Verapamil inhibits the respiration rate of cancer cells

Nifedipine improves blood flow and oxygen supply, but not steady-state oxygenation of tumours in perfusion pressure-controlled isolated limb perfusion

Isolated limb perfusion allows the direct application of therapeutic agents to a tumour-bearing extremity. The present study investigated whether the dihydropyridine-type Ca(2+)-channel blocker nifedipine could improve blood flow and oxygenation status of experimental tumours during isolated limb perfusion. Perfusion was performed by cannulation of the femoral artery and vein in rats bearing DS-sarcoma on the hind foot dorsum. Perfusion rate was adjusted to maintain a perfusion pressure of 100-140 mmHg throughout the experiment. Following equilibration, nifedipine was continuously infused for 30 min (8.3 microg min(-1) kg(-1) BW). During constant-pressure isolated limb perfusion, nifedipine can significantly increase perfusion rate (+100%) and RBC flux (+60%) through experimental leg tumours. "Steal phenomena" in favour of the surrounding normal tissue and oedema formation were not observed. Despite the increased oxygen availability (+63%) seen upon application of this calcium channel blocker, nifedipine does not result in a substantial reduction of tumour hypoxia, most probably due to an increase in O(2) uptake with rising O(2) supply to the tumour-bearing hind limb. Nifedipine application during isolated limb perfusion can enhance tumour microcirculation and may therefore promote the delivery (pharmacokinetics) of anti-cancer drugs to the tumour and by this improve the efficacy of pressure-controlled isolated limb perfusion.

Modulation of tumor oxygenation

There is a large body of evidence suggesting that deficiencies in the O2 supply of tumors exist due to restrictions (i) in the O2 delivery by perfusion and/or diffusion, and (ii) in the O2 transport capacity. Whereas the former are mostly based on inadequate and heterogeneous microcirculatory functions, the latter are predominantly due to tumor-associated anemia. Possible uses and limitations of measures are discussed which can increase the microvascular O2 content and thus may preferentially serve to enhance diffusion-limited O2 availability. In addition, means are described for improving and increasing the uniformity of microcirculation thus possibly enhancing perfusion-limited O2 delivery. Reducing cellular respiration rate should be of benefit in both pathophysiological conditions. Because both types of O2 limitation coexist in solid tumors, appropriate combinations should be aimed at eradicating tumor hypoxia which is present in at least one third of cancers in the clinical setting.

Tetrachlorodecaoxide improves the oxygenation status of multicellular tumor spheroids

The benefit of Tetrachlorodecaoxide (TCDO) in improving tumor tissue oxygenation has been tested using multicellular tumor spheroids. Measurements of PO2 values with O2-sensitive microelectrodes revealed a distinct enhancement of the spheroid oxygenation after bolus injection of TCDO into the medium around the spheroid (peak concentration: 0.7 mM). Small spheroids exhibited a uniform, transient rise in PO2 at different locations within the spheroid. Larger spheroids showed a smaller, yet still significant increase in PO2 in inner parts compared to the spheroid periphery. The increase in PO2 after TCDO injection appeared to be less in spheroid areas with low initial PO2 values versus well-oxygenated spheroid regions. Continuous infusion of TCDO for 15 minutes at steady state concentrations in the medium of 33 microM resulted in a substantial and persistent elevation of the local PO2 within spheroids. The PO2 returned to the control level 20 minutes after the stoppage of the infusion.