Mucormycosis, a fungal infection caused by fungi from the order Mucorales, can cause severe disease, especially in immunocompromised subjects. These fungi are ubiquitous and can be found in environmental sources such as crop residues and soil. Among the multiple factors that increase the risk of mucormycosis infection are immunosuppression and diabetes mellitus.
The infection is highly invasive, with a mortality rate exceeding 40%, and closer to 100% in individuals where the infection is disseminated and in patients with neutropenia who are unable to mount a defense against infection, thus representing an area of unmet need.
In a paper appearing March 12, 2025, in Science Translational Medicine, researchers from Vitalex Biosciences LLC, Lundquist Institute, Harbor-University of California at Los Angeles (UCLA) Medical Center and other collaborators describe humanizing a murine C2 antibody, as a step toward translating a mAb developed for mucormycosis into a clinical candidate. The humanized antibody, VX-01, targets the Mucorales spore coat protein (CotH3), which are fungal invasins that bind to glucose-regulated protein 78 and integrins in host cells.
“One of the things that … is considered to be a hallmark of the disease is the angioinvasion, the ability of the organism to invade blood vessels. If you talk to any clinician, they will tell you the same thing, that this is a fungus that likes to go after blood vessels. And this is also accompanied by a lot of necrosis. You know, you will see that there is a lot of destruction of the tissues,” said Ashraf Ibrahim, senior investigator at the Lundquist Institute and professor of medicine at David Geffen School of Medicine at UCLA.
“Treatment with antifungals is extremely, extremely tough because you cannot really get the antifungal to the site of infection if the blood vessels are destroyed. You know, it is just impossible. And as a result, there is always this high mortality rate associated with mucormycosis,” Ibrahim told BioWorld.
After humanizing the anti-CotH3 murine C2 monoclonal into VX-01, the researchers optimized its affinity for fungal CotH3, aligning the light and heavy chains and the variable region of the antibody. Following this, VX-01 showed a 10-fold increase in binding affinity for CotH3 antigen and demonstrated comparable in vitro and in vivo efficacy to the murine C2 antibody. Immunostaining assays showed VX-01 recognized various Mucorales fungi, including Rhizopus and Cunninghamella.
In earlier work, the researchers have shown that anti-CotH3 polyclonal antibodies enhanced the ability of polymorphonuclear leukocytes (PMNs) to induce damage on Rhizopus delemar by opsonization-mediated killing. In vitro assays were conducted to test VX-01 using PMNs isolated from human peripheral blood cells of healthy subjects and incubated with R. delemar in presence of VX-01 or isotype control IgG.
The results indicate VX-01 doubled the ability of neutrophils to kill R. delemar compared to control isotype at both 1:1 and 1:2 ratios of PMNs:spores cultures (p=0.0299 and 0.0097, respectively), suggesting that VX-01 is opsonophagocytic and a potent candidate against mucormycosis.
When neutropenic mice were infected with R. delemar and treated with VX-01 at 30 µg, the antibody prolonged the survival compared to isotype control (p<0.05). In addition, VX-01 conferred the same level of protection against mucormycosis as the murine antibody C2 clone.
Both C2- and VX-01-treated mice showed a median survival time of >21 days and 60% survival rate, compared to 7 days and 0% rate in mice treated with isotype control IgG. Importantly, since both angioinvasion and vascular leakage are hallmarks of mucormycosis, it was shown that VX-01 significantly reduced the ability of R. delemar to invade human umbilical vein endothelial cells (HUVECs) (p<0.0001), but it had no impact on the ability of the fungus to adhere to HUVECs (p=0.4829), suggesting that VX-01 significantly reduced the fungus angioinvasion/endocytosis ability by 30% compared with isotype control. Moreover, incubating R. delemar-infected HUVECs with VX-01 at 50 μg/mL resulted in around 40% protection of these cells compared to infected cells incubated with the isotype control IgG1 (p=0.0164).
“We started thinking about if we raise antibodies against the binding facet of CotH receptor, we might be able to intervene with the process of invasion. And by doing so, even if you are not killing the organism, … you are doing two things,” Ibrahim said. “One, you are holding the progression of the disease, so, you are preventing it from invading cells. And as a result, you basically stop that process of infection. And then secondly, which is very important, by reducing the ability of the organism to angioinvade, then you are basically increasing the chances of antifungal reaching the site of infection and mopping out and killing basically the fungus.”
The tissue cross-reactivity studies that were conducted in human tissues seem to show VX-01 is probably going to be safe, and there is no toxicity in mice. “The really surprising thing is the amount of protection that we have seen of the humanized anybody in the mouse model, because now this is really a foreign antibody, it is not a mouse antibody anymore,” Ibrahim noted.
The in vivo pharmacokinetics of VX-01 showed average serum concentrations of 0.57, 4.08 and 8.94 μg/mL after 8 h of intravenous injection (elimination phase) in mice after 10-, 30- and 100-μg dosing, respectively. Murine C2 showed concentrations in serum of 2.51, 9.68 and 25.6 μg/mL after injection of 10-, 30- and 100-μg doses, respectively. This indicates C2 murine antibody was more stable in mice serum, but both antibodies demonstrated comparable serum half-life from 3 to 7 days.
Finally, treating neutropenic and diabetic ketoacidosis mice with VX-01 protected them from developing pulmonary mucormycosis by preventing fungal angioinvasion and enhancing the phagocytic killing ability of the immune system. Interestingly, VX-01 could be combined with antifungals such as liposomal amphotericin B or posaconazole to protect mice from mucormycosis, with the mice having a 70% survival rate from combined therapy, compared to 20% survival with VX-01 alone.
Prolonged exposure of R. delemar to VX-01 did not induce resistance mechanisms, with VX-01 still recognizing the fungal spores after being passaged for 20 generations, as shown by flow cytometric analysis.
“The next plan is hopefully we have funding for conducting GLP toxicity studies, so we will do [that] this year,” Ibrahim said. The U.S. National Institute of Allergy and Infectious Diseases has made Mucorales a priority in its Discovery and Development of Novel Therapeutics for Select Fungal Pathogens grant program. “We just applied for it in February, and if we are fully awarded that broad agency announcement contract, we would be able to basically take the antibody all the way to two phase I clinical testing, one in adults and the other one basically would be in seniors.” (Gu, Y. et al. Sci Transl Med 2025, 17(789): eads7369).