Extracellular matrix modifications by oligoguluronates for cancer treatment

Abstract

Type I collagen is the main structural protein of the extracellular matrix, and is abnormally produced in many types of solid tumours. The presence of a thick and linearised collagen fibres constituting a dense network in a tumours microenvironment has been linked to high malignancy and chemoresistance of cancers. Rixova is a novel drug-candidate based on G-blocks that has demonstrated promising results in normalising the extracellular matrix, reducing tumour growth and enhancing drug delivery in preliminary clinical studies. This thesis investigates the modifications of collagen network structure and viscoelastic properties by treatment with G-blocks, which are highly defined and short, bioactive guluronate oligomers derived from alginate. The effect of G-blocks on the fibrillation of type I tropocollagen monomers was investigated by simultaneous timelapse confocal reflectance microscopy visualising the structure of the collagen network, and by multiple-particle tracking with meansquare displacement- analysis measuring the microrheology of the solution. This new method of monitoring the sol-gel transition combines two established techniques and has provided accurate information about the relation between structure and viscoelasticity of the collagen network during gelation. This tool can potentially be used to study the sol-gel transition of other biopolymer-systems. The study determined that short chained G-blocks with a DPn=12 had the strongest effect on collagen, accelerating the formation of initial aggregates in fibrillogenesis. The premature aggregation resulted in a final-network structure where fibers with larger diameters were organised in a more intertwined and densely connected network. Corresponding to the accelerated development of fibres, there was an accelerated development of viscoelastic properties of the gel. With increasing Gblock concentrations the suspended particles exhibited earlier sub-diffusive motion patterns due to increasing viscosity of the fluid within pores of the network and increasing confinement by the surrounding network-structures. In this thesis, G-blocks have been observed to interact with type 1 tropocollagen monomers, modulating the network-structure forming a stiffer and less penetrable matrix. This does not fully explain the beneficial effects seen in clinical studies of Rixova, so the mechanism behind the effect of G-blocks in vivo is yet to be determined. Further studies need to be performed to narrow down the knowledge gap between the results observed on in vivo and in vitro systems.