8th Annual Retrovirus Conference
New Drugs Reported at Retrovirus
Reported for NATAP by Nancy Shulman, MD, Asst Prof of Medicine at Stanford University, Palo Alto, California
Entry Inhibitor in Early Development: CCR5 antagonist
One of the most exciting new class of drugs in development was presented by Schering-Plough at a state-of-the-art lecture.› They have two new drugs that block the binding of HIV to the CCR5 co-receptor, a step required before the virus can fuse and enter into a cell.› We know that people who have a genetic defect in all their CCR5 co-receptor are resistant to HIV infection (homozygotes) and if they carry half this defective gene (heterozygotes) they are slow progressors of HIV.› These people are otherwise totally healthy, so we think that blocking CCR5 should be safe (although there are some lingering concerns about safety).› They are developing two compounds (SCH-C and SCH-D) that can be taken by mouth, are well absorbed into the bloodstream and are potent inhibitors of HIV in vitro and in animal models with no significant toxicities to the animals. They also have a long half-life so will probably be once a day.› They are synergistic with nucleosides and should also be synergistic with other drugs that block HIV from entering at different steps such as T-20 and T-1249 as well AMD3100.› We all have been hoping for other drugs to give T-20 with in our patients with resistance to the available drugs.› HIV spontaneously changes co-receptor preference from CCR5 to CXCR4 in 40% of patients with HIV during their illness, usually late in disease.› This switches the favored cells of HIV from macrophages to lymphocytes and can be associated with a rise in viral load and drop in CD4 count.› One fear of using this drug is that this may promote this switch.› In vitro, resistance developed to SCH-C, but fortunately, it was not due to a CXCR4 switch. (abstract L11)
(Editor's note: I believe Greg Reyes, who presented the data on SCH-C, said they did not see a switch to CXCR4 in in vitro experiments, which of course needs to be confirmed in human studies).
Several posters discussed using CCR5 inhibitors with CXCR4 inhibitors like AMD3100 for synergy and to block the co-receptor switch by the virus.› Phase I trials are in progress.› The only side affect seen (with SCH-C) is at high doses was prolongation of the QT interval on EKG which poses a threat of developing an arrhythmia (heart rhythm problem) called Torsades that can be fatal. Lots of drugs on the market prolong the QT interval including common antibiotics like Zithromax, Cipro, Levoquin, and Quinine to name a few.› Progenics is also developing a CCR5 inhibitor (PRO-140).
Protease Inhibitors For Resistance to Current Protease Inhibitors
Descriptions of three protease inhibitors DMP681 and 684 from Dupont and TMC126 from Tibotec, all early in development were presented by the companies.› All are very potent inhibitors of HIV-1 in vitro and retain activity against many isolates with substantial PI resistance.› Unfortunately no data was presented on what resistance mutations are selected for in vitro with these compounds.› That type of data provides important information on cross-resistance.› All these agents are entering phase I trials soon. (abstract 11)
NNRTI for NNRTI Resistance
Tibotec also presented phase I/II data on their new NNRTI, TMC-120 (previously called R147681). The drug was administered to antiretroviral naÔve patients as one week of monotherapy prior to initiation of a standard HAART regimen.› At one week, both 50mg and 100mg BID resulted in about 1.5 logs reduction of viral load. Side effects were mild and included somnolence, insomnia, and rare headaches (sounds like Sustiva).› No liver side affects were seen.› No one developed detectable resistance mutations during the 7-day study.› In vitro resistance data was presented in a poster.› It retains activity against G190A mutants (as does delavirdine), has only 4-fold reduced susceptibility against K103N isolates (EFV is about 40 fold and NVP and DLV are even higher), and 7-fold against Y181C (2-fold with EFV, and over 1000- with NVP and DLV).› Again, no data on what mutations it selects for in vitro was presented. (abstracts 13 & 304)
T-1249: fusion inhibitor cousin of T-20
Joe Eron presented phase I/II data on Trimerisí son (or daughter) of T-20 called T-1249. This is an injectable fusion inhibitor that retains activity activity against T-20 resistant isolates.› This was a study of 72 predominantly advanced patients (CD4 counts 85-135) who were not on any therapy for one month prior to receiving 2 weeks of T-1249.› Multiple doses were tested and there was a dose-dependent reduction of HIV.› The highest dose tested (25mg BID) yielded a 1.4 log viral load reduction at 2 weeks.› PK data was collected and support the use of a once daily subcutaneous dosing regimen.› The next study will need to test even higher once daily doses to see if it could reduce the viral load even further.› 71% had adverse reactions, mainly injection site pain, irritation, or less frequently redness.› One person had an allergic reaction with rash, fever, and oral ulcers that resolve when drug was stopped.› Another had neutropenia (low white cell count).› Overall the drug looks good so far and is tolerated well. (abstract 14 & 473)
FTC: once a day NRTI for treatment naive
Charlie Van Der Horst presented results from 2 phase III studies of FTC, a new drug similar to 3TC that is somewhat more potent and has a longer half-life so can be dosed once daily.› FTC-303 was a randomized, open label switch study in patients who were on D4T, 3TC, and either NVP or EFV and undetectable.› Two-thirds of the 440 patients were switched to FTC 200mg once a day, and the other one-third remained on their 3TC.› The other study (302) took place in South Africa and was a randomized, double-blinded study looking at D4T with 3TC or FTC (each in half the patients) with NVP (for VL <100,000) or EFV (for VL>100,000).›› I am not sure why they didnít give everyone efavirenz or nevirapine, but they didnít.› There was a substantial amount of nevirapine-related liver toxicity in this study (17%) with two women dying of liver failure.› One had chronic hepatitis B.› They have not unblinded the study to see if this was associated with FTC.› This study enrolled mainly women (59%), and most were African (88%).› The liver toxicity was disproportionately› in the women.› It could be a hormonal-related, a pharmacokinetic, or a weight-related issue.› Ultimately both studies showed that FTC was equivalent to 3TC in suppressing and keeping peopleís HIV suppressed. (abstract 18)
BMS-232632: once a day protease inhibitor
Kate Squires presented phase II data on BMS new PI, BMS-232632, a once daily PI that appears not to raise the serum glucose, cholesterol or triglycerides like the rest of the PIís. Two studies have been conducted: stage I (safety& efficacy) 48 weeks, n=98) and stage II (24 weeks, n=322). The first part of the studies were two weeks of BMS at 3 different doses (200, 400 & 500 mg), followed by a comparative study looking at the three doses with D4T and DDI vs. nelfinavir 750mg TID with D4T and DDI. BMS has chosen 400 mg for further studies due to consideration of safety & antiviral activity. The efficacies in stage II were about 65% <400 (ITT) at 24 weeks and 30-35% <50 (ITT) in the two higher dose arms of BMS and the NFV arm showing comparability with NFV in naÔve subjects (median baseline CD4 was 305 & viral load 51,000 copies/ml). Viral load 48-week data in stage I showed durability, as reduction was 2.3 to 2.8 log. Lipid abnormalities were only seen in the NFV arm.› Although it was no more effective than NFV, this is the first once daily PI and it really seems not to have the lipid abnormalities we see in all the other PIs.› Unfortunately no data was collected on lipodystrophic body habitus changes in this study.› Side affects were nausea and diarrhea (20% vs.50% with NFV), and a dose dependent elevation in the bilirubin (like indinavir) that occurred in 70% of patients.› Grade 3/4 ALT elevations in stage II were 6%(n=4) in the BMS 500 mg, 12% (n=10) in the BMS 400 mg arm vs 4% in the NFV arm (n=3). Phase III studies are planned that compare this PI at 400mg per day vs. efavirenz both with two nucleosides, probably D4T and DDI. (Edit note: Criticism from observers was that antiviral activity did not appear very potent, and response from Squires was that additional studies are planned comparing BMS to other treatments which I think she said was efavirenz). (abstract 15)
Protein Design of an HIV-1 Entry Inhibitor
In the late-breakers, researchers from the Whitehead Institute at MIT described another drug that inhibits HIV entry different from the other inhibitors of entry like fusion inhibitors (T-20 and the like), the chemokine receptor antagonists (SCH-C, D, and AMD3100). This is a small protein inhibitor called 5-helix.› HIV-1 cellular entry has a step where it forms a trimer-of-hairpins structure.› This serves to bring the N- and C-terminal regions (ends) of the gp41 together, enabling fusion of the virus with the cell. 5-Helix was engineered to contain five of the six helices that make up the core of the gp41 trimer-of-hairpins structure. 5-Helix lacks a third C-peptide helix, and therefore binds tightly to the C-terminal of the GP41 protein.› 5-Helix inhibits diverse HIV-1 strains in vitro. (Edit note: this may be difficult drug to develop; the presenter suggested drug may have utility in development of vaccine.) (abstract LB1)
In another late breaker, Jay Lalezari presented interim 16-week data on a phase II randomized controlled trial of 71 patients looking at 3 doses of T-20 added to abacavir, amprenavir, lo-dose ritonavir, and efavirenz in 72 PI and NRTI experienced, NNRTI naÔve subjects.› The 3 doses were 50, 75 or 100 mg bid of T-20 (50 mg/mL). The three dosing arms were compared to a control arm with the same regimen without T-20.› T-20 is currently administered by subcutaneous injection. The baseline viral load across all study arms was about 19,000 copies/ml. CD4s ranged from 176 to 326 across the study arms. The median change in VL at week 16 in the 100 mg bid T-20 treatment arm was -2.27 logs compared to› -1.65 in the control arm and the other dose arms.› There was a trend at increased suppression of HIV and higher CD4 counts in the highest two doses. This study was a pilot exploratory study and as such was not designed to compare antiviral efficacy. 65% of patients had pain or redness at the T-20 injection sites, otherwise side affects between the T-20 and control arms were similar.
(Edit notes: Early 2-week studies in naÔve patients demonstrated about a 1.5 log reduction in viral load.› Fifty-three of the 71 patients who started the study completed week 16. Phase III studies are ongoing. Application to the FDA is expected in 2002 if all goes well. There were 6 serious adverse events determined to be possibly or probably drug related by the investigators: on 50 mg bid dose--grade 4 neutropenia; chest discomfort, primary immune complex reaction, shortness of breath. On 100 mg bid dose--abnormal wall abscess, grade 4 ALT, dizziness, nausea, dehydration, abacavir hypersensitivity. Lalezari said no single event occurred more than once suggesting no consistent T-20 toxicity except for the abnormal wall abscess from injections. Prior to showing ITT percent below detection data, Lalezari said 7 patients in the T-20 arms discontinued study prior to first viral load analysis and were considered failures by ITT analysis.)
HIV-RNA Response at Week 16 (ITT missing=failure)
Control arm (n=19) Total T-20 (n=52)
|37% control arm|
|48% T-20 arms|
|58% control arm|
|71% T-20 arms|
showed viral load response after eliminating those 7 patients from the analysis
and including patients who were available for at least 1 viral load measure
(control n=19, total T-20 n=45): <50 copies/ml, 37% vs 56% (T-20); <400
copies/ml, 58% vs 82% (T-20).
ACH-126,433: NRTI in early development
Achillon pharmaceuticals in New Haven has a nucleoside in pre-clinical development that should eventually go into clinical development by some company called ACH-126,443.› It is an L-nucleoside analog (theoretically less toxic to our cells) that good activity against all HIV strains including strains with mutli-nucleoside resistance.› It also is active against HBV including some resistant strains. It doesnít inhibit cell mitochondrial DNA production (in vitro) like the other nucleosides so may not produce side affects like neuropathy, lipodystrphy or liver toxicity all associated with cell mitochondrial toxicity.› In animal studies it has been safe and gets good sustained levels with an oral dose.› The pharmacokinetics in animals looks like it could be dosed once daily.›(abstract 303)
Mycophenolate or Ribivarin in HIV
Mycophenolate acid (same class as ribavirin), MPA, shows antiHIV activity in vitro, is used in oncology, and was shown to increase the anti-HIV affect of DDI, abacavir, and tenofovir in vitro (abstract 307) against wild-type & NRTI resistant viruses.. Some of this data has been presented before. A dose dependent antiviral effect of MPA was seen. In a clinical study of 3 HIV infected individuals, viral load decline of 1 log was seen 3-6 weeks following only the addition of MPA (abstract 351). Further testing for safety and antiviral activity is ongoing in ACTG studies. Similarly, ribavirin was shown to synergize with DDI and when added with alpha interferon has potent anti-HIV activity in vitro making DDI (and probably Abacavir or Tenofovit) an ideal part of an antiretroviral regimen for patients getting treated for HCV (abstract 574). Remember, ribavirin inhibits the anti-HIV affect of AZT and D4T in vitro, although most patients in my practice and in the reports of patients treated with IFN and ribavirin for HCV and who are on AZT or D4T have not seen any increase in HIV viral load during therapy.› This interaction is being formally studied in an ACTG co-infection treatment study.