William B. Looney

Adenosine 3′,5′-monophosphate and guanosine 3′,5′-monophosphate: concentrations in Morris hepatomas of different growth rates

Abstract Cyclic AMP and cyclic GMP levels were examined in Morris hepatoma explants in vivo . All eight tumor lines examined had significantly elevated cyclic AMP and cyclic GMP levels when compared to normal liver from tumor-bearing rats. No apparent correlation was observed between the rates of tumor growth and cyclic nucleotide levels; however, two tumor lines (3924A and 7288ctc) had very high levels of cyclic GMP.

A mathematical evaluation of tumour growth curves in rapid, intermediate and slow growing rat hepatomata.

A mathematical evaluation of tumour growth curves in rapid, intermediate and slow growing rat hepatomata

Solid tumor models for the assessment of different treatment modalities XII. Combined chemotherapy‐radiotherapy: Variation of time interval between time of administration of 5‐fluorouracil and radiation and its effect on the control of tumor growth

The combined effects of radiation and 5‐fluorouracil (5‐FU) on control of tumor growth rates in the experimental solid tumor 3924A have been determined when radiation (1500 rads) was given 14, 7, 4, 2, 1 and 0.5 days before 5‐FU (150 mg/kg); and 1, 2, 4, 7, 11, and 15 days after 5‐FU. These results were compared to single doses of each modality given alone and both modalities given simultaneously. Two methods of evaluation were utilized, tumor growth delay and “overall treatment efficiency.” The widely used method of tumor growth delay indicates that the combined effect of radiation and 5‐FU significantly increased tumor growth delay over the additive effect of the two modalities given independently for schedules in which radiation was given from 4 days prior to 2 days after 5‐FU. Maximum tumor growth delay occurred when radiation was given 4 days before 5‐FU; being 2.5 times the additive effects of each modality. Separation of the administration of radiation and 5‐FU by ± 7 to 14 days resulted in two distinct perturbations in tumor growth curves and was less effective than when the two agents were given at shorter intervals. The term “overall treatment efficiency”(OTE) has been introduced to determine the magnitude of tumor volume changes following treatment. The OTE indicates that maximum tumor volume reduction also occurred when radiation was given 4 days before 5‐FU. OTE was 1.5 times the additive effect of the two modalities given independently at this time. Radiation given 4 days after 5‐FU gave less than additive responses, with tumor growth delay and OTE for this combination of 5‐FU and radiation being 0.8 and 0.6 of the additive effects, respectively. The effects of combining radiation with 5‐FU did not reduce animal survival below the survival level of the group given 5‐FU alone in 8 of 10 groups evaluated. Cancer 44:437‐445, 1979.

Rationale for different chemotherapeutic and radiation therapy strategies in cancer management

The two primary therapeutic strategies in cancer have been to give either chemotherapy and radiation therapy together or give a complete course of one treatment modality before starting the second. Clinical studies show that toxicity has been one of the major deterrents to substantial improvements in cancer management when the two modalities are administered together. On the other hand, the prolonged time necessary to administer all of one modality followed by the other makes it likely that repopulation of the tumor during sequential treatment will diminish therapeutic effectiveness. A third strategy of giving chemotherapy and radiation therapy has been developed. This new regimen was designed to give chemotherapy initially, maintain the chemotherapy schedule to avoid any reduction in its effectiveness, and add radiation therapy as early as possible in between courses of chemotherapy to minimize the development of cross resistance. One of the primary objectives of alternating chemotherapy and radiation therapy is to increase the therapeutic index by reducing toxicity without a significant reduction in therapeutic effectiveness. Recent clinical, experimental, and theoretic results with radiation therapy and chemotherapy for cancer management emphasize the necessity of giving both modalities with the greatest intensity possible in the initial phase of induction therapy. Cancer treatment scheduling determines the toxicity and thereby limits the dose intensity that can be tolerated. Scheduling may also govern the antitumor effect directly; however, normal host tissue makes the determination of the direct effects on the tumor difficult, if not impossible, in clinical studies. Well‐defined experimental solid‐tumor systems provide the means for determining directly the relationship between toxicity and antitumor effects in relation to tumor burden and total therapeutic dose. In addition, its relationship to dose intensity and scheduling can be determined by the using more sophisticated research techniques, such as response surface methods. Well‐defined clinical protocols to determine how to interact chemotherapy with radiation therapy more effectively hold considerable potential for rapid improvement in treatment of radiosensitive and chemosensitive cancers.

Solid tumour models for the assessment of different treatment modalities: IV. the combined effects of radiation and 5-fluorouracil.

Neither radiation alone (375 to 1500 rad) nor5-fluorouracil (FU) alone (50-250 mg/kg) is sufficient to prevent an increase in the volume of the solid tumour model hepatoma 3924A. However, as little as 750 rad with 100 mg/kg FU can reduce the tumour below the volume at the time of treatment for as long as 14 days. A series of combined FU and radiation doses given every 11 days should then result in successively smaller tumour volumes until the tumour is eradicated. Changes in tumour volume were analysed by two different methods: (1) tumours in each treatment mode were grouped together and the average response to treatment determined, and (2) tumour volume changes in individual tumours were analyzed utilizing the chi2 technique, which fits the logarithmic tumour volume change with time to polynomials. This two-directional method of analysis has the advantage of permitting both an overview of the main effects of treatment via the averages, and at the same time a detailed examination of the mechanism by which these effects occur through the analysis of individual response. The results suggest that, in addition to concentrating on the cellular response immediately after therapy, greater emphasis should be placed on the kinetic changes of the tumour 1-3 weeks after single or multiple modality therapy. These findings demonstrate how the sequencing of single and/or combined treatment modalities may be investigated in order to detemine how best to obtain maximum effects of treatment on different types of tumours following recovery of the host from the previous treatment series.

Tumour-cord parameters in two rat hepatomas that differ in their radiobiological oxygenation status.

SummaryTumour cords have been examined quantitatively in two rat hepatomas, 3924A and H-4-II-E, that differ in their radiobiological oxygenation status (oxygen enhancement ratio for growth delay [tumour clamped: tumor ‘in air’] was 1.35 for 3924A and only 1.08 for H-4-II-E). The average thickness of tumour cords in 3924A was 118 µm and only 69 µm in H-4-II-E. The migration rates across the cords of the two tumours were approximately the same (1.7 and 1.4 µm ⋅ h−1) but for any given distance from the subtending blood vessel, the proportion of histologically-dead cells within the cord was always higher for H-4-II-E. Volume for volume, H-4-II-E contained four times as much vascular space as 3924A but it is suggested that the poorquality of this vasculature in H-4-II-E contributed to its relative radioresistance.

Changes in Cellularity Induced by Radiation in a Solid Tumour

The growth, and cellular responses of Morris hepatoma 3924 A to a locally-administered dose of 3750 R X-rays were studied using the following parameters; (1) relative tumour volume changes; (2) tritiated thymidine (3H-TdR) incorporation into DNA; (3) tumour DNA content and (4) cellular analysis, including 3H-TdR labelling index, mitotic index, aberrant mitotic frequency and relative cell density. Before depression of tumour growth, cell proliferation is temporarily interuppted. As proliferation is reinitiated, a short-lived synhcrony and prolongation of cell-cycle traverse are reflected in (a) the labelling index and mitotic index, (b) the relative cell density, and (c) the rate of incorporation of 3H-TdR into DNA. Within 4 days after radiation, cell proliferation and 3H-TdR incorporation are significantly depressed. Simultaneously there are reductions in both the relative cell density and tumour DNA contents, and these remain depressed as the tumours initiate regression. From these studies, it is apparent that the cellular responses to radiation insult occur well in advance of measurable volume changes and are observed both in tumours that continue to regress and in those that initiate regrowth.

Solid tumor models for the assessment of different treatment modalities: XXIII. A new approach to the more effective utilization of radiotherapy alternated with chemotherapy.

This study with the rat hepatoma 3924A demonstrated the marked improvement in tumor cure rates and control of tumor growth that can be achieved by the addition of cyclophosphamide (CP) to multiple fractions of radiation per day (MFD) schedules given intermittently. MFD radiation was delivered over a 2-day period followed by CP (150 mg/kg or 0.9 g/m2) 1 day later; this combined course was repeated at 11-day intervals (to allow for gastrointestinal tract and bone marrow recovery) for a total of 3 courses over a 23-day period. Cure rates of 30, 50 and 60% were achieved with total radiation doses of 4500, 6000 and 7500 rad, respectively, when the MFD radiation was given with CP. No cures and no complete responses were realized when the same intermittent MFD schedules for radiation were employed up to 9000 rad without CP. Other groups of 10 animals each were treated with daily fractions of 100, 150, 188, 250 and 375 rad given on days 0-9, 11-20 and 22-31. A 150 mg/kg or 0.9 g/m2 dose of CP was given after each course of daily radiation on days 10, 21 and 32 in the combined treatment groups. No complete responses or tumor cures occurred with radiation alone given daily for total radiation doses, which were increased from 3000 to 11,250 rad. Only the highest radiation dose given, 375 rad per day to a total of 11,250 rad, resulted in a complete response rate and tumor cure rate of 50% when CP was added. The addition of CP to the daily fractionation schedules reduced the total dose needed to give a growth delay of 100 days by 39% (5600 rad versus 9200 rad). The addition of CP to the intermittent MFD schedules further reduced the total dose needed to give a growth delay of 100 days to 4200 rad. Major improvements in some types of cancer treatment may be realized if we can develop clinical protocols for the alternate use of chemotherapy and radiotherapy as we have done successfully in our experimental program. The finding that intermittent MFD radiation schedules are as effective as daily schedules when given alone suggests that greater flexibility of patient management in clinical radiotherapy may be possible without a major loss of therapeutic effectiveness. These alternated fractionated schedules offer the possibility of optimizing treatment in terms of patient convenience and economy as well as the potential for improving the effectiveness of the interaction of radiotherapy with radiosensitizers, radioprotectors, and hyperthermia in addition to chemotherapy.

Response and recovery kinetics of a solid tumour after irradiation.

The effects of local tumour radiation over the dose range 7.5-30 Gy on the growth and cell kinetics of rat hepatoma H-4-II-E have been investigated. A plot of growth delays against log surviving fraction was linear below a fraction of 0.03, but failed to extrapolate to the origin. Following a single dose of 15 Gy to the tumour, DNA-precursor incorporation, labelling and mitotic indices were depressed for 7 days. Tumour cellularity, measured as DNA/g tumour, was reduced and the rate of increase of total clonogenic cells slower than after complete tumour recovery. From Day 7 to Day 9 all indices of proliferation recovered to about control levels, clonogenic cell numbers increased more rapidly and tumour cellularity was restored. Repopulation of the tumour therefore appeared to take place mainly after Day 7. Incorporation of [3H]-TdR into tumour DNA reached twice the control values on Day 9. The rate of tumour growth accelerated after the initial decrease, and maximum tumour growth rate was also twice the control values on Day 13. Accelerated growth rates in irradiated tumours, above those of control tumours, occurred 10-16 days after treatment. The effectiveness of sequential therapy may therefore be improved if given during this period of of accelerated tumour growth.

Effects of 5-fluorouracil on the cell kinetic and growth parameters of hepatoma 3924A.

The effect of 5-fluorouracil (5-FU) on the growth and cellular proliferation of hepatoma 3924A was studied using the following parameters as indices of tumour response: (1) volume measurements, (2) cell kinetic analysis including estimates of both growth and cell loss fractions, (3) changes in tumour histology and (4) tumour DNA content and DNA synthesis. Of a series of single intraperitoneally injected doses (25-300 mg/kg body weight), 150 mg/kg interrupted tumour growth most effectively with minimal toxicity within 168 h, and after 10 days treated tumour volumes were only 42% of untreated tumour size. Doses of 25 mg/kg failed to change the rate of growth while 300 mg/kg exceeded the LD50. Alterations of both tumour cell proliferation and histology developed well in advance of changes observed in growth. A dose of 150 mg/kg body weight blocked the transition of cells from G1 through S for a 24 h interval when cell kinetics were measured by 3H-TdR autoradiography. However, 3H-UdR incorporation into DNA following 5-FU suggested that cellular recovery from the drug was delayed for an additional 24 h. Concurrently, significant losses of tumour tissue and tumour DNA occurred during the first 48 h with an expected increase in both necrotic and connective tissue. During the subsequent 120 h both tumour and necrotic tissue had returned to non-treated levels, while kinetic analysis revealed (a) a slight reduction in the cell cycle time and growth fraction and (b) an increased cell loss factor. The observations from this tumour model system suggest that before using tumour volume or weight as an index of therapeutic response, the relationship between the kinetics of tumour cellularity and tumour volume must be defined.