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

Modulation of Cytotoxicity by Transcription-Coupled Nucleotide Excision Repair Is Independent of the Requirement for Bioactivation of Acylfulvene

Bioactivation as well as DNA repair affects the susceptibility of cancer cells to the action of DNA-alkylating chemotherapeutic drugs. However, information is limited with regard to the relative contributions of these processes to the biological outcome of metabolically activated DNA alkylating agents. We evaluated the influence of cellular bioactivation capacity and DNA repair on cytotoxicity of the DNA alkylating agent acylfulvene (AF). We compared the cytotoxicity and RNA synthesis inhibition by AF and its synthetic activated analogue iso-M0 in a panel of fibroblast cell lines with deficiencies in transcription-coupled (TC-NER) or global genome nucleotide excision repair (GG-NER). We related these data to the inherent bioactivation capacity of each cell type on the basis of mRNA levels. We demonstrated that specific inactivation of TC-NER by siRNA had the largest positive impact on AF activity in a cancer cell line. These findings establish that transcription-coupled DNA repair reduces cellular sensitivity to AF, independent of the requirement for bioactivation.

Topoisomerase I inhibitors for the treatment of brain tumors

Patients with primary malignant brain tumors have a poor prognosis. Standard treatment includes surgical resection, radiation therapy and chemotherapy. Topoisomerase I inhibitors such as topotecan and irinotecan (CPT-11) represent one class of chemotherapy drugs that have been used in this disease. Recent clinical trials have shown major antitumor activity in recurrent glioblastoma when adding the antiangiogenesis drug bevacizumab with CPT-11. The combination of targeted agents to topoisomerase I inhibitors represent a novel and promising approach. This review will summarize clinical trials with topoisomerase I inhibitors and discuss new treatment strategies for primary malignant brain tumors.

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.

Fanconi anemia D2 protein confers chemoresistance in response to the anticancer agent, irofulven

The Fanconi anemia-BRCA pathway of genes are frequently mutated or epigenetically repressed in human cancer. The proteins of this pathway play pivotal roles in DNA damage signaling and repair. Irofulven is one of a new class of anticancer agents that are analogues of mushroom-derived illudin toxins. Preclinical studies and clinical trials have shown that irofulven is effective against several tumor cell types. The exact nature of irofulven-induced DNA damage is not completely understood. Previously, we have shown that irofulven activates ATM and its targets, NBS1, SMC1, CHK2, and p53. In this study, we hypothesize that irofulven induces DNA double-strand breaks and FANCD2 may play an important role in modulating cellular responses and chemosensitivity in response to irofulven treatment. By using cells that are proficient or deficient for FANCD2, ATR, or ATM, we showed that irofulven induces FANCD2 monoubiquitination and nuclear foci formation. ATR is important in mediating irofulven-induced FANCD2 monoubiquitination. Furthermore, we showed that FANCD2 plays a critical role in maintaining chromosome integrity and modulating chemosensitivity in response to irofulven-induced DNA damage. Therefore, this study suggests that it might be clinically significant to target irofulven therapy to cancers defective for proteins of the Fanconi anemia-BRCA pathway.

BRCA1 contributes to cell cycle arrest and chemoresistance in response to the anticancer agent irofulven

Tumor suppressor gene BRCA1 is frequently mutated in familial breast and ovarian cancer. BRCA1 plays pivotal roles in maintaining genomic stability by interacting with numerous proteins in cell cycle control and DNA repair. Irofulven (6-hydroxymethylacylfulvene, HMAF, MGI 114, NSC 683863) is one of a new class of anticancer agents that are analogs of mushroom-derived illudin toxins. Preclinical studies and clinical trials have demonstrated that irofulven is effective against several tumor cell types. The exact nature of irofulven-induced DNA damage is not completely understood. We demonstrated previously that irofulven activates ATM and its targets, NBS1, SMC1, CHK2, and p53. In this study, we hypothesize that irofulven induces DNA double-strand breaks and that BRCA1 may affect chemosensitivity by controlling cell cycle checkpoints, DNA repair, and genomic stability in response to irofulven treatment. We observed that irofulven induces the formation of chromosome breaks and radials and the activation and foci formation of gamma-H2AX, BRCA1, and RAD51. We also provided evidence that irofulven induces the generation of DNA double-strand breaks. By using BRCA1-deficient or -proficient cells, we demonstrated that in response to irofulven, BRCA1 contributes to the control of S and G(2)/M cell cycle arrest and is critical for repairing DNA double-strand breaks and for RAD51-dependent homologous recombination. Furthermore, we found that BRCA1 deficiency results in increased chromosome damage and chemosensitivity after irofulven treatment.

Irofulven induces replication-dependent CHK2 activation related to p53 status

CHK2 and p53 are frequently mutated in human cancers. CHK2 is known to phosphorylate and stabilize p53. CHK2 has also been implicated in DNA repair and apoptosis induction. However, whether p53 affects CHK2 activation and whether CHK2 activation modulates chemosensitivity are unclear. In this study, we found that in response to the DNA damage agent, irofulven, CHK2 activation, rather than its expression, is inversely correlated to p53 status. Irofulven inhibits DNA replication and induces chromosome aberrations (breaks and radials) and p53-dependent cell cycle arrest. Pretreatment of cells with the DNA polymerase inhibitor, aphidicolin, resulted in reduction of irofulven-induced CHK2 activation and foci formation, indicating that CHK2 activation by irofulven is replication-dependent. Furthermore, by using ovarian cancer cell lines expressing dominant-negative CHK2 and CHK2-knockout HCT116 cells, we found that CHK2 activation contributes to the control of S and G2/M cell cycle arrests, but not chemosensitivity to irofulven. Overall, this study demonstrates that in response to irofulven-induced DNA damage, the activation of CHK2 is dependent on DNA replication and related to p53 status. By controlling cell cycle arrest and DNA replication, p53 affects CHK2 activation. CHK2 activation contributes to cell cycle arrest, but not chemosensitivity.

Phase I trial of irofulven (MGI 114) in pediatric patients with solid tumors

PURPOSE

We performed a Phase I trial of irofulven (MGI 114) to determine the maximum tolerated dose (MTD), the dose-limiting toxicity (DLT), and the plasma pharmacokinetics of irofulven in children < or=21 years of age with refractory/recurrent malignancies.

EXPERIMENTAL DESIGN

Thirty-five patients were entered into the study, of whom 34 were eligible. Patients received Irofulven daily x 5 days every 28 days over 10 min, following pre-treatment with ondansetron (0.45 mg/kg) and dexamethasone (12 mg/m(2)). The initial dose of irofulven was 8 mg/m(2) daily, with subsequent escalations to 10, 13, and 17 mg/m(2). Plasma pharmacokinetic samples were obtained in a subset patients.

RESULTS

Thirty-two patients were assessable for toxicity, and 30 were assessable for response. In heavily pre-treated patients, dose-limiting thrombocytopenia was observed in two patients at the 8 mg/m(2)/day, and in one patient at the 6 mg/m(2)/day dose level. In less heavily pre-treated patients, proteinuria and elevated creatinine were dose limiting in two patients at the 17 mg/m(2)/day dose level. At 13 mg/m(2)/day, constipation, hyperkalemia with elevated creatinine, and thrombocytopenia was dose limiting in three patients. There were no complete or partial responses. One patient with poorly differentiated carcinoma had stable disease and received 11 courses of therapy. Patients demonstrated a lower systemic exposure and greater clearance than adults treated at similar dose levels.

CONCLUSION

The MTD of irofulven administered daily x 5 every 28 days with concomitant ondansetron and dexamethasone is 6 mg/m(2)/day in heavily pre-treated patients and 10 mg/m(2)/day in less heavily pre-treated patients.

Pure multiplicative stochastic resonance of a theoretical anti-tumor model with seasonal modulability

Pure multiplicative noise-induced stochastic resonance, which appears in an anti-tumor system modulated by a seasonal external field, is studied by using theoretical analyses of the generalized potential and numerical simulations. For optimally selected values of the multiplicative noise intensity stochastic resonance is observed, which is manifested by the quasisymmetry of two potential minima. Theoretical results and numerical simulations are in good quantitative agreement.

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.

MYCN deregulation as a potential target for novel therapies in rhabdomyosarcoma

Rhabdomyosarcoma is the most common soft-tissue sarcoma of childhood. Treatment requires a multimodality approach combining chemotherapy with surgery and radiotherapy. Although overall outcomes have improved considerably, the outlook for patients with high-risk disease, particularly the alveolar subtype, remains bleak and there is a clear need for new chemotherapeutic strategies. This review focuses on the possibilities for interventions targeting myc myelocytomatosis viral related oncogene, neuroblastoma derived (MYCN). The importance of aberrant expression of this oncogene is well established in neuroblastoma and recent data indicate that MYCN deregulation also occurs in up to a quarter of alveolar subtype cases. A range of possible approaches to target MYCN is discussed, including nucleic acid-based and immunotherapy strategies.

Characterizations of irofulven cytotoxicity in combination with cisplatin and oxaliplatin in human colon, breast, and ovarian cancer cells

PURPOSE

This study assessed the cytotoxic effects of irofulven in combination with oxaliplatin and cisplatin in a panel of human cancer cell lines.

METHODS

Growth inhibition studies were performed using the human HT29 colon cancer cell line, irofulven-resistant derivative HT29/IF2, breast cancer cell line MCF7, and ovarian cancer line CAOV3. Irofulven-oxaliplatin combinations were compared with irofulven-cisplatin combinations in the same cell lines using similar experimental settings. Cells were exposed for 1 h to irofulven and then for 24 h to oxaliplatin or cisplatin and vice versa.

RESULTS

Single agent irofulven displayed cytotoxic effects against human colon HT29 cells, human breast cancer cell lines including MCF7, SKBR3, and ZR-75-1, and human ovarian cancer cell lines CAOV3, OVCAR3, and IGROV1, with OVCAR3 being the most sensitive cancer cell line (IC50: 2.4 microM). In all tested cell lines the oxaliplatin-irofulven combination led to clear evidence of synergistic activity. In HT29 and HT29/IF2, the sequence oxaliplatin followed by irofulven appears to be the most effective whereas in MCF7 cells, irofulven given prior to or simultaneously with oxaliplatin is more effective than the other schedule. The combination displays additive activity toward CAOV3 ovarian cells when irofulven was administered prior to or simultaneously with oxaliplatin and partially synergistic when oxaliplatin was followed by irofulven. In most of the cell lines, the sequence oxaliplatin followed by irofulven appears to be the most effective as compared to other schedules. A combination of irofulven with cisplatin has the same efficacy as with oxaliplatin for the same cell lines. Cell cycle studies show that irofulven increases the proportion of cells in the S phase. Cisplatin-irofulven and oxaliplatin-irofulven combinations block cells in G1/S and potently induce apoptosis.

CONCLUSION

Irofulven displays synergistic antiproliferative and pro-apoptotic effects when combined with oxaliplatin over a broad range of concentrations in human colon and breast cancer cells. Acquired resistance to irofulven has limited impact on the effects of cisplatin-irofulven and oxaliplatin-irofulven combinations. Based on these data, irofulven-oxaliplatin and cisplatin-irofulven combinations will be further explored in clinical trials, favoring the use schedules of oxaliplatin given prior to irofulven in patients with cancer.