Anti-leukemic action of the novel agent MGI 114 (HMAF) and synergistic action with topotecan

Non-peptide secondary metabolites from poisonous mushrooms: overview of chemistry, bioactivity, and biosynthesis

Covering: up to June 2021A wide variety of mushrooms have traditionally been recognized as edible fungi with high nutritional value and low calories, and abundantly produce structurally diverse and bioactive secondary metabolites. However, accidental ingestion of poisonous mushrooms can result in serious illnesses and even death. Chemically, mushroom poisoning is associated with secondary metabolites produced in poisonous mushrooms, causing specific toxicity. However, many poisonous mushrooms have not been fully investigated for their secondary metabolites, and the secondary metabolites of poisonous mushrooms have not been systematically summarized for details such as chemical composition and biosynthetic mechanisms. The isolation and identification of secondary metabolites from poisonous mushrooms have great research value since these compounds could be lethal toxins that contribute to the toxicity of mushrooms or could provide lead compounds with remarkable biological activities that can promote advances in other related disciplines, such as biochemistry and pharmacology. In this review, we summarize the structures and biological activities of secondary metabolites identified from poisonous mushrooms and provide an overview of the current information on these metabolites, focusing on their chemistry, bioactivity, and biosynthesis.

Mushroom Toxins: Chemistry and Toxicology

Mushroom consumption is a global tradition that is still gaining popularity. However, foraging for wild mushrooms and accidental ingestion of toxic mushrooms can result in serious illness and even death. The early diagnosis and treatment of mushroom poisoning are quite difficult, as the symptoms are similar to those caused by common diseases. Chemically, mushroom poisoning is related to very powerful toxins, suggesting that the isolation and identification of toxins have great research value, especially in determining the lethal components of toxic mushrooms. In contrast, most of these toxins have remarkable physiological properties that could promote advances in chemistry, biochemistry, physiology, and pharmacology. Although more than 100 toxins have been elucidated, there are a number of lethal mushrooms that have not been fully investigated. This review provides information on the chemistry (including chemical structures, total synthesis, and biosynthesis) and the toxicology of these toxins, hoping to inspire further research in this area.

DNA minor groove binders: back in the groove

With recent approval of the minor groove binding agent trabectidin in Europe for the treatment of patients with soft tissue sarcomas, there has been renewed interest in minor groove binders. Though previously considered to be without clinical value due to their initial significant toxicities, new minor groove binders are emerging which are challenging that perception. Toxicities in the most recently completed and ongoing trials have been easily manageable. These agents have demonstrable anti-tumor activity against a wide variety of tumor types including leukemias, sarcomas, melanomas, breast and ovarian cancers. Applying these agents according to a particular tumor's context of vulnerability might reveal previously unconsidered applications for this diverse class of agents. This review provides a look at how minor groove binding agents have progressed from the lab through the clinic with particular emphasis on identifying the contexts of vulnerabilities of patient tumors which increase the effectiveness of these drugs.

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.

Xenograft models for the preclinical evaluation of new therapies in acute leukemia

Major advances in understanding the pathophysiology of acute leukemia have resulted in a dramatic increase in the availability of novel compounds for clinical trials. However, since the number of new drugs far exceeds the number of clinical trials that can be conducted because of the availability of eligible patients, there is an urgent need to utilize reliable preclinical models for the prioritization of the most promising potential therapies for those clinical trials. The most widely used preclinical models for the acute leukemias are human tumor xenografts established in immune-deficient mice, and genetically engineered mouse strains. This review summarizes the recent developments and considerations in the use of xenograft models of acute lymphoblastic leukemia, acute myeloid leukemia, and acute promyelocytic leukemia for the preclinical testing of new therapies.

Comparison of antitumor activities in tumor xenograft treatment

To compare treatment effects with antitumor therapies, we proposed an intuitive approach to compare the antitumor effects of two different antitumor treatments by investigating tumor volumes which were measured in a given period of time. The approach is, in essence, a comparison of two unknown functions. The implementation of the approach is simple and straightforward. The approach is applied to analyze a real xenograft study of a new antitumor agent, irofulven, combined with irinotecan.

Caspase-mediated apoptosis and caspase-independent cell death induced by irofulven in prostate cancer cells

Irofulven (hydroxymethylacylfulvene) is a novel antitumor drug, which acts by alkylating cellular macromolecular targets. The drug is a potent inducer of apoptosis in various types of tumor cells, whereas it is nonapoptotic in normal cells. This study defined molecular responses to irofulven involving mitochondrial dysfunction and leading to death of prostate tumor LNCaP-Pro5 cells. Irofulven caused early (2–5 hours) translocation of the proapoptotic Bax from cytosol to mitochondria followed by the dissipation of mitochondrial membrane potential and cytochrome c release at 4 to 12 hours. These effects preceded caspase activation and during the first 6 hours were not affected by caspase inhibitors. Processing of caspase-9 initiated the caspase cascade at ∼6 hours and progressed over time. The activation of the caspase cascade provided a positive feedback loop that enhanced Bcl-2-independent translocation and cytochrome c release. General and specific caspase inhibitors abrogated irofulven-induced apoptotic DNA fragmentation with the following order of potency: pan-caspase ≥ caspase-9 > caspase-8/6 > caspase-2 > caspase-3/7 > caspase-1/4. Abrogation of caspase-mediated DNA fragmentation failed to salvage irofulven-treated cells from growth inhibition and loss of viability, demonstrating a substantial contribution of a caspase-independent cell death. Monobromobimane, an inhibitor of alternative caspase-independent apoptotic pathway that is mediated by mitochondrial permeability transition, antagonized both apoptosis, measured as phosphatidylserine externalization, and cytotoxicity of irofulven. Collectively, the results indicate that irofulven-induced signaling is integrated at the level of mitochondrial dysfunction. The induction of both caspase-dependent and caspase-independent death pathways is consistent with pleiotropic effects of irofulven, which include targeting of cellular DNA and proteins.

Enhanced antitumor activity of irofulven in combination with irinotecan in pediatric solid tumor xenograft models

PURPOSE

Irofulven, a novel chemotherapeutic agent with a broad spectrum of activity, is effective against preclinical models of pediatric tumors. The cytotoxic activity of irofulven is augmented when combined with agents that interact with DNA topoisomerase I; however, none of the reported studies have used the protracted dosing schedule found to be active clinically in treatment of childhood cancers. The objective of this study was to evaluate the antitumor activity of irofulven in combination with irinotecan administered on a protracted schedule in a panel of pediatric solid tumor xenografts.

METHODS

Irofulven and irinotecan were evaluated alone or in combination against eight independent xenografts, which included childhood brain tumors (n=5), neuroblastoma (n=1), and rhabdomyosarcoma (n=2). Irofulven was administered i.v. daily for 5 days with courses repeated every 21 days for a total of three cycles. Doses of irofulven ranged from 1.33 to 4.6 mg/kg. Irinotecan was given i.v. daily for 5 days each week for 2 weeks repeated every 21 days for three cycles at doses between 0.28 and 1.25 mg/kg.

RESULTS

Irofulven and irinotecan, given as single agents, induced few responses in pediatric solid tumor xenografts at the selected doses. At the same doses, irofulven in combination with irinotecan demonstrated superior antitumor activity, inducing complete responses in seven of the eight xenograft lines.

CONCLUSIONS

These studies show that the cytotoxic activity of irofulven is greater when combined with protracted administration of irinotecan. Although the systemic exposure of irofulven required to induce objective responses in this panel of pediatric solid tumors was in excess of that achievable in patients receiving maximally tolerated doses using this schedule of drug administration, the enhanced activity of irofulven in combination with irinotecan supports the pursuit of alternative administration strategies and combinations.

Anti-tumour compounds illudin S and Irofulven induce DNA lesions ignored by global repair and exclusively processed by transcription- and replication-coupled repair pathways

Illudin S is a natural sesquiterpene drug with strong anti-tumour activity. Inside cells, unstable active metabolites of illudin cause the formation of as yet poorly characterised DNA lesions. In order to identify factors involved in their repair, we have performed a detailed genetic survey of repair-defective mutants for responses to the drug. We show that 90% of illudin's lethal effects in human fibroblasts can be prevented by an active nucleotide excision repair (NER) system. Core NER enzymes XPA, XPF, XPG, and TFIIH are essential for recovery. However, the presence of global NER initiators XPC, HR23A/HR23B and XPE is not required, whereas survival, repair and recovery from transcription inhibition critically depend on CSA, CSB and UVS, the factors specific for transcription-coupled NER. Base excision repair and non-homologous end-joining of DNA breaks do not play a major role in the processing of illudin lesions. However, active RAD18 is required for optimal cell survival, indicating that the lesions also block replication forks, eliciting post-replication-repair-like responses. However, the translesion-polymerase DNA pol eta is not involved. We conclude that illudin-induced lesions are exceptional in that they appear to be ignored by all of the known global repair systems, and can only be repaired when trapped in stalled replication or transcription complexes. We show that the semisynthetic illudin derivative hydroxymethylacylfulvene (HMAF, Irofulven), currently under clinical trial for anti-tumour therapy, acts via the same mechanism.

Irofulven, a novel inhibitor of DNA synthesis, in metastatic renal cell cancer

Irofulven (6-Hydroxymethylacylfulvene, MGI-114) is the first of a new class of anticancer compounds the acylfulvenes which are derived from the natural product, illudin S. Irofulven is a potent anticancer agent with activity against a broad range of human tumors in vitro and in vivo. Irofulven covalently binds to DNA, inhibits DNA synthesis and induces apoptosis. Clinical activity has been observed in phase I studies. Because disease stabilizations were observed in kidney cancer patients in the phase I trials, we performed a phase II trial of irofulven in this patient population. Twenty patients were accrued. Irofulven (11 milligrams per meter squared per day) was administered as a 5 minute intravenous infusion for 5 consecutive days, and response was evaluated every 8 weeks. There were no objective responses. The most common toxicities were nausea, emesis, and thrombocytopenia. Irofulven, at the dose and schedule administered in this trial, showed no effect in metastatic renal cell cancer.

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.

A phase II study of Irofulven (MGI 114) in patients with stage IV melanoma

Sixteen patients with stage IV melanoma, who were heavily pretreated, received 11 mg/m2/day of intravenous Irofulven for five consecutive days every 28 days. There were no objective tumor responses, although one patient exhibited stable disease after 4 cycles. The most common toxicities were grade 1/2 nausea, vomiting, fatigue, anemia, and thrombocytopenia. One patient required a dose reduction for an elevated creatinine while another patient required cessation of treatment because of acute ataxia that may have been related to Irofulven. Based upon these data, Irofulven does not demonstrate significant antitumor activity to warrant further investigation in advanced melanoma.

Irofulven induces apoptosis in breast cancer cells regardless of caspase-3 status

Caspase-3 deficiency can limit the efficiency of pro-apoptotic anticancer treatments. Irofulven (hydroxymethylacyl-fulvene, HMAF. MGI 114, NSC 683863) is an antitumor drug, currently in a Phase III and multiple Phase II trials, which can differentiate between tumor and normal cells in apoptosis induction. This study investigated whether apoptosis induced by irofulven requires caspase-3. Irofulven action was compared in breast cancer cells differing in caspase-3 status: deficient MCF-7 cells and proficient MDA-MB-231 cells and in normal human mammary epithelial cells, HMEC. Irofulven induces significant, concentration and time-dependent apoptotic DNA fragmentation in breast cancer cell lines, regardless of caspase-3 status. After 12, 24 and 48 h incubation at 1 microM irofulven (approximately 3 x GI50), fragmented DNA comprised 3.7, 14.1 and 34.6% and 8.4, 12.6 and 20.3% of total DNA in MCF-7 and MDA-MB-231 cells, respectively. Cell viability (trypan blue exclusion) remained largely unaffected during the first 24 h but decreased markedly after 48 h, indicating secondary necrosis. Net losses in cell numbers were apparent at 48 h. Normal HMEC cells were refractory to 1 microM drug with only approximately 3-9% fragmented DNA after 12-48 h, although apoptosis was observed at drug levels >3 microM. The broad-spectrum caspase inhibitor Z-VAD-fmk inhibited irofulven-induced apoptosis of all cell lines at 20 microM with nearly complete abrogation of apoptosis at 100 microM. Irofulven treatment resulted in marginal caspase-3 processing in MDA-MB-231 and HMEC cells. These results indicate that whereas the caspase cascade mediates irofulven- induced apoptosis, caspase-3 is dispensable (supported by NIH CA70091 and CA78706).

Phase I study of irofulven (MGI 114), an acylfulvene illudin analog, in patients with acute leukemia

Irofulven (MGI 114, 6-hydroxymethylacylfulvene, HMAF) is a semisynthetic illudin analog with broad in vitro anti-neoplastic activity. In this leukemia phase I study, we investigated the toxicity profile and activity of Irofulven in patients with primary refractory or relapsed acute myeloid leukemia (AML), acute lymphocytic leukemia (ALL), or myelodysplastic syndromes (MDS). Irofulven was given as an intravenous infusion over five minutes daily for five days. The starting dose was 10 mg/m2/day (50 mg/m2/course). Courses were scheduled to be given every 3-4 weeks according to toxicity and antileukemic efficacy. Twenty patients [AML: 17 patients; MDS: one patient; ALL: one patient; mixed lineage acute leukemia: one patient] were treated. Nausea, vomiting, hepatic dysfunction, weakness, renal dysfunction, and pulmonary edema were dose limiting toxicities, occurring in two of five patients treated at 20 mg/m2/day and two of three patients treated at 12.5 mg/m2/day. The MTD was defined as 10 mg/m2/day for five days. One patient with primary resistant AML achieved complete remission. Proposed phase II studies will further define the activity of Irofulven in patients with better prognosis AML and in other hematological malignancies, both as a single agent and in combination regimens, particularly with topoisomerase 1 inhibitors.