9-Aminoacridine-based anticancer drugs target the PI3K/AKT/mTOR, NF-kappaB and p53 pathways.

Acquisition of a transformed phenotype involves deregulation of several signal transduction pathways contributing to unconstrained cell growth. Understanding the interplay of different cancer-related signaling pathways is important for development of efficacious multitargeted anticancer drugs. The small molecule 9-aminoacridine (9AA) and its derivative, the antimalaria drug quinacrine, have selective toxicity for tumor cells and can simultaneously suppress nuclear factor-kappaB (NF-kappaB) and activate p53 signaling. To investigate the mechanism underlying these drug activities, we used a combination of two-dimensional protein separation by gel electrophoresis and mass spectrometry to identify proteins whose expression is altered in tumor cells by 9AA treatment. We found that 9AA treatment results in selective downregulation of a specific catalytic subunit of the phosphoinositide 3-kinase (PI3K) family, p110 gamma. Further exploration of this observation demonstrated that the mechanism of action of 9AA involves inhibition of the prosurvival AKT/mammalian target of rapamycin (mTOR) pathway that lies downstream of PI3K. p110 gamma translation appears to be regulated by mTOR and feeds back to further modulate mTOR and AKT, thereby impacting the p53 and NF-kappaB pathways as well. These results reveal functional interplay among the PI3K/AKT/mTOR, p53 and NF-kappaB pathways that are frequently deregulated in cancer and suggest that their simultaneous targeting by a single small molecule such as 9AA could result in efficacious and selective killing of transformed cells.

Mycoplasma infection suppresses p53, activates NF-kappaB and cooperates with oncogenic Ras in rodent fibroblast transformation.

Prokaryotes of the genus Mycoplasma are the smallest cellular organisms that persist as obligate extracellular parasites. Although mycoplasma infection is known to be associated with chromosomal instability and can promote malignant transformation, the mechanisms underlying these phenomena remain unknown. Since persistence of many cellular parasites requires suppression of apoptosis in host cells, we tested the effect of mycoplasma infection on the activity of the p53 and nuclear factor (NF)-kappaB pathways, major mechanisms controlling programmed cell death. To monitor the activity of p53 and NF-kappaB in mycoplasma-infected cells, we used a panel of reporter cell lines expressing the bacterial beta-galactosidase gene under the control of p53- or NF-kappaB-responsive promoters. Cells incubated with media conditioned with different species of mycoplasma showed constitutive activation of NF-kappaB and reduced activation of p53, common characteristics of the majority of human tumor cells, with M. arginini having the strongest effect among the species tested. Moreover, mycoplasma infection reduced the expression level and inducibility of an endogenous p53-responsive gene, p21(waf1), and inhibited apoptosis induced by genotoxic stress. Infection with M. arginini made rat and mouse embryo fibroblasts susceptible to transformation with oncogenic H-Ras, whereas mycoplasma-free cells underwent irreversible p53-dependent growth arrest. Mycoplasma infection was as effective as shRNA-mediated knockdown of p53 expression in making rodent fibroblasts permissive to Ras-induced transformation. These observations indicate that mycoplasma infection plays the role of a p53-suppressing oncogene that cooperates with Ras in cell transformation and suggest that the carcinogenic and mutagenic effects of mycoplasma might be due to inhibition of p53 tumor suppressor function by this common human parasite.

Targeted disruption of the mouse ing1 locus results in reduced body size, hypersensitivity to radiation and elevated incidence of lymphomas.

Ing1 belongs to the family of evolutionary conserved genes encoding nuclear PHD finger-containing proteins implicated in a variety of processes, including tumorigenesis, replicative senescence, excision repair and response to genotoxic stress. We have generated mice deficient in all the isoforms of Ing1 by targeted disruption of the exon that is common for all ing1 transcripts. Embryonic fibroblasts from ing1-knockout mice were similar to the wild-type cells in their growth characteristics, replicative lifespan in culture, p53 induction and sensitivity to various cytotoxic treatments with minor alterations in cell cycle distribution in response to genotoxic stress. ing1-deficient animals are characterized by reduced size with no obvious morphological, physiological or behavioral abnormalities, indicating that ing1 function is dispensable for the viability of mice under normal physiological conditions. Loss of ing1 was associated with earlier onset and higher incidence of lymphomas. Consistent with the possible involvement of Ing1 in DNA repair, ing1-deficient mice were more sensitive to total body gamma radiation. Our observations are well in line with the suggested role of ing1 as a candidate tumor suppressor gene involved in control of DNA damage response.

Structure and regulation of the mouse ing1 gene. Three alternative transcripts encode two phd finger proteins that have opposite effects on p53 function.

The human ING1 gene encodes nuclear protein p33(ING1), previously shown to cooperate with p53 in cell growth control (Garkavtsev, I., Grigorian, I. A., Ossovskaya, V. S., Chernov, M. V., Chumakov, P. M., and Gudkov, A. V. (1998) Nature 391, 295-298). p33(ING1) belongs to a small family of proteins from human, mouse, and yeast of approximately the same size that show significant similarity to one another within the C-terminal PHD finger domain and also contain an additional N-terminal region with subtle but reliably detectable sequence conservation. Mouse ing1 is transcribed from three differently regulated promoters localized within a 4-kilobase pair region of genomic DNA. The resulting transcripts share a long common region encoded by a common exon and differ in their 5'-exon sequences. Two transcripts are translated into the same protein of 185 amino acids, the mouse equivalent of the human p33(ING1), while the third transcript encodes a longer protein that has 94 additional N-terminal amino acids. Overexpression of the longer protein interferes with the accumulation of p53 protein and activation of p53-responsive promoters after DNA damage. Between the two products of ing1, only the longer one forms a complex with p53 detectable by immunoprecipitation. These results indicate that a single gene, ing1, encodes both p53-suppressing and p53-activating proteins that are regulated by alternative promoters.

Accumulation in "normal" lungs of live tumorigenic cells during sub-cutaneous growth of weakly and highly metastasizing tumors and their in vitro sensitivity to growth regulation by normal fibroblasts.

The main purposes of the study were: (1) in vivo comparison of accumulation of live tumorigenic cells (LTC) in macroscopically normal lungs of animals bearing 6 s.c. Syrian hamster sarcomas differing in spontaneous metastasizing activity (SMA); (2) in vitro examination of the sensitivity of these cell strains to the growth-regulating signals of normal fibroblasts. Cell strains used differed in SMA from very weak (WM) to extremely high (HM). The numbers of LTC doses in "normal" lung tissue of tumor-bearing animals were determined in s.c. transplantation tests by titrating single-cell suspensions prepared from the lung tissues of 5 tumor-bearing animals, for each cell strain, every 5 days during 30 days of s.c. tumor growth, until the appearance of the first spontaneous lung metastases. The sensitivity of WM and HM cells to growth-regulating signals of normal hamster embryo fibroblasts (HEFs) was examined by in vitro co-culturing during 6 days with daily determination of 3H-TdR incorporation in the WM and HM cells grown with or without contact with HEFs. The data presented demonstrate (1) the surprisingly similar efficiency in the occupation of macroscopically normal lung tissues by live tumorigenic cells of WM and HM strains, disseminating spontaneously from the s.c. tumors; (2) the significantly lower sensitivity of HM cells, in contrast to WM, to growth inhibition by contact with HEFs and especially their marked ability to usurp the growth-stimulating signals of normal HEFs.