Autophagy in cancer resistance to paclitaxel: Development of combination strategies

Revisiting the standards of cancer detection and therapy alongside their comparison to modern methods

In accordance with the World Health Organization data, cancer remains at the forefront of fatal diseases. An upward trend in cancer incidence and mortality has been observed globally, emphasizing that efforts in developing detection and treatment methods should continue. The diagnostic path typically begins with learning the medical history of a patient; this is followed by basic blood tests and imaging tests to indicate where cancer may be located to schedule a needle biopsy. Prompt initiation of diagnosis is crucial since delayed cancer detection entails higher costs of treatment and hospitalization. Thus, there is a need for novel cancer detection methods such as liquid biopsy, elastography, synthetic biosensors, fluorescence imaging, and reflectance confocal microscopy. Conventional therapeutic methods, although still common in clinical practice, pose many limitations and are unsatisfactory. Nowadays, there is a dynamic advancement of clinical research and the development of more precise and effective methods such as oncolytic virotherapy, exosome-based therapy, nanotechnology, dendritic cells, chimeric antigen receptors, immune checkpoint inhibitors, natural product-based therapy, tumor-treating fields, and photodynamic therapy. The present paper compares available data on conventional and modern methods of cancer detection and therapy to facilitate an understanding of this rapidly advancing field and its future directions. As evidenced, modern methods are not without drawbacks; there is still a need to develop new detection strategies and therapeutic approaches to improve sensitivity, specificity, safety, and efficacy. Nevertheless, an appropriate route has been taken, as confirmed by the approval of some modern methods by the Food and Drug Administration.

Benserazide, a cystathionine beta-synthase (CBS) inhibitor, potentially enhances the anticancer effects of paclitaxel via inhibiting the S-sulfhydration of SIRT1 and the HIF1-α/VEGF pathway

Cancer targeted therapy is essential to minimize damage to normal cells and improve treatment outcomes. The elevated activity of Cystathionine beta-synthase (CBS), an enzyme responsible for producing endogenous hydrogen sulfide (H2S), plays a significant role in promoting tumor growth, invasiveness, and metastatic potential. Consequently, the selective inhibition of CBS could represent a promising therapeutic strategy for cancer. Currently, there is much interest in combining paclitaxel with other drugs for cancer treatment. This study aimed to investigate the efficacy of combining benserazide, a CBS inhibitor, with paclitaxel in treating tumors. Firstly, we demonstrated CBS is indeed involved in the progression of multiple cancers. Then it was observed that the total binding free energy between the protein and the small molecule is -98.241 kJ/mol. The release of H2S in the group treated with 100 μM benserazide was reduced by approximately 90% compared to the negative control, and the thermal denaturation curve of the complex protein shifted to the right, suggesting that benserazide binds to and blocks the CBS protein. Next, it was found that compared to paclitaxel monotherapy, the combination of benserazide with paclitaxel demonstrated stronger antitumor activity in KYSE450, A549, and HCT8 cells, accompanied by reduced cell viability, cell migration and invasion, as well as diminished angiogenic and lymphangiogenic capabilities. In vivo studies showed that the combined administration of benserazide and paclitaxel significantly reduced the volume and weight of axillary lymph nodes in comparison to the control group and single administration group. Further mechanistic studies revealed that the combination of benserazide and paclitaxel significantly suppressed the S-sulfhydration of SIRT1 protein, thereby inhibiting the expression of SIRT1 protein and activating SIRT1 downstream Notch1/Hes1 signaling pathway in KYSE450, A549, and HCT8 cells. Meanwhile, we observed that benserazide combined with paclitaxel induced a more significant downregulation of HIF-1α, VEGF-A, VEGF-C, and VEGF-D proteins expression levels in KYSE450, A549, and HCT8 cells compared to paclitaxel alone. These findings indicated that benserazide enhances the anticancer effects of paclitaxel via inhibiting the S-sulfhydration of SIRT1 and down-regulating HIF-1α/VEGF signaling pathway. This study suggests that benserazide may have potential as a chemosensitizer in cancer treatment.

Targeting PNPO to suppress tumor growth via inhibiting autophagic flux and to reverse paclitaxel resistance in ovarian cancer

Our previous study showed that pyridoxine 5'-phosphate oxidase (PNPO) is a tissue biomarker of ovarian cancer (OC) and has a prognostic implication but detailed mechanisms remain unclear. The current study focused on PNPO-regulated lysosome/autophagy-mediated cellular processes and the potential role of PNPO in chemoresistance. We found that PNPO was overexpressed in OC cells and was a prognostic factor in OC patients. PNPO significantly promoted cell proliferation via the regulation of cyclin B1 and phosphorylated CDK1 and shortened the G2M phase in a cell cycle. Overexpressed PNPO enhanced the biogenesis and perinuclear distribution of lysosomes, promoting the degradation of autophagosomes and boosting the autophagic flux. Further, an autolysosome marker LAMP2 was upregulated in OC cells. Silencing LAMP2 suppressed cell growth and induced cell apoptosis. LAMP2-siRNA blocked PNPO action in OC cells, indicating that the function of PNPO on cellular processes was mediated by LAMP2. These data suggest the existence of the PNPO-LAMP2 axis. Moreover, silencing PNPO suppressed xenographic tumor formation. Chloroquine counteracted the promotion effect of PNPO on autophagic flux and inhibited OC cell survival, facilitating the inhibitory effect of PNPO-shRNA on tumor growth in vivo. Finally, PNPO was overexpressed in paclitaxel-resistant OC cells. PNPO-siRNA enhanced paclitaxel sensitivity in vitro and in vivo. In conclusion, PNPO has a regulatory effect on lysosomal biogenesis that in turn promotes autophagic flux, leading to OC cell proliferation, and tumor formation, and is a paclitaxel-resistant factor. These data imply a potential application by targeting PNPO to suppress tumor growth and reverse PTX resistance in OC.

TRF2 as novel marker of tumor response to taxane-based therapy: from mechanistic insight to clinical implication

BACKGROUND

Breast Cancer (BC) can be classified, due to its heterogeneity, into multiple subtypes that differ for prognosis and clinical management. Notably, triple negative breast cancer (TNBC) - the most aggressive BC form - is refractory to endocrine and most of the target therapies. In this view, taxane-based therapy still represents the elective strategy for the treatment of this tumor. However, due variability in patients' response, management of TNBC still represents an unmet medical need. Telomeric Binding Factor 2 (TRF2), a key regulator of telomere integrity that is over-expressed in several tumors, including TNBC, has been recently found to plays a role in regulating autophagy, a degradative process that is involved in drug detoxification. Based on these considerations, we pointed, here, at investigating if TRF2, regulating autophagy, can affect tumor sensitivity to therapy.

METHODS

Human TNBC cell lines, over-expressing or not TRF2, were subjected to treatment with different taxanes and drug efficacy was tested in terms of autophagic response and cell proliferation. Autophagy was evaluated first biochemically, by measuring the levels of LC3, and then by immunofluorescence analysis of LC3-puncta positive cells. Concerning the proliferation, cells were subjected to colony formation assays associated with western blot and FACS analyses. The obtained results were then confirmed also in mouse models. Finally, the clinical relevance of our findings was established by retrospective analysis on a cohort of TNBC patients subjected to taxane-based neoadjuvant chemotherapy.

RESULTS

This study demonstrated that TRF2, inhibiting autophagy, is able to increase the sensitivity of TNBC cells to taxanes. The data, first obtained in in vitro models, were then recapitulated in preclinical mouse models and in a cohort of TNBC patients, definitively demonstrating that TRF2 over-expression enhances the efficacy of taxane-based neoadjuvant therapy in reducing tumor growth and its recurrence upon surgical intervention.

CONCLUSIONS

Based on our finding it is possible to conclude that TRF2, already known for its role in promoting tumor formation and progression, might represents an Achilles' heel for cancer. In this view, TRF2 might be exploited as a putative biomarker to predict the response of TNBC patients to taxane-based neoadjuvant chemotherapy.

A novel electrospun nanofiber system with PEGylated paclitaxel nanocrystals enhancing the transmucus permeability and in situ retention for an efficient cervicovaginal cancer therapy

Overcoming the vaginal barrier to achieve sufficient drug penetration and retention is a huge obstacle for drug delivery in chemotherapeutics for cervical cancer. In this study, we investigate the feasibility of a novel composite nanocrystal/nanofiber system for improving the transmucus penetration and, thus, enhancing retention and drug delivery to the lesion of a cervicovaginal tumor. Herein, paclitaxel (PTX) was sequentially formulated in the form of nanocrystals, coated with polydopamine (PDA), and modified with PEG. The nanocrystals (NCs@PDA-PEG) were creatively fabricated to create a composite nanofibrous membrane (NCs@PDA-PEG NFs) by using an electrospinning technique. The morphology, size distribution, drug loading, encapsulation efficiency, X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectra, in vitro release, in vivo vaginal retention, apoptosis index, anti-tumor efficacy in a murine cervicovaginal tumor model, and local irritation were characterized. The NCs@PDA-PEG were formulated in a cube-like shape with an average size of 385.6 ± 35.47 nm; they were dispersed in electrospun nanofibers, and the drug loading was 7.94 %. The XRD curves indicated that the phase state of PTX changed after the creation of the nanocrystals. The FTIR spectra showed that the drug and the excipients were compatible with each other. In vitro delivery showed that the dissolution of PTX in the electrospun nanofibers was significantly faster than that when using bulk PTX. Compared with the PTX NC NFs, the NC@PDA-PEG NFs exhibited prolonged vaginal residence, superior transmucus penetration, minimal mucosal irritation, and significant tumor inhibition efficacy after the intravaginal administration of the NFs in tumor-bearing mice. In conclusion, by acting as novel pharmaceutical repositories, NCs@PDA-PEG NFs can be promising candidates for non-invasive local treatment, leading to efficient tumor inhibition in cervicovaginal cancer.

Chloroquine and Chemotherapeutic Compounds in Experimental Cancer Treatment

Chloroquine (CQ) and its derivate hydroxychloroquine (HCQ), the compounds with recognized ability to suppress autophagy, have been tested in experimental works and in clinical trials as adjuvant therapy for the treatment of tumors of different origin to increase the efficacy of cytotoxic agents. Such a strategy can be effective in overcoming the resistance of cancer cells to standard chemotherapy or anti-angiogenic therapy. This review presents the results of the combined application of CQ/HCQ with conventional chemotherapy drugs (doxorubicin, paclitaxel, platinum-based compounds, gemcitabine, tyrosine kinases and PI3K/Akt/mTOR inhibitors, and other agents) for the treatment of different malignancies obtained in experiments on cultured cancer cells, animal xenografts models, and in a few clinical trials. The effects of such an approach on the viability of cancer cells or tumor growth, as well as autophagy-dependent and -independent molecular mechanisms underlying cellular responses of cancer cells to CQ/HCQ, are summarized. Although the majority of experimental in vitro and in vivo studies have shown that CQ/HCQ can effectively sensitize cancer cells to cytotoxic agents and increase the potential of chemotherapy, the results of clinical trials are often inconsistent. Nevertheless, the pharmacological suppression of autophagy remains a promising tool for increasing the efficacy of standard chemotherapy, and the development of more specific inhibitors is required.

The high-grade serous ovarian cancer metastasis and chemoresistance in 3D models

High-grade serous ovarian cancer (HGSOC) is the most frequent and aggressive type of epithelial ovarian cancer, with high recurrence rate and chemoresistance being the main issues in its clinical management. HGSOC is specifically challenging due to the metastatic dissemination via spheroids in the ascitic fluid. The HGSOC spheroids represent the invasive and chemoresistant cellular fraction, which is impossible to investigate in conventional two-dimensional (2D) monolayer cell cultures lacking critical cell-to-cell and cell-extracellular matrix interactions. Three-dimensional (3D) HGSOC cultures, where cells aggregate and exhibit relevant interactions, offer a promising in vitro model of peritoneal metastasis and multicellular drug resistance. This review summarizes recent studies of HGSOC in 3D culture conditions and highlights the role of multicellular HGSOC spheroids and ascitic environment in HGSOC metastasis and chemoresistance.

Flubendazole Enhances the Inhibitory Effect of Paclitaxel via HIF1α/PI3K/AKT Signaling Pathways in Breast Cancer

Paclitaxel, a natural anticancer drug, is widely recognized and extensively utilized in the treatment of breast cancer (BC). However, it may lead to certain side effects or drug resistance. Fortunately, combination therapy with another anti-tumor agent has been explored as an option to improve the efficacy of paclitaxel in the treatment of BC. Herein, we first evaluated the synergistic effects of paclitaxel and flubendazole through combination index (CI) calculations. Secondly, flubendazole was demonstrated to synergize paclitaxel-mediated BC cell killing in vitro and in vivo. Moreover, we discovered that flubendazole could reverse the drug resistance of paclitaxel-resistant BC cells. Mechanistically, flubendazole was demonstrated to enhance the inhibitory effect of paclitaxel via HIF1α/PI3K/AKT signaling pathways. Collectively, our findings demonstrate the effectiveness of flubendazole in combination with paclitaxel for treating BC, providing an insight into exploiting more novel combination therapies for BC in the future.

A Novel Bromophenol Compound from Leathesia nana Inhibits Breast Cancer in a Direct Tumor Killing and Immunotherapy Manner

Considering the resistance and toxicity of traditional chemotherapeutic drugs, seeking potential candidate for treating breast cancer effectively is a clinical problem that should be solved urgently. Natural products have attracted extensive attention, owing to their multi-target advantages and low toxicity. In the current study, the effects of XK-81, a novel bromophenol compound extracted from Leathesia nana, on breast cancer, and its underlying mechanisms, were explored. Firstly, data from in vitro experiments indicated that 4T-1, one of common mouse breast cancer cell lines, was a XK-81-susceptible cell line, and ferroptosis was the major death manner in response to XK-81 treatment, which was evidenced by increasing intracellular Fe²⁺ and ROS level with condensed mitochondrial membrane densities, as well as decreasing the protein expressions of SLC7A11 and GPX4. In vivo, XK-81 suppressed the growth of 4T-1 breast-tumor in both BALB/C mice and zebrafish. Obviously, XK-81 decreased the protein expression of SLC7A11 and GPX4 in tumor tissues, hinting at the occurrence of ferroptosis. Moreover, XK-81 increased CD8+ T cells and NK cells numbers and regulated M1/M2 macrophage ratio in tumor tissues, indicating XK-81's immunotherapeutic effect. Additionally, the secretions of immune-related cytokines, including TNF-α, IL-1β, and IL-12, were elevated with XK-81 stimulation in RAW 264.7 cells. Intriguingly, compared with doxorubicin-induced heart damage, XK-81 demonstrated the therapeutic advantage of little cardiotoxicity on the heart. XK-81 demonstrated potential antitumor advantage by both directly inducing ferroptosis-mediated death of tumor cells and immunization.

Identification of Fangjihuangqi Decoction as a late-stage autophagy inhibitor with an adjuvant anti-tumor effect against non-small cell lung cancer

BACKGROUND

Clinically, although chemotherapy is one of the most commonly used methods of treating tumors, chemotherapeutic drugs can induce autophagic flux and increase tumor cell resistance, leading to drug tolerance. Therefore, theoretically, inhibiting autophagy may improve the efficacy of chemotherapy. The discovery of autophagy regulators and their potential application as adjuvant anti-cancer drugs is of substantial importance. In this study, we clarified that Fangjihuangqi Decoction (FJHQ, traditional Chinese medicine) is an autophagy inhibitor, which can synergistically enhance the effect of cisplatin and paclitaxel on non-small cell lung cancer (NSCLC) cells.

METHODS

We observed the changes of autophagy level in NSCLC cells under the effect of FJHQ, and verified the level of the autophagy marker protein and cathepsin. Apoptosis was detected after the combination of FJHQ with cisplatin or paclitaxel, and NAC (ROS scavenger) was further used to verify the activation of ROS-MAPK pathway by FJHQ.

RESULTS

We observed that FJHQ induced autophagosomes in NSCLC cells and increased the levels of P62 and LC3-II protein expression in a concentration- and time-gradient-dependent manner, indicating that autophagic flux was inhibited. Co-localization experiments further showed that while FJHQ did not inhibit autophagosome and lysosome fusion, it affected the maturation of cathepsin and thus inhibited the autophagic pathway. Finally, we found that the combination of FJHQ with cisplatin or paclitaxel increased the apoptosis rate of NSCLC cells, due to increased ROS accumulation and further activation of the ROS-MAPK pathway. This synergistic effect could be reversed by NAC.

CONCLUSION

Collectively, these results demonstrate that FJHQ is a novel late-stage autophagy inhibitor that can amplify the anti-tumor effect of cisplatin and paclitaxel against NSCLC cells.