Given a passage with a context and an answer, construct a question on the basis of the information present in the passage. Construct the question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) it answer uses text phrases from the passage. Avoid creating questions that (i) can't be answered correctly without actually understanding the passage and (ii) uses the same words or phrases given in the passage.

[EX Q]: Context: Most solid human tumors exist in an acidic microenvironment, due in part to inefficient vasculature and a higher intrinsic rate of glycolysis. This leads to a tumor-selective pH gradient, which can be exploited therapeutically with antitumor agents such as the camptothecins (CPTs). Previous work in this laboratory has shown that camptothecin activity is enhanced 40- to 60-fold in monolayer cell culture by reducing the extracellular pH to 6.8. Three-dimensional histoculture has been shown to be a technique that allows human tumor tissue to grow in an in vivo-like way with maintenance of tissue histology and function and drug sensitivity for long periods of time.', 'In the current study, we utilized these features of histoculture to study new analogues of camptothecin that have superior pharmacological properties.', 'We evaluated six CPT analogues in histocultures of human brain, neuroblastoma, breast, colon, and prostate tumors. Fragments were exposed to 10,11-methylenedioxy-CPT (MDC), 7-chloromethyl-MDC, SN-38, topotecan (TPT), 9-amino-CPT, 10-amino-CPT, paclitaxel, 5-fluorouracil, 4-hydroperoxycyclophosphamide and doxorubicin, and antitumor activity was assessed. For in vivo tumor outgrowth studies, fragments were treated in parallel, implanted into nude mice, and monitored for development of tumors. RESULTS. Against 15 of 16 tumor xenografts and all primary tumor samples tested, all compounds were cytotoxic at pH 7.4 (IC(50) range 13-921 microM). MDC, SN-38, TPT, and 9-amino-CPT achieved an average 5-fold increase in activity (range 3-14) at pH 6.8, while 7-chloromethyl-MDC was enhanced 8-fold (range 6-14). The most potentiated analogue was 10-amino-CPT at 27-fold (range 17-49). In contrast, the other agents were active against one or more tumor types but were not enhanced by acidic pH. Importantly, the toxicity of MDC in histoculture of D54 glioma xenografts strongly correlated with the outgrowth of treated fragments subsequently implanted in vivo.
Answer: Evaluation of anticancer drug activity in native-state histoculture supports the concept that pH modulation may be an important approach to improve the selectivity and antitumor effectiveness of camptothecin-based chemotherapy.
[EX A]: Is the activity of camptothecin analogues enhanced in histocultures of human tumors and human tumor xenografts by modulation of extracellular pH?

[EX Q]: Context: Material loss at the taper junction of metal-on-metal total hip arthroplasties has been implicated in their early failure. The mechanisms of material loss are not fully understood; analysis of the patterns of damage at the taper can help us better understand why material loss occurs at this junction.', 'We mapped the patterns of material loss in a series of 155 metal-on-metal total hip arthroplasties received at our center by scanning the taper surface using a roundness-measuring machine. We examined these material loss maps to develop a 5-tier classification system based on visual differences between different patterns. We correlated these patterns to surgical, implant, and patient factors known to be important for head-stem taper damage.', 'We found that 63 implants had "minimal damage" at the taper (material loss <1 mm
Answer: These material loss maps allow us to suggest different mechanisms that dominate the cause of the material loss in each pattern: (1) corrosion, (2) mechanically assisted corrosion, or (3) intraoperative damage or poor size tolerances leading to toggling of trunnion in taper.
[EX A]: Does damage Patterns at the Head-Stem Taper Junction help Understand the Mechanisms of Material Loss?

[EX Q]: Context: Shear stress alteration has been recognized as a predisposing factor for the impairment of endothelial function. Myocardial bridging is a congenital condition associated with alteration in shear stress, however, its impact upon vasoreactivity remains undetermined.', 'This was a case-control designed study with 29 patients with myocardial bridging and 58 patients without myocardial bridging. Endothelium-dependent and endothelium-independent changes in coronary artery diameters, blood flow and wall shear stress were determined after intracoronary infusion of acetylcholine (ACH, 10(-6)-10(-4) mol/L) and nitroglycerine (NTG, 200 microg). Coronary flow velocity reserve (CFVR) was determined after intracoronary injection of adenosine (18-36 microg). In response to ACH, there was more epicardial vasoconstriction at the myocardial bridging site compared with the proximal and distal segments (-29.6+/-21.7 vs. -9.6+/-22.5 and -17.4+/-21.5%, p<0.05) and compared with the control group (-29.6+/-21.7 vs. -5.9+/-36.5%, p<0.001). The response to NTG and CFVR was the same in the case and the control group. Wall shear rate (WSR) was higher in the MB site at baseline and in response to ACH.
Answer: MB is characterised by enhanced WSR and impairment in endothelium-dependent vasorelaxation. These functional alterations may add to the severity of structural lumen compression and thus to the clinical presentation of this congenital abnormality.
[EX A]:
Is myocardial bridging associated with alteration in coronary vasoreactivity?