Synthesis and evaluation of novel antivascular agents for two-photon activation

Barnes, N

Abstract

Cancer is one of the major causes of death worldwide, hence the development of novel effective treatments to combat this disease is important. Combretastatins are powerful anticancer drugs with some derivatives in advanced clinical trials for cancer therapy. Combretastatins are stilbenes isolated from the African shrub Combretum caffrum. These agents interact with tubulin in a similar way to colchicine, causing destruction of blood vessels within tumours by binding to tubulin dimers and inhibiting angiogenesis in developing tumours. Cis-combretastatins are effective chemotherapeutic agents showing potent activity, but their overall use has been limited due to associated toxicity in normal tissues; the corresponding trans-isomers are around 2 orders of magnitude less cytotoxic. Combretastatins undergo reversible photoisomerization upon irradiation with UV/visible light.
Previously, a novel form of two-photon phototherapy was proposed, in which the “inactive” trans(E)-combretastatins are used as pro-drugs that may be activated (converted to the cis-isomer) by localized irradiation with light at the tumour site. The use of near-infrared (NIR) light to trigger a nonlinear two-photon excited photoactivation process provides deeper light penetration into tissues.
This thesis describes the synthesis and characterisation of a range of combretastatin derivatives with improved two-photon cross sections as target compounds for two photon excited anticancer phototherapy. The cytotoxicity and cell cycle analysis of the drug candidates were determined on live mammalian cell lines and candidates were screened for their inhibitory effects on tubulin polymerization; stilbenes with a B ring substitution of a para-carbonyl caused cell cycle arrest in the G2M phase and were cytotoxic in the nanomolar range (MTT HepG2, HeLa, HCT 116 50 – 250 nM, tubulin polymerisation inhibition 280 – 390 nM). Photochemical properties such as fluorescence lifetimes, fluorescence quantum yields, and two-photon absorption characteristics of the combretastatin derivatives were investigated spectroscopically. Fluorescence-lifetime imaging microscopy (FLIM) and light sheet fluorescence microscopy (LSFM) were used to determine the real-time uptake of the inactive pro-drugs into live mammalian cell monolayers and spheroids and their intracellular distribution. In conclusion, the two-photon excited activation of E-combretastatins on live cells was demonstrated, making these E-combretastatins promising pro-drug candidates for two photon excited anticancer phototherapy.

Citation

Barnes, N. (in press). Synthesis and evaluation of novel antivascular agents for two-photon activation. (Thesis). University of Salford

• Thesis Type: Thesis
• Acceptance Date: Jul 31, 2018
• Deposit Date: Sep 25, 2018
• Publicly Available Date: Sep 25, 2018
• Additional Information: Funders : Engineering and Physical Sciences Research Council (EPSRC);Science and Technology Facilities Council;Kidscan - Children's Cancer Research‎; Projects : Two photon-activation of combretastatins;Two-photon photophysics of novel stilbene-based drugs and activation in 3-dimensional (3D) tissue models; Grant Number: 1817912; Grant Number: 17230084