pH-responsive tumor-targeted drug delivery is a specialized form of targeted drug delivery that utilizes nanoparticles to deliver therapeutic drugs directly to cancerous tumor tissue while minimizing its interaction with healthy tissue. Scientists have used drug delivery as a way to modify the pharmacokinetics and targeted action of a drug by combining it with various excipients, drug carriers, and medical devices. These drug delivery systems have been created to react to the pH environment of diseased or cancerous tissues, triggering structural and chemical changes within the drug delivery system. This form of targeted drug delivery is to localize drug delivery, prolongs the drug's effect, and protect the drug from being broken down or eliminated by the body before it reaches the tumor.
Tumor Environment
The microenvironment of a tumor is different compared to normal healthy tissues in the body. One distinct difference is the pH levels. The human body overall tends to have a more alkaline pH level of 7.4 while tumor tissue ranges from 7.0- 7.2 pH level, which is known as tumor acidosis. Tumor acidosis can occur due to various factors, including hypoxia, the Warburg effect, and the release of acidic metabolites by the tumor cells.
Tumor hypoxia occurs when a tumor’s environment has low or severely depleted oxygen levels compared to healthy tissue, which could lead to tumor acidosis. Rapidly reproducing tumor cells become more extensive in size and do not have a sufficient blood supply. Some studies show that this leads tumor environments to become hypoxic, which then leads to metabolic changes.
The Warburg Effect refers to cancer cells using aerobic glycolysis for cell metabolism, which results in an increased rate of glucose uptake and a preference for lactate production, despite the presence of oxygen. It is still unknown why cancer cells switch their metabolism method as it is energy inefficient. Even though this method is inefficient in producing ATP, some studies show that cancer cells may be using aerobic glycolysis to produce energy because it is faster than the normal process of respiration. This process allows these malignant cells to produce energy quickly. This is particularly useful in an environment where they must rapidly grow and divide. The acidic metabolite build-up occurs due to an excess of lactate production.
As a result, targeting the acidic microenvironment of tumors has emerged as a promising strategy for cancer therapy. One approach involves the use of creating drug delivery carriers that are sensitive to pH levels and have triggered drug release at the tumor site, thereby enhancing the efficacy of chemotherapy and other treatments.
Mechanism of pH-responsive tumor-targeted drug delivery
Mechanisms
pH-responsive tumor-targeted drug delivery detects the changes in the pH within the body. These polymer drug carriers carry the therapeutic drugs to allow for targeted drug delivery. The purpose of the pH- triggered drug release is to deliver the drug precisely to the area of the tumor and not activate and release the drug in healthy tissue. The complex compromises a drug delivery unit made up of a carrier molecule made up of organic nanomaterials, inorganic nanomaterials, composite nanomaterials, and anti-tumor drugs. The carrier compromises pH-sensitive molecules, which allows the drug vehicle to activate at the tumor site at the optimal pH range it is set to get triggered at and release the drug.