Posttreatment exposure to camptothecin enhances the lethal effects of x-rays on radioresistant human malignant melanoma cells

Radiosensitizing Effects of Irinotecan versus Oxaliplatin Alone and in Combination with 5-Fluorouracil on Human Colorectal Cancer Cells

To date, oxaliplatin and irinotecan are used in combination with 5-flourouracil (5-FU) for metastatic colorectal cancer. In this study it was tested whether oxaliplatin and irinotecan and their combinations with 5-FU have an enhanced effect when treated simultaneously with ionizing radiation. In addition, it should be compared whether one combination therapy is more effective than the other. Colorectal cancer cells (HT-29) were treated with irinotecan or oxaliplatin, both alone and in combination with 5-FU, and subsequently irradiated. The cell growth, metabolic activity and proliferation of cells were investigated, and the clonogenic survival was determined. Furthermore, the assessment of radiation-induced DNA damage and the influence of the drugs and their combinations on DNA damage repair was investigated. Treatment with irinotecan or oxaliplatin in combination with 5-FU inhibited proliferation and metabolic activity as well as clonogenic survival and the DNA damage repair capacity of the tumor cells. The comparison of oxaliplatin and irinotecan with simultaneous irradiation showed the same effect of both drugs. When oxaliplatin or irinotecan was combined with 5-FU, tumor cell survival was significantly lower than with monotherapy; however, there was no superiority of either combination regimen. Our results have shown that the combination of 5-FU and irinotecan is as effective as the combination of 5-FU with oxaliplatin. Therefore, our data support the use of FOLFIRI as a radiosensitizer.

A comprehensive review on β-lapachone: Mechanisms, structural modifications, and therapeutic potentials

β-Lapachone (β-lap, 1), an ortho-naphthoquinone natural product isolated from the lapacho tree (Tabebuia avellanedae) in many regions of South America, has received extensive attention due to various pharmacological activities, such as antitumor, anti-Trypanosoma cruzi, anti-Mycobacterium tuberculosis, antibacterial, and antimalarial activities. Related mechanisms of β-lap have been widely investigated for a full understanding of its therapeutic potentials. Numerous derivatives of β-lap have been reported with aims to generate new chemical entities, improve the corresponding biological potency, and overcome disadvantages of its physical and chemical properties and safety profiles. This review will give insight into the pharmacological mechanisms of β-lap and provide a comprehensive understanding of its structural modifications with regard to different therapeutic potentials. The available clinical trials related to β-lap and its derivatives are also summarized.

Synthesis and biological evaluation of β-lapachone and nor-β-lapachone complexes with 2-hydroxypropyl-β-cyclodextrin as trypanocidal agents

We study βLAP and its derivative nor-β-Lapachone (NβL) complexes with 2-hydroxypropyl-β-cyclodextrin to increase the solubility and bioavailability. The formation of true inclusion complexes between βLAP or NβL in 2-HP-β-CD in solid solution was characterization by FT-IR, DSC, powder X-ray was and was confirmed by one- and two-dimensional ¹H NMR experiments. Additionally, the biological activities of βLAP, NβL, ICβLAP, and ICNβL were investigated through trypanocidal assays with T. cruzi and cytotoxicity studies with mouse peritoneal macrophages. Originally, we tested these complexes against T. cruzi viability and observed higher biological activities and lower cytotoxicity when compared to βLAP and NβL. Thus, the complexation of βLAP and NβL with 2-HP-β-CD increases the drug solubility, in addition vectorization was observed, increasing the biological activity against epimastigotes and trypomastigotes T. cruzi forms. Reduced the toxicity of the compounds against mammalian cells. In addition, the selectivity indices higher of the inclusion complexes comparing to substance free and those of benznidazole.

Increased local failure for patients with intermediate-risk rhabdomyosarcoma on ARST0531: A report from the Children's Oncology Group

BACKGROUND

The objective of this study was to evaluate local control for patients with intermediate-risk rhabdomyosarcoma (RMS) treated on Children's Oncology Group (COG) protocol ARST0531.

METHODS

This study analyzed 424 patients with intermediate-risk RMS. Patients were randomized to chemotherapy with either vincristine, dactinomycin, and cyclophosphamide (VAC) or VAC alternating with vincristine and irinotecan. With the goal of improving local control, radiation therapy (RT) was delivered early at week 4 and was concurrent with irinotecan in the experimental arm. Individualized local control plans for children 24 months old or younger were allowed. Local failure on ARST0531 was compared with local failure on the preceding COG intermediate-risk study, D9803.

RESULTS

For patients with group I/II alveolar RMS (n = 55), the 5-year cumulative incidence of local failure was 13.4%; for group III alveolar RMS (n = 141), it was 20.2%; and for group III embryonal RMS (n = 228), it was 27.9% (P = .03). Among patients with group III disease, local failure did not differ by histology, site, nodal status, RT modality, or treatment arm. Local failure was worse for a tumor size >5 cm (32.3% vs 16.7%; P = .001). Among patients with group III embryonal RMS, local failure was higher on ARST0531 than D9803 (27.9% vs 19.4%; P = .03). After the exclusion of patients 24 months old or younger or patients who did not receive radiation, local failure remained significantly increased on ARST0531 (P = .02). After adjustments for clinical prognostic factors, event-free survival and overall survival were worse on ARST0531 (P = .004 and P = .05, respectively).

CONCLUSIONS

Despite interventions designed to enhance local control, local control was inferior on ARST0531 in comparison with D9803. The reason for this is unclear, but it could be the reduced cyclophosphamide dose on ARST0531.

Radiosensitization by irinotecan is attributed to G2/M phase arrest, followed by enhanced apoptosis, probably through the ATM/Chk/Cdc25C/Cdc2 pathway in p53-mutant colorectal cancer cells

Irinotecan, an analog of camptothecin, which is an inhibitor of topoisomerase I, is currently used in the treatment of metastatic colorectal cancer. Camptothecin derivatives have been demonstrated to exert radiosensitizing effects on several types of cancer cells. However, to date, at least to the best of our knowledge, few studies have examined these effects in colorectal cancer cell lines. In the present study, we examined the radiosensitizing effects of irinotecan on the p53-mutant colorectal cancer cell lines, HT29 and SW620, and explored the potential underlying mechanisms. Drug cytotoxicity tests revealed that the 24 h half-maximal inhibitory concentrations (IC50s) of irinotecan as a single agent were 39.84 µg/ml (HT29 95% CI, 38.27-41.48) and 96.86 µg/ml (SW620 95% CI, 89.04-105.4); finally, concentrations <2 µg/ml were used in the subsequent experiments. Clonogenic assays revealed that irinotecan exerted radiosensitizing effects on the HT29 and SW620 cells, and the sensitivity enhancement ratios (SERs) at 2 Gy increased with increasing concentrations (SER at 2 Gy, 1.41 for the HT29 cells, 1.87 for the SW620 cells; with irinotecan at 2 µg/ml). Subsequently, the cells were divided into 4 groups: The control group, irinotecan group, radiation group and combination group. Compared with the control, irinotecan and radiation groups, the combination group had the slowest cell growth rate and the most obvious foci of Ser139p‑γH2AX. Combined treatment resulted in a firstly decreased and then increased M phase arrest and led to the most significant G2/M phase arrest, followed by the most significant increase in apoptosis. The results of western blot analysis indicated that the expression levels of proteins related to the DNA damage response system (Ser1981p‑ATM, Ser345p‑Chk1, Thr68p‑Chk2 and Ser139p‑γH2AX) and the cell cycle (Tyr15p‑Cdc2 and cyclin B1) exhibited the greatest increase in the combined group. In addition, the expression of Ser216p‑Cdc25C was also increased in the combined group, indicating that irinotecan likely radiosensitized the p53-mutant HT29 and SW620 cells through the ATM/Chk/Cdc25C/Cdc2 pathway.

Inhibition of poly(ADP-Ribose) polymerase enhances the toxicity of 131I-metaiodobenzylguanidine/topotecan combination therapy to cells and xenografts that express the noradrenaline transporter

Targeted radiotherapy using (131)I-metaiodobenzylguanidine ((131)I-MIBG) has produced remissions in some neuroblastoma patients. We previously reported that combining (131)I-MIBG with the topoisomerase I inhibitor topotecan induced long-term DNA damage and supraadditive toxicity to noradrenaline transporter (NAT)-expressing cells and xenografts. This combination treatment is undergoing clinical evaluation. This present study investigated the potential of poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP-1) inhibition, in vitro and in vivo, to further enhance (131)I-MIBG/topotecan efficacy.

METHODS

Combinations of topotecan and the PARP-1 inhibitor PJ34 were assessed for synergism in vitro by combination-index analysis in SK-N-BE(2c) (neuroblastoma) and UVW/NAT (NAT-transfected glioma) cells. Three treatment schedules were evaluated: topotecan administered 24 h before, 24 h after, or simultaneously with PJ34. Combinations of PJ34 and (131)I-MIBG and of PJ34 and (131)I-MIBG/topotecan were also assessed using similar scheduling. In vivo efficacy was measured by growth delay of tumor xenografts. We also assessed DNA damage by γH2A.X assay, cell cycle progression by fluorescence-activated cell sorting analysis, and PARP-1 activity in treated cells.

RESULTS

In vitro, only simultaneous administration of topotecan and PJ34 or PJ34 and (131)I-MIBG induced supraadditive toxicity in both cell lines. All scheduled combinations of PJ34 and (131)I-MIBG/topotecan induced supraadditive toxicity and increased DNA damage in SK-N-BE(2c) cells, but only simultaneous administration induced enhanced efficacy in UVW/NAT cells. The PJ34 and (131)I-MIBG/topotecan combination treatment induced G(2) arrest in all cell lines, regardless of the schedule of delivery. In vivo, simultaneous administration of PJ34 and (131)I-MIBG/topotecan significantly delayed the growth of SK-N-BE(2c) and UVW/NAT xenografts, compared with (131)I-MIBG/topotecan therapy.

CONCLUSION

The antitumor efficacy of topotecan, (131)I-MIBG, and (131)I-MIBG/topotecan combination treatment was increased by PARP-1 inhibition in vitro and in vivo.

Role of cell cycle perturbations in the combination therapy of chemotherapeutic agents and radiation

The combination of radiotherapy with chemotherapeutic agents that sensitize tumor cells to ionizing radiation has long been regarded as a promising strategy to enhance cancer therapy. Many chemotherapeutic agents interact with radiation and enhance the cytotoxic or anti-tumor effect of radiation through a number of mechanisms. These include an increase in initial radiation damage, inhibition of cellular repair, cell cycle redistribution, enhancement of apoptosis, counteracting hypoxia and overcoming accelerated repopulation. This article focuses on the role of cell cycle perturbations in the radiosensitivity of cancer cells.

Calcium-dependent modulation of poly(ADP-ribose) polymerase-1 alters cellular metabolism and DNA repair

After genotoxic stress poly(ADP-ribose) polymerase-1 (PARP-1) can be hyperactivated, causing (ADP-ribosyl)ation of nuclear proteins (including itself), resulting in NAD(+) and ATP depletion and cell death. Mechanisms of PARP-1-mediated cell death and downstream proteolysis remain enigmatic. beta-lapachone (beta-lap) is the first chemotherapeutic agent to elicit a Ca(2+)-mediated cell death by PARP-1 hyperactivation at clinically relevant doses in cancer cells expressing elevated NAD(P)H:quinone oxidoreductase 1 (NQO1) levels. Beta-lap induces the generation of NQO1-dependent reactive oxygen species (ROS), DNA breaks, and triggers Ca(2+)-dependent gamma-H2AX formation and PARP-1 hyperactivation. Subsequent NAD(+) and ATP losses suppress DNA repair and cause cell death. Reduction of PARP-1 activity or Ca(2+) chelation protects cells. Interestingly, Ca(2+) chelation abrogates hydrogen peroxide (H(2)O(2)), but not N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced PARP-1 hyperactivation and cell death. Thus, Ca(2+) appears to be an important co-factor in PARP-1 hyperactivation after ROS-induced DNA damage, which alters cellular metabolism and DNA repair.

Modulation of radiation response by inhibiting topoisomerase II catalytic activity

Due to the essential role played by DNA topoisomerases (topos) in cell survival, the use of topoisomerase inhibitors as chemotherapeutic drugs in combination with radiation has become a common strategy for the treatment of cancer. Catalytic inhibitors of these enzymes would be promising to improve the effectiveness of radiation and therefore, it appears reasonable to incorporate them in combined modality trials. In this work, we have investigated the capacity of both ICRF-193 and Aclarubicin (ACLA), two catalytic inhibitors of topoisomerase II (Topo II), to modulate radiation response in Chinese hamster V79 cell line and its radiosensitive mutant irs2. We also have explored potential mechanisms underlying these interactions. Experiments were performed in the presence and absence of either ICRF-193 or ACLA, and topo II activity was measured using an assay based upon decatenation of kinetoplast DNA (kDNA). For the combined experiments cells were incubated for 3 h in the presence of various inhibitor concentrations and irradiated 30 min prior to the end of treatments and cell survival was determined by clonogenic assay. DNA-damaging activity was measured by single-cell gel electrophoresis. Our results demonstrate that combinations of catalytic inhibitors of topo II and radiation produce an increase in cell killing induced by ionising radiation. The mechanism of radiation enhancement may involve a direct or indirect participation of topo II in the repair of radiation-induced DNA damage.

A phase I study of concurrent 9-nitro-20(s)-camptothecin (9NC/Orathecin) and radiation therapy in the treatment of locally advanced adenocarcinoma of the pancreas

BACKGROUND AND PURPOSE

In vitro studies have suggested that 9-nitro-20(s)-Camptothecin (9NC/Orathecin/Rubitecan) can enhance the effects of radiation. We conducted a phase I study to assess the toxicity and determine the maximum tolerated dose of 9NC when combined with radiation in patients with locally advanced adenocarcinoma of the pancreas.

PATIENTS AND METHODS

Eleven patients with locally advanced adenocarcinoma of the pancreas received 9NC, orally during radiation. Radiation therapy consisted of 45 Gy in 25 fractions given over 5 weeks. The starting dose of 9NC was 1 mg/m2/day.

RESULTS

Eight patients received 9NC at a dose of 1 mg/m2/day and three patients received a dose of 1.25 mg/m2/day. Dose-limiting toxicity (DLT) was defined as >or=grade 3 non-hematologic toxicity and >or=grade 4 hematologic toxicity. Dose-limiting toxicity of grade 3 nausea/vomiting developed in one patient at the first dose level. At dose level 2, two of three patients developed DLT. Both developed grade 3 nausea, fatigue, and anorexia. Additionally, one of these patients had grade 3 dehydration and the other had grade 4 leukopenia, grade 3 vomiting, and grade 3 weakness.

CONCLUSIONS

9NC, 1 mg/m2/day, can be given concurrently with radiation with acceptable toxicity.

[131I]MIBG and topotecan: a rationale for combination therapy for neuroblastoma

MIBG is selectively concentrated in neuroblastoma cells, and radioiodinated MIBG has been used with some success for targeted radiotherapy. However, long-term cure remains elusive, and the topoisomerase I inhibitor topotecan may improve upon existing [131I]MIBG therapy. While synergistic killing by combinations of ionising radiation and topoisomerase I inhibitors has been reported, there is no consensus on optimal scheduling. Furthermore, there has been no attempt to demonstrate radio-potentiation by topoisomerase I inhibitors and targeted radiotherapy. We are investigating various scheduled combinations of topotecan and [131I]MIBG on neuroblastoma cells, and preliminary data suggests that topotecan induces increased accumulation of [131I]MIBG in vitro.

Phase I Study of Concomitant Chemoradiotherapy with Irinotecan, 5-FU., and Hydroxyurea for Patients with Advanced and/or Recurrent Head and Neck Cancer

PURPOSE

We sought to investigate CPT-11 as a promising agent to our established regimen of 5-fluorouracil (5-FU), hydroxyurea, and hyperfractionated radiation therapy. A phase I study was conducted to determine the maximum tolerated dose and dose-limiting toxicities of this regimen.

PATIENTS AND METHODS

Eligible patients included patients with poor prognosis advanced head and neck cancer who required radiation therapy. All patients were treated on a 14-day cycle. Each patient received 5-FU (600 mg/m(2)/d), hydroxyurea (500 mg orally every 12 hours), radiation therapy twice daily (150 cGy each fraction), and CPT-11 at a starting dose of 5 mg/m(2)/d for 5 consecutive days followed by a 9-day break. CPT-11 was escalated in five mg/m(2)/d increments. Dose-limiting toxicity was defined as grade 4 hematologic toxicity, persistent grade 4 dermatitis and mucositis, grade 4 diarrhea despite maximal pharmacologic intervention, and inability to receive full-dose chemotherapy with the next cycle of treatment. Fourteen patients were treated at maximum tolerated dose to verify the recommended phase II dose.

RESULTS

Between August 1998 and August 2001, 31 patients with advanced and/or recurrent head and neck cancer were enrolled. Cohorts of nine, four, three, and 14 patients were treated at 5-, 10-, 15-, and 10-mg/m(2)/d dose levels of CPT-11. The 5- and 10-mg/m(2)/d dose levels were well tolerated All three patients treated at 15 mg/m(2)/d experienced neutropenic dose-limiting toxicity during cycles 1-2.

DISCUSSION

The maximum tolerated dose and recommended phase II dose of CPT-11 with hyperfractionated radiation therapy is 10 mg/m(2)/d.

Silatecan DB-67 is a novel DNA topoisomerase I–targeted radiation sensitizer

The silatecan 7-tert-butyldimethylsilyl-10-hydroxy-camptothecin (DB-67) represents a new generation of camptothecin derivatives that exhibits a potent in vitro DNA topoisomerase I (TOP1)–mediated DNA-damaging activity, improved blood stability, and holds significant promise for the treatment of human cancers. In this study, we characterize the role of TOP1 in mediating the radiosensitization activity of DB-67. As examined by clonogenic survival assay, DB-67 exhibited potent radiosensitization activity at a concentration 10-fold lower than camptothecin in the human glioma D54-MG and T-98G cells, which harbor wild-type and mutant p53, respectively. Analyzed by the single-hit multitarget model, DB-67 induced radiosensitization by obliterating the “shoulder” of the radiation survival curve in the D54-MG cells. The in vivo targeting of TOP1 by DB-67 was investigated by immunoblot analysis. In a dose-dependent manner, DB-67 specifically stimulates covalent linking of TOP1 to chromosomal DNA at concentrations 10-fold lower than camptothecin in the D54-MG cells. The potency of in vivo targeting of TOP1 by DB-67 correlates well with its cytotoxicity and radiosensitization activity. Furthermore, DB-67 exhibited substantially less cytotoxicity and radiosensitization activity in the TOP1 mutant Chinese hamster lung fibroblast DC3F/C-10 cells than in their parental DC3F cells. Together, our data show that DB-67 exhibits potent cytotoxicity and radiosensitization activity by targeting TOP1 in mammalian cells and has great potential for being developed to treat human cancers.

Enhancement of radiotherapy with DNA topoisomerase I-targeted drugs

Since its discovery more than a century ago, ionizing radiation has become a mainstay therapy for patients suffering from cancers. Currently, radiotherapy provides cure or palliative care for approximately one half of the cancer population. The anticancer efficacy of radiotherapy is, however, largely limited by its lack of tumor specificity and, consequently, normal tissue toxicity. There is an urgent need to develop systemic adjuncts that can enhance the efficacy and the selectivity of radiotherapy toward tumor cells. DNA topoisomerase I (TOP1)-targeted drugs such as camptothecin derivatives represent a novel class of chemotherapeutic agents that have recently been shown to be excellent radiation sensitizers. Combined modality therapy with TOP1-targeted drugs and radiotherapy represents a new promising cancer therapy. The mechanism of enhancement of radiotherapy by TOP1-targeted drugs is under intense investigation. Clinical trials using combinations of radiation and camptothecin derivatives are also currently ongoing in various solid tumors including brain, head and neck, and lung cancers. A better understanding of the radiosensitization (RS) mechanism of TOP1-targeted drugs is pivotal to their clinical application, as well as in guiding the development of better radiation sensitizers.

A phase I study of Topotecan, as a radiosensitizer, for thoracic malignancies

PURPOSE

To determine the maximum-tolerated dose (MTD) of daily Topotecan with full-dose thoracic radiotherapy (XRT).

METHODS AND MATERIALS

Patients with advanced thoracic malignancies requiring full dose radiation received daily I.V. Topotecan prior to each daily session of XRT to 60 Gy over 6 weeks. Dose levels (and subjects studied at each) have been 0.2 (N=7), 0.3 (N=5), 0.4 (N=7), and 0.5mg/m(2) per day (N=5) in a best-of-five design. Tumor response was assessed at 4-8 weeks after completion of therapy.

RESULTS

From March 1995 to December 1999, a total of 24 patients were treated. The MTD of Topotecan was 0.4 mg/m(2) per day, based on dose limiting toxicities (DLTs) observed at 0.5 mg/m(2) per day, which were grade 4 hematological toxicities or diarrhea and grade 3 esophagitis. Tumor responses included: zero complete response (CR), nine partial responses (PR), five stable disease (SD), nine progressive disease (PD) and one not evaluated (NE). Additionally, local response was also assessed separately (within the XRT ports) and there were 10 PR, 12 SD, 1 PD, and 1 NE.

CONCLUSION

the MTD of Topotecan with concomitant thoracic radiotherapy is 0.4 mg/m(2) per day. The DLTs observed were grade 4 diarrhea, grade 3 esophagitis and grade 4 hematological toxicities. Based on the known radiosensitizing effect of Topotecan, this dose is recommended for phase II testing.

Radiosensitization by inhibition of IkappaB-alpha phosphorylation in human glioma cells

To assess the role of nuclear factor kappaB (NFKB) in cellular radiosensitivity, three different IkappaB-alpha (also known as NFKBIA) expression plasmids, i.e., S-IkappaB (mutations at (32, 36)Ser), Y-IkappaB (a mutation at (42)Tyr), and SY-IkappaB, were constructed and introduced into human brain tumor M054 cells. The clones were named as M054-S8, M054-Y2 and M054-SY4, respectively. Compared to the parental cell line, M054-S8 and M054-Y2 cells were more sensitive to X rays while M054-SY4 cells exhibited the greatest sensitivity. After treatment with N-acetyl-Leu-Leu-norleucinal, a proteasome inhibitor, the X-ray sensitivity of M054-S8 and M054-SY4 cells did not change, while that of M054-Y2 cells and the parental cells was enhanced. An increase in X-ray sensitivity accompanied by a decrease in translocation of NFKB to the nucleus in parental cells was observed after treatment with pervanadate, an inhibitor of tyrosine phosphatase, as well as in M054-S8 and M054-SY4 cells. Repair of potentially lethal damage (PLD) was observed in the parental cells but not in the clones. Four hours after irradiation (8 Gy), the expression of TP53 and phospho-p53 ((15)Ser) was induced in the parental cells but not in M054-S8, M054-Y2 or M054-SY4 cells. Our data suggest that inhibition of IkappaB-alpha phosphorylation at serine or tyrosine acts independently in sensitizing cells to X rays. NFKB may play a role in determining radiosensitivity and PLD repair in malignant glioma cells; TP53 may also be involved.

Irinotecan in the treatment of glioma patients: current and future studies of the North Central Cancer Treatment Group

Other than nitrosoureas (carmustine and lomustine) and temozolomide, no agents have consistently demonstrated clinically meaningful benefits for patients with gliomas. The active metabolite of irinotecan, 7-ethyl-10-hydroxy camptothecin (SN-38), exhibited promising antitumor effects in preclinical glioma models. Clinical trials using weekly or every 3 weeks dosing of irinotecan have been completed. Toxicity consisted primarily of mild to moderate neutropenia and diarrhea with both schedules, with occasional severe toxicity including one death from neutropenia and infection. Preliminary analyses have suggested imaging responses in 10-15% of patients. Preclinical models and our understanding of the mechanism of action suggest that irinotecan may sensitize glioma cells to the cytotoxic actions of radiation therapy and alkylating agents; clinical trials designed to assess the therapeutic benefit of combination therapy currently are in progress. There is substantial clinical evidence that the concurrent administration of irinotecan with certain anticonvulsants produces reduced exposure to SN-38. In the absence of anticonvulsants, there is also substantial interpatient variability in drug exposure, perhaps reflecting inherited differences in drug metabolism. Finally several mechanisms of tumor cell resistance to irinotecan have been hypothesized, but the clinical significance of these observations has not been confirmed. Correlative studies to address these pharmacokinetic, pharmacogenetic, and drug resistance questions are ongoing.

Phase II study of topotecan plus cranial radiation for glioblastoma multiforme: results of Radiation Therapy Oncology Group 9513

PURPOSE

A Phase II trial was conducted by the Radiation Therapy Oncology Group (RTOG) to compare the survival of patients with glioblastoma multiforme treated with topotecan combined with standard cranial radiotherapy (RT) for matched patients treated in prior RTOG studies. A secondary objective was to document the acute and late toxicities of this combination of chemotherapy and RT.

METHODS AND MATERIALS

Eighty-seven patients with histologically confirmed glioblastoma multiforme received standard cranial RT (60 Gy/30 fractions in 6 weeks) plus topotecan 1.5 mg/m2 per day i.v. for 5 d/wk every 3 weeks for 3 cycles. Eighty-four patients were evaluated, of whom 60 (71%) were > or =50 years, 44 (52%) were men, and 61 (73%) had a Karnofsky performance status of > or =80. Twenty-nine percent of patients had undergone biopsies, 48% partial resections, and 21% gross total resections. Two resections were unspecified as to the extent of tumor removal. Fourteen percent of patients were recursive partitioning analysis Class III, 46% were Class IV, 35% were Class V, and 5% were Class VI.

RESULTS

The median survival was 9.3 months. Sixty-seven patients (80%) had progression. The 1-year survival rate was 32%. One patient remained alive without recurrence. RTOG 9513 patients were matched with patients in an RTOG clinical trial database from previous clinical trials. The matching variables were age, Karnofsky performance status, mental status, and prior surgery. No statistically significant difference was found between the survival of the study patients and that of the matched patients from the RTOG database. Fifty-four percent of patients had Grade IV acute toxicity. The toxicity was primarily hematologic. Four patients had Grade III late central nervous system toxicities.

CONCLUSION

Topotecan administered at a dose of 1.5 mg/m2 per day i.v. for 5 d/wk every 3 weeks for 3 cycles given concurrently with standard cranial RT for glioblastoma does not produce a statistically significant survival advantage over previously tested therapies. Other methods of administration of topotecan or other camptothecins may provide more effective radiosensitization.

Potentiation of cell killing by low-dose-rate radiation by camptothecin is related to an increase in the level of DNA double-strand breaks

We investigated the ability of camptothecin to potentiate cell killing by low-dose-rate irradiation and whether this potentiation was associated with an increase in the level of residual DNA double-strand breaks (DSBs). Human melanoma (Sk-Mel-3) cells, grown to the confluent phase, were treated with low-dose-rate radiation (0.88 cGy/min) alone, camptothecin alone, or concurrent camptothecin and low-dose-rate radiation. Cell survival was determined using a clonogenic assay. The interactions between camptothecin and low-dose-rate radiation were analyzed further using isobolograms. DNA DSBs were determined using the neutral comet assay. We found that 10 and 25 microM camptothecin, but not 1 microM, camptothecin potentiated cell killing significantly relative to that seen with low-dose-rate radiation alone. Unexpectedly, the potentiation of the effects of low-dose-rate radiation by camptothecin was accompanied by large increases in the alpha parameter of the linear-quadratic fit rather than in the beta parameter. This suggests a modification of intrinsic radiosensitivity rather than of repair of sublethal damage. From isobologram analysis, low-dose-rate radiation interacted either additively or supra-additively with 25 or 10 microM camptothecin. Conversely, the interaction of low-dose-rate radiation with 1 microM camptothecin was subadditive. Finally, there were strong correlations (correlation coefficients >0.9) between surviving fraction and either comet tail length or comet tail moment after concurrent treatment with 25 microM camptothecin and low-dose-rate radiation. This suggests that the level of residual DNA DSBs was a good indicator of cell killing after treatment with low-dose-rate radiation plus 25 microM camptothecin.

Pharmacotherapy of malignant astrocytomas of children and adults: current strategies and future trends

This article reviews the conceptual progression in the pharmacological therapy of malignant astrocytoma (MA) over the past decade, and its future trends. It is a selective rather than an exhaustive inventory of literature citations. The experience of the Brain Tumour Cooperative Group (BTCG) and earlier phase III trials are summarised to place subsequent phase II and I studies of single and combination agent chemotherapy in perspective. The BTCG experience of the 1970s to 1980s may be summarised to indicate that external beam radiotherapy (EBRT) is therapeutic, although not curative, and not further improved upon by altering fractionation schedules, or the addition of radioenhancers. Whole brain and reduced whole brain EBRT with focal boost were comparable regimens. Nitrosourea-based, adjuvant chemotherapy provided a modest improvement in survival among adult patients, which was comparable with that of other single drugs or multidrug regimes. The multiagent schedules, however, had a correspondingly higher toxicity rate. Intra-arterial administration was associated with significant risk, which conferred no therapeutic advantage. The trend of the past decade has been towards multiagent chemotherapy although its benefit cannot be predicted from the classic prognostic factors. Published experience with investigational trials utilising myeloablative chemotherapy with autologous bone marrow or peripheral blood stem cell haemopoietic support, drug delivery enhancement methods and radiosensitisers is critically reviewed. None of these approaches have achieved wide-spread acceptance in the treatment of adult patients with MA. Greater attention is placed on recent 'chemoradiotherapy' trials, which attempt to integrate and maximise the cytoreductive potential of both modalities. This approach holds promise as an effective means to delay or overcome the evolution of tumour resistance, which is probably one of the dominant determinants of prognosis. However, the efficacy of this approach remains unproven. New chemotherapeutic agents as well as biological response modifiers, protein kinase inhibitors, angiogenesis inhibitors and gene therapy are also discussed; their role in the therapeutic armamentarium has not been defined.

Radiation enhancement by the combined use of topoisomerase I inhibitors, RFS-2000 or CPT-11, and topoisomerase II inhibitor etoposide in human lung cancer cells

BACKGROUND AND PURPOSE

We have tested the camptothecin analogs, RFS-2000 or CPT-11, in combination with both etoposide and ionizing radiation in vitro to examine the radiation enhancing potential of topoisomerase I plus topoisomerase II (Topo I+Topo II) inhibition in human cancer cells.

MATERIALS AND METHODS

H460 human lung carcinoma cells were plated and treated with 10nM RFS-2000 or 4.5microM CPT-11 for 4h. Cells were then irradiated with various doses and treated with 1microM etoposide for 1.5h. Cell survival and sublethal damage recovery (SLDR) were determined by clonogenic assay. 7-aminoactinomycin D (7-AAD) staining and flow cytometry were used to analyze cell viability/apoptosis after combined treatment of drugs with radiation.

RESULTS

Survival experiments showed radiation dose enhancement ratios (DER) of 1.26, 1.34, and 1.63 for RFS-2000, etoposide, and RFS-2000 plus etoposide, respectively; the corresponding DER values were 1.30, 1.39, and 1.65 for CPT-11, etoposide, and CPT-11 plus etoposide. The analysis of cell viability/apoptosis using 7-AAD staining and flow cytometry showed an additive effect. Greater inhibition of SLDR was observed with RFS-2000 plus etoposide than with either agent separately, but CPT-11 plus etoposide showed a more modest effect upon SLDR.

CONCLUSIONS

These data show that the combination of Topo I inhibitors, RFS-2000 or CPT-11 plus Topo II inhibitor etoposide, is a more effective radiation enhancer than either agent alone in human lung cancer cells. The mechanism of radiation enhancement may involve inhibition of SLDR with RFS-2000 plus etoposide, but other mechanisms may be involved in the combined treatment including CPT-11.

Biological basis for chemo-radiotherapy interactions

For over 10 years, chemo-radiotherapeutic combinations have been used to treat locally advanced epithelial tumours. The rationale for these combinations relies on spatial cooperation or interaction between modalities. Interactions may take place (i) at the molecular level, with altered DNA repair or modification of the lesions induced by drugs or radiation, (ii) at the cellular level, notably through cytokinetic cooperation arising from differential sensitivity of the various compartments of the cell cycle to the drug or radiation, and (iii) at the tissue level, including reoxygenation, increased drug uptake or inhibition of repopulation or angiogenesis. Some mechanisms underlying interaction of radiation with cis-diammino-platinum (II) (cis-Pt), 5-fluoro-2'-deoxyuridine (5-FU), taxanes and gemcitabine are described. It is shown how various mechanisms including cell synchronisation and reoxygenation concur to paclitaxel-induced radiosensitisation. In the future, specific targeting of tumours, for example, with the epidermal growth factor receptor (EGFR) or angiogenesis inhibitors, should be achieved in order to increase the therapeutic index.

Evaluation of cell survival, DNA double strand breaks, and DNA synthesis during concurrent camptothecin and X-radiation treatments

We evaluated cell survival, DNA double strand breaks (dsbs), and DNA synthesis following camptothecin (CPT) alone or concurrent CPT and X-radiation treatments in exponential-phase cultures of a radioresistant human melanoma cell line. Cell survival was measured by a clonogenic assay. DNA dsbs were measured by pulsed-field gel electrophoresis. DNA synthesis was measured by incorporation of (3)H-thymidine. We found that (i) concurrent CPT and X-radiation interacted additively, unlike previous results with plateau-phase cultures of these cells, which showed synergistic interaction; (ii) there were strong negative correlations (correlation coefficients of at least 0.82) between clonogenic surviving fractions and DNA dsbs following CPT alone or concurrent CPT and radiation treatments; and (iii) concurrent CPT and radiation (10 Gy) treatment did not completely inhibit DNA synthesis, even though addition of radiation to CPT did further decrease DNA synthesis (relative to CPT alone) at CPT concentrations below 20 microM. Our results suggest that during concurrent CPT and radiation treatment residual DNA dsb levels were good indicators of cell killing and that the absence of complete inhibition of DNA synthesis could at least in part explain the additive interaction between CPT and radiation.

Genistein, a tyrosine kinase inhibitor, enhanced radiosensitivity in human esophageal cancer cell lines in vitro: possible involvement of inhibition of survival signal transduction pathways

PURPOSE

The effect of genistein, a tyrosine kinase inhibitor, on radiosensitivity was examined, especially focusing on "survival signal transduction pathways."

METHODS AND MATERIALS

Two human esophageal squamous cell cancer cell lines, TE-1 (p53, mutant) and TE-2 (p53, wild), were used. Radiosensitivity was determined by clonogenic assay, and activation of survival signals was examined by Western blot.

RESULTS

Genistein (30 microM) greatly enhanced radiosensitivity in these cell lines by suppressing radiation-induced activation of survival signals, p42/p44 extracellular signal-regulated kinase and AKT/PKB. Significant increase in the percentage of apoptotic cells and increased poly[ADP-ribose] polymerase cleavage were observed in TE-2, but not in TE-1 even after combination of genistein with irradiation. In terms of changes in expression of p53-related proteins, increase in expression of Bax and decrease in that of Bcl-2 were observed in TE-2 but not in TE-1, suggesting that the main mode of cell death induced by genistein in a cell line with wild type p53 differed from that with mutant p53.

CONCLUSIONS

This study suggested that survival signals, including p42/p44 ERK and AKT/PKB, may be involved in determining radiosensitivity, and genistein would be a potent therapeutic agent that has an enhancing effect on radiation.

Cellular and molecular responses to topoisomerase I poisons. Exploiting synergy for improved radiotherapy

The efficacy of topoisomerase (Topo) I-active drugs may be improved by better understanding the molecular and cellular responses of tumor compared to normal cells after genotoxic insults. Ionizing radiation (IR) + Topo I-active drugs (e.g., Topotecan) caused synergistic cell killing in various human cancer cells, even in cells from highly radioresistant tumors. Topo I poisons had to be added either during or immediately after IR. Synergy was caused by DNA lesion modification mechanisms as well as by concomitant stimulation of two pathways of cell death: necrosis (IR) + apoptosis (Topo I poisons). Cumulative data favor a mechanism of synergistic cell killing caused by altered DNA lesion modification and enhanced apoptosis. However, alterations in cell cycle regulation may also play a role in the synergy between these two agents in certain human cancers. We recently showed that NF-kappa B, a known anti-apoptotic factor, was activated in various cancer cells after poisoning Topo I using clinically active drugs. NF-kappa B activation was dependent on initial nuclear DNA damage followed by cytoplasmic signaling events. Cytoplasmic signaling leading to NF-kappa B activation after Topo I poisons was diminished in cytoplasts (lacking nuclei) and in CEM/C2 cells that expressed a mutant Topo I protein that did not interact with Topo I-active drugs. NF-kappa B activation was intensified in S-phase and blocked by aphidicolin, suggesting that activation was a result of double-strand break formation due to Topo I poisoning and DNA replication. Dominant-negative I kappa B expression augmented Topo I poison-mediated apoptosis. Elucidation of molecular signal transduction pathways after Topo I drug-IR combinations may lead to improved radiotherapy by blocking anti-apoptotic NF-kappa B responses. Recent data also indicate that synergy caused by IR + Topo I poisons is different from radiosensitization by beta-lapachone (beta-lap), a "reported" Topo I and II-alpha poison in vitro. In fact, beta-lap does not kill cells by poisoning either Topo I or II-alpha in vivo. Instead, the compound is "activated" by an IR (damage)-inducible enzyme, NAD(P)H:quinone oxidoreductase (NQO1), a gene cloned as x-ray-inducible transcript #3, xip3. Unlike the lesion modification pathway induced by IR + Topo I drugs, beta-lap kills cells via NQO1 futile cycle metabolism. Downstream apoptosis caused by beta-lap appears to be noncaspase-mediated, involving calpain or a calpain-like protease. Thus, although Topo I poisons or beta-lap in combination with IR both synergistically kill cancer cells, the mechanisms are very different.

Phase I study of topotecan plus cranial radiation for glioblastoma multiforme: results of Radiation Therapy Oncology Group Trial 9507

PURPOSE

A phase I trial was conducted by the Radiation Therapy Oncology Group (RTOG) to determine the maximum-tolerated dose of topotecan that could be safely combined with standard cranial radiation for glioblastoma multiforme. A secondary objective was to document the acute and late toxicities of this combination of chemotherapy and radiation.

PATIENTS AND METHODS

Forty-seven patients with histologically confirmed glioblastoma multiforme were entered onto this phase I trial. Three cycles of topotecan were administered at 21-day intervals commencing at day 1 of cranial radiotherapy (60 Gy/30 fractions). Each cycle consisted of daily 30-minute intravenous (IV) infusions for 5 days. The dose of topotecan was escalated in three-dose increments from 0.5 mg/m(2)/d to 1.0 mg/m(2)/d to 1.5 mg/m(2)/d in different patient groups.

RESULTS

The majority of patients were over age 50. Three dose levels of topotecan were tested. Fifteen patients accrued to level 1 (topotecan dose 0.5 mg/m(2)/d). No grade 4 toxicities were seen. Sixteen patients accrued to level 2 (topotecan dose 1.0 mg/m(2)/d), five of whom had brief episodes of grade 4 neutropenia. Seventeen patients accrued to level 3 (1.5 mg/m(2)/d). Six of these patients had brief episodes of grade 4 neutropenia and four developed grade 3 thrombocytopenia. No serious nonhematologic or late toxicities were seen. Median survival for all patients was 9.7 months. There was no apparent difference in survival by topotecan dose schedule.

CONCLUSION

Toxicity was acceptable at an IV topotecan dose of 1.5 mg/m(2)/d administered daily for 5 days every 21 days for three cycles. A phase II trial has been performed using this dose of topotecan.

Elevated topoisomerase I activity in cervical cancer as a target for chemoradiation therapy

OBJECTIVE

The aim of this study was to determine whether the activity of topoisomerase I (topo I), the target of the anti-neoplastic drug camptothecin (CPT), is elevated in cervical cancer and whether CPT can radiosensitize cervical tumors.

METHODS

The topo I activity of 11 normal cervix and 30 cervical carcinoma tumors was assayed by measuring the relaxation of supercoiled DNA. Subconfluent or postconfluent CaSki human cervical carcinoma cells were exposed to CPT (1-5000 ng/ml) and immediately X-irradiated (0-800 cGy). Cell survival was determined by clonogenic assay.

RESULTS

Mean topo I activity in cervical cancer (3.0 +/- 0.06 h(-1)) was significantly greater than in normal cervix tissue (0.29 +/- 0.06 h(-1)). Stage 3 and 4 cervical carcinoma specimens displayed a trend of greater topo I activity (5.88 +/- 3.7 h(-1)) than stage 1 and 2 tumors (2.57 +/- 0.47 h(-1)). No correlation between topo I protein levels and catalytic activity was found. Combined treatment of subconfluent CaSki cells with CPT and ionizing radiation resulted in additive killing of cells. Combined treatment of postconfluent CaSki cells with low doses of radiation (200 and 400 cGy) and 1 or 10 ng/ml CPT for 2 or 48 h produced significant cytotoxicity compared to CPT or radiation alone, which were ineffective at these doses.

CONCLUSIONS

Topo I activity is elevated in cervical cancer compared to normal cervix. The radiosensitivity of noncycling cells within cervical tumors may be increased by simultaneous treatment with low doses of CPT or other topo I inhibitors.

Preclinical evaluation of the orally active camptothecin analog, RFS-2000 (9-nitro-20(S)-camptothecin) as a radiation enhancer

PURPOSE

To test for enhancement of radiation effects in vitro and in vivo by the orally administered camptothecin derivative, 9-nitrocamptothecin (RFS-2000); to study whether the mechanism of this enhancement involves inhibition of sublethal damage recovery.

METHODS AND MATERIALS

In vitro: H460 human lung carcinoma cells were incubated with RFS-2000 for various times at 37 degrees C, irradiated, immediately rinsed, and assessed for colony-forming ability. Sublethal damage recovery (SLDR) was also assessed using two split doses of radiation. In vivo: H460 cell xenografts were used in nude mice. Tumors were grown subcutaneously on the flank, then treated with RFS-2000 (1 mg/kg) and/or radiation (2 Gy) for 5 consecutive days. Tumor growth delay was then measured for each treatment group.

RESULTS

Radiation enhancement was observed in vitro for incubation times between 4 and 24 hr with 10 nM RFS-2000. Using a 24-hr treatment, the radiation dose enhancement ratio values (DER) for 5, 10, and 15 nM were 1.22, 1.54, and 2.0, respectively. Incubation with 10 nM RFS-2000 inhibited SLDR by a factor of 2. The results of three independent in vivo experiments showed that RFS-2000 can enhance the effects of fractionated radiotherapy, with an enhancement factor (EF) of 1.64.

CONCLUSION

Our results show that RFS-2000 can enhance the effects of radiation in human lung cancer cells both in vitro and in vivo, and that the mechanism of this effect may involve the inhibition of SLDR.

A Phase I Trial of Outpatient Weekly Irinotecan/Carboplatin and Concurrent Radiation for Stage III Unresectable Non–Small-Cell Lung Cancer: A Vanderbilt-Ingram Cancer Center Affiliate Network Trial

Irinotecan (CPT-11), a topoisomerase I inhibitor, has been shown in preclinical studies to be a potent radiosensitizer. Carboplatin, a known radiosensitizer with single-agent activity in non small-cell lung cancer (NSCLC), is felt to be a rational choice in combination with irinotecan. We have completed the initial portion of a phase I study, in patients with locally unresectable lung cancer, combining irinotecan with thoracic radiation. Thirteen patients have been entered onto this study through three dose levels (30 to 50 mg/m2/week) of irinotecan. There were seven partial responses in 12 evaluable patients, for an over-all response rate of 58%. Nausea, vomiting, and esophagitis were the principal toxicities of weekly irinotecan and concurrent thoracic radiation. As the maximum tolerated dose (MTD) of irinotecan with radiation has been established at 40 mg/m2/week, we are currently accruing patients to the second phase of this study with the addition of carboplatin (AUC = 2). Thus far toxicity has primarily been esophagitis.

Activation of a cysteine protease in MCF-7 and T47D breast cancer cells during beta-lapachone-mediated apoptosis

beta-Lapachone (beta-lap) effectively killed MCF-7 and T47D cell lines via apoptosis in a cell-cycle-independent manner. However, the mechanism by which this compound activated downstream proteolytic execution processes were studied. At low concentrations, beta-lap activated the caspase-mediated pathway, similar to the topoisomerase I poison, topotecan; apoptotic reactions caused by both agents at these doses were inhibited by zVAD-fmk. However at higher doses of beta-lap, a novel non-caspase-mediated "atypical" cleavage of PARP (i.e., an approximately 60-kDa cleavage fragment) was observed. Atypical PARP cleavage directly correlated with apoptosis in MCF-7 cells and was inhibited by the global cysteine protease inhibitors iodoacetamide and N-ethylmaleimide. This cleavage was insensitive to inhibitors of caspases, granzyme B, cathepsins B and L, trypsin, and chymotrypsin-like proteases. The protease responsible appears to be calcium-dependent and the concomitant cleavage of PARP and p53 was consistent with a beta-lap-mediated activation of calpain. beta-Lap exposure also stimulated the cleavage of lamin B, a putative caspase 6 substrate. Reexpression of procaspase-3 into caspase-3-null MCF-7 cells did not affect this atypical PARP proteolytic pathway. These findings demonstrate that beta-lap kills cells through the cell-cycle-independent activation of a noncaspase proteolytic pathway.

NAD(P)H:Quinone oxidoreductase activity is the principal determinant of beta-lapachone cytotoxicity

beta-Lapachone activates a novel apoptotic response in a number of cell lines. We demonstrate that the enzyme NAD(P)H:quinone oxidoreductase (NQO1) substantially enhances the toxicity of beta-lapachone. NQO1 expression directly correlated with sensitivity to a 4-h pulse of beta-lapachone in a panel of breast cancer cell lines, and the NQO1 inhibitor, dicoumarol, significantly protected NQO1-expressing cells from all aspects of beta-lapachone toxicity. Stable transfection of the NQO1-deficient cell line, MDA-MB-468, with an NQO1 expression plasmid increased apoptotic responses and lethality after beta-lapachone exposure. Dicoumarol blocked both the apoptotic responses and lethality. Biochemical studies suggest that reduction of beta-lapachone by NQO1 leads to a futile cycling between the quinone and hydroquinone forms, with a concomitant loss of reduced NAD(P)H. In addition, the activation of a cysteine protease, which has characteristics consistent with the neutral calcium-dependent protease, calpain, is observed after beta-lapachone treatment. This is the first definitive elucidation of an intracellular target for beta-lapachone in tumor cells. NQO1 could be exploited for gene therapy, radiotherapy, and/or chemopreventive interventions, since the enzyme is elevated in a number of tumor types (i.e. breast and lung) and during neoplastic transformation.

Cyclophosphamide, ara-C and topotecan (CAT) for patients with refractory or relapsed acute leukemia

Topotecan is a topoisomerase I inhibitor with significant activity in patients with myelodysplastic syndrome and chronic myelomonocytic leukemia. Pre-clinical data suggest a synergistic activity with DNA damaging agents such as cyclophosphamide, where topotecan might prevent the repair of cyclophosphamide-induced DNA damage. We thus designed a combination including cyclophosphamide 500 mg/m2 every 12 hours given on days 1 to 3; topotecan 1.25 mg/m2/day by continuous infusion on days 2 to 6, and cytosine arabinoside (ara-C) 2 g/m2 over 4 hours daily for 5 days on days 2 to 6 (CAT). Sixty six (63 evaluable) patients were treated. Fifty two patients had refractory (n=12) or relapsed (n=40) acute myelogenous leukemia (AML), and eleven had acute lymphocytic leukemia (ALL) (refractory n=3, relapsed n=8); their median age was 57 years (range, 18 to 79 years). Eleven patients (17%) achieved a complete remission (CR), and two patients (3%) had a hematologic improvement (HI; met all criteria for CR except for platelets < 100x10(9)/L), for an overall response rate of 20%. Responses occurred in 12 of 52 AML patients (23%), including 10 CR (19%) and 2 HI (4%), and in 1 of 11 patients with ALL (9%). Myelosuppression was universal; there were 23 episodes of pneumonia or sepsis and 18 episodes of fever of unknown origin complicating 74 courses of CAT. Non-hematologic toxicity was mostly gastrointestinal, including nausea, vomiting, diarrhea and mucositis, but was severe in only 8%. In summary, the CAT regimen is well tolerated and has significant anti-leukemia activity which warrants further investigation.

Coordinate modulation of Sp1, NF-kappa B, and p53 in confluent human malignant melanoma cells after ionizing radiation

Regulation of transcriptional responses in growth-arrested human cells under conditions that promote potentially lethal damage repair after ionizing radiation (IR) is poorly understood. Sp1/retinoblastoma control protein (RCP) DNA binding increased within 30 min and peaked at 2-4 h after IR (450-600 cGy) in confluent radioresistant human malignant melanoma (U1-Mel) cells. Increased phosphorylation of Sp1 directly corresponded to Sp1/RCP binding and immediate-early gene induction, whereas pRb remained hypophosphorylated. Transfection of U1-Mel cells with the human papillomavirus E7 gene abrogated Sp1/RCP induction and G(0)/G(1) cell cycle checkpoint arrest responses, increased apoptosis and radiosensitivity, and augmented genetic instability (i.e., increased polyploidy cells) after IR. Increased NF-kappaB DNA binding in U1-Mel cells after IR treatment lasted much longer (i.e., >20 h). U1-Mel cells overexpressing dominant-negative IkappaBalpha S32/36A mutant protein were significantly more resistant to IR exposure and retained both G(2)/M and G(0)/G(1) cell cycle checkpoint responses without significant genetic instability (i.e., polyploid cell populations were not observed). Nuclear p53 protein levels and DNA binding activity increased only after high doses of IR (>1200 cGy). Disruption of p53 responses in U1-Mel cells by E6 transfection also abrogated G(0)/G(1) cell cycle checkpoint arrest responses and increased polyploidy after IR, but did not alter radiosensitivity. These data suggest that abrogation of individual components of this coordinate IR-activated transcription factor response may lead to divergent alterations in cell cycle checkpoints, genomic instability, apoptosis, and survival. Such coordinate transcription factor activation in human cancer cells is reminiscent of prokaryotic SOS responses, and further elucidation of these events should shed light on the initial molecular events in the chromosome instability phenotype.-Yang, C.-R., Wilson-Van Patten, C., Planchon, S. M., Wuerzberger-Davis, S. M., Davis, T. W., Cuthill, C., Miyamoto, S., Boothman, D. A. Coordinate modulation of Sp1, NF-kappa B, and p53 in confluent human malignant melanoma cells after ionizing radiation.

Potentially lethal damage repair and its inhibitory effect of caffeine in two yolk sac tumor cell lines with different radiosensitivities

PURPOSE

In order to investigate the role of potentially lethal damage repair (PLDR) in cellular radiosensitivity, PLDR and its inhibitory effect by caffeine was examined. In addition, cell cycle distribution was also examined.

MATERIALS AND METHODS

Two rat yolk sac tumor cell lines, NMT-1 and NMT-1R, with different radiosensitivities in vitro were used. The capacity for PLDR was examined using confluent-phase cells, and evaluated by calculating the recovery ratio. Inhibitory effect of caffeine on PLDR was examined with doses of 1, 5 and 10 mM.

RESULTS

The capacity of PLDR in two cell lines reflected radiosensitivity. The recovery ratio after irradiation of 5 Gy was 2.8 in the radiosensitive NMT-1 and 5.2 in the radioresistant NMT-1R, and recovery reached its peak level at 6 h in both cell lines. The degree of inhibition of PLDR was weaker in NMT-1R than that in NMT-1 at the same dose level, and was correlated with reduction of G2-arrested cells by caffeine.

CONCLUSIONS

The results of this study suggest that the capacity of PLDR may be one of the determinant factors for radiosensitivity in the two cell lines used, and the inhibitory effect of caffeine on PLDR was in part attributable to the modification of the cell cycle progression.

Effects of SN-38 (an active metabolite of CPT-11) on responses of human and rodent cells to irradiation

PURPOSE

Modulators of the DNA-unwinding enzyme, topoisomerase I (Topo I), inhibit DNA repair and have been reported to increase the lethal effects of X rays, which create breaks in DNA. CPT-11 is a derivative of camptothecin, a Topo I inhibitor, and is clinically available. In this study, we tested the in vitro combination effects of SN-38, an active form of CPT-11, and irradiation on several cell lines.

MATERIALS AND METHODS

Exponentially growing or confluent cultures of CHO cells were treated with SN-38 for 30 min. Cells were then irradiated. Thereafter, the cells were further incubated with the drug for 0 to 3 h. Exponentially growing other cell lines were exposed to 200 nM SN-38 for 30 min before, during, and 3 h after irradiation. The cell survival rate was determined using a conventional clonogenic assay.

RESULTS

SN-38 (200 nM to 4 microM) alone showed slight toxicity to CHO cells in the confluent culture after a 3.5-h incubation. When the cells were treated with the lower doses of SN-38 (50 to 800 nM) during the exponentially growing phase, the cell survival rates were much lower. In combination with irradiation, SN-38 showed only additive effects to irradiation when cells were treated in confluent cultures. However, higher combination effects of SN-38 and irradiation were observed in the cells treated in the exponentially growing phase. When cells were irradiated during the exponentially growing phase, a significant combination effect of 200 nM SN-38 and irradiation was also observed in some cell lines, but not in others.

CONCLUSION

SN-38 and irradiation showed supraadditive effects in some cell lines, when treated in the exponentially growing phase, but not in other cell lines or when cells were treated in the confluent phase.

Na+, K+-ATPase inhibitor, ouabain accentuates irradiation damage in human tumour cell lines

Two normal, two tumour, one transformed fibroblast cell line established from Ataxia telangiectasia (AT) patients and one corrected AT hybrid were characterised with regard to alpha, beta, SF2, and D values. Survival of 60Co gamma-irradiated tumour and transformed cells was markedly reduced when the Na+, K+-ATPase inhibitor ouabain was present 1 hr before and 3 hr post irradiation. Under these conditions, the radiosensitivity in normal cells remained virtually unchanged. Suppression of repair was found to play a role in the ouabain-induced inhibition of the cell survival. In A549 lung carcinoma cells, addition of 10(-8) M ouabain decreases the sublethal damage recovery ratio from 56.5 to 13.3. The same drug concentration decreases the recovery ratio in L132 epithelial cells only from 5.1 to 4.9. The fast repair component, as measured over the first 1.5 hr after irradiation, decreases from 1.83 to 0.36 hr(-1) in A549 cells and from 0.35 to 0.16 hr(-1) in HeLa cells. For 2 Gy fractions, the presence of 10(-8) M ouabain 1 hr before irradiation and 3 hr after irradiation induces dose enhancement ratios of 1.15-1.5. A more pronounced effect on cell inactivation may be expected from multiple fractions. The concentrations required to downregulate sublethal damage repair fall within the range where cardiac glycosides are used clinically. Application of these drugs in radiotherapy thus seems feasible.

Cellular interactions of 5-fluorouracil and the camptothecin analogue CPT-11 (irinotecan) in a human colorectal carcinoma cell line

CPT-11 (irinotecan) is a DNA topoisomerase I inhibitor active against metastatic colorectal carcinoma. We investigated, in a human colon carcinoma cell line, HT-29, the effects of CPT-11 and 5-fluorouracil (5FU) combinations. A strong synergism between CPT-11 and 5FU was observed after sequential exposure and only additivity or antagonism after simultaneous exposure. When cells were first exposed to 5FU, the product of cellular CPT-11 concentrations versus time (CxT) was 6895 +/- 1020 pmol x hr/10(6) cells, while it was 3875 +/- 121 pmol x hr/10(6) cells with CPT-11 alone (p < 0.01). The same phenomenon was observed with SN-38: 148.2 +/- 49.5 versus 83.4 +/- 23.6 pmol x hr/10(6) cells (p < 0.05). Consequently, the formation of protein-DNA complexes was 1.4 times greater with 5FU pretreatment than with CPT-11 alone (p = 0.03). Moreover, the incorporation of 5FU derivatives into DNA was multiplied by a factor of 1.5 24 hr after CPT-11 exposure. When cells were first incubated with CPT-11, the decrease in thymidylate synthase (TS) activity was identical to that obtained after 5FU exposure (1.09 to 0.023 pmol/min/mg protein), but this decrease persisted for 24 hr (0.014 pmol/min/mg protein) (p = 0.035). At the same time, a 1.8-fold increase in the incorporation of 5FU derivatives into DNA and a 2-fold increase in DNA-protein complex formation were evidenced. With the two sequential associations, we observed a persistent S-phase arrest, as compared with CPT-11 alone. These results suggest that CPT-11 and 5FU combinations are of clinical interest, and mechanisms of interaction between the two drugs seem to be multifactorial.

Of what use is molecular biology to the practicing radiation oncologist?

BACKGROUND AND PURPOSE

We are in a period of rapid advance in understanding the basic mechanisms behind the induction and progression of cancer. The relevance of this new knowledge to the daily clinical practice of radiation oncology may not necessarily be readily apparent. Familiarity with a few of the concepts of molecular biology and biochemistry are necessary to fully appreciate the clinical relevance of the new biology.

METHODS AND RESULTS

To illustrate how the new knowledge affects the practice of radiation oncology, examples of the use of molecular biology are presented for different clinical aspects of clinical oncology, i.e. screening and prevention, prognostic factors, predictive factors, treatment decision, novel therapy and follow-up. A number of the molecular biology techniques are illustrated.

CONCLUSIONS

The advances from molecular biology directly impact the role of radiation oncologists in the clinic. While major new therapies are still in development in the laboratory, these will likely have a very significant role in patient care and cancer prevention in the not-too-distant future. Given the central role of radiation oncologists in cancer management, a basic knowledge of molecular biology techniques and their application is essential so that we can be current with our colleagues and patients and as a specialty, participate actively in improving the outcome of patients with or at risk of developing cancer.

Risk factors of pneumonitis following chemoradiotherapy for lung cancer

The purpose of this retrospective study was to identify risk factors associated with development of pneumonitis following chemoradiotherapy (CRT). We examined 60 patients (pts) who received CRT from May 1993 to August 1995. Factors evaluated included total radiation dose, field-size, irradiated site, type of chemotherapy, pulmonary fibrosis and treatment schedule (concurrent versus sequential). There were 17 pts (28.3%) who had > or = Grade 2 pulmonary toxicity. There was no significant relationship between total radiation dose, field-size > or = 200 cm2, pulmonary fibrosis or treatment schedule and risk of pneumonitis. In the sequential treatment group (22 pts), no relationship was noted between any factor and the risk of pneumonitis, while in the concurrent treatment group (38 pts), the incidence of pneumonitis was more frequent (53.8%) in patients with field-size > or = 200 cm2 than in patients with field-size < 200 cm2 (P < 0.05). In those who received concurrent treatment, including weekly CPT-11, pneumonitis was more frequent (56.3%) than in those without CPT-11 (13.6%, P < 0.01). When the lower lung field was included in the radiation site, the incidence of pneumonitis was 70% compared with 20% for other sites (P < 0.01). Multivariate analysis revealed a significant relationship between radiation site and the risk of pneumonitis (P = 0.0096). CPT-11 was significant (P = 0.038) only in the concurrent group. Pneumonitis was reversible in all but one pt by steroid therapy. Thus, irradiated site (included lower lung field) and concurrent CRT used with weekly CPT-11 were treatment factors significantly associated with a higher risk of pneumonitis following CRT.

Topoisomerase-I inhibitors for human malignant glioma: differential modulation of p53, p21, bax and bcl-2 expression and of CD95-mediated apoptosis by camptothecin and beta-lapachone

Beta-lapachone and camptothecin are structurally unrelated agents thought to inhibit topoisomerase-I activity through distinct mechanisms. We find that beta-lapachone is much more potent than camptothecin in inducing acute cytotoxic effects on human malignant glioma cells. Acute cytotoxicity induced by both drugs is apoptotic by electron microscopy, but not blocked by inhibitors of RNA or protein synthesis and not associated with changes in the expression of bcl-2, bax, p53, p21 or GADD45 proteins. In contrast, prolonged exposure of glioma cells to both drugs for 72 hr results in growth inhibition and apoptosis, with EC50 values around 1 microM. None of 7 glioma cell lines tested were resistant to either drug. LN-229 cells which have partial p53-wild-type activity show enhanced expression of p53, p21 and bax protein, whereas bcl-2 levels decrease, after exposure to camptothecin. In contrast, beta-lapachone increases bax protein expression in the absence of p53 activation. T98G cells are mutant for p53. In these cells, p53 levels do not change and p21 is not induced. bax accumulation in T98G cells is induced by both drugs, with bcl-2 levels unaltered. Surprisingly, ectopic expression of murine bcl-2 fails to abrogate the toxicity of either drug. Camptothecin, but not beta-lapachone, sensitizes human malignant glioma cells to apoptosis induced by the cytotoxic cytokines, tumor necrosis factor-alpha and CD95 ligand. Thus, both drugs have potent anti-glioma activity that may be mediated by enhanced bax expression but is not inhibited by ectopic bcl-2 expression. Camptothecin-like agents are particularly promising for immunochemotherapy of malignant glioma using cytotoxic drugs and CD95 ligand.

Damage-sensing mechanisms in human cells after ionizing radiation

Human cells have evolved several mechanisms for responding to damage created by ionizing radiation. Some of these responses involve the activation or suppression of the transcriptional machinery. Other responses involve the downregulation of enzymes, such as topoisomerase I, which appear to be necessary for DNA repair or apoptosis. Over the past five years, many studies have established links between DNA damage, activation of transcription factors that are coupled to DNA repair mechanisms, increased gene transcription and altered cell cycle regulation to allow for repair or cell death via apoptosis or necrosis. Together these factors determine whether a cell will survive with or without carcinogenic consequences. The immediate responses of human cells to ionizing radiation, in terms of sensing and responding to damage, are therefore, critical determinants of cell survival and carcinogenesis.

SN-38, a metabolite of the camptothecin derivative CPT-11, potentiates the cytotoxic effect of radiation in human colon adenocarcinoma cells grown as spheroids

BACKGROUND AND PURPOSE

CPT-11 (7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin) is anew semisynthesized derivative of camptothecin. SN-38 (7-ethyl-10-hydroxycamptothecin), a metabolite of CPT-11, plays a key role in the action of CPT-11.

MATERIALS AND METHODS

To determine whether SN-38 potentiates the cytotoxic effect of radiation, we investigated the interaction of SN-38 and radiation in vitro in monolayer cultures and multicellular spheroids of HT-29 human colon adenocarcinoma cells.

RESULTS

HT-29 spheroids were more resistant to both SN-38 and irradiation than monolayer cells. SN-38 at a concentration of 2.5 microg/ml, which by itself was not cytotoxic, greatly increased the lethal effects of radiation in spheroids, but not in monolayer cultures. Exposure to SN-38 following irradiation inhibited the potentially lethal damage repair (PLDR) in spheroids. It is suggested that the mechanism of the radiosensitization by SN-38 is due to the PLDR inhibition.

CONCLUSIONS

These results indicate that CPT-11 may play a role as radiosensitizer and that a combination of CPT-11 and irradiation could prove to be a particularly effective strategy with which to treat human colon adenocarcinoma.

Enhancement of tumor radio-response by irinotecan in human lung tumor xenografts

We investigated the ability of 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin (CPT-11) to increase tumor radio-response in vivo using human lung tumor xenografts. The xenografts were treated with (1) CPT-11 (10 mg/kg) intraperitoneally on days 1, 5 and 9, (2) single dose radiation (10 Gy/leg) on day 1, or (3) a combination regimen of both treatments in which radiation was given 1 h after the first dose of CPT-11. DNA flow cytometry studies were performed to define the cell cycle changes following treatment for 1 to 12 h with 0, 0.5, 2.0 or 8.0 ng/ml SN-38, the major active metabolite of CPT-11. In both small cell lung cancer (MS-1) and small cell/large cell carcinoma (LX-1) xenografts, combination treatment resulted in significant tumor regression compared with the use of CPT-11 (P = 0.0005, 0.0053) or radiation treatment (P = 0.00221, 0.0035) alone. Neither severe body weight loss nor enhanced skin reaction was observed following the combined treatment. In flow cytometry studies, the proportion of cells in G2/M-phase, the most radio-sensitive phase, increased after 1 h exposure to the lowest dose of SN-38 (0.5 ng/ml). These findings suggest that CPT-11 is a potent radiosensitizing agent, and that its activity is related to the cell cycle. This is the first report to indicate that CPT-11 serves as a radiosensitizer in vivo.