Effect of donation time on platelet concentrates and fresh-frozen plasma. An in vitro study.

To investigate the effect of donation time on the quality of blood components, we measured the platelet count and pH on platelet concentrates, and the factor V and VIII:C levels and fibrinopeptide A concentration on fresh-frozen plasma by duration of donation time. Platelet concentrates and fresh-frozen plasma were classified into three groups according to donation time: group 1, less than 10 min; group 2, 10-15 min, and group 3, longer than 15 min. Mean platelet counts of platelet concentrate were: group 1, 8.6 +/- 2.5 (in x 10(10], group 2, 8.1 +/- 2.6, and group 3, 6.5 +/- 3.2 (p less than 0.05). The same pH was maintained in all three groups. The fibrinopeptide A concentrations in groups 1 and 2 were 24 +/- 53 and 169 +/- 64 ng/ml, respectively, while in group 3 all were greater than 200 ng/ml, indicating correlation of a higher fibrinopeptide A level with longer donation time. Although a higher fibrinopeptide A level indicated a greater degree of thrombin generation, assays of factors V and VII:C did not show decreased activity in groups 2 and 3.

Increased cytotoxicity and reversal of resistance to cis-diamminedichloro-platinum(II) with entrapment of cis-Bis-neodecanoato-trans-R,R-1,2-diaminocyclohexaneplatinum (II) in multilamellar lipid vesicles.

The role of liposome entrapment in modulating the cytotoxicity of a lipophilic cisplatin derivative was assessed. cis-Bis-neodecanoato-trans-R,R-1,2-diaminocyclohexaneplatinum++ +(II) (NDDP) was tested in suspension (free NDDP) or entrapped in multilamellar vesicles composed of dimyristoylphosphatidyl choline and dimyristoylphosphatidyl glycerol (L-NDDP). Against LoVo colon carcinoma cells sensitive to cisplatin, L-NDDP was two times more cytotoxic in vitro than free NDDP and cisplatin (Do 7 microM for L-NDDP, 15 microM for free NDDP, and 16 microM for cisplatin). Against LoVo cells resistant to a concentration of 3 micrograms/ml of cisplatin, L-NDDP was three times more cytotoxic than free NDDP and cisplatin (Do 14 microM for L-NDDP, 45 microM for free NDDP, and 48 microM for cisplatin). In in vivo studies, free NDDP was less potent and less active than L-NDDP against i.p. L-1210 leukemia (free NDDP, optimum %T/C 148 at a dose of 75 mg/kg; L-NDDP, optimum %T/C 185 at a dose of 25 mg/kg) and i.p. L1210/PDD leukemia (free NDDP, optimum %T/C 128 at a dose of 50 mg/kg on Days 1, 5, and 9; L-NDDP, optimum %T/C 200 at a dose of 12.5 mg/kg on Days 1, 5, and 9). Free NDDP administered i.v. was inactive against liver metastases of M5076 reticulosarcoma (%T/C 102) while L-NDDP showed significant activity (%T/C 140). The single dose i.v. LD50 in mice of free NDDP and L-NDDP were similar (79.4 mg/kg for free NDDP and 64.5 mg/kg for L-NDDP). These studies show that NDDP is a liposome-dependent drug since it can only be satisfactorily formulated in the liposomal form and since the liposomal carrier plays a crucial role in determining its antitumor activity.

Flow cytochemical patterns of white blood cells in human hematopoietic malignancies: III. Miscellaneous hemopoietic diseases.

Peripheral blood samples from 48 untreated and 20 treated patients with disease entities that directly or indirectly affect hematopoiesis [dys-myelopoietic syndrome (DMS), refractory anemia with excess blasts (RAEB) or in transformation (RAEBIT), lymphoma, myeloma, acquired immunodeficiency syndrome (AIDS), and solid tumors with uninvolved bone marrow] were measured with the Technicon H-6000 automated hematology analyzer; this instrument provides a differential count on 10(4) white blood cells (WBC) effected by means of flow cytochemistry (peroxidase content) and volume (light scatter) discrimination. Cases with DMS and RAEB showed statistically significantly lower WBC counts than normal, whereas cases with lymphoma showed significantly higher values. No disease entity demonstrated changes in mean peroxidase activity (MPA) that were significantly different from normal, although all disease entities, including cases with solid tumors, showed significantly higher (two to severalfold) proportions of cells with high peroxidase (HPX) content, probably as a reflection of a disturbance of normal hemopoiesis with the emergence of younger granulocytic forms. All cases with paraleukemia (DMS, RAEB, and RAEBIT) showed significantly higher values of large unstained cells (LUC), whereas cases with lymphoma showed significantly lower LUC values. There were no statistically significant differences for any parameter (WBC counts, MPA, HPX, or LUC) among the paraleukemia subtypes. However, based on the displayed trends, a case presenting with dyserythropoiesis, relatively low WBC counts, abnormal HPX values, and LUC below 10% should be suspected for RAEB, whereas the presence of greater than 10% LUC and almost normal or even slightly elevated WBC counts should suggest a more accelerated phase of RAEB. Unless complicated by a leukemic phase, cases of lymphoma or myeloma did not display changes in any of the parameters analyzed by the H-6000. Similarly, patients with AIDS had no overt changes other than a trend to lower WBC counts with occasionally higher or lower absolute lymphocyte counts than normal. The peripheral blood of patients with solid tumors displayed a slight increase in HPX, suggesting an indirect effect on hemopoiesis since careful workup failed to demonstrate bone marrow involvement. Our data demonstrates that an H-6000 analysis has a role in the evaluation and follow-up of all these entities particularly to document leukemic transformation of either lymphoma, myeloma, or RAEB.

The heterogenous cytotoxic response of colon cancer cells is unrelated to phenotypic differentiation characteristics.

Six colon cancer cell lines segregated into three groups with distinct biological properties (i.e., morphological differentiation, DNA content, carcinoembryonic antigen production, etc.) were treated with ten antitumor drugs. Cytotoxic responses were heterogenous and not associated to biological grouping, in fact, for some drugs, the response of one member of the group resembled that of a member of another group rather than its group counterpart. Thus the most common phenotypic characteristics that identify colon cancer cells did not predict the cytotoxic response and do not appear useful for stratifying patients into categories with distinct responses to currently available chemotherapeutic agents.

Failure of human myeloma cells to heterotransplant into the brain of athymic rats.

Sixty-four separate intracranial inoculations of bone marrow cells obtained from 26 patients with human myeloma were performed and the animals were kept under observation for 9-10 months. Samples were obtained from a heterogenous group of patients with diverse types of paraprotein production, clinical status, and response to treatment. Inocula size ranged from 3.5 x 10(5) nucleated cells to about 2 x 10(7), while the percentage of plasma cells varied from nondetectable to 90%. Only one animal (of 2) injected with an aliquot of the bone marrow aspirate from a patient developed a small, clinically undetectable tumor, noticed at the end of the observation period. No other animal developed tumors. Thus, our studies indicate that the intracerebral inoculation of human myeloma cells may not be a profitable means of establishing additional human myeloma cell lines.

Flow cytochemical patterns of white blood cells in human haematopoietic malignancies. II. Chronic leukaemias.

Peripheral blood samples from 73 patients with chronic leukaemia were measured with the Technicon H-6000 automated haematology analyser to provide flow cytochemical (peroxidase content) and volume (light scatter) discriminated scattergram patterns. For chronic granulocytic leukaemia (CGL), these patterns were so reproducible and distinct that they allowed an immediate diagnosis even without the benefit of microscopic examination. Relative and absolute basophilia was an invariable feature, and remained detected by the H-6000 even when the patient was in haematologic and cytogenetic remission or progressed into blast crisis (BC). Most patients in BC also demonstrated an inordinately high number of large unstained cells (LUC) and high proportions of 'lymphocytes' (small blasts with no peroxidase content by visual inspection). Thus, for patients with CGL, LUC values above 10%, and/or steady increments in the proportion of 'lymphocytes', merit concern as these changes may herald an accelerated phase of disease. The scattergram pattern of untreated chronic lymphocytic leukaemia (CLL) showed a dense accumulation of data points within the lymphocytic 'box' with a small cluster of granulocytic elements. Most patients also had a frankly abnormal proportion of LUC. Sixteen patients with CLL were compared for ratios of LUC to lymphocytes and stage of disease; patients with the most advanced stage (IV) had the highest, statistically significant values, than the patients with more benign disease. Thus, it is possible that follow up with this instrument of patients with CLL will also allow early detection of an impending prolymphocytoid transformation (accelerated phase) of this disease.

Untreated prostatic carcinoma is not associated with frequent thrombohemorrhagic disorders.

We conducted an evaluation of the hemostatic integrity of patients with untreated cancer of the prostate. Of 60 patients analyzed retrospectively, only 1 had a mild case of disseminated intravascular coagulation, possibly associated with concomitant estrogen therapy, and in 1 patient mild deep vein thrombosis developed preoperatively, also possibly associated with multiple medications for concurrent disorders. Of 16 other patients prospectively evaluated on admission, only 1 had frankly abnormal levels of fibrinopeptide A unaccompanied by other coagulation abnormalities. Occasional individuals had minimal, negligible deviations of partial thromboplastin times, thrombin time, or antithrombin III values. In none of these patients did hemostatic complications develop during their hospital stay. These results demonstrate that although an occasional coagulation abnormality may occur in patients with cancer of the prostate (albeit with a lower incidence than in other neoplasms), this malignancy does not require increased precautions with respect to those given to the patient population at large.

Flow cytochemical patterns of white blood cells in human haematopoietic malignancies. I. Acute leukaemias.

Peripheral blood samples from 118 patients with acute leukaemia (68 untreated; 50 treated) were measured with the Technicon H-6000 automated haematology analyser. This instrument provides, in addition to measurements of the classical haematology parameters (i.e. cell counts, haemoglobin concentration, etc.), a differential count on 10(4) WBC effected by means of flow cytochemistry (peroxidase content) and volume (light scatter) discrimination. Disregarding RBC and platelet counts and their volume distribution profiles, the most important diagnostic parameters for leukaemic disease were the WBC count, the WBC differential count, and the proportions of large unstained cells (LUC) and high peroxidase (HPX) cells obtained by the automated differential count as well as the mean value of the WBC peroxidase content distribution (MPA). Granulocytic leukaemias had lower MPA than normal and lymphocytic leukaemias had MPA values above normal. M1 leukaemias were also characterized by large proportions of LUC and low fractions of HPX, while M2 leukaemias showed low LUC with high HPX. M3 leukaemias had low LUC and very high HPX. M4 leukaemias had large LUC and 'monocytic' components and a modest fraction of HPX. M5 leukaemias had very large numbers of LUC, 'monocytes' and 'lymphocytes' and a normal HPX. For M1 leukaemia, the presence of less than 7% LUC following induction treatment was related to morphological changes of normal cells induced by chemotherapy while LUC above 10% usually indicated unsuccessful induction associated with the presence of residual blasts. If treatment was successful, M2 and M3 leukaemias characteristically decreased their HPX population. All M4 leukaemias studied by us failed to enter remission and continued to display high proportions of HPX and LUC. Similarly, most M5 leukaemias had a poor response to treatment and always showed a very high proportion of LUC. Untreated lymphocytic leukaemias demonstrated high LUC, normal HPX and a high proportion of 'lymphocytes'. Hairy cell leukaemias showed almost equal proportions of 'lymphocytes' and LUC. Successful chemotherapy of all lymphoid leukaemia entities was associated with rapid decreases in LUC, slower decrements of 'lymphocytes' and moderate and transient increments in HPX. Thus, flow cytochemistry can assist not only in the segregation of acute leukaemias along with FAB classification with nonmorphologic criteria, but also in the follow up of patients with these diseases.

Evaluation of growth fractions with monoclonal antibodies to human alpha-DNA polymerase.

We have established and partially characterized a panel of monoclonal antibodies against alpha-DNA polymerase. One of the hybridomas, clone 5F, has been exploited for cell kinetic studies on three colon cancer cell lines, LOVO, SW 620, and SW 403, which are endowed with different growth patterns and differentiation status. By an immunoperoxidase method, we could demonstrate the specific intranuclear localization of alpha-DNA polymerase during the exponential phase of in vitro growth and contrast it with the diffuse distribution of the enzyme throughout the cytoplasm during the resting state. The percentage of intranuclear staining positive cells, evaluated at successive time points of in vitro growth, changed from 75 to 95% (assayed on Days 3 and 7) to 15 to 25% in confluent and resting populations assayed on Days 12 to 14. In agreement with the assumption that the enzyme moves from nucleus to cytoplasm after entering quiescence, alpha-DNA polymerase was still present in the cytoplasm or in the cytoplasmic perinuclear area of cells in resting phase cultures. Comparisons between traditional kinetic parameters (thymidine labeling index and primer-dependent alpha-DNA polymerase) and proliferative state determined by the monoclonal antibody supported the feasibility of this approach to define the proportion of actively proliferating elements in a tumor cell population. Moreover, parallel flow cytometric analysis performed on Days 5 and 14 of continuous culture showed fluctuations of alpha-DNA polymerase content in relation to exponential and steady-state phases, with a significant increase in the amount of alpha-DNA polymerase in actively proliferating populations and a progressive reduction of the enzyme as the cultures entered the resting stage.

Expression of transferrin receptors is unrelated to proliferative status in cultured human colon cancer cells.

Transferrin is an iron-carrying compound that stimulates cell growth and division by binding to specific receptors (TR) which are preferentially expressed by actively growing cells or by the malignant counterpart of normal cells. However, quiescent cells may not necessarily cease expressing TR. We evaluated TR expression by flow cytometric analysis utilizing a monoclonal antibody (OKT-9) specific for TR on six established human colon cancer cell lines with distinct degrees of phenotypic differentiation and growth rates at sequential stages of in vitro growth (exponential and stationary phase). There were no significant differences in the proportion of cells expressing TR among the fast and slow growing cell lines at any time point of the study, nor did the cultures change the proportion of TR positive cells in their transit from exponential into stationary phase of growth. Hence, direct measurements of TR expression in malignant cell populations may not provide a useful clinical marker to distinguish highly proliferative tumors from those with a slower growth resulting from a larger proportion of quiescent cells.

Correlative patterns of neutrophil and platelet counts during very early remission of acute myeloblastic leukemia.

Patterns of recovery for peripheral blood neutrophils and platelets were analyzed in 65 patients with acute myeloblastic leukemia (AML) undergoing their first course of induction chemotherapy. Specifically, for every patient linear correlation coefficients (r values) were computed for neutrophils versus platelet counts every three days from Day 12 to 27 of therapy. Correlations were designated as "significant" if r greater than or equal to 0.82 (p less than or equal to 0.05). Patients who would enter complete remission with the first course of therapy were significantly more likely to have significant neutrophil-platelet correlations in the recovery phase than patients who did not achieve remission with the first course or who would have resistant disease (76% versus 20% and 76% versus 15%, respectively, both p less than 0.001). Although these data are preliminary and retrospective they nonetheless demonstrate a trend that may prove useful for patient monitoring if proven correct by formal studies. A prospective investigation examining neutrophil and platelet correlations within a defined period of early hematologic recovery is indicated to assess if such parameters have early prognostic value for the prediction of remission in individual patients receiving induction therapy for AML.

The technicon H*1--an automated hematology analyzer for today and tomorrow. Complete blood count parameters.

The performance of the Technicon H*1 was evaluated in the computerized, high-volume hematology laboratory at M.D. Anderson Hospital and Tumor Institute and compared with that of reference instrumentation used for routine patient care. The precision, linearity, and lack of carry-over of this instrument was excellent for the entire dynamic range of all nine tested parameters (white blood cells [WBCs], red blood cells [RBCs], hemoglobin [Hgb], hematocrit [Hct], mean corpuscular volume [MCV], mean corpuscular hemoglobin [MCH], mean corpuscular hemoglobin concentration [MCHC], red blood cell distribution width [RDW], and platelets [Plts]). Coefficients of correlation for all directly measured parameters were always 0.98 or greater, with the exception of the MCV and RDW parameters, for which r = 0.89 and 0.93, respectively. Special emphasis was placed on WBC and Plt counts at low ranges. When compared with reference methods the correlation for both parameters was very good, r = 0.99 for WBCs less than 4.0 X 10(3)/microL (4.0 X 10(9)/L) and 0.91 for Plt less than 100 X 10(3)/microL (100 X 10(9)/L). These excellent performance characteristics for the CBC parameters, combined with the ability of the analyzer to perform a full WBC differential (to be described in the next report), make the H*1 a superior advancement in the field of automated hematology.

Ligands of second generation platinum analogs decrease both platinum-induced DNA cross-linking and its ability to interact with 1-beta-D-arabinofuranosyl cytosine to potentiate cytotoxic efficacy.

We evaluated the cytotoxic and DNA cross-linking (CL) ability of four second generation platinum coordination complexes (TNO-6, JM-89, JM-8 and JM-9) delivered alone or in combination with 1-beta-D-arabinofuranosyl cytosine (ara-C) to human colon cancer cells (LoVo). Cell survival varied markedly as a function of the particular substitution moiety. JM-8 and JM-9 were virtually ineffective, even at concentrations as high as 50 micrograms/ml. At that concentration cis-diamminedichloroplatinum(II) (cis-DDP) killed greater than 99.99% of the cells. JM-82 was slightly more active while TNO-6 was the only derivative with appreciably higher cytotoxic activity due to an abrogation of the shoulder region of the type C survival curve. The highest CL effect was observed for cis-DDP followed closely by TNO-6. Very little CL effects were demonstrated for the other three analogs JM-82, JM-8 and JM-9 when measured 6 h after treatment. The combination of cis-DDP and ara-C augmented 10-fold the cytotoxic activity of cis-DDP alone, an effect accompanied by an almost 2-fold increase in CL; every other analog failed to interact in a potentiating manner (either cytotoxicity, or CL at 6 h) with the antimetabolite. Thus, it appears clear that the associated moieties of the Pt coordination complex play a fundamental role in reducing the interaction of the analogs with DNA (as reflected by the decreased CL and cytotoxic effects produced by each agent alone) and in totally preventing their interaction with ara-C to yield a potentiating lethal effect.

New monoclonal antibodies against colon cancer-associated antigens.

Established human colon cancer cells with distinct degrees of differentiation (LoVo, well-differentiated; SW620, intermediate differentiation; and SW1116, poorly differentiated) were used to produce monoclonal antibodies (MoAbs) by standard hybridoma techniques. Specificity was tested by an enzyme-linked immunosorbent assay against human foreskin cells, 7 established human colon cancer lines, a panel of 17 established human tumor lines of different histological origins, purified carcinoembryonic antigen, panels of red blood cells, and a suspension of lymphocytes obtained from 30 random normal donors. MoAb LoVo-F4 3E4/1A1/2E10 (MoAb F4/2E10) reacted with five colon cancer lines and only slightly with MCF-7 cells (estrogen receptor positive breast carcinoma). MoAb LoVo-F4 3E4/1A1/5C10 also reacted with the previous five colon cancer lines and with two gastric cancer lines. A MoAb obtained with a LoVo 3 M KCl membrane extract reacted exclusively with LoVo cells. MoAb SW620-F1 4E5/1A3 reacted with only three colon cancer cell lines and an estrogen receptor negative breast cancer line. MoAb SW1116-F2 1E3/1A1 reacted with four colon carcinoma cell lines, one gastric cancer line, MCF-7 cells, and a lung cancer line. MoAb SW1116-F2 1F3/1B1 reacted intensely with purified carcinoembryonic antigen and with every carcinoembryonic antigen-producing cell line available in our laboratory. Further studies concentrated on the immunoglobulin G1 MoAb F4/2E10. We demonstrated that the purified MoAb did not inhibit binding of MoAb CA19-9 to any colon Ca lines and reacted with fresh human colon carcinoma specimens regardless of whether they were processed by cryostat or paraffin embedding after fixation in formalin for 24 through 96 h. Using the peroxidase-antiperoxidase technique, MoAb F4/2E10 did not react with 23 normal adult and 18 fetal (less than 3 months old) human tissue specimens. When tested on 312 specimens of diverse histological origins and diseases, the MoAb was positive in 57 of 62 colorectal cancers, in 12 of 19 villous adenomas, in 5 of 7 adenomatous polyps, and in 10 of 12 cases of ulcerative colitis. With the exception of 2 of 15 cases of Crohn's disease that were slightly positive, all tissues from nonmalignant diseases (regardless of histological origin) were consistently negative. There was only weak reactivity in 2 of 18 breast cancers, 7 of 21 squamous cell carcinomas, 4 of 27 lung tumors, 1 of 13 kidney carcinomas and in 7 miscellaneous tumors.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro cytotoxicity patterns of standard and investigational agents on human bone marrow granulocyte-macrophage progenitor cells.

Inhibitory concentrations (ICs) against human bone marrow granulocyte-macrophage colony forming cells (GM-CFC) were established for 26 cancer chemotherapy agents, including seven investigational agents by ten day exposure. Each drug was tested at four or more concentrations to generate reliable survival curves. The analysis of the survival curves produced three patterns according to which drugs were classified: class A drugs had a shouldered curve with terminal exponential kill of GM-CFC, class B drugs produced initial exponential component followed by a plateau, and class C drugs produced linear curves. These categories provide the relationship between drug concentration and cytotoxicity, e.g., the cytotoxicity of class B drugs, after initial kill, did not increase in spite of serial doubling of concentrations whereas the class C drugs had proportional killing with two-fold concentration increment. A number of drugs were active at in vitro concentrations of less than or equal to 0.01 microgram ml-1 and caused log reduction of GM-CFC with an approximate concentration of 0.0001 microgram ml-1. Drugs known to require in vivo bioactivation, namely dacarbazine, procarbazine, and ifosfamide were active at high concentrations (greater than 10.0 micrograms ml-1). We propose that for myelosuppressive agents the GM-CFC provides a useful biologic reference to determine in vitro cut off concentrations to be utilized for drug screening. For nonmyelosuppressive agents, however, it may be suboptimal.

Potential drugs for elimination of acute lymphatic leukemia cells from autologous bone marrow.

Five drugs, selected because of minimal in vivo myelotoxicity, have been investigated for inhibition of the growth of three acute lymphatic leukemia-derived cell lines. Granulocyte-macrophage colony-forming units (GM-CFU) inhibition with these five drugs after 60-min incubation was first established. Drug concentrations giving up to 90% kill of GM-CFU were then used. Spirogermanium and L-asparaginase did not have an effect on any of the three cell lines under the culture conditions tested, while 4-hydroperoxycyclophosphamide (4-HC) and vincristine inhibited the growth of all three cell lines tested, and bleomycin inhibited the growth of two cell lines. In addition to 4-HC, bleomycin and vincristine should be considered as possible agents in eliminating leukemic cells from autologous marrow grafts. These drugs also deserve further investigation in clonal systems.

Pancreatic carcinoma and Trousseau's syndrome: experience at a large cancer center.

It is common belief that carcinoma of the pancreas has an inherent and unique ability to induce a hypercoagulable diathesis that leads to clinically significant thrombosis. We evaluated 130 consecutive patients with adenocarcinoma of the pancreas to document the incidence and the predisposing factors related to the postulated increased association of thromboembolic disorder (TED) and pancreatic carcinoma. Only nine such patients (6.9%) demonstrated TED complications of the classical Trousseau syndrome. In these instances, the location of the tumor and its mucin-producing potential were significant predisposing factors. In our series, TED was usually associated with tumors of the body and tail, which had a greater likelihood to be mucinogenic as compared with those localized to the head of the pancreas. Routine tests for hemostasis were not helpful in predicting the development of TED except, perhaps, for decreased platelet counts. Therefore, we believe that the relationship between cancer of the pancreas and TED should be de-emphasized since it is neither unique nor especially common to pancreatic carcinoma and since it may be frequently encountered in other varieties of visceral malignancies of the cancer patient population.

Phase I study of thymidine (dThd) and cisplatin (DDP) given in combination.

Twenty-three patients with a variety of solid tumors were given thymidine (dThd) at a single dose of 30 g/m2 along with cisplatin (DDP) at escalating doses ranging from 25 to 120 mg/m2. The dThd was administered first, and then after 50% of the total dThd dose had been infused over 1 h, the remaining 50% was given simultaneously with DDP at a separate intravenous site over the next 2 h. Treatment was repeated at 3-week intervals. Gastrointestinal toxicity was dose-limiting and dose-related with increasing dosages of DDP. Central nervous system manifestations occurred in 17% of the patients. Mild myelosuppression was observed only at DDP doses of greater than or equal to 75 mg/m2. Thrombocytopenia was more severe than leukopenia. The maximum tolerated doses on this schedule were 30 g/m2 of dThd and 100 mg/m2 of DDP.

Kinetics and mechanism of the 1-beta-D-arabinofuranosylcytosine-induced potentiation of cis-diamminedichloroplatinum(II) cytotoxicity.

Certain aspects of the potentiation induced by 1-beta-D-arabinofuranosylcytosine (ara-C) on cis-diamminedichloroplatinum(II) (cis-DDP) cytotoxicity were investigated. The time dependency of additions of ara-C and cis-DDP was established by allowing cells to grow for various intervals in fresh medium following the removal of one agent before adding the second one. ara-C had no potentiating effect on cis-DDP toxicity when given to the cells before the addition of cis-DDP. When the experiment was reversed so that cis-DDP was added first and ara-C second, a slight potentiating effect was observed even if the drugs were added 4 h apart. The optimal toxic effect was obtained when ara-C and cis-DDP were added together. Continuous exposure of cells to concentrations of ara-C and cis-DDP 10 times lower than those used in pulse treatment experiments resulted in an additive rather than a synergistic effect. ara-C, unable to kill cells in pulse treatment, killed 96% of the cells after 24 h of continuous incubation. Thiourea was able to prevent the cytotoxic effect of cis-DDP in a concentration-dependent manner when given to the cells immediately following their treatment with cis-DDP; at 0.1 M thiourea, the cytotoxic effect of cis-DDP was almost completely prevented. Similar results were obtained when the cells were exposed to a combination of cis-DDP and ara-C. In this case, 0.1 M thiourea resulted in over 80% survival of cells treated with the drug combination. Thiourea had to be added to the cells either together with cis-DDP or immediately following removal of the drug in order to completely prevent the cytotoxic effect. A similar time factor was involved when cells were treated with a combination of cis-DDP and ara-C before their exposure to thiourea, but in this case thiourea was only able to prevent completely the cytotoxic effect when added simultaneously with the drug combination. In other experiments, the effect of thiourea on cis-DDP-induced DNA cross-linking was measured by the alkaline elution technique. Thiourea was capable of preventing DNA cross-link formation both in cells treated with cis-DDP alone, and in cells exposed to the combination of cis-DDP and ara-C These observations further support the contention that ara-C potentiates cis-DDP cytotoxicity by increasing the ability of the platinum compound to form earlier, more stable DNA cross-links regardless of whether it is present in free or monoadducted form.(ABSTRACT TRUNCATED AT 400 WORDS)

Mathematical model for human myeloma relating growth kinetics and drug resistance.

We present a computer-based mathematical model that can simulate characteristic features of the clinical time course of human myeloma. It asserts that therapy resistance in myeloma cells is an inherited trait associated with the longer inter-mitotic times of some cells and that the strength of this trait affects tumour growth characteristics. These kinetic differences within the malignant cell clone may also influence therapeutic efficacy. In the model, the same total therapy, administered in different time-dose fractions, could be 'curative' or 'minimally effective' depending on kinetic properties. For example, as others have shown, in myeloma pulsed intermittent therapy is often more effective than low dose continuous therapy. According to our model this finding is compatible with a high coefficient of inheritability of resistance from one cell generation to the next. The model also suggests that if there are subclones of varying resistance, a therapy must have some effect on each of them if it is to be employed in a curative fashion. While many aspects of the model are not yet clinically testable, exploration of its concepts might increase knowledge about fundamental neoplastic mechanisms.