Interaction of ionizing radiation and ZRBA1, a mixed EGFR/DNA-targeting molecule

Down-Regulation of the Proteoglycan Decorin Fills in the Tumor-Promoting Phenotype of Ionizing Radiation-Induced Senescent Human Breast Stromal Fibroblasts

Simple Summary

Ionizing radiation (a typical remedy for breast cancer) results in the premature senescence of the adjacent to the neoplastic cells stromal fibroblasts. Here, we showed that these senescent fibroblasts are characterized by the down-regulation of the small leucine-rich proteoglycan decorin, a poor prognostic factor for the progression of the disease. Decorin down-regulation is mediated by secreted growth factors in an autocrine and paracrine (due to the interaction with breast cancer cells) manner, with bFGF and VEGF being the key players of this regulation in young and senescent breast stromal fibroblasts. Autophagy activation increases decorin mRNA levels, indicating that impaired autophagy is implicated in the reduction in decorin in this cell model. Decorin down-regulation acts additively to the already tumor-promoting phenotype of ionizing radiation-induced prematurely senescent human stromal fibroblasts, confirming that stromal senescence is a side-effect of radiotherapy that should be taken into account in the design of anticancer treatments.

Abstract

Down-regulation of the small leucine-rich proteoglycan decorin in the stroma is considered a poor prognostic factor for breast cancer progression. Ionizing radiation, an established treatment for breast cancer, provokes the premature senescence of the adjacent to the tumor stromal fibroblasts. Here, we showed that senescent human breast stromal fibroblasts are characterized by the down-regulation of decorin at the mRNA and protein level, as well as by its decreased deposition in the pericellular extracellular matrix in vitro. Senescence-associated decorin down-regulation is a long-lasting process rather than an immediate response to γ-irradiation. Growth factors were demonstrated to participate in an autocrine manner in decorin down-regulation, with bFGF and VEGF being the critical mediators of the phenomenon. Autophagy inhibition by chloroquine reduced decorin mRNA levels, while autophagy activation using the mTOR inhibitor rapamycin enhanced decorin transcription. Interestingly, the secretome from a series of both untreated and irradiated human breast cancer cell lines with different molecular profiles inhibited decorin expression in young and senescent stromal fibroblasts, which was annulled by SU5402, a bFGF and VEGF inhibitor. The novel phenotypic trait of senescent human breast stromal fibroblasts revealed here is added to their already described cancer-promoting role via the formation of a tumor-permissive environment.

Anticancer Triazenes: from Bioprecursors to Hybrid Molecules

Triazenes are a very useful and diverse class of compounds that have been studied for their potential in the treatment of many tumors including brain tumor, leukemia and melanoma. Novel compounds of this class continue to be developed as either anticancer compounds or even with other therapeutic applications. This review focused on several types of triazenes from the simplest ones like 1,3-dialkyl-3-acyltriazenes to the more complex ones like combi-triazenes with an emphasis on how triazenes have been developed as effective antitumor agents.

Adipose mesenchymal stromal cells response to ionizing radiation

BACKGROUND AIMS

This study evaluates the biological response of adipose tissue-derived mesenchymal stromal cells (aMSCs) to ionizing radiation (IR).

METHODS

Irradiated BALB/c mice aMSCs were characterized for functionality and phenotype. The clonogenic capacity of irradiated aMSCs was assessed and compared with those of metastatic breast cancer cell line (4T1) and normal mouse fibroblasts (NIH3T3-wt). We investigated the IR-induced DNA damage response, apoptosis, changes in cell cycle (CC) dynamics and protein and gene expression.

RESULTS

Irradiated and non-irradiated aMSCs were able to differentiate into adipocytes, chondrocytes and osteocytes with no significant difference. Irradiated aMSCs maintained the expression of mesenchymal stromal cells (MSCs) surface antigens and, as expected, were negative for hematopoietic stem cells (HSCs) surface antigens when tested up to 7 days after IR for all irradiation doses with no significant difference. Clonogenically, irradiated aMSCs had higher relative survival fraction and plating efficiency than 4T1 and NIH3T3-wt. Irradiated aMSCs expressed higher □H2AX and significantly showed faster and more time-efficient IR-induced DNA damage response evident by up-regulated DNA-PKcs and RAD51. Two hours after IR, most of aMSCs DNA damage/repair-related genes showed up-regulation that disappeared within 6 h after IR. Irradiated aMSCs showed a significant rise and an earlier peak of p-ATM-dependent and -independent (p84/5E10-mediated) G2/M CC arrest compared with 4T1 and NIH3T3-wt.

CONCLUSIONS

After IR exposure, aMSCs showed a robust and time-efficient radiation-induced DNA damage repair response, stable phenotypical characteristics and multi-lineage differentiation potential, suggesting they may be reliable candidates for cell therapy in radiation oncology regenerative medicine.

ZRBA1, a Mixed EGFR/DNA Targeting Molecule, Potentiates Radiation Response Through Delayed DNA Damage Repair Process in a Triple Negative Breast Cancer Model

PURPOSE

ZRBA1 is a combi-molecule designed to induce DNA alkylating lesions and to block epidermal growth factor receptor (EGFR) TK domain. Inasmuch as ZRBA1 downregulates the EGFR TK-mediated antisurvival signaling and induces DNA damage, we postulated that it might be a radiosensitizer. The aim of this study was to further investigate the potentiating effect of ZRBA1 in combination with radiation and to elucidate the possible mechanisms of interaction between these 2 treatment modalities.

METHODS AND MATERIALS

The triple negative human breast MDA-MB-468 cancer cell line and mouse mammary cancer 4T1 cell line were used in this study. Clonogenic assay, Western blot analysis, and DNA damage analysis were performed at multiple time points after treatment. To confirm our in vitro findings, in vivo tumor growth delay assay was performed.

RESULTS

Our results show that a combination of ZRBA1 and radiation increases the radiation sensitivity of both cell lines significantly with a dose enhancement factor of 1.56, induces significant numbers of DNA strand breaks, prolongs higher DNA damage up to 24 hours after treatment, and significantly increases tumor growth delay in a syngeneic mouse model.

CONCLUSIONS

Our data suggest that the higher efficacy of this combination could be partially due to increased DNA damage and delayed DNA repair process and to the inhibition of EGFR. The encouraging results of this combination demonstrated a significant improvement in treatment efficiency and therefore could be applicable in early clinical trial settings.

Receptor activation and inhibition in cellular response to chemotherapeutic combinational mimicries: the concept of divergent targeting

The antiproliferative effect of tandem somatostatin receptor (SSTR) activation, epidermal growth factor receptor (EGFR) inhibition, and induction of DNA damage was analyzed using octreotide (OCT), a SSTR agonist, the clinical DNA methylating agent temozolomide (TMZ), Iressa, an EGFR inhibitor, and dual EGFR-DNA targeting agents termed "combi-molecules". Using SSTR-expressing glioma cells harbouring low levels of EGFR (U87MG) or transfected to overexpress EGFR (U87/EGFR) or a variant (U87/EGFRvIII), we showed that Iressa, alone or in combination with the DNA damaging agent TMZ, and combi-molecules RA2 and RA5 inhibited EGF-induced phosphorylation of EGFR in U87MG and more moderately in U87/EGFR and U87/EGFRvIII transfected cells. This translated into equivalent levels of Erk 1/2 inhibition. Activation of SSTRs with OCT did not modulate the effects of the various treatments on Erk 1/2 phosphorylation. Likewise, SSTR activation did not alter TMZ- or DNA-damaging combi-molecules, RA2 and RA5, induced p53 activation nor upregulation. However, SSTR activation significantly shifted TMZ-, RA2- and RA5-induced cell-cycle arrest to earlier phases (i.e., G2/M to late S, late S to S, S to G1). Further analysis showed that apoptosis was not induced. This was in agreement with the fact that p53 activation did not induce Bax upregulation nor did EGFR inhibition promote Bad dephosphorylation. Moreover, enhancement of survivin, an anti-apoptotic protein, expression was observed. The results in toto suggest that the combination of SSTR activation with EGFR inhibition and DNA damage affects cell-cycle progression but a disconnection between the targeted signalling pathways in these brain tumour cells precludes synergistic cell-killing by the triple growth inhibitory events.