X-ray responses of human colon tumor cells grown in artificial capillary culture.

Clone A human colon adenocarcinoma cells were grown in three-dimensional artificial capillary culture (ACC) to determine responses of capillaries treated 3 weeks after tumor cell inoculation with a specific, easily quantifiable cytotoxic agent, ionizing radiation. The high-density growth of tumor cells in ACC can be considered to be an in vitro analogue of a solid tumor. Changes in extracapillary space (ECS) fluid concentrations of lactate dehydrogenase (LDH) and aspartate aminotransferase (GOT) and the utilization of glucose in circulating medium were monitored after a supralethal radiation dose (90 Gy) of X-rays. Immediately after irradiation, increased levels of LDH and GOT were found that reached maximum levels about four to five times those found in nonirradiated control capillaries at 10-13 days post irradiation and then declined. Patterns of enzyme production appeared to correlate with the numbers of nonviable tumor cells collected from the ECS of the artificial capillaries. In contrast, glucose utilization showed little correlation with either enzyme concentration or dead cell production. It was determined that, while capillaries grown and treated in this manner appear to respond in a dose-dependent manner to ionizing radiation (as indicated by changes in LDH and GOT levels), these particular end points are relatively insensitive and are not suitable for studies in which therapeutic levels of X-radiation might be given. In other studies, tumor cells were removed from unirradiated capillaries by trypsinization and used to obtain complete survival curves after graded doses of X-radiation. The dose-response curves obtained indicate that clone A colon tumor cells grown in ACC show a marked decrease in their ability to accumulate sublethal radiation injury as compared to responses of these cells growing exponentially in asynchronous monolayer cultures, to synchronized mid-G1 tumor cells, or to tumor cells in stationary growth phase. These data suggest that ACC is a potentially useful model to study the effects of cytotoxic agents on human tumor cells.

In vitro effects of N,N-dimethylformamide on sublethal and potentially lethal damage recovery processes after X-irradiation in heterogeneous human colon tumor cells.

The responses of unfed plateau-phase cultures of two clonal subpopulations of cells (clones A and D) from a human colon adenocarcinoma (DLD-1) to X-irradiation were examined in detail either as control cultures or after growth in medium containing the differentiating agent N,N-dimethylformamide (DMF, 0.8%, three passages). Specifically, the cultures were studied with regard to their ability to express both potentially lethal and sublethal damage recovery (PLDR and SLDR, respectively). In PLDR studies on control cells, clone D expressed more PLDR than clone A, although recovery half-times were the same. DMF treatment increased the expression of PLDR in both cell lines and decreased the half-times for recovery. When recovery from sublethal radiation injury was assessed, the rate and extent of SLDR in non-DMF-treated clone A and D cells were identical. In contrast to the PLDR results, DMF treatment had no significant effect on SLDR in either cell line. These studies show that, while DMF treatment of human colon tumor cells increases cell killing in the clinically relevant, low-dose ("shoulder") region of the X-ray survival curve, this increase in cytotoxicity is not due to an inhibition of the repair of sublethal damage.

Thermal survival characteristics of cell subpopulations isolated from a heterogeneous human colon tumor.

Responses of a heterogeneous human colon adenocarcinoma model tumor system to in vitro hyperthermic treatment at various temperatures have been studied. This model tumor system consists of an original tumor line (DLD-1) obtained from surgical biopsy, and two derivative subpopulations termed clones A and D. These 3 tumor cell populations differ in many properties, including karyotype and DNA content, production of specific antigens, and sensitivities to other cytotoxic agents such as chemotherapeutic drugs and X-irradiation. In these experiments, exponentially growing tumor cells were exposed to hyperthermia (42.2, 42.5, 43.0, 44.0, or 45.0 degrees) for graded time periods. A single-hit, multitarget equation was used to express the dependence of survival on time at a given temperature, and values for extrapolation numbers, quasi-threshold time (min), and T0 (mean lethal time; min) were obtained for the initial regions of survival. At the lower temperatures of 42.2 and 42.5 degrees, biphasic survival curves were obtained for all three tumor lines and, as a consequence, a second mean lethal time (T0,f) was also determined for the final thermal-resistant portion of the survival curves. Using the T0 values as an index of relative resistance, values at 42.2 and 42.5 degrees indicated that, in this temperature region, the parent (DLD-1) line was the most sensitive, the clone A line showed intermediate sensitivity, and the clone D line was the most resistant. In the thermally resistant portion of the survival curve, T0 values indicated that the clone A subpopulation was the most sensitive, the DLD-1 line showed intermediate sensitivity, and the clone D tumor subpopulation remained the most resistant. At the higher temperatures of 43, 44, and 45 degrees, in which thermotolerance is not observed during heat treatment, values for T0 indicated the parent (DLD-1) tumor line was still the most sensitive tumor line, and the clone A and clone D lines showed approximately equal resistance. These data indicate that significant differences may exist among subpopulations of heterogeneous tumors in their survival responses to hyperthermia.

Enhancement by N-methylformamide of the effect of ionizing radiation on a human colon tumor xenografted in nude mice.

Polar solvents, which induce differentiation in murine and human tumor cells, enhance the effect of ionizing radiation on cultured mouse mammary and human colon cancer cells. To determine whether this enhancement occurs in vivo, DLD-2 human colon carcinoma xenografts in nude mice were treated with combinations of 6 MV photon irradiation, the polar solvent N-methylformamide (NMF), or combinations of the two agents. Nude mice bearing 300-mg s.c. implants of DLD-2 tumors were treated i.p. with 150 mg NMF/kg daily for 19 days. Local tumor irradiations were administered as graded single doses or as fractionated doses, daily for 4 days, following the third NMF injection. The growth-inhibiting effect of the radiation treatment for both single dose and fractionation protocols was enhanced by the polar solvent. NMF alone increased the time required for a doubling of initial tumor volume by 1.7 days, compared to control tumors. Initial tumor volume doubling times compared to untreated controls were increased by 3.6 and 7.6 days by photon doses of 10.0 and 13.75 Gy, respectively, whereas NMF plus 10.0 or 13.75 Gy increased the DLD-2 regrowth delay time by 7.5 or 12.9 days. NMF caused essentially equivalent enhancements, whether split-dose schedules of 2.5 Gy daily for 4 days, and 3.44 Gy daily for 4 days, or single doses of 10.0 and 13.75 Gy were used; therefore, radiation enhancement was not due to effects on sublethal damage repair. The results support the use of NMF, currently in Phase 1-Phase 2 clinical trials, with radiation in the therapy of selected human neoplasms.

Intrinsic and extrinsic heterogeneity in the responses of parent and clonal human colon carcinoma xenografts to photon irradiation.

Responses to photon irradiation of xenografted human colon tumors derived from the heterogeneous DLD-1 line or its derivative A and D subpopulations were determined using excision assay and tumor regrowth delay assays. Differential responses among the three xenografted carcinomas were demonstrated. Clone A tumors treated with up to 17.5 Gy showed no actual regression below pretreatment volume. In contrast, clone D tumors were sensitive to doses as low as 3.5 Gy, and tumor volumes were reduced by 65% with a dose of 17.5 Gy. The responses of DLD-1 tumors were intermediate between the clone A and clone D tumor responses. The survival parameters obtained in the excision assay studies for the DLD-1, clone A, and clone D tumors were, respectively: n = 3.3, 1.4, and 1.0; D0 (Gy) = 2.1, 2.2, and 2.7; and DQ (Gy) = 2.6, 0.6, and 0.0. These data indicate that the DLD-1 tumors were the most resistant, with clone A of intermediate sensitivity, clone D being the most sensitive tumor. In addition to the interclonal diversity among xenograft lines, intraclonal variation was also observed with clone A (but not clone D or DLD-1) tumors. A biphasic survival curve of cells from clone A xenografts irradiated in air-breathing hosts clearly indicated a minority (approximately 3%) subpopulation of hypoxic cells. Similar results indicating a small percentage of hypoxic cells in clone A solid tumors were obtained from the tumor regrowth delay studies. Also, excision assay data from experiments in which the heterografted carcinomas were irradiated under anoxic conditions support the interpretation that clone A tumors contain a small fraction of hypoxic cells. This study indicates that: (a) heterogeneity in vivo to ionizing radiation exists in the DLD-1 system; and (b) intraclonal variation occurs in vivo due to extrinsic (e.g., environmental hypoxia) factors, such that the intrinsic radioresistance of a subpopulation (clone A) of a heterogeneous human tumor can be further increased.

Differential responses to x-irradiation of subpopulations of two heterogeneous human carcinomas in vitro.

The responses of two heterogeneous human cancer cell lines and their derivative clones to graded single doses of X-rays were examined in vitro. One system consisted of the human colon carcinoma line DLD-1 and two subpopulations (clones A and D). The second system consisted of the human lung carcinoma line (LX1) and four subpopulations (LX1-1, LX1-2, LX1-3, and LX1-9). These subpopulations have previously been shown to be markedly heterogeneous in terms of such characteristics as karyotype, morphology, drug sensitivity, tumorigenicity, and expression of membrane glycoproteins (such as carcinoembryonic antigen and tumor colonic mucoprotein antigen). Exponentially growing cultures were irradiated with graded single doses of 100-kVp X-rays. Survival was assessed using colony formation as the end point, and responses from multiple experiments were fitted to the single-hit, multitarget equation of cell survival. Values for the mean lethal dose (D0, grays), quasithreshold dose (Dq, grays), and extrapolation number (n) were obtained. For the human colon adenocarcinoma system, these values for the three tumor lines were: DLD-1, 0.95, 2.34, and 11.7; clone A, 1.06, 2.23 and 8.20; and clone D, 1.08, 1.89, and 5.80. For the human lung carcinoma system, these values for the five sublines were: LX1, 1.14, 0.19, and 1.20; LX1-1, 0.96, 2.06, and 8.54; LX1-2, 0.98, 0.88, and 2.48; LX1-3, 0.68, 2.05, and 20.3; and LX1-9, 1.12, 0.00, and 1.00. These two human tumor systems therefore exhibit variability in their intrinsic sensitivity to X-irradiation. The data indicate that failure of some human carcinomas to respond to physical treatment modalities can be due to preexisting resistant subpopulations.

Interobserver variability in the detection of cervical-thoracic Hodgkin's disease by computed tomography.

PURPOSE: Computed tomography (CT) scans of the neck and chest are obtained at diagnosis of Hodgkin's disease to establish disease extent, plan radiotherapy, and serve as baseline studies for subsequent evaluation of response to therapy. However, differences in interpretation may occur even among experienced radiologists. This study was designed to test the extent of variation among expert radiologists' interpretations and to assess how their interpretations differed from that of the primary (institutional) radiologists. MATERIALS AND METHODS: Five radiologists independently reviewed randomly selected CT scans of 59 patients enrolled onto two Pediatric Oncology Group Hodgkin's disease treatment protocols. For each patient, 31 potential disease sites were scored as positive, negative, uncertain, or unassessable. Agreement among the reviewers and between the reviewers and the primary readers was analyzed. RESULTS: For 58% of the sites, at least four of the five reviewers agreed in >/= 80% of the cases. Kappa analysis showed moderate agreement in approximately two thirds of the sites and poor agreement in the remainder. There was moderate agreement between a majority of the expert readers and the primary radiologist reports for approximately one third of the sites, and agreement was poor in two thirds. CONCLUSION: There are disparities among radiologists' interpretations of cervical-thoracic CT imaging of patients with Hodgkin's disease. This variability may affect patient care and the performance and results of multi-institutional clinical trials. We propose that a standardized method of reporting might improve the consistency of interpretation of CT scans in these patients.

The effects of postinduction intensification treatment with cytarabine and daunorubicin in adult acute lymphocytic leukemia: a prospective randomized clinical trial by Cancer and Leukemia Group B.

Cancer and Leukemia Group B undertook a randomized trial of intensification treatment in adults aged 15 to 79 years with acute lymphocytic leukemia (ALL) in complete remission (CR). Daunorubicin (DNR), prednisone, vincristine (VCR), intrathecal (IT) methotrexate (MTX), and asparaginase produced 177 CRs in 277 patients. One hundred fifty-one patients were randomly assigned to receive treatment as follows: 74 received intensive cytarabine and DNR, and 77 received cycles of mercaptopurine (6-MP) and MTX, followed by 6MP, MTX, VCR, and prednisone for 3 years in all. One hundred twelve patients received CNS prophylaxis. Intensification produced major myelosuppression but did not improve remission duration (median, 21 months). Of the 151 patients with CRs who entered the intensification phase, 29% remain in continuous CR (43 to 117 months); in 19 patients, CRs have lasted for longer than 7 years. No relapses occurred after 60 months. Median survival from the time of randomization was 30 months. Those under 30 years of age responded more frequently, with longer CR and survival. While 53% of those aged 15 to 19 years remain in continuous CR, 92% of patients over 59 years have relapsed. The presence of a myeloid antigen on the leukemic cells was adversely prognostic for CR achievement and for survival. Pretreatment WBC and platelet levels independently affected CR duration and survival. Early M1 marrow development presaged longer remissions. CNS relapse occurred in 47 of 256 patients with normal CSF before treatment, in 29 before CNS prophylaxis. CNS disease occurred after CNS prophylaxis in 18 patients: 13 of 61 who had received standard premaintenance and five of 51 who received intensification. No advantage in CR duration or survival resulted from intensive treatment with DNR and cytarabine following induction of CR.

Effects of different forms of central nervous system prophylaxis on neuropsychologic function in childhood leukemia.

A comparison of the late effects on intellectual and neuropsychologic function of three different CNS "prophylaxis" regimens was conducted in 104 patients treated for childhood acute lymphocytic leukemia. Of the children studied, 33 were randomized to treatment with intrathecal (IT) methotrexate alone, 36 to IT methotrexate plus 2,400 rad cranial irradiation, and 35 to IT methotrexate plus intravenous intermediate dose methotrexate. All patients were in their first (complete) continuous remission, were a minimum of one year post-CNS prophylaxis and had no evidence of CNS disease at the time of evaluation. In contrast to the other two treatment groups, children whose CNS prophylaxis included cranial irradiation attained significantly lower mean Full Scale IQs (P less than .001), performed more poorly on the Wide Range Achievement Test, a measure of school abilities, and exhibited a greater number of difficulties on a variety of other neuropsychologic measures. The poorer performance of the irradiated group was independent of sex of the patient, time since treatment and age at diagnosis. These data suggest that the addition of 2,400 rad cranial irradiation to CNS prophylaxis in ALL puts these children at greater risk for mild global loss in intellectual and neuropsychologic ability.

The effects of prior radiation therapy and age on the frequency and duration of complete remission among various four-drug treatments for advanced Hodgkin's disease.

The current report examines the clinical response observed in 137 patients with advanced Hodgkin's disease who had relapsed from an initial complete response following radiation therapy (RTF) in comparison to 280 patients with no prior therapy (NPT). Patients were prospectively randomized to therapy with a four-drug combination chemotherapy program to determine whether CCNU and/or vinblastine are more effective than mechlorethamine and/or vincristine when combined with procarbazine and prednisone. The frequency of complete remission (CR) was 75% for the RTF group compared to 60% of those with NPT (P = .005). In the RTF group, those patients receiving a nitrosourea (CCNU) had a significantly greater CR frequency than those receiving mechlorethamine (P = .006). Significant risk factors favoring longer duration of remission were age less than 40 (P = .005), the absence of splenic involvement (P = .007), and the use of CCNU-containing programs (P = .015). The advantage for CCNU-containing programs was seen only in patients less than 40 years of age. In this study, the strongest factors favorably affecting response to therapy were prior RTF, age less than 40 years, and treatment with a nitrosourea (CCNU).

The influence of patient age on the diagnosis and treatment of lung and colorectal cancer.

We examined the relationship between patient age and medical care received by patients diagnosed with the following two common cancers: non-small-cell lung cancer and colorectal cancer. Controlling for the influence of sex, marital status, presence of comorbid disease, and socioeconomic status, we found that age was not related to the diagnostic tests ordered for either cancer type. However, lung cancer patients with local disease who were older than age 74 years underwent definitive surgical treatment less often than did younger patients. Few patients at any age (less than 9%) with colorectal cancer did not undergo definitive surgical treatment. Patients with regional colorectal disease who were older than 74 years of age underwent radiation therapy to the abdomen less often than did younger patients. These results add to the growing body of literature suggesting that older cancer patients are less likely to undergo the same type of care received by younger patients.

Combined modality therapy for stage IIIA non-small cell carcinoma of the lung.

53 patients with stage IIIA non-small cell carcinoma of the lung (NSCCL) were treated with multimodality therapy consisting of induction radiotherapy (55.8 Gy) and two cycles of concurrent chemotherapy with cisplatin, 25 mg/m2 for 4 days by continuous infusion and bolus etoposide, 100 mg/m2 on days 2 and 4 of each cycle followed by surgery and adjuvant chemotherapy. Of 53 evaluable patients, 47 achieved clinical responses (9 complete response, 38 partial response) after induction therapy for a response rate of 89%. 47 patients were resectable after induction therapy, but 8 patients refused surgery and 6 patients were not eligible for surgery based on poor pulmonary function (medical contraindications). 33 patients underwent thoracotomy and in 6 patients, resection was technically unfeasible. Thus complete surgical resection was accomplished in 27 patients. After all therapy, 28 patients achieved a complete response (53%) and 19 patients a partial response (36%). Toxicities were mild. At a maximum of 75 months (median, 28 months) of follow-up, the median survival of the entire group is 24 months. The median survival of resected patients has not been reached; their 6-year survival rate is 55%. Unresected patients survived for a median of 11 months. This multimodality regimen is well-tolerated, induces a high response and resectability rate and prolongs survival in resected patients.

Mediastinal irradiation for chronic lymphocytic leukemia.

Thirty-one patients with chronic lymphocytic leukemia were treated with mediastinal radiation. In none of the patients was complete remission achieved; either partial remission or clinical improvement was achieved in 52 per cent, but the duration of response was short. The response rate was 77 per cent for the patients receiving a total radiation dose greater than 3,000 rads and 45 per cent for those receiving less than 3,000 rads. Severe life-threatening toxicity was noted in 11 patients and seven of these patients died; two patients died with progressive disease. Severe toxicity was manifested by one or more of the following: bone marrow aplasia, pancytopenia, gram-negative sepsis, generalized herpes zoster and severe esophagitis. Neither the total dose of radiation nor the dose per week correlated withe the severity of reaction or death.

Radiation qualities of x-ray beams in cooperative clinical trials.

X-ray beams are usually described by "MV" numbers which represent accelerating potentials (AP) and approximations to the maximum energies in the photon spectra. However, these numbers do not uniquely specify the properties of the beams. Current high energy photon dosimetry protocols specify radiation quality in terms of a measured ionization ratio which is equivalent to the ratio of the tissue-maximum ratios at depths 10 cm and 20 cm, for field size 10 cm X 10 cm [TMR)20(10]. For convenience, the American Association of Physicists in Medicine introduced a new parameter, known as the Nominal Accelerating Potential (NAP), which was derived from (TMR)20(10) and features values in MV units that are similar to those of the conventional accelerating potentials. (TMR)20(10) and Nominal Accelerating Potential may be considered to be expressions of the penetrating powers of x-ray beams. We determined (TMR)20(10) and Nominal Accelerating Potential for 460 treatment machines with stated accelerating potentials from 4 MV to 25 MV in the Quality Assurance Review Center's files of machine data from institutions that participate in cooperative clinical trials. The results demonstrate appreciable variability of the two parameters at each stated accelerating potential, with overlapping of adjacent groups of machines. It is concluded that the manufacturers' MV numbers do not reliably identify x-ray beams in terms of their depth dose properties. To promote standardization and consistency of energy specification in clinical trials as well as in general practice, we propose that x-ray beams be designated by their Nominal Accelerating Potential values as an adjunct to the use of (TMR)20(10) in radiation therapy.

Field matching considerations in craniospinal irradiation.

Radiotherapy of the craniospinal axis in leukemia and medulloblastoma patients usually involves parallel-opposed lateral cranial fields adjacent and orthogonal to a posterior spinal field. Most current treatment protocols require rotation of the cranial fields to compensate for the divergence of the spinal field such that the adjacent field edges abut along the match line in the mid-saggital plane. Some departments introduce gaps up to 1-2 cm wide between the matched fields out of concern for overdosing the spinal cord. The behavior of the dose distribution was studied in the junction region of divergence-compensated fields as the separation of their edges varied from 0.5 cm overlap to a gap 1 cm wide. Composite dose profiles and isodose maps were calculated for 60Co and 4 MV photon beams using static and moving junction (feathering) techniques. When the fields are appropriately matched there is no gap between them in the mid-saggital plane and the dose varies smoothly across the junction. Gapping of divergence-compensated fields is detrimental to dose uniformity, producing underdosage in a volume that extends to all depths in the body. With proper localization, there is no way that the commonly accepted critical dose for myelopathy can be exceeded in typical treatments of leukemia patients. It can occur in the treatment of medulloblastoma patients only in the unlikely situation where there is gross overlapping of the adjacent fields. Feathering may be considered as a safety margin against spinal cord damage in medulloblastoma but it is superfluous in leukemia. The importance of treatment machine quality assurance and verification of patient set up geometry are emphasized.

The structure for a radiation oncology protocol. The Committee of Radiation Oncology Group Chairmen.

Multi-institutional Cooperative Group clinical trials involving radiotherapy require unambiguous therapeutic guidelines, so that patients entered from each of the participating institutions will receive essentially uniform treatment. The technical guidelines for a Radiation Oncology Protocol presented in this report represents a consensus of the Radiotherapy Committees in the major NCI funded Cooperative Groups and is derived from over a decade of experience. Although they have been written for external beam therapy, they are applicable to brachytherapy with appropriate technical considerations. It is anticipated that further evolution will occur with the introduction of new technologies such as 3-D treatment planning and delivery, multi-leaf collimation and small field irradiation.

Low acute gastrointestinal and genitourinary toxicities in whole pelvic irradiation of prostate cancer.

PURPOSE: This retrospective study was done to determine the frequency and severity of acute gastrointestinal (GI) and genitourinary (GU) toxicity associated with whole pelvic radiotherapy of localized prostate cancer. METHODS AND MATERIALS: Between 1989 and 1994, we treated 156 patients with localized prostate cancer, ranging in age from 54 to 86 (median 71), of which 86 were older than 70 years of age. No attempt at selection was made, and many were from the Veteran's Administration Hospital where they had been precluded from their surgical program because of comorbidities and/or advanced age. Of 156 patients, 45 (28.8%) underwent pretreatment laparoscopic lymphadenectomy (LAP); 40 had negative findings. Four-field box technique was used for all patients. We treated the whole pelvis to 45 Gy, followed by a cone-down and a final boost to a total dose of 72 Gy. The cone-down to the lower pelvis and boost to the prostate were based on computed tomography and/or magnetic resonance imaging findings for volume reconstruction with field size of approximately 8 x 8 and 6 x 6 cm, respectively. Diet instructions were given before treatment and emphasized weekly. Toxicities were evaluated weekly by physicians and nurses independently using Cancer and Leukemia Group B (CALGB) grading criteria. RESULTS: The acute GI and GU toxicities gradually increased from Week 2, peaked at Week 5, and then declined after that. During Week 5, acute Grade 1-3 GI morbidities were observed in 19 (12.2%), 2 (1.3%), and 1 (0.6%) patients, respectively. Genitourinary toxicity was similar, accounting for 17 (10.9%), 6 (3.8%), and 1 (0.6%), respectively. Overall Grade 2 toxicities occurred in 30 of 156 patients (19%). Comorbidity was associated with more GI toxicity. Patients over 70 years of age tended to reach the maximal GI and GU toxicity 1-2 weeks earlier than did patients under the age of 70. Of the patients who did not follow the diet instruction, all experienced side effects. CONCLUSIONS: Whole pelvic irradiation was very well tolerated in this group of patients. The frequency of acute Grade 2 GI and GU toxicity compared favorably with the reported results of conformal treatment. Diet restriction and psychosocial input may have had a positive impact. Late sequelae will be evaluated in long-term follow-up.

Impact of a dosimetry review program on radiotherapy in group trials.

The impact of a quality assurance program on protocol compliance has been explored. A sample of 2258 patients, who received radiation therapy on 18 different NCI funded protocols, was selected for this study from the more than 6200 cases reviewed by the Quality Assurance Review Center (QARC) from 1974 to 1983. Analysis of this sample reveals a significant decrease in the protocol non-compliance rate as a function of QA participation time (35% down to 5%). The educational impact of the QA program is demonstrated by the drop in the protocol dose deviation rate from 11.4% (before QARC feedback) to 3.6% (after feedback, p less than .001). The corresponding drop in protocol deviations in treatment volume is from 21.5% to 10.5% (p less than .001). The effect of the "on-treatment" review process is studied; it is demonstrated that this process cuts the rate of major deviations in half. The technical discrepancies in dose are also analyzed and discussed.

Potentiation of in vitro cytotoxic effects of misonidazole on human colon tumor cells by the differentiation-inducing agent N-methylformamide.

Human colon tumor cells (clone A) were studied in vitro with regard to modification of dose-dependent cytotoxicity to misonidazole (MISO) treatment by pre-exposure growth in medium containing the differentiation-inducing agent N-methylformamide (NMF). Cells were grown as exponential cultures and were exposed for 2 passages to 170 mM NMF before exposure to graded doses of MISO (0-100 mM, 3 hours at 37 degrees C, oxic or hypoxic). Both oxic and hypoxic cells could be sensitized to MISO cell killing. Using the 10% level of survival for comparison, the calculated MISO doses (mM) were: 105, 37, 50, and 10 for oxic control cells, hypoxic control cells, oxic-NMF treated cells, and hypoxic-NMF treated cells, respectively. Therefore, for NMF treated oxic cells, cell killing was increased by a factor of about 2.1, while for NMF treated hypoxic cells, cell killing increased by a factor of about 3.7. These data indicate that NMF treatment, while potentiating effects on both oxic and hypoxic cells, appears to have selectivity towards hypoxic cells. NMF may therefore have use in combined modality radiation therapy of solid tumors with electron-affinic radiosensitizers.

Contrasting effects of the differentiating agent sodium butyrate on recovery processes after x-irradiation in heterogeneous human colon tumor cells.

The X ray survival responses of two clonal subpopulations of cells (clones A and D) from a heterogeneous human colon adenocarcinoma (DLD-l) were studied in unfed plateau phase cultures either as control cultures or in cultures grown for three passages in medium containing the differentiating agent sodium butyrate (NaB, 2 mM). Specifically, the cultures were studied with regard to their ability to express both potentially lethal and sublethal damage recovery (PLDR and SLDR). Growth in NaB-containing medium enhanced the radiation sensitivity of both cell lines in the low dose ("shoulder") region of the survival curve. For clone A, the Dq value was reduced by 59%, and for clone D, the Dq value was reduced by 96%. NaB treatment increased both the rate and the extent of PLDR in both cell lines as assessed by single dose kinetic studies. However, when split dose experiments are performed to assess the expression of SLDR, NaB pretreatment was shown to totally inhibit the expression of SLDR, and also to alter the expression of PLDR under these conditions. These data suggest that PLDR and SLDR are separate, yet related, cellular recovery processes. In addition, NaB may be useful as an adjunct to radiotherapy by virtue of its ability to sensitize tumor cells in the dose range conventionally used for therapy, as well as by inhibition of sublethal damage recovery.