PIK3CA-Related Disorders: From Disease Mechanism to Evidence-Based Treatments

Recent advances in genetic sequencing are transforming our approach to rare-disease care. Initially identified in cancer, gain-of-function mutations of the PIK3CA gene are also detected in malformation mosaic diseases categorized as PIK3CA-related disorders (PRDs). Over the past decade, new approaches have enabled researchers to elucidate the pathophysiology of PRDs and uncover novel therapeutic options. In just a few years, owing to vigorous global research efforts, PRDs have been transformed from incurable diseases to chronic disorders accessible to targeted therapy. However, new challenges for both medical practitioners and researchers have emerged. Areas of uncertainty remain in our comprehension of PRDs, especially regarding the relationship between genotype and phenotype, the mechanisms underlying mosaicism, and the processes involved in intercellular communication. As the clinical and biological landscape of PRDs is constantly evolving, this review aims to summarize current knowledge regarding PIK3CA and its role in nonmalignant human disease, from molecular mechanisms to evidence-based treatments. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 25 is August 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

A homoeostatic switch causing glycerol-3-phosphate and phosphoethanolamine accumulation triggers senescence by rewiring lipid metabolism

Cellular senescence affects many physiological and pathological processes and is characterized by durable cell cycle arrest, an inflammatory secretory phenotype and metabolic reprogramming. Here, by using dynamic transcriptome and metabolome profiling in human fibroblasts with different subtypes of senescence, we show that a homoeostatic switch that results in glycerol-3-phosphate (G3P) and phosphoethanolamine (pEtN) accumulation links lipid metabolism to the senescence gene expression programme. Mechanistically, p53-dependent glycerol kinase activation and post-translational inactivation of phosphate cytidylyltransferase 2, ethanolamine regulate this metabolic switch, which promotes triglyceride accumulation in lipid droplets and induces the senescence gene expression programme. Conversely, G3P phosphatase and ethanolamine-phosphate phospho-lyase-based scavenging of G3P and pEtN acts in a senomorphic way by reducing G3P and pEtN accumulation. Collectively, our study ties G3P and pEtN accumulation to controlling lipid droplet biogenesis and phospholipid flux in senescent cells, providing a potential therapeutic avenue for targeting senescence and related pathophysiology.

IL-22 is secreted by proximal tubule cells and regulates DNA damage response and cell death in acute kidney injury

Acute kidney injury (AKI) affects over 13 million people worldwide annually and is associated with a 4-fold increase in mortality. Our lab and others have shown that DNA damage response (DDR) governs the outcome of AKI in a bimodal manner. Activation of DDR sensor kinases protects against AKI, while hyperactivation of DDR effector proteins, such as p53, induces cell death and worsens AKI. The factors that trigger DDR to switch from pro-repair to pro-cell death remain to be resolved. Here we investigated the role of interleukin 22 (IL-22), an IL-10 family member whose receptor (IL-22RA1) is expressed on proximal tubule cells (PTCs), in DDR activation and AKI. Using cisplatin and aristolochic acid (AA) induced nephropathy as models of DNA damage, we identified PTCs as a novel source of urinary IL-22. Functionally, IL-22 binding IL-22RA1 on PTCs amplified the DDR. Treating primary PTCs with IL-22 alone induced rapid activation of the DDR. The combination of IL-22 and either cisplatin- or AA-induced cell death in primary PTCs, while the same dose of cisplatin or AA alone did not. Global deletion of IL-22 protected against cisplatin- or AA-induced AKI, reduced expression of DDR components, and inhibited PTC cell death. To confirm PTC IL-22 signaling contributed to AKI, we knocked out IL-22RA1 specifically in kidney tubule cells. IL-22RA1ΔTub mice displayed reduced DDR activation, cell death, and kidney injury compared to controls. Thus, targeting IL-22 represents a novel therapeutic approach to prevent the negative consequences of the DDR activation while not interfering with repair of damaged DNA.

Alpelisib for treatment of patients with PIK3CA-related overgrowth spectrum (PROS)

PURPOSE

PIK3CA-related overgrowth spectrum (PROS) encompasses several rare conditions resulting from activating variants in PIK3CA. Alpelisib, a PI3Kα-selective inhibitor, targets the underlying etiology of PROS, offering a novel therapeutic approach to current management strategies. This study evaluated the safety and efficacy of alpelisib in pediatric and adult patients with PROS.

METHODS

EPIK-P1 (NCT04285723) was a non-interventional, retrospective chart review of 57 patients with PROS (≥2 years) treated with alpelisib through compassionate use. Patients had severe/life-threatening PROS-related conditions and confirmed PIK3CA pathogenic variant. The primary end point assessed patient response to treatment at Week 24 (6 months).

RESULTS

Twenty-four weeks (6 months) after treatment initiation, 12 of 32 (37.5%) patients with complete case records included in the analysis of the primary end point experienced a ≥20% reduction in target lesion(s) volume. Additional clinical benefit independent from lesion volume reduction was observed across the full study population. Adverse events (AEs) and treatment-related AEs were experienced by 82.5% (47/57) and 38.6% (22/57) of patients, respectively; the most common treatment-related AEs were hyperglycemia (12.3%) and aphthous ulcer (10.5%). No deaths occurred.

CONCLUSION

EPIK-P1 provides real-world evidence of alpelisib effectiveness and safety in patients with PROS and confirms PI3Kα as a valid therapeutic target for PROS symptom management.

Hemifacial myohyperplasia is due to somatic muscular PIK3CA gain-of-function mutations and responds to pharmacological inhibition

Hemifacial myohyperplasia (HFMH) is a rare cause of facial asymmetry exclusively involving facial muscles. The underlying cause and the mechanism of disease progression are unknown. Here, we identified a somatic gain-of-function mutation of PIK3CA in five pediatric patients with HFMH. To understand the physiopathology of muscle hypertrophy in this context, we created a mouse model carrying specifically a PIK3CA mutation in skeletal muscles. PIK3CA gain-of-function mutation led to striated muscle cell hypertrophy, mitochondria dysfunction, and hypoglycemia with low circulating insulin levels. Alpelisib treatment, an approved PIK3CA inhibitor, was able to prevent and reduce muscle hypertrophy in the mouse model with correction of endocrine anomalies. Based on these findings, we treated the five HFMH patients. All patients demonstrated clinical, esthetical, and radiological improvement with proof of target engagement. In conclusion, we show that HFMH is due to somatic alteration of PIK3CA and is accessible to pharmacological intervention.

Precision medicine in rare diseases: What is next?

Molecular diagnostics is a cornerstone of modern precision medicine, broadly understood as tailoring an individual's treatment, follow-up, and care based on molecular data. In rare diseases (RDs), molecular diagnoses reveal valuable information about the cause of symptoms, disease progression, familial risk, and in certain cases, unlock access to targeted therapies. Due to decreasing DNA sequencing costs, genome sequencing (GS) is emerging as the primary method for precision diagnostics in RDs. Several ongoing European initiatives for precision medicine have chosen GS as their method of choice. Recent research supports the role for GS as first-line genetic investigation in individuals with suspected RD, due to its improved diagnostic yield compared to other methods. Moreover, GS can detect a broad range of genetic aberrations including those in noncoding regions, producing comprehensive data that can be periodically reanalyzed for years to come when further evidence emerges. Indeed, targeted drug development and repurposing of medicines can be accelerated as more individuals with RDs receive a molecular diagnosis. Multidisciplinary teams in which clinical specialists collaborate with geneticists, genomics education of professionals and the public, and dialogue with patient advocacy groups are essential elements for the integration of precision medicine into clinical practice worldwide. It is also paramount that large research projects share genetic data and leverage novel technologies to fully diagnose individuals with RDs. In conclusion, GS increases diagnostic yields and is a crucial step toward precision medicine for RDs. Its clinical implementation will enable better patient management, unlock targeted therapies, and guide the development of innovative treatments.

Genome-wide association analyses define pathogenic signaling pathways and prioritize drug targets for IgA nephropathy

IgA nephropathy (IgAN) is a progressive form of kidney disease defined by glomerular deposition of IgA. Here we performed a genome-wide association study of 10,146 kidney-biopsy-diagnosed IgAN cases and 28,751 controls across 17 international cohorts. We defined 30 genome-wide significant risk loci explaining 11% of disease risk. A total of 16 loci were new, including TNFSF4/TNFSF18, REL, CD28, PF4V1, LY86, LYN, ANXA3, TNFSF8/TNFSF15, REEP3, ZMIZ1, OVOL1/RELA, ETS1, IGH, IRF8, TNFRSF13B and FCAR. The risk loci were enriched in gene orthologs causing abnormal IgA levels when genetically manipulated in mice. We also observed a positive genetic correlation between IgAN and serum IgA levels. High polygenic score for IgAN was associated with earlier onset of kidney failure. In a comprehensive functional annotation analysis of candidate causal genes, we observed convergence of biological candidates on a common set of inflammatory signaling pathways and cytokine ligand-receptor pairs, prioritizing potential new drug targets.

IL-22 promotes acute kidney injury through activation of the DNA damage response and cell death in proximal tubule cells

Acute kidney injury (AKI) affects over 13 million people world-wide annually and is associated with a fourfold increase in mortality. Our lab and others have shown that DNA damage response (DDR) governs the outcome of AKI in a bimodal manner. Activation of DDR sensor kinases protects against AKI, while hyperactivation of DDR effector proteins, such as p53, induces to cell death and worsens AKI. The factors that trigger the switch from pro-reparative to pro-cell death DDR remain to be resolved. Here we investigate the role of interleukin 22 (IL-22), an IL-10 family member whose receptor (IL-22RA1) is expressed on proximal tubule cells (PTCs), in DDR activation and AKI. Using cisplatin and aristolochic acid (AA) induced nephropathy as models of DNA damage, we identify PTCs as a novel source of urinary IL-22, making PTCs the only epithelial cells known to secret IL-22, to our knowledge. Functionally, IL-22 binding its receptor (IL-22RA1) on PTCs amplifies the DDR. Treating primary PTCs with IL-22 alone induces rapid activation of the DDR in vitro. The combination of IL-22 + cisplatin or AA treatment on primary PTCs induces cell death, while the same dose of cisplatin or AA alone does not. Global deletion of IL-22 protects against cisplatin or AA induced AKI. IL-22 deletion reduces expression of components of the DDR and inhibits PTC cell death. To confirm PTC IL-22 signaling contributes to AKI, we knocked out IL-22RA1 in renal epithelial cells by crossing IL-22RA1floxed mice with Six2-Cre mice. IL-22RA1 KO reduced DDR activation, cell death, and kidney injury. These data demonstrate that IL-22 promotes DDR activation in PTCs, switching pro-recovery DDR responses to a pro-cell death response and worsening AKI. Targeting IL-22 represents a novel therapeutic approach to prevent the negative consequences of the DDR activation while not interfering with the processes necessary for repair of damaged DNA.

PIK3CA gain-of-function mutation in adipose tissue induces metabolic reprogramming with Warburg-like effect and severe endocrine disruption

PIK3CA-related overgrowth syndrome (PROS) is a genetic disorder caused by somatic mosaic gain-of-function mutations of PIK3CA. Clinical presentation of patients is diverse and associated with endocrine disruption. Adipose tissue is frequently involved, but its role in disease development and progression has not been elucidated. Here, we created a mouse model of PIK3CA-related adipose tissue overgrowth that recapitulates patient phenotype. We demonstrate that PIK3CA mutation leads to GLUT4 membrane accumulation with a negative feedback loop on insulin secretion, a burst of liver IGFBP1 synthesis with IGF-1 sequestration, and low circulating levels. Mouse phenotype was mainly driven through AKT2. We also observed that PIK3CA mutation induces metabolic reprogramming with Warburg-like effect and protein and lipid synthesis, hallmarks of cancer cells, in vitro, in vivo, and in patients. We lastly show that alpelisib is efficient at preventing and improving PIK3CA-adipose tissue overgrowth and reversing metabolomic anomalies in both animal models and patients.

Renal and vascular outcomes in patients with isolated antiphospholipid syndrome nephropathy

BACKGROUND

Antiphospholipid syndrome (APS) nephropathy (APSN) is a rare pattern with specific features resulting from microvascular lesions. The prognosis of APSN, outside of lupus nephritis, is unknown. The aim of this study was to describe the renal, vascular and overall outcomes of patients with APSN.

METHODS

Retrospective multicenter study of patients with antiphospholipid antibodies (aPL) associated with histological APSN lesions and no other nephropathy, identified through a national call for medical records. End-stage renal disease (ESRD)-free survival, thrombosis recurrence-free survival and overall survival were assessed.

RESULTS

Thirty patients were included (19 women) with a median age of 40 years (34-52 years). Fifteen patients had APS, 26/28 had lupus anticoagulant, and 15/26 had triple positivity for aPL. Median eGFR was 50 (31-60) mL/min/1.73 m². Glomerular thrombotic microangiopathy was found in 12/24 cases, fibrous intimal hyperplasia in 12/22 cases and focal cortical atrophy in 17/29 cases. Nineteen patients had moderate to severe interstitial fibrosis (>25%). Six patients developed ESRD at a median follow-up of 6.2 (1.8-9.1) years. The ESRD-free survival rates at 5 and 10 years were 80.0% (95% CI 57.6%-91.4%) and 72.7% (95% CI, 46.9%-87.4%) respectively. None of the histological factors considered was significantly associated with a decrease in eGFR at 12 months. Thrombosis recurrence-free survival was 77.8% (95% CI 48.2%-91.6%) at 10 years. Overall survival was 94% at 10 years (95% CI 65.0%-99.2%).

CONCLUSIONS

The renal prognosis of isolated APSN is poor. The severe fibrotic lesions observed are suggestive of late diagnosis.

Alpelisib (ALP), a breast cancer therapy, for PIK3CA-related overgrowth spectrum (PROS): A real-world data approach to a rare disease indication

e18694

Background: PIK3CA mutations seen in cancer also drive other disease, exciting interest in repurposing oncology therapies for non-oncology indications. ALP is a PI3Kα inhibitor approved for HR+, HER2– ABC with fulvestrant. Clinical benefit of ALP in PROS, a group of rare phenotypically varied disorders driven by mutations in PIK3CA, was found in 19 pts (Venot, 2018). EPIK-P1 (NCT04285723) collected real-world data (RWD) to confirm ALP’s efficacy and safety in PROS. In the primary analysis of the primary endpoint, 12/32 pts (37.5%; 95% CI, 21.1-56.3%) with complete cases responded (≥20% reduction in the sum of target lesion volume from index/treatment [tx] start). Adverse events (AEs) and tx-related AEs were experienced by 82.5% (n = 47) and 38.6% (n = 22) of pts, respectively. The most common tx-related AE was hyperglycemia (n = 7, 12.3%). No deaths were reported (Canaud, ESMO 2021 LBA23). Methods: EPIK-P1 retrospectively abstracted data from the medical charts of pts aged ≥2 y with PROS experiencing severe/life-threatening conditions receiving ALP under compassionate use. Secondary endpoints evaluated safety and clinical benefit. Results: 57 pts were enrolled and followed for a median of 18.1 mo. No pt in the primary analysis (complete cases, n = 32) had progressive disease (PD) at wk 24; 1 pt discontinued ALP prior to wk 24 and considered a nonresponder. Of the 12 responders, median duration of response (time from first documented response to first documented PD or death due to any cause) was not estimable. Median time to censoring (date of last adequate lesion assessment) was 63.3 wk (̃14.6 mo; range, 1 d-186.7 wk); 2 pts had no further imaging assessments, 10 pts did not experience an event and tx was ongoing at data cutoff. Time to censoring was > 6 mo in 7 pts and > 12 mo in 6 pts. 11/20 nonresponders (55.0%) had target lesion volume reduction ranging from 0.7 to 19.6%. No pt required rescue surgery between index and wk 24. At index all pts reported ≥1 PROS-related symptom (eg, fatigue, pain). At wk 24, 82.5% (n = 47) reported symptom improvement regardless of primary analysis response status (responders, 10/12, 83.3%; nonresponders, 16/20, 80.0%). Median daily dose was 50 mg for pediatrics and 250 mg for adults. Dose reductions or interruptions were experienced by 15.8% of pts (n = 9); AEs led to dose reductions and interruptions in 3.5% (n = 2) and 10.5% (n = 6) of pts, respectively. 52 pts (91.2%) remained on tx at data cutoff; among 5 pts (8.8%) who discontinued, pt decision was the leading cause. Conclusions: RWD from EPIK-P1 demonstrate alpelisib as well tolerated, providing clinical benefit to pts with PROS regardless of response status in the primary analysis of the primary endpoint. Continued RWD collection complements planned prospective, randomized, placebo-controlled studies, facilitating access to alpelisib as an emerging pharmacologic option for PROS. Clinical trial information: NCT04285723.

Treatment of two infants with PIK3CA-related overgrowth spectrum by alpelisib

PIK3CA-related overgrowth spectrum (PROS) includes rare genetic conditions due to gain-of-function mutations in the PIK3CA gene. There is no approved medical therapy for patients with PROS, and alpelisib, an approved PIK3CA inhibitor in oncology, showed promising results in preclinical models and in patients. Here, we report for the first time the outcome of two infants with PROS having life-threatening conditions treated with alpelisib (25 mg) and monitored with pharmacokinetics. Patient 1 was an 8-mo-old girl with voluminous vascular malformation. Patient 2 was a 9-mo-old boy presenting with asymmetrical body overgrowth and right hemimegalencephaly with West syndrome. After 12 mo of follow-up, alpelisib treatment was associated with improvement in signs and symptoms, morphological lesions and vascular anomalies in the two patients. No adverse events were reported during the study. In this case series, pharmacological inhibition of PIK3CA with low-dose alpelisib was feasible and associated with clinical improvements, including a smaller size of associated complex tissue malformations and good tolerability.

Treatment strategies for mosaic overgrowth syndromes of the PI3K-AKT-mTOR pathway

INTRODUCTION OR BACKGROUND

Mosaic overgrowth syndromes (OS) are a proteiform ensemble of rare diseases displaying asymmetric overgrowth involving any tissue type, with degrees of severity ranging from isolated malformation to life-threatening conditions such as pulmonary embolism. Despite discordant clinical presentations, all those syndromes share common genetic anomalies: somatic mutations of genes involved in cell growth and proliferation. The PI3K-AKT-mTOR signaling pathway is one of the most prominent regulators of cell homeostasis, and somatic oncogenic mutations affecting this pathway are responsible for mosaic OS. This review aims to describe the clinical and molecular characteristics of the main OS involving the PI3K-AKT-mTOR pathway, along with the treatments available or under development.

SOURCES OF DATA

This review summarizes available data regarding OS in scientific articles published in peer-reviewed journals.

AREAS OF AGREEMENT

OS care requires a multidisciplinary approach relying on clinical and radiological follow-up along with symptomatic treatment. However, no specific treatment has yet shown efficacy in randomized control trials.

AREAS OF CONTROVERSY

Clinical classifications of OS led to frequent misdiagnosis. Moreover, targeted therapies directed at causal mutated proteins are developing in OSs through cancer drugs repositioning, but the evidence of efficacy and tolerance is still lacking for most of them.

GROWING POINTS

The genetic landscape of OS is constantly widening and molecular classifications tend to increase the accuracy of diagnosis, opening opportunities for targeted therapies.

AREAS TIMELY FOR DEVELOPING RESEARCH

OS are a dynamic, expanding field of research. Studies focusing on the identification of genetic anomalies and their pharmacological inhibition are needed.

Alpelisib administration reduced lymphatic malformations in a mouse model and in patients

[Figure: see text].

Reappraisal of Renal Arteritis in ANCA-associated Vasculitis: Clinical Characteristics, Pathology, and Outcome

BACKGROUND

Renal involvement in ANCA-associated vasculitis (AAV) is associated with poor outcomes. The clinical significance of arteritis of the small kidney arteries has not been evaluated in detail.

METHODS

In a multicenter cohort of patients with AAV and renal involvement, we sought to describe the clinicopathologic characteristics of patients with AAV who had renal arteritis at diagnosis, and to retrospectively analyze their prognostic value.

RESULTS

We included 251 patients diagnosed with AAV and renal involvement between 2000 and 2019, including 34 patients (13.5%) with arteritis. Patients with AAV-associated arteritis were older, and had a more pronounced inflammatory syndrome compared with patients without arteritis; they also had significantly lower renal survival (P=0.01). In multivariable analysis, the ANCA renal risk score, age at diagnosis, history of diabetes mellitus, and arteritis on index kidney biopsy were independently associated with ESKD. The addition of the arteritis status significantly improved the discrimination of the ANCA renal risk score, with a concordance index (C-index) of 0.77 for the ANCA renal risk score alone, versus a C-index of 0.80 for the ANCA renal risk score plus arteritis status (P=0.008); ESKD-free survival was significantly worse for patients with an arteritis involving small arteries who were classified as having low or moderate risk, according to the ANCA renal risk score. In two external validation cohorts, we confirmed the incidence and phenotype of this AAV subtype.

CONCLUSIONS

Our findings suggest AAV with renal arteritis represents a different subtype of AAV with specific clinical and histologic characteristics. The prognostic contribution of the arteritis status remains to be prospectively confirmed.

REST and Stress Resistance in the Aging Kidney

BACKGROUND

CKD is associated with the loss of functional nephr ons, leading to increased mechanical and metabolic stress in the remaining cells, particularly for cells constituting the filtration barrier, such as podocytes. The failure of podocytes to mount an adequate stress response can lead to further nephron loss and disease progression. However, the mechanisms that regulate this degenerative process in the kidney are unknown.

METHODS

We combined in vitro, in vivo, and organ-on-chip approaches to identify the RE1-silencing transcription factor (REST), a repressor of neuronal genes during embryonic development, as a central regulator of podocyte adaptation to injury and aging.

RESULTS

Mice with a specific deletion of REST in podocytes exhibit albuminuria, podocyte apoptosis, and glomerulosclerosis during aging, and exhibit increased vulnerability to renal injury. This phenotype is mediated, in part, by the effects of REST on the podocyte cytoskeleton that promote resistance to mechanical stressors and augment podocyte survival. Finally, REST expression is upregulated in human podocytes during aging, consistent with a conserved mechanism of stress resistance.

CONCLUSIONS

These results suggest REST protects the kidney from injury and degeneration during aging, with potentially important therapeutic implications.

A review of mechanisms of disease across PIK3CA-related disorders with vascular manifestations

BACKGROUND

PIK3CA-related disorders include vascular malformations and overgrowth of various tissues that are caused by postzygotic, somatic variants in the gene encoding phosphatidylinositol-3-kinase (PI3K) catalytic subunit alpha. These mutations result in activation of the PI3K/AKT/mTOR signaling pathway. The goals of this review are to provide education on the underlying mechanism of disease for this group of rare conditions and to summarize recent advancements in the understanding of, as well as current and emerging treatment options for PIK3CA-related disorders.

MAIN BODY

PIK3CA-related disorders include PIK3CA-related overgrowth spectrum (PROS), PIK3CA-related vascular malformations, and PIK3CA-related nonvascular lesions. Somatic activating mutations (predominantly in hotspots in the helical and kinase domains of PIK3CA, but also in other domains), lead to hyperactivation of the PI3K signaling pathway, which results in abnormal tissue growth. Diagnosis is complicated by the variability and overlap in phenotypes associated with PIK3CA-related disorders and should be performed by clinicians with the required expertise along with coordinated care from a multidisciplinary team. Although tissue mosaicism presents challenges for confirmation of PIK3CA mutations, next-generation sequencing and tissue selection have improved detection. Clinical improvement, radiological response, and patient-reported outcomes are typically used to assess treatment response in clinical studies of patients with PIK3CA-related disorders, but objective assessment of treatment response is difficult using imaging (due to the heterogeneous nature of these disorders, superimposed upon patient growth and development). Despite their limitations, patient-reported outcome tools may be best suited to gauge patient improvement. New therapeutic options are needed to provide an alternative or supplement to standard approaches such as surgery and sclerotherapy. Currently, there are no systemic agents that have regulatory approval for these disorders, but the mTOR inhibitor sirolimus has been used for several years in clinical trials and off label to address symptoms. There are also other agents under investigation for PIK3CA-related disorders that act as inhibitors to target different components of the PI3K signaling pathway including AKT (miransertib) and PI3K alpha (alpelisib).

CONCLUSION

Management of patients with PIK3CA-related disorders requires a multidisciplinary approach. Further results from ongoing clinical studies of agents targeting the PI3K pathway are highly anticipated.

PIK3CA-related overgrowth spectrum: animal model and drug discovery

This review recapitulates the recent knowledge accumulation on overgrowth syndrome related to gain of function of the phosphoinositide3 kinase (PI3K)-alpha. These disorders, known as PIK3CA related overgrowth syndromes (PROS) are caused by somatic PIK3CA mutation occurring during embryogenesis. We summarize here the currently available animal models and new treatments undergoing development.

EPIK-P2: A prospective phase 2, double-blind, randomized, placebo-controlled study of alpelisib in pediatric and adult patients (Pts) with PIK3CA-related overgrowth spectrum (PROS)

TPS3160

Background: Somatic gain-of-function mutations in the PIK3CA gene, encoding the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) catalytic α subunit (p110α), can result in PI3K pathway hyperactivation. PROS is an umbrella term for rare, phenotypically varied, but overlapping features driven by PIK3CA mutations. Disease onset is often congenital or in early childhood; presentation ranges widely from localized overgrowth to pleiotropic, severe overgrowth. Complications depend on anatomical site and extent of overgrowth. Management of PROS currently involves symptomatic treatment of its manifestations; an unmet need exists for targeted, systemic therapies. Alpelisib, a PI3Kα inhibitor, has demonstrated encouraging clinical observations and a promising safety profile; after 6 mo of treatment, pediatric and adult pts with PROS experienced improvements in symptoms without requiring surgery. A low rate of side effects was observed (Venot Q, et al. Nature. 2018;558:540-6). Methods: EPIK-P2 is a prospective, phase 2, multicenter study with an upfront 16-week, randomized, double-blind, placebo-controlled period. Key eligibility criteria include male or female ≥6 yr of age with PROS and symptomatic and/or progressive overgrowth; ≥1 PROS-related measurable lesion confirmed by a Blinded Independent Review Committee (BIRC) and documented somatic PIK3CA mutation. Pts with isolated cases of macrodactyly, epidermal nevus/nevi, or macrocephaly in absence of other PROS-related lesions; previous treatment with PI3K inhibitor(s); or debulking surgery within 3 mo are not eligible. Approximately 138 pts will be enrolled into 2 groups comprising adult (age ≥18 yr) and pediatric (ages 6-17 yr) pts. Pts will be randomized 2:1 to daily oral alpelisib or matching placebo; adults will receive 125 mg and pediatric pts 50 mg. After 16 weeks, pts randomized to placebo will switch to alpelisib in a blinded fashion; pts receiving alpelisib will continue alpelisib. Treatment will continue for up to 5 yr. The primary objective is to demonstrate the efficacy of alpelisib by the proportion of pts randomized to alpelisib with a response at Week 24 in each group. Response is defined as ≥20% volume reduction in the symptomatic target lesion(s) per BIRC. The key secondary objective is to demonstrate efficacy of alpelisib vs placebo based on the proportion of pts in each group with response at Week 16. Other secondary outcomes include safety and tolerability, duration of response, overall clinical response rates, changes in symptoms and comorbidities, patient-reported outcomes, pharmacokinetics, and healthcare utilization. An exploratory group of pts (n = 12) ages 2-5 yr will be later enrolled once a starting dose of alpelisib is confirmed in these pts. Enrollment of 150 pts is anticipated. Clinical trial information: NCT04589650.

[Segmental overgrowth syndromes and therapeutic strategies]

Overgrowth syndromes are a large group of rare disorders characterized by generalized or segmental excessive growth. Segmental overgrowth syndromes are mainly due to genetic anomalies appearing during the embryogenesis and leading to mosaicism. The numbers of patients with segmental overgrowth with an identified molecular defect has dramatically increased following the recent advances in molecular genetic using next-generation sequencing approaches. This review discusses various syndromes and pathways involved in segmental overgrowth syndromes and presents actual and future therapeutic strategies.

[Renal transplantation: Procedure and early follow-up]

More than fifty years after the success of the two first renal transplantations in Boston and in Necker hospital in Paris, renal transplantation became the treatment of choice of end stage renal failure, because it improves not only the quality of life of the patients but also their long-term survival. In France, more than 3,700 kidney transplantations are performed every year and more than 40,000 patients are living with a functioning kidney allograft. This treatment of end stage renal disease requires a fine-tuned pre-transplant evaluation and a multidisciplinary post-transplant care in order to prevent, to detect and to treat comorbidities and complications of immunosuppression. The ambition of this manuscript is not to describe in an exhaustive way all the aspects of renal transplantation but starting from the experience of a team, recently published data, and national and international guidelines, to try to provide a synthetic and chronological view of the early post-transplant monitoring.

Membranous Nephropathy Posttransplantation: An Update of the Pathophysiology and Management

Membranous nephropathy (MN) is a common cause of nephrotic syndrome after transplantation and is associated with an increased risk of allograft loss. MN may occur either as a recurrent or as a de novo disease. As in native kidneys, the pathophysiology of the MN recurrence is in most cases associated with antiphospholipid A2 receptor antibodies. However, the posttransplant course has some distinct features when compared with primary MN, including a lower chance of spontaneous remission and a greater requirement for adjuvant immunosuppressive therapy to induce complete remission. Although the efficacy of rituximab in primary MN is now well established, no randomized studies have assessed its effectiveness in MN after transplant, and there are no specific recommendations for the management of these patients. This review aims to synthesize and update the pathophysiology of posttransplant MN, as well as to address unsolved issues specific to transplantation, including the prognostic value of antiphospholipid A2 receptor, the risk of living-related donation, the link between de novo MN and rejection, and different therapeutic strategies so far deployed in posttransplant MN. Lastly, we propose a management algorithm for patients with MN who are planning to receive a kidney transplant, including pretransplant considerations, posttransplant monitoring, and the clinical approach after the diagnosis of recurrence.

Cyclin G1 and TASCC regulate kidney epithelial cell G2-M arrest and fibrotic maladaptive repair

Fibrosis contributes to the progression of chronic kidney disease (CKD). Severe acute kidney injury can lead to CKD through proximal tubular cell (PTC) cycle arrest in the G₂-M phase, with secretion of profibrotic factors. Here, we show that epithelial cells in the G₂-M phase form target of rapamycin (TOR)-autophagy spatial coupling compartments (TASCCs), which promote profibrotic secretion similar to the senescence-associated secretory phenotype. Cyclin G1 (CG1), an atypical cyclin, promoted G₂-M arrest in PTCs and up-regulated TASCC formation. PTC TASCC formation was also present in humans with CKD. Prevention of TASCC formation in cultured PTCs blocked secretion of profibrotic factors. PTC-specific knockout of a key TASCC component reduced the rate of kidney fibrosis progression in mice with CKD. CG1 induction and TASCC formation also occur in liver fibrosis. Deletion of CG1 reduced G₂-M phase cells and TASCC formation in vivo. This study provides mechanistic evidence supporting how profibrotic G₂-M arrest is induced in kidney injury and how G₂-M-arrested PTCs promote fibrosis, identifying new therapeutic targets to mitigate kidney fibrosis.

Minimal change nephrotic syndrome in patients infected with human immunodeficiency virus: a retrospective study of 8 cases

Background

Human immunodeficiency virus (HIV) is associated with diverse glomerular diseases. Characteristics of minimal change nephrotic syndrome (MCNS) in this setting have been little studied, and the specific features of this uncommon association remain to be determined.

Methods

We conduct a retrospective study. Clinical, biological and pathological characteristics of patients with MCNS and HIV infection were assessed. We evaluated HIV infection by in situ hybridization and CMIP expression by immunochemistry on kidney biopsies and compared it to HIV-associated nephropathy (HIVAN) and idiopathic MCNS.

Results

Eight patients were identifies. In all but one of these cases, MCNS occurred after HIV diagnosis (mean of 9.5 years). Acute kidney injury was detected in three cases. Mean CD4⁺ lymphocyte count was 733/mm³ and three patients had a detectable HIV viral load. In situ hybridization for HIV-1 RNA detection yielded a positive signal in a few tubular cells in the renal parenchyma in two of four patients with HIV infection associated with MCNS. Podocytes of these patients presented strong positive immunostaining for CMIP (4/4). Three patients suffered steroid-dependent nephrotic syndrome, and another two patients had at least one relapse. Rituximab treatment was initiated in four cases. After a median follow-up of 20 months, all patients were in remission (complete in 5 cases).

Conclusions

In patients with MCNS occurring in a context of HIV infection, podocyte injury seems to be associated with CMIP induction rather than renal HIV infection but further studies are needed to determine the molecular link between these two conditions.

Targeted therapy in patients with PIK3CA-related overgrowth syndrome

CLOVES syndrome (congenital lipomatous overgrowth, vascular malformations, epidermal naevi, scoliosis/skeletal and spinal syndrome) is a genetic disorder that results from somatic, mosaic gain-of-function mutations of the PIK3CA gene, and belongs to the spectrum of PIK3CA-related overgrowth syndromes (PROS). This rare condition has no specific treatment and a poor survival rate. Here, we describe a postnatal mouse model of PROS/CLOVES that partially recapitulates the human disease, and demonstrate the efficacy of BYL719, an inhibitor of PIK3CA, in preventing and improving organ dysfunction. On the basis of these results, we used BYL719 to treat nineteen patients with PROS. The drug improved the disease symptoms in all patients. Previously intractable vascular tumours became smaller, congestive heart failure was improved, hemihypertrophy was reduced, and scoliosis was attenuated. The treatment was not associated with any substantial side effects. In conclusion, this study provides the first direct evidence supporting PIK3CA inhibition as a promising therapeutic strategy in patients with PROS.

Vascular Manifestations in Antiphospholipid Syndrome (APS): Is APS a Thrombophilia or a Vasculopathy?

PURPOSE OF REVIEW

Antiphospholipid antibody syndrome (APS) is characterized primarily by thrombosis and pregnancy morbidity. Chronic vascular lesions can also occur. While the underlying mechanisms of these vascular lesions are not entirely known, there have been multiple theories describing the potential process of vasculopathy in APS and the various clinical manifestations associated with it.

RECENT FINDINGS

Recently, it has been demonstrated that endothelial proliferation in kidneys can be explained by the activation of the mammalian target of rapamycin complex (mTORC) pathway by antiphospholipid antibodies (aPL). These data support the existence of an APS-related vasculopathy in different locations which can explain-in part-the different manifestations of APS. This review focuses on the various manifestations of APS as a result of APS-related vasculopathy, as well as pathophysiology, current screening, and treatment options for clinicians to be aware of.

Antiphospholipid syndrome and kidney disease

The antiphospholipid syndrome is a common autoimmune disease caused by pathogenic antiphospholipid antibodies, leading to recurrent thrombosis and/or obstetrical complications. Importantly for nephrologists, antiphospholipid antibodies are associated with various renal manifestations including large renal vessel thrombosis, renal artery stenosis, and a constellation of intrarenal lesions that has been termed antiphospholipid nephropathy. This last condition associates various degrees of acute thrombotic microangiopathy, proliferative and fibrotic lesions of the intrarenal vessels, and ischemic modifications of the renal parenchyma. The course of the disease can range from indolent nephropathy to devastating acute renal failure. The pejorative impact of antiphospholipid antibody-related renal complication is well established in the context of systemic lupus erythematous or after renal transplantation. In contrast, the exact significance of isolated antiphospholipid nephropathy remains uncertain. The evidence to guide management of the renal complications of antiphospholipid syndrome is limited. However, the recent recognition of the heterogeneous molecular mechanisms underlying the progression of intrarenal vascular lesions in antiphospholipid syndrome have opened promising tracks for patient monitoring and targeted therapeutic intervention.

The costimulatory receptor B7-1 is not induced in injured podocytes

Recent research on podocytes has proposed B7-1 as an important player in podocyte biology and as a potential new therapeutic target. B7-1 was upregulated in injured podocytes and described as a biomarker to identify patients who may benefit from abatacept, a B7-1 blocker. However, after this initial enthusiasm, several reports have not confirmed the efficiency of abatacept at inducing proteinuria remission in patients. In order to resolve these discrepancies, we explored the role of B7-1 in the injured podocyte. Both primary cultured and immortalized podocytes were exposed to lipopolysaccharides, but this failed to induce B7-1 expression at the mRNA and protein levels. Importantly, TLR-4 engagement confirmed lipopolysaccharide efficacy. We then evaluated B7-1 expression in several mouse models of podocyte injury including treatment with lipopolysaccharide or Adriamycin, a lupus prone model (NZB/W F1) and subtotal nephrectomy. Using 3 commercially available anti-B7-1 antibodies and appropriate controls, we could not find B7-1 expression in podocytes, whereas some infiltrating cells were positive. Thus, our findings do not support a role for B7-1 in podocyte biology. Hence, further studies are mandatory before treating proteinuric patients with B7-1 blockers.

B7-1 Blockade Does Not Improve Post-Transplant Nephrotic Syndrome Caused by Recurrent FSGS

FSGS is a common glomerular disorder that has a high propensity for recurrence after kidney transplant. The pathophysiology of FSGS is unknown, but podocytes seem to be the target of one or several circulating factors that lead to cytoskeleton reorganization and proteinuria. Research on podocytes has identified B7-1 as an important factor in podocyte biology and a new therapeutic target in renal disease. Indeed, in four patients with recurrent FSGS after transplant, treatment with the B7-1 blocker abatacept was associated with proteinuria remission. Here, we prospectively treated nine patients with recurrent FSGS after transplant using either abatacept or belatacept, a B7-1 blocker with higher affinity, and did not induce proteinuria remission. Furthermore, we did not detect B7-1 expression by immunofluorescence in podocytes of biopsy specimens from these or other kidney grafts or podocytes of native kidney biopsy specimens. In conclusion, B7-1 blockade did not induce FSGS remission after transplant in our study.

A circulating antibody panel for pretransplant prediction of FSGS recurrence after kidney transplantation

Recurrence of focal segmental glomerulosclerosis (rFSGS) after kidney transplantation is a cause of accelerated graft loss. To evaluate pathogenic antibodies (Abs) in rFSGS, we processed 141 serum samples from 64 patients with and without primary rFSGS and 34 non-FSGS control patients transplanted at four hospitals. We screened about 9000 antigens in pretransplant sera and selected 10 Abs targeting glomerular antigens for enzyme-linked immunosorbent assay (ELISA) validation. A panel of seven Abs (CD40, PTPRO, CGB5, FAS, P2RY11, SNRPB2, and APOL2) could predict posttransplant FSGS recurrence with 92% accuracy. Pretransplant elevation of anti-CD40 Ab alone had the best correlation (78% accuracy) with rFSGS risk after transplantation. Epitope mapping of CD40 with customized peptide arrays and rFSGS sera demonstrated altered immunogenicity of the extracellular CD40 domain in rFSGS. Immunohistochemistry of CD40 demonstrated a differential expression in FSGS compared to non-FSGS controls. Anti-CD40 Abs purified from rFSGS patients were particularly pathogenic in human podocyte cultures. Injection of anti-CD40/rFSGS Ab enhanced suPAR (soluble urokinase receptor)-mediated proteinuria in wild-type mice, yet no sensitizing effect was noted in mice deficient in CD40 or in wild-type mice that received blocking Ab to CD40. In conclusion, a panel of seven Abs can help identify primary FSGS patients at high risk of recurrence before transplantation. Intrarenal CD40 (and possibly other specific glomerular antigens) is an important contributor to FSGS disease pathogenesis. Human trials of anti-CD40 therapies are warranted to evaluate their efficacy for preventing rFSGS and improving graft survival.

Inhibition of the mTORC pathway in the antiphospholipid syndrome

BACKGROUND

Although thrombosis is considered the cardinal feature of the antiphospholipid syndrome, chronic vascular lesions are common, particularly in patients with life-threatening complications. In patients who require transplantation, vascular lesions often recur. The molecular pathways involved in the vasculopathy of the antiphospholipid syndrome are unknown, and adequate therapies are lacking.

METHODS

We used double immunostaining to evaluate pathway activation in the mammalian target of rapamycin complex (mTORC) and the nature of cell proliferation in the vessels of patients with primary or secondary antiphospholipid syndrome nephropathy. We also evaluated autopsy specimens from persons who had catastrophic antiphospholipid syndrome. The molecular pathways through which antiphospholipid antibodies modulate the mTORC pathway were evaluated in vitro, and potential pharmacologic inhibitors were also tested in vitro. Finally, we studied the effect of sirolimus in kidney-transplant recipients with the antiphospholipid syndrome.

RESULTS

The vascular endothelium of proliferating intrarenal vessels from patients with antiphospholipid syndrome nephropathy showed indications of activation of the mTORC pathway. In cultured vascular endothelial cells, IgG antibodies from patients with the antiphospholipid syndrome stimulated mTORC through the phosphatidylinositol 3-kinase (PI3K)-AKT pathway. Patients with antiphospholipid syndrome nephropathy who required transplantation and were receiving sirolimus had no recurrence of vascular lesions and had decreased vascular proliferation on biopsy as compared with patients with antiphospholipid antibodies who were not receiving sirolimus. Among 10 patients treated with sirolimus, 7 (70%) had a functioning renal allograft 144 months after transplantation versus 3 of 27 untreated patients (11%). Activation of mTORC was also found in the vessels of autopsy specimens from patients with catastrophic antiphospholipid syndrome.

CONCLUSIONS

Our results suggest that the mTORC pathway is involved in the vascular lesions associated with the antiphospholipid syndrome. (Funded by INSERM and others.).