Table 2.

Summary of published clinical trials using hypoxia targeting strategies

Target	IMP	Treatment	Trial Phase	Patients Treated	Disease type	Findings	Reference
Hypoxia-activated Prodrugs	Evofosfamide (TH-302)	Pazopanib + Evofosfamide	I	30	All solid tumours	Partial response in 10%, stable disease in 57%, progressive disease in 23% of patients	(Riedel et al., 2017) [114]
		Evofosfamide monotherapy in relapsed/refractory leukaemia	I	49	Acute myeloid/lymphoid leukaemia	Reduced HIF1a/CAIX but only 6% overall response rate	(Badar et al., 2016) [115]
		Gemcitabine Vs Gemcitabine + Evofosfamide	II	214	Pancreatic	Extended progression-free survival (5.6 vs 3.6 months; p = 0.005), greater reduction in tumour burden (p = 0.04) and CA19.9 levels (p = 0.008) with addition of Evofosfamide. No significant difference in overall survival	(Borad et al., 2015) [116]
		Evofosfamide + Dexamethasone ± Bortezomib	I-II	59	Multiple myeloma	Stable disease (38/59) or better in 80% patients across all cohorts	(Laubach et al., 2019)
		Doxorubicin Vs Doxorubicin + Evofosfamide	III	640	Soft-tissue sarcoma	No survival benefit (18.4 months combination therapy Vs 19.0 months Doxorubicin monotherapy median overall survival)	(Tap et al., 2017) [117]
		Gemcitabine Vs Gemcitabine + Evofosfamide	III	693	Pancreatic	Overall survival endpoint not quite met (8.7 months combination therapy Vs 7.6 months Gemcitabine monotherapy; p = 0.059). Median progression-free survival 5.5 months combination therapy V 3.7 months Gemcitabine monotherapy (P = 0.004)	(Van Cutsem et al., 2016) [119]
	Tirapazamine (SR-4233)	Tirapazamine (TPZ) + Carboplatin + Paclitaxel	I	42	All solid tumours	8% complete response, 5% partial response, 60% stable disease, 26% progression of disease	(Lara et al., 2003) [120]
		Cisplatin + radiotherapy + Tirapazamine	I	16	Oesophageal adenocarcinoma	Three year overall survival 88%, but omission of Tirapazamine needed in latter cycles to avoid dose-limiting toxicity of neutropenia	(Rischin et al., 2001) [121]
		Arterial Embolisation + Tirapazamine	I	27	Hepatocellular carcinoma	60% complete response, 84% objective response	(Abi-Jaoudeh et al., 2021) [122]
		Cisplatin + Etoposide + radiotherapy + Tirapazamine	II	69	Limited-stage small cell lung cancer	Median progression-free survival 11 months, median overall survival 21 months	(Le et al., 2009) [123]
		Paclitaxel + Carboplatin ± Tirapazamine	III	367	Non-small cell lung cancer	Overall survival end-points not reached, significantly more adverse events leading to treatment cessation when Tirapazamine added to combination therapy (p < 0.05), mostly due to myelosuppression	(Williamson et al., 2005) [124]
	PR-104	PR-104 + Docetaxel or Gemcitabine	I	42	All solid tumours	9.5% partial response overall, significant myelosuppression prevented further analysis of combo + Gemcitabine	(McKeage et al., 2012) [125]
		PR-104	I	27	All solid tumours	No objective responses were observed	(Jameson et al., 2010) [126]
		PR-104	I-II	50	Acute myeloid/lymphoid leukaemia	Objective response in 32% AML and 20% ALL patients	(Konopleva et al., 2015) [127]
HIF Signalling	Belzutifan	Belzutifan	I	98	Renal cell carcinoma	Objective response in 25%, median progression-free survival was 14.5 months	(Choueiri et al., 2021) [112]
		Belzutifan	II		VHL-associated tumours	Objective response in 49% renal cell carcinomas, 77% pancreatic lesions, 30% CNS haemangioblastomas, 100% retinal haemangioblastomas	(Jonasch et al., 2021) [111]
	PT2385	PT2385	I	51	Renal cell carcinoma	2% complete response, 12% partial response, 52% stable disease	(Courtney et al., 2018) [113]
	CRLX101	CRLX101 + Bevacizumab	I-II	22	Renal cell carcinoma	23% partial response, 55% achieving progression-free survival of more than four months	(Keefe et al., 2016) [109]
		CRLX101 + Bevacizumab Vs standard of care (SOC) therapy	II	111	Renal cell carcinoma	No improvement in progression-free survival (3.7 months CRLX101 + Bevacizumab Vs 3.9 months SOC therapy; p = 0.831) or objective response (5% CRLX101 + Bevacizumab Vs 14% SOC therapy; p = 0.836)	(Voss et al., 2017) [110]
	PX-12	PX-12 (thioredoxin-1 inhibitor)	I	38	All solid tumours	18% stable disease, as best response observed	(Ramanathan et al., 2007) [128]
		PX-12	I	14	All solid tumours	7% stable disease, as best response observed	(Ramanathan et al., 2012) [129]
	Tanespimycin	Tanespimycin + Bortezomib	I	17	All solid tumours	6% stable disease, as best response observed	(Schenk et al., 2013) [102]
CXCR4 (haematological malignancies)	BL-8040	BL-8040 + Ara-C	II	42	Acute myeloid leukaemia	29% complete remission ± incomplete haematological recovery. Median overall survival 8.4 months	(Borthakur et al., 2021) [130]
	Plerixafor	Plerixafor + high-dose cytarabine + etoposide	I	19	Acute myeloid/lymphoid leukaemia, myelodysplastic syndrome	16% objective response, exclusively in acute myeloid leukaemia	(Cooper et al., 2017) [131]
		Plerixafor + Decitabine	I	69	Acute myeloid/lymphoid leukaemia, myelodysplastic syndrome	43% objective response	(Roboz et al., 2018) [132]
		Plerixafor + FLAG-IDA	I-II	41	Acute myeloid leukaemia	Complete remission ± incomplete haematological recovery in 50% and 47% of primary refractory and early relapse groups respectively	(Martínez-Cuadrón et al., 2018) [133]
	Ulocuplumab	Ulocuplumab + MEC (mitoxantrone + etoposide + cytarabine)	I	73	Acute myeloid leukaemia	Complete remission ± incomplete haematological recovery in 51% combination therapy compared with 24–28% in those receiving MEC alone	(Becker et al., 2014) [134]

Evofosfamide is a second-generation hypoxia-activated prodrug (HAP) consisting of a dual moiety in which bromo-iso-phosphoramide (Br-IPM) is attached to the enzyme responsible for its reduction-dependent activation, 2-nitroimidazole. Tirapazamine generates an oxidative radical following reduction in hypoxic conditions. This occurs preferentially in the nucleus leading to DNA double-strand breaks, chromosomal degradation and ultimately to apoptosis. PR-104 contains a nitrogen mustard moiety which, when activated by reduction in hypoxia, is able to cross-link DNA to prevent further replication. Belzutifan is a small molecule selective HIF2α inhibitor. PT2385 similarly acts as an antagonist of HIF2α. CRLX-101 is a nanopharmaceutical agent which conjugates a camptothecin moiety to a polyethene glycol co-polymer. PX-12 is a small molecule inhibitor of thioredoxin-1 (Trx-1), a redox protein pivotal for HIF1α and VEGF. Tanespimycin is a Geldanamycin semi-synthetic derivative inhibitor of heat shock protein 90 (HSP90) which binds to and stabilises HIF1α. BL-8040 is a CXCR4 antagonist, a downstream target of HIF1a. Plerixafor is similarly a CXCR4 antagonist whilst Ulocuplumab is a fully human IgG4 monoclonal antibody which prevents the binding of CXCR4 to CXCL12