Regina Loomis

Triapine (3-aminopyridine-2-carboxaldehyde- thiosemicarbazone): A potent inhibitor of ribonucleotide reductase activity with broad spectrum antitumor activity.

Previous studies from our laboratories have shown that (a) Triapine() is a potent inhibitor of ribonucleotide reductase activity and (b) hydroxyurea-resistant L1210 leukemia cells are fully sensitive to Triapine. In an analogous manner, Triapine was similarly active against the wild-type and a hydroxyurea-resistant subline of the human KB nasopharyngeal carcinoma. Triapine was active in vivo against the L1210 leukemia over a broad range of dosages and was curative for some mice. This agent also caused pronounced inhibition of the growth of the murine M109 lung carcinoma and human A2780 ovarian carcinoma xenografts in mice. Optimum anticancer activity required twice daily dosing due to the duration of inhibition of DNA synthesis which lasted about 10 hr in L1210 cells treated with Triapine in vivo. DNA synthesis in normal mouse tissues (i.e. duodenum and bone marrow) uniformly recovered faster than that in L1210 leukemia cells, demonstrating a pharmacological basis for the therapeutic index of this agent. Triapine was more potent than hydroxyurea in inhibiting DNA synthesis in L1210 cells in vivo, and the effects of Triapine were more pronounced. In addition, the duration of the inhibition of DNA synthesis in leukemia cells from mice treated with Triapine was considerably longer than in those from animals treated with hydroxyurea. Combination of Triapine with various classes of agents that damage DNA (e.g. etoposide, cisplatin, doxorubicin, and 1-acetyl-1,2-bis(methylsulfonyl)-2-(2-chloroethyl)hydrazine) resulted in synergistic inhibition of the L1210 leukemia, producing long-term survivors of tumor-bearing mice treated with several dosage levels of the combinations, whereas no enhancement of survival was found when Triapine was combined with gemcitabine or cytosine arabinoside. The findings demonstrate the superiority of Triapine over hydroxyurea as an anticancer agent and further suggest that prevention by Triapine of repair of DNA lesions created by agents that damage DNA may result in efficacious drug combinations for the treatment of cancer.

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.

Activity of C-7 Substituted Cyclic Acetal Derivatives of Mitomycin C and Porfiromycin Against Hypoxic and Oxygenated EMT6 Carcinoma Cells In Vitro and In Vivo

A series of cyclic acetal derivatives of mitomycin C (MC) and porfiromycin (POR) were tested for their ability to kill hypoxic and oxygenated EMT6 tumor cells. Amino methyl acetal and thioacetal substitutions at C-7 of MC and POR dramatically increased the cytotoxicity of the compounds to hypoxic EMT6 tumor cells in vitro but had little effect on the aerobic toxicities. In contrast, a methyl substitution at N1a markedly decreased the aerobic cytotoxicities of the compounds but did not alter the hypoxic cytotoxicities. The POR acetal, BMY-42355, had the largest differential between hypoxic and aerobic cytotoxicities yet observed among MC analogs. Preliminary studies in mice showed that BMY-42355 had good antineoplastic activity when used alone or in combination with radiation and was less toxic than POR; the therapeutic ratio of this compound in these initial studies was higher than those of either MC or POR.

Thiolysable prodrugs of 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine with antineoplastic activity

Abstract Several 2-alkoxycarbonyl- and 2-aryloxycarbony-1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazines, conceived as thiolysable prodrugs of 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine, were synthesized and their antineoplastic activity evaluated against the L1210 leukemia in mice. In addition to producing ‘cures’ of mice bearing this tumor, many of the analogues were preferentially activated by glutathione (GSH) and/or glutathione S-transferase (GST), making them potentially useful in the treatment of multidrug resistant tumors with increased intracellular levels of GSH and/or GST.