John E. Mata

Resistance to chemotherapeutic drugs overcome by c-Myc inhibition in a Lewis lung carcinoma murine model

Chemotherapy resistance is a significant obstacle in lung cancer therapy, and has been found to frequently correlate with amplification and overexpression of the c-myc oncogene. Earlier studies have shown that c-Myc inhibition alone is not always effective in cancer models. The purpose of this study was to test different dosing regimen, which included commonly used chemotherapeutic drugs in combination with c-Myc inhibition in a Lewis lung syngeneic drug-resistant murine tumor model. Inhibition of c-myc was specifically achieved by using phosphorodiamidate Morpholino oligomer (PMOs), a novel, non-toxic antisense DNA chemistry for inhibition of gene expression by an RNase H-independent mechanism. When administration of cisplatin overlapped with c-myc PMO (AVI-4126) treatment there was no additional effect on tumor growth inhibition compared to cisplatin alone. In contrast, using a dosing regimen in which cisplatin or taxol treatment preceded AVI-4126, a dramatic decrease in tumor growth rate was observed with tumor areas less then 0.5 cm2 in 60% of the animals at the end of the study. This effect was specific to c-Myc inhibition as other antisense PMOs against p21 or Rad51 showed no such effect in combination with chemotherapy. Immunoblot and HPLC-based analysis of tumor lysates at the end of the study confirmed c-Myc inhibition and detection of intact AVI-4126, respectively. In conclusion, AVI-4126 potentiates the efficacy of chemotherapeutic drugs in a manner that is schedule dependent.

Tumor cell growth is inhibited by suppressing metallothionein-I synthesis

The effect of metallothionein (MT)-I antisense oligodeoxynucleotide (ODN) on the growth of three kinds of tumor cells was studied, since MTs may be involved in cell growth. When MT-I antisense ODN was added to leukemia P388 cells, cell growth was inhibited in a manner dependent on the dose and incubation time. MT-I antisense ODN was also inhibitory for other tumor cell lines, i.e. Ehrlich carcinoma and sarcoma 180. A significant decrease in the level of MT, but not of Zn, was observed in MT-I antisense ODN-treated cells. On the other hand, control ODN did not inhibit the cell growth appreciably. These results indicate that MT-I expression may be necessary for the growth and survival of these tumor cells.

Evidence of enhanced Iron excretion during systemic Phosphorothioate oligodeoxynucleotide treatment

Background: Phosphorothioate oligonucleotides, in general, possess properties that could be utilized in the development of therapeutic heavy metal chelators. Methods: Iron excretion was measured in 16 patients participating in studies to test the safety of OL(1)p53, a 20-mer phosphorothioate oligonucleotide complementary to p53 mRNA. Patients were given OL(1)p53 at doses of 0.05 to 0.25 mg/kg/h for 10 days by continuous intravenous infusion. Urine was collected during the study and analyzed for iron, copper, cadmium, and zinc. Results: We found that phosphorothioate oligonucleotides have a high affinity for iron as well as several other clinically relevant toxic metals. Analysis of patient urine following administration of OL(1)p53 reveals a 7.5-fold increase in iron excretion at low doses (0.05 mg/kg/h). Conclusions: Phosphorothioate oligonucleotides may have therapeutic potential as heavy metal chelators. Low doses of phosphorothioate oligonucleotide facilitated the excretion of iron. Renal clearance of iron-phosphorothioate oligonucleotide complexes most likely involves secretion into proximal tubules.

The suppression of metallothionein synthesis inhibits the growth of leukemia P388 cells

Metallothionein (MT) isoforms, by regulating the homeostasis of zinc, influence aspects of molecular and cellular biology and regulate events over a wide rage of physiological and/or pathological parameters. For example, tumor cells with acquired resistance to antineoplastic agents over-express MTs. By using MT-I antisense phosphorothioate oligodeoxyribonucleotide (ODN) (18-mer) complementary to the intron 2/exon 3 splice site of the mouse MT-I and human MT-If mRNA, we learned that MT-I antisense ODN caused a suppression of MT synthesis and hence inhibited the growth of Leukemia P388 cells, Ehrlich carcinoma cells and sarcoma 180 cells in a dose-and time-dependent fashion; whereas, MT-II antisense ODN inhibited the growth of Chinese hamster lung V79 cells. Moreover, treatment with MT-I antisense ODN attenuated the growth and progression of tumors in mice. The tumor inhibitory effects of MT-I antisense ODN, evident in both in vivo and in vitro systems, was specific since ceruloplasmin antisense ODN was devoid of any action. The results of these studies are interpreted to suggest that the growth of neoplastic cells depends on the expression of MT, and in this area, MT-I and the MT-II exhibit distinct actions, which may provide a unique avenue for chemotherapy against certain neoplasms.