The addition of Valproic acid to concurrent radiation therapy and temozolomide improves patient outcome: a Correlative analysis of RTOG 0525, SEER and a Phase II NCI trial.

PURPOSE/OBJECTIVES: Valproic Acid (VPA) is an antiepileptic agent with HDACi (histone deacetylase inhibitor) activity shown to radiosensitize glioblastoma (GBM) cells. We evaluated the addition of VPA to standard radiation therapy (RT) and temozolomide (TMZ) in an open-label, phase II study (NCI-06-C-0112). The intent of the current study was to compare our patient outcomes with modern era standard of care data (RTOG 0525) and general population data (SEER 2006-2013). MATERIALS/METHODS: 37 patients with newly diagnosed GBM were treated in a phase II NCI trial with daily VPA (25 mg/kg) in addition to concurrent RT and TMZ (2006 - 2013) and 411 patients with newly diagnosed GBM were treated in the standard TMZ dose arm of RTOG 0525 (2006 - 2008). Using the SEER database, adult patients (age > 15) with diagnostic codes 9440-9443 (third edition (IDC-O-3) diagnosed between 2006 - 2013 were identified and 6083 were included in the analysis. Kaplan-Meier method was used to estimate OS and PFS. The effect of patient characteristics and clinical factors on OS and PFS was analyzed using univariate analysis and a Cox regression model. A landmark analysis was performed to correlate recurrence to OS and conditional probabilities of surviving an additional 12 months at diagnosis, 6, 12, 18, 24 and 30 months were calculated for both the trial data and the SEER data. RESULTS: Updated median OS in the NCI cohort was 30.9m (22.2- 65.6m), compared to RTOG 0525 18.9m (16.8-20.3m) (p= 0.007) and the SEER cohort of 11m. Median PFS in the NCI cohort was 11.1m (6.6 - 49.6m) compared to RTOG 0525 with a median PFS of 7.5m (6.9-8.2m) (p = 0.004). Younger age, class V RPA and MGMT status were significant for PFS in both the NCI cohort and the RTOG 0525 cohort, in addition KPS was also significant for OS. In comparison to RTOG 0525, the population in the NCI cohort had a more favorable KPS and RPA, and a higher proportion of patients receiving bevacizumab after protocol therapy however with the exception of RPA (V) (8% vs 18%) (0.026), the effects of these factors on PFS and OS were not significantly different between the two cohorts. CONCLUSION: Previously reported improvements in PFS and OS with the addition of VPA to concurrent RT and TMZ in the NCI phase II study were confirmed by comparison to both a trial population receiving standard of care (RTOG 0525) and a contemporary SEER cohort. These results provide further justification of a phase III trial of VPA/RT/TMZ.

Effect of cell-cell interactions on drug sensitivity and growth of drug-sensitive and -resistant tumor cells in spheroids.

Multicellular spheroids were grown from mixtures of rat brain tumor cells sensitive (9L) and resistant (R3) to 1,3-bis(2-chloroethyl)-1-nitrosourea. Percentages of each cell subpopulation in these spheroids were estimated with the sister chromatid exchange assay and were found to be approximately the same as those used to initiate spheroids. Spheroids grown from 9L cells alone had a higher growth rate than spheroids grown from R3 cells alone. However, the growth rate of mixed-cell spheroids was essentially the same as that of pure 9L spheroids and was independent of the percentages of R3 cells in mixed-cell spheroids. The sensitivity of 9L cells in mixed-cell spheroids treated with 1,3-bis(2-chloroethyl)-1-nitrosourea, estimated by changes in the number of sister chromatid exchanges per metaphase induced by treatment, decreased as the percentage of R3 cells increased. These effects are probably the result of an interaction between the two cell subpopulations held in three-dimensional contact, a situation similar to that in tumors in situ. The results suggest why one cell subpopulation of tumors does not become dominant during growth and indicate that interactions between cell subpopulations can influence the sensitivity of one subpopulation to 1,3-bis(2-chloroethyl)-1-nitrosourea.

alpha-Difluoromethylornithine-induced polyamine depletion of 9L tumor cells modifies drug-induced DNA cross-link formation.

Depletion of intracellular levels of polyamines, which are believed to have a role in the intranuclear stabilization of DNA, alters the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea and cis-diamminedichloroplatinum II in 9L rat brain tumor cells. Alkaline elution techniques were used to show that polyamine depletion alters the number of DNA cross-links formed by these cytotoxic agents.

Polyamine depletion influences drug-induced chromosomal damage.

Polyamines have been implicated in the intracellular stabilization of DNA. Depletion of intracellular polyamines influences the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea and cis-diamminedichloroplatinum II. By means of the sister chromatid exchange assay, it was found that intracellular polyamine depletion can also alter the induction of chromosomal damage by these cytotoxic agents.

Combination of N-methylformamide with cis-diamminedichloroplatinum (II) in murine mammary carcinoma: importance of timing.

The maturational agent N-methylformamide (NMF) is an antitumor agent that also enhances the response of tumor cells in vitro to chemotherapeutic agents. Here, we tested whether NMF can improve therapy of the murine MCA-K mammary carcinoma with cis-diamminedichloroplatinum(II) (cis-DDP). Although the in vitro cell cultures of MCA-K tumor cells exhibited increased sensitivity to cis-DDP cytotoxicity when they were first treated with NMF, administration of NMF to mice bearing MCA-K tumors did not enhance cis-DDP-induced tumor growth delay. However, when NMF treatment was begun after cis-DDP administration, the growth delays were significantly greater than those induced by the individual treatment, with an increase in temporary tumor regression and a small proportion of cures. These results indicate that therapeutic benefit can be achieved in this experimental tumor system when NMF is administered after cis-DDP. In addition, they demonstrate the significance of the timing of administration in combined protocols involving NMF.

Nitrosourea-induced sister chromatid exchanges and correlation to cell survival in 9L rat brain tumor cells.

The ability of various nitrosoureas to induce sister chromatid exchanges (SCEs) in 9L rat brain tumor cells was investigated. Treatment of cells for 1 hr with the alkylating and cross-linking agents 1,3-bis(2-chloroethyl)-1-nitrosourea or chlorozotocin produced concentration-dependent increases in SCEs; elevations above controls were detected at concentrations of 1 microM or more. Above 0.25 mM, the alkylating agent ethylnitrosourea produced a dose-dependent increase in SCEs. Treatment with the carbamoylating agent 1,3-bis(trans-4-hydroxycyclohexyl)-1-nitrosourea did not induce SCEs. The maximum drug concentration at which SCEs are readily scored kills approximately 50% of cells. When accurate cell survival data in this dose range were obtained, a direct correlation between nitrosourea-induced cell kill, measured by a colony-forming efficiency assay, and SCE induction was found. Thus, analysis of the levels of SCE production may provide information about the efficacy of antineoplastic drugs.

Prediction of in vivo tumor response to chemotherapeutic agents by the in vitro sister chromatid exchange assay.

The ability of the in vitro sister chromatid exchange (SCE) assay to predict in vivo tumor drug sensitivity was investigated using a spontaneous hepatocarcinoma in C3Hf/Kam mice and 3 chemotherapeutic agents: melphalan; cis-platinum; and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). For hepatocarcinoma cells grown in monolayer culture, melphalan was the most efficient at inducing SCEs, and BCNU, the least. cis-Platinum induced a range in SCEs that overlapped those of BCNU and melphalan, suggesting that hepatocarcinoma is not a homogeneous population with intermediate sensitivity, but is a mixture of cis-platinum-sensitive and -resistant cells. According to in vitro cell survival curves, hepatocarcinoma was most sensitive to melphalan, less sensitive to cis-platinum, and essentially resistant to BCNU. The relative antineoplastic effects of melphalan, cis-platinum, and BCNU in vivo were compared by the response of artificial and spontaneous pulmonary metastases and solid tumors to these agents. For artificial metastases, there was a dose-dependent decrease in the number of lung nodules in mice treated with melphalan or cis-platinum, with melphalan being the more effective. BCNU had no effect. Spontaneous pulmonary metastases generated from hepatocarcinoma leg tumors were reduced in those mice treated with melphalan, unaffected by cis-platinum, and increased by BCNU. In hepatocarcinoma leg tumors (5 to 6 mm in diameter), melphalan induced the longest growth delay, and BCNU the least. Therefore, the relative effects produced by these three drugs in vivo were the same as predicted by SCE induction in vitro. The SCE assay may thus have potential clinical application.

Chromatin modifications associated with N-methylformamide-induced radiosensitization of clone A cells.

Exposure of certain cell lines to the differentiation-inducing agent N-methylformamide (NMF) enhances their radiosensitivity. As part of an attempt to elucidate the mechanism of NMF-induced radiosensitization, we examined the effects of NMF on chromatin structure, as reflected by changes in DNA-protein cross-links (DPCs) and the chromatin protein/DNA ratio, in two cell lines, clone A and HCA-1. Both lines form a better-differentiated phenotype upon exposure to NMF, yet only clone A is radiosensitized. Ionizing radiation induced DPCs in a linear manner beginning at about 10 Gy and continuing to at least 50 Gy in both cell types. NMF treatment of HCA-1 cells did not affect the background level of DPCs, but it enhanced the formation of radiation-induced DPCs at each dose tested. In clone A cells, NMF exposure elevated the DPC background level more than two-fold, and modified radiation-induced DPCs. The dose response for radiation-induced DPCs in NMF-treated clone A cells consisted of a linear increase up to 12.5 Gy, which was greater than in untreated cells, followed by a plateau level of DPCs out to 50 Gy, the highest dose tested. NMF treatment of clone A, but not HCA-1, cells also increased the chromatin protein/DNA ratio by about 30-35%. In clone A cells, the increases in DPC background level and chromatin protein/DNA ratio as a function of NMF exposure time followed a pattern similar to that of the enhancement of radiosensitivity. These data suggested that modifications of chromatin structure, not involved in differentiation, may be associated with the radiosensitizing actions of NMF.

Comparison of the sister chromatid exchange and cell survival assays as a measure of tumor cell sensitivity in vitro to cis-diamminedichloroplatinum (II).

Cytotoxic effects of treating RIF-1, EMT6, and 9L tumor cell lines with cis-diamminedichloroplatinum(II) were measured with the sister chromatid exchange assay and compared to results obtained with the colony-forming efficiency assay. The greatest number of sister chromatid exchanges was induced in RIF-1 cells, fewer in EMT6 cells, and the least in 9L cells. Cell survival data obtained with the colony-forming efficiency assay paralleled data obtained with the sister chromatid exchange assay. These studies suggest that the sister chromatid exchange assay may be a useful method with which to determine the in vitro sensitivity of tumor cells to some antineoplastic agents.

Prediction of human tumor cell chemosensitivity using the sister chromatid exchange assay.

The sister chromatid exchange (SCE) assay has been used to predict the chemosensitivity to 1,3-bis(2-chloroethyl)-1-nitrosourea of various neoplastic cell subpopulations in eight cell lines derived from human brain tumors. Because the SCE assay is based on analysis of individual cells, data obtained can be plotted as frequency histograms of SCEs per chromosome, and the range of chemosensitivities of cell subpopulations can be identified easily. Results suggest that the SCE assay has predictive value as a clinical assay for drugs for which a strong correlation between cell kill and induction of SCEs has been established.

cis-Diamminedichloroplatinum(II)-induced sister chromatid exchange: an indicator of sensitivity and heterogeneity in primary human tumor cell cultures.

The effect of cis-diamminedichloroplatinum(II) (cPt) on sister chromatid exchange (SCE) induction was determined in 13 human primary tumor cell cultures. Primary cultures were derived from surgical specimens of solid tumors composed of a variety of histologies. Three to 16 days after biopsy, depending on the growth rate, cultures were treated with graded concentrations of cPt for 1 h and the SCE assay was performed. SCE dose-response curves (SCEs induced per chromosome versus cPt concentration) showed a wide range in cPt sensitivities that was not dependent on histology. SCE frequency histograms showed that several of the primary cultures contained both cPt-sensitive and -resistant cells. For six of the cultures, the SCEs induced per chromosome at 15 microM cPt were plotted versus the IC90 determined from a survival assay. A line fit to those points yielded a correlation coefficient of -0.74. These results show a relationship between the activity of cPt in the SCE assay and in the survival assay, which suggests that SCE analysis may be useful for predicting cPt sensitivity. In addition, characterization of cellular heterogeneity in cPt sensitivity using the SCE assay may provide additional information useful in the prediction of tumor response to treatment.

Cyclooxygenase-2 expression in human gliomas: prognostic significance and molecular correlations.

Cyclooxygenase (COX)-2, the inducible isoform of prostaglandin H synthase, has been implicated in the growth and progression of a variety of human cancers. Although COX-2 overexpression has been observed in human gliomas, the prognostic or clinical relevance of this overexpression has not been investigated to date. In addition, no study has analyzed the relationship between COX-2 expression and other molecular alterations in gliomas. Consequently, we examined COX-2 expression by immunohistochemistry in tumor specimens from 66 patients with low- and high-grade astrocytomas and correlated the percentage of COX-2 expression with patient survival. We also analyzed the relative importance of COX-2 expression in comparison with other clinicopathological features (age and tumor grade) and other molecular alterations commonly found in gliomas (high MIB-1 level, p53 alteration, loss of retinoblastoma (Rb) protein or p16, and high bcl-2 level). Kaplan-Meier analyses demonstrated that high COX-2 expression (>50% of cells stained positive) correlated with poor survival for the study group as a whole (P < 0.0001) and for those with glioblastoma multiforme in particular (P < 0.03). Cox regression analyses demonstrated that COX-2 expression was the strongest predictor of outcome, independent of all other variables. In addition, high COX-2 expression correlated with increasing histological grade but did not correlate with positive p53 immunostaining, bcl-2 expression, loss of p16 or retinoblastoma protein expression, or high MIB-1 expression. These findings indicate that high COX-2 expression in tumor cells is associated with clinically more aggressive gliomas and is a strong predictor of poor survival.

Preferential enhancement of tumor radioresponse by a cyclooxygenase-2 inhibitor.

Cyclooxygenase-2 (COX-2), an inducible isoform of cyclooxygenase, is overexpressed in many types of malignant tumors, where it mediates production of prostaglandins (PGs), which in turn may stimulate tumor growth and protect against damage by cytotoxic agents. This study investigated whether SC-'236, a selective inhibitor of COX-2, potentiates antitumor efficacy of radiation without increasing radiation injury to normal tissue. Mice bearing the sarcoma FSA in the hind legs were treated daily for 10 days with SC-'236 (6 mg/kg given in the drinking water) when tumors were 6 mm in diameter. When tumors reached 8 mm in diameter, the mice were given 11- to 50-Gy single-dose local tumor irradiation with or without SC-'236. SC-'236 inhibited tumor growth on its own, and it greatly enhanced the effect of tumor irradiation. The growth delay was increased from 14.8 days after 25-Gy single dose to 28.4 days after the combined treatment (P = 0.01). SC-'236 reduced TCD50 (radiation dose yielding 50% tumor cure) from 39.2 Gy to 20.9 Gy (enhancement factor = 1.87). SC-'236 did not appreciably alter radiation damage to jejunal crypt cells and tissue involved in the development of radiation-induced leg contractures. The SC-'236-induced enhancement of tumor radioresponse was associated with a decrease in PGE2 levels in FSA tumors. The drug had no effect on radiation-induced apoptosis. Neoangiogenesis was inhibited by SC-'236, which could account for some of the increase in tumor radioresponse. Overall, our findings demonstrated that treatment with a selective inhibitor of COX-2 greatly enhanced tumor radioresponse without markedly affecting normal tissue radioresponse. Thus, COX-2 inhibitors have a high potential for increasing the therapeutic ratio of radiotherapy.

Differential potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea by alpha-difluoromethylornithine in chloroethylnitrosourea-sensitive and -resistant 9L rat brain tumor cells in vitro.

alpha-Difluoromethylornithine, an enzyme-activated, irreversible inhibitor of ornithine decarboxylase, inhibited the growth of both chloroethylnitrosourea-sensitive and -resistant 9L rat brain tumor cells in vitro. After 48 hr of treatment with 10 mM alpha-difluoromethylornithine, the putrescine and spermidine contents of both resistant and sensitive cells were less than 5% of control levels, but the spermine level was slightly elevated. The cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea, as measured by a colony-forming efficiency assay, was significantly increased in alpha-difluoromethylornithine-pretreated sensitive cells but not in resistant cells treated with this polyamine inhibitor. With the sister chromatid exchange assay, we found that alpha-difluoromethylornithine pretreatment increased 1,3-bis(2-chloroethyl)-1-nitrosourea-induced damage to chromosomes in sensitive but not in resistant cells.

Radiosensitization of human tumor cell lines induced by the adenovirus-mediated expression of an anti-Ras single-chain antibody fragment.

The expression of activated ras genes has been implicated as a contributing factor to the radioresistance of tumor cells. As a strategy for compromising Ras protein activity and potentially enhancing the radiosensitivity of tumor cells, we have investigated the application of the AV1Y28 adenovirus, which expresses a single-chain antibody fragment directed against p21 Ras proteins. The ability of AV1Y28 transduction to modulate radioresponse was investigated using four human tumor cell lines--U251 glioblastoma, MIA PaCa-2 pancreatic carcinoma, and the colon carcinomas SW620 and HT29. Cultures were exposed to sufficient levels of AV1Y28 to transduce more than 90% of the cells; 24 h later, cultures were exposed to ionizing radiation, and clonogenic cell survival was determined. Tumor cell survival was reduced by 40-50% when the tumor cell lines were exposed to AV1Y28 only. In addition, for each tumor cell line, AV1Y28 exposure enhanced the level of radiation-induced cell killing. Dose enhancement factors at a surviving fraction of 0.1 ranged from 1.3 to 1.5. Furthermore, for each of the cell lines, the surviving fraction at 2 Gy was significantly reduced by AV1Y28 exposure. In contrast to the results seen in tumor cells, the radiosensitivity of a normal human fibroblast cell line was not affected by AV1Y28. These data indicate that this anti-Ras adenovirus enhances the radiosensitivity of tumor cells but does not affect the radiosensitivity of normal cells.

Measurement of sister chromatid exchanges and their relationship to DNA damage, repair and cell killing.

We have concentrated on how SCE is measured, how it correlates with other measures of cellular damage, and how SCE can be used as a tool to study cell cycle kinetics. We have not discussed the biological significance of SCEs, i.e. why they occur spontaneously, and what role, if any, in cellular preservation they play. Similarly, our discussion of the mechanisms of formation of SCE has been deliberately brief. These are important considerations, but the answers to them are still largely only speculative. What is clear is that SCE is an extremely interesting biological phenomenon from a variety of points of view, and even though the mechanisms underlying SCE are not yet well understood, measurement of these events has produced much useful and provocative information.

Enhancement of intrinsic tumor cell radiosensitivity induced by a selective cyclooxygenase-2 inhibitor.

The antitumor effects of the selective cyclooxygenase (COX)-2 inhibitor SC-236 alone and in combination with radiation were investigated using the human glioma cell line U251 grown in monolayer culture and as tumor xenografts. On the basis of Western and Northern blot analyses, these cells express COX-2 protein and mRNA to levels similar to those in the human colon carcinoma cell line HT29. Treatment of U251 cells in monolayer culture with 50 microM SC-236 resulted in a time-dependent decrease in cell survival as determined by a clonogenic assay. The cell death induced by SC-236 was associated with apoptosis and the detachment of cells from the monolayer. After 2 days of drug treatment, the cells that remained attached were exposed to graded doses of radiation, and the clonogenic assay was performed. Comparison of the survival curves for drug-treated and untreated cultures revealed that SC-236 enhanced radiation-induced cell death. In these combination studies, SC-236 treatment resulted in a dose-enhancement factor of 1.4 at a surviving fraction of 0.1, with the surviving fraction at 2 Gy (SF2) reduced from 0.61 to 0.31. These data indicate that in vitro SC-236 induces U251 apoptotic cell death and enhances the radiosensitivity of the surviving cells. To extend these investigations to an in vivo situation, U251 glioma cells were grown as tumor xenografts in the hind leg of nude mice, and SC-236 was administered in drinking water. SC-236 alone slowed tumor growth rate, and when administered in combination with local irradiation, SC-236 caused a greater than additive increase in tumor growth delay. These in vitro and in vivo results suggest that the selective inhibition of COX-2 combined with radiation has potential as a cancer treatment.

Enhancement of in vitro chemotherapeutic activity by dimethylsulfoxide.

The effects of the differentiation-inducing polar solvent dimethylsulfoxide (DMSO) on the in vitro response of murine hepatocarcinoma cells to cisplatinum, BCNU, and melphalan were investigated using the sister chromatid exchange (SCE) and cell survival assays. Growth of cells in medium containing 2 per cent DMSO enhanced drug-induced SCEs and cell kill. In order for the enhancement to occur, cells had to be exposed to DMSO for at least 48 h prior to drug treatment. The presence of DMSO during drug treatment did not affect cell response to the three chemotherapeutic agents. The enhancement of chemosensitivity was eliminated within 24 h of DMSO removal. These data suggest that the differentiation-inducing polar solvents may provide antineoplastic benefits when administered in combination with standard chemotherapeutic agents.

Antitumor and antimetastatic activity of the differentiating agent N-methylformamide in murine tumor systems.

N-Methylformamide (NMF), a cell-differentiating agent, was assessed for its antitumor activity against a fibrosarcoma (FSA), a hepatocarcinoma (HCA-I) and a mammary carcinoma (MCA-K), syngeneic to C3Hf/Kam mice. Tumors were grown as solitary tumors in the leg or as artificial or spontaneous micrometastases in the lung. NMF, at a dose of 300 mg/kg, was administered i.p. daily for 6 to 18 days. NMF slowed the growth of FSA and HCA-I tumors and totally inhibited the growth of the MCA-K tumor. However, the effect was transient; tumors resumed their pretreatment growth rate upon cessation of the treatment. Histologically, MCA-K tumors treated with NMF (300 mg/kg daily for six days) underwent considerable cell depopulation and reduction in mitotic activity. The number of artificial metastases, as well as the incidence and the number of spontaneous metastases, were markedly reduced by NMF. This resulted in a prolongation of the survival of mice that had artificial metastases of MCA-K tumor. The in vitro clonogenicity of MCA-K, but not of FSA or HCA-I cells, was reduced. However, in vivo reduction of MCA-K cell clonogenicity was minimal, if any. Thus, NMF is effective in restricting the growth of both solitary tumors and metastases, but the degree of response is highly dependent on tumor type.

Radiosensitization of primary human tumor cell cultures by N-methylformamide.

The effects of the differentiation-inducing agent N-methylformamide (NMF) on the radiation response of ten primary human tumor cell cultures were investigated. Cell survival was determined using an adhesive tumor cell culture system. NMF (1%) was added to cultures on Day 1 and was left for 6 days; cultures were irradiated with graded doses of X rays (1.0-6.0 Gy) on Day 4. Using survival at 2.0 Gy as a comparative endpoint, eight of ten cultures tested exhibited enhanced radiosensitivity upon exposure to NMF. In sensitized cultures, the dose-enhancement factors ranged from 1.3 to 2.5. The NMF-mediated radiosensitization did not appear to be dependent on the histologic cell type. The results presented support previous data obtained from established cell lines and suggest that NMF may offer clinical benefits against a variety of tumor types when used in combination with radiotherapy.