Deferoxamine to Minimize Fibrosis During Radiation Therapy

Abstract

Significance:

By 2030, there will be >4 million radiation-treated cancer survivors living in the United States. Irradiation triggers inflammation, fibroblast activation, and extracellular matrix deposition in addition to reactive oxygen species generation, leading to a chronic inflammatory response. Radiation-induced fibrosis (RIF) is a progressive pathology resulting in skin pigmentation, reduced elasticity, ulceration and dermal thickening, cosmetic deformity, pain, and the need for reconstructive surgery.

Recent Advances:

Deferoxamine (DFO) is a U.S. Food and Drug Administration (FDA)-approved iron chelator for blood dyscrasia management, which has been found to be proangiogenic, to decrease free radical formation, and reduce cell death. DFO has shown great promise in the treatment and prophylaxis of RIF in preclinical studies.

Critical Issues:

Systemic DFO has a short half-life and is cumbersome to deliver to patients intravenously. Transdermal DFO delivery is complicated by its high atomic mass and hydrophilicity, preventing stratum corneum penetration. A transdermal drug delivery system was developed to address these challenges, in addition to a strategy for topical administration.

Future Directions:

DFO has great potential to translate from bench to bedside. An important step in translation of DFO for RIF prophylaxis is to ensure that DFO treatment does not affect the efficacy of radiation therapy. Furthermore, after an initial plethora of studies reporting DFO treatment by intravenous and subcutaneous routes, a significant advantage of recent studies is the success of transdermal and topical delivery. Given the strong foundation of basic scientific research supporting the use of DFO treatment on RIF, clinicians will be closely following the results of the ongoing human studies.

Derrick C. Wan, MD

SCOPE AND SIGNIFICANCE

It is projected that there will be >4 million radiation-treated cancer survivors in the United States alone by 2030. Radiation, an indispensable component of cancer therapy, also leads to acute and chronic sequelae, such as fibrosis. Radiation-induced fibrosis (RIF) typically occurs 4–12 months after radiation therapy and progresses over several years. Manifestations of RIF occur in the skin and subcutaneous tissue, lungs, gastrointestinal and genitourinary tracts, as well as any other organs in the treatment field. Here, we first define RIF before performing a comprehensive literature review describing the use of deferoxamine (DFO) in the treatment and prophylaxis of RIF.

TRANSLATIONAL RELEVANCE

The mechanism of RIF can be likened to chronic wound healing. The initial injury triggers acute inflammation, fibroblast activation, and extracellular matrix deposition. Radiation generates reactive oxygen species (ROS), which damage all components of cells, leading to a nonspecific inflammatory response. DFO is a U.S. Food and Drug Administration (FDA)-approved iron chelator for use in blood dyscrasias, which was subsequently found to have proangiogenic properties, while also reducing free radical formation and resultant cell death. DFO has been shown to have preclinical success in the treatment and prophylaxis of radiation-induced bone and skin fibrosis.

CLINICAL RELEVANCE

RIF results in significant suffering, representing a huge unmet biomedical burden. For example, RIF affects 20% of all breast cancer patients resulting in skin pigmentation, reduced elasticity, inhibition of angiogenesis, ulceration, and dermal thickening leading to dehiscence, cosmetic deformity, pain, and need for revisionary reconstructive surgery. DFO is a large molecule, which exceeds the size of molecules that easily penetrate the human stratum corneum (500 Da). The use of reverse micelle (RM) technology has led to an effective transdermal route of administration in the treatment and prophylaxis of RIF in murine studies. Human studies are on the horizon.

BACKGROUND

Radiation therapy and associated complications

Radiation therapy is a cornerstone in the management of patients diagnosed with cancer, and >60% of patients with cancer undergo radiation therapy as part of their primary treatment.¹ It is projected that there will be 4.17 million radiation-treated cancer survivors in the United States alone by 2030.² Radiotherapy is most commonly implemented in the care of patients with breast, prostate, head and neck, and hematological malignancies.² In fact, there were 1.25 million radiation-treated breast cancer survivors in 2016, and this population is projected to exceed 2 million by 2030.² In addition, the absolute numbers of head and neck, rectal and lung cancer survivors are projected to increase over the next decade.²

While radiation certainly confers survival benefit in the treatment of many cancers, it is not without complications. Ionizing radiation induces damage to rapidly proliferating tumor cells in addition to normal tissue within the radiation field. Acute effects of therapeutic radiation typically involve organs with rapid self-renewal potential such as the skin, hematopoietic system, and gastrointestinal tract.¹ The primary targets for acute radiation injury are resident stem cells and active proliferating tissues. In the skin, dermal stem cells are around the basement membrane and are the active proliferating cell component underneath keratinized cells. Dermal cell division and migration occur every 14–21 days and thus, radiation doses of five Gray (radiation dose unit) can generate early erythema, followed by vasodilation, fluid exudation, cellular migration, and loss of plasma proteins.³

In the setting of breast cancer, patients usually receive 45–50 Gray over a period of 5–7 weeks.⁴ Acute radiation dermatitis is extremely common, occurring in upward of 85% of treated patients, and leading to erythema, edema, desquamation, hyperpigmentation, and ulceration.^5,6 In the hematopoietic system, total body irradiation leads to a rapid reduction in circulating B and T lymphocytes, and inhibits the body's ability to respond to new antigens.^3,7 With regard to the gastrointestinal tract, the gastric mucosa renews nearly every day, the small intestine renews every 3 days, and the mucosa of the head and neck and large bowel renew every 2 weeks, thus patients can suffer from early postexposure symptoms, including pain, dry mouth, difficulty swallowing, nausea and vomiting, and poor absorption of nutrients.⁷

On the contrary, RIF represents a long-term side effect secondary to external beam radiation therapy for the treatment of cancer. It occurs in the skin and subcutaneous tissue, lungs, gastrointestinal and genitourinary tracts, as well as any other organs in the treatment field.⁸ RIF typically occurs 4–12 months after radiation therapy and continues to progress over several years.⁸

DISCUSSION

RIF: mechanism

The mechanism of RIF can be likened to the process of chronic wound healing. The initial injury results in an acute inflammatory response, fibroblast recruitment and activation, and extracellular matrix deposition. Radiation works by two primary mechanisms: (1) direct damage to DNA and (2) generation of ROS.^8,9 ROS, including superoxide, hydrogen peroxide, and hydroxyl radicals, are instrumental in the pathogenesis of RIF, and damage all components of cells, including proteins, nucleic acids, and lipids.¹⁰ Subsequently injured cells release chemoattractant molecules, triggering a nonspecific inflammatory response.¹¹ Furthermore, thrombosis and ischemia ensue, enacting further local injury, and leading to additional inflammatory chemokine and cytokine release.^7,8

Proinflammatory cytokines such as tumor necrosis factor alpha, interleukin-1, and interleukin-6 perpetuate the development of ROS, resulting in increased local inflammation and monocyte and lymphocyte trafficking. Platelet-derived growth factor, secreted by macrophages, stimulates the migration of fibroblasts into the injured tissue.¹² This then leads to increased transforming growth factor-beta (TGF-β) secretion in the injured tissue, which is thought to increase fibroblast production and myofibroblast differentiation.¹³ In response to TGF-β, collagen, fibronectin, and proteoglycan secretion by myofibroblasts increases and matrix metalloproteinase (MMP) activity decreases, leading to increased stiffness and thickening of the injured tissue.¹⁴ Excess collagen deposition leads to reduced vascularity and gradual ischemia, which may result in tissue atrophy, organ dysfunction, and tissue necrosis (Fig. 1).^1,11,15,16 Importantly, proinflammatory and profibrotic cytokine cascades and signaling pathways are upregulated for many years after the initial radiation insult, leading to a progressive pathology that ultimately results in substantial fibrosis.

Figure 1.

Proposed mechanism of RIF of the skin: normal wound healing (A) versus RIF (B). Normal wound healing (A) is defined by three phases (left to right): inflammation, proliferation, and remodeling. Inflammation results in an immediate platelet response, cytokine and chemoattractant release, and inflammatory immune cells migration. Proliferation results in fibroblast proliferation, transformation of fibroblasts to myofibroblasts, and angiogenesis leading to scar formation by extracellular matrix and collagen deposition. Remodeling leads to degradation of extra collagen and extracellular matrix, resulting in restoration of skin architecture.⁸⁹ In the case of RIF (B), after acute radiation injury, there is a prolonged phase of proliferation and a defective phase of remodeling, resulting in extensive deposition of extracellular matrix and collagen, which progresses over many years postradiation. Legend shown in upper right figure panel. Figure adapted with permission from Ejaz et al.⁹⁰ and created with Biorender.com. RIF, radiation-induced fibrosis.

RIF: clinical presentation

The clinical presentation is dependent on the type of tissue exposed to irradiation and may manifest, for example, as skin induration and thickening, muscle atrophy, reduced joint mobility, lymphedema, mucosal inflammation and fibrosis, ulceration or fistula and/or pain.¹⁷ RIF can affect any part of the body in the radiation field with clinical manifestations broadly ranging from skin thickening to pulmonary fibrosis, osteonecrosis, neuropathy, proctitis, and cystitis leading to urinary symptoms, enteritis resulting in diarrhea, and loss of reproductive function.¹⁸ Interestingly, RIF usually develops 4–12 months after radiation exposure and progresses over many years.⁸ RIF results in significant suffering and thus represents a huge unmet biomedical burden on modern health care systems. For example, RIF is a common complication of radiation therapy for breast cancer and affects 20% of all breast cancer patients, resulting in skin pigmentation, reduced elasticity, inhibition of angiogenesis, ulceration and dermal thickening leading to wound dehiscence, cosmetic deformity, pain, and need for revisionary reconstructive surgery.¹⁹ Furthermore, it has been demonstrated that overall esthetic results and patient satisfaction are diminished when breast reconstruction is performed in patients who have a history of radiation.^20,21 RIF thus represents a critical barrier to a satisfactory cosmetic result after breast reconstruction and is a visual reminder of past illness.²² With a breast cancer survivorship of >3 million in the United States alone, RIF represents a significant clinical challenge.²³

Influence of RIF on wound healing

RIF of the skin and subcutaneous tissues can further complicate wound healing in patients who develop traumatic or surgical wounds in areas affected by RIF. Due to progressive changes of RIF including cellular depletion, extracellular matrix changes and aberrant collagen deposition, microvascular damage and proinflammatory mediator presence, wound healing after radiation is impaired.²⁴ Wound healing is reported to occur in an ordered sequence of cellular interactions in three main phases: inflammation, proliferation, and maturation. RIF affects each phase of wound healing by dysregulation of key signaling pathways necessary for each phase to result in soft-tissue reconstitution.²⁴ For example, keratinocytes are key cells present in wound healing. Keratinocytes obtained from wounds with RIF show a predominance of low molecular keratins in comparison with high molecular weight keratins in nonirradiated tissue. The irradiated keratinocytes also show reduced expression of TGF-β, FGF-1 (fibroblast growth factor-1), FGF-2 (fibroblast growth factor-2), and vascular-endothelial growth factor (VEGF) in comparison with nonirradiated tissue. In addition, expression of MMPs has been shown to be elevated in irradiated keratinocytes and fibroblasts, and this excess protease activity can lead to chronic nonhealing wounds.^25,26

Furthermore, fibroblasts, the key cells involved in deposition and remodeling of the extracellular matrix, are affected by RIF. Irradiated fibroblasts deposit collagen in a disorganized manner, most likely secondary to RIF-induced MMP and tissue inhibitors of matrix metalloproteinase dysfunction.^26–28 Impaired postoperative wound healing resulting from chronic RIF sequelae can result in the need for plastic and reconstructive surgery, whereby healthy tissue is brought into the area by means of complex reconstructive surgery (e.g., regional or free tissue transfer).

As plastic surgeons, the chronic effects of RIF on postoperative wound healing are commonly seen. A frequently observed example of the chronic progressive effects of RIF occurs in the setting of tissue-expander-based breast reconstruction. Here, patients with a remote prior history of chest irradiation who undergo tissue-expander-based breast reconstruction have an increased rate of complications relative to patients without a history of prior chest irradiation. Not only do these patients have an elevated rate of wound healing complications due to the sequelae discussed above, but tissue expansion is also difficult due to the fibrotic changes of the skin and subcutaneous tissue with increased rates of breast asymmetry postreconstruction.^29–32

Existing treatment modalities for RIF

Prevention is better than cure, as fibrotic complications are among the most difficult sequelae to address in oncology patients.²² Although some modalities currently exist to delay the onset or reduce the severity of RIF, strategies that minimize the exposure of healthy tissues to the radiation field are the key. However, there are tissues that cannot be avoided in the radiation field, thus leading to RIF. There are limited interventions that target the improvement of the adverse effects of RIF, and restore the appearance and function of the skin. Symptomatic treatment is common, and specific interventions vary by the severity and location of the fibrosis.

Supportive measures include pain management, physical therapy and massage, and wound care, including hyperbaric oxygen therapy.²² Results regarding massage therapy are varied. In a randomized control trial, mechanical massage was found to be superior to observation alone leading to reduced erythema, pain, pruritis, and skin induration³³; however, a contrasting study demonstrated no improvement in the skin appearance but did note an improvement in muscular spasm.^34,35 Physical therapy can aid in jaw opening in radiation-associated trismus, usually occurring in the setting of head and neck cancer; however, it requires motivated patients and therapists.⁸ Botulinum toxin A injection can also be used for palliation in this setting to improve pain and reduce masticator muscle spasm, but it has not been shown to significantly affect jaw opening.^8,36

Systemic therapy such as pentoxifylline and vitamin E has been used to mitigate the effects of RIF and associated skin fibrosis. While randomized control trials of pentoxifylline and vitamin E have been favorable even when administered years after the development of RIF, patient compliance with therapy can be challenged by adverse effects including severe nausea.^37–39 Topical steroids including betamethasone, methylprednisolone, and mometasone have also been studied extensively in RIF of the skin, and are found to delay the development of RIF but do not prevent its occurrence, and also have a significant side effect profile with prolonged use.^40,41 Surgical treatment in the form of autologous fat grafting has been shown to improve skin vascularization, reduce fibrosis, and lead to visible and symptomatic improvements in patients with postirradiated, fibrotic skin.^35,42–44 However, this technique requires an invasive procedure along with a donor site for fat harvest with attendant risk of additional morbidity.

Therapeutic effects and mechanism of DFO

DFO mesylate is an FDA-approved iron-chelating agent, which was initially implemented in the clinical treatment of hemochromatosis,⁴⁵ and later in thalassemia management,^46,47 and which has subsequently been explored in animal models of diabetic ulcers.⁴⁸ DFO is a naturally occurring trihydroxamic acid produced by Streptomyces pilosus. Clinical trials of DFO demonstrated that regular chelation therapy decreases hepatic iron and ameliorates multisystemic dysfunction when administered intramuscularly,⁴⁹ intravenously,⁵⁰ or subcutaneously.⁵¹ Interestingly, it was subsequently shown that DFO increases VEGF production through the hypoxia-inducible factor 1 alpha (HIF-1α) pathway when administered locally.⁵² Beerepoot et al. demonstrated that decreased cellular iron availability after DFO treatment of myriad cell lines increases VEGF mRNA expression and VEGF protein translation.⁵² Iron is a necessary cofactor for prolyl 4-hydroxylase (PHD), the enzyme responsible for constitutively degrading HIF-1α. By sequestering iron, DFO inactivates PHD resulting in increased HIF-1α accumulation and increased VEGF transcription⁵³ (Fig. 2).

Figure 2.

Proposed mechanism of action of DFO. Decreased cellular iron availability after DFO treatment increases VEGF mRNA expression and VEGF protein translation.⁵² Iron (Fe²⁺) is a necessary cofactor for PHD, the enzyme responsible for constitutively degrading HIF-1α. By sequestering iron, DFO inactivates PHD resulting in increased HIF-1α accumulation and increased VEGF transcription.⁵³ DFO prevents iron-catalyzed reactive oxygen stress,⁴⁸ while also reducing free radical formation and resultant cell death.^54,55 Figure created with Biorender.com. HIF-1α, hypoxia-inducible factor 1 alpha; DFO, deferoxamine; PHD, prolyl 4-hydroxylase; VEGF, vascular-endothelial growth factor.

Further work by Duscher reported that DFO corrects impaired HIF-1α-mediated transactivation in diabetes by preventing iron-catalyzed reactive oxygen stress,⁴⁸ while also reducing free radical formation and resultant cell death.^54,55 These findings led to the development of a local transdermal DFO drug delivery system, as systemic DFO is not a viable therapeutic option in diabetic patients due to risk of potential toxicity and its short plasma half-life.⁵⁶ The IC-50 (describing the half-maximal inhibitory concentration, which is a measure of the potency of an inhibitor) is cited as 10–22 μM for in vitro experiments, but has not been reported in the setting of in vivo treatment.⁵⁷ Furthermore, chelation theoretically occurs on a 1:1 molar basis, hence it is estimated that 100 parts by weight of DFO can bind ∼8.5 and 4.1 parts by weight of trivalent iron and aluminum, respectively.⁵⁸

Transdermal delivery of DFO is complicated by a high atomic mass and hydrophilicity, which prevents penetration of the lipophilic stratum corneum, the outermost layer of the skin.⁵⁹ Thus, a matrix type of transdermal drug delivery system (TDDS) was developed encapsulating DFO with nonionic surfactants and polymers for delivery enhancement.^48,59,60 This so-called “reverse micelle” delivery system then permitted delivery of DFO through the hydrophobic stratum corneum^48,61,62 (Fig. 3). When this transdermal technology was then implemented in an animal model of diabetic pressure sores, Duscher et al. demonstrated that it resulted in prevention of ulcer formation and improvement of diabetic wound healing by reducing hyperglycemia-induced oxidative stress, which impairs HIF-1α activation.⁴⁸ Building on this work, Bonham et al. then demonstrated that transdermal DFO delivery can similarly prevent pressure ulcers and normalize wound healing in aging mice, and that these findings were also mediated by the HIF-1α pathway, resulting in stabilization of HIF-1α and improved neovascularization.⁶³

Figure 3.

Development of a TDDS for DFO. DFO aggregates with PVP and surfactants to form RMs. RMs are dispersed in the polymer ethyl cellulose. After release from the polymer matrix, the RMs enter the stratum corneum and disintegrate. PVP dissolves and DFO is delivered to the dermis. Figure adapted with permission from Shen et al.⁸⁵ and designed using Biorender.com. PVP, polyvinylpyrrolidone; RM, reverse micelle; TDDS, transdermal drug delivery system.

Lower extremity ulcers are also a devastating complication of sickle cell disease, and can form over the medial or lateral malleoli. These ulcers are slow to heal and prone to recidivism. Work by Rodrigues et al. demonstrated the utility of transdermal delivery of DFO in dysfunctional wound healing.⁶⁴ In their work, they implemented DFO released from TDDS into wounds of a transgenic animal model of sickle cell disease with resultant chelation of excess dermal free iron and improved wound healing when compared with control.⁶⁴ A randomized double-blind placebo-controlled pilot study of the safety and efficacy of DFO intradermal delivery patch in sickle cell ulcer treatment is ongoing, with results expected in 2022.⁶⁵ The beneficial effects of DFO have also been seen with ischemic flaps in both a porcine model with intramuscular DFO delivery⁶⁶ and a mouse model after subcutaneous DFO delivery with resultant increased skin flap perfusion and increased capillary density seen in treated animals.⁶⁷

DFO and RIF

Iron chelators were first proposed as radioprotective agents in the late 1980s^68–71 and were implemented clinically as adjunctive radioprotective agents together with vasoactive medications for protection of the spinal cord in the 1990s.⁷² A hallmark feature of RIF is obliteration of the microvasculature and tissue ischemia, and as DFO has been demonstrated to augment angiogenesis and reduce ROS, a logical step was to investigate the role of DFO in ameliorating RIF. As RIF is a progressive disease, for maximal effect one could argue the importance of the early use of DFO in RIF intervention, as this will theoretically allow minimization of progressive dysregulated downstream wound healing signaling pathways characteristic of RIF.

In 2012, Farberg et al. demonstrated that DFO reversed radiation-induced hypovascularity during bone regeneration and repair in the murine mandible.⁷³ Donneys et al. then examined the role of local injection of DFO in the setting of radiation-induced pathologic mandible fractures, demonstrating that local DFO therapy remediated the severe vascular diminution after human equivalent dose of radiotherapy in a rat model.⁷⁴ Building upon many promising animal studies,^75–78 Momeni et al. described the novel clinical use of DFO in a young man undergoing maxillary distraction osteogenesis in the setting of radiation-induced maxillary hypoplasia. Interestingly, both the bone area and density with DFO treatment were increased relative to untreated distracted maxillary bone after a period of 3 months.⁷⁹

One of the most troubling sequelae of RIF for our patients is due to radiation-induced dysfunction of the salivary glands, which results in a dry mouth, difficulty swallowing, and trouble eating. Zhang et al. administered DFO intraperitoneally pre- and/or postradiation in a mouse model, which led to improvements in salivary flow rate, a surrogate for salivary gland function, while also increasing angiogenesis in irradiated tissues. The authors hypothesized that the improvement in salivary flow rate was due to reduced apoptosis of acinar cells, increased angiogenesis, and preservation of stem cells.⁸⁰

Soft-tissue reconstruction using autologous tissue transfer is commonly performed after extirpation of tumors of the breast, and head and neck. In breast reconstruction, a requirement for postoperative radiation can lead to a common practice of delaying autologous reconstruction, resulting in a need for further surgeries beyond the index cancer resection, due to the chronic sequelae of RIF (including atrophy, fat necrosis, breast mound distortion, and skin changes⁸¹) on the transferred soft tissue. In 2015, Mericli et al. implemented subcutaneous injections of DFO 4 weeks after transverse rectus abdominus myocutaneous flap creation and adjuvant radiotherapy in a rat model.⁸² Using histologic assessment, micro-CT angiography, and tensiometry, the authors demonstrated that irradiated flaps, which underwent DFO treatment, had thicker epidermis, increased vascularity, and increased elasticity in comparison with the control-untreated group.⁸²

Incorporating the topical method of DFO administration generated by Gurtner and colleagues, and discussed above,⁴⁸ Snider demonstrated the efficacy of DFO in alleviation of skin injury after radiation in a murine implant-based breast reconstruction model. Here, they observed a lack of radiation-associated alopecia, grossly normal collagen I fibril organization, and sixfold reduction in skin ulceration in the DFO group relative to control.⁸³

Dassoulas et al. further validated the efficacy of topical DFO in their study of tissue-expander-based breast reconstruction in an irradiated rat model.⁵³ In their work, they described using a proprietary preparation of topical DFO⁸⁴ with 20% wt/wt DFO (Hospira, Inc., Lake Forest, IL) in dimethylsulfoxide (Gaylord Chemical Company, Slidell, LA) added to Unguentum M (Hermal, Reinbek, Germany), a paraffin-based moisturizing cream. After a 10-day treatment regimen, topical DFO treatment was associated with greater vascularity in expanded and irradiated tissue relative to nontreated irradiated controls. In addition, they demonstrated that radiation resulted in reduced skin pliability, which manifested as a lower mean final expander volume when compared with nonirradiated rats. Topical DFO application led to mean final expander volume in irradiated rats, which was similar to that of the control (nonirradiated, no DFO) treatment group.

More recently, Shen et al. questioned whether topical DFO administration using a TDDS, as described by Gurtner and colleagues,⁴⁸ could mitigate the chronic effects of radiation damage to the skin. As RIF is a progressive disease, here, the authors also examined the treatment effects when DFO was administered prophylactically—before radiation therapy commencement. After assessment of multiple study groups (including irradiation alone, DFO treatment 2 weeks after irradiation, DFO with treatment pre- and postirradiation and sham [no irradiation/no DFO]), their results showed that topical DFO reduced levels of ROS and apoptotic cell markers, ameliorated skin perfusion and vascularity, and decreased fibrotic skin changes, with the most significant benefit seen in mice that received continuous DFO topical therapy before initiation of irradiation.⁸⁵ These results certainly highlight a potential role of prophylactic transdermal DFO treatment for patients undergoing radiation therapy (Fig. 4).

Figure 4.

DFO is effective in prophylaxis of RIF in a mouse model. Laser Doppler analysis and vascularity of scalp skin. Note here “ppx” denotes “prophylaxis.” (A) CD1 Nude mouse with the irradiated area of skin represented by the overlying white box. (B) Representative images of laser Doppler perfusion imaging of treatment and control mouse scalps showing perfusion immediately after radiation (left; irradiated without DFO [top] or with DFO prophylactic treatment [bottom]) and 6 weeks after IR (right). Black/dark blue colors represent lower perfusion and yellow/red colors represent higher perfusion. (C) Quantification of the laser Doppler perfusion index immediately after IR (*p < 0.05, **p < 0.01) and (D) 6 weeks after IR (**p < 0.01). (E) Immunohistochemical staining showing vascular density in all four groups of mice. Endothelial cells were stained with CD31 (PECAM, red) and nuclei were stained with DAPI (blue). Scale bar: 100 μm. (F) Quantification of mean pixels positive for CD31 in all four groups of mice. The skin of nonirradiated mice was significantly more vascularized than the skin of irradiated mice receiving no DFO treatment (****p < 0.0001) and DFO postirradiation only (***p < 0.001). The skin of mice receiving prophylactic DFO treatment was significantly more vascularized than the skin of irradiated mice receiving no DFO (*p < 0.05). Reproduced with permission from Shen et al.⁸⁵

Finally, fat grafting is a technique implemented by plastic surgeons to improve the quality of irradiated skin and restore soft-tissue deficit after cancer treatment. Fat is harvested using liposuction and prepared for injection in the operating room. However, fat graft retention volume in irradiated tissue is lower than that in nonirradiated tissues.^43,86 As DFO has been shown to improve angiogenesis,⁸⁷ Flacco et al. explored DFO as an adjunct to fat grafting therapy of irradiated tissues. In their study, they explored if preconditioning of irradiated skin with DFO or saline control resulted in improved fat graft retention. After 8 weeks of radiographic examination, they demonstrated that DFO importantly improved fat graft volume retention. Fat graft treatment in concert with DFO treatment also led to histologic improvement in the irradiated skin.⁸⁸

Next steps

As DFO is already FDA approved for use in blood dyscrasias, it has great potential to translate from bench to bedside. Importantly, it remains to be verified whether DFO will impact oncologic outcomes. An important step in translation of DFO for RIF prophylaxis and treatment is to ensure that DFO treatment does not affect the efficacy of radiation therapy, a cornerstone of oncologic treatment. Furthermore, after an initial plethora of studies reporting DFO treatment by intravenous and subcutaneous routes, a significant advantage in recent studies is the predominance of transdermal and topical studies. DFO is a large molecule measuring 656.7 Da, which exceeds the size of molecules that easily penetrate the human stratum corneum (500 Da).⁸⁹ The use of RM technology has led to a viable transdermal route of administration, and was shown to be effective for both ulcer treatment and prevention in wounded and intact skin of mice.^48,63,64 Both transdermal and topical DFO administration routes have yet to be verified in large animal and human studies. Certainly given the strong foundation of basic scientific research supporting the use of DFO, and delineating the mechanism of DFO treatment of RIF, clinicians will be closely following the results of upcoming human studies.

SUMMARY

By 2030, there will be >4 million radiation-treated cancer survivors in the United States alone. Radiation, a cornerstone of cancer therapy, leads to chronic sequelae, such as fibrosis. RIF typically occurs 4–12 months after radiation therapy and progresses over several years. Irradiation triggers acute inflammation, fibroblast activation, and extracellular matrix deposition in addition to the generation of ROS, which damage all components of cells, leading to a nonspecific inflammatory response. DFO is an FDA-approved iron chelator for use in blood dyscrasias, which was subsequently found to be proangiogenic, and to reduce free radical formation and resultant cell death. By sequestering iron, DFO inactivates PHD resulting in increased HIF-1α accumulation and increased VEGF transcription. DFO has been shown to have preclinical success in the treatment and prophylaxis of diabetic and sickle cell ulcers, in addition to utility with radiation-injured bone and skin fibrosis.

Topical and transdermal delivery is ideal in the setting of dermatologic disorders, avoiding the need for repeated intravenous access. Transdermal delivery of DFO is complicated by a high atomic mass and hydrophilicity, which prevents penetration of the lipophilic stratum corneum and thus, different strategies have been implemented to augment topical therapy. As DFO is already FDA approved for use in blood dyscrasias, it has great potential to translate from bench to bedside. An important step in translation of DFO for RIF prophylaxis and treatment is to ensure that DFO treatment does not affect the efficacy of radiation therapy, a cornerstone of oncologic treatment. Furthermore, after an initial plethora of studies reporting DFO treatment by intravenous and subcutaneous routes, a significant advantage in recent studies is the predominance of transdermal and topical studies. With strong foundation of basic scientific research supporting the use of DFO treatment on RIF, this therapeutic strategy holds great promise for future treatment of radiation-associated soft-tissue injury.

TAKE HOME MESSAGES

• >60% of cancer survivors undergo irradiation, which is associated with acute and chronic sequelae.

• RIF is a chronic, progressive process that leads to hypovascularity, ulceration, poor wound healing, and functional and cosmetic defects.

• DFO is an FDA-approved iron chelator that has been shown to increase angiogenesis, scavenge ROS, and reduce cell death.

• Studies demonstrate the efficacy of systemic, subcutaneous, and transdermal DFO therapy in the reduction of radiation-induced fibroses in mouse and rat models. Topical and transdermal therapy is preferred in the management of cutaneous fibrosis.

• Randomized prospective studies are awaited but, as DFO is already FDA approved for use in blood dyscrasias, it has great potential to translate from the bench to bedside.

Abbreviations and Acronyms

DFO

deferoxamine

FDA

U.S. Food and Drug Administration

FGF-1

fibroblast growth factor 1

FGF-2

fibroblast growth factor 2

HIF-1α

hypoxia-inducible factor 1 alpha

MMP

matrix metalloproteinase

PVP

polyvinylpyrrolidone

RIF

radiation-induced fibrosis

RM

reverse micelle

ROS

reactive oxygen species

TDDS

transdermal drug delivery system

TGF-β

transforming growth factor-beta

VEGF

vascular endothelial growth factor

ACKNOWLEDGMENTS AND FUNDING SOURCES

The authors thank Paulo Pereira and Virginia Ford for excellence in laboratory management. This work was supported by the Oak Foundation and the Hagey Laboratory for Pediatric Regenerative Medicine. R.T. was also supported by the Plastic Surgery Research Council Research Fellowship Grant and the Stanford University Transplant and Tissue Engineering Center of Excellence Research Grant. M.T.L. was supported by NIH Grant R01 GM136659 and R01 GM116892. D.C.W. was supported by NIH Grant R01 DE027346, R01 GM136659, and U24 DE026914.

AUTHOR DISCLOSURE AND GHOSTWRITING

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

ABOUT THE AUTHORS

Ruth Tevlin, MB, BAO, BCh, MRCSI, MD, is a Postdoctoral Research Fellow at Stanford University and a Plastic Surgery Resident at Stanford Hospital and Clinics. Michael T. Longaker, MD, MBA, FACS, is a federally funded board-certified General and Plastic Surgeon Scientist. Derrick C. Wan, MD, is a federally funded board-certified Plastic Surgeon Scientist.

AUTHORS' CONTRIBUTIONS

R.T., M.T.L., and D.C.W. wrote, edited, and approved the final article. They agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.