Synergy of gemcitabine and lidamycin associated with NF-kappaB downregulation in pancreatic carcinoma cells

Bacteria as a treasure house of secondary metabolites with anticancer potential

Cancer stands in the frontline among leading killers worldwide and the annual mortality rate is expected to reach 16.4 million by 2040. Humans suffer from about 200 different types of cancers and many of them have a small number of approved therapeutic agents. Moreover, several types of major cancers are diagnosed at advanced stages as a result of which the existing therapies have limited efficacy against them and contribute to a dismal prognosis. Therefore, it is essential to develop novel potent anticancer agents to counteract cancer-driven lethality. Natural sources such as bacteria, plants, fungi, and marine microorganisms have been serving as an inexhaustible source of anticancer agents. Notably, over 13,000 natural compounds endowed with different pharmacological properties have been isolated from different bacterial sources. In the present article, we have discussed about the importance of natural products, with special emphasis on bacterial metabolites for cancer therapy. Subsequently, we have comprehensively discussed the various sources, mechanisms of action, toxicity issues, and off-target effects of clinically used anticancer drugs (such as actinomycin D, bleomycin, carfilzomib, doxorubicin, ixabepilone, mitomycin C, pentostatin, rapalogs, and romidepsin) that have been derived from different bacteria. Furthermore, we have also discussed some of the major secondary metabolites (antimycins, chartreusin, elsamicins, geldanamycin, monensin, plicamycin, prodigiosin, rebeccamycin, salinomycin, and salinosporamide) that are currently in the clinical trials or which have demonstrated potent anticancer activity in preclinical models. Besides, we have elaborated on the application of metagenomics in drug discovery and briefly described about anticancer agents (bryostatin 1 and ET-743) identified through the metagenomics approach.

Apoptotic Melanoma B16-F1 Cells Induced by Lidamycin Could Initiate the Antitumor Immune Response in BABL/c Mice

In the process of tumor cell apoptosis induced by specific regents, calreticulin (CRT) was transferred from endoplasmic reticulum (ER) onto the cell membrane. These tumor cells, when used as the cellular vaccine to immunize experimental animals, could initiate effective antitumor immunoresponse against homologous tumor cells. This is referred to as immunogenic cell death. Lidamycin (LDM) is an enediyne antibiotic, which has extremely potent cytotoxicity to cancer cells. In this study, the mouse melanoma B16-F1 cancer cells were used to investigate the ability of LDM in promoting immunogenic cell death. Our data showed that LDM could induce apoptosis of B16-F1 cancer cells, accompanied by CRT translocation onto the cell membrane. These LDM-treated B16-F1 cells could be recognized and phagocytosed more efficiently by macrophage and dendritic cells. When the LDM-treated apoptotic B16-F1 cells were used as a whole-cell tumor vaccine to immune mice, the mice obtained resistance against rechallenged B16-F1 living cells. At the same time, the specific antitumor immune response was observed in these vaccinated mice. The splenocytes from the mice vaccinated with LDM-treated B16-F1 cells showed significantly enhanced NK lymphocyte activities and also faster growth rate and increased secretion of IFN-γ when encountering the cellular antigens from B16-F1 cells. All these results suggested that LDM could promote immunogenic cell death in B16-F1 cells, and these LDM-treated B16-F1 cells could be used as a sort of cell vaccine to initiate effective antitumor immunoresponse in mice.

Simultaneous determination of lidamycin enediyne chromophore (LDC) and its aromatized derivative (LDCA) using puerarin as internal standard in rat plasma by LC-MS/MS

Lidamycin (LDM), a promising enediyne antitumor antibiotic, was quantified by detecting lidamycin enediyne chromophore (LDC) using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the first time. A simple, rapid and reliable method was developed and validated to determine LDC and its aromatized derivative (LDCA) simultaneously in plasma. Puerarin was used as an internal standard (IS), and plasma samples were pretreated with one-step precipitation by acetonitrile. Separation was achieved on a reverse-phase C(18) column with a mobile phase composed of methanol and water containing 5 mm ammonium acetate at pH 3.5 in gradient elution mode. Detection was performed on a triple quadrupole tandem mass spectrometer using electrospray ionization (ESI) by multiple reaction monitoring (MRM) in the negative ion mode. Good linearity was obtained over the concentration range of 0.2-100 µg/mL for LDM. Precision and accuracy were validated by RSD% values in the range of 2.6-13.0% and RE% values between -4.6 and 3.8%, respectively. In addition, no specificity and matrix effects were observed. The recovery was found to be 99.2-111.0% and stability in various conditions was found to be acceptable. This method was applied in preclinical pharmacokinetic studies for routine monitoring of LDM in rat plasma.

Targeting apoptosis pathways in pancreatic cancer

Pancreatic cancer - here in particular pancreatic ductal adenocarcinoma (PDAC) - is still a highly therapy refractory disease. Amongst the mechanisms by which PDAC cells could escape any non-surgical therapy, anti-apoptotic protection seems to be the most relevant one. PDAC cells have acquired resistance to apoptotic stimuli such as death ligands (FasL, TRAIL) or anti-cancer drugs (gemcitabine) by a great number of molecular alterations either disrupting an apoptosis inducing signal or counteracting the execution of apoptosis. Thus, PDAC cells exhibit alterations in the EGFR/MAPK/Ras/raf1-, PI3K/Akt-, TRAIL/TRAF2-, or IKK/NF-κB pathway accompanied by deregulations in the expression of apoptosis regulators such as cIAP, Bcl2, XIAP or survivin. Along with protection against apoptosis, PDAC cells also overexpress histone deacetylases (HDACs) giving rise to epigenetic patterns of chemoresistance and to acetylation of other regulatory proteins, as well. With respect to the multitude of anti-apoptotic pathways, a great number of molecular targets might be of high potential in novel therapy strategies. Thus, natural compounds as well as novel synthetic drugs are considered to be used in single or combined therapy of PDAC. A number of proteasome and HDAC inhibitors or selective inhibitors of IKK, EGFR, Akt and mTOR have been widely explored in preclinical settings and clinical studies. Even though these early studies encouraged an application in a clinical setting, most of the trials have been rather disappointing yet. Thus, new molecular targets and novel concepts of combination therapies need to get access into clinical trials - either in neoadjuvant/adjuvant or in palliative treatments.

Lidamycin shows highly potent cytotoxic to myeloma cells and inhibits tumor growth in mice

AIM

To investigate the effects of lidamycin (LDM) on a mouse myeloma cell line (SP2/0) and human multiple myeloma cell lines (U266 and SKO-007), and provide the basis for the use of LDM in cancer therapy.

METHODS

A 3-[4,5-dimethylthiazol-2-yl]5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]2H-tetrazolium inner salt (MTS) assay was used to determine the degree of growth inhibition by the drugs analyzed in this study. Cell cycle distribution and analysis were measured by flow cytometry combined with propidium iodide (PI) staining. The effects on apoptosis were measured by Hoechst 33342 staining and by flow cytometry combined with fluorescein-isothiocyanate-Annexin V/propidium iodide (FITC-Annexin V/PI) staining. Protein expression was determined by Western blot analysis. In vivo antitumor activity was measured using a murine myeloma model in BALB/c mice.

RESULTS

There was a significant reduction in cell proliferation after treatment with LDM. The overall growth inhibition correlated with increased apoptotic cell death. LDM-induced cell apoptosis was associated with the activation of c-Jun-N-terminal kinase (JNK), and cleavage of caspase-3/7 and poly (ADP-ribose) polymerase (PARP). LDM markedly suppressed tumor growth in a murine myeloma model.

CONCLUSION

LDM induces apoptosis in murine myeloma SP2/0 cells as well as in human myeloma U266 and SKO-007 cell lines. The sustained activation of JNK might play a critical role in LDM-induced apoptosis in the SP2/0 cell line. LDM demonstrates significant antitumor efficacy against myeloma SP2/0 cells in mice. Taken together, our data provide some clues for further research of the effects of LDM on human multiple myeloma.Acta Pharmacologica Sinica (2009) 30: 1025-1032; doi: 10.1038/aps.2009.75.