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Improved treatment of a brain-tumor model

Part 2: Sequential therapy with BCNU and 5-fluorouracil

Massimo A. Gerosa, Dolores V. Dougherty, Charles B. Wilson, and Mark L. Rosenblum

✓ A combination chemotherapy regimen for brain tumors was developed, based on investigations of the survival of animals harboring the intracerebral 9L rat brain-tumor model and on analyses of their clonogenic tumor cells. Fischer 344 rats harboring 9L brain tumors were treated with 2-day courses of 5-fluorouracil (5-FU), in order to expose all cycling tumor cells to the drug during DNA synthesis and achieve maximum anti-tumor activity for this cell-cycle-specific anti-metabolite. Although a 74% cell kill was obtained for a total dose of 45 mg/kg or greater, animal life span was not increased over that of untreated tumor-bearing controls. However, when 5-FU (48 to 96 mg/kg total dose over 2 days) was administered after a single LD10 dose of BCNU (13.3 mg/kg), additive cell kill was suggested. In three large series, long-term animal survivors and occasional tumor cures were observed with this drug combination, a result never observed following BCNU alone. Schedule dependency was not apparent. A previously published protocol for treating recurrent malignant gliomas with sequential courses of BCNU and 5-FU was partially planned based upon these initial observations. Anti-tumor activity with the combination of drugs was superior to therapy with BCNU alone. Both animal and human studies confirm that, contrary to presently accepted oncological tenets, a chemotherapeutic agent that kills significant numbers of tumor cells but is clinically ineffective when given alone might, nevertheless, be useful in combination therapy regimens.

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Improved treatment of a brain-tumor model

Part 1: Advantages of single- over multiple-dose BCNU schedules

Mark L. Rosenblum, Massimo A. Gerosa, Dolores V. Dougherty, and Charles B. Wilson

✓ Clonogenic cell and animal survival studies were used to determine the most effective BCNU therapy schedule in the 9L rat brain-tumor model. Survival of tumor cells following a single LD10 dose of BCNU (13.3 mg/kg intraperitoneally) was compared to cell survival after one to four daily 0.5 × LD10 doses. The posttreatment kinetics of surviving clonogenic cells were investigated at various times after BCNU was given in single doses of 0.25 to 1 × LD10 and in two daily doses of 0.5 × LD10. The cell kill was greater, time to reinitiation of cell growth was later, posttreatment rate of clonogenic cell proliferation was slower, and the interval to total repopulation of the clonogenic cell pool was longer with a single LD10 dose as compared to the multiple-dose schedules. Animal survival studies confirmed that a single LD10 dose of BCNU was at least as effective as a cumulative level of up to 1½ times that amount when treatment was administered in smaller doses, regardless of the fractionation schedule.

Clinical experience with patients harboring malignant brain tumors has shown that a single BCNU dose of 185 to 200 mg/sq m is tolerated well. Results of these animal experiments suggest that this therapy should have anti-tumor activity at least equivalent to the more commonly employed schedule of 80 mg/sq m/day given for 3 days. Although direct comparison of treatment efficacy using the two schedules is not possible, no adverse clinical effects have been observed with the recently adopted single-dose schedule. Furthermore, the duration of patient hospitalization for chemotherapy has decreased.

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Stem cell studies of human malignant brain tumors

Part 1: Development of the stem cell assay and its potential

Mark L. Rosenblum, Massimo A. Gerosa, Charles B. Wilson, Geoffrey R. Barger, Bertran F. Pertuiset, Nicolas de Tribolet, and Dolores V. Dougherty

✓ A stem cell assay for human malignant gliomas has been developed. Cells obtained from tumor biopsies grew into colonies composed of malignant glial cells, as documented by histochemical, immunohistochemical, and immunobiological techniques. Studies suggest that the disaggregated cells are representative of the cells within the solid tumor.

Clonogenic cells were obtained from 48 tumors and analyzed for their in vitro sensitivity to graded doses of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). The in vitro anti-tumor activity of BCNU at clinically achievable doses was compared to clinical response to the agent based on changes in computerized tomographic scan, radionuclide brain scan, and neurological examinations. Twenty-two patients received nitrosoureas before or after tumor specimen analysis, and were eligible for in vitro-in situ correlations. Clinical tumor sensitivity to nitrosoureas was predicted by culture results in 42% of all evaluable patients, and clinical resistance was predicted in 100%. The capability of the assay can be appreciated best for the 13 patients not treated with BCNU prior to culture; the in vitro prediction of clinical sensitivity and resistance was 71% and 100%, respectively.

Preliminary findings show that clinical tumor resistance to BCNU may result from “intrinsic” cell resistance in some patients and from inadequate delivery of drug to tumor cells in other cases. The potential utility of this method to study the reason(s) for tumor cell resistance to drugs, to screen new chemotherapeutic agents, to individualize patient treatment, and to investigate tumor biology is discussed.

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James E. Boggan, Mark L. Rosenblum, and Charles B. Wilson

✓ A tumor of the trochlear nerve sheath with an unusual but diagnostic presentation is described. The rarity of reported cases may reflect failure to differentiate tumors originating from the trochlear and trigeminal nerves.

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Brain-tumor therapy

Quantitative analysis using a model system

Mark L. Rosenblum, Kathy D. Knebel, Dolores A. Vasquez, and Charles B. Wilson

✓ A recently developed colony-formation assay has been used to evaluate in vivo 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU) therapy of a transplantable rat brain-tumor model. A comparison of the in vitro colony-forming capacity of treated and untreated tumor cells permits calculation of the fraction of clonogenic tumor cells surviving in vivo therapy. The plateau that we previously observed on the BCNU dose-response curve is not the result of repair of potentially lethal damage, since no change in the 0.1% of surviving clonogenic tumor cells occurs during the first 2 to 4 days after treatment. Although reanalysis of the dose-response curve indicates that sublethal damage exists, its repair is probably minimal. The most likely explanation for the observed limitation of the BCNU effect is the drug's failure to reach all clonogenic cells. A dose of BCNU that kills more than 99.9% of clonogenic tumor cells within 30 minutes of treatment results in only a 60% decrease in tumor weight by Day 14. This disparity is explained by retarded removal of dead cells, and, along with a previously determined 90% cell-kill threshold necessary to appreciate increased animal survival, demonstrates the inherent limitations of measurements of tumor size (including brain scans and clinical patient evaluations) in evaluating the efficacy of brain-tumor therapy. Following an LD10 dose of BCNU the surviving clonogenic tumor cells increase in number after a latency period of 2 to 4 days; during regrowth the cell doubling time is 40 hours. Marked variability in tumor response and regrowth was noted. The determination of information regarding disturbed tumor cell kinetics and tumor heterogeneity is essential for the proper planning of combination chemotherapy and multimodality regimens.

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Takao Hoshino, Charles B. Wilson, Mark L. Rosenblum, and Marvin Barker

✓Four patients received 3H-thymidine 4 to 7 days and vinblastine 4 to 6 hours prior to operation for recurrent malignant gliomas (three glioblastomas and one anaplastic astrocytoma). Tumor biopsies obtained at operation were fixed for routine histological studies and radioautography. The tumors' growth fractions averaged 0.28 with a range of 0.14 to 0.39. The tumor cell cycle time calculated in three patients had a mean duration of 57 hours with a standard deviation of 6 hours. The authors concluded that: 1) single short-term courses of cell-cycle specific chemotherapeutic agents alone will probably fail to achieve either significant reduction in tumor mass or dramatic clinical improvement; 2) cell-cycle phase-specific drugs should be administered to maintain effective blood levels over 2 to 3 days for maximal tumor cell kill. Tumor growth rate appears to correlate with the fraction of proliferating cells rather than the length of the tumor cell cycle. The scientific basis for combination drug and multimodality therapy is discussed.