Potentiation of Anticancer Drugs: Effects of Pentoxifylline on Neoplastic Cells

The drug efflux activity of P-glycoprotein (P-gp, a product of the mdr1 gene, ABCB1 member of ABC transporter family) represents a mechanism by which tumor cells escape death induced by chemotherapeutics. In this study, we investigated the mechanisms involved in the effects of pentoxifylline (PTX) on P-gp-mediated multidrug resistance (MDR) in mouse leukemia L1210/VCR cells. Parental sensitive mouse leukemia cells L1210, and multidrug-resistant cells, L1210/VCR, which are characterized by the overexpression of P-gp, were used as experimental models. The cells were exposed to 100 μmol/L PTX in the presence or absence of 1.2 μmol/L vincristine (VCR). Western blot analysis indicated a downregulation of P-gp protein expression when multidrug-resistant L1210/VCR cells were exposed to PTX. The effects of PTX on the sensitization of L1210/VCR cells to VCR correlate with the stimulation of apoptosis detected by Annexin V/propidium iodide apoptosis necrosis kit and proteolytic activation of both caspase-3 and caspase-9 monitored by Western blot analysis. Higher release of matrix metalloproteinases (MMPs), especially MMP-2, which could be attenuated by PTX, was found in L1210/VCR than in L1210 cells by gelatin zymography in electrophoretic gel. Exposure of resistant cells to PTX increased the content of phosphorylated Akt kinase. In contrast, the presence of VCR eliminated the effects of PTX on Akt kinase phosphorylation. Taken together, we conclude that PTX induces the sensitization of multidrug-resistant cells to VCR via downregulation of P-gp, stimulation of apoptosis and reduction of MMPs released from drug-resistant L1210/VCR cells. These facts bring new insights into the mechanisms of PTX action on cancer cells

Reversal of P-glycoprotein mediated vincristine resistance of L1210/VCR cells by analogues of pentoxifylline - A QSAR study

In our previous papers we described the ability of methylxanthine pentoxifylline (PTX) to depress the P-glycoprotein (P-gp) mediated multidrug resistance (MDR) of the mouse leukemic cell line L1210/VCR. Other methylxanthines like caffeine and theophylline were found to be ineffective in this respect. In the present paper we have analysed the capability of 25 methylxanthines to depress MDR of L1210/VCR cells. These methylxanthines structurally differ in substituents located in positions N1, N3, N7 and C8. The results indicate that for an effective reversal of P-gp mediated MDR of our cells the existence of a longer polar substituent in the position N1 plays a crucial role. The elongation of the substituent in the positions N3 and N7 (from methyl to propyl) increases and in the position C8 (from H to propyl) decreases the efficacy of xanthines to reverse the vincristine resistance of L1210/VCR cells. The multiple linear regression for effectiveness of methylxanthines in reversal of P-gp mediated MDR of L1210/VCR cells (expressed as respective IC50r values) has been computed, with molar weight: Mw, molar volume: VM, molar refractivity: RM, crystal density: d and partition coefficient n-octanol/water: log P as descriptors. A high intercorrelation of MW, VM and R M was found for the tested group of methylxanthines indicating that only one of these parameters is necessary for testing a potential correlation. The best fit in the multiple linear regression was obtained for RM applied together with d and log P and resulted in a QSAR model given by the following equation: IC50r = -[(32.3 ± 7.2) × 10 -3 × RM] + [(10.1 ± 2.3) × d] + [(0.74 ± 0.10) × log P] - [10.5 ± 3.2]. Model revealed that: (i) the molar refractivity influences the effectiveness of xanthine positively; (ii) the crystal density and partition coefficient influence the MDR reversal effectiveness of xanthine negatively