Rocco Carbone

Linear relationship between Wnt activity levels and apoptosis in colorectal carcinoma cells exposed to butyrate

We have reported that butyrate, a fatty acid produced by dietary fiber that induces cell cycle arrest, differentiation and/or apoptosis in colorectal carcinoma (CRC) cells in vitro, modulates Wnt activity in 2 CRC cell lines (Bordonaro et al., Int. J. Cancer, 2002; 97:42–51). Our study determines how changes in the levels of Wnt activity induced by butyrate relate to the effects of butyrate on apoptosis, cell cycle arrest and differentiation of CRC cells. In 10 human CRC cell lines a direct relationship was shown between apoptosis and butyrate‐induced increase in Wnt activity, as well as between suppressed clonal growth and increased Wnt activity. No correlation existed between butyrate‐induced increase in Wnt activity and differentiation. The direct relationship between apoptosis and Wnt activity was supported by analyses of DLD‐1 and HCT‐116 cells expressing a dominant negative form of Tcf4, and therefore, with repressed Wnt activity, as well as by measuring the ratio of apoptotic to live cells in flow cytometry‐sorted cell fractions with high and low Wnt activity. Novel flow cytometric methodology was utilized to show that butyrate differentially increases the number of cells with Wnt activity in different CRC cell lines. Thus, CRC cell lines in which butyrate upregulated Wnt activity to relatively high levels were most susceptible to the apoptotic effects of butyrate, whereas cell lines in which butyrate modestly modulated Wnt activity were less affected.

Anti-HIV-1 activity and cellular pharmacology of various analogs of gossypol

We previously reported that the racemic mixture and both enantiomers of gossypol inhibit the replication of human immunodeficiency virus-type 1 (HIV-1) (Lin et al., Antimicrob Agents Chemother 33: 2149-2151, 1989). The present study evaluates the activities of a variety of analogs of gossypol as well as a few non-gossypol analogs. Compounds 2, 3, 10, and 13 were slightly more inhibitory than (-)-gossypol to the replication of HIV-1 in cell culture. Compounds 4 and 8 were cytotoxic to human peripheral blood monocyte (PBM) cells, and compounds 2 and 3 were cytotoxic to Vero cells but not PBM cells. The effects of the two enantiomers of gossypol on the cell volume and migration of H9 cells through the cell cycle were evaluated during 72 hr of incubation. The (-)-enantiomer of gossypol was more toxic to H9 cells than the (+)-enantiomer of gossypol as evidenced by cell destruction. Prior to cell destruction, there appeared to be no significant effect on cell cycle distribution with either enantiomer.

Systemic Bcl-2 antisense oligodeoxynucleotide in combination with cisplatin cures EBV+ nasopharyngeal carcinoma xenografts in SCID mice

Nasopharyngeal carcinoma (NPC) is causally linked to Epstein‐Barr virus (EBV), and the EBV oncoprotein, latent membrane protein 1 (LMP‐1), is expressed in the majority of NPCs. LMP‐1 upregulates antiapoptotic genes, including bcl‐2, and Bcl‐2 protein is overexpressed in NPC. Given the antiapoptotic and chemoprotective effects of Bcl‐2, it represents a rational therapeutic target in NPC. We have investigated the antitumor and chemosensitizing effects of the Bcl‐2 antisense oligodeoxynucleotide G3139 (oblimersen, Genasense) in NPC. For these studies, we used the C666‐1 line, a stably infected NPC‐derived line that co‐expresses LMP‐1 and Bcl‐2. We have shown that G3139 treatment of C666‐1 in vitro caused sequence‐dependent suppression of Bcl‐2 protein, inhibition of cell growth and enhanced sensitivity to cisplatin (CDDP), as measured by increased antiproliferative and apoptotic effects. In vivo, G3139 treatment (25 mg/kg every 3 days × 5 doses) delayed engraftment and significantly inhibited growth of established C666‐1 xenografts in SCID mice compared to control oligo‐treated animals. However, G3139 alone did not prevent engraftment or cure established tumors in any animals. In contrast, G3139 treatment (25 mg/kg every 3 days × 5 starting on day 7) in combination with CDDP (8 mg/kg on day 14) completely abrogated tumor engraftment in 80% of animals compared to CDDP (0%) or CDDP + control oligo (0%). When treatment was delayed until tumor was established, G3139 in combination with CDDP significantly inhibited tumor growth compared to CDDP or CDDP + control oligo, and cured 69% animals with established tumors. No animals treated with G3139, CDDP or CDDP + control oligo were cured. Tumor burden and response to treatment correlated with EBV DNA load in serum, measured by real‐time PCR. Western blots of tumor extracts obtained during oligo treatment showed that Bcl‐2 levels were significantly decreased in G3139‐treated animals. Our studies have demonstrated that the Bcl‐2 antisense oligodeoxynucleotide, G3139, has proapoptotic effects in C666‐1, and in combination with CDDP, is curative in C666‐1 NPC xenograft tumors in vivo. The sequence‐dependency of these effects is consistent with an antisense mechanism. These studies suggest that Bcl‐2 may represent a biologically relevant target for the development of novel combinatorial therapies for NPC.

Combined proteasome and Bcl‐2 inhibition stimulates apoptosis and inhibits growth in EBV‐transformed lymphocytes: a potential therapeutic approach to EBV‐associated lymphoproliferative diseases

Objectives:  Epstein–Barr virus (EBV) transforms B‐cells into immortalized lymphoblastoid cells (LCLs) by triggering signaling pathways that lead to activation of multiple transcription factors and anti‐apoptotic proteins, including NF‐κB and Bcl‐2, respectively. Since proteasome inhibition suppresses NF‐κB activity, we sought to determine whether the proteasome inhibitor, bortezomib, alone or in combination with Bcl‐2 inhibition, has potential as a therapeutic strategy in EBV‐driven B‐cell neoplasms.

Rapid stimulation of rhodamine 123 efflux from multidrug-resistant KB cells by progesterone

Rhodamine 123 is a mitochondrial dye that is retained for prolonged periods by carcinoma cells. While investigating causes of retention of this dye, we found that 10 microM progesterone caused a rapid stimulation of efflux of rhodamine 123 within 15 min from KB V20C cells, which overexpress the multidrug resistance pump. Progesterone did not stimulate efflux from KB cells that do not overexpress the pump, and verapamil blocked rhodamine 123 efflux in the presence or absence of progesterone, indicating that rhodamine 123 is removed from KB V20C cells by the multidrug resistance pump. Progesterone, however, is unlikely to stimulate rhodamine 123 efflux by simply increasing pump activity for two reasons: (1) progesterone inhibited the efflux of daunomycin from KB V20C cells, so it did not stimulate efflux of all drugs, and (2) progesterone inhibited efflux of rhodamine 123 from L1210/VMDRC cells and had little effect on Adr MCF7 cells; both overexpress the multidrug resistance pump. In the experiments with KB V20C cells, progesterone was the most active steroid tested. At 10 microM, progesterone caused a 70-fold stimulation, desoxycorticosterone, testosterone, promegestone and estradiol about 20-fold, and others had little or no effect. Progesterone may act by a non-genomic mechanism to decrease intracellular binding of rhodamine 123, making the dye accessible to the multidrug resistance pump.

Induction of the differentiation of synchronized HL-60 leukemia cells by tiazofurin

Tiazofurin is an effective inducer of the maturation of HL-60 promyelocytic leukemia cells, as monitored by increased phagocytic ability and the capacity to reduce nitroblue tetrazolium (NBT). The antimetabolite acts as a potent inhibitor of IMP dehydrogenase, which results in a profound depression in the cellular levels of guanine nucleotides. Flow cytometric analysis of DNA histograms indicated that the commitment of HL-60 cells to differentiate when exposed to tiazofurin was preceded by a transient delay in the G1 phase of the cell cycle. HL-60 leukemia cells enriched in the various phases of the cell cycle by centrifugal elutriation were utilized to further characterize the relationship between the phase of the cell cycle and the commitment to enter a pathway of differentiation. Fractions composed mainly of G1 cells demonstrated an increased capacity to mature when exposed to tiazofurin, whereas fractions containing cells from the S and G2 + M phases of the cell cycle had a lower ability to enter a differentiation pathway. The findings suggest that the commitment of HL-60 cells to mature when exposed to tiazofurin is mediated during the G1 phase of the cell cycle.

Modulation of Wnt-specific colon cancer cell kill by butyrate and lithium.

Colorectal cancer (CRC) may be particularly amenable to gene therapy because CRCs exhibit constitutive upregulation of Wnt signaling. We have previously demonstrated that butyrate, found in the colonic lumen, modulates Wnt signaling and nonspecifically upregulates transcription from minimal promoters. Because both of these actions may influence the efficiency and specificity of Wnt-targeted expression, the effects of butyrate on Wnt-targeted gene therapy were determined. Lithium is another agent known to upregulate Wnt activity in HCT-116 CRC cells and therefore may induce Wnt-targeted CRC cell kill. CRC cells were cotransfected with an expression vector for green fluorescent protein (GFP) and different versions of vectors coupling Wnt-sensitive promoters to FADD or diphtheria toxin A-chain (DT) effector genes. Cells were treated with butyrate and/or lithium chloride and flow cytometry was used to determine the percentage of remaining transfected (GFP-positive) cells. We demonstrate that promoter and cell type-specific differences occur in Wnt-specific cell kill induced by FADD and DT. A Wnt-sensitive version of the CMV promoter (TcfCMV) exhibited the optimum combination of efficient SW620 CRC cell kill and Wnt specificity; in addition, treatment with a physiologically relevant concentration of butyrate enhanced cell kill induced by TcfCMV-FADD while maintaining specificity. In HCT-116 CRC cells, optimum results were achieved utilizing TcfFos-DT constructs and cotreatment with both butyrate and lithium. The findings suggest that effective CRC cell kill can be achieved by gene therapy through modulation of Wnt signaling by butyrate and/or lithium.

Induction of Apoptosis and Suppression of Clonogenicity of Ovarian Carcinoma Cells with Estrogen Mustard

This study was conducted to evaluate whether estramustine (estrogen mustard [EM]) is a promising alternative in the treatment of patients with epithelial ovarian carcinoma (OVCA). EM is a microtubule‐associated protein (MAP) specific antimicrotubule agent with low toxicity.