Rilpivirine plus cobicistat-boosted darunavir as alternative to standard three-drug therapy in HIV-infected,virologically suppressed subjects: Final results of the PROBE 2 trial

Abstract

Background

Primary analysis at 24 weeks showed that switching to rilpivirine plus darunavir/cobicistat was non-inferior to continuing a standard three-drug antiretroviral regimen in virologically suppressed people with HIV. We present efficacy and safety data from the 48-week analysis.

Methods

PROBE 2 is a randomized, open-label trial. Adults who were on a three-drug therapy and had had <50 HIV-1 RNA copies/mL for at least 6 months were randomly assigned (1:1) to 25 mg rilpivirine plus 800/150 darunavir/cobicistat once daily (early switch group) or to continue their regimen for 24 weeks before switching (late switch group). In the 48-week analysis, the efficacy endpoint was the proportion of participants with <50 copies/mL of HIV-RNA (US Food and Drug Administration snapshot algorithm). The trial is registered with ClinicalTrials.gov, number NCT04064632.

Findings

160 participants were recruited and randomized. At week 48, 70 (87.5%) in the early switch group and 76 (94.8%) in the late switch group maintained HIV-RNA <50 copies/mL. Virological failure (≥50 HIV-RNA copies/mL) was not seen in any patient of the early switch group and in 2 subjects in the late switch group none of which had treatment emergent resistance-associated mutation. Adverse events leading to treatment discontinuation occurred in 7 (8.7%) participants in the early switch group and in none in the late switch group.

Interpretation

The combination of rilpivirine plus darunavir/cobicistat sustained virological suppression, was associated with a low frequency of virological failure, and had a favorable safety profile, which support its use as a nucleoside reverse transcriptase inhibitor-sparing and integrase inhibitor-sparing alternative to three-drug regimens.

Introduction

For over 2 decades, three-drug regimens have been the gold standard of antiretroviral therapy (ART) for both treatment naïve and treatment experienced people with HIV [1].Usually, guideline recommended ART regimens include two nucleoside reverse transcriptase inhibitors plus a third drug: either a boosted protease inhibitor, an integrase strand transfer inhibitor, or non-nucleoside reverse transcriptase inhibitor [1].The lifelong nature of ART has highlighted the need to minimize potential adverse drug–drug interactions and cumulative drug exposure [2].

As a consequence, in the last years, various two-drug regimens have been proposed and studied as possible alternatives to standard three-drug regimens. Most of studies have been performed for maintenance of virological suppression in pre-treated HIV patients [3-7].

The PROBE 2 trial investigated rilpivirine plus darunavir/cobicistat (RPV+DRV/c) as a two-drug regimen for maintenance of HIV suppression. The primary analysis at week 24 showed that switching to RPV+DRV/c from a three-drug regimen was safe, well tolerated and with virological suppression non-inferior to remaining on a three-drug regimen. According to FDA snapshot analysis 72 (90.0%) of participants of the early switch group and 75 (93.8%) of the late switch group maintained an HIV-RNA <50 copies per mL (difference −3.75%; 95% CI −11.63 to 5.63). Non-inferiority was confirmed considering a HIV-RNA greater than 50 copies per mL (0% for early switch; 3.7% for late switch; 95% CI -0.4–7.9), too [8].

Here we report, as planned final analysis, the uncontrolled part of the study with all subjects switched to RPV+DRV/c and the secondary endpoints assessed at week 48.

Study design and participants

The PROBE 2 study is a randomized, open-label, parallel group, active controlled clinical trial. Its aim is to assess the non-inferiority of rilpivirine plus cobicistat-boosted darunavir to standard ART in the maintenance of virological suppression for 24 weeks in individuals with HIV infection and subsequently to assess the longer term efficacy and safety of RPV+DRV/c. We performed the week 48 analysis after the last participant completed the week 48 study visit.

People aged 18 years or older who were on an ART regimen, comprising two nucleoside reverse transcriptase inhibitors plus a non-nucleoside reverse transcriptase inhibitor, or an integrase strand transfer inhibitor, or a boosted protease inhibitor, and had stable suppression of HIV-RNA to less than 50 copies per mL for at least 6 months were eligible for inclusion.

Exclusion criteria included documented evidence of major resistance-associated protease inhibitor or non-nucleoside reverse transcriptase inhibitor substitutions as demonstrated by a baseline genotype or from a genotype performed in the case of a previous virological failure. We also excluded subjects with concurrent hepatitis B virus infection; known allergy to protease inhibitors or non-nucleoside reverse transcriptase inhibitors and pregnant or breastfeeding women.

PROBE 2 was done in accordance with the 2008 Declaration of Helsinki under the approval of investigational sites ethics committees. All participants provided written informed consent before screening.

Randomization

We randomly assigned eligible participants (1:1) to receive RPV+DRV/c for 48 weeks (early switch group) or to continue standard three-drug ART for 24 weeks before switching to RPV+DRV/c from week 24 to week 48 (late switch group). The randomization sequence was computer generated and was used to centrally allocate participants to study groups. As open-label study, no masking was required.

Procedures

Participants in the early switch group took 25 mg rilpivirine and 800/150 mg of darunavir/cobicistat orally once daily for 48 weeks. The drugs were taken with a meal at roughly the same time each day. Participants in the late switch group continued the ART regimen they were taking at screening for 24 weeks, and then switched to RPV+DRV/c thereafter, provided that virological suppression was maintained.

HIV- RNA, CD4 and CD8 cell count, and safety parameters were assessed at every visit along with fasting lipids, glucose, renal markers, and body weight. Adherence was evaluated at each visit by pill counting. A substantial sub-set of patients (145/160) accepted to participate in the bone mineral density sub-study. The quantitative ultrasound (QUS) of the dominant heel scan was measured using the Hologic Sahara (Marlborough, MA, USA). The outputs included the stiffness index, the QUS T-score, and QUS Z-score.

Outcomes

The primary endpoint was the proportion of participants with fewer than 50 HIV-RNA copies per mL of plasma (i.e., virological success) at week 24 according to the US Food and Drug Administration (FDA) snapshot algorithm. Results for this outcome have been previously reported [8].

Secondary endpoints assessed at week 48 and reported here as part of this planned final analysis are the proportion of participants with fewer than 50 HIV-RNA copies per mL of plasma; viral resistance in participants who met the criteria for confirmed virological withdrawal; CD4 and CD8 cell counts; lipid assets; bone stiffness, and safety and tolerability assessments.

Statistical analysis

Sample size calculation and statistical analysis of the primary endpoint have been described previously [8]. The proportion of participants with fewer than 50 HIV-RNA copies per mL of plasma at week 48 was assessed in all randomly assigned participants who received at least one dose of any study drugs (intention to treat). Participants without HIV-RNA data in the week 48 snapshot window were classified as virological non-successes. Changes in all other secondary endpoints were assessed from baseline in the early switch group and from the late switch baseline (i.e. 24-week visit) in the late switch group.

All variables were summarized with simple statistics (i.e., median and IQR and percentages); p values were calculated with chi-square or t-test as appropriate.

No imputation of missing data was done, and analyses of all biomarkers and clinical parameters were based on recorded data. We used SPSS software (version 17.0) for data analysis. The trial is registered with ClinicalTrials.gov, number NCT04064632.

Results

We screened for participants from February 2017 to November 2018. Of 165 participants screened, 160 (97%) were randomly assigned to the early switch (n = 80) or to continue to the late switch (n = 80). The most common reason leading to exclusion from randomization was withdrawal of consent (3 cases), while two more subjects were not randomized because of protocol deviations: insufficient time with viral load below detection (1 case) and viral load >50 copies per mL (1 case).

During the controlled phase of the study, eight patients in the early switch group withdrew from the study, while in the late switch group, 3 patients withdrew because lost to follow-up.⁸ At week 24, 2 participants assigned to continue their standard ART regimen (i.e., in the late switch group) discontinued the study and did not receive RPV+DRV/c. Two more subjects stopped the study during the uncontrolled phase in the early switch group. Therefore, 155 participants switched to RPV+DRV/c and 145 completed the study (Figure 1). Adverse events counted for a minority of subjects’ withdrawals and, overall, they were all already described for the studied drugs.

Figure 1.

Patient disposition.

Participant demographic and key baseline clinical characteristics were similar in the early switch and late switch groups (Table 1); 132 (82.5%) participants were men, 95.6% were white, and their median age was 50 years. Similar proportions of participants in each group were taking protease inhibitors, non-nucleoside reverse transcriptase inhibitors, and integrase strand transfer inhibitors at baseline (Table 1). Specifically, as far as the two studied drugs are concerned, 36.4% of subjects were already on a RPV containing regimen while 13.3% were taking DRV/c.

Table 1.

Main baseline characteristics of patients. No difference was statistically significant.

Variable (discrete; frequency of percentage)	Early switch	Late switch
Subjects (number)	80	80
Male/female (number)	62/18	70/10
Origin
Italy	91.3	100
Sub-Saharan Africa	7.5	0
South America	1.3	0
Risk factor for HIV infection
Heterosexual contacts	43.8	40.0
MSM	33.8	41.3
IDU	20.0	17.5
Other	2.5	1.3
CDC classification
A3	16.3	6.3
B3	10.0	8.8
C3	15.0	15.0
Backbone
ABC	22.5	12.5
TAF	30.0	35.0
TDF	47.5	52.5
Core agent
PI	21.3	17.5
NN	72.4	65.0
INI	6.3	17.5
Number of pills
1	55.0	67.5
2	36.3	28.8
3	8.8	3.8

Variable (continuous; median and IQR)	Early switch	Late switch
Age (years)	51 (43–56)	49 (43–56)
Time on cART (years)	10 (6–19)	11 (5–17)
Time on current cART (months)	39 (16–74)	22 (10–56)
Last VL > 50 copies/ml (years)	7 (3–12)	7 (3–11)
Number of ART regimens	3 (1–5)	3 (1–4)
CD4 baseline (cells/mcL)	713 (532–883)	829 (582–1094)
CD8 baseline (cells/mcL)	840 (558–1110)	909 (740–1190)

At week 48, 70 (87.5%) of participants in the early switch group and 76 (94.8%) in the late switch group maintained virological suppression (<50 HIV-RNA copies per mL; Figure 2).

Figure 2.

Virological outcome and FDA snapshot algorithm. In the uncontrolled phase of the graph, results are those obtained after 48 weeks in the early switch group and 24 weeks in the late switch group of RPV/DRV/cobi therapy.

Interestingly, virological failure (≥50 HIV-RNA copies per mL) was not seen in any patient of the early switch group and in 2 subjects in the late switch group that also met the criteria for confirmed virological withdrawal. None of them, however, had any treatment emergent resistance-associated mutation.

More in detail, these two individuals were followed at the same center. Their baseline therapy was FTC/TAF + DRC/cobicistat in both cases and they were both randomized in the late switch group. During the first controlled phase, both of them presented a viral blip to 81 and 82 copies/ml, respectively. The first patients presented a second measurable viral load 12 weeks after shifting to the dual therapy (263 copies/ml) and maintained an HIV-RNA level of 150 copies at retest. The genotype was performed on this second sample but turned out negative for resistance conferring mutations. In the second case, the first measure of incremented HIV-RNA was at week 24 after switch (1024 copies/ml). The retest was performed 15 days later and, in this case, the viral load was 150 copies/ml. Genotype testing did not show any resistance conferring mutation. Both subjects were withdrawn from the study and, at the caring doctor discretion, put on a three-drug regimen with subsequent re-suppression of viral load. In both cases, there were indications of problematic adherence. No other patient during the whole follow-up period presented any virological blip.

The median change in CD4 cell count from baseline to week 48 was 36 (IQR –76 to 85) cells per µL in the early switch group. In the late switch group, the median change from the late switch baseline to week 48 was –24 (IQR –93 to 100) cells per µL. The same figures for CD8 cell count were −1 (IQR –107 to 88) and −28 (IQR –94 to 175) cells per µL (Table 2).

Table 2.

Variation over time of immunological markers and lipids. Intercurrent time is 48 weeks for the early switch group and 24 weeks for the late switch group. Data are medians and interquartile range.

	Early switch			Late switch
Variable	Baseline	Week 48	P	Baseline	Week 48	P
CD4 (cells/mcL)	713 (532–883)	749 (522–899)	0.796	778 (599–965)	754 (573–971)	0.310
CD((cells/mcL)	840 (558–1110)	830 (582–1116)	0.726	901 (663–1261)	873 (635–1083	0.549
T-C (mg/dl)	200 (180–219)	208 (182–244)	0.051	188 (171–207)	210 (181–243)	<0.001
HDL-C (mg/dl)	48 (40–55)	48 (39–53)	0.320	46 (38–58)	46 (40–56)	0.783
LDL-C (mg/dl)	125 (100–147)	135 (107–167)	0.002	125 (108–147)	1.39 (117–166)	<0.001
Triglycerides (mg/dl)	126 (94–171)	156 (95–216)	0.004	125 (88–184)	164 (125–209)	0.001

In the early switch group, at week 48, we noted an increment of bone stiffness from 83.9 g/cm² (IQR 74.5–99.8, baseline) to 86.0 g/cm² (IQR 75.8–99.8) and the change was significant from week 24 to week 48 (p = 0.017). In the late switch group, bone stiffness incremented from 85.4 g/cm² (IQR 73.8–98.2) at late switch baseline, to 87.1 g/cm² (IQR 73.6–100.5) at week 48 (p = 0.894) (Figure 3).

Figure 3.

Bone stiffness variation (median values).

As far as changes in serum lipids are concerned, in both the early switch or late switch groups, we observed a slight increment of median values from baseline or from the late switch baseline to week 48 often statistically significant but apparently with little or no clinically relevant meaning (Table 2). Interestingly, when analyzed accordingly to the baseline pre-switch backbone of ART, increments were statistically significant for total cholesterol (p = 0.015 early switch group; p < 0.001 late switch group), LDL cholesterol (p < 0.001 in both groups), and triglycerides (p = 0.005 early switch group; p = 0.001 late switch group) only when the withdrawn backbone included tenofovir disoproxil fumarate. Finally, we did not observe any variation in body weight that changed from 69.5 kg (IQR 62–80) to 69.0 kg (IQR 62–80) in the early switch group and from 73.0 kg (IQR 68–84) to 73.0 kg (IQR 68–84) in the late switch group.

Discussion

The results of 48-week analysis of the PROBE 2 study show that the high prevalence of virological suppression in patients taking RPV+DRV/c at week 24 was maintained throughout the study period. Additionally, the proportion of patients in the late switch group reproduces the clinical efficacy described for this two-drug regimen at 24 weeks in the early switch group [8] (Figure 1). Together, these results confirm the efficacy of RPV+DRV/c in virologically suppressed adults who switched from a standard three-drug regimen.

This analysis after 48 weeks of treatment did not reveal any safety concerns related to longer exposure to the combination of RPV+DRV/c as only patients stopped therapy because of an adverse event in the early switch group.

At screening, 47.5% of participants in the early switch group and 52.5% in the late switch group were taking tenofovir disoproxil fumarate, which has been associated with negative effects on bone mass and bone calcium content [9].Switching to RPV+DRV/c induced an improvement of the ultrasound measured bone stiffness that progressed over time. These results were clinically significant for several patients that returned to bone stiffness values compatible with their age. Overall, obtaining an improvement on a parameter linked to age and therefore worsening over time seems a result on line with similar outcomes observed with ARV therapies not including a NRTI.

On the other hand, from the metabolic point of view, switching to RPV+DRV/c induced a slight increment of total cholesterol, LDL cholesterol, and triglycerides levels with stable levels of HDL cholesterol. These limited median increments are of small or no clinical relevance and from a statistical point of view are significant only in those subjects that stopped taking tenofovir disoproxil fumarate. It is, therefore, possible that these changes are more likely related to the absence of the statin-like effect of tenofovir disoproxil fumarate than to a direct effect of the RPV+DRV/c combination [10].

Finally, in our patients we did not observe any change of body-weight, a common alteration several times linked to ARV therapies [11,12].

Overall, these results indicate the possible indications of this regimen. As other dual regimens currently available, this dual therapy is not indicated for PLWH with a concomitant HBV infection, nor for women who are pregnant or wishing to conceive. Further, before using this ARV combination, one should evaluate the risk of drug-to-drug interactions either with the rilpivirine component or with the booster. On the other hand, both drugs of this combination were not associated with weight gain that, conversely, has been documented in patients taking other drugs commonly present in dual combinations [11]. Finally, the high genetic barrier of the combination, documented also by our results, may forgive errors connected to lower adherence.

Limitations of PROBE 2 study include the absence of a long-term follow-up that was not planned when the study was designed. We also acknowledge that the open-label design could have caused bias in both participants and study investigators affecting reporting of adverse events. However, a double-blind, double-dummy study design was not feasible for logistic and relevant study medication adherence reasons.

Another limitation of this study, being conducted solely in Italy, is that the demographics of included participants may not reflect those of the global population living with HIV. Nevertheless, the study recruited about 20% of women mimicking the proportion of the overall Italian epidemic and about 50% of people aged 50 years or older, thus reflecting the evolution of most Western World cohorts.

The data we report here show that the combination of rilpivirine plus darunavir/cobicistat maintained a steady virological suppression, was associated with a very low incidence of virological failure, and was not associated with any new safety concerns in adults with HIV who had previously received a standard triple drug regimen. Our data suggest no added risk of emergent resistance after switching to this two-drug regimen, which provides a nucleoside reverse transcriptase inhibitor-sparing and integrase inhibitor-sparing alternative to three-drug regimens and reduces total drug exposure.

Footnotes

Author note

Presented at the 12^th ICAR Conference, 12–16/OCT/2020, web-based.

Authors’ contribution

Maggiolo F: PI, protocol ideation, statistical analysis, and manuscript writing.

Gianotti N: manuscript discussion and revision.

Comi L: database management, manuscript discussion, and revision.

Di Filippo E: database management, manuscript discussion, and revision.

Fumagalli L: database management.

Nozza S: database management.

Galli L: manuscript discussion and revision.

Valenti D: database management.

Rizzi M: manuscript discussion and revision.

Castagna A: PI, manuscript discussion, and revision,

Disclosure statement

F.M. has received honoraria and consulting fees from Gilead Sciences, Merck Sharp & Dohme, Janssen, and ViiV Healthcare. N.G. and A.C. have received consultancy payments and speaking fee from Bristol–Myers Squibb, Gilead, ViiV Healthcare, Merck Sharp Dohme, and Janssen. Other Authors no disclosure

Funding

The trial was partially funded by an unrestricted research grant by Janssen. The funding source had no role in study design; in the collection, analysis, and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.

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