Response to cladribine in previously treated patients with chronic lymphocytic leukaemia identified by ex vivo assessment of drug sensitivity by DiSC assay

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.

Drug induction apoptosis assay as predictive value of chemotherapy response in patients with B-cell chronic lymphocytic leukemia

A large number of prognostic factors are available to help predict the course of the disease for patients with B-cell chronic lymphocytic leukemia (B-CLL). However, it is not clear the involvement of these well established prognostic factors in the clinical response of the patients with B-CLL to the chemotherapy. The possible association of the patient clinical-biological characteristics and the in vitro response to chemotherapic agents may serve to provide powerful predictive information to identify optimum treatment for patients. An apoptosis induction assay displays the patient in vitro responses to chemotherapy and the possible association with their clinical-biological characteristics. In this study, patients showed a significant better in vitro response to drugs when they were in the initial stages of the disease or with low beta(2) microglobulin serum level. Response to purine analogues was significantly higher in patients with long lymphocyte doubling time (LDT), few cells expressing CD38, normal karyotype or no p53 deletion, whereas there was no correspondence with ZAP-70 expression. Furthermore, a good correlation was shown between in vitro apoptosis induction assay and the patient clinical response to purine analogues. In conclusion, association between in vitro drug sensitivity and some of the markers considered as prognostic factors could help to develop personalised therapeutic regimens for patients with B-CLL.

VH gene mutation status and cellular drug resistance in chronic lymphocytic leukaemia

OBJECTIVE

B-cell chronic lymphocytic leukaemia (B-CLL) can be divided into two clinical entities based on the immunoglobulin variable heavy chain (VH) gene mutation status, as cases with unmutated VH genes display a more aggressive disease with shorter survival time than mutated cases. The aim of this study was to investigate whether differences in cellular drug resistance could give an explanation for these divergent clinical courses.

METHODS

The VH gene mutation status was analysed in patients with previously untreated B-CLL using VH gene family-specific PCR amplification and nucleotide sequencing. In vitro sensitivity to cytarabine, fludarabine, cladribine, doxorubicin, idarubicin, vincristine, cyclophosphamide, melphalan and prednisolone was assessed using the non-clonogenic in vitro assay, fluorometric microculture cytotoxicity assay.

RESULTS

The VH genes and in vitro drug resistance were successfully analysed in 46 cases, revealing that 25 (54%) cases showed unmutated and 21 (46%) cases mutated VH genes. Interestingly, the unmutated group generally tended to be more chemosensitive than the mutated group with significant differences for cytarabine and prednisolone (P < or = 0.01).

CONCLUSION

The propensity of inferior drug response in mutated B-CLL may reflect a more differentiated disease than in unmutated B-CLL. We conclude that the difference in prognosis between B-CLL cases with unmutated and mutated VH genes could not be explained by difference in cellular drug resistance.

Interference by Anti-Cancer Chemotherapeutic Agents in the MTT-Tumor Chemosensitivity Assay

BACKGROUND

One of the major goals of oncology is to predict the response of patients with cancer to chemotherapeutic agents by employing laboratory methods variously called 'tumor chemosensitivity assays', 'drug response assays', or 'drug sensitivity assays', in vitro. The MTT assay is one of the methods used to predict the drug response in malignancies. However, it may suffer from interference by the anticancer drugs with the MTT assay.

METHODS

The MTT assay, a colorimetric viability assay, was checked in a cell-free system in terms of its possible chemical interactions with 22 different anticancer drugs.

RESULTS

It was found that epirubicine, paclitaxel, doxetaxel, and cisplatin caused a relatively significant increase in absorbance values, resulting in the MTT assay giving rise to false results (untrue increase in viability) although most of the drugs tested did not seem to cause any significant change.

CONCLUSIONS

It was concluded that before employing the MTT assay, drugs (or any kind of substances) to be included in the assay should be checked first in terms of possible chemical interactions with MTT, otherwise it may be impossible to evaluate the MTT viability assay results correctly.

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.

Chronic lymphocytic leukemia

Chronic lymphocytic leukemia continues to attract much basic and clinical research interest. Despite recent advances, the disease still has no established cure. Nonetheless, significant strides have been made in our understanding of the genetics, biology, and clinical staging of this disease. This understanding may improve our ability to segregate patients into subtypes that differ in their cytogenesis, propensity toward disease progression, or response to standard or innovative forms of therapy. Finally, several promising new modalities of treatment are being evaluated in clinical trials, involving novel drugs or drug-combinations, monoclonal antibodies, stem cell transplantation, or gene therapy.

In vitro chemosensitivity testing in acute non lymphocytic leukemia using the bioluminescence ATP assay

The ATP assay is a short term in vitro chemosensitivity assay where the amount of viable cells are determined by their content of ATP. The aim of the study was to compare the in vitro results of six cytostatic drugs to the clinical outcome in 83 acute non-lymphocytic leukemia (ANLL) patients. The secondary ANLL at diagnosis showed an in vitro resistance to daunorubicin that was significantly higher compared to de novo ANLL at diagnosis (P<0.003). De novo ANLL at diagnosis that achieved complete remission (CR) were significantly more sensitive to daunorubicin compared to those who didn't achieve CR (P<0.05). There was an vitro correlation between topoisomerase II active drugs but not between these drugs and ara-C. In vitro ara-C sensitivity (< or = the median of the de novo ANLL at diagnosis) was correlated to poor overall survival (P = 0.02). In vitro sensitivity to daunorubicin and mitoxantrone was associated with prolonged disease free survival (P = 0.03 and P = 0.04). We conclude that despite significant correlation to clinical parameters for daunorubicin and mitoxantrone the predictive value of the ATP assay in this material was insufficient for directing therapy.

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

With a mean age at diagnosis for chronic lymphocytic leukaemia (CLL) of 65 years, development of optimal therapeutic regimens has been hampered by the advanced age of patients. In general, because of comorbidity older patients are not treated with the intent of achieving a complete response and so do not attain the quality of response of younger patients and do not survive as long. We have investigated whether or not ex vivo cellular sensitivity to cytotoxic drugs could be an underlying biological basis for this age differential in response and survival by comparing ex vivo drug response with age in untreated CLL patients. Cells from 365 untreated CLL patients aged 31.1-87.1 years (average 65.3 years) were tested for drug response by differential staining cytotoxicity (DiSC) assay with a panel of 10 drugs. An average of 280 results (range 196-361) obtained for each drug was compared with patient age. For chlorambucil, cyclophosphamide, prednisolone, vincristine, doxorubicin, epirubicin, fludarabine, cladribine and methylprednisolone, no relationship was found between ex vivo drug response and age (r<0.12). For pentostatin, a possible but very weak relationship (r = 0.18; n = 210; P = 0.06) was found. We conclude that cellular sensitivity to cytotoxic drugs does not support the differential treatment of older and younger CLL patients.

Prognosis for fludarabine therapy of chronic lymphocytic leukaemia based on ex vivo drug response by DiSC assay

The cytotoxic antimetabolite fludarabine is a widely used active agent in chronic lymphocytic leukaemia (CLL). However, cost and occasional adverse side-effects necessitate careful use. Identifying before treatment patients not likely to benefit from fludarabine could advance disease management both clinically and financially. We used the DiSC (differential staining cytotoxicity) assay, an ex vivo apoptotic drug response test, to identify the sensitivity or resistance to fludarabine of lymphocytes from B-cell CLL patients and compared the results with subsequent patient treatment, response and survival. Patients were grouped thus: those receiving fludarabine within 1 year of assay (+/- other cytotoxic drugs), and those receiving other chemotherapy (excluding fludarabine) within 1 year of assay. Fludarabine-test-resistance was found in 12/100 (12%) of untreated patients and 45/143 (31%) of previously treated patients (17/32 (53%) of patients previously treated with fludarabine). Treating fludarabine-test-resistant patients with fludarabine resulted in poor response compared with fludarabine-test-sensitive patients (7% v 69%) and short survival (median 7.9 v 41.7 months; relative risk (RR) = 14.8; P < 0.0001). 81% of fludarabine-test-resistant patients were test sensitive to other regimens. If treated with chemotherapy other than fludarabine, test-resistant patients responded better and survived substantially longer than those treated with fludarabine (RR = 2.9; P = 0.001). Not all CLL patients should receive fludarabine. Fludarabine-test-resistance by DiSC assay is a powerful independent prognostic factor. Pretreatment DiSC assay results could enable the toxic, clinical and financial costs of fludarabine treatment to be avoided in fludarabine-test-resistant patients. Disease management, response, survival and use of financial resources might be significantly improved if therapy choice in CLL patients was guided by DiSC assay.