Partial or even complete cancer regression can be achieved in some patients with current cancer treatments. However, such initial responses are almost always followed by relapse, with the recurrent cancer being resistant to further treatments. The discovery of therapeutic approaches that counteract relapse is, therefore, essential for advancing cancer medicine. Cancer cells are extremely heterogeneous, even in each individual patient, in terms of their malignant potential, drug sensitivity, and their potential to metastasize and cause relapse. Indeed, hypermalignant cancer cells, termed cancer stem cells or stemness-high cancer cells, that are highly tumorigenic and metastatic have been isolated from cancer patients with a variety of tumor types. Moreover, such stemness-high cancer cells are resistant to conventional chemotherapy and radiation. Here we show that BBI608, a small molecule identified by its ability to inhibit gene transcription driven by Stat3 and cancer stemness properties, can inhibit stemness gene expression and block spherogenesis of or kill stemnesshigh cancer cells isolated from a variety of cancer types. Moreover, cancer relapse and metastasis were effectively blocked by BBI608 in mice. These data demonstrate targeting cancer stemness as a novel approach to develop the next generation of cancer therapeutics to suppress cancer relapse and metastasis.cancer stemness | relapse | BBI608 C urrent cancer treatments ultimately fail owing to metastasis and relapse. Although chemotherapy can induce partial or even complete cancer regression in some patients, such initial responses are invariably followed by relapse, with the recurrent cancer being highly resistant to further chemotherapy, resulting in very limited survival benefits (1-3). Modern therapeutics designed to specifically target activating mutations are quite effective in inducing cancer regression in patients driven by such activating mutations; however, these treatments are also invariably followed by relapse with tumors that no longer respond to the targeted agent (2, 3). The discovery of novel therapeutic approaches that counteract cancer relapse is, therefore, urgently required for advancing cancer treatment.The idea that cancer is composed of a group of near-homogenous, ectopically growing cells has been replaced with a more complex model in which cancer cells are extremely heterogeneous, even in each individual patient, in terms of their malignant potential to metastasize and cause relapse. The increased understanding of the genomic and proteomic complexity of tumor heterogeneity further highlights the extreme heterogeneity of cancer cells (4).Subpopulations of cancer cells with extremely high tumorigenic potential, termed cancer stem cells or stem-like cancer cells, have been isolated from cancer patients with a variety of tumor types (5-13) and found to have high stemness properties (5-15). Stemness, initially defined by the expression of stem cells genes, is a property shared by embryonic stem cells and adult stem cells (16). In ...
The retinoblastoma protein (Rb)/E2F pathway links cellular proliferation control to apoptosis and is critical for normal development and cancer prevention. Here we define a transcription-mediated pathway in which deregulation of E2F1 by ectopic E2F expression or Rb inactivation by E7 of human papillomavirus type 16 signals apoptosis by inducing the expression of Chk2, a component of the DNA damage response. E2F1-and E7-mediated apoptosis are compromised in cells from patients with the related disorders ataxia telangiectasia and Nijmegen breakage syndrome lacking functional Atm and Nbs1 gene products, respectively. Both Atm and Nbs1 contribute to Chk2 activation and p53 phosphorylation following deregulation of normal Rb growth control. E2F2, a related E2F family member that does not induce apoptosis, also activates Atm, resulting in phosphorylation of p53. However, we found that the key commitment step in apoptosis induction is the ability of E2F1, and not E2F2, to upregulate Chk2 expression. Our results suggest that E2F1 plays a central role in signaling disturbances in the Rb growth control pathway and, by upregulation of Chk2, may sensitize cells to undergo apoptosis.
RNA interference (RNAi) has become an indispensable technology for biomedical research and has demonstrated the potential to become a new class of therapeutic. Current RNAi technology in mammalian cells relies on short interfering RNA (siRNA) consisting of symmetrical duplexes of 19-21 base pairs (bp) with 3' overhangs. Here we report that asymmetric RNA duplexes with 3' and 5' antisense overhangs silence mammalian genes effectively. An asymmetric interfering RNA (aiRNA) of 15 bp was incorporated into the RNA-induced silencing complex (RISC) and mediated sequence-specific cleavage of the target mRNA between base 10 and 11 relative to the 5' end of the antisense strand. The gene silencing mediated by aiRNA was efficacious, durable and correlated with reduced off-target silencing by the sense strand. These results establish aiRNA as a scaffold structure for designing RNA duplexes to induce RNAi in mammalian cells.
It has been proposed that the E2F1 transcription factor serves as a link between the Rb/E2F proliferation pathway and the p53 apoptosis pathway by inducing the expression of p19ARF, a protein that regulates p53 stability. We find that although p19ARF contributes to p53 accumulation in response to E2F expression, p19ARF is not required for E2F1-mediated apoptosis. E2F1 can signal p53 phosphorylation in the absence of p19ARF, similar to the observed modifications to p53 in response to DNA damage. These modifications are not observed in the absence of p19ARF following expression of E2F2, an E2F family member that does not induce apoptosis in mouse embryo fibroblasts but can induce p19ARF and p53 protein expression. p53 modification is found to be crucial for E2F1-mediated apoptosis, and this apoptosis is compromised when E2F1 is coexpressed with a p53 mutant lacking many N-and C-terminal phosphorylation sites. Additionally, E2F1-mediated apoptosis is abolished in the presence of caffeine, an inhibitor of phosphatidylinositol 3-kinaserelated kinases that phosphorylate p53. These findings suggest that p53 phosphorylation is a key step in E2F1-mediated apoptosis and that this modification can occur in the absence of p19ARF.
Small interfering RNAs (siRNAs) are short, double-stranded RNAs that mediate efficient gene silencing in a sequence-specific manner by utilizing the endogenous RNA interference (RNAi) pathway. The current standard synthetic siRNA structure harbors a 19-base-pair duplex region with 3' overhangs of 2 nucleotides (the so-called 19+2 form). However, the synthetic 19+2 siRNA structure exhibits several sequence-independent, nonspecific effects, which has posed challenges to the development of RNAi therapeutics and specific silencing of genes in research. In this study, we report on the identification of truncated siRNA backbone structures with duplex regions shorter than 19 bp (referred to as asymmetric shorter-duplex siRNAs or asiRNAs) that can efficiently trigger gene silencing in human cell lines. Importantly, this asiRNA structure significantly reduces nonspecific effects triggered by conventional 19+2 siRNA scaffold, such as sense-strand-mediated off-target gene silencing and saturation of the cellular RNAi machinery. Our results suggest that this asiRNA structure is an important alternative to conventional siRNAs for both functional genomics studies and therapeutic applications.
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