Human cancer xenografts in immunocompromised mice provide an advanced genuine tumor model for research and drug development-A revisit of murine models for human cancers.

Molecular and cell biology studies have proven that human cancers are an enormously heterogenous disease, even if they originate from the same organ and tissue with identical morphological characteristics. Cancer cells in tumors from different individuals exhibit somewhat different characteristics on multiple levels, such as with respect to 1) their genetic polymorphism; 2) epigenetic mechanisms; 3) group gene activation/inactivation; 4) cell metabolism behavior; 5) aberrant incomplete terminal differentiation; 6) proliferative potential; and 7) hierarchical structure. These multiple parameters and their different combinations determine the biological characteristics of the cancer cells and their malignant/metastatic manifestations. With progress in medical research, numerous unique vulnerable targets of cancer cells have been identified from different tumors. Modern anti-cancer drug development focuses on target-based cancer cell inhibition and elimination have greatly improved the outcome of patients with some specific cancers. The murine model of human cancer has proven to be an essential procedure for the evaluation of drug efficacy in mammalian and a key link in transferring anti-cancer drug from laboratory to clinics. As classical murine cancer xenograft models with different human cancer cell lines display limited value for personalized precision medicine, creating a complete human xenograft cancer bank with all levels of abnormalities in mice has become desperately needed. This article is a review of the pros and cons of different human x murine cancer models and an attempt to find a more suitable model for the study and discovery of new anti-cancer drugs and different combination therapies in this small animal model.

Synergistic antitumor activity of oncolytic reovirus and chemotherapeutic agents in non-small cell lung cancer cells.

BACKGROUND: Reovirus type 3 Dearing strain (ReoT3D) has an inherent propensity to preferentially infect and destroy cancer cells. The oncolytic activity of ReoT3D as a single agent has been demonstrated in vitro and in vivo against various cancers, including colon, pancreatic, ovarian and breast cancers. Its human safety and potential efficacy are currently being investigated in early clinical trials. In this study, we investigated the in vitro combination effects of ReoT3D and chemotherapeutic agents against human non-small cell lung cancer (NSCLC). RESULTS: ReoT3D alone exerted significant cytolytic activity in 7 of 9 NSCLC cell lines examined, with the 50% effective dose, defined as the initial virus dose to achieve 50% cell killing after 48 hours of infection, ranging from 1.46 +/- 0.12 approximately 2.68 +/- 0.25 (mean +/- SD) log10 pfu/cell. Chou-Talalay analysis of the combination of ReoT3D with cisplatin, gemcitabine, or vinblastine demonstrated strong synergistic effects on cell killing, but only in cell lines that were sensitive to these compounds. In contrast, the combination of ReoT3D and paclitaxel was invariably synergistic in all cell lines tested, regardless of their levels of sensitivity to either agent. Treatment of NSCLC cell lines with the ReoT3D-paclitaxel combination resulted in increased poly (ADP-ribose) polymerase cleavage and caspase activity compared to single therapy, indicating enhanced apoptosis induction in dually treated NSCLC cells. NSCLC cells treated with the ReoT3D-paclitaxel combination showed increased proportions of mitotic and apoptotic cells, and a more pronounced level of caspase-3 activation was demonstrated in mitotically arrested cells. CONCLUSION: These data suggest that the oncolytic activity of ReoT3D can be potentiated by taxanes and other chemotherapeutic agents, and that the ReoT3D-taxane combination most effectively achieves synergy through accelerated apoptosis triggered by prolonged mitotic arrest.

IgM, not IgG, a key for HIV vaccine.

Although HIV infections induce a very strong humoral immune reaction with various neutralization activities and a well-defined cellular immunity, HIV vaccine development based on traditional approaches failed. The fact that neither specific antibodies nor activated CD8+ cytotoxicity T-cells could provide primary protection in high risk populations raises the question concerning whether a specific vaccine is feasible. While the immune system as an intact defense system against HIV is ineffective or may even enhance the virus spread, a distinct small part of the system plays important role in delaying the progress of the disease. After carefully dissecting the different immune reactions against the virus, a new HIV vaccine strategy is indicated.

Ex vivo expanded murine bone marrow cells with a multiple cytokine cocktail retain long-term hematopoietic reconstitution potentials.

BACKGROUND: Although ex vivo expansion of bone marrow (BM) cells has been proposed as an effective method for the early recovery from pancytopenia in patients with bone marrow stem cell transplantation (BMT), the expansion potential and the long-term reconstitution capability of such BM cells is still controversial. We describe here a multiple cytokine medium (MCM) containing major hematopoietic stimulation factors and conditioned medium from PHA-stimulated murine spleen cells that permits the expansion of BM cells with long-term hematopoietic reconstitution capacity. MATERIAL/METHODS: Male murine BM cells were expanded in MCM for 4 to 14 days and injected into lethally irradiated syngeneic female mice. The mice were maintained for 18 months after transplantation for evaluation of hematopoietic reconstitution. RESULTS: The expanded cells contained pluripotent hematopoietic stem cells and lineage committed progenitors as well as terminally differentiated cells. They permitted full recovery of lethally irradiated mice in both early and late stages in same numbers equivalent to that of unexpanded cells. More than 80% of the progenitor cells were donor originated after 18 months. Expanded cells were able to be transduced with a retroviral vector expressing Beta-galactosidase, and continued to express the marker following BMT. CONCLUSIONS: With the use of MCM, the quantity of donor cells from BM and other sources might be greatly reduced. Ex vivo expanded BM cells might also facilitate gene manipulation in vitro by retroviral vectors.

Discovery of small-molecule human immunodeficiency virus type 1 entry inhibitors that target the gp120-binding domain of CD4.

The interaction between human immunodeficiency virus type 1 (HIV-1) gp120 and the CD4 receptor is highly specific and involves relatively small contact surfaces on both proteins according to crystal structure analysis. This molecularly conserved interaction presents an excellent opportunity for antiviral targeting. Here we report a group of pentavalent antimony-containing small molecule compounds, NSC 13778 (molecular weight, 319) and its analogs, which exert a potent anti-HIV activity. These compounds block the entry of X4-, R5-, and X4/R5-tropic HIV-1 strains into CD4(+) cells but show little or no activity in CD4-negative cells or against vesicular stomatitis virus-G pseudotyped virions. The compounds compete with gp120 for binding to CD4: either immobilized on a solid phase (soluble CD4) or on the T-cell surface (native CD4 receptor) as determined by a competitive gp120 capture enzyme-linked immunosorbent assay or flow cytometry. NSC 13778 binds to an N-terminal two-domain CD4 protein, D1/D2 CD4, immobilized on a surface plasmon resonance sensor chip, and dose dependently reduces the emission intensity of intrinsic tryptophan fluorescence of D1/D2 CD4, which contains two of the three tryptophan residues in the gp120-binding domain. Furthermore, T cells incubated with the compounds alone show decreased reactivity to anti-CD4 monoclonal antibodies known to recognize the gp120-binding site. In contrast to gp120-binders that inhibit gp120-CD4 interaction by binding to gp120, these compounds appear to disrupt gp120-CD4 contact by targeting the specific gp120-binding domain of CD4. NSC 13778 may represent a prototype of a new class of HIV-1 entry inhibitors that can break into the gp120-CD4 interface and mask the gp120-binding site on the CD4 molecules, effectively repelling incoming virions.

Eradication of HIV in infected patients: some potential approaches.

Although at present, highly active antiretroviral therapy (HAART) has greatly reduced the number of viral copies to an undetectable level and has slowed down the progress of the disease in patients with human immunodeficiency virus (HIV) infection, the HIV-infected cells are not eradicated by this therapy. Virus replication rebounds once the drug therapy is terminated, regardless of duration of the therapy, primarily due to the establishment of a viral reservoir. Therefore, viral suppressive therapy is a lifelong task and may be accompanied by many as yet unidentified serious side effects. In addition, the maximum therapeutic benefits of HAART appear to have been reached recently in the U. S, and the incidences of multi-drug resistant viral strain infections are slowly but steadily increasing. Without an effective vaccine, which has already proved to be very difficult to develop, for the protection of the uninfected population and a feasible eradication strategy to cure infected patients, the number of HIV-infected persons will inevitably continue to rise. While the vast majority of endeavors are focused on developing new drugs that target different steps of HIV replication for suppressive therapy, researchers need to find a therapeutic strategy that directly aims at HIV-infected cells to cure the disease. In this article, I review and discuss some potential approaches to eradicate HIV-infected cells from the patients.

Human immunodeficiency virus reservoir might be actively eradicated as residual malignant cells by cytotoxic chemotherapy.

A unique characteristic of human immunodeficiency virus (HIV) infection is that the virus must incorporate its cDNA into the host genomic DNA for replication. Once the virus gets into the host genome and becomes a part of the host genetic materials, elimination of the virus without killing the infected cells is virtually impossible. The use of highly active antiretroviral therapy (HAART) can result in a substantial decline in viremia. However, HAART does not eradicate HIV. The progressive HIV infection will unavoidably rebound after a cessation of the treatment. Searching for a new combination therapeutic strategy with cytotoxic agents that eliminate or significantly reduce the HIV reservoir is a potential way for better control of the disease. Theoretically, the HIV reservoir can be gradually eradicated by long-term use of certain antimetabolic cytotoxic drugs coupled with proper activation of latently infected cells, if viral replication is completely blocked by antiretroviral chemotherapy to protect uninfected, susceptible cells.

Update on D-ala-peptide T-amide (DAPTA): a viral entry inhibitor that blocks CCR5 chemokine receptors.

Peptide T, named for its high threonine content (ASTTTNYT), was derived by a database search which assumed that a relevant receptor binding epitope within env (gp120) would have sequence homology to a known signaling peptide. Binding of radiolabeled gp120 to brain membranes was displaced by peptide T and three octapeptide analogs (including "DAPTA", Dala1-peptide T-amide, the protease-resistant analog now in Phase II clinical trials) with the same potency that these four octapeptides blocked infectivity of an early passage patient isolate. This 1986 report was controversial due to a number of laboratories' failure to find peptide T antiviral effects; we now know that peptide T is a potent HIV entry inhibitor selectively targeting CCR5 receptors with minimal effects on the X4 tropic lab adapted virus exclusively in use at that time. Early clinical trials, which demonstrated lack of toxicity and focused on neurological and neurocognitive benefits, are reviewed and data from a small ongoing Phase II trial--the first to assess peptide T's antiviral effects--are presented. Studies using infectivity, receptor binding, chemotaxis, and blockade of gp120-induced neurotoxicity in vitro and in vivo are reviewed, discussed and presented here. Peptide T and analogs of its core pentapeptide, present near the V2 stem of numerous gp120 isolates, are potent ligands for CCR5. Clinical data showing peptide T's immunomodulation of plasma cytokine levels and increases in the percentage of IFNgamma secreting CD8+ T cells in patients with HIV disease are presented and suggests additional therapeutic mechanisms via regulation of specific immunity.

Identification of HIV-1 nucleocapsid protein: nucleic acid antagonists with cellular anti-HIV activity.

The crucial functions of HIV-1 nucleocapsid-p7 protein (NC-p7) at different stages of HIV replication are dependent on its nucleic acid binding properties. In this study, a search has been made to identify antagonists of the interaction between NC-p7 and d(TG)(4). A chemical library of approximately 2000 small molecules (the NCI Diversity Set) was screened, of the 26 active inhibitors that were identified, five contained a xanthenyl ring structure. Further analysis of 63 structurally related compounds led to the identification of 2,3,4,5-tetrachloro-6-(4('),5('),6(')-trihydroxy-3(')-oxo-3H-xanthen-9(')-yl)benzoic acid, which binds to NC-p7 stoichiometrically. This compound exerted a significant anti-HIV activity in vitro with an IC(50) of 16.6+/-4.3 microM (means+/-SD). Synthetic variants lacking the two hydroxyls at positions 4(') and 5(') in the xanthenyl ring system failed to bind NC-p7 and showed significantly less protection against HIV infection. Molecular modeling predicts that these hydroxyl groups would bind to the amide nitrogen of Gly(35) with other contacts at the carbonyl oxygens of Gly(40) and Lys(33).

Eradication of human immunodeficiency virus type 1-infected cells by a combination of antimetabolic cytotoxic chemotherapy and antiviral chemotherapy in vitro: a pilot study.

Although highly active antiretroviral therapy against human immunodeficiency virus (HIV) type 1 reduces the mortality of persons with acquired immunodeficiency syndrome, it does not eliminate HIV reservoirs. In this study, which used a 6-thioguanine (6-TG) resistant clone (4C6) of the MT-2 cell line as a model, the combination of 6-TG with both reverse-transcriptase (RT) inhibitor and protease inhibitor or 6-TG with a protease inhibitor alone completely eradicated HIV-1-carrying cells from the culture and protected uninfected 4C6 cells from HIV-1 infection. The combination of 6-TG and a RT inhibitor, azidothymidine, provided partial protection. Protection was extended to human peripheral blood mononuclear cells. These results suggest that adding a cytotoxic drug in combination antiviral chemotherapy may reduce the establishment of virus reservoirs and prevent virus spread. The clinical value of this and similar strategies should be further evaluated in HIV-infected patients.