J.H. Mulder

Synchronization in tumour chemotherapy

IN MOST cell populations--in tissue culture and in vivo, both in many normal tissues and in tumours--cell divisions are distributed at random in time. Various types of treatment may disturb this random distribution to some extent for a limited period of time. There is a larger fraction of cells passing simultaneously through the phases of the cell cycle, until the variation between cells in the speed of progress through the cycle once more evens out the inequality in distribution. Synchronization is the name given to the phenomenon where larger than average fractions pass simultaneously through the various recognizable phases of the cycle. It can be identified by a temporary peak in the mitotic index or in the thymidine labelling index. Synchronized cells have been used in tissue culture on a large scale for experimental studies of the biochemical processes associated with the various phases of the cell division cycle and for this purpose highly effective methods of in vitro synchronization have been developed such as treatment with cold shock [1], excess thymidine [2, 3], detachment of mitotic cells [4, 5] or isoleucine deprivation [6, 7]. Study of synchronized cells has shown that cells vary over the division cycle in their sensitivity to radiation and to a large number of cytostatic drugs. One group of drugs kills cells especially if applied during DNA synthesis, other agents kill cells preferentially after exposure in G 2 or during mitosis (for a systematic review see MadocJones and Mauro [8]). Conversely it has become evident that many types of drug treatment or irradiation may also lead to partial synchronization and cytostatic

5-fluorouracil and methotrexate combination chemotherapy: The effect of drug scheduling

Abstract The effect of combination chemotherapy with 5 -FU and MTX administered either simultaneously or sequentially with time intervals of up to 24 hr was studied in the L1210 leukaemia, the mouse osteosarcoma C22LR and the Lewis lung carcinoma. Tumour growth delay, the number of lung metastases and lung colonies and survival times of leukaemic mice were used as parameters. Sequential treatment with MTX followed by 5 -FU was the most effective antitumour schedule in the L1210 leukaemia and the osteosarcoma. This sequence of drug administration, however, also resulted in a marked weight loss and in early toxic deaths of the animals, in contrast to the other schedules investigated. The implications of our findings along with an analysis of the experimental data from the literature are discussed in relation to the clinical applicability of this drug combination.

Schedule dependent effectiveness of CCNU and 5-fluorouracil in experimental chemotherapy

Abstract The effect of combination chemotherapy with CCNU and 5-FU given either simultaneously or with a time interval of 24 hr was studied in the Lewis lung carcinoma and in the mouse osteosarcoma C22LR. Tumour growth delay, number of lung metastases and lung colonies as well as the survival time of mice with and without surgical removal of the primary tumour were used as parameters. Treatment with CCNU followed by 5-FU was the least effective schedule in both tumour lines. In order to evaluate therapeutic gain, we also investigated the cell killing effect of both drugs in different schedules on resting and on rapidly proliferating bone marrow stem cells: CCNU followed by 5-FU was the most toxic treatment sequence. Consequently, the therapeutic effect (the ratio between effect on tumour and effect on normal tissues) must be low when this sequence is given. If a combination of CCNU and 5-FU is considered for the clinical treatment of gastrointestinal cancer, the most frequently used scheme is a nitrosourea on the first day of a 5-day course of 5-FU. Based on our preclinical studies, we suggest a schedule in which 5-FU is followed within a short time interval by CCNU.

Why Do Colon Tumours Respond Poorly to Chemotherapeutic Agents

In theory any of the following mechanisms, singly or in combination, may form the basis of a poor response to cytostatic agents: a) Inherent cellular insensitivity to cytostatic drugs b) Inhomogeneity in drug sensitivity among tumours of a certain type c) Few proliferating cells in each tumour, since proliferating cells respond better to drugs d) Poor vascularization of the tumour preventing the cytostatic drugs from reaching the tumour cells e) Early emergence of a drug-resistant cell line after exposure to each agent f) Surviving tumour cells proliferating rapidly during treatment.

Lack of vincristine-cyclophosphamide potentiation in different experimental tumour lines.

Abstract Combination chemotherapy with vincristine and cyclophosphamide was investigated in the L 1210 leukaemia, the Lewis lung carcinoma, the mouse C 22 LR osteosarcoma and in two experimental colon tumour lines. Therapeutic synergism could not be demonstrated in any of the tumour cell lines. In the L 1210 experiments, simultaneous treatment resulted in therapeutic antagonism. This less than additive effect could be avoided by using scheduling with a time interval of at least 12hr . The sequence in which the two drugs were administered did not influence the results. Studies on haemopoietic stem cells showed an additive effect in all of the schedules investigated. It seems preferable to treat L 1210 leukaemia and possibly other rapidly proliferating neoplastic lines by a sequential application of vincristine and cyclophosphamide, not because of any potentiating effect but because drug antagonism can be circumvented in this way.

Schedule-dependent cytotoxicity of 5-fluorouracil and cyclophosphamide in experimental cancer chemotherapy☆

Abstract The effect of drug scheduling of 5 -fluorouracil and cyclophosphamide was investigated in L1210 leukaemia, the Lewis lung carcinoma and the mouse C22LR osteosarcoma. The optimum antitumour schedule was found to be that in which the drugs were given simultaneously. In the treatment of L1210 and the Lewis lung carcinoma, drug synergism was observed when the two agents were administered simultaneously. A similar trend was less pronounced for the osteosarcoma. The most cytotoxic schedule for bone marrow stem cells was cyclophosphamide followed by 5 -fluorouracil. As a consequence of this differential effect, the best tolerated and generally also the most effective antitumour schedule was the simultaneous administration of the two drugs. These experimental data should lead to critical testing of clinically used multi-drug combinations, e.g., Bonadonnas CMF regimen in patients with metastatic mammary carcinoma.

Vincristine-methotrexate combination chemotherapy and the influence of weight loss on experimental tumour growth

SummaryAccording to pharmacokinetic reports, vincristine administration should precede methotrexate therapy. Our sequential treatment of L1210 leukaemic mice, in which vincristine was administered before methotrexate therapy, was as effective as treatment with the two drugs given simultaneously. In solid tumour experiments we were unable to show any increase in the antitumour effect of methotrexate when vincristine was injected before methotrexate administration. Consequently, we advocate the re-evaluation of the practice of vincristine →methotrexate therapy as used in many clinical protocols for the treatment of patients with osteosarcoma.Pretreatment with vincristine resulted in methotrexate-induced weight loss and sometimes in toxic death of the mice. Since the growth of tumours can be modified by regulation of the caloric intake of the host, this aspect was investigated in more detail. The effect of starvation, which was comparable to the effect of drug-induced weight loss, had a retarding effect on tumour growth. The growth rates of smaller tumour volumes were less severely affected than were those of large tumour masses.

Adriamycin/cyclophosphamide combination chemotherapy: The importance of drug scheduling☆

Abstract The effect of adriamycin/cyclophosphamide combination chemotherapy was evaluated against a spectrum of transplantable tumours in mice (L1210 leukaemia, Lewis lung carcinoma and C22LR osteosarcoma) and critical normal tissue. Treatment was given either simultaneously or sequentially with a time interval of 24 hr. Drug synergism was observed in the treatment of L1210 when the two agents were administered simultaneously. In the solid tumour experiments, neither synergism nor schedule dependency could be demonstrated. From the bone marrow stem cell assays, it is concluded that simultaneous treatment is the least effective and therefore the least toxic schedule. Based on these data, it may be recommended that, in clinical cancer treatment, adriamycin and cyclophosphamide be given simultaneously and not sequentially.

Cell Kinetic Factors, Single Drugs and Combination*

This communication focuses on the problems that exist in the application of cell kinetic information in cancer chemotherapy. From selected historical work, the following conclusions can be drawn. 1) Theoretically optimal drug sequences may fail to show the expected effect. 2) Similar drug sequences cause different effects in different tumors, even when the tumors have similar proliferation characteristics. The unpredictability and the heterogeneity in response make the extrapolation to clinical cancer chemotherapy very difficult. Better prediction may be made from the integration of results from studies combining cell kinetic factors, cellular pharmacokinetics, and biochemistry of drug exposure.

Tumour Load Dependent Effectiveness of Cyclophosphamide in Lewis Lung Carcinoma

The concept of adjuvant chemotherapy is attractive: when the residual tumour load is minimal, a given treatment will be more effective than in the advanced stage of the disease. In the design of a treatment protocol, the chemotherapist must take at least two basic problems into account: 1) which drugs should be applied in the adjuvant format? and 2) which group of patients should be selected for the adjuvant treatment?