A New Potential Therapeutic Approach Targeting Cancer Metabolism: Adipose Manipulation Transplantation (AMT)

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Colin Ong

Altered Metabolism in Cancer Cells

Metabolic rewiring is one of the key features of cancer cells¹. These cells display altered metabolism as a way to meet their constant energy needs. This increased energy requirement is essential for the continuous proliferation and survival of these cells within the tumor microenvironment. Metabolic reprogramming of cancer cells was first reported by Otto Warburg in 1956, who demonstrated that cancer cells grown in vitro used aerobic glycolysis as the main pathway to catabolize glucose. This phenomenon is known as the Warburg effect². Research has revealed that cancer cells’ metabolic rewiring affects not only aerobic glycolysis but also several other metabolic pathways. These changes lead to increased production of serine and leucine³, higher lipogenesis and fatty acid oxidation⁴, and enhanced glutamine metabolism or glutaminolysis⁵. 

The dependence of cancer cells on various altered metabolic pathways has made them vulnerable, and this susceptibility can be exploited for therapeutic purposes. Thus, the development of therapies targeting these metabolic pathways to suppress cancer cell growth, induce cancer cell death, or both is currently under investigation. Presently, more than 100 chemical inhibitors of glycolysis, the tricarboxylic acid cycle, oxidative phosphorylation, glutaminolysis, fatty acid oxidation, fatty acid synthesis, lactate dehydrogenase, glucose transport, monocarboxylate transport, and amino acid transport are in preclinical or clinical testing⁶.

Using Adipose Tissue to Compete With Cancer for Nutrients

In the investigation of other strategies to treat cancer by exploiting the cancer cells’ reliance on glucose and fatty acid metabolism, Nguyen and colleagues of the Ahituv Laboratory at the University of California, San Francisco, proposed using white fat cells or adipocytes to outcompete cancer cells for nutrients. Their hypothesis was based on earlier findings by Seki and colleagues who showed that the growth of several solid tumors in mice exposed to cold conditions (4°C) was suppressed compared to the growth of tumors in mice exposed to thermoneutral conditions (30°C). These tumors included colorectal cancer, breast cancer, melanoma, fibrosarcoma, and pancreatic ductal adenocarcinoma (PDA). After cold treatment, the tumors exhibited slower proliferation, reduced tumor hypoxia, and decreased angiogenesis. They also observed that under cold acclimatization, brown adipose tissue (BAT) exhibited higher glucose uptake compared to tumors. However, surgical removal of BAT abolished the cold-induced suppression of tumor growth. Based on these findings, Seki and colleagues concluded that BAT plays a key role in tumor inhibition during cold acclimatization⁷.

So, what are the functions of BAT? BAT helps maintain energy balance, regulate glucose and lipid homeostasis, and generate heat⁸. Stimuli such as cold exposure can activate BAT to generate heat. Heat production is mediated by uncoupling protein 1 (UCP1), which is located in the inner mitochondrial membrane⁹. Then, what is the relationship between white adipose tissue (WAT) and BAT? WAT can be converted into BAT-like tissue through a process known as browning or beiging, which involves increasing  transcriptional activators such as PR domain containing 16 (PRDM16)¹⁰.  Similar to BAT, beige adipocytes can also generate heat and regulate whole-body energy levels¹¹.     

These results led Nguyen and co-workers to hypothesize that adipocytes could be used to deprive tumors of nutrients, thereby inhibiting their growth. Furthermore, white adipocytes can be easily isolated in clinical settings through liposuction, genetically engineered to transform into beige adipocytes, and then reintroduced into the body through plastic surgery. 

Browning of White Adipocytes Through Genetic Engineering

As an initial step, Nguyen and colleagues assessed the generation of beige adipocytes from white adipocytes. To achieve this goal, they used CRISPRa, a genetic modification technology, to increase the expression of UCP1, PRDM16, or peroxisome proliferation activated receptor gamma coactivator 1a (PPARɣC1a) genes in white adipocytes. These genes have been reported to be involved in BAT development and function. They found that all CRISPRa-modified adipocytes expressed brown fat marker genes such as DIO2 that encodes Iodothyronine deiodinase 2. Other brown fat-like phenotypes, including elevated glucose uptake, increased oxygen consumption, and fatty acid oxidation, were observed in the CRISPRa-modified adipocytes, with the UCP1 CRISPRa-modified adipocytes showing the greatest increases¹².   

Do CRISPRa-modified Adipocytes Prevent Cancer Cell Growth In Vitro? 

Initial experiments assessed whether the CRISPRa-modified adipocytes could suppress cancer cell growth in cell cultures. Cell co-culture systems using Transwell plates were set up. After 3 days of co-culturing, cancer cell growth was suppressed in the presence of UCP1-, PRDM16-, or PPARɣC1a-CRISPRa-modified adipocytes, but not in cancer cells co-cultured with non-CRISPRa-treated adipocytes. This inhibitory effect was detected in five different cancer cell lines, namely, MCF-7 and MDA-MB-436 (breast cancer), SW-1417 (colon cancer), Panc 10.05 (pancreatic cancer), and DU-145 (prostate cancer). The co-cultured cancer cells also showed decreased basal and maximal glycolytic rates, lowered glucose uptake, and reduced fatty acid oxidation¹². 

CRISPRa-modified Human Adipose Organoids Impair Xenograft Tumor Growth

Further investigations were performed to determine if the inhibitory effects on cancer cell growth mediated by CRISPRa-modified adipocytes could be observed in vivo. Nguyen and colleagues transplanted cancer cells subcutaneously into severe combined immunodeficient mice. Four cancer cell lines were tested (MCF-7, MDA-MB-436, Panc 10.05, and DU-145). After 8 weeks, they co-transplanted CRISPRa-modified adipose organoids near the palpable tumors. However, instead of using adipocytes alone, they developed human adipose organoids, reasoning that the three-dimensional culture would better represent adipose tissue heterogeneity. Furthermore, these organoids could create tissue microenvironments that integrate with cancer cells, and they showed improved responses to endogenous stimuli. In this and all subsequent experiments, UCP1-CRISPRa-modified adipose organoids were used as co-transplants because these adipocytes displayed the strongest suppressive effects in cell culture studies. After 3 weeks of co-transplantation, tumors co-transplanted with UCP1-CRISPRa-modified adipose organoids were less than half the volume of corresponding tumors co-transplanted with control organoids.  These inhibited tumors also showed lower hypoxia levels, decreased microvessel density, and reduced glycolysis and fatty acid oxidation. 

Nguyen and co-workers also investigated glucose and lipid metabolism in mice co-transplanted with tumors and adipose organoids. The UCP1-CRISPRa-modified adipose mice showed higher whole-body oxygen consumption, lower plasma insulin levels, and improved glucose tolerance compared to control mice co-transplanted with non-CRISPRa-modified adipose organoids. The UCP1-CRISPRa-modified adipose organoids also displayed higher glucose levels compared to the non-CRISPRa-modified adipose organoids.  By contrast, the xenograft tumors co-transplanted with UCP1-CRISPRa-modified adipose organoids had lower glucose levels. These tumors also displayed reduced levels of glycolytic intermediates such as fructose-6-phosphate and lower levels of fatty acids such as oleic and palmitoleic acids compared to control tumors. These findings indicate that UCP1-CRISPRa-modified adipose organoids could outcompete and starve the co-transplanted tumors of nutrients. 

Investigating the Effect of AMT on Genetic Models of Mouse Cancer and Cancer Organoids Derived from Human Breast Tumor

To further explore the therapeutic potential of this adipose cell-based approach or AMT, a term coined by Nguyen and colleagues, they examined the effects of co-transplanted UCP1-CRISPRa-modified adipose organoids on cancer cell growth in the following tumors:  

(a) pancreatic cancer mouse and breast tumor mouse models.  The KPC mouse, a pancreatic cancer mouse model, was used. In this model, the mouse develops PDA upon tamoxifen administration. For the breast tumor, the mouse mammary tumor virus long terminal repeat upstream of the polyomavirus middle T antigen (MMTV-PyMT) mouse model was examined. 

(b) xenograft of breast cancer organoids derived from human breast tumor tissues or from metastatic pleural effusions.

In both (a) and (b), application of the AMT technology resulted in blunted tumor growth.

AMT Can Be Used to Inhibit Growth of Tumors Dependent on Other Metabolic Pathways 

Nguyen and colleagues tested the ability of AMT to suppress PDA xenografts grown in mice, which are uridine-dependent in glucose-restricted conditions. They generated uridine phosphorylase 1-CRISPRa modulated adipose organoids and co-transplanted them with PDA xenografts. Uridine phosphorylase 1 is an enzyme that catalyzes the breakdown of uridine to uracil and ribose-1-phosphate. Ribose-1-phosphate serves as an intermediate for nucleic acid synthesis. The co-transplantation of uridine phosphorylase 1-CRISPRa-modified adipose organoids with PDA xenografts resulted in tumor growth inhibition. In addition, the levels of lactate and NADH, which are byproducts of uridine metabolism, were lower in inhibited tumors compared to control tumors. These investigations suggest that AMT can be used to treat cancers dependent on different metabolic pathways.  

In conclusion, Nguyen and colleagues have demonstrated that AMT has potential as a therapy to suppress cancer cell proliferation. Adipocytes are highly amenable in that they can be easily isolated, genetically engineered, and reintroduced into the body. AMT is versatile, customizable, and adaptable to target various cancer metabolic pathways. This technology holds promise and may join a host of expanding cell-based therapies that are currently in clinical trials or have received FDA approval. 

Header Image Source: Wikimedia Commons

Edited by Dolores Mruk

References

1. Hanahan D. Hallmarks of Cancer: New Dimensions. Cancer Discov. 2022 Jan;12(1):31-46. doi: 10.1158/2159-8290.CD-21-1059.

2. Warburg O. On respiratory impairment in cancer cells. Science. 1956 Aug 10;124(3215):269-70.

3. Amelio I, Cutruzzolá F, Antonov A, Agostini M, Melino G. Serine and glycine metabolism in cancer. Trends Biochem Sci. 2014 Apr;39(4):191-8. doi: 10.1016/j.tibs.2014.02.004.

4. Yang J, Shay C, Saba NF, Teng Y. Cancer metabolism and carcinogenesis. Exp Hematol Oncol. 2024 Jan 29;13(1):10. doi: 10.1186/s40164-024-00482-x.

5. Yang L, Venneti S, Nagrath D. Glutaminolysis: A Hallmark of Cancer Metabolism. Annu Rev Biomed Eng. 2017 Jun 21;19:163-194. doi: 10.1146/annurev-bioeng-071516-044546.

6. Tufail M, Jiang CH, Li N. Altered metabolism in cancer: insights into energy pathways and therapeutic targets. Mol Cancer. 2024 Sep 18;23(1):203. doi: 10.1186/s12943-024-02119-3.

7.    Seki T, Yang Y, Sun X, Lim S, Xie S, Guo Z, Xiong W, Kuroda M, Sakaue H, Hosaka K, Jing X, Yoshihara M, Qu L, Li X, Chen Y, Cao Y. Brown-fat-mediated tumour suppression by cold-altered global metabolism. Nature. 2022 Aug;608(7922):421-428. doi: 10.1038/s41586-022-05030-3.

8.    Symonds ME, Aldiss P, Pope M, Budge H. Recent advances in our understanding of brown and beige adipose tissue: the good fat that keeps you healthy. F1000Res. 2018 Jul 24;7:F1000 Faculty Rev-1129. doi: 10.12688/f1000research.14585.1.

9. Fedorenko A, Lishko PV, Kirichok Y. Mechanism of fatty-acid-dependent UCP1 uncoupling in brown fat mitochondria. Cell. 2012 Oct 12;151(2):400-13. doi: 10.1016/j.cell.2012.09.010.

10. Kajimura S. Promoting brown and beige adipocyte biogenesis through the PRDM16 pathway. Int J Obes Suppl. 2015 Aug;5(Suppl 1):S11-4. doi: 10.1038/ijosup.2015.4.

11. Wu J, Boström P, Sparks LM, Ye L, Choi JH, Giang AH, Khandekar M, Virtanen KA, Nuutila P, Schaart G, Huang K, Tu H, van Marken Lichtenbelt WD, Hoeks J, Enerbäck S, Schrauwen P, Spiegelman BM. Beige adipocytes are a distinct type of thermogenic fat cell in mouse and human. Cell. 2012 Jul 20;150(2):366-76. doi: 10.1016/j.cell.2012.05.016.

12. Nguyen HP, An K, Ito Y, Kharbikar BN, Sheng R, Paredes B, Murray E, Pham K, Bruck M, Zhou X, Biellak C, Ushiki A, Nobuhara M, Fong SL, Bernards DA, Lynce F, Dillon DA, Magbanua MJM, Huppert LA, Hammerlindl H, Klein JA, Valdiviez L, Fiehn O, Esserman L, Desai TA, Yee SW, Rosenbluth JM, Ahituv N. Implantation of engineered adipocytes suppresses tumor progression in cancer models. Nat Biotechnol. 2025 Feb 4. doi: 10.1038/s41587-024-02551-2.