alpha-Difluoromethylornithine inhibits liver metastasis produced by intrasplenic injection of human tumor cells into nude mice

Heparanase Inhibition by Pixatimod (PG545): Basic Aspects and Future Perspectives

Pixatimod is an inhibitor of heparanase, a protein which promotes cancer via its regulation of the extracellular environment by enzymatic cleavage of heparan sulfate (HS) and non-enzymatic signaling. Through its inhibition of heparanase and other HS-binding signaling proteins, pixatimod blocks a number of pro-cancerous processes including cell proliferation, invasion, metastasis, angiogenesis and epithelial-mesenchymal transition. Several laboratories have found that these activities have translated into potent activity using a range of different mouse cancer models, including approximately 30 xenograft and 20 syngeneic models. Analyses of biological samples from these studies have confirmed the heparanase targeting of this agent in vivo and the broad spectrum of anti-cancer effects that heparanase blockade achieves. Pixatimod has been tested in combination with a number of approved anti-cancer drugs demonstrating its clinical potential, including with gemcitabine, paclitaxel, sorafenib, platinum agents and an anti-PD-1 antibody. Clinical testing has shown pixatimod to be well tolerated as a monotherapy, and it is currently being investigated in combination with the anti-PD-1 drug nivolumab in a pancreatic cancer phase I trial.

DFMO/eflornithine inhibits migration and invasion downstream of MYCN and involves p27Kip1 activity in neuroblastoma

Neuroblastoma (NB) is the most common extracranial pediatric tumor. NB patients over 18 months of age at the time of diagnosis are often in the later stages of the disease, present with widespread dissemination, and often possess MYCN tumor gene amplification. MYCN is a transcription factor that regulates the expression of a number of genes including ornithine decarboxylase (ODC), a rate-limiting enzyme in the biosynthesis of polyamines. Inhibiting ODC in NB cells produces many deleterious effects including G₁ cell cycle arrest, inhibition of cell proliferation, and decreased tumor growth, making ODC a promising target for drug interference. DFMO treatment leads to the accumulation of the cyclin-dependent kinase inhibitor p27^Kip1 protein and causes p27^Kip1/Rb-coupled G₁ cell cycle arrest in MYCN-amplified NB tumor cells through a process that involves p27^Kip1 phosphorylation at residues Ser10 and Thr198. While p27^Kip1 is well known for its role as a cyclin-dependent kinase inhibitor, recent studies have revealed a novel function of p27^Kip1 as a regulator of cell migration and invasion. In the present study we found that p27^Kip1 regulates the migration and invasion in NB and that these events are dependent on the state of phosphorylation of p27^Kip1. DFMO treatments induced MYCN protein downregulation and phosphorylation of Akt/PKB (Ser473) and GSK3-β (Ser9), and polyamine supplementation alleviated the DFMO-induced effects. Importantly, we provide strong evidence that p27^Kip1 mRNA correlates with clinical features and the survival probability of NB patients.

Antiproliferative effect of ascorbic acid is associated with the inhibition of genes necessary to cell cycle progression

Background

Ascorbic acid (AA), or Vitamin C, is most well known as a nutritional supplement with antioxidant properties. Recently, we demonstrated that high concentrations of AA act on PMP22 gene expression and partially correct the Charcot-Marie-Tooth disease phenotype in a mouse model. This is due to the capacity of AA, but not other antioxidants, to down-modulate cAMP intracellular concentration by a competitive inhibition of the adenylate cyclase enzymatic activity. Because of the critical role of cAMP in intracellular signalling, we decided to explore the possibility that ascorbic acid could modulate the expression of other genes.

Methods and Findings

Using human pangenomic microarrays, we found that AA inhibited the expression of two categories of genes necessary for cell cycle progression, tRNA synthetases and translation initiation factor subunits. In in vitro assays, we demonstrated that AA induced the S-phase arrest of proliferative normal and tumor cells. Highest concentrations of AA leaded to necrotic cell death. However, quiescent cells were not susceptible to AA toxicity, suggesting the blockage of protein synthesis was mainly detrimental in metabolically-active cells. Using animal models, we found that high concentrations of AA inhibited tumor progression in nude mice grafted with HT29 cells (derived from human colon carcinoma). Consistently, expression of tRNA synthetases and ieF2 appeared to be specifically decreased in tumors upon AA treatment.

Conclusions

AA has an antiproliferative activity, at elevated concentration that could be obtained using IV injection. This activity has been observed in vitro as well in vivo and likely results from the inhibition of expression of genes involved in protein synthesis. Implications for a clinical use in anticancer therapies will be discussed.

TAC-101, a benzoic acid derivative, inhibits liver metastasis of human gastrointestinal cancer and prolongs the life-span

We examined the anti-tumor effect of a novel benzoic acid derivative, TAC-101 (4-[3,5-bis(trimethylsilyl) benzamide] benzoic acid) on models with liver metastasis. Oral administration of TAC-101 significantly inhibited spontaneous liver metastasis of AZ-521 (human gastric cancer ) by orthotopic implantation to athymic nude mice. It also inhibited both the liver metastasis of AZ-521 induced by intrasplenic injection and the secondary lung metastasis from the liver. In addition, TAC-101 inhibited the proliferation of Co-3 (human colon adenocarcinoma) that formed a single nodule in the liver of athymic nude mice by intrahepatic implantation. The growth inhibitory effect of TAC-101 on AZ-521 experimental liver metastasis was observed when treatment was started on day 7, 14, or 21 which may correspond to the progressive stage of liver metastasis in clinical settings. Multiple administration of TAC-101 (8 mg/kg/day) significantly prolonged survival time of the animals with liver metastasis by intrasplenic injection of AZ-521 (T/C = 230%) and A549 (human lung adenocarcinoma; T/C = 186%). These effects of TAC-101 were stronger than those of 5-FU, CDDP or ATRA. Furthermore, TAC-101 inhibited the binding of AP-1 to DNA on electrophoretic mobility shift assay using nuclear extract of AZ-521 cells, although ATRA did not inhibit. These findings suggested that TAC-101 may be a candidate for a new class of anti-cancer agents for liver metastasis.

Polyamine profiles and growth properties of ornithine decarboxylase overexpressing MCF-7 breast cancer cells in culture

To determine the direct influence of the polyamine (PA) pathway on breast cancer phenotype, we employed a transfection approach to induce overexpression of the PA biosynthetic enzyme ornithine decarboxylase (ODC) in the hormone-responsive MCF-7 breast cancer cell line. Using a modified calcium phosphate method and an ODC cDNA coding for a truncated and more stable enzyme, we were able to achieve a moderate to marked degree of ODC overexpression (up to 150-fold) in a transient transfection system. ODC-overexpressing MCF-7 cells exhibited a selective increase in cellular putrescine content, while the levels of spermidine and spermine remained unaffected. Under defined culture conditions, overexpression of ODC resulted in a consistent but modest increase in [3H]thymidine incorporation into DNA which was similar in the presence and absence of 17-beta-estradiol, TGF-alpha, and IGF-I. In the presence of serum, the effect of ODC overexpression on basal [3H]-thymidine incorporation into DNA was inconsistent, possibly as a result of subtle differences in culture conditions. Overall, our results support the hypothesis that activation of the PA biosynthetic pathway may confer a growth advantage to breast cancer cells.

Sensitivity of human colon tumor metastases to anticancer drugs in athymic (nude) mice

We have studied the metastatic behavior of five human colon tumor cell lines (LS174T, WiDr, Caco-2, SW 620 and SW 480) using intrasplenic-nude mouse (ISMS) and intravenous-nude mouse (IVMS) model systems. LS174T was highly metastatic in both systems. In the IVMS system, LS174T cells produced lung metastasis and also grew in the skin as if the cells had been injected subcutaneously. We have also studied the anti-metastatic activity of three anticancer drugs (5-fluorouracil (5-FU), doxorubicin (DX) and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) using LS174T cells and both ISMS and IVMS systems. The drugs were given intravenously on day 19 and 26 of tumor cell injection. Mice were sacrificed and organs observed for metastatic growth 4-6 weeks after cell injection. The results show that in the ISMS system, BCNU and 5-FU are inactive against both the liver metastasis and primary growth in the spleen. DX inhibits metastatic growth but not the primary growth. In the IVMS system, BCNU is inactive, whereas 5-FU and DX are active against the metastatic growth. Thus, DX may have activity against blood-borne human colon tumor metastasis.

Transglutaminase activity in human colorectal carcinomas of differing metastatic potential

Transglutaminase (TGA) activity in four human colorectal carcinoma cell lines of differing metastatic potential, and the effects of mild proteolysis on this activity, was investigated. Rank order of metastatic activity measured in nude mice (intrasplenic injection) was found to be LS174T greater than SW620 greater than WiDr greater than SW480. Rank orders of TGA activity were SW480 greater than WiDr greater than SW620 greater than LS174T. Proteolysis of cell lysates increased LS174T TGA activity 42-fold, SW620 2-fold without affecting WiDr or SW480 activity. Hence a negative association exists between metastatic potential and TGA activity in human colorectal carcinoma cells. Furthermore, a positive association exists between proteolytic activation of TGA and metastatic potential.

In vitro response of a human colon tumor xenograft and a lung adenocarcinoma cell line to alpha-difluoromethylornithine alone and in combination with 5-fluorouracil and doxorubicin

We have investigated effects of alpha-difluoromethylornithine (DFMO), both as a single agent and in combination with 5-fluorouracil (5-FU) against a human colon tumor xenograft (T6) grown as primary tissue culture in serum-free medium and in combination with doxorubicin (DX) against a human lung adenocarcinoma cell line (A549). DFMO showed a dose-dependent growth-inhibitory effect against human colon tumor xenograft and lung adenocarcinoma cells. Growth-inhibitory activity of DFMO against T6 cells was reversed completely when the cells were treated simultaneously with putrescine (PU) (10(-6) M) and DFMO (10(-3) M). When 5-FU and DFMO were used in combination against T6 cells, no antagonism or synergism between the two drugs was seen. However, in the case of A549 cells, when DFMO was used in combination with DX, there was a consistent increase in growth inhibition that surpassed the inhibition of either agent given alone.