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The effects of cyclophosphamide given for 18 weeks in small daily doses on CFU-S, CFU-C, and CFU-E content in mice bone marrow and spleen were studied. In the bone marrow, after an initial drop, the stem cell content rises above the normal values and remains there throughout a long period. In the spleen the stem cell content shows an initial several fold increase followed by a steady decline. It seems possible that this behaviour reflects a compensative effect to the toxic action of the drug at more differentiated levels of the haemopoietic cells.

The effect of N-acetylcysteine on hemopoietic stem cells was studied. The drug was given to mice untreated and injected with a single dose of cyclophosphamide or doxorubicin. The results show that the antioxidant drug N-acetylcysteine does not induce any significant decrease in the cytotoxic effect of cyclophosphamide or doxorubicin.

The effects of the cytotoxin busulphan (myleran) have been investigated in order to ascertain the unique nature of the lesion which it induces. It is one of only few compounds which can cause marked residual marrow dysfunction and the only drug reported to induce a marrow lesion of such magnitude that after a prolonged interval mice may die of the effects of pancytopaenia resulting from hypoplastic marrow failure. We have found that busulphan has a major microenvironmental effect as assessed by the ability of the marrow to form a complete organ in an ectopic site, which confirms existing evidence from a range of putative stromal assays. The effects upon CFU-S are known to include a selective action against certain subpopulations. Our investigation of the dose relationship of busulphan effects have shown that induction of the prolonged marrow lesion is not dependent on the dose of drug administered, or the fractionation regime employed, and is not dependent therefore on the number of CFU-S removed by the drug. The unique action of busulphan probably rests therefore in its ability to damage the microenvironment and the most primitive stem cells which are closely associated with it, if not entirely dependent on it, for their existence.

The effect of bleeding on spleen colony-forming units (CFU-S) and on in vitro colony-forming cells with colony-stimulating factor (CFU-C) and erythropoietin (CFU-E) has been evaluated. The in vivo and in vitro colony-forming cells of the bone marrow show a decrease which for the CFU-E, CFU-C follows a short-lived increase. In the spleen, all progenitor cells assayed have shown a significant and sustained increase.

The alleged possibility that testosterone propionate (TP) has a protective effect on hemopoietic cells submitted to the damaging effect of antitumoral drugs was studied. The bone marrow content and the proliferating fraction of CFUs were determined following a single dose on 450 mg/kg of TP. At selected times after TP injection (2 and 4 days), TP-treated mice received a single dose of azathioprine, hydroxyurea, vinblastine, cyclophosphamide, BCNU and doxorubicin. The bone marrow of CFUs were determined 24 h after drug administration. The CFUs-surviving fraction in all cases appeared similar to or lower than that found in controls not treated with TP. It seems therefore that in this experimental setting TP does not reduce the toxic effect of anticancer drugs on hemopoietic pluripotent stem cells. However, this finding does not exclude a possible protective effect of TP at different levels of hemopoiesis or when the steroid is administered with a different schedule.

The hematologic toxicity of 4-demethoxydaunorubicin (4-dmDNR), a new anthracycline more potent and less cardiotoxic than doxorubicin (Dx), was studied. Dose-survival curves of bone marrow hematopoietic precursor cells (HPC) in situ were determined with the use of (C57BL X C3H)F1 mice and with assays of colony-forming units--spleen, culture, and erythroid--by in vivo and in vitro methods. Time response of HPC was followed in mice treated at days 0, 2, and 5 with 0.75 mg 4-dmDNR/kg of 4.5 mg Dx/kg and in mice receiving 2.23 mg 4-dmDNR/kg or 3.96 mg Dx/kg twice a week for 4 weeks. The dose-survival curves of HPC for 4-dmDNR were exponential. Slight differences in sensitivity among assayed populations were seen. Although the doses of 4-dmDNR required to reduce the survival of HPC to 37% were similar or lower than those of Dx, following intermittent treatment with doses of 4-dmDNR with the same optimal antitumor activity as with Dx, 4-dmDNR seemed to have a lesser effect on hematopoietic progenitors and a greater effect on peripheral blood cells than did Dx. However, during prolonged administration 4-dmDNR appeared to be toxic at every hematopoietic level.

The effect of some cycle-dependent anticancer drugs on CFUs has been studied in transfused polycythemic mice. In untreated animals during passive plethora erythropoiesis is depressed but the content of CFUs per femur remains constant. In treated plethoric mice the femural content of CFUs is similar or higher than that found in treated controls after administration of adriamycin, vinblastine, cyclophosphamide, it is lower when the mice receive azathioprine or hydroxyurea. These results suggest that suppression of erythropoiesis does not uniformly affect the susceptibility of pluripotent stem cells to anticancer drugs. Interpretation of the reported findings is difficult as it must take into account a complex interplay of a number of factors.

The effects of 4'epi-doxorubicin (4'-epi-DX) on survival of in situ murine bone marrow hematopoietic precursor cells (HPC) were studied. The drug was given to (C57BL X C3H)F1 mice in increasing single doses, in repeated administration (three time in 5 days), or for a long period (twice a week for 10 weeks). Survival of colony-forming units (CFUs, spleen; CFUc, culture; and CFUe, erythroid) was assayed by in vivo and in vitro methods; dose survival curves were exponential. It appears that single doses of 4'epi-DX have a greater impact on murine HPC than single doses of the parent compound. Following repeated administrations, pluripotential stem cells recover better after the derivative than after its parent drug. During prolonged treatment, the bone marrow content of committed progenitors is depleted to a lesser extent in the animals treated with 4;-epi-DX than in those receiving DX. It is, however, possible that, following the same prolonged treatment, this difference is minimal. The conclusion, these experimental data seem to indicate that 4'-epi-DX has lower toxicity in murine HPC than DX and that this is evident mainly after repeated administrations for a short period of time.

The effects of vincristine on bone marrow hemopoietic stem cells were studied in mice. After the administration of a single dose of the drug there is a sharp decline in the content of CFUs. When the drug is given in small, weekly doses for 16 weeks, after an initial drop, the stem cell content rises at a normal level where it remains, although with wide oscillations. On the whole the effects of vincristine on b.m. CFUs are comparable with that observed after vinblastine administration.

The effect of Adriamycin and 4-Eip-Adriamycin was studied on CFUs, CFUc, CFUe of murine bone marrow and spleen. Differences among the bone marrow stem cells and the spleen stem cells have been observed. It seems possible to explain some of these differences admitting a process of redistribution from the bone marrow to the spleen.

Haematologic effects of delayed 16 h administration of leucovorin (LV) following high-dose methotrexate (HDMTX) were analyzed in C57Bl X C3H F1 mice. Results show that 16 h administration of LV significantly reduces the toxic effects of HDMTX on hemopoietic progenitors and bone marrow cells. At 12 days after HDMTX administration, the bone marrow level of CFUs was significantly higher in HDMTX-LV treated mice than in HDMTX treated animals. In comparison with previous data obtained when LV was injected 2 h after HDMTX, the delay in administration of LV does not appear to reduce the protective effect of the vitamin.

Peptichemio, administered in a single LD50, dose, induces a significant reduction of mice bone marrow and spleen CFUs. The lesive action appears to be similar to that observed after a single dose of various antineoplastic agents. The effects of increasing doses of Peptichemio are also reported.

In an experimental setting, 4'-deoxydoxorubicin (4'-deoxy-DX) shows minimal cardiotoxicity as well as the marked antitumoral activity shown by doxorubicin, its parent compound. In this experimental study, the haematologic toxicity of the new anthracycline was investigated by haematopoietic precursor cell (HPC) assays using in vivo (colony-forming units - spleen, CFUs) and in vitro (CFUc-culture) methods with (C57B1 X C3H)F1 mice. Dose-survival curves and time response of HPC in situ following 4'-deoxy-DX administration were determined. In the time-related experiments, the effects of a single dose, an intermittent treatment (Days 0, 2, and 5) and a prolonged biweekly administration were studied. All dose-survival curves were exponential, with statistically significant differences between the effects on the various cell classes. CFUc appeared more sensitive than CFUs. In time-related experiments, 4'-deoxy-DX toxicity for HPC seemed to be relatively mild. However, CFUc sensitivity was again high in comparison with other populations assayed. In long-term administration, the 4-deoxy-DX effects on the haematopoietic system were also rather slight.

This study compares the effects of a high dose of methotrexate (HDMTX) to that of a high dose of methotrexate plus leucovorin protection on the hemopoietic stem cells in a murine model. C57BL X C3H F1 mice were treated with a single large bolus (500 mg/kg body weight) of methotrexate or with the same dose of the drug plus leucovorin administered in fractionated doses during the following 24 hr. At 1 to 2 days after the administration of HDMTX, there was a large bone marrow and spleen depopulation of pluripotent stem cells and of committed and recognizable progenitors. At 2 to 3 days, a severe fall of white blood cells and reticulocytes ensued. The recovery process of hemopoietic precursors followed alternate phases of overshooting and secondary falls. Leucovorin administration appeared to protect all stages of hemopoiesis and prevented the severe drops of bone marrow cellularity and stem cell content which followed the HDMTX bolus. However, the effect of leucovorin on peripheral blood cell reduction was less significant. After treatment with HDMTX, the recovery of bone marrow cells and the burst of splenic hemopoietic activity followed a pattern similar in both leucovorin-protected and unprotected animals, but in the former, the increase in stem cells and hemopoietic progenitors appeared to reach higher values and to last longer. In particular, the overshooting of colony-forming units, culture and erythroid, reached a higher peak in leucovorin-treated mice and was more prolonged. Our results indicate that, in HDMTX-treated mice, leucovorin protection involves the earliest stages of hemopoiesis, assuring the maintenance of a satisfactory endowment of stem and progenitor cells.