascular function, necrosis and immune cell infiltration in solid tumours were determined. Mean arterial BP (MABP) was measured to monitor systemic interactions and the vasodilator, hydralazine, was used to control for the hypotensive effects of Y27632.Key ResultsY27632 caused a rapid drop in blood flow in SW1222 tumours, with recovery by around 3 h, which was paralleled by MABP changes. Y27632 pretreatment reduced CA4P-induced ROCK activation and partially blocked CA4P-induced tumour vascular effects, in both tumour types. Y27632 also partially inhibited CA4P-induced tumour necrosis and was associated with reduced immune cell infiltration in SW1222 tumours. Hydralazine caused a similar hypotensive effect as Y27632 but had no protective effect against CA4P treatment.Conclusions and ImplicationsThese results demonstrate that ROCK activity is critical for full manifestation of the vascular activity of CA4P in vivo, providing the evidence for pharmacological intervention to enhance the anti-tumour efficacy of CA4P and related VDAs.

Sydnone Cycloaddition Route to Pyrazole-Based Analogs of Combretastatin A4

“…42,43 As shown in Figure 7, CA4P treated tumors were significantly more necrotic than the untreated tumors, with % necrosis very similar for CA4P and 31 treated tumors. However, the tendency for necrosis to increase with 31 treatment just failed to reach significance with the animal numbers used ( Figure 7).…”

“…The percentage of necrosis was measured from H&E sections and quantified according to a random points scoring (Chalkley) system. 42,43 Statistics. Statistical analysis was carried out using GraphPad Prism 6 for Windows 8.1.…”

Evaluation of Sydnone‐Based Analogues of Combretastatin A‐4 Phosphate (CA4P) as Vascular Disrupting Agents for Use in Cancer Therapy

“…Tumours were allowed to reach 8 mm in diameter and then treated with either vehicle (50 % Na 2 CO 3 /NaCl), CA4P (100 mg kg −1 , 0.227 mmol kg −1 ) or a solution of 23 (339 mg kg −1 , 0.681 mmol kg −1 ). Tumours were excised 24 h later and necrosis levels calculated in H&E stained 5 μm thick sections by a random point scoring microscopy method using a “Chalkley” eyepiece graticule . As shown in Figure , CA4P treated tumours were significantly more necrotic than the untreated tumours, However, treatment with 23 did not have an effect on tumour necrosis.…”

Exaggerated hypertensive response to combretastatin A-4 phosphate in hypertensive rats: Effective pharmacological inhibition by diltiazem

“…A number of studies have demonstrated that depolymerization of tubulin in proliferating endothelial cells resulted in both morphological and functional changes in the tumor vasculature, leading to a dramatic decrease in tumor blood flow [27][28][29][30]. This selective tumor vascular targeting action has been demonstrated both in animal models [11,16,31,32] and human cancer patients [15,17,26,33].…”