Characterization of salvicine-resistant lung adenocarcinoma A549/SAL cell line

Investigating the Anticancer Potential of Salvicine as a Modulator of Topoisomerase II and ROS Signaling Cascade

Salvicine is a new diterpenoid quinone substance from a natural source, specifically in a Chinese herb. It has powerful growth-controlling abilities against a broad range of human cancer cells in both in vitro and in vivo environments. A significant inhibitory effect of salvicine on multidrug-resistant (MDR) cells has also been discovered. Several research studies have examined the activities of salvicine on topoisomerase II (Topo II) by inducing reactive oxygen species (ROS) signaling. As opposed to the well-known Topo II toxin etoposide, salvicine mostly decreases the catalytic activity with a negligible DNA breakage effect, as revealed by several enzymatic experiments. Interestingly, salvicine dramatically reduces lung metastatic formation in the MDA-MB-435 orthotopic lung cancer cell line. Recent investigations have established that salvicine is a new non-intercalative Topo II toxin by interacting with the ATPase domains, increasing DNA-Topo II interaction, and suppressing DNA relegation and ATP hydrolysis. In addition, investigations have revealed that salvicine-induced ROS play a critical role in the anticancer-mediated signaling pathway, involving Topo II suppression, DNA damage, overcoming multidrug resistance, and tumor cell adhesion suppression, among other things. In the current study, we demonstrate the role of salvicine in regulating the ROS signaling pathway and the DNA damage response (DDR) in suppressing the progression of cancer cells. We depict the mechanism of action of salvicine in suppressing the DNA-Topo II complex through ROS induction along with a brief discussion of the anticancer perspective of salvicine.

Discovery of Novel Indoleamine 2,3-Dioxygenase 1 (IDO1) and Histone Deacetylase 1 (HDAC1) Dual Inhibitors Derived from the Natural Product Saprorthoquinone

The discovery of IDO1 and HDAC1 dual inhibitors may provide a novel strategy for cancer treatment by taking advantages of both immunotherapeutic and epigenetic drugs. In this paper, saprorthoquinone (1) and 13 of its analogues from Salvia prionitis Hance were investigated for their SAR against IDO1, the results demonstrated the ortho-quinone was a key pharmacophore. Then a series of IDO1 and HDAC dual inhibitors connected by appropriate linkers were designed, synthesized, and evaluated from the hit compound saprorthoquinone (1). Among them, compound 33d showed balanced activity against both IDO1 (IC₅₀ = 0.73 μM) and HDAC1 (IC₅₀ = 0.46 μM). Importantly, the structure of 33d suggested that an ortho-quinone pharmacophore and a N-(2-aminophenyl) amide pharmacophore were necessary for the IDO inhibition and HDAC inhibition respectively. Meanwhile, these two pharmacophore groups should be combined by a pentane linker. Moreover, the binding modes of 33d to the enzyme active site showed that the hydrogen bond with Leu234 of IDO1 appeared to confer increased potency to this class of inhibitors, which may explain the higher activity of 33d. This study provides a new strategy for future IDO1/HDAC dual inhibitors with synergistic antitumor activity started from lead compound 33d.

Acquired resistance of phosphatase and tensin homolog-deficient cells to poly(ADP-ribose) polymerase inhibitor and Ara-C mediated by 53BP1 loss and SAMHD1 overexpression

With increasing uses of poly(ADP‐ribose) polymerase (PARP) inhibitors (PARPi) for cancer therapy, understanding their resistance is becoming urgent. However, acquired PARPi resistance in the phosphatase and tensin homolog (PTEN)‐deficient background is poorly understood. We generated 3 PARPi‐resistant PTEN‐deficient glioblastoma U251 variants separately with olaparib (U251/OP), talazoparib (U251/TP) and simmiparib (U251/SP). These variants displayed consistent resistance (2.46‐71.78‐fold) to all 5 PARPi, including niraparib and rucaparib, and showed higher degrees of resistance to the PARPi to which the parental cells were more sensitive. The resistance was characteristic of fast emergence and high stability. However, the resistance acquirement did not cause an increasingly aggressive phenotype. The resistance was not correlated to various factors, including PTEN mutations. The PARPi‐treated variants produced less γH2AX and G2/M arrest. Consistently, loss of 53BP1 occurred in all variants and its compensation enhanced their sensitivity to PARPi by approximately 76%. The variants revealed slightly different cross‐resistance profiles to 13 non‐PARPi anticancer drugs. All were resistant to Ara‐C (6‐8‐fold) but showed differential resistance to 5‐fluorouracil, gemcitabine and paclitaxel. Almost no resistance was observed to the rest drugs, including cisplatin. SAMHD1 was overexpressed in all the variants and its knockout completely restored their sensitivity to Ara‐C but did not affect their PARPi sensitivity. The present study demonstrates a consistent resistance profile to PARPi and a unique cross‐resistance profile to non‐PARPi drugs in different PARPi‐resistant U251 cells and reveals 53BP1 loss and SAMHD1 overexpression as the primary mechanisms responsible for their resistance to PARPi and Ara‐C, respectively. These effects probably result from heritable gene change(s) caused by persistent PARPi exposure.

p53 overexpression increases chemosensitivity in multidrug-resistant osteosarcoma cell lines

PURPOSE

Multidrug resistance (MDR) is a major obstacle to the successful treatment of osteosarcoma with chemotherapy. Effectiveness of cancer therapy correlates with the ability to induce a p53-dependent apoptotic response. p53 is a tumor suppressor gene that is mutated in 22 % of osteosarcomas. While impaired p53 has been implicated in the oncogenesis of osteosarcoma, it is unclear whether overexpression of wild-type p53 can increase chemosensitivity in MDR osteosarcoma cells.

METHODS

We transfected a plasmid encoding the wild-type p53 gene to MDR osteosarcoma cell lines, which have different p53 statuses, U-2OSR2 with wild-type p53 (Wt-p53) and KHOSR2 with mutant p53 (Mt-p53), and determined the effect of p53 overexpression on chemosensitivities.

RESULTS

Both of the U-2OSR2 and KHOSR2 cell lines displayed similar trends in p53-induced drug sensitivities. However, it seems that the impact of p53 overexpression is different based on the differential intrinsic p53 status in these cell lines. In the KHOSR2 cell line (Mt-p53), overexpression of p53 up-regulates the expression of pro-apoptotic protein p21 and Bax, while in the U-2OSR2 cell line (Wt-p53), overexpression of p53 down-regulates IGF-1r expression significantly.

CONCLUSIONS

These results demonstrated that transfection of wild-type p53 increases chemosensitivity either through inhibiting IGF-1r or through increasing the expression of pro-apoptotic proteins p21 and Bax in human MDR osteosarcoma cell lines.

DJ-1 mediates the resistance of cancer cells to dihydroartemisinin through reactive oxygen species removal

Dihydroartemisinin (DHA), one of the main metabolites of artemisinin and its derivatives, presents anti-cancer potential in vitro and in vivo. To explore the mechanisms of resistance toward DHA, a DHA-resistant cell line, HeLa/DHA, was established with a resistance factor of 7.26 in vitro. Upon DHA treatment, apoptotic cells were significantly elicited in parental HeLa cells but minimally induced in HeLa/DHA cells. HeLa/DHA cells also displayed much less sensitivity to DHA-induced tumor suppression in cancer xenograft models than HeLa cells. Intriguingly, DHA-resistant cells did not display a multidrug-resistant phenotype. Based on a proteomic study employing LC-ESI-MS/MS together with pathway analysis, DJ-1 (PARK7) was found to be highly expressed in HeLa/DHA cells. Western blot and immunofluorescence assays confirmed the higher expression of DJ-1 in HeLa/DHA cells than in parental cells in both cell line and xenograft models. DJ-1 is translocated to the mitochondria of HeLa/DHA cells and oxidized, providing DJ-1 with stronger cytoprotection activity. Further study revealed that DJ-1 knockdown in HeLa/DHA cells abolished the observed resistance, whereas overexpression of DJ-1 endowed the parental HeLa cells with resistance toward DHA. Reactive oxygen species (ROS) were also significantly induced by either DHA or hydrogen peroxide in HeLa cells but not in resistant HeLa/DHA cells. When the cells were pretreated with N-acetyl-l-cysteine, the effect of DJ-1 knockdown on sensitizing HeLa/DHA cells to DHA was significantly attenuated. In summary, our study suggests that overexpression and mitochondrial translocation of DJ-1 provides HeLa/DHA cells with resistance to DHA-induced ROS and apoptosis.

Synthesis, characterization, and in vitro evaluation of palmitoylated arabinogalactan with potential for liver targeting

Arabinogalactan (AG), a water soluble polysaccharide with more than 80 mol% galactose units, was hydrophobized by covalent attachment of palmitoyl chains using a base-catalyzed esterification reaction with the objective of effective amalgamation of arabinogalactan in liposomes for targeting asialoglycoprotein receptors (ASGPR) on liver parenchymal cells. Palmitoylated AG (PAG) was characterized by physico-chemical parameters, IR, (1)H NMR, and (13)C NMR and molecular weight determination by gel permeation chromatography. PAG was incorporated in liposomes and the liposomes were characterized by dynamic light scattering, optical microscopy, zeta potential, and transmission electron microscopic (TEM) techniques. The liposomal system was evaluated for acute toxicity in swiss albino mice and was found to be safe. Targeting ability of PAG was confirmed by in vitro binding affinity to Ricinus communis agglutinin (RCA(120)), a lectin specific for galactose. The liposomal system with PAG was evaluated for cytotoxicity on HepG2, MCF7, and A549 cancer cell lines. Cytotoxicity study revealed enhanced activity on ASGPR-expressive HepG2 cells as compared to MCF7.

Drug transporter-independent liver cancer cell killing by a marine steroid methyl spongoate via apoptosis induction

Hepatocellular carcinoma (HCC) is inherently resistant to the majority of clinical anticancer drugs. To obtain drugs that can circumvent or evade such inherent drug resistance of HCC, we investigated the effect of the marinely derived steroid methyl spongoate (MESP) on HCC cells. MESP displayed potent cell killing against a panel of six HCC cell lines, independent of their expression of drug transporters. MESP did not change the function of the drug transporters, and its cell killing was not impaired in multidrug-resistant cancer cells overexpressing the transporters. The cell killing of MESP was irrelevant to estrogen or androgen signaling and was not associated with cell cycle progression, inhibition of microtubules, and topoisomerases. In contrast, MESP potently induced apoptosis via activation of a proapoptotic caspase cascade and relief of the suppression of antiapoptotic signal transducers and activators of transcription 3 (STAT3) signaling. MESP inhibited the phosphorylation of STAT3, a critical survival signaling factor that reduced the expression of the antiapoptotic protein x-linked inhibitor of apoptosis protein but enhanced the expression of the proapoptotic protein Bax, thus promoting caspase-dependent apoptosis. These data reveal that MESP may well serve as an important candidate drug lead for HCC therapy.

Structure and biological evaluation of novel cytotoxic sterol glycosides from the marine red alga Peyssonnelia sp

Bioactivity-guided fractionation of the extract from a Fijian red alga Peyssonnelia sp. led to the isolation of two novel sterol glycosides 19-O-β-d-glucopyranosyl-19-hydroxy-cholest-4-en-3-one (1) and 19-O-β-d-N-acetyl-2-aminoglucopyranosyl-19-hydroxy-cholest-4-en-3-one (2), and two known alkaloids indole-3-carboxaldehyde (3) and 3-(hydroxyacetyl)indole (4). Their structures were characterized by 1D and 2D NMR and mass spectral analysis. The sterol glycosides inhibited cancer cell growth with mean IC₅₀ values (for 11 human cancer cell lines) of 1.63 and 1.41μM for 1 and 2, respectively. The most sensitive cancer cell lines were MDA-MB-468 (breast) and A549 (lung), with IC₅₀'s in of 0.71-0.97μM for 1 and 2. Modification of the sterol glycoside structures revealed that the α,β-unsaturated ketone at C-3 and oxygenation at C-19 of 1 and 2 are crucial for anticancer activity, whereas the glucosidic group was not essential but contributed to enhanced activity against the most sensitive cell lines.

Dihydroartemisinin accelerates c-MYC oncoprotein degradation and induces apoptosis in c-MYC-overexpressing tumor cells

Artemisinin and its derivatives (ARTs) are effective antimalarial drugs and also possess profound anticancer activity. However, the mechanism accounted for its distinctive activity in tumor cells remains unelucidated. We computed Pair wise Pearson correlation coefficients to identify genes that show significant correlation with ARTs activity in NCI-55 cell lines using data obtained from studies with HG-U133A Affymetrix chip. We found c-myc is one of the genes that showed the highest positive correlation coefficients among the probe sets analyzed (r=0.585, P<0.001). Dihydroartemisinin (DHA), the main active metabolite of ARTs, induced significant apoptosis in HL-60 and HCT116 cells that express high levels of c-MYC. Stable knockdown of c-myc abrogated DHA-induced apoptosis in HCT116 cells. Conversely, forced expression of c-myc in NIH3T3 cells sensitized these cells to DHA-induced apoptosis. Interestingly, DHA irreversibly down-regulated the protein level of c-MYC in DHA-sensitive HCT116 cells, which is consistent to persistent G1 phase arrest induced by DHA. Further studies demonstrated that DHA accelerated the degradation of c-MYC protein and this process was blocked by pretreatment with the proteasome inhibitor MG-132 or GSK 3beta inhibitor LiCl in HCT116 cells. Taken together, ARTs might be useful in the treatment of c-MYC-overexpressing tumors. We also suggest that c-MYC may potentially be a biomarker candidate for prediction of the antitumor efficacies of ARTs.

DNA repair inhibitors in cancer treatment

Chemotherapy and radiation are two important modalities for cancer treatment. Many agents in clinical used have the ability to induce DNA damage, however they may be highly cytotoxic as a secondary effect. Different mechanisms are involved both, in detection and repair of DNA damage. The modulation of these pathways, has a great impact on clinical outcome and is frequently responsible of therapeutic resistance. Therefore, pharmacological inhibition of DNA damage repair pathways has been explored as a useful strategy to enhance chemo and radiosensitivity, thus it could be used for reversing drug resistance. Different agents have shown excellent results in preclinical studies in combination with radiation or chemotherapy. Early phase clinical trials are now being carried out using different DNA repair inhibitors targeting several enzymes such as PARP, DNA-PK or MGMT.

New tricks for old drugs: the anticarcinogenic potential of DNA repair inhibitors

Defective or abortive repair of DNA lesions has been associated with carcinogenesis. Therefore it is imperative for a cell to accurately repair its DNA after damage if it is to return to a normal cellular phenotype. In certain circumstances, if DNA damage cannot be repaired completely and with high fidelity, it is more advantageous for an organism to have some of its more severely damaged cells die rather than survive as neoplastic transformants. A number of DNA repair inhibitors have the potential to act as anticarcinogenic compounds. These drugs are capable of modulating DNA repair, thus promoting cell death rather than repair of potentially carcinogenic DNA damage mediated by error-prone DNA repair processes. In theory, exposure to a DNA repair inhibitor during, or immediately after, carcinogenic exposure should decrease or prevent tumorigenesis. However, the ability of DNA repair inhibitors to prevent cancer development is difficult to interpret depending upon the system used and the type of genotoxic stress. Inhibitors may act on multiple aspects of DNA repair as well as the cellular signaling pathways activated in response to the initial damage. In this review, we summarize basic DNA repair mechanisms and explore the effects of a number of DNA repair inhibitors that not only potentiate DNA-damaging agents but also decrease carcinogenicity. In particular, we focus on a novel anti-tumor agent, beta-lapachone, and its potential to block transformation by modulating poly(ADP-ribose) polymerase-1.

Emerging cancer therapeutic opportunities target DNA-repair systems

DNA-damaging agents have a central role in non-surgical cancer treatment. The balance between DNA damage and repair determines the final therapeutic consequences. An elevated DNA-repair capacity in tumor cells leads to drug or radiation resistance and severely limits the efficacy of these agents. Interference with DNA repair has emerged as an important approach in combination therapy against cancer. Anticancer targets in DNA-repair systems have emerged, against which several small-molecule compounds are currently undergoing clinical trials.