No abstract

The subterranean blind mole rat, Spalax, experiences acute hypoxia-reoxygenation cycles in its natural subterranean habitat. At the cellular level, these conditions are known to promote genomic instability, which underlies both cancer and aging. However, Spalax is a long-lived animal and is resistant to both spontaneous and induced cancers. To study this apparent paradox we utilized a computational procedure that allows detecting differences in transcript abundance between Spalax and the closely related above-ground Rattus norvegicus in individuals of different ages. Functional enrichment analysis showed that Spalax whole brain tissues maintain significantly higher normoxic mRNA levels of genes associated with DNA damage repair and DNA metabolism, yet keep significantly lower mRNA levels of genes involved in bioenergetics. Many of the genes that showed higher transcript abundance in Spalax are involved in DNA repair and metabolic pathways that, in other species, were shown to be downregulated under hypoxia, yet are required for overcoming replication- and oxidative-stress during the subsequent reoxygenation. We suggest that these differentially expressed genes may prevent the accumulation of DNA damage in mitotic and post-mitotic cells and defective resumption of replication in mitotic cells, thus maintaining genome integrity as an adaptation to acute hypoxia-reoxygenation cycles.

Diffusing alpha-emitters radiation therapy (DaRT) is the only known method for treating solid tumors with highly destructive alpha radiation. More importantly, as a monotherapy, DaRT has been shown to induce a systemic antitumor immune response following tumor ablation. Here, immunomodulatory strategies to boost the antitumor immune response induced by DaRT, and the response specificity, were investigated in the colon cancer CT26 mouse model. Local treatment prior to DaRT, with the TLR3 agonist poly I:C, was sufficient to inhibit tumor growth relative to poly I:C or DaRT alone. DaRT used in combination with the TLR9 agonist CpG, or with the TLR1/2 agonist XS15 retarded tumor growth and increased tumor-rejection rates, compared to DaRT alone, curing 41% and 20% of the mice, respectively. DaRT in combination with CpG, the Treg inhibitor cyclophosphamide, and the MDSC inhibitor sildenafil, cured 51% of the animals, compared to only 6% and 0% cure when immunomodulation or DaRT was used alone, respectively. Challenge and Winn assays revealed that these high cure rates involved a specific immunological memory against CT26 antigens. We suggest that DaRT acts in synergy with immunomodulation to induce a specific and systemic antitumor immune response. This strategy may serve as a safe and efficient method not only for tumor ablation, but also for in situ vaccination of cancer patients.

Diffusing alpha-emitting radiation therapy (DaRT) employs intratumoral Ra-224-coated seeds that efficiently destroy solid tumors by slowly releasing alpha-emitting atoms inside the tumor. In immunogenic tumor models, DaRT was shown to activate systemic antitumor immunity. Agonists of the membrane-bound toll-like receptors (TLRs) enhanced these effects and led to tumor rejection. Here, we examined the combination of DaRT with agents that activate a different type of pattern recognition receptors, the cytoplasmatic RIG1-like receptors (RLRs). In response to cytoplasmatic viral dsRNA, RLRs activate an antiviral immune response that includes the elevation of antigen presentation. Thus, it was postulated that in low-immunogenic tumor models, RLR activation in tumor cells prior to the induction of their death by DaRT will be superior compared to TLR activation. Intratumoral cytoplasmatic delivery of the dsRNA mimic polyIC by polyethylenimine (PEI), was used to activate RLR, while polyIC without PEI was used to activate TLR. PolyIC(PEI) prior to DaRT synergistically retarded 4T1 triple-negative breast tumors and metastasis development more efficiently than polyIC and rejected panc02 pancreatic tumors in some of the treated mice. Splenocytes from treated mice, adoptively transferred to naive mice in combination with 4T1 tumor cells, delayed tumor development compared to naïve splenocytes. Low-dose cyclophosphamide, known to reduce T regulatory cell number, enhanced the effect of DaRT and polyIC(PEI) and led to high long-term survival rates under neoadjuvant settings, which confirmed metastasis clearance. The epigenetic drug decitabine, known to activate RLR in low doses, was given intraperitoneally prior to DaRT and caused tumor growth retardation, similar to local polyIC(PEI). The systemic and/or local administration of RLR activators was also tested in the squamous cell carcinoma (SCC) tumor model SQ2, in which a delay in tumor re-challenge development was demonstrated. We conclude that RIG-I-like activation prior to intratumoral alpha radiation may serve as a potent combination technique to reduce both tumor growth and the spread of distant metastases in low-immunogenic and metastatic tumor models.

Blind mole rats of the genus are the only mammalian species to date for which spontaneous cancer has never been reported and resistance to carcinogen-induced cancers has been demonstrated. However, the underlying mechanisms are still poorly understood. The fact that spp. are also hypoxia-tolerant and long-lived species implies the presence of molecular adaptations to prevent genomic instability, which underlies both cancer and aging. We previously demonstrated the upregulation of transcripts related to DNA replication and repair pathways in Yet, to date, no direct experimental evidence for improved genomic maintenance has been demonstrated for this genus. Here, we show that compared with skin fibroblasts of the above-ground rat, skin fibroblasts in culture resist several types of genotoxic insult, accumulate fewer genotoxic lesions and exhibit an enhanced DNA repair capacity. Our results strongly support that this species has evolved efficient mechanisms to maintain DNA integrity as an adaptation to the stressful conditions in the subterranean habitat.