I will just make a few remarks before opening this General Discussion on the Cytological and Haematological effects of Antimitotics. I believe that numerous and interesting will be your comments. Let me first go back very briefly to the pioneer of these compounds, colchicine, already mentioned in the Egyptian, Greek, and Roman Pharmacology, but whose stathmokinetic effect was illustrated by P. Dustin Sr. just in 1934. We are lucky enough to have in our program the Dustin name perpetrated through his son, A. P. Dustin Jr.

Several years ago, since 1947 on, my group adopted colchicine to perform a test for evaluating in tissue culture the proliferative activity of the blood-forming cells from different physio-pathologic conditions. Using that method, among other it was possible to ascertain that — contrary to expectations — the proliferative activity of the bone marrow cells in human leukaemias is rather low, and this finding has been later confirmed by many investigators using different approachments and methods. Quite recently, in collaboration with Gociu M. and Airò R., I have started investigating the effect of colchicine on the blastic transformation of human peripheral blood lymphocytes stimulated with Phytohaemagglutinin (Phyto) in cell culture. The main purposes of this research project are:

1. To test the effect of colchicine on the blastic development process, which occurs as a consequence of such an intense RNA- and DNA- synthesis presented by human lymphocytes in the Phyto-culture system;

2. To evaluate the extent of proliferation of the Phyto-stimulated lymphocytes, because the divisions which occur in these cells could definitely contribute in making higher their number. (In fact, the number of the blast-like cells obtained after 3-4 days of cell culture with Phyto is a function not only of the number of the lymphocytes which undergo blastic transformation, but also of the number of the same blastlike cells which undergo mitotic division).

Recently discovered substances with antimitotic action fall in the two categories which have been defined since many years, i. e. spindle poisons and chromatin (or “radiomimetic”) poisons. The most recently studied are hydroxyurea — a powerful inhibitor of DNA synthesis — and the Vinca alcaloids — which destroy the tubular components of the spindle, bringing a prolonged arrest in metaphase.

The mechanisms of action of many of these drugs remain most obscure. In the field of spindle-poisons, there has been no explanation sofar of the relationship between their chemical structure and cytological action. While it is known that minor changes in the chemical structure of colchicine can prevent its specific action on the spindle, the precise relation which appears to exist between this complex molecule and the spindle structures remains obscure. The same remark applies to the Vinca alcaloids. Progress is being made however in this field. The ultrastructural aspects of the spindle have been analysed by electron microscopy, and a precise definition in chemical terms of the spindle may be close. These observations have shown the similarity between the tubules of the spindle and other tubular structures of identifical size: the neurotubules. Some recent observations indicate that these may also be destroyed by colchicine, a fact which may be related to the well-known and severe neurotoxicity of this alcaloid. What remains to be explained is the fact that the most effective spindle poisons are molecules of the size and complexity of those of vinblastine, while simple inorganic substances (arsenicals, heavy metals) may exert identical if not so powerful effects on the spindle structures. Another point which needs further research is the cause of the extensive cellular destruction which follows, in animal cells, any prolonged inhibition of the spindle function. The chemotherapic actions of spindle poisons are most probably related, not only to the growth inhibiting effects of these drugs, but most of all to the cellular breakdown which is observed in cells when they have been kept for several hours in metaphase.

Stathmokinetic agents are a class of antimitotic agents which possess the ability of arresting cell division at the metaphase stage.

They are also called spindle poisons because they act by inactivating or distructing the mitotic spindle. Some new discovered stathmokinetic compounds, like vinblastine and vincristine, are effective anti-tumour agents. The mechanism of action of spindle poisons is briefly discussed.

1. Vinblastine (VLB) and vincristine (VCR) are both naturally occurring alkaloids derived from the flowering periwinkle plant, Vinca rosea, Linn.

2. Both drugs have large molecules and are very similar in chemical structure. They differ only in that VLB has a methyl group (-CH3) while VCR has a formyl group (-CHO) attached to one of the nitrogen atoms in the molecule.

3. In spite of this chemical similarity, VLB and VCR differ greatly in the types of malignancy against which they are effective, their toxicities, and their potencies.

4. With these differences in mind, it appeared logical to produce more alkaloids of the series by modifying one of the side chains of VLB.

5. Vinglycinate sulfate (VGL), the first of these semisynthetic VLB derivatives to undergo clinical trial, has proved useful in the treatment of some patients with malignant disease. There was no cross-resistance between VGL and its parent substance, VLB, or with VCR.

Vinblastine (VLB) and vincristine (VCR) are two alkaloids (extracted from the plant Catahranthus roseus) which possess a definite antitumor activity. The antitumor activity. The antimitotic action of these two alkaloids was studied both on normal bone marrow and leukemic cells. Comparative studies showed that they are, like colchicine, spindle poisons. They, however, differ from colchicine and its derivatives in some of their biological activities.

The problem of the relationship between antitumor and antimitotic activity of VLB and VCR is discussed.

41 children with acute leukemia were treated with Vincristine Sulphate. Total remission was obtained in 17 out of 22 patients (77%) in whom Vincristine was used as the first drug.

19 patients who had been treated previously with other antimitotic drugs and have become resistant to them, received Vincristine: total remission occurred in 7 cases and partial remission in 3 cases within 4-10 weeks of therapy.

A case is reported of a child still surviving three years and seven months from the beginning of the disease and two years and 4 months from completion of therapy with Vincristine.

The Authors describe the therapeutic effects obtained with Vincristine and Imuran in patients with acute leukaemia.

The results obtained with Vincristine indicate that the drug may be usefully employed in some cases of lymphoblastic leukaemia, both in the untreated phase or when the disease has become resistant to other antimetabolites. The remissions are of shorter duration compared with those obtained with other available compounds and are substantially confined to the lymphoblastic variety of acute leukaemia.

The preliminary clinical trial with Imuran has shown that the drug is better tolerated than 6-mercaptopurine and is able to produce good and satisfactory remissions in lymphoblastic and myeloblastic leukaemia, as well as in the blastic crisis of chronic granulocytic leukaemia, provided the dosage employed reaches 7-8 mg/Kg body weight daily.

Results of Chemotherapic treatment in Hodgkin's disease are reported. 23 cases were treated by Vincaleucoblastine, 19 by Methylhydrazine, and 12 by both drugs. With VLB we obtained 6 complete remissions, 12 partial remissions and 5 failures; with MH the remissions were 9 complete, 4 partial and 6 failures. An improvement was obtained by the use of both drugs successively administered and repeatedly.

Many drugs have been recently tested in the treatment of leukaemias and hematosarcomas. Some of them have been found active: Dibromomannitol in chronic myeloid leukemia, Leurocristine in lymphoblastic diseases, Vincaleucoblastine and Methyl-Hydrazine in reticulohistiocytal diseases, and Methyl-Glyoxal-Bis (Guanylhydrazone) associated with 2-Hydroxystilbamidine in acute granulocytic leukaemias. Besides, multiple chemotherapy, coupled with the use of stored bone marrow has already given encouraging results in the treatment of hematosarcomas.

Our experience in the Imuran treatment of acute leukemia is rather scarce. Indeed because of the difficulty to get this drug, we could use it in 6 cases only. These 6 cases belonged to the following forms: 3 to the stem cells type, 1 to the myelomonocytic type, 1 to the histiomonocytic ungranulated type, 1 to the promyelocytic type (acute terminal crisis of chronic myeloid leukemia). All these patients had been already treated with other antiblastics.

Positive results we had just in 2 cases, precisely in a case of stem cells leukemia and in the last case above mentioned. Similar results in acute relapsing phase of chronic myeloid leukemia obtained Eridani et al. (1965). Where we applied strong doses (mg 30c of Imuran daily for 10 days), following the advice of Storti and Traldi (1965), and thus obtained a full three months remission (Fig. 1).

According to this modest experience of ours Azathioprine is a drug that does not present clear advantages on 6-Mercaptopurin.

The report presents the clinical results of treatment with Azathioprine 6 [(methyl-4-nitro-5-imidazolyl) thio] purine, in patients with acute leukaemia, the acute relapsing phase of chronic myelocytic leukaemia and in a group of patients affected by illness which have probably an autoimmune pathogenesis.

Favorable results were obtained in the group of patients suffering from acute leukaemia with a percentage of clinical and/or haematological remission of 57%.

A comparative analysis of the length of survival in these patients compared to that of a similar group of patients treated with 6-mercaptopurine is also reported.

A fair response was also obtained in the group of patients in the acute relapsing phase of C.M.L.

In the group of patients affected by diseases probably due to an immune pathogenesis, a favorable response was obtained in 2 cases of systemic lupus erithematosus with haemolytic anaemia and 1 case of acquired autoimmune haemolytic anaemia.

1. Lists have been made of the more frequently occurring malignant diseases and of those commonly available oncolytic drugs which, in the author's opinion, are most appropriate for their treatment.

2. Those tumors which do not usually respond to oncolytic drugs have also been listed.

3. For several malignant diseases it has been found that small doses of oncolytic drugs have proved just as effective for inducing remission and even more effective in prolonging remission than have larger doses of these drugs. The explanation for this may be that smaller doses do less harm to the body's immune defense mechanism than do larger doses.

Antimitotic drugs essentially induce a direct inhibition on the malignant cellular proliferation. Secondary mechanisms should even be considered: i.e. neoplastic clonal disadvantage, indirect antivitaminic mechanism for the intestinal atrophy caused by antimitotic drugs, endocrine failance due to the antimitotic drugs damages in the endocrine glands (pharmacological « hypophysectomy » and « castraction ») etc.

The selectivity of cytostatic action depends of the following factors:

a) the compound, its mode of action, the applied dosage, the localization and the speed of activation, its metabolites and excretion;

b) the sensitivity or resistance of the proliferated tissue;

c) the individual general condition of the patient, the degree of malnutrition, the integrity of defense mechanisms and the ability of detoxication and the regenerative capacity of hemopoiesis.

The action of cytostatic agents directed against specific cell functions of different cell systems develops distinct differences in clinical effects and toxicity among alkylating agents, antimetabolites and mitotic inhibitors. Comparative data of these compounds are given. Due to its selectivity of action each cytostatic agent possesses a specific optimal indication in hemoblastoses, neoplasias or immune reactions.

210 cases of polycythemia vera were observed over a period of 15 years. The majority of them received P32; treatment with Myleran instead of with radioactive phosphorus was instituted only recently. To a small number of patients chemotherapy was given alternately with P32. The differing response pattern to either kind of treatment and the possible interference of therapy with the natural development of the disease process are demonstrated in a few selected cases.