Background

A critical treatment gap exists in SLE management: hydroxychloroquine (~$6/month) serves as the universal backbone therapy, but the next escalation step jumps to expensive biologics (belimumab, anifrolumab) costing thousands per month — largely inaccessible in low- and middle-income countries. An affordable intermediate option targeting the underlying metabolic dysfunction in lupus T-cells is urgently needed.

Hypothesis

In SLE patients with incomplete disease control on hydroxychloroquine, adding low-dose sirolimus (1–2 mg/day) plus metformin (500–1000 mg/day) will achieve superior restoration of T-cell metabolic homeostasis — measured by normalization of mitochondrial membrane potential and reversal of the Th17/Treg ratio — compared to hydroxychloroquine monotherapy alone.

Mechanistic Rationale

Lupus T-cells exhibit constitutive mTORC1 hyperactivation, driving HRES-1/Rab4 GTPase overexpression, TCRζ chain loss, and enhanced calcium signalling. Sirolimus directly reverses mTOR hyperactivity and normalizes downstream S6K1/4E-BP1 phosphorylation in lupus T-cells. Metformin inhibits mitochondrial complex I, activates AMPK, and suppresses mTOR through a complementary pathway — creating convergent metabolic reprogramming. Proof-of-concept from oncology shows that sirolimus + metformin combination in CAR-T cells induces AMPK activation, PGC-1α induction, and enhanced mitochondrial spare respiratory capacity, suggesting synergistic effects translatable to lupus T-cell biology.

Novelty

No clinical trial has tested the triple combination. A Phase 1 study has assessed sirolimus + hydroxychloroquine, and metformin is being evaluated separately as add-on therapy with promising retrospective data (reduced lupus nephritis and cardiovascular events). The triple combination targeting the mTOR-autophagy-mitochondrial axis simultaneously is untested — representing a critical research gap.

Proposed Study Design

Randomized Phase II trial: SLE patients (SLEDAI ≥4 despite ≥3 months HCQ 200–400mg/day) randomized 1:1 to HCQ alone vs HCQ + sirolimus (1mg/day, trough 3–8 ng/mL) + metformin (500mg BID). Primary endpoint: proportion achieving T-cell mitochondrial membrane potential normalization at 24 weeks (flow cytometry, TMRM staining). Secondary endpoints: Th17/Treg reversal, SLEDAI-2K reduction ≥4, glucocorticoid-sparing, safety.

Clinical Significance

All three drugs are generic and affordable. If effective, this combination could serve as a cost-accessible escalation strategy between HCQ and biologics — particularly meaningful for the 80%+ of SLE patients in LMIC settings.

Grounded via AUBRAI. Key references: NCT04582136, NCT01687179, PMC2676112, PMC3131182