Recombinant Lysyl Oxidase Propeptide Protein Inhibits Growth and Promotes Apoptosis of Pre-Existing Murine Breast Cancer Xenografts

Abstract

Lysyl oxidase propeptide (LOX-PP) ectopic overexpression inhibits the growth of cancer xenografts. Here the ability and mode of action of purified recombinant LOX-PP (rLOX-PP) protein to inhibit the growth of pre-existing xenografts was determined. Experimental approaches employed were direct intratumoral injection (i.t.) of rLOX-PP protein into murine breast cancer NF639 xenografts, and application of a slow release formulation of rLOX-PP implanted adjacent to tumors in NCR nu/nu mice (n = 10). Tumors were monitored for growth, and after sacrifice were subjected to immunohistochemical and Western blot analyses for several markers of proliferation, apoptosis, and for rLOX-PP itself. Direct i.t. injection of rLOX-PP significantly reduced tumor volume on days 20, 22 and 25 and tumor weight at harvest on day 25 by 30% compared to control. Implantation of beads preloaded with 35 micrograms rLOX-PP (n = 10) in vivo reduced tumor volume and weight at sacrifice when compared to empty beads (p<0.05). A 30% reduction of tumor volume on days 22 and 25 (p<0.05) and final tumor weight on day 25 (p<0.05) were observed with a reduced tumor growth rate of 60% after implantation. rLOX-PP significantly reduced the expression of proliferation markers and Erk1/2 MAP kinase activation, while prominent increases in apoptosis markers were observed. rLOX-PP was detected by immunohistochemistry in harvested rLOX-PP tumors, but not in controls. Data provide pre-clinical findings that support proof of principle for the therapeutic anti-cancer potential of rLOX-PP protein formulations.

Lysyl oxidase in colorectal cancer

“…However, an equal number of studies have shown that LOX expression is capable of increasing proliferation of certain cell types, for example osteoblasts (24) and breast cancer (34) as well as CRC (discussed shortly). Coupled with reports that the LOX propeptide will inhibit cell proliferation in models of prostate (53) and breast cancer (3,51), data suggests that the precise location of LOX, its activity, its processing, and more importantly the context of its expression are all important in determining its function. It has thus become necessary to reconcile the contrasting roles of the LOX propeptide and the mature enzymatically active LOX in terms of cancer progression, and much work is being done to address this.…”

LOXL2 in Epithelial Cell Plasticity and Tumor Progression

“…Interestingly, increased matrix stiffness alone cannot promote tumor invasion and cooperation with oncogenic signaling is required for malignant progression [51]. On the other hand, opposing actions of the secreted propeptide of LOX (Figure 2) have been reported [53] and recently attributed to antiproliferative and proapoptotic effects [54].…”

Lysyl oxidases: emerging promoters of senescence escape, tumor initiation and progression

“…Indeed, it was first named the ras recision gene (rrg) because of its ability to counteract RAS-induced transformation. It has since been demonstrated that the propeptide, possessing no enzymatic activity, is responsible for this anti-tumoral property [9,10] , due to its pro-apoptotic effect [11] . It is less clear if other LOX members share those, or other, anti-tumoral properties.…”