Ex vivo assessment of drug response by differential staining cytotoxicity (DiSC) assay suggests a biological basis for equality of chemotherapy irrespective of age for patients with chronic lymphocytic leukaemia

Differential Staining Cytotoxicity assay: a review

Differential Staining Cytotoxicity (DiSC) assay is the prototype for a closely related family of assays based on the concept of total cell kill, or, in other words, cell death occurring in the entire population of tumor cells. It is probably the most versatile of the cell-death end points, in that it (1) can be applied to both solid and hematologic neoplasms, (2) can be applied to specimens in which it is not possible to obtain a pure population of highly enriched tumor cells, and (3) can be applied to a wide variety of drugs, ranging from traditional cytotoxic agents to biological response modifiers with activity mediated through tumor-infiltrating effector cells, to "targeted" kinase inhibitors, and to antivascular agents, such as bevacizumab and pazopanib. The basic principles of the assay are to culture three-dimensional fresh tumor cell clusters in anchorage-independent conditions. At the conclusion of the culture period, Fast Green dye is added to the microwells, the contents of which are then sedimented onto permanent Cytospin centrifuge slides and then counterstained with hematoxylin-eosin or Wright-Giemsa. "Living" cells stain with the cytologic stain in question and can be identified as either normal or neoplastic, based on standard morphologic criteria. "Dead" cells stain blue-green. Nonviable endothelial cells appear as strikingly hyperchromatic, blue-black, and often refractile objects, which may be readily distinguished from other types of dead cells. This assay has been biologically and clinically validated in a number of ways, as described in this chapter.

Conventional Dose Fludarabine-based Regimens are Effective but have Excessive Toxicity in Elderly Patients with Refractory Chronic Lymphocytic Leukemia

The best approach to elderly patients with relapsing chronic lymphocytic leukemia (CLL) or disease refractory to conventional therapy with alkylating agents has not yet been established. Fludarabine and its combination with mitoxantrone and/or cyclophosphamide, which is the most effective treatment in younger patients, has not been extensively utilized in the elderly CLL. Here we report our results with fludarabine-based chemotherapy in 32 previously treated patients over the age of 65 years. The overall response rate was 59% with no complete remission, 3 nodular partial remissions and 16 partial remissions. The median time to progression of disease was 7 months. Only 10 patients completed the entire treatment program, because of poor compliance due to toxicity. Eight patients developed neutropenic fever, 14 severe bacterial infections and 2 patients showed progressive encephalopathy. For comparison, in a younger group of patients with refractory CLL (< 65 years), 38 of 50 patients completed the treatment plan, and the ORR was 80% (10 CR, 11 PR-nodular, 19 PR) with a median response of 12 months. Neutropenic fever was diagnosed in 10 and severe bacterial infection in 4 patients. In conclusion, fludarabine-based chemotherapy is effective for refractory CLL, however, excessive toxicity such as severe infections and neurological complications, do not allow completion of treatment in the majority of the elderly patients. Because maintenance of a good quality of life should be the main goal in the elderly CLL population, dose reduction of fludarabine and the appropriate use of myeloid growth factors and prophylactic antibiotics appear mandatory in this group of patients.

In vitro activity of 20 agents in different prognostic subgroups of chronic lymphocytic leukemia--rolipram and prednisolone active in cells from patients with poor prognosis

BACKGROUND

There is a need for development of new drugs for treatment of B-cell chronic lymphocytic leukemia (CLL), especially for poor-prognostic subgroups resistant to conventional therapy.

OBJECTIVE

The in vitro antileukemic activity of 20 different anticancer agents was characterized in tumor cells from CLL, aiming at identifying agents active in poor-prognostic subgroups.

DESIGN AND METHODS

In tumor cells from 40 CLL patients and in peripheral blood mononuclear cells (PBMC) from three healthy controls, the activity of 20 substances was assessed using a non-clonogenic assay. The CLL samples were characterized regarding genomic aberrations by interphase fluorescence in situ hybridization and immunoglobulin heavy-chain variable (IGHV) gene mutational status.

RESULTS

In line with clinical experience, cells from patients with unfavourable genomic aberrations [del(11q)/del(17p)] showed lower drug sensitivity to fludarabine and chlorambucil than cells from patients with favourable cytogenetics [del(13q)/no aberration]. Most investigated drugs demonstrated similar activity in CLL cells from patients with unmutated and mutated IGHV genes as well as in CLL cells vs. PBMC. Interestingly, prednisolone and rolipram displayed high CLL specificity, high activity in CLL cells with unmutated IGHV genes and retained the effect in several cases with 11q/17p deletion. Further studies on prednisolone and rolipram revealed a synergy when these agents were combined in CLL cells, and suggested correlation between drug sensitivity and difference in downstream signaling.

CONCLUSION

Prednisolone and rolipram are interesting for further studies in CLL with inferior prognosis. The study can also be considered a basis for future efforts to find drugs active in subsets of CLL patients that are resistant to conventional therapy.

Silencing of APAF-1 in B-CLL results in poor prognosis in the case of concomitant p53 mutation

Apoptosis protease-activating factor 1 (APAF-1), a transcriptional target of p53, is a cytosolic adaptor protein that links the mitochondrial apoptosis pathway to the caspase cascade. Here, we aimed to study the impact of APAF-1 expression levels on cell death induced by anticancer drugs or ionizing irradiation (IR) and disease prognosis in B-type chronic lymphocytic leukemia (B-CLL) patients. Samples from 138 patients with B-CLL were investigated for APAF-1 expression and p53 mutations. The results were related to survival data, in vitro cytotoxicity of various cytotoxic drugs and IR and clinico-pathological data. Variable APAF-1 expression was observed in all investigated B-CLL samples. Reduction in APAF-1 expression was observed at both mRNA and protein level indicating transcriptional silencing whereas mutation of p53 or the immunoglobulin heavy chain variable genes (IgH(V)) had no impact on APAF-1 expression. Surprisingly, APAF-1 loss did not result in resistance to cytotoxic therapies. Likewise, APAF-1 downregulation on its own showed no impact on disease prognosis. Nevertheless, a poor prognosis was observed in patients with loss of APAF-1 expression and additional p53 mutation. Thus, loss of APAF-1 may become relevant when additional core apoptosis signaling components are disrupted.

In B-CLL, the codon 72 polymorphic variants of p53 are not related to drug resistance and disease prognosis

Background

A common sequence polymorphism at codon 72 of the p53 gene encoding either arginine or proline was recently shown to be functionally relevant for apoptosis induction in vitro. In B-type chronic lymphocytic leukemia (B-CLL), p53 gene mutations occur in a subset of patients and are associated with impaired survival and drug resistance. Here, we address the functional relevance of the codon 72 single nucleotide (SNP) polymorphism for cell death sensitivity following exposure to clinically employed cytotoxic drugs and γ-irradiation.

Methods

138 B-CLL samples were analysed by SSCP-PCR and sequencing for single nucleotide polymorphism at codon 72 of the p53 gene. The in vitro cytotoxicity assay (DiSC-assay) was performed with 7 drugs (chlorambucil, mafosfamide, fludarabine phosphate, methylprednisolone, doxorubicin, vincristine) or γ-irradiation.

Results

Of the138 B-CLL samples, 9 samples were homozygous for proline (Pro/Pro), 78 samples homozygous for arginine (Arg/Arg), and 49 samples heterozygous (Arg/Pro). No differences were found for patient survival and cell death triggered by 7 cytotoxic drugs or γ-irradiation.

Conclusion

These data indicate that polymorphic variants of p53 codon 72 are not clinically relevant for apoptosis induction or patient survival in B-CLL.

Determination of caspase-3 activation fails to predict chemosensitivity in primary acute myeloid leukemia blasts

Background

Ex-vivo chemosensitivity tests that measure cell death induction may predict treatment outcome and, therefore, represent a powerful instrument for clinical decision making in cancer therapy. Such tests are, however, work intensive and, in the case of the DiSC-assay, require at least four days. Induction of apoptosis is the mode of action of anticancer drugs and should, therefore, result in the induction of caspase activation in cells targeted by anticancer therapy.

Methods

To determine, whether caspase activation can predict the chemosensitivity, we investigated enzyme activation of caspase-3, a key executioner caspase and correlated these data with chemosensitivity profiles of acute myeloid leukemia (AML) blasts.

Results

There was, however, no correlation between the ex-vivo chemosensitivity assessed by measuring the overall rates of cell death by use of the DiSC-assay and caspase-3 activation.

Conclusion

Thus, despite a significant reduction of duration of the assay from four to one day, induction of apoptosis evaluated by capase-3 activity does not seem to be a valid surrogate marker for chemosensitivity.

Mutation of p53 and consecutive selective drug resistance in B-CLL occurs as a consequence of prior DNA-damaging chemotherapy

Inactivation of p53 has been shown to correlate with poor prognosis and drug resistance in malignant tumors. Nevertheless, few reports have directly shown such effects in primary tumor cells. Here, we investigated the p53 mutational status in 138 B-CLL samples and compared these findings with drug and gamma-irradiation sensitivity profiles. p53 mutations resulted not only in a shorter survival but, notably also in selective resistance to alkylating agents, fludarabine and gamma-irradiation. In contrast, no such effect was observed for vincristine, anthracyclines and glucocorticoids. Thus, these latter compounds induce cell death at least in part by p53-independent pathways. Interestingly, p53 mutations clustered in patients who had received prior chemotherapy. In fact, we show for the first time that treatment with DNA-damaging alkylating agents correlates with occurrence of p53 mutations in a clinical setting. This finding may explain at least to some extent the development of resistance to second-line anticancer chemotherapy.

Bax expression correlates with cellular drug sensitivity to doxorubicin, cyclophosphamide and chlorambucil but not fludarabine, cladribine or corticosteroids in B cell chronic lymphocytic leukemia

In B-CLL, non-proliferating B cells accumulate due to defective apoptosis. Cytotoxic therapies trigger apoptosis and deregulation of apoptotic pathways contributes to chemoresistance. Loss of the apoptosis-promoting Bax has been implicated in resistance to cytotoxic therapy. We therefore evaluated ex vivo drug sensitivity of CLL, producing chemoresponse data which are prognostic indicators for B-CLL, in particular in the case of purine nucleoside analogs. To analyze the underlying mechanisms of drug resistance, we compared endogenous Bax and Bcl-2 expression to ex vivo response to eight drugs, and to survival in 39 B-CLL patients. We found that reduced Bax levels correlated well with ex vivo resistance to traditional B-CLL therapies - anthracyclines, alkylating agents and vincristine (all P < 0.04). Surprisingly, no such relationship was observed for the purine nucleoside analogs or corticosteroids (all P > 0.5). Mutational analysis of p53 could not explain the loss of Bax protein expression. Levels of Bcl-2 were not associated with sensitivity to any drug. In contrast to the ex vivo data, neither Bax or Bcl-2 expression nor doxorubicin sensitivity were associated with increased survival whereas sensitivity to fludarabine correlated with better overall survival (P = 0.031). These findings suggest that the resistance to purine nucleoside analogs and corticosteroids in B-CLL is due to inactivation of pathways different from those activated by anthracyclines, vinca alkaloids and alkylating agents and may be the molecular rationale for the efficacy of purine analogs in this disease.

Parameters affecting the ex vivo cytotoxic drug sensitivity of human hematopoietic cells

The drug sensitivity of normal cells provides a baseline for determining the therapeutic index, and therefore the effectiveness, of cytotoxic drugs, yet little is known about the factors that affect normal cell chemosensitivity. Some parameters are known to have a profound effect on tumor cell sensitivity. The purpose of this study was to determine how cytotoxic drug sensitivity of hematopoietic cells isolated from cancer patients was affected by various parameters. These included previous chemotherapy (yes or no), sex, age, tumor type (leukemias or solid tumors), sample source (blood, bone marrow, serous effusions, or tumor biopsies) and predominant cell lineage (lymphoid, myeloid, macrophage, or mixed). Mononuclear cells isolated from blood, bone marrow, serous effusions, and tumor biopsies were incubated for four days with a median of 16 drugs. The differential staining cytotoxicity assay, an ex vivo apoptotic drug sensitivity test in which cell survival is determined morphologically, was used to assess normal hematopoietic and tumor cell response to cytotoxic drugs. One hundred forty-six specimens yielded hematopoietic cell chemosensitivity results with 3-36 drugs. Compared with tumor cells, there was far less interpatient variation in chemosensitivity of hematopoietic cells. Mean hematopoietic cell drug sensitivity showed little variation due to previous chemotherapy, sex, age, tumor type, and sample source or cell lineage. We therefore concluded that cytotoxic drug sensitivity of hematopoietic cells from a variety of sources could be used for assessment of therapeutic index. Drug therapeutic index results are a valuable tool in identifying novel cytotoxic agents and individually tailored chemotherapy regimens.