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.
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Question: 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.

Answer: Is the activity of camptothecin analogues enhanced in histocultures of human tumors and human tumor xenografts by modulation of extracellular pH?

Question: Context: Side effects of mitotane (o,p'-DDD) have suggested estrogenic effects.", "The objective of the study was to explore o,p'-DDD potential estrogenic effect on SHBG and corticosteroid-binding globulin (CBG).", 'Human hepatoma cell lines (HepG2), lacking estrogen receptor (ER)-alpha, and Hep89, stably transfected by ERalpha, were used.', 'The study was conducted at an academic research laboratory and medical center.', 'The study included 10 male patients with recurrent adrenal carcinoma, receiving mitotane (4-6.5 g daily) for more than 6 months.', 'The main outcome measures were SHBG/CBG mRNA levels measured by real-time PCR, culture medium SHBG/CBG concentrations measured by specific immunoassays, and transient transfection experiments with human SHBG proximal promoter reporter constructs.', "Increased serum SHBG and CBG concentrations, which exceeded normal male limits, were observed in most mitotane-treated patients. In the HepG2 cell line, 17beta-estradiol (E2) or o,p'-DDD treatment had no effect on mRNA or SHBG/CBG concentrations. In contrast, in the Hep89 cell line, E2 increased concentrations of SHBG (r = 0.44, P < 0.0001) and CBG (r = 0.585, P < 0.0001) secreted into culture media in a dose-dependent manner. o,p'-DDD significantly increased SHBG (150% vs. control, P < 0.05) and CBG (184% vs. control, P < 0.05) production by Hep89 cells, at a concentration of 2 x 10(-5) m. Transient transfection experiments in Hep89 cells showed that E2 or o,p'-DDD treatment did not increase the transcriptional activity of the minimal proximal promoter of human SHBG gene.
Answer: Mitotane increased SHBG/CBG gene expression and liver production by mechanisms requiring the presence of ERalpha.

Answer: Does mitotane have an estrogenic effect on sex hormone-binding globulin and corticosteroid-binding globulin in humans?

Question: Context: Tyrosinase, the rate-limiting enzyme required for melanin production, has been targeted to develop active brightening/lightening materials for skin products. Unexpected depigmentation of the skin characterized with the diverse symptoms was reported in some subjects who used a tyrosinase-competitive inhibiting quasi-drug, rhododendrol.', 'To investigate the mechanism underlying the depigmentation caused by rhododendrol-containing cosmetics, this study was performed.', 'The mechanism above was examined using more than dozen of melanocytes derived from donors of different ethnic backgrounds. The RNAi technology was utilized to confirm the effect of tyrosinase to induce the cytotoxicity of rhododendrol and liquid chromatography-tandem mass spectrometry was introduced to detect rhododendrol and its metabolites in the presence of tyrosinase.', 'Melanocyte damage was related to tyrosinase activity at a certain threshold. Treatment with a tyrosinase-specific siRNA was shown to dramatically rescue the rhododendrol-induced melanocyte impairment. Hydroxyl-rhododendrol was detected only in melanocytes with higher tyrosinase activity. When an equivalent amount of hydroxyl-rhododendrol was administered, cell viability was almost equally suppressed even in melanocytes with lower tyrosinase activity.
Answer: The generation of a tyrosinase-catalyzed hydroxyl-metabolite is one of the causes for the diminishment of the melanocyte viability by rhododendrol.

Answer:
Is depigmentation caused by application of the active brightening material , rhododendrol , related to tyrosinase activity at a certain threshold?