Inhibition of cellular esterases by the antitumour imidazotetrazines mitozolomide and temozolomide: demonstration by flow cytometry and conventional spectrofluorimetry

Interleukin-24 overcomes temozolomide resistance and enhances cell death by down-regulation of O6-methylguanine-DNA methyltransferase in human melanoma cells

Melanoma is the most malignant of skin cancers, highly resistant to chemotherapy and radiotherapy. Temozolomide, a promising new derivative of dacarbazine, is currently being tested for treatment of metastatic melanoma. Resistance to alkylating agents such as temozolomide correlates with increased expression of DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). Interleukin-24 (IL-24; mda-7) is a tumor suppressor cytokine that selectively inhibits tumor cell growth by inducing apoptosis and cell cycle arrest in melanoma cell lines and solid tumors. This tumor-selective activity has been observed in multiple preclinical animal models and in clinical trials. In this study, we analyzed the ability of Ad-IL-24 and its protein product, IL-24, to overcome temozolomide resistance in human melanoma cells. We have shown that Ad-IL-24 via exogenous IL-24 protein induces combinatorial synergy of temozolomide-induced cell killing in temozolomide-resistant melanoma cells by inhibition of MGMT. Neutralizing antibodies against IL-24 or its receptors significantly blocked the apoptotic activity of IL-24 + MGMT treatment. We show that accumulation of functional p53 is essential for IL-24-induced down-regulation of MGMT. Using either MGMT small interfering RNA, p53 small interfering RNA, or a p53 dominant-negative mutant to block MGMT protein expression resulted in increased sensitization to temozolomide. However, MGMT blockade in combination with IL-24 + temozolomide resulted in loss of combinatorial synergy, indicating that MGMT expression is required for the reversal of temozolomide resistance in melanoma cells. This study shows that IL-24 can play a significant role in overcoming temozolomide resistance and that the clinical efficacy of temozolomide may be improved by using a biochemotherapy combination with IL-24.

Monitoring of Intracellular Enzyme Kinetic Characteristics of Peripheral Mononuclear Cells in Breast Cancer Patients

A new methodology for the detection of functional response of peripheral blood mononuclear cells against breast cancer (BC) antigens was developed. The method is based on cellular enzymatic activity measurements, using a fluorogenic substrate. We used this method to estimate the kinetic activity of lymphocytes derived from cancer patients and healthy donors. The aim of the study was to determine a possible correlation between the basic characteristics (K(m) and V(max)) of biochemical enzymatic reactions in live peripheral white mononuclear cells and common clinical-pathological characteristics in BC patients. Our method shows that the enzymatic activity, upon interaction with mitogen or tumor antigens, of the peripheral blood cells in BC patients is different from the enzymatic reactions in healthy individuals. This holds true in the early stages, and the difference persists throughout all of the stages of the disease. This difference is manifested, primarily, by an increase in the K(m) values after cell incubation with tumor tissue. It was also demonstrated that higher K(m) values of tumor tissue-activated peripheral blood mononuclear cells are associated with a better prognostic status of the BC patients (lymph node-negative tumors, hormone receptor preservation, and the absence of Her-2/neu protein overexpression). Thus, the present methodology may serve as an additional criterion for prognosis and monitoring, both in BC patients, and in individuals associated with high cancer risk.

Analysis of enzyme kinetics in individual living cells utilizing fluorescence intensity and polarization measurements

BACKGROUND

The Cellscan mark-S (CS-S) scanning cytometer was used for tracing enzymatic reactions in the same individual cells under various physiological conditions over periods of minutes. On-line reagent addition and changes in the experimental conditions (buffers, ions, substrates and inhibitors) were performed.

METHODS

Kinetic events were monitored by fluorescence intensity (FI) and fluorescence polarization (FP) measurements of fluorescein diacetate (FDA) and chloromethyl fluorescein diacetate (CMFDA) intracellular hydrolysis. FP measurements have been used to assess the intracellular marker's mobility restrictions.

RESULTS

Kinetic measurement along 1000 s of FDA labeled individual Jurkat T cells, indicated variation of 65% for FI(t) and approximately 10% for FP(t). While FI increased linearly with time, FP(t) decreased nonlinearly and asymptotically, reaching a constant value. The FP(t) of CMFDA-labeled cells was different from that of FDA-labeled cells. Average cellular Km of 3.9 microM was calculated from individual cell FDA hydrolysis curves.

CONCLUSIONS

(1) Analysis of the reaction kinetics of intracellular enzymes can be refined by using FP measurements of the products of fluorogenic substrates in addition to the FI measurements. (2) Subpopulations or individual cells could be classified according to their reaction rates. (3) A specific dependence of FP(t) on type of enzyme substrate is suggested.