Multicellular resistance: a paradigm for clinical resistance?

Research on resistance to cancer treatment was mainly focused for 20 years on multidrug resistance (MDR). No useful method of reversing MDR, suitable for clinical use, has yet emerged from this large quantity of work. The reason could be an inadequate evaluation of the target. When grown in spheroids, cancer cells exhibit a phenomenon known as 'multicellular resistance' (MCR). Tumours in patients seem to present the same characteristics. The mechanisms underlying MCR can be classified into two forms: contact resistance and resistance inherent in the spheroid structure. Mechanisms of MCR include: inhibition of apoptosis, high proportion of quiescent cells, modulation of protein expression (including topoisomerases and repair enzymes), potential permeability problems, presence of a hypoxic and necrotic centre and other possible mechanisms that remain to be discovered. A new therapeutic class of drugs is required to overcome MCR. Compounds, which are able to disrupt communication and binding between tumour cells and their microenvironment, seem to be able to circumvent MCR. Interesting results are obtained in vitro and in vivo in mice with specific antibodies or peptides recognised by cell binding proteins. Interestingly, these compounds also appear to be able to inhibit metastasis. Hyaluronidase has already been used with anticancer drugs in patients and was shown to increase drug potency. The explanation given is that it improves drug penetration into spheroids. We now hypothesise that hyaluronidase, in fact, decreases MCR and thus could be the first member of a new therapeutic class.

Individual dose adaptation of anticancer drugs.

The dose of anticancer drugs is currently adjusted to the patient body surface area, although patients have different abilities to clear anticancer drugs. The dose adjustment to physiological functions permits major toxic accidents to be avoided. The adjustment to tumour drug content is considered, but for ethical or technical reasons, it cannot be used routinely The best criterion for the dose adjustment seems to be drug plasma concentration. The relationship between plasma concentration and efficacy may not be excellent, since it depends on the presence of resistant cells and on the blood flow through the tumour. A relationship between plasma concentration and/or the area under the curve (AUC) with toxicity has been reported with all major anticancer drugs. Different methods of dose adjustment to the drug plasma concentration are reported. In conclusion, dose adjustment to the drug plasma concentration or to the AUC can improve the chemotherapy efficacy, while reducing toxicity.

Evaluation of a prediction model of cisplatin dose based on total platinum plasma concentration.

The aim of this study was to validate prospectively a model of cisplatin dose adjustment. 27 patients (63 courses) with lung cancer were treated by a 5 day continuous infusion of cisplatin and etoposide. The dose of cisplatin was adjusted in order to reach a target plasma concentration of total platinum (TP) of 2000 mu/l at the end of the infusion. The target concentration was reached with a mean bias of 2.7% and a precision of 7.8%. The results were compared with those of a population of 38 patients (97 courses) with lung cancer and treated with the same protocol of chemotherapy, but without dose adjustment. The average dose adjustment was an increase of cisplatin dose of 20.2%. This augmentation was most important during the first course, decreasing during the following courses. There was also an increase in the etoposide AUC, although its dose was not modified. Toxicity to polymorphonuclear cells was significantly increased and was linked to etoposide AUC.

Cofactors in in vitro induction of apoptosis in HL60 cells by all-trans retinoic acid (ATRA).

The aim of this study was to determine the culture conditions that could modulate the induction of apoptosis by all-trans retinoic acid (ATRA). Cell viability was evaluated by trypan blue test, differentiation by nitro blue tetrazolium test, and apoptosis by morphological analysis. ATRA induced apoptosis in HL60 cells only when more than 100,000 cells/mL were seeded, while differentiation was induced regardless of the seeded cell concentration. Reduction in the concentration of foetal calf serum or glutamine in the medium led to a weak increase in apoptosis. In contrast, a dramatic enhancement of apoptosis occurred when the culture medium was supplemented with glucose or when the culture pH was decreased. These characteristics were independent of the mechanism of action of ATRA, but the action of glucose could be of significance in diabetic patients. An exchange of supernatants after 3 days of culture showed that supernatants from control cultures seeded at high cell density were better apoptosis inducers than supernatants from cultures treated with ATRA, but seeded at low cell density. Factor(s) in this supernatant which induced apoptosis was (were) removed by ultrafiltration. In conclusion, our results showed that ATRA alone cannot induce apoptosis, but can do so in conjunction with cofactors. The depletion of some components of the medium and the appearance of secreted macromolecule(s) could be cofactor(s) in the induction of apoptosis.

The antileukemic alkaloid fagaronine is an inhibitor of DNA topoisomerases I and II.

The antileukemic alkaloid, fagaronine, is a potent differentiation inducer of various hematopoietic cell lines. We show here that fagaronine is a DNA base-pair intercalator with a K(app) of 2.1 x 10(5) M-1 for calf thymus DNA. Fagaronine inhibits the catalytic activity of purified calf thymus topoisomerase I as shown by relaxation of supercoiled plasmid DNA followed by electrophoresis in neutral as well as in chloroquine-containing gels. The catalytic activity of topoisomerase I is inhibited at concentrations above 30 microM. Fagaronine also inhibits the catalytic activity of purified calf thymus topoisomerase II at concentrations above 25 microM as shown by decatenation of kinetoplast DNA. Fagaronine stabilizes the covalent DNA-enzyme reaction intermediate (the cleavable complex) between topoisomerase I and linear pBR322 DNA at concentrations up to 1 microM. Further increase of the fagaronine concentration leads to a progressive decrease in the cleavable complex formation, which is totally inhibited at 100 microM. In contrast, up to 1 microM fagaronine has no effect on cleavable complex formation between purified calf thymus topoisomerase II and linear pBR322 DNA, whereas cleavable complex formation is inhibited at higher concentrations. Exposure to fagaronine results in an increase in DNA-protein complex formation in intact P388 murine leukemia cells. P388CPT5 cells, which have an altered topoisomerase I activity, are 4-fold resistant to the growth inhibitory effects of fagaronine compared to the parental cell line. Similarly, DC-3F/9-OH-E Chinese hamster fibrosarcoma cells, which have an altered topoisomerase II activity, are about 5-fold resistant to the growth inhibitory effects of fagaronine. We conclude that fagaronine is an inhibitor of both DNA topoisomerase I and II and propose that this might play a role in the cytotoxic activity.

Effect of fagaronine on cell cycle progression of human erythroleukemia K562 cells.

Fagaronine (Fine) is a novel antileukemic drug extracted from Fagara xanthoxyloides Lam. (Rutaceae). In an attempt to know more about its mechanism of action we describe here its inhibitory activity on cell division, 3H-thymidine incorporation and on cell cycle progression. Fine inhibits cell proliferation of K562 cells by 50% at a concentration of 3 x 10(-6) mol/l at day 4. It stimulates incorporation of labelled macromolecular thymidine on day 1, but decreases incorporation on days 2, 3 and 4. Fine induces a cell accumulation in G2 and late-S phases. This accumulation (i) increases with Fine concentration, but a complete blockade is not observed, (ii) reaches a plateau after approximately 48 h, (iii) is reversible, whereas we have previously shown that cell growth inhibition and differentiation were not reversible.

The antileukemic alkaloid fagaronine and the human K 562 leukemic cells: effects on growth and induction of erythroid differentiation.

In view of new antitumor compounds which could exert their therapeutic effect through a combination of cell growth inhibition and cell maturation, we describe here the effects of a novel antileukemic alkaloid, fagaronine, on the growth and the induction of hemoglobin synthesis in the K 562 cell line. We found that fagaronine, after 3 days, reduces in a concentration dependent relationship the cell growth rate without lethality and this effect on the cell growth is irreversible. Reducing the cell growth rate by 50% (IC50 = 3 X 10(-6)M) is sufficient to induce an optimal amount of hemoglobin synthesis (75% benzidine-positive cells, 13-15 pg hemoglobin/cell) after 4 days of culture. Considering the variation of the total intracellular protein content during the response, it appears that fagaronine stimulated mainly hemoglobin synthesis, and to a lesser extent non-hemoglobin proteins. These results suggest that the novel antileukemic alkaloid, fagaronine, can be considered as a potent inducer of differentiated-associated properties in the human K 562 leukemic cells.

Reversion of resistance to adriamycin by vanadate on 4 friend-cell sublines.

The retention of adriamycin in 5 Friend cell sublines of increasing degree of resistance was enhanced in vitro by three compounds: verapamil, nigericine and vanadate. Vanadate had the strongest activity, it enhanced also the incorporation in sensitive cells. Its efficacy was increased by a pre-incubation with H2O2. The effect of vanadate was then tested in vivo. When the tumor was transplanted i.p. and the treatment was also i.p., vanadate enhanced the efficacy of adriamycin, but it had also an antitumor activity by itself. Vanadate alone had some efficacy on the Friend cells of the lowest degree of resistance, when adriamycin had no effect. Nevertheless, vanadate had a partial cross resistance with adriamycin on these cells. When the tumor was transplanted subcutaneously and the treatment was still i.p., vanadate had no effect whilst adriamycin was still active.

HL60 cells exhibit particular ultrastructural features during all-trans retinoic acid-induced apoptosis.

Ultrastructural features induced by 1 micromol/l all-trans retinoic acid (ATRA) treatment of HL60 cells were observed with transmission electron microscopy. Whilst some cells were unaffected, most of the others underwent granulocytic differentiation, starting point for apoptosis and then, possibly, secondary necrosis. First steps of apoptosis led to nuclear fragmentation into dense bodies. Then three different ways were observed: i) cells shrank and dense bodies were expelled, mostly associated with a fine lamellae of cytoplasm, ii) a secondary necrosis involved the release of apoptotic bodies without cytoplasm or iii) cells showed a dual or bipolar structure, not previously described.

Phosphatase isoenzymes as bone metastasis markers in prostatic carcinoma.

Bone alkaline phosphatase (b-ALP) and tartrate resistant acid phosphatase (tr-ACP) are markers of the activity of osteoblasts and osteoclasts, respectively. We have already shown that the serum activity of these isoenzymes was elevated in breast cancer patients with bone metastasis (BM); we show here that the serum activity of b-ALP and tr-ACP were also elevated in prostate cancer patients with BM. Specificity and sensitivity of b-ALP for BM were 0.90 and 0.75, respectively; and for tr-ACP, 0.60 and 0.60, respectively. The accuracy of b-ALP as a BM marker was higher than the accuracy of usual markers of prostatic carcinoma (tartrate labile ACP [tl-ACP], prostatic acid phosphatase [PAP] and prostate specific antigen [PSA]). The highest value predictive of a positive bone scan was obtained with b-ALP (0.88); this increased to 0.97 when b-ALP was coupled with PAP.

Anticancer drug resistance and inhibition of apoptosis.

Apoptosis is a new concept which could be of great importance in the understanding and treatment of cancer. An important feature is the discovery of inhibitors of apoptosis, because they induce resistance to chemotherapeutic drugs and irradiation. Bcl-2 is the most well known of these apoptosis inhibitors. When it is overexpressed cells are less sensitive to cytotoxic drugs; on the contrary, when it is underexpressed they are more sensitive. Clinically, bcl-2 expression is associated with a poor prognosis in several cancers. Bcl-2 protein, p26-bcl-2, is located in the outer mitochondrial membrane, the nuclear envelope and the smooth endoplasmic reticulum. P26-bcl-2 is an antioxidant; this property could explain the anti-apoptotic activity since peroxides seem to be important mediators of apoptosis. Bcl-2 antisense oligonucleotides are able to reverse the apoptosis inhibition. New cancer treatments should take into account the expression of bcl-2.

Response of primary tumour, spontaneous metastases and recurrence of Lewis lung carcinoma (3LL) to flavone acetic acid (FAA, LM975).

B6D2F1 mice bearing 3LL were more sensitive to FAA than control mice, the LD50 being 180 x 2 and 336 x 2 mg/kg respectively. At a dosage of 140 mg/kg, injected i.p. at day 4 and 11, FAA significantly decreased the primary tumour growth, the occurrence and the growth of spontaneous pulmonary metastases. The effect of two injections was dose-dependent on the primary tumour and metastases; the survival time was also dose-related. Combined with primary tumour ablation, FAA administered before any dissemination (at day 3) was more efficient against metastases than when it was injected after the end of the dissemination (i.e. after primary tumour ablation). When all treatment schedules were pooled, the number of mice without metastasis was significantly higher in treated than in control groups. The effect of FAA on recurrences was also notable.

Cell culture as spheroids: an approach to multicellular resistance.

Cells cultured as spheroids present an heterogeneity similar to that of tumours in vivo. In the spheroid peripheral layers, cells are proliferating, deeper cells are non-cycling, when in the aggregate centre, cells form often a necrotic core. A multicellular resistance is related on the cell contact to other cells or to the extracellular matrix. The mechanism of this resistance remains unknown. It seems to be linked to the spheroid centre hypoxia, quiescence of a large fraction of the cell population and to the apoptose inhibition. The "classical" or "unicellular" mechanisms of resistance, as mdr1, MRP, can coexist but are not responsible of this type of resistance. This culture model is a good opportunity to study a resistance which looks close to the patient tumour resistance. A new class of therapeutic molecules appears that can reverse multicellular resistance, inhibit tumours growth and preclude metastases. The mechanism of action of this new pharmacological class is the disruption of the cell adhesion forces.

Puzzles in the clinical pharmacokinetics of fluorouracil.

The pharmacokinetics of fluorouracil (5FU) were studied in two groups of patients, the administration of 105 i.v. as daily bolus (x5) or 5-day continuous infusions. The 5FU pharmacokinetics were extremely variable from day to day, i.e. from one bolus to the next or during the continuous infusion, especially in some patients. The variations were lower for the daily bolus, but still remained high. The pharmacokinetics of cisplatin, given simultaneously during continuous infusions did not show the same variability; therefore the variability could be specific for 5FU. The role of implantable subcutaneous ports as the most probable source of this extraordinary variability is discussed. We hypothesise that in some patients the implantable subcutaneous ports used for 5FU infusion, could cause transient and extremely high plasma concentrations, exacerbated by the very short half life of the drug and by saturation of its catabolism.

Evaluation of two dose individualisation methods for carboplatin.

The pharmacokinetics of carboplatin are usually evaluated by measuring plasma concentrations of ultrafiltered platinum (UP). This approach, however may be less reliable than measuring the plasma concentration of total platinum (TP). In a group of 14 patients, which constituted a reference group, the clearance of TP was highly correlated with creatinine clearance, as estimated by the method of Cockroft and Gault. This relationship, together with only morphological and biological parameters, was used to estimate TP clearance, Vc and AUC, in a validation group of 8 patients. Estimated TP clearance was 97.9 +/- 18% of the actual value. The TP pharmacokinetic parameters of the reference group were used to estimate those of the validation group, using only two or three plasma concentration measurements (Bayesian approach). With the Bayesian approach, the estimated TP clearance was up to 99.9 +/- 2.7% of the actual value. In conclusion, estimation of TP pharmacokinetics may be reliably estimated as an alternative to UP in clinical practice.

Plasma acid and alkaline phosphatase in patients with breast cancer.

Acid and alkaline phosphatase were determined in 107 breast cancer patients to study their potential value in case of bone metastases. The patients were divided into 4 groups: A, patients without metastases (n = 34); B, metastatic patients without bone lesions (n = 37); C, patients with metastases in and outside of bones (n = 24), D, patients with bone-only metastases (n = 12). Tartrate resistant acid phosphatase (TR-ACP), and bone alkaline phosphatase (bone-ALP) were significantly higher in patients with metastases than in patients without. However, no difference in TR-ACP was observed between subgroups of metastatic patients.

Culture conditions modulate the effects of aclacinomycin A on growth, differentiation and apoptosis of HL60 cells.

The continuous incubation for several days of HL60 cells, in exponential growth, with aclacinomycin A (ACM) induces growth inhibition, necrosis, differentiation and apoptosis. Differentiation and apoptosis were assessed by optical microscopy (OM) and flow cytometry (FCM). ACM displayed dose-dependent effects, except for the differentiation induction, which was biphasic. Differentiation and apoptosis could also be induced after a 1 h ACM exposure only. The poor reproducibility of apoptosis induction led us to study the culture conditions described in the literature (without renewing the medium) where control cells are not growing exponentially during the 5 day incubation period. During kinetic studies with different ACM concentrations, the differentiation was detected earlier by FCM than by OM, while it was not the case for apoptosis. This induction appeared more reproducible when non optimal conditions of culture were used.

Chronology of combined chemotherapy (5FU) and radiotherapy. I. In vitro study.

Since radiotherapy or chemotherapy alone may be ineffective, they are more and more often combined. In this in vitro studies the effects of the chronology of the treatments and of the time interval between them are evaluated. In murine leukaemia L1210 cells and in murine mammary adenocarcinoma Ca755 cells the highest efficacy, i.e. the lowest survival fraction, was observed when radiotherapy was administered 6 h before Fluorouracil (FU). To mimic treatment in man, a daily combined treatment was also tested. Under these circumstances, the chronology of the treatments and the time interval between them had different consequences, the highest efficacy being noticed when both treatments were given at the same time.

Isoenzymes of alkaline and acid phosphatases as bones metastasis marker in breast cancer patients.

Bone alkaline phosphatase (B-ALP) and tartrate resistant acid phosphatase (TR-ACP) are markers of osteoblastic and osteoclastic activities respectively. During a period of up to two years, these isoenzymes have been assayed in the sera of 191 breast cancer patients; 80 had bone metastases (BM). In BM bearing patients, B-ALP activity was 261 IU/l and 63 IU/l for patients without BM; TR-ACP was respectively 6.6 and 3.3 IU/l. Specificity and sensitivity were calculated according to several criteria. These isoenzyme serum levels were well correlated with those of two breast cancer markers (CEA and CA15.3) and radiograph.

Comparison of two dose prediction models for cisplatin.

Cisplatin toxicity could be decreased by adjusting its dosage to each patient. For this purpose, a limited sampling method was established and validated based on a Bayesian approach taken using the values of assays during a 5-day continuous infusion of cisplatin. Using this method, a dosing model to achieve a target plasma concentration of total platinum (Pt) was evaluated retrospectively; the calculated dose of cisplatin was 95.0 to 104.8% of the actual dose. This model was then studied prospectively and the actual plasma Pt concentration reached at the end of the infusion was 94.9% of the target concentration. A strong correlation was observed between the clearance of Pt and the calculated clearance of creatinine or Cockroft index (p = 1.7 x 10(-11), and this correlation was used to develop another cisplatin dosing model. With this model the actual concentration reached at the end of the infusion was 85.3% of the theoretical concentration. The Bayesian approach gave reliable results for most clinical uses, whereas the creatinine based model has to be improved.