Carbonic Anhydrase Inhibitors

Combination therapy, a treatment modality that combines two or more therapeutic agents, is a cornerstone of cancer therapy. The amalgamation of anti-cancer drugs enhances efficacy compared to the mono-therapy approach because it targets key pathways in a characteristically synergistic or an additive manner. This approach potentially reduces drug resistance, while simultaneously providing therapeutic anti-cancer benefits, such as reducing tumour growth and metastatic potential, arresting mitotically active cells, reducing cancer stem cell populations, and inducing apoptosis. The 5-year survival rates for most metastatic cancers are still quite low, and the process of developing a new anti-cancer drug is costly and extremely time-consuming. Therefore, new strategies that target the survival pathways that provide efficient and effective results at an affordable cost are being considered. One such approach incorporates repurposing therapeutic agents initially used for the treatment of different diseases other than cancer. This approach is effective primarily when the FDA-approved agent targets similar pathways found in cancer. Because one of the drugs used in combination therapy is already FDA-approved, overall costs of combination therapy research are reduced. This increases cost efficiency of therapy, thereby benefiting the "medically underserved". In addition, an approach that combines repurposed pharmaceutical agents with other therapeutics has shown promising results in mitigating tumour burden. In this systematic review, we discuss important pathways commonly targeted in cancer therapy. Furthermore, we also review important repurposed or primary anti-cancer agents that have gained popularity in clinical trials and research since 2012.

Carbonic anhydrases (CAs) catalyze the reversible hydration of carbon dioxide to produce bicarbonate and a proton. Multiple CA isoforms are implicated in a range of diseases, including cancer. In solid tumors, continuously dividing cells create hypoxic conditions that eventually lead to an acidic microenvironment. Hypoxic tumor cells have different mechanisms in place to regulate and adjust the surrounding microenvironment for survival. These mechanisms include expression of CA isoform IX (CA IX) and XII (CA XII). These enzymes help maintain a physiological intracellular pH while simultaneously contributing to an acidic extracellular pH, leading to tumor cell survival. Expression of CA IX and CA XII has also been shown to promote tumor cell invasion and metastasis. This review discusses the characteristics of CA IX and CA XII, their mechanism of action, and validates their prospective use as anticancer targets. We discuss the current status of small inhibitors that target these isoforms, both classical and non-classical, and their future design in order to obtain isoform-specificity for CA IX and CA XII. Biologics, such as monoclonal antibodies, monoclonal-radionuclide conjugated chimeric antibodies, and antibody-small molecule conjugates are also discussed.

Carbonic anhydrases (CAs) catalyze a reaction fundamental for life: the bidirectional conversion of carbon dioxide (CO2) and water (H2O) into bicarbonate (HCO3-) and protons (H+). These enzymes impact numerous physiological processes that occur within and across the many compartments in the body. Within compartments, CAs promote rapid H+ buffering and thus the stability of pH-sensitive processes. Between compartments, CAs promote movements of H+, CO2, HCO3-, and related species. This traffic is central to respiration, digestion, and whole-body/cellular pH regulation. Here, we focus on the role of mathematical modeling in understanding how CA enhances buffering as well as gradients that drive fluxes of CO2 and other solutes (facilitated diffusion). We also examine urinary acid secretion and the carriage of CO2 by the respiratory system. We propose that the broad physiological impact of CAs stem from three fundamental actions: promoting H+ buffering, enhancing H+ exchange between buffer systems, and facilitating diffusion. Mathematical modeling can be a powerful tool for: (1) clarifying the complex interdependencies among reaction, diffusion, and protein-mediated components of physiological processes; (2) formulating hypotheses and making predictions to be tested in wet-lab experiments; and (3) inferring data that are impossible to measure.

Persistent vulnerability to drug-seeking is driven by enduring synaptic adaptations, yet current μ-opioid receptor-targeting pharmacotherapies provide limited efficacy against these neuroadaptations. Thus, there is a critical need for mechanistically distinct, non-opioid interventions. We recently found that carbonic anhydrase 4 (CA4) disruption reduces cocaine-induced synaptic adaptations and drug-seeking. Building on this foundation, we sought to determine whether deleting CA4 or pharmacological inhibition with acetazolamide (AZD), a clinically employed carbonic anhydrase inhibitor-could mitigate opioid withdrawal-associated plasticity and thus might reduce relapse vulnerability. We studied synaptic and behavioral adaptations to withdrawal from oxycodone in mice and found that prolonged withdrawal from oxycodone increased the AMPAR/NMDAR ratio and promoted synaptic incorporation of Ca2+-permeable AMPARs in nucleus accumbens core (NAcC) medium spiny neurons (MSNs). We found synaptic changes after protracted withdrawal from multiple opioids, which were most pronounced in D1-expressing MSNs, and were prevented by CA4 disruption. Moreover, AZD reversed withdrawal-induced synaptic alterations both in vitro and in vivo, in a CA4- and acid-sensing ion channel 1A (ASIC1A)-dependent manner. Unlike withdrawal from cocaine, withdrawal from oxycodone did not alter dendritic spine density in NAcC MSNs, suggesting a distinct mode of plasticity. Finally, following oxycodone self-administration, both CA4 deletion and a single systemic AZD dose reduced drug-seeking after prolonged abstinence. Together, these findings identify CA4 as a regulator of opioid-induced synaptic adaptations and suggest AZD as a promising, readily translatable pharmacological intervention. By targeting a pathway independent of classical opioid receptor signaling, CA4 inhibition represents a mechanistically distinct strategy that may reduce relapse vulnerability in OUD.