The paradoxical role of inositol in cancer: a consequence of the metabolic state of a tumor

Investigating the mechanism of inositol against paclitaxel chemoresistance on triple-negative breast cancer by using 7T multiparametric MRI and mitochondrial changes

BACKGROUND

The emerging triple-negative breast cancer (TNBC) treatments target mitochondrial fission to combat paclitaxel (PTX) resistance. Inositol's inhibition of this process makes it a potential therapy. Multiparametric MRI provides an early and effective assessment of these innovations.

OBJECTIVE

To monitor the efficacy of Inositol on PTX-resistant TNBC mice using 7T multiparametric MRI, and to further explore the mechanism of inositol inhibiting PTX chemoresistance in combination with the morphological changes of isolated mitochondria.

MATERIALS AND METHODS

BALB/c mice aged 6-8 weeks were subcutaneously inoculated with PTX-resistant 4T1 cells and divided into three groups: PTX-treated mice (n = 24), "PTX + Inositol"-treated mice (n = 24) and untreated mice (n = 24). Six mice in each group underwent diffused weighted imaging (DWI) and diffusion kurtosis imaging (DKI) every 7 days after administration. To observe the dynamic changes of inositol within the tumor tissue post-treatment, chemical exchange saturation transfer (CEST) imaging was performed. Six mice in each group were sacrificed on day 0, 7, and 14 respectively for histopathological examination. After a 3-week scanning cycle, the remaining mice in each group were euthanized for histopathological analysis. The therapeutic response of inositol was assessed via Hematoxylin & Eosin (H&E) staining and Ki-67 immunohistochemistry. The effects of inositol on mitochondrial structure and PTX resistance were studied by Western Blot and electron microscopy. One-way analysis of variance, independent samples t-test, paired samples t-test, Kruskal-Wallis, and Spearman rank correlation were used.

RESULTS

The CEST signal of inositol in tumor tissue was significantly higher after 1 h of inositol administration than before (2.75 ± 0.71% vs. 1.80 ± 0.33%, p < 0.05). On day 21 after treatment, the tumor volume in the PTX + Ins group was smaller than that in the PTX group (191.52 ± 27.98 mm3 vs. 388.98 ± 32.62 mm3, p < 0.001). The MD, MK, and ADC values were correlated significantly with tumor cell density (MD, r = -0.872; MK, r = 0.723; ADC, r = -0.858) and Ki-67 level (MD, r = -0.975; MK, r = 0.680; ADC, r = -0.860). The p-AMPK levels of PTX + Ins group were lower than that of PTX group (0.50 ± 0.06 vs. 0.60 ± 0.05, p = 0.04), and the mitochondrial length was longer than that of PTX group (0.86 ± 0.10 vs. 0.44 ± 0.09, p < 0.001), with a significant correlation to Ki-67 levels (r = -0.853, p < 0.001).

CONCLUSION

Inositol may counteract PTX resistance in TNBC by disrupting mitochondrial fission, and DWI combined with DKI effectively tracked this effect.

Maternal Myo-Inositol Deficiency Involved Autophagy Impairment by PI3K/Akt/mTOR Signaling in Neural Tube Defects During Pregnancy

Previous studies have demonstrated that peri-conceptional inositol supplementation could effectively ameliorate the recurrence of neural tube defects (NTDs); though, the mechanism remains unclear. In the current investigation, we detected the myo-inositol (MI) levels in maternal plasma and embryonic tissues in a Chinese population with high prevalence of NTDs and found maternal MI deficiency increased NTD susceptibility in this area. Pregnant mice were randomly divided into 2 groups. The control group was treated with 0.9% saline, while the experimental group was treated with IMPase inhibitor by intraperitoneal injection on E7.5 to generate the maternal MI-deficient mouse model, followed by comprehensive phenotypic and molecular analysis at E13.5. Corresponding in vitro experiments treated neural stem cells (NSCs) for 16 h with IMPase inhibitor, MI supplementation, or specific PI3K and mTOR inhibitors to systematically investigate the downstream signaling pathways. We observed aberrant activation PI3K/Akt/mTOR signaling and reduced autophagy in a maternal MI deficiency mouse model after ruling out the genetic perturbations. Further in vitro kinase assay showed that MI negatively regulated PI3K activity, in a dose-dependent manner, which possibly due to the hydrogen bond interactions between amino acid residues in the ATP-binding site of PI3K and inositol. MI deficiency NSCs also presented PI3K/AKT/mTOR pathway activation concurrent with reduced autophagy level; MI supplementation or inhibition of the PI3K/Akt/mTOR pathway could rescue MI deficiency-induced autophagy impairment. Finally, we validated decreased autophagy levels as well as hyperactivation of the PI3K/Akt/mTOR pathway by MI deficient human NTD embryonic neural tissues. Our results suggested that maternal MI deficiency might increase susceptibility to NTDs. Low levels of MI might impair autophagy in the developing neural tube involving upregulation of PI3K/Akt/mTOR pathway.

Metabolic readouts of tumor instructed normal tissues (TINT) identify aggressive prostate cancer subgroups for tailored therapy

Introduction

Prostate cancer (PC) diagnosis relies on histopathological examination of prostate biopsies, which is restricted by insufficient sampling of all tumors present. Including samples from non-PC but tumor instructed normal tissues (TINT) may increase the diagnostic power by displaying the adaptive responses in benign tissues near tumors.

Methods

Here, we applied high-resolution magic angle spinning nuclear magnetic resonance (HR MAS NMR) to identify metabolomic biomarkers of possible diagnostic value in benign prostate tissues near low/high-grade tumors.

Results

Benign samples near high-grade tumors (B ISUP 3 + 4) exhibited altered metabolic profiles compared to those close to low-grade tumors (B ISUP 1 + 2). The levels of six metabolites differentiated between the two groups; myo-inositol, lysine, serine and combined signal of lysine/leucine/arginine were increased in benign samples near high-grade tumors (B ISUP 3 + 4) compared to near low-grade tumors (B ISUP 1 + 2), while levels of ethanolamine and lactate were decreased. Additionally, we revealed metabolic differences in non-cancer tissues as a function of their distance to the nearest tumor. Eight metabolites (glutathione, glutamate, combined signal of glutamate/glutamine - glx, glycerol, inosine, ethanolamine, serine and arginine) differentiated between benign tissue located close to the tumor (d ≤ 5 mm) compared to those far away (d ≥ 1 cm).

Conclusion

Our HR MAS NMR-based approach identified metabolic signatures in prostate biopsies that reflect the response of benign tissues to the presence of nearby located tumors in the same prostate and confirmed the power of the TINT concept for improved PC diagnostics and understanding of tumor-tissue interactions.

PI3K-Akt-SGF1-Dimm pathway mediates the nutritional regulation of silk protein synthesis in Bombyx mori

The efficient synthesis of silk protein is heavily reliant on the ingestion of massive nutrients during the peak growth phase in the silkworm. However, the molecular mechanism of nutritional regulation of silk protein synthesis remains unknown. In this study, we investigated the impact of nutrient deficiency on the synthesis of silk protein. Nutritional deficiency led to a reduction in silk yield, accompanied by decreased levels of silk proteins and fibroin heavy chain (FibH)-activating transcription factors SGF1 and Dimm. Furthermore, insulin enhanced the protein levels of SGF1 and Dimm, which can be attenuated by specific inhibitors of PI3K. Co-immunoprecipitation analysis showed that the nutrient pathway factor protein kinase B (Akt) could interact with SGF1 protein. Knockdown of Akt reduced the phosphorylation level of SGF1 and impedes its nuclear translocation. Further studies revealed that SGF1 was directly bound to Fkh site in the 22-43 region upstream of ATG of Dimm gene to activate its transcription. In conclusion, during the peak growth phase, nutrition promotes the massive synthesis of silk protein through the PI3K-Akt-SGF1-Dimm pathway. This study offers valuable insights into the efficient synthesis of silk proteins and establishes a theoretical foundation for improving silk yield.

Mechanistic insights into inositol-mediated rumen function promotion and metabolic alteration using in vitro and in vivo models

Inositol is a bioactive factor that is widely found in nature; however, there are few studies on its use in ruminant nutrition. This study investigated the effects of different inositol doses and fermentation times on rumen fermentation and microbial diversity, as well as the levels of rumen and blood metabolites in sheep. Rumen fermentation parameters, microbial diversity, and metabolites after different inositol doses were determined in vitro. According to the in vitro results, six small-tailed Han sheep fitted with permanent rumen fistulas were used in a 3 × 3 Latin square feeding experiment where inositol was injected into the rumen twice a day and rumen fluid and blood samples were collected. The in vitro results showed that inositol could increase in vitro dry matter digestibility, in vitro crude protein digestibility, NH3-N, acetic acid, propionic acid, and rumen microbial diversity and affect rumen metabolic pathways (p < 0.05). The feeding experiment results showed that inositol increased the blood concentration of high-density lipoprotein and IgG, IgM, and IL-4 levels. The rumen microbial composition was significantly affected (p < 0.05). Differential metabolites in the rumen were mainly involved in ABC transporters, biotin metabolism, and phenylalanine metabolism, whereas those in the blood were mainly involved in arginine biosynthesis and glutathione and tyrosine metabolism. In conclusion, inositol improves rumen function, affects rumen microorganisms and rumen and blood metabolites and may reduce inflammation, improving animal health.

IMPA2 promotes basal-like breast cancer aggressiveness by a MYC-mediated positive feedback loop

Basal-like breast cancer (BLBC) is the most aggressive subtype with poor prognosis; however, the mechanisms underlying aggressiveness in BLBC remain poorly understood. In this study, we showed that in contrast to other subtypes, inositol monophosphatase 2 (IMPA2) was dramatically increased in BLBC. Mechanistically, IMPA2 expression was upregulated due to copy number amplification, hypomethylation of IMPA2 promoter and MYC-mediated transcriptional activation. IMPA2 promoted MI-PI cycle and IP3 production, and IP3 then elevated intracellular Ca2+ concentration, leading to efficient activation of NFAT1. In turn, NFAT1 up-regulated MYC expression, thereby fulfilling a positive feedback loop that enhanced aggressiveness of BLBC cells. Knockdown of IMPA2 expression caused the inhibition of tumorigenicity and metastasis of BLBC cells in vitro and in vivo. Clinically, high IMPA2 expression was strongly correlated with large tumor size, high grade, metastasis and poor survival, indicating poor prognosis in breast cancer patients. These findings suggest that IMPA2-mediated MI-PI cycle allows crosstalk between metabolic and oncogenic pathways to promote BLBC progression.

Valproate regulates inositol synthesis by reducing expression of myo-inositol-3-phosphate synthase

Inositol depletion is a hypothesized mechanism of action of mood stabilization drugs used in the treatment of bipolar disorder. It was previously reported that the mood stabilizer valproate (VPA) increased phosphorylation of myo-inositol-3-phosphate synthases (MIPS), the rate limiting enzyme of inositol synthesis. Phosphosites were identified and examination of site-directed mutants suggested that phosphorylation leads to decreased enzymatic activity. In this study, we examined the extent of MIPS phosphorylation in response to VPA and used two interaction screens to identify protein kinases that interact with MIPS. Using an epitope tagged MIPS construct, we determined the fraction of phosphorylated MIPS to be very low (less than 2% of total), and we could not detect phosphorylation of untagged MIPS in response to VPA. In vitro analyses of phosphorylation revealed that putative protein kinases, PKC and CKII, have low specificity toward MIPS. These findings suggest that VPA likely depletes inositol via a mechanism other than MIPS phosphorylation. Consistent with this, mRNA levels of the MIPS-encoding gene INO1 and MIPS protein levels were significantly reduced during the mid-log growth phase in response to VPA treatment. These findings suggest that the mechanism whereby VPA causes inositol depletion is by reducing expression of the rate-limiting enzyme MIPS.

The myo-inositol biosynthesis rate-limiting enzyme ISYNA1 suppresses the stemness of ovarian cancer via Notch1 pathway

Cancer stem cells (CSCs) play a central role in ovarian cancer (OC), understanding regulatory mechanisms governing their stemness is critical. Here, we report ISYNA1, the rate-limiting enzyme in myo-inositol biosynthesis, as a suppressor of OC regulating cancer stemness. We identified ISYNA1 as a differentially expressed gene in normal ovary and ovarian cancer tissues, as well as OC cells and OCSCs. Low ISYNA1 expression correlated with poor prognosis in OC patients. In addition, ISYNA1 was negatively correlated with CSC markers, and ISYNA1-related pathways were enriched in Wnt, Notch, and other critical cancer pathways. ISYNA1 deficiency promoted OC cell growth, migration, and invasion ability in vitro and in vivo. Knockdown of ISYNA1 increased stemness of OC cells, including self-renewal, CSC markers expression, ALDH activity, and proportion of CD44⁺/CD117⁺ CSCs. Conversely, ectopic overexpression of ISYNA1 suppresses cell proliferation, migration, invasion and stemness of OC cells. Mechanistically, ISYNA1 inhibits OC stemness by regulating myo-inositol to suppress Notch1 signaling. In summary, these data provide evidence that ISYNA1 act as a tumor suppressor in OC and a regulator of stemness, providing insight into potentially targetable pathways for ovarian cancer therapy.

Emerging role of inositol monophosphatase in cancer

Inositol monophosphatase (IMPase) is an enzyme with two homologs-IMPA1 and IMPA2-that is responsible for dephosphorylating myo-inositol monophosphate to generate myo-inositol. IMPase has been extensively studied in neuropsychiatric diseases and is regarded as a susceptibility gene. Recently, emerging evidence has implied that IMPase is linked to cancer development and progression and correlates with patient survival outcomes. Interestingly, whether it acts as a tumor-promoter or tumor-suppressor is inconsistent among different research studies. In this review, we summarize the latest findings on IMPase in cancer, focusing on exploring the underlying mechanisms for its pro- and anticancer roles. In addition, we discuss the potential methods of IMPase regulation in cancer cells and the possible approaches for IMPase intervention in clinical practice.