Hydroxyurea derivatives of irofulven with improved antitumor efficacy.

Irofulven is a semi-synthetic derivative of Illudin S, a toxic sesquiterpene isolated from the mushroom Omphalotus illudens. Irofulven has displayed significant antitumor activity in various clinical trials but displayed a limited therapeutic index. A new derivative of irofulven was prepared by reacting hydroxyurea with irofulven under acidic conditions. Acetylation of this new compound with acetic anhydride produced a second derivative. Both of these new derivatives displayed significant antitumor activity in vitro and in vivo comparable to or exceeding that of irofulven.

Absence of MGST1 mRNA and protein expression in human neuroblastoma cell lines and primary tissue.

A recent study identified a haplotype on a small region of chromosome 12, between markers D12S1725 and D12S1596, shared by all patients with familial neuroblastoma (NB). We previously localized the human MGST1 gene, whose gene product protects against oxidative stress, to this very same chromosomal region (12p112.1-p13.33). Owing to the chromosomal location of MGST1; its roles in tumorigenesis, drug resistance, and oxidative stress; and the known sensitivity of NB cell lines to oxidative stress, we considered a role for MGST1 in NB development. Surprisingly there was no detectable MGST1 mRNA or protein in either NB cell lines or NB primary tumor tissue, although all other human tissues, cell lines, and primary tumor tissue examined to date express MGST1 at high levels. The mechanism behind the failure of NB cells and tissue to express MGST1 mRNA is unknown and involves the failure of MGST1 pre-mRNA expression, but does not involve chromosomal rearrangement or nucleotide variation in the promoter, exons, or 3' untranslated region of MGST1. MGST1 provides significant protection against oxidative stress and constitutes 4 to 6% of all protein in the outer membrane of the mitochondria. As NB cells are extremely sensitive to oxidative stress, and often used as a model system to investigate mitochondrial response to endogenous and exogenous stress, these findings may be due to the lack of expression MGST1 protein in NB. The significance of this finding to the development of neuroblastoma (familial or otherwise), however, is unknown and may even be incidental. Although our studies provide a molecular basis for previous work on the sensitivity of NB cells to oxidative stress, and possibly marked variations in NB mitochondrial homeostasis, they also imply that the results of these earlier studies using NB cells are not transferable to other tumor and cell types that express MGST1 at high concentrations.

Synergy of irofulven in combination with other DNA damaging agents: synergistic interaction with altretamine, alkylating, and platinum-derived agents in the MV522 lung tumor model.

PURPOSE: Irofulven (MGI 114, NSC 683863) is a semisynthetic derivative of illudin S, a natural product present in the Omphalotus illudins (Jack O'Lantern) mushroom. This novel agent produces DNA damage, that in contrast to other agents, is predominately ignored by the global genome repair pathway of the nucleotide excision repair (NER)(2) system. The aim of this study was to determine the antitumor activity of irofulven when administered in combination with 44 different DNA damaging agents, whose damage is in general detected and repaired by the genome repair pathway. METHODS: The human lung carcinoma MV522 cell line and its corresponding xenograft model were used to evaluate the activity of irofulven in combination with different DNA damaging agents. RESULTS: Two main classes of DNA damaging agents, platinum-derived agents, and select bifunctional alkylating agents, demonstrated in vivo synergistic or super-additive interaction with irofulven. DNA helicase inhibiting agents also demonstrated synergy in vitro, but an enhanced interaction with irofulven could not be demonstrated in vivo. There was no detectable synergistic activity between irofulven and agents capable of inducing DNA cleavage or intercalating into DNA. CONCLUSION: These results indicate that the antitumor activity of irofulven is enhanced when combined with platinum-derived agents, altretamine, and select alkylating agents such as melphalan or chlorambucil. A common factor between these agents appears to be the production of intrastrand DNA crosslinks. The synergistic interaction between irofulven and other agents may stem from the nucleotide excision repair system being selectively overwhelmed at two distinct points in the pathway, resulting in prolonged stalling of transcription forks, and subsequent initiation of apoptosis.

Synergy of Irofulven in combination with various anti-metabolites, enzyme inhibitors, and miscellaneous agents in MV522 lung carcinoma cells: marked interaction with gemcitabine and 5-fluorouracil.

The novel agent Irofulven (HMAF, NSC 683863) has demonstrated significant antitumor activity against solid tumors in various xenograft models and human clinical trials. The antitumor potential of combining irofulven with 72 different anti-metabolite, enzyme inhibiting, and miscellaneous agents was investigated in this study. The human lung carcinoma MV522 cell line and its corresponding xenograft model were used to evaluate the activity of irofulven in combination with these different agents. Irofulven in combination with select anti-metabolites, notably cytidine or adenine-derived agents, displayed strong synergistic activity in both in vitro and in vivo studies. Agents demonstrating strong synergistic interaction with irofulven included gemcitabine, cyclocytidine, cytarabine, fludarabine phosphate, cladribine, and 5-fluorouracil. Other anti-metabolites, enzyme inhibitors, and a variety of miscellaneous agents failed to interact beneficially when administered in combination with irofulven. The therapeutic activity of irofulven is enhanced considerably when irofulven is combined with select anti-metabolite agents, and further clinical evaluation of these combinations is warranted. The synergistic interaction with these combinations may stem from a variety of actions including inhibition of the nucleotide excision repair (NER) pathway, topoisomerase I activity, and caspase-dependent and independent induction of apoptosis.

Enhanced antitumor activity of irofulven in combination with antimitotic agents.

The aim of this study was to determine the antitumor activity of irofulven when administered in combination with a variety of antimitotic agents. Irofulven in combination with either paclitaxel or docetaxel demonstrated synergistic activity in both the in vitro and in vivo studies. The majority of xenograft bearing animals that received suboptimal (< MTD) doses of irofulven and a taxane demonstrated complete cures. In contrast, in vitro studies produced either an additive or an antagonistic effect when irofulven was combined with other antimitotic agents such as vinca alkaloids, rhizoxin, s-trityl cysteine, or allocolchicine. Xenograft studies of irofulven and vinca alkaloids reflected in vitro results, as the tumor response in combination treated animals was less than the response in irofulven (monotherapy) treated animals. These results indicate that the therapeutic activity of irofulven is enhanced when combined with taxanes, and warrant further evaluation of these combinations.

Enhanced antitumor activity of irofulven in combination with thiotepa or mitomycin C.

PURPOSE: Irofulven (6-hydroxymethylacylfulvene, MGI 114, NSC 683863) is a semisynthetic derivative of illudin S, a toxin present in the Omphalotus mushroom. Irofulven has demonstrated activity against a broad range of solid tumors in both xenograft models and human trials. The potential application of administering irofulven in combination with aziridine-containing chemotherapeutic agents was evaluated in this study. METHODS: Human lung carcinoma MV522 cells and BALB/c athymic mice bearing the human lung carcinoma MV522 xenograft were used to evaluate the activity of irofulven in combination with aziridine-containing drugs. RESULTS: Irofulven in combination with either thiotepa or mitomycin C demonstrated a strong synergistic (supraadditive) activity both in vitro and in vivo, that exceeded results obtained with monotherapy at the same or higher doses of these agents. The majority of xenograft-bearing animals that received subtoxic doses of irofulven, and either thiotepa or mitomycin C, demonstrated a complete cure. In contrast, there was no detectable synergistic activity between irofulven and other aziridine-containing drugs, including AZQ and thiotepa metabolites such as TEPA or AZD. CONCLUSIONS: These results indicate that the therapeutic activity of irofulven is enhanced when combined with mitomycin C or thiotepa, and further evaluation of these combinations is therefore warranted.