Lipid metabolism in malignant tumor brain metastasis: reprogramming and therapeutic potential

Autophagy in cancer development, immune evasion, and drug resistance

Macroautophagy/autophagy is a highly conserved evolutionary mechanism involving lysosomes for the degradation of cytoplasmic components including organelles. The constitutive, basal level of autophagy is fundamental for preserving cellular homeostasis; however, alterations in autophagy can cause disease pathogenesis, including cancer. The role of autophagy in cancer is particularly complicated, since this process acts both as a tumor suppressor in precancerous stages but facilitates tumor progression during carcinogenesis and later stages of cancer progression. This shift between anti-tumor and pro-tumor roles may be influenced by genetic and environmental factors modulating key pathways such as those involving autophagy-related proteins, the PI3K-AKT-MTOR axis, and AMPK, which often show dysregulation in tumors. Autophagy regulates various cellular functions, including metabolism of glucose, glutamine, and lipids, cell proliferation, metastasis, and several types of cell death (apoptosis, ferroptosis, necroptosis and immunogenic cell death). These multifaceted roles demonstrate the potential of autophagy to affect DNA damage repair, cell death pathways, proliferation and survival, which are critical in determining cancer cells' response to chemotherapy. Therefore, targeting autophagy pathways presents a promising strategy to combat chemoresistance, as one of the major reasons for the failure in cancer patient treatment. Furthermore, autophagy modulates immune evasion and the function of immune cells such as T cells and dendritic cells, influencing the tumor microenvironment and cancer's biological behavior. However, the therapeutic targeting of autophagy is complex due to its dual role in promoting survival and inducing cell death in cancer cells, highlighting the need for strategies that consider both the beneficial and detrimental effects of autophagy modulation in cancer therapy. Hence, both inducers and inhibitors of autophagy have been introduced for the treatment of cancer. This review emphasizes the intricate interplay between autophagy, tumor biology, and immune responses, offering insights into potential therapeutic approaches that deploy autophagy in the cancer suppression.

A Graphene-Based Lipid Modulation Nanoplatform for Synergetic Lipid Starvation/Chemo/Photothermal Therapy of Oral Squamous Cell Carcinoma

Purpose

Chemotherapy is one of the most commonly used treatments for oral squamous cell carcinoma (OSCC), but its use is limited by drug resistance and severe systemic toxicity. To eliminate these side effects and improve anti-tumor efficacy, several therapeutic approaches have been developed for use with chemotherapy. In this study, we developed a graphene-based lipid modulation nanoplatform (NSD) that carries SB-204990, a small molecule inhibitor specific for ATP citrate lyase (ACLY), and doxorubicin (DOX), a chemotherapeutic agent, and the trio enables synergistic treatment of OSCC with lipid starvation, chemotherapy, and photothermal therapy.

Methods

We first determined whether ACLY expression was upregulated in OSCC, and then assessed the growth inhibitory effects of SB-204990 on SCC-15 cells and changes in lipid (acetyl coenzyme A, free fatty acids, and cholesterol) levels. We characterized NSD and then evaluated the stability, photothermal properties, drug loading, and release ability of NSD. Finally, the therapeutic effects of NSD on OSCC were investigated by in vitro and in vivo experiments, and the changes in lipid levels in OSCC tissues after ACLY inhibition were further evaluated.

Results

The results showed that ACLY was highly expressed in OSCC, and ACLY inhibition produced reproductive suppression and decreased lipid levels in SCC-15 cells. The NSD nanoplatform possessed good stability, photothermal properties, high drug loading capacity and controlled release. In addition, the triple therapy achieved satisfactory anticancer effects in both in vivo and in vitro assays, and the inhibition rate of tumors was as high as 99.4% in the NSD+Laser treatment group.

Conclusion

The changes in tumor cell lipid levels and cell proliferation arrest induced by ACLY inhibition suggest that ACLY may be a promising target for lipid starvation therapy and resistance to chemoresistance, and its inhibitors are expected to become new anticancer drugs. The NSD nanocarrier system enables synergistic treatment with lipid starvation, chemotherapy, and photothermal therapy, which represents an innovative approach to combating tumors.

Suppressing Wnt signaling of the blood‒tumor barrier to intensify drug delivery and inhibit lipogenesis of brain metastases

Lipogenesis is often highly upregulated in breast cancer brain metastases to adapt to intracranial low lipid microenvironments. Lipase inhibitors hold therapeutic potential but their intra-tumoral distribution is often blocked by the blood‒tumor barrier (BTB). BTB activates its Wnt signaling to maintain barrier properties, e.g., Mfsd2a-mediated BTB low transcytosis. Here, we reported VCAM-1-targeting nano-wogonin (W@V-NPs) as an adjuvant of nano-orlistat (O@V-NPs) to intensify drug delivery and inhibit lipogenesis of brain metastases. W@V-NPs were proven to be able to inactivate BTB Wnt signaling, downregulate BTB Mfsd2a, accelerate BTB vesicular transport, and enhance tumor accumulation of O@V-NPs. With the ability to specifically kill cancer cells in a lipid-deprived environment with IC50 at 48 ng/mL, W@V-NPs plus O@V-NPs inhibited the progression of brain metastases with prolonged survival of model mice. The combination did not induce brain edema, cognitive impairment, and systemic toxicity in healthy mice. Targeting Wnt signaling could safely modulate the BTB to improve drug delivery and metabolic therapy against brain metastases.

Selective and brain-penetrant ACSS2 inhibitors target breast cancer brain metastatic cells

Breast cancer brain metastasis (BCBM) typically results in an end-stage diagnosis and is hindered by a lack of brain-penetrant drugs. Tumors in the brain rely on the conversion of acetate to acetyl-CoA by the enzyme acetyl-CoA synthetase 2 (ACSS2), a key regulator of fatty acid synthesis and protein acetylation. Here, we used a computational pipeline to identify novel brain-penetrant ACSS2 inhibitors combining pharmacophore-based shape screen methodology with absorption, distribution, metabolism, and excretion (ADME) property predictions. We identified compounds AD-5584 and AD-8007 that were validated for specific binding affinity to ACSS2. Treatment of BCBM cells with AD-5584 and AD-8007 leads to a significant reduction in colony formation, lipid storage, acetyl-CoA levels and cell survival in vitro. In an ex vivo brain-tumor slice model, treatment with AD-8007 and AD-5584 reduced pre-formed tumors and synergized with irradiation in blocking BCBM tumor growth. Treatment with AD-8007 reduced tumor burden and extended survival in vivo. This study identifies selective brain-penetrant ACSS2 inhibitors with efficacy towards breast cancer brain metastasis.

Single-cell RNA sequencing reveals epithelial cells driving brain metastasis in lung adenocarcinoma

Brain metastases (BM) of lung adenocarcinoma (LUAD) are the most common intracranial malignancy leading to death. However, the cellular origins and drivers of BM from LUAD have not been clarified. Cellular composition was characterized by single-cell sequencing analysis of primary lung adenocarcinoma (pLUAD), BM and lymph node metastasis (LNM) samples in GSE131907. Our study briefly analyzed the tumor microenvironment (TME), focusing on the role of epithelial cells (ECs) in BM. We have discovered a population of brain metastasis-associated epithelial cells (BMAECs) expressing SPP1, SAA1, and CDKN2A, and it has been observed that this population is mainly composed of aneuploid cells from pLUAD, playing a crucial role in brain metastasis. Our study concluded that both LNM and BM in LUAD originated from pLUAD lesions, but there is currently insufficient evidence to prove a direct association between BM lesions and LNM lesions, which provides inspiration for further investigation of the TME in BM.