Table 4.

Data on both the experimental and clinical trials devoted to targeting the OCSCs.

Target	Drug	Mechanism of action	Trial	Reference
CD44	ALM201	ALM201 is a residue peptide of FKBPL, which targets angiogenesis and CD44+ OCSCs by affecting the CD44/STAT3 pathway ALM201 is safe and well-tolerated, with stabilization of the disease in 22% of patients	Experimental Phase I dose-escalation human trial EudraCT	(266) (267)
CD117	Imatinib mesylate monotherapy Imatinib mesylate + docetaxel	Inhibition of CD117/PDGF signaling pathway. Treatment was well-tolerated, but no complete or partial responses were documented during a median follow-up of 6.6 months. However, 33% of patients had stable disease lasting from 4 to 8+ months. There was no relationship between best response (stable disease) and target expression Treatment showed low toxicity but also unsatisfactory anti-tumor activity. There were no objective responders. Median PFS was 2 months, and median OS was 10 months. Higher pre-treatment plasma concentrations of PDGF and VEGF were associated with shorter PFS and survival Patients with heavily pre-treated recurrent ovarian cancer expressing CD117 or PDGFRα showed ORR of 22%, which included one complete and four partial responses, and additional three patients had stable disease for more than 4 months	Phase II NCT00510653 Gynecologic Oncology Group study Southwest Oncology Group Protocol S0211 Hoosier Oncology Group trial	(268) (269) (270) (271)
CD44/ CD117	Salinomycin monotherapy Salinomycin + paclitaxel Metformin + bevacizumab + cisplatin	Salinomycin is the mono carboxylic polyether antibiotic inhibiting ABC-transporter system and promoting OCSC apoptosis. Encapsulated salinomycin in the form of salinomycin-loaded high-density lipoprotein showed effective cellular uptake and reduced the EMT, stemness, and angiogenesis mediated by OCSCs Combined treatment reduced stemness and spheroid forming capability and enhanced apoptosis of ascitic OCSCs Combination of drugs reduced a significant number of CD44+CD117+ OCSCs and inhibited tumor growth	Experimental Experimental Experimental	(272) (273) (274)
CD44/ MyD88	NV128	Isoflavone derivative causing depression of mitochondrial function and cellular starvation of OCSCs	Experimental	(275)
ALDH	673A CM37 ATRA + carboplatin 673A Disulfiram	The result of ALDH1A inhibition is an accumulation of toxic aldehyde metabolites in OCSCs. The effects are stronger in combination with ATR inhibitors ALDH1A inhibitor that disturbed spheroid production by the OCT4 and SOX2 downregulation A vitamin A derivative, in combination with carboplatin, suppresses ALDH1 expression and downregulates functionality of OCSCs The pan-ALDH1A inhibitor that preferentially kills CD133+ OCSCs through initiation of necroptosis and sensitizes tumor to platinum-based chemotherapy The anti-alcoholic medication, ALDH inhibitor, in combination with cisplatin, induced apoptosis and necrosis in ALDH+ cisplatin-resistant OCSCs	Experimental Experimental Experimental Experimental Experimental	(276) (277) (278) (279) (280)
	Selumetinib + Saracatinib PNA3 + guadecitabine	Both Src and MEK signaling kinases are co-activated in 31% of HGSOC. Combined treatment with Src inhibitor saracatinib and MEK inhibitor selumetinib decreased ALDH1+ cell sphere formation and loss of ALDH1+ OCSCs LncRNA HOTAIR is upregulated in HGSOC and especially in ALDH1+ OCSCs. Peptide nucleic acid PNA3 inhibits HOTAIR, and enhancer of zeste homolog 2 (EZH2) interaction and when combined with DNMT inhibitor guadecitabine abrogates ALDH1+ spheroid formation and decreases their number and tumor-promoting ability	Experimental Experimental	(281) (282)
ALDH/ CD133	Salinomycin monotherapy Licofelone Metformin	Graphene oxide–silver nanocomposite combined with salinomycin showed high toxicity against ALDH+CD133+ OCSCs COX/5-LOX inhibitor that reversed stem-like properties in spheroids and augmented paclitaxel activity resulting in prolongation of mice survival Ovarian cancer II-IV FIGO. Metformin in combination with standard chemotherapy in neoadjuvant and adjuvant setting. Median PFS of 18 months, and median OS of 58 months. Tumors treated with metformin had a 2.4-fold decrease in ALDH+CD133+ CSCs and showed increased sensitivity to cisplatin	Experimental Experimental Phase II NCT01579812	(283) (284) (285)
CD133	Salinomycin monotherapy dCD133KDEL anti-CD133 CAR-NK cells + cisplatin	Conjugates of salinomycin with anti-CD133 antibody and nanoparticles are effective in transportation of the antibiotic into CD133+ OCSCs Deimmunized Pseudomonas endotoxin conjugated to anti-CD133 antibody inhibits tumor growth Sequential treatment using CAR-NK cells and cisplatin eradicated CD133+ OCSCs from cell lines and cell cultures obtained from ascites samples	Experimental Experimental Experimental	(286) (287) (288)
EpCAM	EpCAM-specific CAR-T cells Catumaxomab	Infusion of CAR-T cells delayed tumor progression in xenograft mice model of peritoneal carcinomatosis Hybrid moAb against EpCAM/CD3. Intraperitoneal use of this moAb resulted in prolongation of puncture-free interval (two-fold from 12 to 27.5 days) and time to first therapeutic puncture (four-fold from 12 to 52 days) in heavily pre-treated patients with EpCAM+ recurrent tumors complicated with malignant ascites. The median puncture-free survival and overall survival were 29.5 and 111 days, respectively Deterioration of quality of life appeared earlier in control than in catumaxomab-treated group of patients with ascites (19–26 days vs. 47–49 days) In patients with malignant ascites, peritoneal catumaxomab infusion enhanced the expression of the CD69 and CD38 activation molecules in T CD4+ and T CD8+, NK cells, and macrophages and enhanced T CD8+ accumulation into the peritoneal cavity	Experimental NCT00326885 Phase II European Medicines Agency approved Phase II/III NCT00836654 CASIMAS Phase IIIb NCT00822809	(289) (290) (291) (292)
ATR	Ceralasertib (AZD6738) + olaparib M6620 (VX-970) + carboplatin	ATR is a protein kinase involved in recognition of DNA damage and activation of DNA damage checkpoint. Inhibitors of ATR combined with PARP inhibitors (PARPi) were able to overcome PARPi and platinum resistance in BRCA and CCNE1 wild and mutated cell lines Well-tolerated therapy with reduction in tumor burden, especially in BRCA-mutated patients (median PFS was 4.2 months overall and 8.2 months for patients with BRCA1 mutations) Partial response in platinum-resistant patients with BRCA1 mutation. A patient with advanced germline BRCA1 ovarian cancer achieved RECIST partial response despite being platinum-refractory and PARP inhibitor–resistant	Experimental CAPRI phase II Phase I	(293) (294) (295)
FAK	Defactinib (VS-6063) + paclitaxel VS-4718 + platinum APG-2449	FAK is a tyrosine kinase activated by matrix and integrin receptors controlling cell motility. FAK inhibitor VS-6063 enhances chemosensitivity and decreases CD44 OCSC marker. Combination with paclitaxel reduces >90% tumor weight. Modest activity in advanced platinum-resistant ovarian cancer FAK inhibitor combined with platinum triggered ovarian cancer cell apoptosis and restored chemosensitivity A multikinase inhibitor of FAK, ROS proto-oncogene 1 receptor tyrosine kinase (ROS1), and anapestic lypmphoma kinase (ALK). Combination of APG-2449 and osimertinib (EGFR tyrosine kinase inhibitor) and mitogen-activated extracellular signal–regulated kinase inhibitor trametinib overcomes osimertinib resistance	Experimental NCT01778803 Phase I Experimental Experimental	(296) (297) (298) (299)
Calcium channels	Manidipine Lacipidine Benidipine Lomerizine Manidipine + paziotinib	Calcium channel blockers were found to target the OCSC function by decreasing steroid formation, proliferation, and induction of apoptosis. Use of these drugs downregulated expression of stemness markers OCT4, NANOG, SOX2, ALDH1, and CD133. Combination of calcium channel blocker with pan-HER inhibitor paziotinib showed synergism in reduction of OCSC spheroid formation, expression of stemness markers, and enhancement of apoptosis	Experimental Experimental	(300) (301)
MSH-1/MSH-2	siRNA	Dual knockdown of MSH-1 and MSH-2 downregulated OCSC ALDH4A1 and Myc and improved chemosensitivity	Experimental	(302)
ERβ receptor	LY5000307 (Erteberel) monotherapy	Selective agonist of estrogen receptor ERβ. Treatment with the agonist reduced the viability, sphere formation capacity, self-renewal, and invasion of OCSCs while augmenting their apoptosis	Experimental	(303)
NAMPT	FK866 + cisplatin	NAMPT is an enzyme for the NAD+ biosynthetic salvage pathway and is overexpressed in cancers. Combination of NAMPT inhibitor and cisplatin inhibited expression of ALDH1 and CD133 OCSCs and improved survival in the mouse model	Experimental	(304)
Survivin	AS602801 CEP-1347	Inhibitor of c-Jun N-terminal kinase downregulates survivin. Chemo-sensitization of OCSCs to carboplatin and paclitaxel A small-molecule kinase inhibitor downregulates survivin and sensitizes OCSCs to standard chemotherapy	Experimental Experimental	(305) (306)
Wnt signaling pathway	Ipafricept (OMP54F28) + carboplatin + docetaxel WNT974 + carboplatin Vantictumab (OMP-18R5)	Inhibitor of Fc-Frizzled-8 receptor antagonizing Wnt signaling. Sequential combined treatment is well-tolerated but has limited efficacy. The ORR was 76%. Median PFS was 10.3 months and OS was 33 months Inhibitor of PORCN that lowers secretion and binding of Wnt to its receptor. Combined therapy caused cell cycle arrest and cytotoxicity of cells isolated from ascites of patients with HGSOC moAB that inhibits Wnt pathway by targeting the Frizzled receptors on cancer cells. Treatment with vantictumab before paclitaxel therapy sensitizes cancer cells to death	NCT02050178 Phase I Experimental Experimental	(307) (308) (309)
Hedgehog signaling pathway	Cyclopamine Vismodegib (GDC-0449) monotherapy Sonidegib (LDE225) + paclitaxel	Steroidal alkaloid isolated from poisonous plant Veratrum californicum that inhibits Hedgehog signaling. Inhibition of spheroid-forming cells in the cell culture was observed upon treatment with cyclopamine The SMO receptor antagonist. Therapy was well-tolerated; however, the anticipated increase in PFS was not achieved. Median PFS was 7.5 months the in treated group and 5.8 months in the placebo group. Hedgehog expression was detected only in 13.5% of tissues The SMO receptor antagonist. Combination of drugs was well-tolerated and showed partial responses or stabilization of the disease in ovarian cancer	Experimental NCT00739661 phase II Phase I	(69) (310) (311)
NOTCH signaling pathway	LY900009 monotherapy MK-0752 + cisplatin RO4929097 monotherapy Enoticumab (REGN421) monotherapy Enoticumab + aflibercept Demcizumab (OMP-21M18) + paclitaxel Navicixizumab (OMP-305B83) monotherapy Navicixizumab (OMP-305B83) + paclitaxel	Inhibitor of γ-secretase protein. Therapy was well-tolerated, and five patients with solid tumors including ovarian cancer had stabilization of the disease Inhibitor of γ-secretase protein. Combination effectively stimulated cancer cells apoptosis and reduced growth of ovarian cancer xenografts in mice Inhibitor of γ-secretase protein. Monotherapy in recurrent ovarian cancer was well-tolerated but had insufficient activity. Fifteen of the 40 patients had stabilization of the disease lasting with median of 3 months. The results were better in HGSOC with high expression of intracellular NOTCH protein moAb against DLL4–NOTCH ligand involved in angiogenesis. Therapy had acceptable toxicity. In the group of patients with solid tumors including ovarian cancer, two partial responses and 15 stabilizations of the disease were observed Combination of anti-DLL4 and anti-VEGF therapy showed greater anti-tumor effects compared to either monotherapy in murine model of ovarian cancer moAb against DLL4. Combination showed ORR of 21% with manageable toxicity in the group of patients with highly pre-treated HGSOC with platinum-resistant tumors Combined dual moAb anti-DLL4/anti-VEGF. Showed acceptable toxicity profile and reduced the tumors in seven of the 11 of patients with pre-treated ovarian cancer Combination demonstrated manageable toxicity and ORR of 33% in bevacizumab pre-treated patients, 64% in bevacizumab naive patients, and 62% in the biomarker (high angiogenesis and suppressed immune response)–positive group	Phase I Experimental Princess Margaret, Chicago and California consortium Phase II Phase I Experimental SIERRA Phase Ib Phase Ia Phase Ib	(312) (313) (314) (315) (316) (317) (318) (319)
PI3K/AKT/mTOR signaling pathway	Metformin monotherapy Metformin + cisplatin/paclitaxel LY294002 + carboplatin Atorvastatin	Activation of AMPK followed by inhibition of signaling and reduction of energy consumption by OCSCs. Metformin inhibited cell viability, invasion, and autophagy while promoting apoptosis in paclitaxel-resistant ovarian cancer cell lines via downregulation of lncRNA SNHG—a regulator of PI3K/AKT/mTOR pathway Combination of Metformin with chemotherapy significantly reduced cell proliferation and migration and increased chemosensitivity by reducing the OCSCs in treated cell lines Addition of metformin to standard adjuvant or neo-adjuvant chemotherapy reduced two-fold concentration of ALDH+CD133+ OCSCs and increased cisplatin sensitivity of tumors, resulting in median OS of 58% PI3K antagonist combined with carboplatin enhances its anti-cancer effect in mouse xenograft model Statin that, through inhibition of AKT/mTOR pathway, stimulates apoptosis of ovarian cancer cells and inhibits cell invasion	Experimental Experimental NCT01579812 Phase II Experimental Experimental	(320) (321) (285) (322) (323)
NF-κB signaling pathway	Metformin + cisplatin/paclitaxel MK-5108 monotherapy	Metformin through inhibition of NF-κB signaling pathway enhanced sensitivity to standard chemotherapeutics in both sensitive and resistant cell lines Aurora-A kinase inhibitor. Its use in ovarian cancer cell lines caused cell cycle arrest, inhibition of NF-κB signaling, and cytokine secretion	Experimental Experimental	(324) (325)
Hippo/YAP signaling	Verteporfin Verteporfin + carboplatin/taxol	Photosensitizer releases a singlet oxygen and ROS toxic to cancer cells upon exposure to light of particular wavelength. Verteporfin-loaded lipid nanoparticles inhibited tumor xenografts in mice upon laser light exposure Combination was efficient in reducing proliferation, invasion, and clonogenic capacity of ovarian cancer cell lines	Experimental Experimental	(326) (327)
JAK/STAT signaling	Ruxolitinib + paclitaxel TG101209 CYT387 + paclitaxel JQ1	Inhibitor of JAK, thus inhibiting the JAK/STAT pathway. Synergic effects of combined therapy on tumor growth in mouse model of advanced/ascites+ ovarian cancer JAK2 inhibitor that induced cytotoxicity in spire-forming CD24+ cells, thus inhibiting migration and metastasis of ovarian cancer in murine model Combination of JAK2 inhibitor with chemotherapy inhibited paclitaxel-mediated OCSC enrichment and reduced tumor burden in mouse xenografts Selective small-molecule bromodomain inhibitor that inhibits JAK/STAT pathway. JQ1 resensitized ovarian cancer cells to platinum	Experimental Experimental Experimental Experimental	(328) (329) (38) (330)
TGF-β signaling	SB525334	TGF-β1 receptor inhibitor blocked ALDH1+ OCSCs self-renewal, invasion, and spheroid formation	Experimental	(331)
Src and MAPK signaling kinases	Selumetinib + Saracatinib	MAPK and Src inhibitors showed synergistic induction of apoptosis and tumor inhibition in ovarian cancer mouse model. Treatment decreased spheroid formation and ALDH1 expression	Experimental	(281)
DNA methylation	Decitabine + carboplatin	Decitabine is a DNMT1 inhibitor, a hypomethylating agent. In the group of pre-treated patients with solid tumors, containing two ovarian HGSOC tumors, a partial response to combined therapy was observed	NCT01799083 Phase II	(332)
	Decitabine + carboplatin/paclitaxel + cytokine-induced killer cells (CIK) Guadecitabine + carboplatin Guadecitabine + PNA3 Azacitidine + carboplatin	The population of patients with chemoresistant recurrent ovarian cancer treated with combined regimen showed ORR of 87.5% and prolongation of PFS to 8 months and OS to 19 months This regimen combining DNMT1 inhibitor with chemotherapy, compared to second-line chemotherapy alone, resulted in increased rate of patients having 6-months PFS (37% vs. 11%) PNA3 is HOTAIR inhibitor. Combined with DNMT1 inhibitor showed reduction of spheroids and ALDH1+ OCSCs Combination of DNMT1 inhibitor with carboplatin caused stabilization of the disease > 4 months in three patients with refractory or resistant ovarian cancer Sequential combined treatment significantly slowed platinum-resistant HGSOC growth and activated immune-related pathways priming tumor for checkpoint inhibitor immunotherapy	Phase II Phase II Experimental Phase II Experimental	(333) (334) (282) (335) (336)
Histone deacetylation	Vorinostat monotherapy Vorinostat + carboplatin + gemcytabine Belinostat (PXD-101) + carboplatin + paclitaxel Belinostat (PXD-101) + carboplatin Entinostat (MS-275) monotherapy Entinostat (MS-275) + olaparib	HDAC inhibitor that induces accumulation of acetylated histones and transcription factors that arrest cell cycle. Monotherapy of platinum-resistant progressive HGSOC was well-tolerated; however, clinical efficacy was minimal (two women had PFS over 6 months, with one having a partial response) Combination was effective (partial response in six of the 15 patients) in recurrent platinum-sensitive ovarian cancer but was accompanied with hematological toxicity HDAC inhibitor that induces apoptosis and sensitizes tumor for chemotherapy. Combination had acceptable toxicity; in three of the 35 patients, complete response was obtained, and, in 12 of the 35 patients, partial response was obtained. ORR was 44% in platinum-resistant and 63% in platinum-sensitive patients. Combination was effective in 14 of the 27 patients with platinum-resistant ovarian cancer (one complete and one partial response; 12 patients had disease stabilization) Benzamide derivative of HDAC that inhibits selectively class I and IV HDAC. Entinostat was effective in therapy of intraperitoneal tumors in mouse model; however, its activity depended on immunocompetence represented by upregulation of MHCII and infiltration of T CD8+ cytotoxic cells in the tumors Combination potentiates the effect of olaparib in HR-proficient ovarian cancer and enhances olaparib-induced DNA damage	Gynecologic Oncology Group Phase II Phase I Phase II Gynecologic Oncology Group Phase II Experimental Experimental	(337) (338) (339) (340) (341) (342)
Metabolism	2-deoxy-D-glucose (2DG) Devimistat (CPI-613) TVB-3166 USP13 knockdown Etomoxir Perhexiline CAY-10566	Glycolysis inhibitor. In HGSOC tumors with reduced beta-F1-ATPase/oxidative phosphorylation, it sensitized cancer cells for platinum Mitochondrial metabolism inhibitor. Preferentially targets OCSCs and prevents acquired chemoresistance into olaparib or carboplatin/paclitaxel therapy Fatty acid synthase (FASN) inhibitor. Induced apoptosis in HGSOC model Inhibits ATP citrate synthase (ACLY) followed by inhibition of ovarian HGSOC tumors in the mouse xenograft model An irreversible inhibitor of carnitine palmitoyltransferase-1 (CPT-1) in mitochondria. Targets OCSCs and induces their apoptosis, and inhibits growth of tumor xenografts Inhibitor of carnitine palmitoyltransferase-1 (CPT-1) in mitochondria. Sensitized NKX2-8-deleted HGSOC lines to cisplatin Selective inhibitor of stearoyl-CoA-desaturase-1 (SCD1). Induced apoptosis and ferroptosis in HGSOC lines and eliminated OCSCs and spheroid formation	Experimental Experimental Experimental Experimental Experimental Experimental Experimental	(343) (344) (345) (346) (347) (348) (162, 349)

FKBPL, FK506-binding protein–like; PDGF, platelet-derived growth factor; PDGFR, platelet-derived growth factor receptor; ALDH, aldehyde dehydrogenase; ATRA, all-trans retinoid acid; COX, cyclooxygenase; 5-LOX, Arachidonate 5-lipooxygenase; NK, natural killer cells; CAR, chimeric antigen receptor; EpCAM, epithelial cell adhesion molecule; ATR, ataxia telangiectasia and Rad3-related protein; OCT4, Octamer-binding transcription factor 4; SOX2, sex determining region Y-box 2; NANOG, homeobox protein NANOG; FAK, focal adhesion kinase; CCNE1, cyclin E1; MSH, Musashi protein; siRNA, small interfering RNA; NAMPT, nicotinamide phosphoribosyltransferase; PORCN, porcupine acetyltransferase; SMO, smoothened receptor; moAb, monoclonal antibody; DLL4, delta-like ligand-4; VEGF, vascular endothelial growth factor; ORR, overall response rate; AMPK, AMP-activated protein kinase; lncRNA, long non-coding RNA; SNHG, small nucleolar RNA host gene 1; OS, overall survival; Src, Src non-receptor tyrosine kinase; MAPK, mitogen-activated protein kinase; JAK, Janus kinase; STAT, signal transducer and activator of transcription protein; DNMT1, DNA-(cytosine-5)-methyltransferase-1; ORR, overall response rate; PNA, peptide nucleic acid; HOTAIR, lac RNA HOX antisense intergenic RNA; PFS, progression-free survival; HDAC, histone deacetylase; MHC, major histocompatibility complex; HR, homologous recombination; USP13, ubiquitin specific peptidase 13; NKX2-8, NK2 Homeobox 8 protein.