The Paradoxical Effect of PARP Inhibitor BGP-15 on Irinotecan-Induced Cachexia and Skeletal Muscle Dysfunction

Abstract

Chemotherapy-induced muscle wasting and dysfunction is a contributing factor to cachexia alongside cancer and increases the risk of morbidity and mortality. Here, we investigate the effects of the chemotherapeutic agent irinotecan (IRI) on skeletal muscle mass and function and whether BGP-15 (a poly-(ADP-ribose) polymerase-1 (PARP-1) inhibitor and heat shock protein co-inducer) adjuvant therapy could protect against IRI-induced skeletal myopathy. Healthy 6-week-old male Balb/C mice (n = 24; 8/group) were treated with six intraperitoneal injections of either vehicle, IRI (30 mg/kg) or BGP-15 adjuvant therapy (IRI+BGP; 15 mg/kg) over two weeks. IRI reduced lean and tibialis anterior mass, which were attenuated by IRI+BGP treatment. Remarkably, IRI reduced muscle protein synthesis, while IRI+BGP reduced protein synthesis further. These changes occurred in the absence of a change in crude markers of mammalian/mechanistic target of rapamycin (mTOR) Complex 1 (mTORC1) signaling and protein degradation. Interestingly, the cytoskeletal protein dystrophin was reduced in both IRI- and IRI+BGP-treated mice, while IRI+BGP treatment also decreased β-dystroglycan, suggesting significant remodeling of the cytoskeleton. IRI reduced absolute force production of the soleus and extensor digitorum longus (EDL) muscles, while IRI+BGP rescued absolute force production of the soleus and strongly trended to rescue force output of the EDL (p = 0.06), which was associated with improvements in mass. During the fatiguing stimulation, IRI+BGP-treated EDL muscles were somewhat susceptible to rupture at the musculotendinous junction, likely due to BGP-15’s capacity to maintain the rate of force development within a weakened environment characterized by significant structural remodeling. Our paradoxical data highlight that BGP-15 has some therapeutic advantage by attenuating IRI-induced skeletal myopathy; however, its effects on the remodeling of the cytoskeleton and extracellular matrix, which appear to make fast-twitch muscles more prone to tearing during contraction, could suggest the induction of muscular dystrophy and, thus, require further characterization.

Metronomic 5-Fluorouracil Delivery Primes Skeletal Muscle for Myopathy but Does Not Cause Cachexia

“…on day 1, 3 5, 8, 10 and 12), resulting in a cumulative dose of 138 mg/kg and 90 mg/kg, of 5FU and BGP-15, respectively. The dosage and frequency of 5FU administration, with and without BGP-15, was based on previous published studies by us and our collaborators [12,31]. Animals were weighed prior to the commencement of treatment (Pre), on each day of treatment and at the experimental endpoint (Post).…”

“…Ex vivo evaluation of skeletal muscle contractile properties were performed as previously described by us [12,33], using the predominantly fast-twitch muscle, EDL and the predominantly slow-twitch muscle, SOL. Briefly, muscles were tied with 4.0 surgical silk thread, dissected from the hindlimb and attached to a transducer in individual organ baths of a Myodynamics Muscle Strip Myograph System (DMT, Denmark).…”

“…All histological experiments were completed as previously described [12,29]. To determine whether 5FU had atrophic effects on skeletal muscle and subsequently, whether BGP-15 co-therapy could rescue any atrophy, we histologically assessed TA muscles which were cryopreserved in optimal cutting temperature compound (Sakura Finetek, USA).…”

“…Western blotting was utilised to explore the effect of 5FU treatment and BGP-15 cotherapy on molecular signalling pathways surrounding cell stress, mitochondrial biogenesis and cytoskeletal structural proteins. All western blotting protocols were completed as previously described [12]. Frozen TA muscles were homogenized using an Omni Tissue Homogeniser (TH220, Omni International, USA) for 20 s in ice-cold Western Immunoprecipitation Kinase (WIK) buffer (40mM Tris, pH 7.5; 1mM EDTA; 5mM EGTA; 0.5% TritonX-100; 25mM β-glycerophosphate; 25mM NaF; 1mM Na3VO4; 10 g/ml leupeptin; and 1mM PMSF).…”

“…The FOLFIRI regimen also reduces mitochondrial content, which is associated with abnormalities in muscle morphology at the level of the sarcomere [11,21]. This was of interest to our group since we have recently shown that the chemotherapeutic agent, IRI, compromised cytoskeletal stability through reducing dystrophin protein expression [12]. While the mechanism underlying the effect of chemotherapy on skeletal muscle cytoskeletal composition is still undefined, it may be an event related to chemotherapy-induced NF-κB activation [15], suggesting that NF-κB activity plays a role in the decay of structural integrity of muscles [22].…”