Glioblastoma multiforme is generally recalcitrant to current surgical and local radiotherapeutic approaches. Moreover, systemic chemotherapeutic approaches are impeded by the blood-tumor barrier. To circumvent limitations in the latter area, we developed a multicomponent, chain-like nanoparticle that can penetrate brain tumors, composed of three iron oxide nanospheres and one drug-loaded liposome linked chemically into a linear chain-like assembly. Unlike traditional small molecule drugs or spherical nanotherapeutics, this oblong-shaped, flexible nanochain particle possessed a unique ability to gain access to and accumulate at glioma sites. Vascular targeting of nanochains to the αvβ3 integrin receptor resulted in a 18.6-fold greater drug dose administered to brain tumors than standard chemotherapy. By two hours after injection, when nanochains had exited the blood stream and docked at vascular beds in the brain, the application of an external low-power radiofrequency field was sufficient to remotely trigger rapid drug release. This effect was produced by mechanically induced defects in the liposomal membrane caused by the oscillation of the iron oxide portion of the nanochain. In vivo efficacy studies conducted in two different mouse orthotopic models of glioblastoma illustrated how enhanced targeting by the nanochain facilitates widespread site-specific drug delivery. Our findings offer preclinical proof of concept for a broadly improved method for glioblastoma treatment.

MDC1 is critical component of the DNA damage response (DDR) machinery and orchestrates the ensuring assembly of the DDR protein at the DNA damage sites, and therefore loss of MDC1 results in genomic instability and tumorigenicity. However, the molecular mechanisms controlling MDC1 expression are currently unknown. Here, we show that miR-22 inhibits MDC1 translation via direct binding to its 3′ untranslated region, leading to impaired DNA damage repair and genomic instability. We demonstrated that activated Akt1 and senescence hinder DDR function of MDC1 by upregulating endogenous miR-22. After overexpression of constitutively active Akt1, homologous recombination was inhibited by miR-22–mediated MDC1 repression. In addition, during replicative senescence and stress-induced premature senescence, MDC1 was downregulated by upregulating miR-22 and thereby accumulating DNA damage. Our results demonstrate a central role of miR-22 in the physiologic regulation of MDC1-dependent DDR and suggest a molecular mechanism for how aberrant Akt1 activation and senescence lead to increased genomic instability, fostering an environment that promotes tumorigenesis. Cancer Res; 75(7); 1–13. ©2015 AACR.

MDC1 is critical component of the DNA damage response (DDR) machinery and orchestrates the ensuring assembly of the DDR protein at the DNA damage sites, and therefore loss of MDC1 results in genomic instability and tumorigenicity. However, the molecular mechanisms controlling MDC1 expression are currently unknown. Here, we show that microRNA-22 (miR-22) inhibits MDC1 translation via direct binding to its 3′-UTR, leading to impaired DNA damage repair and genomic instability. We demonstrated that activated Akt1 and senescence hinder DDR function of MDC1 by upregulating endogenous miR-22. After overexpression of constitutively active Akt1, homologous recombination was inhibited by miR-22-mediated MDC1 repression. In addition, during replicative senescence and stress-induced premature senescence, MDC1 was downregulated by upregulating miR-22 and thereby accumulating DNA damage. Our results demonstrate a central role of miR-22 in the physiological regulation of MDC1-dependent DDR and suggest a molecular mechanism for how aberrant Akt1 activation and senescence lead to increased genomic instability, fostering an environment that promotes tumorigenesis.

In recent experiments on isogenetic cancer cell lines, it was observed that exposure to high doses of anti-cancer drugs can induce the emergence of a subpopulation of weakly-proliferative and drug-tolerant cells, that display markers associated with stem cell-like cancer cells. After a period of time, some of the surviving cells were observed to change their phenotype to resume normal proliferation, and eventually repopulate the sample. Furthermore, the drug-tolerant cells could be drug resensitized following drug washout. Here we propose a theoretical mechanism for the transient emergence of such drug tolerance. In this framework, we formulate an individual-based model and an integro-differential equation model of reversible phenotypic evolution in a cell population exposed to cytotoxic drugs. The outcomes of both models suggest that non-genetic instability, stress-induced adaptation, selection and the interplay between these mechanisms can push an actively proliferating cell population to transition into a weakly-proliferative and drug-tolerant state. Hence, the cell population experiences much less stress in the presence of the drugs and, in the long run, reacquires a proliferative phenotype, due to phenotypic fluctuations and selection pressure. These mechanisms can also reverse epigenetic drug tolerance following drug washout. Our study highlights how the transient appearance of the weakly-proliferative and drug-tolerant cells is related to the use of high-dose therapy. Furthermore, we show how stem-like characteristics can act to stabilize the transient, weakly-proliferative and drug-tolerant subpopulation for a longer time window. Finally, using our models as in silico laboratories, we propose new testable hypotheses that could help uncover general principles underlying the emergence of cancer drug tolerance.

Glioma-initiating cells (GIC) have stem-like cell properties thought to be sufficient for recurrence, progression, and drug resistance in glioblastomas. In the present study, we defined miRNA (miR)-340 as a differentially expressed miRNA in human GICs that inhibit GIC-mediated tumorigenesis. Furthermore, we defined tissue plasminogen activator (PLAT) as a critical direct target of miR340 for inhibition. Among miRNAs screened, we found that miR340 expression was decreased in all human GICs and in human glioblastoma tissues, compared with human neural stem cells and normal brain tissues. miR340 overexpression in GICs suppressed their proliferative, invasive, and migratory properties in vitro, triggering cell senescence in vitro and inhibiting GIC-induced tumorigenesis in mouse brains. shRNA-mediated silencing of PLAT in GICs phenocopied the effects of miR340 overexpression in vitro and in vivo, suggesting a potential role for tissue factor in stem-like cell function. Taken together, our results identified miR340 as a tumor suppressor that functions in GIC to enforce PLAT blockade and ablate their stem-like functions. Cancer Res; 75(6); 1–11. ©2015 AACR.