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Combition therapies for HIV infection and genomic durg resistance
THE LANCET
COMMENTARY
Combination therapies for HIV infection and genomic drug resistance See page 983 Drug combinations that reduce HIV plasma RNA and raise CD4 cell numbers are associated with decreased progression to AIDS and increased survival.1-3 The recent discovery of families of chemokine receptors that are second ligands for CD4 for viral entry4 provides evidence that host genomic and phenotypic determinants contribute to the pathogenesis of HIV infection. Drug resistance may explain differences in efficacy between the treatment regimens. In today’s Lancet the authors of the Delta study describe their investigation of whether specific drug-resistance mutations explain the differences in clinical and virological effects between combination regimens and zidovudine alone. According to the point-mutation assay used in the study, in patients on zidovudine alone resistance to this drug develops rapidly through changes in HIV RNA at multiple loci in the reverse-transcriptase gene in most patients during the first year of treatment. These zidovudine-resistance mutations evolve even earlier in those patients on the two combination treatments given in the Delta trial, but genotypic or phenotypic evidence of resistance to the second drug (didanosine or zalcitabine) in the combination regimens was not found. Although evolution of zidovudine resistance was faster with combination therapy, the combinations produced a clinical benefit compared with zidovudine alone. Thus genomic resistance alone does not account for differences in efficacy of treatment regimens. Despite their superiority over zidovudine monotherapy, the effect of the combinations on viral RNA and CD4 measures waned after a year. Limiting disease progression and drug resistance, through reduction in HIV RNA replication to levels below detection by sensitive assays (itself the subject of heated debate), is increasingly being advocated as the next goal of antiretroviral treatment.5 So long as virus replication remains below the limits of detection, drug resistance is not detected, and disease progression is limited. Conversely, the detection of virus replication in vivo in the presence of drug is evidence of drug failure and, commonly, of drug resistance. Failure to maintain virological suppression or increased CD4 counts in many patients after a year, in the Delta and ACTG 1751 trials for example, shows that combination nucleoside regimens are often inadequate. The Delta and ACTG 175 trials were designed in 1991, 970
when only three reverse-transcriptase inhibitors were used for HIV infection. Another eight drugs have been licensed in the USA for treatment of HIV—two additional reversetranscriptase inhibitors (lamivudine and stavudine), two non-nucleoside reverse-transcriptase inhibitors (delaviradine and nevaripine), and four protease inhibitors (saquinavir, indinavir, ritonavir, and nelfinavir), with more to come. Wresting the maximum benefit from drug combinations including protease inhibitors and the nonnucleoside reverse-transcriptase inhibitors is the central challenge in the treatment of HIV infection. Partly suppressive therapies combining zidovudine and a second nucleoside drug reduce plasma HIV RNA and provide clinical benefit but, as shown in the Delta patients, rarely reduce virus replication to sufficiently low levels to limit the emergence of zidovudine resistance. This provides clear evidence for the continued adaptive response of virus through selection in the presence of drug. An understanding of drug-resistance mutations in combination therapies and the genetic pathways towards drug resistance has not kept pace with expansion of the therapeutic options. As antiretroviral therapies are applied earlier in the infection, a growing number of patients have been exposed to zidovudine. In zidovudine-experienced patients the addition of a second nucleoside drug after lengthy zidovudine therapy is less effective than starting with the combination straightaway.6 Patients who have received multiple and sequential nucleoside combinations may show high-level multinucleoside resistance.7 Even more alarming is the observation that patients receiving combinations including protease inhibitors can develop virus resistant to all the currently available drugs.8 Strategies for treatment of HIV infection, especially for patients not responding to combination therapies, will need to take account of genetic pathways towards drug resistance. Partly suppressive regimens, while providing clear clinical benefits, limit the options for further treatment and effective long-term therapy.
David Katzenstein Stanford University Medical Center, Stanford, CA 94305, USA 1
2
Katzenstein DA, Hammer SM, Hughes M, et al. Virologic and immunologic markers and clinical outcomes after nucleoside therapy in adults with 200 to 500 CD4 cells per cubic millimeter: NIAID sponsored AIDS Clinical Trials Group Study 175, a virology substudy. N Engl J Med 1996; 335: 1091-98. Eron JJ, Benoit SL, Jemsek J et al. Treatment with lamivudine,
Vol 350 • October 4, 1997
THE LANCET
COMMENTARY
3
4
5
zidovudine or both in HIV-positive patients with 200-500 CD4+ cells per cubic millimeter. N Engl J Med 1995; 333: 1662-69. Hammer SM, Squires KE, Hughes MD et al. A controlled trial of two nucleoside analogues plus indinavir in persons with human immunodeficiency virus infection and CD4 cell counts of 200 per cubic millimeter or less. N Engl J Med 1997; 337:725-32. Dean M, Carrington M, Winkler C, et al. Genetic restriction of HIV-1 infection and progression to AIDS by a deletion allele of the CKR5 structural gene. Science 1996; 273: 1856-61. Carpenter CCJ, Fischl M, Hammer SM,et al. Antiretroviral therapy for HIV Infection in 1997: Updated recommendations of an International AIDS Society - USA Panel.JAMA 1997; 277:1962-69.
Phyto-oestrogens and breast cancer See page 990 In this issue of The Lancet David Ingram and colleagues report a case-control study showing an inverse relation between the risk of both premenopausal and postmenopausal breast cancer and the urinary excretion of two classes of phytochemicals, lignans and isoflavonoids. Their findings help draw attention to the potential importance of biologically active non-nutrients (phytochemicals) in foods. They also strengthen the notion that, among the phytochemicals, the phytooestrogens in particular (the two dominant chemical classes being lignans and isoflavones) seem to hold promise for reducing risk of hormone-dependent cancers. The phyto-oestrogen and breast cancer hypothesis stems in part from the low breast-cancer mortality rates in Asian countries, where soyfoods, which are high in isoflavones, are commonly consumed. Furthermore, soy intake exerts pronounced physiological effects, such as increasing menstrual cycle length (which has been associated with lower breast-cancer risk) and decreasing serum concentrations of follicular stimulating hormone and luteinising hormone in premenopausal women, effects that correlate with excretion of urinary equol,1 the isoflavan measured by Ingram et al. The findings of Ingram et al are encouraging, but it is important to put them into perspective. Since 1991, five case-control studies (one study included two locations) have examined the relation between soy intake and breast-cancer risk.2-5 Three of those studies found a significantly reduced risk for premenopausal breast cancer2-4 but only one,4 which was conducted in the USA, for postmenopausal breast cancer. In that study, however, protective effects for both premenopausal and postmenopausal women were observed primarily in Asian immigrants, not in US-born Asians.4 In addition to the case-control studies, a cohort study in the USA, reported thus far only in abstract form, found a non-significant decreased breast-cancer risk associated with tofu intake.6 Although attempts were made to control for confounding variables, in non-Asian populations it is difficult to account for all of the factors that might distinguish those who regularly eat soyfoods from those who do not. In the cohort study cited above, fewer than 3% of the population reported eating tofu.6 Although Ingram et al did not report phyto-oestrogen intake, the urinary findings indicate that soy consumption was very low and consistent with the average Western diet. A further complication is the co-association of lignan and fibre intake, since fibre has been postulated to reduce breast-cancer risk.7 Fibre intake was not reported by Ingram et al. Other reasons for cautious interpretation of
Vol 350 • October 4, 1997
Some non-oestrogenic biological properties of phyto-oestrogens Property Reference Genistein influences enzymes involved in signal transduction that regulate cell growth and replication
Akiyama et al. J Biol Chem 1987; 262: 5592–95 Constantinou et al. Cancer Res 1990; 50:2618–24
Genistein augments signalling mechanisms mediated by transforming growth factor , which inhibits progression of cells through G1/S phase
Peterson et al. 2nd International Symposium on Role of Soy in preventing and Treating Chronic Diseases. 1996, abstr p 37
Phyto-oestrogens have antioxidant properties
Wei et al. Proc Soc Exp Biol Med 1995; 208: 124–30 Fotsis et al. Cancer Res 1997; 57: 2916–21 Korzenik et al. 2nd International Symposium on Role of Soy in Preventing and Treating Chronic Diseases. 1996, abstr p 37
the findings are that genistein could not be measured, the interassay coefficient of variation for the control urine pool sample for the phyto-oestrogens ranged from 10·9 to 42·6%, and there were no markers for assessing completeness of urine collection. Interestingly, the phyto-oestrogen metabolites (equol and enterolactone) were more protective than their plant precursors. This finding, as well as other studies, suggest that research is needed to determine the extent to which individual differences in the metabolism of isoflavones and lignans may influence the relation between phytooestrogen intake and breast-cancer risk. Despite the inconclusive epidemiological findings, there are several possible mechanisms that could account for the hypothesised anticancer effects of phytooestrogens. Isoflavones and lignans are classified as phyto-oestrogens because of their uterotrophic activity in immature mice.8 Although there are conflicting findings, weak oestrogens such as isoflavones and lignans have been postulated to exert anti-oestrogenic effects and thereby to reduce risk of hormone-related cancers.9 However, phyto-oestrogens, especially isoflavones, have biological properties that are quite separate from classic oestrogen action and that may influence carcinogenesis (panel). The study by Ingram et al may serve to allay concerns that the oestrogen-like character of isoflavones and lignans would have similar effects as contraceptive steroids or hormone-replacement therapy, both of which may modestly increase risk of breast cancer.10 Whether phyto-oestrogens should be contraindicated for women with oestrogen-receptor-positive breast tumours is uncertain in the absence of scientific data. Interestingly, emerging evidence from animal studies suggests that short-term exposure to dietary isoflavones neonatally or prepubertally decreases carcinogen-induced breast cancer by increasing the proportion of differentiated cells in the mammary gland.11 These studies support a concept derived from other epidemiological investigations that the protective effect of the Southeast Asian diet occurs early in life.12 This may may explain why the epidemiological studies cited above, which in essence focus on the adult consumption of soy, are relatively unimpressive. Ironically, although concerns about the phyto-oestrogen content of soy infant formulas warrant attention, it is possible, but still speculative, that 971
COMMENTARY
Combination therapies for HIV infection and genomic drug resistance See page 983 Drug combinations that reduce HIV plasma RNA and raise CD4 cell numbers are associated with decreased progression to AIDS and increased survival.1-3 The recent discovery of families of chemokine receptors that are second ligands for CD4 for viral entry4 provides evidence that host genomic and phenotypic determinants contribute to the pathogenesis of HIV infection. Drug resistance may explain differences in efficacy between the treatment regimens. In today’s Lancet the authors of the Delta study describe their investigation of whether specific drug-resistance mutations explain the differences in clinical and virological effects between combination regimens and zidovudine alone. According to the point-mutation assay used in the study, in patients on zidovudine alone resistance to this drug develops rapidly through changes in HIV RNA at multiple loci in the reverse-transcriptase gene in most patients during the first year of treatment. These zidovudine-resistance mutations evolve even earlier in those patients on the two combination treatments given in the Delta trial, but genotypic or phenotypic evidence of resistance to the second drug (didanosine or zalcitabine) in the combination regimens was not found. Although evolution of zidovudine resistance was faster with combination therapy, the combinations produced a clinical benefit compared with zidovudine alone. Thus genomic resistance alone does not account for differences in efficacy of treatment regimens. Despite their superiority over zidovudine monotherapy, the effect of the combinations on viral RNA and CD4 measures waned after a year. Limiting disease progression and drug resistance, through reduction in HIV RNA replication to levels below detection by sensitive assays (itself the subject of heated debate), is increasingly being advocated as the next goal of antiretroviral treatment.5 So long as virus replication remains below the limits of detection, drug resistance is not detected, and disease progression is limited. Conversely, the detection of virus replication in vivo in the presence of drug is evidence of drug failure and, commonly, of drug resistance. Failure to maintain virological suppression or increased CD4 counts in many patients after a year, in the Delta and ACTG 1751 trials for example, shows that combination nucleoside regimens are often inadequate. The Delta and ACTG 175 trials were designed in 1991, 970
when only three reverse-transcriptase inhibitors were used for HIV infection. Another eight drugs have been licensed in the USA for treatment of HIV—two additional reversetranscriptase inhibitors (lamivudine and stavudine), two non-nucleoside reverse-transcriptase inhibitors (delaviradine and nevaripine), and four protease inhibitors (saquinavir, indinavir, ritonavir, and nelfinavir), with more to come. Wresting the maximum benefit from drug combinations including protease inhibitors and the nonnucleoside reverse-transcriptase inhibitors is the central challenge in the treatment of HIV infection. Partly suppressive therapies combining zidovudine and a second nucleoside drug reduce plasma HIV RNA and provide clinical benefit but, as shown in the Delta patients, rarely reduce virus replication to sufficiently low levels to limit the emergence of zidovudine resistance. This provides clear evidence for the continued adaptive response of virus through selection in the presence of drug. An understanding of drug-resistance mutations in combination therapies and the genetic pathways towards drug resistance has not kept pace with expansion of the therapeutic options. As antiretroviral therapies are applied earlier in the infection, a growing number of patients have been exposed to zidovudine. In zidovudine-experienced patients the addition of a second nucleoside drug after lengthy zidovudine therapy is less effective than starting with the combination straightaway.6 Patients who have received multiple and sequential nucleoside combinations may show high-level multinucleoside resistance.7 Even more alarming is the observation that patients receiving combinations including protease inhibitors can develop virus resistant to all the currently available drugs.8 Strategies for treatment of HIV infection, especially for patients not responding to combination therapies, will need to take account of genetic pathways towards drug resistance. Partly suppressive regimens, while providing clear clinical benefits, limit the options for further treatment and effective long-term therapy.
David Katzenstein Stanford University Medical Center, Stanford, CA 94305, USA 1
2
Katzenstein DA, Hammer SM, Hughes M, et al. Virologic and immunologic markers and clinical outcomes after nucleoside therapy in adults with 200 to 500 CD4 cells per cubic millimeter: NIAID sponsored AIDS Clinical Trials Group Study 175, a virology substudy. N Engl J Med 1996; 335: 1091-98. Eron JJ, Benoit SL, Jemsek J et al. Treatment with lamivudine,
Vol 350 • October 4, 1997
THE LANCET
COMMENTARY
3
4
5
zidovudine or both in HIV-positive patients with 200-500 CD4+ cells per cubic millimeter. N Engl J Med 1995; 333: 1662-69. Hammer SM, Squires KE, Hughes MD et al. A controlled trial of two nucleoside analogues plus indinavir in persons with human immunodeficiency virus infection and CD4 cell counts of 200 per cubic millimeter or less. N Engl J Med 1997; 337:725-32. Dean M, Carrington M, Winkler C, et al. Genetic restriction of HIV-1 infection and progression to AIDS by a deletion allele of the CKR5 structural gene. Science 1996; 273: 1856-61. Carpenter CCJ, Fischl M, Hammer SM,et al. Antiretroviral therapy for HIV Infection in 1997: Updated recommendations of an International AIDS Society - USA Panel.JAMA 1997; 277:1962-69.
Phyto-oestrogens and breast cancer See page 990 In this issue of The Lancet David Ingram and colleagues report a case-control study showing an inverse relation between the risk of both premenopausal and postmenopausal breast cancer and the urinary excretion of two classes of phytochemicals, lignans and isoflavonoids. Their findings help draw attention to the potential importance of biologically active non-nutrients (phytochemicals) in foods. They also strengthen the notion that, among the phytochemicals, the phytooestrogens in particular (the two dominant chemical classes being lignans and isoflavones) seem to hold promise for reducing risk of hormone-dependent cancers. The phyto-oestrogen and breast cancer hypothesis stems in part from the low breast-cancer mortality rates in Asian countries, where soyfoods, which are high in isoflavones, are commonly consumed. Furthermore, soy intake exerts pronounced physiological effects, such as increasing menstrual cycle length (which has been associated with lower breast-cancer risk) and decreasing serum concentrations of follicular stimulating hormone and luteinising hormone in premenopausal women, effects that correlate with excretion of urinary equol,1 the isoflavan measured by Ingram et al. The findings of Ingram et al are encouraging, but it is important to put them into perspective. Since 1991, five case-control studies (one study included two locations) have examined the relation between soy intake and breast-cancer risk.2-5 Three of those studies found a significantly reduced risk for premenopausal breast cancer2-4 but only one,4 which was conducted in the USA, for postmenopausal breast cancer. In that study, however, protective effects for both premenopausal and postmenopausal women were observed primarily in Asian immigrants, not in US-born Asians.4 In addition to the case-control studies, a cohort study in the USA, reported thus far only in abstract form, found a non-significant decreased breast-cancer risk associated with tofu intake.6 Although attempts were made to control for confounding variables, in non-Asian populations it is difficult to account for all of the factors that might distinguish those who regularly eat soyfoods from those who do not. In the cohort study cited above, fewer than 3% of the population reported eating tofu.6 Although Ingram et al did not report phyto-oestrogen intake, the urinary findings indicate that soy consumption was very low and consistent with the average Western diet. A further complication is the co-association of lignan and fibre intake, since fibre has been postulated to reduce breast-cancer risk.7 Fibre intake was not reported by Ingram et al. Other reasons for cautious interpretation of
Vol 350 • October 4, 1997
Some non-oestrogenic biological properties of phyto-oestrogens Property Reference Genistein influences enzymes involved in signal transduction that regulate cell growth and replication
Akiyama et al. J Biol Chem 1987; 262: 5592–95 Constantinou et al. Cancer Res 1990; 50:2618–24
Genistein augments signalling mechanisms mediated by transforming growth factor , which inhibits progression of cells through G1/S phase
Peterson et al. 2nd International Symposium on Role of Soy in preventing and Treating Chronic Diseases. 1996, abstr p 37
Phyto-oestrogens have antioxidant properties
Wei et al. Proc Soc Exp Biol Med 1995; 208: 124–30 Fotsis et al. Cancer Res 1997; 57: 2916–21 Korzenik et al. 2nd International Symposium on Role of Soy in Preventing and Treating Chronic Diseases. 1996, abstr p 37
the findings are that genistein could not be measured, the interassay coefficient of variation for the control urine pool sample for the phyto-oestrogens ranged from 10·9 to 42·6%, and there were no markers for assessing completeness of urine collection. Interestingly, the phyto-oestrogen metabolites (equol and enterolactone) were more protective than their plant precursors. This finding, as well as other studies, suggest that research is needed to determine the extent to which individual differences in the metabolism of isoflavones and lignans may influence the relation between phytooestrogen intake and breast-cancer risk. Despite the inconclusive epidemiological findings, there are several possible mechanisms that could account for the hypothesised anticancer effects of phytooestrogens. Isoflavones and lignans are classified as phyto-oestrogens because of their uterotrophic activity in immature mice.8 Although there are conflicting findings, weak oestrogens such as isoflavones and lignans have been postulated to exert anti-oestrogenic effects and thereby to reduce risk of hormone-related cancers.9 However, phyto-oestrogens, especially isoflavones, have biological properties that are quite separate from classic oestrogen action and that may influence carcinogenesis (panel). The study by Ingram et al may serve to allay concerns that the oestrogen-like character of isoflavones and lignans would have similar effects as contraceptive steroids or hormone-replacement therapy, both of which may modestly increase risk of breast cancer.10 Whether phyto-oestrogens should be contraindicated for women with oestrogen-receptor-positive breast tumours is uncertain in the absence of scientific data. Interestingly, emerging evidence from animal studies suggests that short-term exposure to dietary isoflavones neonatally or prepubertally decreases carcinogen-induced breast cancer by increasing the proportion of differentiated cells in the mammary gland.11 These studies support a concept derived from other epidemiological investigations that the protective effect of the Southeast Asian diet occurs early in life.12 This may may explain why the epidemiological studies cited above, which in essence focus on the adult consumption of soy, are relatively unimpressive. Ironically, although concerns about the phyto-oestrogen content of soy infant formulas warrant attention, it is possible, but still speculative, that 971