Role of tumor microenvironment on HIF-1 pathway modulation and its association to photodynamic resistance

LAMBERTI MJ; RUMIE VITTAR NB; RIVAROLA, VA

Congreso; 16th World Congress IPA 2017; 2017

The tumor microenvironment (TME) undergoes extensive reciprocal interactions with the cancer cells and provides oncogenic signals that exacerbate cancer progression. One of the most important aspects of the TME crosstalk is the ability of cancer cells to modulate stroma behavior, and vice versa, through the collective action of a variety of soluble mediators which constitute ?cancer secretome?1. Photodynamic therapy (PDT), a promising treatment option for cancer, involves the combination of photosensitizing agents (PS), O2 and light to create a harmful photochemical reaction mediated by reactive oxygen species (ROS)2. Recent observations emphasize the role that the TME plays in drug resistance in general and to PDT in particular, strongly suggesting that the mechanical properties and stromal cellular component need to be taken into account in order to improve efficacy of anticancer therapies3. Thus, we aimed to examine the molecular and biological mechanisms underlying resistance to PDT. In order to recapitulate tumor architecture of the respective original tumor, we developed a multicellular three-dimensional (3D) spheroid co-culture system comprising tumor cells (SW480, TC) and stromal fibroblasts cells (MRC-5, FC). 3D-spheroids exhibited a normoxic periphery surrounding a hypoxic core. The characterization of the homotypic (TC) and heterotypic (TC+FC) spheroids´ secretomes was performed using label-free LCMS. Bioinformatic analysis using PID database revealed that HIF-1 signaling pathway was the most highly enriched within the proteins whose secretion was enhanced in heterotypic spheroids. HIF-1 is a key transcriptional mediator of metabolic adaptation and VEGF-mediated angiogenesis in response to hypoxia4. Using Me-ALA, a prodrug of the PS PpIX, HIF-1 transcriptional activity was strongly up-regulated and mediated PDT resistant phenotype in human colorectal spheroids. RNAi knockdown of HIF-1 impaired resistance to PDT. Oxidative stress-mediated activation of ERK1/2 followed PDT was involved on positive modulation of HIF-1 transcriptional activity after photosensitization. ROS scavenging and MEK/ERK pathway inhibition abrogated the PDT-mediated HIF-1 upregulation. Together our data demonstrated that resistance to PDT is in part mediated by the activation of a ROS-ERK1/2-HIF-1 axis, thus, identifying novel therapeutic targets that could be used in combination with PDT. Consistently, the presence of FCs considerably diminished TCs sensitivity to photodynamic activity. HIF-1 pathway modulation by both PDT and FC was further confirmed through the evaluation of the expression of the HIF-target gene VEGF. Collectively, our results delineated a mechanism by which FCs enhance TCs survival and treatment resistance, which can potentially guide translational research specifically aimed at effective clinical interventions for fibroblast-enriched and consequently HIF-1 pathway overexpressing tumors.